Plant and Soil

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Online ISSN: 1573-5036
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Article
  • Yannik MüllersYannik Müllers
  • Johannes A. PostmaJohannes A. Postma
  • Hendrik PoorterHendrik Poorter
  • [...]
  • Dagmar van DusschotenDagmar van Dusschoten
Purpose Commonly, root length distributions are used as a first approximation of root water uptake profiles. In this study we want to test the underlying hypothesis of a constant water uptake rate per unit root length over depth. Methods Root water uptake profiles were measured using a novel sensor technology. Root length was measured with MRI and by scanning harvested roots. Experiments were performed with pot-grown barley ( Hordeum vulgare ), maize ( Zea mays ), faba bean ( Vicia faba ), and zucchini ( Cucurbita pepo ). Results For barley, maize, and faba bean, we found that roots in the top 15 cm had significantly greater water uptake rates per unit length than roots in the bottom 30 cm. For zucchini, the trend was similar but not significant. Therefore, variation of root water uptake rates with depth could be explained only partly (61–71%) by a variation of root length with depth. Conclusion The common approximation of root water uptake profiles by root length distributions relies on constant water uptake rates per unit root length. This hypothesis does not hold in our study, as we found significantly greater water uptake rates per unit length in shallower than in deeper roots. This trend was consistent among species, despite the partly strong variation in physiological parameters. We suggest that this is caused by a decreasing axial transport conductance with depth. This might result in a general underestimation of water uptake rates in shallow soil layers when they are approximated by the root length distribution.
 
Fixed nitrogen in soil (A) and rice (B), total nitrogen fixation (C), copy numbers of nifH RNA reverse transcription gene (D), copy numbers of nifH DNA gene (E), and nitrogen fixation activity (F) under different residue addition. The same capital letters above the bars indicate non-significant (Tukey’s test, P > 0.05) difference for the same parameter among the treatments. The same small letters above the bars in (A) and (B) indicate non-significant (Tukey’s test, P > 0.05) difference among the different soil layers or rice parts in the same treatment. Note: mean ± standard error (n = 3). Abbreviations: Control (CK), jointing stage wheat straw (JWS), poplar branch (PB), and mature stage wheat straw (MWS)
Spearman correlations between biochemical composition of different carbon materials and the changes of nifH gene numbers, nitrogen fixation amount and nifH transcript gene number (“the change” means: the nifH gene numbers, nitrogen fixation amount and nifH reverse transcription gene number in JWS, PB and MWS minus that in CK). “*” means P < 0.05, “**” means P < 0.01
Article
  • Yanhui ZhangYanhui Zhang
  • Tianlong HuTianlong Hu
  • Hui WangHui Wang
  • [...]
  • Zubin XieZubin Xie
Background and aims Straw amendment can increase nitrogen fixation in paddy field, however, the efficiency of carbon sources with different biochemical properties to enhance N2 fixation and nitrogen fixation activity is still unclear. Methods A ¹⁵N2-labelling system was used in the field environment to determine biological nitrogen fixation (BNF) under the addition of three kinds of straw. The nifH gene (DNA) and nifH RNA gene (cDNA) of soil were amplified by real-time fluorescent quantitative PCR. The diversity and community composition of nitrogen fixing microorganisms were studied by high-throughput sequencing. The study is expected to reveal how different carbon sources impact biological nitrogen fixation and its mechanism in the paddy field system. Results Results showed that the absolute abundance diazotrophs in the treatment of mature stage wheat straw (MWS) was 4.88 times as high as that in the CK treatment, but jointing stage wheat straw (JWS) and poplar branch (PB) did not induce any significant changes. Straw amendment had no impact on cyanobacteria abundance. The proportion of N2 fixation increased by MWS was 2.07 times, but which was much lower than the increase proportion of the heterotrophic diazotrophs, leading to a decrease of diazotrophic nitrogen fixation activity. Conclusions Mature wheat straw addition increased biologically fixed nitrogen in paddy field by increasing the number of heterotrophic nitrogen fixing bacteria. The results indicated that to increase biological N2 fixation in paddy system, straws with low nitrogen content and high C/N ratio were recommended.
 
Article
  • Lena M. WernerLena M. Werner
  • Matthilde KnottMatthilde Knott
  • Doerte DiehlDoerte Diehl
  • [...]
  • Monika A. WimmerMonika A. Wimmer
Purpose Mucilage plays crucial roles in root-soil interactions. Collection systems for maize (Zea mays L.) use primary and seminal roots of aeroponically-grown seedlings (CSA), or brace roots of soil-grown plants (CSB). While each method represents specific plant developmental stages, and root types growing in specific (micro-)environments, these factors are rarely considered. It is unclear whether mucilage exhibits distinct physico-chemical properties related to collection system-inherent factors. Methods Mucilage of maize genotype B73 was collected from systems CSA and CSB. Chemical composition was assessed by pH, nutrient contents, neutral sugar composition, and polysaccharide polymer length. Viscosity, surface tension and contact angle represented physical properties. Results The share of hexoses among total polysaccharides was 11% higher in CSB than in CSA, whereas pentoses were predominant in CSA, together with higher nutrient concentrations and pH values. Mannose was detected only in CSB, which also exhibited higher surface tension, viscosity and contact angle compared to CSA. Conclusions Physico-chemical differences between the two mucilages are related to root type functions, environmental root growth conditions, and plant developmental state. Higher fractions of pentoses in CSA mucilage seem related to semi-sterile system conditions. Higher viscosity of CSB mucilage might reflect the need for enhanced water holding capacity of brace roots growing in drier conditions. A strong influence of environmental factors on mucilage properties even for a single genotype might play additional roles e.g. in the attraction of microbiomes. These aspects are relevant when assessing the role of mucilage in the rhizosphere, or when developing models of rhizosphere processes.
 
Article
Purpose Although the coordination between stomatal closure and aboveground hydraulics has extensively been studied, our understanding of the impact of belowground hydraulics on stomatal regulation remains incomplete. Here, we investigated whether and how the water use of maize (Zea mays L.) varied under hydraulically contrasting soil textures. Our hypothesis is that a textural-specific drop in the hydraulic conductivity is associated with a distinct decrease in transpiration during soil drying. Methods Maize plants were grown in contrasting soil textures (sand, sandy loam, loam) and exposed to soil drying. We measured the relationships between transpiration rate, soil water content as well as soil and leaf water potential. We used a soil-plant hydraulic model to reproduce the experimental observations and infer the hydraulic conductance of the soil-plant system during soil drying. Results We observed the impact of soil texture on plant response to soil drying in various relationships. The soil water potentials at which transpiration decreased were more than one order of magnitude more negative in loam than in sand. The soil-plant conductance decreased not only abruptly but also at less negative soil water potentials in sand than in sandy loam or loam. Stomata closed at less negative leaf water potentials in sand than in loam. The model predictions matched well the experimental observations. Conclusion The results elucidated that the critical soil water content and potential at which plants close stomata depends on the soil texture. These findings support our plea to include soil properties for understanding and predicting stomatal regulation during soil drying.
 
Alpha-diversity indices of total root associated fungi (A), symbiotic fungi (B), saprophytic fungi (C) of three forests in the Southern Himalayas. Pw, Pinus wallichiana; As, Abies spectabilis; Js, Juniperus saltuaria. Alpha diversity indices were based on ASVs richness (Chao 1 index) and diversity (Shannon index). Different letters indicate significant differences at P < 0.05 (ANOVA) between means (n = 5)
Fungal trophic mode based community structure (A), redundancy analysis (B) and variation partition analysis (C) of fungal trophic modes across the three forests in the Southern Himalayas. In B, The fungal trophic modes were statistically analyzed by ANOSIM using Bray Curtis matrix method. P-values and R-values after sequential Bonferroni correction are indicated. Significant P-values (<0.05) are indicated in bold letters
The community composition (at phylum level) (A), redundancy analysis (B) and variation partition analysis (C) of total fungal community across the three forests in the Southern Himalayas. The fungal community composition was analyzed by ANOSIM using Bray Curtis as the similarity measure. P-values and R- values after sequential Bonferroni correction are indicated. Significant P-values (<0.05) are indicated in bold letters. Abbreviations correspond to those described in Table 1
Article
AimsThis study was conducted to synthetically investigate how root-associated fungi react to the environmental variations (plant diversity and soil properties) and changes in their diversity patterns across three different coniferous forests (Pinus wallichiana, Abies spectabilis, Juniperus saltuaria) located in the subalpine-cold regions.Methods Illumina sequencing of fungal biomarker 18S rRNA was used to determine the diversity patterns and drivers of root-associated fungal communities and functional guilds interactions, along with plant diversity survey and soil properties analyses.ResultsThe diversity patterns among fungal trophic guilds the symbiotic and saprophytic communities contrasted significantly. The least saprophytic fungal diversity (low Shannon index) occurred in forests with P. wallichiana and best predicted by the soil organic carbon contents (SOC). Whereas, in the same region, the symbiotic fungal diversity was lowest in forests where J. saltuaria tree species was abundant and closely linked with soil nitrate contents (NO3−). In N deficient soils under P. wallichiana forestation, the root-associated fungal community negatively correlated with plant diversity as indicated by the lowest Shannon index numbers.Conclusions In the investigated coniferous forest soils, the interactions among trophic guilds, plant diversity and soil nutrient conditions determined the diversity of root-associated fungal communities of the three tree species. This study contributes to a deeper understanding of the response and variability in the endemic root-associated fungal functional guilds in the sub-alpine biodiversity hotspot in Southern Himalayas of China.
 
Relationship between growth rate and affinity for high-P soil (effect size) in trees grown on low-P soil (A) and in those subjected to P addition (B) in Panama. (redrawn from Fig. 1; Zalamea et al. 2016). Seedlings were grown in a forest soil with low P availability and amended either with P-free (A) or complete (B) nutrient solution. Each point represents a single species. Species affinity for P was determined from slope of response of species occurrence frequency across a range of plots differing in P availability (Condit et al. 2013). Species with lower P affinity (effect size < 0) exhibited a negative relationship between occurrence frequency and soil P availability. Species with high P affinity (effect size > 0) had a positive relationship between occurrence frequency and soil P availability. Solid and dashed lines indicate significant (p ≤ 0.05) and non-significant (p > 0.05) relationship, respectively. Shaded area indicates 95% confidence intervals (CI). This result shows a direct performance tradeoff across species. Low-P specialists maintain higher growth rates than high-P specialists under low-P conditions and vice-versa
Hypothesized mechanisms by which tree species improve P use efficiency. Foliar P productivity (Eq. 1, 1st component), inter-organ P allocation (Eq. 1, 2nd component), and P residence time (Eq. 1, 3rd component). Relevant references are shown in Table 2
Hypothesized mechanisms by which tree species improve P uptake. P uptake per root mass or length (Eq. 2, 1st component) and root structure (Eq. 2, 2nd and 3rd components). Relevant references are shown in Table 2. Simple monoesters are the most labile organic phosphates and mainly include AMP, sugar phosphates, and phospholipid decomposition products. Phosphate diesters include mainly nucleic acids (DNA and RNA), phospholipids, and certain cyclic phosphates such as cAMP. Inositol phosphates include mainly penta- and hexakisphosphate esters and myo-inositol hexakisphosphate or phytate
Relationship between soil P availability represented by soil resin phosphate and species with rarefied richness (species number per 50 trees with ≥ 100 mm DBH) on 45 plots in Panamanian lowland tropical forests (Condit et al. 2019). Each point represents a single plot. Each plot is ≥ 1 ha. Error bars indicate standard error. Tree and soil data were previously published (Turner et al. 2018). Rarefied function was calculated using the ‘rarefy’ function of the “rich” package in R. Solid line and shaded area indicate linear model fit and 95% CI, respectively. Relationship was significant at p < 0.0005 (adjusted R² = 0.27)
Article
Background Tropical tree species can maintain high growth rates on low-phosphorus (P) soils. However, the physiological basis of the high growth rates of tropical tree species remains unknown. Scope Here, we examine how traits related to P uptake and use efficiency might account for this phenomenon. Based on a comparison of plant physiological responses to P and nitrogen (N) limitation, we hypothesize that distinct evolutionary processes have occurred on strongly weathered tropical soils characterized by low P availability relative to weakly and moderately weathered temperate soils characterized by low N availability. Efficient P-use arises through the synthesis of galactolipids rather than phospholipids, small genome size, preferential and flexible P allocation to leaves, efficient P resorption from wood and leaves, tissue longevity, and a decrease in P allocation to reproduction. Efficient P uptake mechanisms include synthesis of phosphatase in roots to acquire organic P from phosphodiesters and phytate, association with mycorrhizal fungi efficient at acquiring P, secretion of organic anions from roots to mobilize soil P, increased mass flow, and modifications of root depth distribution and structure. Conclusions Despite the prevalence of low P soils throughout the tropics, few studies have explored P-use efficiency and acquisition mechanisms in tropical trees. We predict that the wide range of mechanisms by which plants can efficiently acquire and use P maintains productivity and promotes species diversity on low P soils in the tropics and elsewhere.
 
Article
Purpose The transformation of extractable plant compounds after their incorporation into soil was qualitatively and quantitatively studied in two forests under Juniperus communis L. and Pinus sylvestris L. Methods Leaf, litter and soil samples were taken from representative pine and juniper forests in central Spain. The lipid fraction was extracted with dichloromethane, while methanol was used for polar compounds, which were then derivatized (silylation-oximation). Extracts were analyzed by gas chromatography-mass spectrometry. van Krevelen’s graphical-statistical method, enhanced as surface density maps, was used to study changes in molecular assemblages during their transformation from plant to soil. Shannon Wiener diversity indices were also determined for the main groups of molecules to quantify the progressive removal or the appearance of new compounds throughout the transformation. Results In the lipid fraction up to 126 compounds were identified, mainly alkanes (C 10 –C 30 in pine forest and C 10 –C 36 in juniper forest), fatty acids and cyclic compounds. In the polar extracts, up to 22 compounds were found, mainly sugars, polyols, cyclic acids and fatty acids. Conclusion Comparing the successive stages of evolution of leaf extractive compounds, alkanoic acids and disaccharides tend to accumulate in the soil. On the other hand, the greatest molecular complexity was found in the intermediate stage (litter), and attributed to the coexistence of biogenic compounds with their transformation products, while the molecular complexity was simpler in soil extracts. This preliminary investigation could be extended to specific studies on the factors that determine the quality of soil organic matter under different environmental scenarios.
 
Article
Background Agroforestry has been advocated as a climate-smart agricultural approach to counter extreme climate and as an important sustainable intensification practice to meet Sustainable Development Goals (SDGs). However, its efficacy remains under dispute in drylands where resources, especially water, are limited. Aim and methods This study aimed to study how annual bioenergy crops, soybean (Glycine max) and canola (Brassica rapa), influence soil water availability and fine root distribution in a young apple orchard exposed to varying to drought intensity on the semiarid Loess Plateau of China. Drought was simulated by reducing natural precipitation by 15% (moderate drought) and 25% (severe drought). Result and conclusions Intercropping soybean and canola increased the fine root biomass (FRB) of apple trees in the 80–180 cm soil layer, improved moisture status below the 80 cm soil layer in the wet season, and promoted apple tree growth. Under moderate drought, FRB in the 0–80 cm soil layer increased, making use of the shallow soil water replenished by precipitation. However, the trees switched to absorbing soil water in the 80–180 cm in the dry season. Under severe drought, the apple trees increased FRB in the 0–80 cm and 180–280 cm soil layers and increased the proportion of the total roots in the 180–280 cm layer, aggravating the deep soil desiccation and inhibiting apple tree growth. These findings offer insights into drought effects on root plasticity and soil management practices in rainfed orchards.
 
Cross section of mature litchi pericarp under light microscope. A: normal fruit; B: dark pericarp fruit
Fe, Mn and Al signals in litchi pericarp detected by energy spectrum analysis under scanning electron microscope. A: pericarp of mature normal fruit from the dolomite-amended tree. B: pericarp of mature dark pericarp fruit from the control tree
Activities of antioxidant enzymes in litchi pericarp as affected by treatment and pericarp type. A: SOD; B: POD; C: PPO; D: laccase
Microstructure of mesocarp cell in litchi fruit. A: mesocarp cell of ripe normal fruit. PhG refers to phenol grain in the vacuole. B and C: subcellular location of globular particles of dark materials (DaM in white rectangles) in mesocarp cell of ripe dark pericarp fruit (DPF). D and E: magnified image of globular particle aggregation in mesocarp cell of ripe DPF. F: location of a vesicle containing globular particles in phenol grain in mesocarp cell of ripe DPF; G and H: separation of vesicle from phenol grain in mesocarp cell of ripe DPF; I: excretion of vesicle by vacuole in mesocarp cell of unripe DPF. J: globular particles were growing with tiny phenol grains and long phenol grains in vesicle of mesocarp cell in unripe DPF
Elemental distribution in mesocarp cell of DPF as scanned by scanning transmission electron microscope. A: HAADF image of a part of a mesocarp cell in DPF. PhG and DaM refer to phenol grain and dark materials, respectively. B: C, carbon. C: O, oxygen. D: N, nitrogen. E: P, phosphorous. F: Mg, magnesium; Al, aluminum; S, sulfur; Cl, chloride; K, potassium; Ca, calcium; Mn, manganese; Fe, iron; Mo, molybdenum. G: Mn
Article
Aims A new physiological disorder, dark pericarp disease (DPD) in litchi fruit is recently observed in South China. DPD occurs after heavy rain and is aggregated by insolation, leading to undesirable fruit appearance. This work aims to reveal the cause of DPD, and seek efficient solutions for it. Methods A field experiment was conducted to investigate the link between pericarp nutrients and DPD occurrence in litchi grown in soil with abundant available Mn. The antioxidase activities, subcellular location of dark materials, phenol compounds in dark pericarp fruit (DPF) and soil properties affected by dolomite broadcast and dolomite broadcast plus foliar K2SiO3 spray were examined as well. Results Mn contents in tissues significantly decreased in the order: dark pericarp of DPF > normal pericarp of DPF > pericarp of normal fruit (P < 0.01), indicating that DPD is associated with excessive Mn. Dark materials dominated in the upper mesocarp of DPF. Nanoparticles of dark materials were formed from phenol grains in vacuole, and sequestered into vesicle from vacuole, then excreted to cytoplasm. Dolomite broadcast significantly mitigated DPD by raising soil pH, lowering soil available Mn and regulating antioxidase activities in pericarp (P < 0.05). However, it is unexpected that additional Si spray significantly offset the role of dolomite application, probably due to its alkality. Conclusions This study first reports that DPD is caused by excessive Mn in litchi. Dark materials are probably comprised of oxidized and/or polymerized phenols in pericarp of DPF. Dolomite application efficiently alleviates DPD, but extra foliar alkaline Si spray counteracts its role.
 
Soil inoculum effects on mortality probabilities as a function of the ecoregion, tree type, and soil sterilization. Shown are the overall mortality probability (A), the probability that the plants died late in the experiment (B), and the probability that death was root-related (C). Means are estimated marginal means and error bars are 95% confidence intervals. Ecoregions are split by panel. On the x-axis, live refers to live aspen and dead refers to dead aspen. Soil inoculum from each source was either sterilized or live. Asterisks denote significant differences (* = P < 0.05, ** = P < 0.01, and *** = P < 0.001) between live and sterilized soil for that soil source based on pairwise comparisons when interaction terms were significant. There were no significant differences among tree types based on pairwise comparisons
Soil inoculum effects on seedling shoot (A) and root (B) mass. Shown are the estimated marginal means with their associated 95% confidence intervals. On the x-axis, live refers to live aspen and dead refers to dead aspen. Ecoregion, sterilization, and tree type all had significant main effects with spruce trees differing from both live and dead aspen. There were no significant interactions, so we did not conduct pairwise comparisons
Linear relationships between absolute measures of dead and live aspen PSF (A) and between heterospecific and live aspen PSF (B). Lines represent the result of linear regression and bands the 95% confidence intervals around that regression
Effects of inoculum source on the probability that a root sample was colonized by arbuscular mycorrhizal fungi (A) and the colonization intensity among colonized samples (B). Only plants inoculated with live soils were analyzed for colonization intensity. Shown are estimated marginal means and the 95% confidence intervals around those means. In panel B, letters denote significant differences in means among tree types within an ecoregion as determined by pairwise comparisons
Article
Purpose Most plants interact with soil biota that positively or negatively affect seedling performance. These plant-soil feedbacks (PSFs) can strongly affect recruitment, potentially for years after death. We tested whether PSFs persisted following death for Populus tremuloides Michx. (aspen) and if these effects were environment dependent using soils collected from live and dead aspen and heterospecific Picea glauca (Moench) Voss in 24 stands across two ecosystems. Methods We conducted a greenhouse experiment using soils from 24 aspen stands. At each stand, we collected soil from three trees of each tree type and used live and sterilized versions of these soils to inoculate aspen seedlings. We then recorded mortality and growth of the seedlings over three months. Results Live inocula reduced aspen survival and growth relative to sterilized inocula, suggesting that pathogens drive PSF. Plant responses to live and dead aspen inocula were correlated across environments; however, responses to aspen and heterospecific Picea inocula were uncorrelated, suggesting that specialized pathogens may drive PSF. Conclusions Pathogen-driven negative PSFs can persist for multiple years irrespective of the environment, potentially limiting the regeneration of aspen stands following dieback. Persistent PSFs thus have potential to cause lagged effects on population and community dynamics.
 
The effect of warming on soil temperature (a) at 5 cm depth, and soil moisture content (c) at 10 cm depth compared with the control (△(Warming-Control)) at the end of the experiment (2007–2017). Panel b shows the warming effect on temperature from 25 cm aboveground to 50 cm belowground every 30 min over two days during the sampling period. The data showed in Panels a, b, c was measured by sensor multiplexer in situ, whereas the data presented in panels d, f and e were measured in the lab after we collected the samples. Panels d, f, and e present the warming effect on soil moisture content (0–5 and 5–10 cm), standing litter, and litter moisture content, respectively, for once measurement. The dots in panels a, and c represent the mean value of each parameter for each year. * represents a significant difference between the control and warming treatment at P < 0.05. W, warming effect; D, depth; W × D: the interaction between warming effect and depth. The same below
Effect of warming on soil microbial communities based on phospholipid fatty acid (PLFA) analysis. Data are means ± SE (n = 5). Total PLFA (a); AMF PLFA (b), arbuscular mycorrhizal fungi PLFA; Actinomycetes PLFAs (c); Fungal PLFAs (d); Bacteria (e); F: B ratio (f), fungal to bacterial PLFA ratio; G+ bacteria (g), Gram-positive bacteria; G-bacteria (h), Gram-negative bacteria; G+: G-ratio (i), Gram-positive to Gram-negative bacterial PLFA ratio; βG (j), β-glucosidase activity; NAG (k), β-1,4-N-acetylglucosaminidase; AP (l), acid phosphomonoesterase. *, P < 0.05
Effect of warming on soil organic carbon (SOC, panel a), SOC pool component and their correlation with soil δ¹³C abundance after 10 years of experimental warming. (b) Plant-derived C as a percentage of lignin and phenolics in SOC is determined by pyrolysis gas chromatography-mass spectrometry (Py-GC–MS). (c) Percentage of microbial residual C in SOC. Error bars denote SE (n = 5). Two-way ANOVAs were performed to test the effect size of warming, sampling depth and their interactions; P values are denoted only when the effect size was significant at P < 0.05. Linear regression analysis was performed to test the correlation of plant-derived C and microbial-derived C with SOC (panel d) and δ¹³C (panel e). Dashed lines around each fitted curve represent 95% confidence intervals and R.² and P values (n = 20) are denoted in the figures accordingly. *, P < 0.05
Percentage of mineral-associated organic carbon (MAOC, a), particulate organic carbon (POC, b), and dissolved organic carbon (DOC, c) in soil organic carbon (SOC) based on density fraction analysis in a sodium polytungstate (SPT) solution (Keiluweit et al. 2017)
Conceptual diagram of warming effects on soil organic carbon (SOC) concentrations and components through microbial decomposition and mineral protection pathways in 0–5 and 5–10 cm soil layers. AMF, arbuscular mycorrhizal fungi; G-, Gram-negative bacteria; G + , Gram-positive bacteria; MAOC, mineral-associated organic carbon; POC, particulate organic carbon; DOC, dissolved organic carbon. ↑, increase; ↓, decrease
Article
Aims Soil warming significantly influences soil organic carbon (SOC) pools in terrestrial ecosystems through its impact on the processes of carbon (C) input and decomposition as well as the stabilization of SOC pools. Most studies demonstrated that soil warming reduces SOC pools, but the magnitude is highly variable, and the underlying mechanisms are poorly understood. Methods The concentration, stability (dissolved, particulate, and mineral-associated SOC) and source (plant-derived vs. microbial-derived) of SOC, soil microbial community composition, and enzymatic activities were studied in a 10-year soil warming field experiment in an East Asian monsoon forest. Results 10-year soil warming significantly enhanced SOC in the top 0-10 cm soil. The increased SOC induced by warming was mainly derived from plants, with lignin and phenol markers increasing by 60% on average, accompanied by a 27% decrease in microbial-derived SOC. However, the overall effect of warming on SOC stability was not statistically significant. Conclusions The results suggest that the moist monsoon forest soil could sequester SOC upon long-term warming. The discrepancy between our findings and those from other regions highlights an urgent need for a better understanding of how the contrasting effects of plant- and microbial-derived C mediate the response of the SOC pool to warming across biomes.
 
Four different types of rice flowering time (heading date) responding to N supplies. N0: 75 kg N ha⁻¹; N1: 150 kg N ha⁻¹; N2: 250 kg N ha.⁻¹. All photos were taken at 70 days after transplanting in paddy field (Nanjing, China)
Overview of N-dependent flowering regulatory pathways in Arabidopsis and rice. Flowering is divided into two processes: transition from vegetative stage to reproductive stage, which is associated with regulation in leaf; flower initiation and development, which occurs in shoot apical meristem (SAM). It is bridged by transfer of florigens from leaf to SAM, such as AtFT in Arabidopsis and OsHd3a in rice (Corbesier et al., 2007; Tamaki et al. 2007; Turck et al. 2008; Putterill and Varkonyi-Gasic 2016). Recent studies on Nitrate/nitrogen regulated flowering mainly focus on the first process. Nitrate signaling is perceived by nitrate transceptors, like AtNRT1.1, to induce Ca²⁺ waves and CPKs activation (Liu et al. 2017). AtNRT1.13 has been found to act as a potential nitrate transceptor coupling with AtFLC to modulate low nitrate-dependent floral transition in Arabidopsis (Chen et al. 2021). Overexpression of AtNRT1.1 homolog in rice, OsNRT1.1A, shortens maturation time by repressing OsHd3a expression (Wang et al. 2018a, b, c), but little is known about its function as a nitrate transceptor. One of the main CPK integrators of nitrate signal, AtCPK32, promotes flowering via alternative polyadenylation of AtFCA and altering transcription of AtFLC, which depends on Ca²⁺ response (Li et al. 2021). However, whether this regulation pathway is nitrate-dependent needs further verification. Two transcript factors AtSMZ and AtSNZ are induced by nitrate in a GA-dependent manner and repress expression of AtFT to regulate flowering (Gras et al. 2018). Moreover, low N increases NADPH/NADP + and ATP/AMP ratios following induction of AtFNR1 (Yuan et al. 2016). The high level of ATP/AMP ratio reduces nuclear AMPK/SnRK activity. And then AMPK/SnRK phosphorylates two AtCO transcriptional activators, AtCRY1 and AtFBH4, resulting in protein localization and stability in nuclear (Yuan et al. 2016; Sanagi et al. 2021). In addition, Glutamine (Gln) not ammonium, can induce expression of OsNhd1 (also known as OsLHY) to directly trigger transcription of OsHd3a in rice (Zhang et al. 2021). After delivering from leaves to SAM, the florigens can interact with 14–3-3 protein and FD (AtFD and OsFD) to form “florigen complex” and regulate flower initiation (Taoka et al. 2011). AtFD protein also can be phosphorylated by AtCPK4/6/33, but participation of N in this regulation process is unknown (Kawamoto et al. 2015). AtNLP6/7, acting as master regulators of nitrate signal at downstream of AtCPK, can directly activate expression of AtSOC1 and AtSPL3/5 at SAM (Olas et al. 2019). Thus, Flower development occurs at SAM after establishment of floral meristem identity genes, such as AtLFY, AtAP1 and OsMADS in Arabidopsis and rice (Lee and Lee 2010; Kater et al. 2006). Genes and functional protein in Arabidopsis. AtFT: flowering locus T. AtNRT1.1: nitrate transporter 1.1. AtCPK: trigger calcium-dependent protein kinases. AtFLC: flowering locus C. AtFCA: flowering control locus A. AtSMZ and AtSNZ: SCHLAFMUTZE and SCHNARCHZAPFEN. AtFNR1: ferredoxin-NADP( +)-oxidoreductase 1. AtAMPK: adenosine monophosphate-activated protein kinase. AtCO: CONSTAN. AtCRY1: crytochrome 1. At FBH4: FLOWERING BHLH 4. AtNLP: NIN-like protein 6/7. AtSOC1 overexpression of CONSTANS 1. AtSPL: squamosa promoter binding protein-like. Genes and functional protein in rice. OsHd3a: heading date 3a. OsNhd1: nitrogen regulated heading date 1. OsMADS: MCM1, AG, DEFA and SRF transcript factor family. Lines (including circle lines) in green and orange represent regulatory pathways in Arabidopsis and rice. Solid and dashed lines indicate the characterized direct and indirect regulation, respectively. The transfer of FT and Hd3a protein from leaf to SAM is highlighted respectively in Arabidopsis and rice leaf. Circles indicate “florigen complex” proteins in each species
Article
Flowering is the transition process from vegetative to reproductive growth determined by many endogenous and exogenous factors. Nitrogen (N), as a dominant macronutrient for plant growth, can largely affect flowering time. A complex network integrates multiple environmental signals consisting of N status and photoperiod condition into internal regulation of flowering time in plants. So far, several transcription factors, kinases, N transporters and N assimilation enzymes have been identified to participate in the N-dependent regulation of flowering time. In this review, we summarize prominent mechanisms and key players that govern the N-dependent response of flowering time, and further discuss the interaction between N utilization and growth phase transitions in plants. Since the impact of N status on flowering time varies over plant species and shows large genetic diversities, we focus on current state of knowledge on regulatory pathways of N-determined flowering time in Arabidopsis and graminaceous plants, especially in rice. These understanding of the N-dependent flowering response can provide valuable inspirations and novel strategies to coordinate growth period with N availability for improving N use efficiency and crop productivity.
 
Cd uptake by H. annuus leaves, including (a) leaf Cd concentration, (b) total leaf Cd uptake and (c) Cd bioaccumulation factor (means ± SE) in response to soil Cd concentration and simulated herbivory treatments (Control vs. Sim. Herb.). Different letters indicate statistically significant pairwise comparisons (LSD Test, p < 0.05)
H. annuus performance, including (a) height, (b) aboveground biomass and (c) biomass allocation to flowers, as well as (d) the occurrence of resin secretion on leaves (means ± SE) in response to soil Cd concentration and simulated herbivory treatments (Control vs. Sim. Herb.). Different letters indicate statistically significant pairwise comparisons (LSD Test, p < 0.05)
Article
Background Metal hyperaccumulators are plant species that can uptake and store high concentrations of heavy metals in their aboveground tissues, while maintaining high vigor. Hyperaccumulation of metals was suggested to provide defense against natural enemies such as herbivores. However, heavy-metal uptake can incur physiological and ecological costs, suggesting that, like other anti-herbivore defenses, it might be induced by herbivore attack. Nevertheless, this idea has been scarcely studied. Methods We tested the hypothesis that herbivory could induce enhanced metal uptake in Helianthus annuus, which can accumulate high amounts of heavy metals in its aboveground tissues and is commonly used for phytoremediation of heavy-metal contaminated soils. In a greenhouse experiment, H. annuus plants were grown in low or high soil cadmium (Cd) concentration and subjected to control or herbivory treatments. Herbivory was simulated using both leaf damage and exogenous application of jasmonic acid, which activates anti-herbivore defenses in plants. Results Simulated herbivory increased Cd concentration in the leaves of H. annuus by 24 and 39% under low and high soil Cd availability, respectively. Moreover, while simulated herbivory decreased shoot biomass of H. annuus it resulted in increased total Cd uptake. These results demonstrate that hyperaccumulation of heavy metals might be a facultative trait, whose extent can be enhanced in response to herbivore damage. Conclusions This study provides first evidence that simulated herbivory can enhance total heavy metal uptake in plants that are used for remediation of contaminated soils, which can have important implications on the optimization of phytoremediation practices.
 
Effect of Mn addition on litter mass loss in subtropical plantations of southern China. Data are mean values (n = 5) and error bars are standard errors. For each litter treatment, ns, *, and ** indicate the significant differences in litter mass loss between control and Mn addition treatments at P > 0.05, P < 0.05, and P < 0.01, respectively
Article
Background Manganese (Mn) is believed to be a key variable controlling litter decomposition, especially in the late stage. However, the direct effects of Mn on litter decomposition and litter mixing effects during decomposition have been rarely tested in subtropical forests. Methods We collected leaf litter of four common tree species (two broadleaf tree species, Liquidambar formosana and Schima superba; two coniferous tree species, Pinus massoniana and Pinus elliottii) from subtropical plantations of southern China, and used a field Mn addition experiment to assess the impact of Mn on single and mixed litter mass loss during 780-day decomposition. In addition, we measured soil nutrient availability and hydrolytic enzyme activities. Results Despite unchanged soil nutrient availability, Mn addition generally increased soil β-1,4-glucosidase, cellobiohydrolase, leucine aminopeptidase, and acid phosphatase activities. Irrespective of litter types, Mn addition did not affect litter mass loss in the early stage (mass loss <40%) but enhanced litter mass loss in the late stage (mass loss >40%). During mixed litter decomposition, synergistic effects were more common for coniferous litter than for broadleaf litter. Moreover, Mn addition reduced the magnitudes of synergistic effects on litter decomposition and even changed synergistic effects to additive effects. Thus, the positive effect of Mn addition on litter decomposition was greater for single litter (18%) than for mixed litter (6%). Conclusions Mn availability is crucial for leaf litter decomposition in the late stage rather than in the early stage, and Mn addition influences mixed litter decomposition by reducing non-additive effects in subtropical plantations.
 
Kaplan–Meier survival curves representing plant survival rates along the experiment (in days) per treatment and species. Experiment duration: 82 days for Medicago sativa and 67 days for Cynodon dactylon. Treatments: T1: 90% C0 + 10% GS; T2: 80% C0 + 20% GS; T3: 50% C0 + 50% GS. C0: contaminated soil. GS: Gypsum mining spoil. Different letters represent statistically significant differences between treatments (p < 0.05)
Shoot, root and plant biomass (mean ± SD in g) per treatment and species (Medicago sativa and Cynodon dactylon). Treatments: T1, 90% C0 + 10% GS; T2, 80% C0 + 20% GS; T3, 50% C0 + 50% GS. C0: contaminated soil. GS: Gypsum mining spoil. Different letters represent statistically significant differences (p < 0.05) for the post-hoc Tukey tests performed after the GLMs
Article
Purpose Soil pollution is a major problem worldwide. Some anthropogenic activities, such as mining, may exceed soil capacity, causing relevant health and ecosystem hazards. The use of mineral amendments can help reduce soil pollution. Gypsum mining spoil (GS) is a waste material highly produced in gypsum mining industry, which has never been used in soil remediation despite its high potential as amendment of polluted soils. In this study, we carried out an ex-situ experiment to assess for the first time the capacity of GS to both reduce the availability of Potentially Harmful Elements (PHEs) in soils and promote seed emergence. Methods Soils affected by residual pollution after the Aznalcóllar mine spill were collected, treated with GS in three different proportions, and sown with seeds of two non-genetically related species. Seed emergence and biomass production were monitored, and PHE content in soils and plants were analysed. Results We have observed a direct and very positive relation between GS and both the reduction of PHE availability and PHE uptake by plants, and the increase of plant emergence and growth, especially with the addition of the highest doses of the amendment. Conclusion This study highlights the promising results of GS as a novel soil amendment to be used in the remediation of polluted soils and vegetation recovery. Moreover, using GS as soil amendment will bring the opportunity to sustainably manage this waste material and reduce its social and environmental impact parallelly to the mitigation of PHE hazards.
 
Article
Purpose Alternate wetting and moderate soil drying irrigation (WMD) and nitrogen fertilizer at panicle initiation are widely used in rice production in China. This study investigated the effects of panicle fertilizer optimization on rice root growth, soil properties and grain yield under continuous flooding (CF) and WMD. Methods A factorial combination of two irrigation regimes (CF and WMD) and two N fertilizer rates at panicle initiation (normal N rate [NN] and low N rate [LN]) was designed in both field and pot conditions in 2018–2019. Results Grain yield declined in the order: WMD + NN > CF + NN = WMD + LN > CF + LN. WMD increased grain yield by notably increasing the spikelet number per panicle (SNPP) and could counteract the negative effect of LN. WMD enhanced root morphology and physiology, which was remarkably correlated with SNPP. The urease activity, oxygen content, and the abundance of ammonia-oxidizing archaea/bacteria in rhizosphere soil were significantly increased under WMD compared to CF but were decreased in LN relative to NN under the same irrigation regime. The rice root length, root dry weight, root diameter, root oxidation activity, and soil nitrification rates under WMD + LN were similar to those under CF + NN. Rice root morphology and activity promoted by the enhanced nitrification process and decreased NH4⁺/NO3– ratio under WMD facilitated a higher grain yield. Conclusion Combining WMD with LN at panicle initiation could maintain the rice root growth, leading to comparable grain yields but higher nitrogen use efficiency than the farmers’ practice.
 
Article
Purpose Herbaceous plants are important components of temperate forest structure and its functioning, however, their impacts on arbuscular mycorrhizal fungi (AMF) remain largely unexplored. We studied the influence of forest herbaceous plant species on AMF abundance, morphospecies richness, and community composition in soil. Methods We tested the influence of plant species identity in an outdoor mesocosm experiment, using two soils, differing in physicochemical properties, planted with four plant species of contrasting traits related to morphology, phenology, reproduction, and ecology; the hemicryptophyte, summer-green Aegopodium podagraria, and spring ephemeral geophytes comprising Allium ursinum, Anemone nemorosa, and Ficaria verna. The plants were grown on both soils in four monocultures, in a combination of A. podagraria and A. ursinum, and a mixture of all four species. Results Aegopodium podagraria and A. ursinum promoted AMF abundance and diversity the most. Higher AMF root colonization and/or soil concentrations of AMF structural and storage markers 16:1ω5 PLFA and NLFA, as well as higher AMF spore and morphospecies numbers were found in the A. podagraria and A. ursinum monocultures and mixture. The short period of photosynthetic activity of A. ursinum due to rapid leaf decay does not negatively affect the symbiosis with AMF. Although A. nemorosa and F. verna are mycorrhizal, their effect on AMF in soil was weak. Conclusions The plant impact on AMF may be related to the differences in plant coverage and the character of their interactions with AMF. The herbaceous plants can form niches in soil differing in AMF abundance and diversity.
 
Phenotypic characterizations of rice plants (cv. Esmeralda) subjected to distinct N-stress regimes: NS1 (two successive N-sufficient cycles + one N-stress cycle); NS2 (one N-stress cycle + one N-sufficient cycle + one N-stress cycle); NS3 (three successive N-stress cycles). Control: (three successive N sufficient cycles). The results refer to the last cultivation cycle, in which NS1, NS2, and NS3 received fertilization amounts equivalent to 10 kg N ha⁻¹, while the control plants received fertilization amounts equivalent to 60 kg N ha⁻¹. Scale bars, 10 cm in (A) and 5 cm in (B). Data represent the average of four biological replicates, and error bars represent standard error (SE). Different lowercase letters between treatments within a column indicate statistical differences by the Scott-Knott test (p < 0.05)
Photosynthetic parameters obtained from the chlorophyll “a” transient fluorescence levels in leaves of rice plants (cv. Esmeralda) subjected to distinct N-stress regimes: NS1 (two successive N-sufficient cycles + one N-stress cycle); NS2 (one N-stress cycle + one N-sufficient cycle + one N-stress cycle); NS3 (three successive N-stress cycles). Control: (three successive N sufficient cycles). The parameters were calculated using the JIP test and represent: i) energy fluxes Dio/RC energy flux dissipated as heat per reaction center (RC), ABS/RC RC absorption flux, TRo/RC maximum capture rate per RC, and REo/RC reduction flux of electrons in the final electron acceptor in photosystem I (PSI); ii) productivity φ(Po) photochemical maximum quantum yield, φ(Eo) quantum yield of electron transport from quinone A (QA-) to the electron acceptor intersystem, and φ(Ro) quantum yield of electron transport from QA- to the final PSI electron acceptor; iii) performance Piabs partial photosynthetic performance index and Pitotal total photosynthetic performance index. Yellow, light blue, red, and dark blue lines correspond to control, NS1, NS2, and NS3 treatments, respectively. DAE days after emergence
Cluster analysis by using orthogonal partial least squares-discriminant analysis (OrthoPLS-DA) of the metabolites identified in the flag leaves of rice plants (cv. Esmeralda) subjected to distinct N-stress regimes: NS1 (two successive N-sufficient cycles + one N-stress cycle); NS2 (one N-stress cycle + one N-sufficient cycle + one N-stress cycle); NS3 (three successive N-stress cycles). Control: (three successive N sufficient cycles). Only metabolites regulated differently by ANOVA test (p < 0.05) were used. Raw data to be found in Table S4. Red, green, dark blue, and light blue colors correspond to control, NS1, NS2, and NS3 treatments, respectively
Metabolite contents in the flag leaves of rice plants (cv. Esmeralda) subjected to distinct N-stress regimes: NS1 (two successive N-sufficient cycles + one N-stress cycle); NS2 (one N-stress cycle + one N-sufficient cycle + one N-stress cycle); NS3 (three successive N-stress cycles). Control: (three successive N sufficient cycles). Data represent the average of three biological replicates, and error bars represent standard error (SE). Different lowercase letters between treatments within a column indicate statistical differences by the Scott-Knott test (p < 0.05)
Pearson correlation between ratio of hemi-methylated and fully-methylated bands, and photosynthetic (A), metabolite (B), agronomic (C), and N use (D) parameters in rice plants (cv. Esmeralda) subjected to distinct N-stress regimes. HMR Hemi-methylated ratio; FMR Fully-methylated ratio; ABS.RC absorption flux per reaction center (RC); Dio.RC energy flux dissipated as heat per RC; Tro.RC maximum capture rate per RC; REo.RC reduction flux of electrons in the final electron acceptor in photosystem I (PSI); φ(Po) photochemical maximum quantum yield; φ(Eo) quantum yield of electron transport from Quinone A (QA-) to the electron acceptor intersystem; Piabs partial photosynthetic performance index; NT Number of tillers per plant; SDW Shoot dry weight; TWFG Total weight of filled grains; FGN Filled grains number; NUpE N uptake efficiency; NUtE N utilization efficiency; NUE N use efficiency. Crossed-out boxes indicate non-significant differences (p > 0.05)
Article
Aims DNA methylation and demethylation are epigenetic responses to abiotic stresses. The aims of this study were to i) identify alterations in the DNA methylation patterns among rice plants grown with sufficient and low nitrogen (N) levels; ii) observe whether conditioning to N stress promoted alterations in methylation patterns; and iii) search for possible relationships among methylation alterations and phenotypic, physiological, and metabolic changes. Methods The N-stress treatments applied were as follows: over three consecutive generations, plants were either exposed to sufficient N (60 kg N ha⁻¹ – Control group) or N stress (10 kg N ha⁻¹) for only the last generation (NS1), the first and third generations (NS2 – intermittent stress), or all three generations (NS3 – recurrent stress). Non-stress cycles received sufficient N. Results It was observed that N stress led to a reduction in total DNA methylation compared to control. The greatest reduction was observed in the hemi-methylated bands. NS1- and NS3-treated plants had similar reductions in the total hemi-methylated and fully-methylated bands, as well as similar phenotypic characteristics and photosynthetic efficiencies. On the other hand, the NS2 treatment increased the number of fully-methylated bands, which corresponded with a strong reduction in grain yield and photosynthetic efficiency. Conclusion It was found that N stress stimulates changes in DNA methylation and that the duration of N-stress conditioning interferes with the methylation patterns of plants. Finally, a strong relationship between methylation status and photosynthetic, agronomic and N-use parameters was found.
 
Article
Background and aims Biostimulants of natural origin represent a growing ecological strategy to increase crops productivity, especially when applied in combination with microbial bioeffectors. We studied the effect of biostimulants such as Potassium Humates (KH) from Leonardite and Compost Tea (CT) from green compost on both productivity and nutritional status of lettuce plants, as well as on the primary and secondary metabolism of treated plants, when amended either alone or in combination with a commercial microbial inoculum (M+), mainly based on arbuscular mycorrhizal fungi (Micosat TabPlus). Results The biomass production as well as the uptake of both macro- and micronutrients by lettuce plants significantly increased when amended by the mixture of both humic materials (MIX) combined with the microbial inoculum. Similarly, the synergic MIX_M+ treatment significantly affected both the primary and secondary metabolism of lettuce more than their individual applications, by increasing, respectively, the biosynthesis of essential amino acids and carbohydrates, and that of antioxidant polyphenolic compounds, such as hydroxycinnamic acids, flavonols and coumarins. Conclusions Our findings suggest that a calibrated mixture of humic bioactive molecules in combination with microbial consortia represents a potential tool to improve crop productivity and its nutritional and metabolic status.
 
Effects of altered precipitation amount (P) and land-use regime (L) on soil temperature (a–d) and moisture (e–h) at 5 cm depth, aboveground (ANPP, i–l) and belowground (BNPP, n–p) net primary productivities. The box plots showed the mean and median (solid and dashed black lines in the boxes), interquartile ranges (boxes) and 10th and 90th percentiles (short black lines). Black cycles represent actual mean values. Results (F values) of the analysis of variance are shown in figure and indicated by *** when P < 0.001, ** when P < 0.01, * when P < 0.05, # when P < 0.10 and n.s. (not statistically significant) when P > 0.10. Different lower-case letters represent significant differences between precipitation amount treatments under the same land use and different upper-case letters represent significant differences between land uses under the same precipitation treatment (pairwise t test, P < 0.10)
Effects of altered precipitation amount (P) and land-use regime (L) on soil microbial biomass carbon (MBC, a) and nitrogen (MBN, b). The box plots showed the mean and median (solid and dashed black lines in the boxes), interquartile ranges (boxes) and 10th and 90th percentiles (short black lines). Black cycles represent actual mean values. Results (F values) of the analysis of variance are shown in figure and indicated by *** when P < 0.001, ** when P < 0.01, * when P < 0.05, # when P < 0.10 and n.s. (not statistically significant) when P > 0.10. Different lower-case letters represent significant differences between precipitation amount treatments under the same land use and different upper-case letters represent significant differences between land uses under the same precipitation treatment (pairwise t test, P < 0.10)
Effects of altered precipitation amount (P) and land-use regime (L) on soil respiration (Rs, a–d) and its autotrophic (Ra, e–h) and heterotrophic (Rh, i–l) components. The box plots showed the mean and median (solid and dashed black lines in the boxes), interquartile ranges (boxes) and 10th and 90th percentiles (short black lines). Black cycles represent actual mean values. Results (F values) of the analysis of variance are shown in figure and indicated by *** when P < 0.001, ** when P < 0.01, * when P < 0.05, # when P < 0.10 and n.s. (not statistically significant) when P > 0.10. Different lower-case letters represent significant differences between precipitation amount treatments under the same land use and different upper-case letters represent significant differences between land uses under the same precipitation treatment (pairwise t test, P < 0.10)
Diagrams of final structural equation models (SEMs) for relating the autotrophic (a) and heterotrophic (b) components of soil respiration to their biotic and abiotic driving factors. These SEMs were constructed by using observations only in 2019 (n = 27 observations for each variable). All arrows are scaled in relation to the strength of the relationship, with numbers showing the standard path coefficients and indicated by *** when P < 0.001, ** when P < 0.01, * when P < 0.05, # when P < 0.10 and n.s. (not statistically significant) when P > 0.10. R² values are proportions of variance explained by dependent variables in the model. Model-fit statistics such as χ²-test, RMSEA and GFI are shown in each panel. Details of these SEMs can also be found in Table S5–S6. Details of initial SEMs can be found in Fig. S13 and Table S3–S4
Article
Purpose Grasslands are facing the threat of climate change and intensive land use. Soil respiration (Rs) in grassland ecosystems can be potentially altered by changes in precipitation and land use. We aimed to quantify the impact of changes in precipitation and common land use practices in an Inner Mongolia grassland, i.e., mowing and grazing, on soil respiration. Methods We performed an in situ experiment with altered precipitation (+ 50%, ambient, and -50%) and land use (control or fencing, mowing, and grazing) to explore their impacts on soil respiration and its autotrophic (Ra) and heterotrophic (Rh) components. Results Altered precipitation had stronger impacts on abiotic and biotic drivers than land use, leading to stronger impacts on Rs and its components. Over the 3-year experiment, Rs, Ra and Rh decreased by 36%, 42% and 33% with reduced precipitation and increased by 29%, 36% and 25% with increased precipitation, respectively. Grazing and mowing caused relatively small decreases in Rs compared to fencing (generally < 10%). However, precipitation and land use interactively impacted abiotic and biotic drivers and thus Rs. The decrease in Rs with reduced precipitation was greater with grazing (38%) and mowing (37%) than with fencing (32%). Conclusions Rs and its components may decrease under the projected decrease in precipitation and may further decrease with grazing and mowing compared to fencing. Therefore, land use should be considered when predicting grassland carbon cycling in response to future precipitation changes.
 
Relative abundances of the major endophytic diazotrophs at the level of phylum (a), order (b), and genus (c) as percentages of all the nifH gene sequences in each sample grouped by plant species and tissue type. The letters underneath each column represent that P: Populus purdomii; Se: Salix ernestii; Sr: Salix rehderiana; A: Astragalus mahoshanicus; H: Hippophae rhamnoides; L: leaf; S: stem; R: root; N: nodule; P_L: leaf of P. purdomii and likewise for the others
Heatmap depicting the distribution of major endophytic diazotrophs operational taxonomic units (OTUs, > 1000 reads) in pioneer species. Color tones range from cool (blue) to warm (red) indicate the lowest and highest abundances. Cluster analysis was performed based on Bray–Curtis similarities. The letters under-neath each column represent that P: Populus purdomii; Se: Salix ernestii; Sr: Salix rehderiana; A: Astragalus mahoshanicus; H: Hippophae rhamnoides; L: leaf; S: stem; R: root; N: nodule; P_L: leaf of P. purdomii and so are the others
Nonmetric multidimensional scaling (a) ordinations and redundancy analysis (b) of the endophytic diazotroph community compositions within pioneer plants. Each point corresponds to a sample with the plant species indicated by color (green = Populus purdomii; red = Salix ernestii; blue = Salix rehderiana; orange = Astragalus mahoshanicus; gray = Hippophae rhamnoides) and tissue type of each sample indicated by shape (circle = leaf; triangle = stem; square = root; rhombus = nodule). The arrows in (b) indicate N, nitrogen concentration; C, carbon concentration; P, phosphorus concentration; C:N, C:N ratio; C:P, C:P ratio; N:P, N:P ratio
Venn diagrams displaying the number of endophytic diazotrophs operational taxonomic units shared among plant species (but in the same tissue type: a, leaf; b, stem; c, root) and tissue type (but in the same species: d, Populus purdomii; e, Salix ernestii; f, Salix rehderiana; g, Astragalus mahoshanicus; h, Hippophae rhamnoides)
Article
Background and Aims Nitrogen (N2) fixation through endophytic diazotrophs within the non-nodulated plants has been considered a novel source of N inputs in terrestrial ecosystems. However, little is known about the composition and diversity of endophytic diazotrophs within the non-nodulated plants, especially when compared with the diazotrophs in nodulated plants. Methods High-throughput nifH amplification sequencing was conducted to characterize endophytic diazotrophs within different tissues (leaf, stem, and root) of non-nodulated plants (Salix rehderiana Schneid, S. ernestii Schneid, and Populus purdomii Rehd.) and nodulated plants (Astragalus mahoshanicus and Hippophae rhamnoides L.) which dominate in the newly formed N-limited glacier floodplain in the eastern Qinghai-Tibetan Plateau. Results We found endophytic diazotrophs, primarily Proteobacteria, in all tissue types of non-nodulated plants and leaf and stem of nodulated plants. The dominant genera were Bradyrhizobium, Ideonella, Azotobacter, and Geobacter. In comparison, diazotrophs within the nodule of leguminous Astragalus mahoshanicus and actinorhizal Hippophae rhamnoides were predominantly of genera Rhizobium and Frankia, respectively. Further, the community composition of diazotrophs was structured by plant species (P = 0.001), tissue types (P = 0.001), and nutrient concentrations (P = 0.001). Leaves of non-nodulated plants exhibited higher Chao1 indices and lower Simpson and Shannon indices than their stem and root, but these were not significantly different among different tissue types of nodulated plants. Conclusions Endophytic diazotrophs might be prevalent in pioneer plants occurring in the N-limited habitat and have a high degree of host specificity; these findings could help to understand the ability of those pioneer plants to acquire N.
 
Soil and air temperature (a), precipitation (b) and soil water content (SWC; wt.%) (c) measured in seven forests at two sampling dates in summer/autumn 2015 and one sampling date in summer 2014 (precipitation only) (means ± SE). Temperatures are means of seven-day periods prior to exudate sampling of each 5 sensors per stand, precipitation data are interpolated from gridded weather station data of the German Weather Service (DWD) corrected for elevation, and SWC data are gravimetric samples taken in the organic layer and 0–10 cm mineral soil at the date of sampling (n = 5)
Fine root biomass of beech in the organic layer (grey bars) and the mineral topsoil (0–10 cm) of the seven beech forests in November 2018 (means ± SE of 12 samples per layer). Different letters indicate significantly different means of organic layer samples (capital letters) and mineral soil samples (small letters)
Specific root length, specific root area, root tissue density and root tip frequency of the fine root biomass samples used for exudation collection in the seven forests. Shown are means and standard errors of n = 9 samples per site and sampling date with averaging over the three sampling dates
Means (and SE) of (a) measured average mass-specific root exudation rate, (b) daily exudation for the fine root mass in the organic layer expressed per m² ground area, (c) extrapolated annual mass-specific carbon flux with exudation, and (d) estimated annual C flux with exudation per m² ground area in the topsoil of the seven beech forests along the elevation gradient (averaged over n = 9 samples taken per date and site and n = 3 sampling dates in 2014 and 2015). Annual exudation (c and d) was estimated from the site-specific exudation-temperature relationship, temperature variation across the vegetation period, and the specific length of the vegetation period (number of days with mean temperature ≥ 10 °C) at the sites. As we calculated annual totals with pooled data, no SD can be given in figures c) and d). The exudation flux per ground area was extrapolated using the fine root biomass data from the organic layer (b) or the organic layer and the mineral topsoil (0–10 cm) (d). Different capital letters denote significantly different means at p < 0.05 with p-values adjusted by the Benjamini–Hochberg procedure for multiple comparisons (Kruskal–Wallis test)
Relationships between site-specific daily air temperature (means of the seven days prior to exudate measurement; left panels) or long-term mean summer air temperature (right panels) and (a) and (d) mass-specific root exudation rates, (b) and (e) cumulated annual C exudation per root mass, and (c) and (f) cumulated annual C exudation per ground area in the seven beech forests along the elevation gradient in summer 2015 (averaged over n = 9 samples per date and site; only 2015 data considered). Temperature data were measured with I-button loggers at the sampling sites. Annual rates take the variable length of the vegetation period (no. of days ≥ 10 °C) at the sites into account. Different colour of symbols indicates elevation of sites
Article
Aims Root exudation may have a large impact on soil biological activity and nutrient cycling. Recent advances in in situ -measurement techniques have enabled deeper insights into the impact of tree root exudation on rhizosphere processes, but the abiotic and biotic controls of exudation rate remain poorly understood. We explored the temperature dependence of root exudation in mature beech ( Fagus sylvatica L.) trees. Methods We measured fine root exudation in seven beech forests along an elevational gradient (310–800 m a.s.l.) and related carbon (C)-flux rates to mean daily temperature, actual precipitation, mean summer temperature (MST) and precipitation (MAP), soil moisture (SWC), and stand structure. Results Average mass-specific exudation (averaged over all sampling dates) ranged from 12.2 µg C g ⁻¹ h ⁻¹ to 21.6 µg C g ⁻¹ h ⁻¹ with lowest rates measured at highest elevations and peak rates at mid-elevation (490 m). Regression analyses showed a highly significant positive effect of site-specific daily air and soil temperature on exudation rates ( p < 0.01) with an average increase by 2 µg C g ⁻¹ h ⁻¹ per 1 °C-temperature increase, while the relation to mean summer or annual temperature and mean temperature of the measuring year was less tight. Exudation decreased with increases in mean annual precipitation and soil moisture, but increased with increasing stem density. Conclusions The root exudation rate of beech trees roughly triples between 10 °C and 20 °C mean daily temperature, evidencing a large temperature influence on root-borne C flux to the soil.
 
Article
Abstract Background and aims: Vegetable production under the plastic tunnel is a steadily growing sector worldwide, but this type of cultivation threatens environmental sustainability by degrading soil through continuous cropping conditions (CMC). This study aimed to assess the role of crop rotation (CR) with different winter leafy vegetables in ameliorating CMC problems by manipulating soil chemical and biological properties. Method: Four different leafy vegetables, including Welsh Onion (WO), Celery (CL), No Heading Chinese Cabbage (NCC), Lettuce (LT), and fallow eggplant (FE), were introduced during the eggplant fallow period (November–March) in two consecutive years, i.e., 2017 and 2018 following eggplant. We assessed eggplant production, soil chemical properties and described the soil microbial community under the introduced rotation system. Results: The results revealed that CR with winter leafy vegetables modified the soil environment by improving soil organic carbon (SOC), soil chemical, and biochemical characteristics in both years. Sequencing results showed significant variations in fungal and bacterial community structures at the genus and phylum levels in response to CR. CR reduced some disease-causing pathogens at the fungal genus levels, including Fusarium and Ascomycota, in both years and increased the abundance of some beneficial taxa such as Mortierella and Bacillus. Conclusion: These findings revealed the significance of crop rotation systems for sustainable production of eggplant under the plastic tunnel by enhancing soil physicochemical properties and soil beneficial microbes and reducing certain disease-causing soilborne pathogens. Keywords: Soil microbial community · Crop rotation · Winter vegetables · Soil enzyme activities · Soilborne pathogen suppression
 
The effect of leachate species and preparation method on Day-6 germination rates. Error bars represent ± 1 SE. The striped bars indicate average seed germination rates in the water control treatment ± 1 SE
The effect of water versus leachate seedling growth. Error bars represent ± 1 SE. Asterisks mark treatment contrasts that are significantly different at the p = 0.05 level
Article
Purpose Allelopathy is a plant interaction in which a donor species releases chemicals that suppress the development of receptor species. Allelopathy has been suggested as one explanation for catastrophic loss of native biodiversity in some invaded biomes; however, experimental tests of this hypothesis have had inconsistent results. Here, we examine if a previous finding of strong allelopathic effects of the warm-season, invasive C4 grass Bothriochloa ischaemum on North American prairie grasses can be reproduced in a different geographic setting. Methods We examined the effects of sterilized (autoclaved or microfiltered) and unsterilized leachate on germination and the effect of sterilized leachate on seedling growth, including five native species and two exotic warm season grass species. For nine weeks, seedlings were irrigated with water or autoclaved leachate from B. ischaemum or Schizachyrium scoparium, a native species. Results Germination rates were significantly suppressed only in the two invasive species and only when treated with sterilized leachates. Seedling biomass at harvest was largely insensitive to leachate application. Conclusions The present study did not replicate earlier results, though many details of the experimental designs were similar. However, we used sterilized leachates and soils, whereas the previous study did not, which could indicate mediation by indirect microbial effects in the previous study. In addition, historic differences in the introduction of B. ischaemum in Oklahoma and Texas, along with climatic differences, may have affected the evolution of allelopathy post-invasion. Future studies would benefit from comparisons of allelopathic effects across invasive species’ ecotypes, using sterilized and unsterilized extracts.
 
(a) Impact of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) co-inoculation (AMF-PGPR), only PGPR or AMF inoculation and of the tested control (non-inoculated) on wheat plant growth (b) Screening of PGPR’s isolates for 1-aminocyclopropane-1-carboxylate (ACC) deaminase enzyme production; 1.Bacillus amyloliquefaciens2.Bacillus megaterium3.Bacillus licheniformis4.Corynebacterium glutamicum (c) Light micrographs of mycorrhizal colonization of wheat roots
Influence of different water regimes (WW = Well-watered; 80% field water capacity, MSW = Moderate water stress; 55% field water capacity, and SWS = Severe water stress; 35% field water capacity) on (a) ACC accumulation (b) Root colonization (%) (c) Microbial biomass carbon and (d) Microbial biomass nitrogen in wheat plants inoculated with arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) co-inoculation (AMF-PGPR), only PGPR or AMF and in control (non-inoculated) across three developing stages (Tillering, Anthesis, and Pre-harvesting). Data are the mean ± SE of three biological replicates, while the same letter within the same water regime is statistically similar at p < 0.05 according to Tukey’s multiple range test
(a) Chlorophyll a (b) Chlorophyll b (c) Total chlorophyll content and (d) Carotenoid content in wheat plant leaves under three water regimes (WW = Well-watered; 80% field water capacity, MSW = Moderate water stress; 55% field water capacity and SWS = Severe water stress; 35% field water capacity) of the arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) co-inoculated (AMF-PGPR), only PGPR or AMF inoculated and of the tested control (non-inoculated) plants across three developing stages (Tillering, Anthesis, and Pre-harvesting). Data are mean ± SE of three biological replicates, while NS indicates non-significant, **, ***, **** indicate significance level at 0.01, 0.001, and 0.0001, respectively
(a) Photosynthetic rate (Pn) (b) Stomatal conductance (gs) (c) Intracellular carbon dioxide (Ci) and (d) Transpiration rate (E) in wheat plant leaves under three water regimes (WW = Well-watered; 80% field water capacity, MSW = Moderate water stress; 55% field water capacity and SWS = Severe water stress; 35% field water capacity) of the arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) co-inoculated (AMF-PGPR), only AMF or PGPR inoculated and of the tested control (non-inoculated) plants across three developing stages (Tillering, Anthesis, and Pre-harvesting). Data are mean ± SE of three biological replicates, while **, ***, **** indicate significance levels at 0.01, 0.001, and 0.0001, respectively
Principal component analysis (PCA) of the different studied traits and treatments under three water treatments [(a): (WW = Well-watered; 80% field water capacity (b): MSW = Moderate water stress; 55% field water capacity (c): SWS = Severe water stress; 35% field water capacity)] across three developing stages (Tillering, Anthesis, and Pre-harvesting). Chla, chlorophyll a; Chlb, chlorophyll b; TChl, total chlorophyll; IntraC, intracellular carbon dioxide; TransR, transpiration rate; StomCon, stomatal conductance; PhotoR, photosynthesis; RC, Root colonization; ACC; 1-aminocyclopropane-1-carboxylate, MBC; Microbial biomass carbon, MBN; Microbial biomass nitrogen
Article
Purpose In drought-prone soils, plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungus (AMF) might positively affect water uptake and crop yield via rhizosphere interactions. Methods Sole and combined additions of Bacillus amyloliquefaciens producing 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and Rhizophagus irregularis into rhizospheric soils were performed under well-watered (WW; 80% field water capacity), moderate water stress (MWS; 50% FWC) and severe water stress (SWS; 35% FWC) in pot-cultured wheat (Triticum aestivum L.). Results In moderate and severe drought stress, water use efficiency (WUEB) was increased by 27.9–34.3% in PGPR and 20–22.1% in AMF treatments, respectively, and grain yield was improved by 20.03–30.77% in PGPR and 12.13–34.34% in AMF treatments, respectively, compared with control (CK). Importantly, the co-inoculation of AMF and PGPR significantly promoted WUEB by 11.12–27.77% and grain yield by 18.26–21.68% compared to the average value of two sole inoculations in MWS and SWS treatments, respectively. WUEY and biomass production followed a similar trend as WUEB and yield. Particularly, the above parameters were significantly enhanced with the prolonged developmental stages (p < 0.05). ACC deaminase significantly reduced ACC accumulation in MWS and SWS, enhanced AMF root colonization, and promoted rhizosphere microbial biomass carbon and nitrogen levels across all three developing stages. Furthermore, AMF-PGPR co-inoculation enhanced chlorophyll and carotenoid contents during anthesis while reducing them during pre-harvesting. Enhanced water uptake and root activities upsurged photosynthetic traits throughout the growing season. Conclusion AMF-PGPR co-inoculation acted as a promising solution to cope with the droughted environment via root activities for stronger water capture.
 
Article
Aims Nitrate content in crops might be affected by soil abiotic properties and endophytic and soil microbes. This study aimed to reveal the effects of spent mushroom substrate (SMS) and nitrification inhibitor dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) on the nitrate content of pepper fruit and to link the nitrate with soil abiotic properties and endophytic and soil bacterial communities. Methods Our current study contained four different treatments: blank control (CK); sole SMS application (SAA); SMS + DCD (SDCD); and SMS + DMPP (SDMPP). The nitrate contents and bacterial communities in fruit, root and soil samples were quantified and linked. Results Compared with the CK treatment, the nitrate contents of pepper fruit decreased by 43.2%, 66.8% and 64.4% in the SAA, SDCD and SDMPP treatments, respectively. The combined applications of SMS and nitrification inhibitors significantly enhanced the pH and bacterial community diversity of soil samples. The SMS applications significantly changed bacterial community structures in the soils and roots rather than in the fruit. The relative abundances of aerobic chemoheterotrophy function in the fruit samples were 0.28, 0.17, 0.10 and 0.15 for the CK, SAA, SDCD and SDMPP treatments, respectively. The relative abundances of Bacteroidetes and aerobic chemoheterotrophy were significantly and positively correlated with nitrate contents in the fruit. Conclusions Apart from promoting fruit yield, the SMS and nitrification inhibitor applications could also decrease the health risk of crop nitrate accumulation via affecting the soil pH, ammonium content and endophytic bacterial community diversity, structures and functions in fruit samples.
 
Chromatogram of soil MOC in the 0–0.1 m layer assigned by GC/MS. Table 2 contains the full list of peak identifications
Chromatogram after pyrolysis of MOC in the 0–0.1 m (a) and 28–29 m (b) layers assigned by GC/MS. Table 3 contains the full list of peak identifications
Article
Aims Organic carbon has been reported in deep regolithic profiles to depths of tens of metres, but the composition of the carbon compounds is unknown. Methods Residual carbon in the form of non-volatile low molecular weight compounds (LMWC) was characterised in three deep soil profiles to a depth of 19 m under farmland in south-western Australia following extraction with ethyl acetate and analysis by GC/MS. Pyrolysis and off-line thermochemolysis were used to characterise macromolecular organic carbon (MOC) to a depth of 29 m at a fourth site. Results Three compound classes occurred across the three different field locations: (1) terpenes, (2) fatty acids, amides and alcohols, and (3) plant steroids; indicating the influence of input of the past and present vegetation. Compounds related to fatty acids were the predominant residual carbon species in deep soils, and may be derived from plants and microorganisms. Biomarkers such as lignin, polysaccharides, proteins and terpenes at 0–0.1 m implied influences of vegetation, fire events and microorganisms. Pyrolysis found that polysaccharides were distributed mainly from 0 to 0.1 m, while aromatic compounds were consistently detected down to 29 m. Conclusions Carbon was stabilised in the form of aromatic compounds in deep soil, whereas other carbon sources such as cellulose, chitin, and N-containing compounds were confined to the surface soil. LMWC (Z)-docos-13-enamide and bis(6-methylheptyl) phthalate, were the main components throughout the soil profiles representing 53–81% of the LMWC, and were a greater proportion of the organic matter at depths of 18–19 m.
 
Article
Purpose Herbivore grazing and nitrogen (N) input may alter the multiple ecosystem functions (i.e., multifunctionality, hereafter) associated with carbon (C), N, and phosphorus (P) cycling. Most studies on variations in plant diversity, soil biotic or abiotic factors, and linkages to ecosystem functions have focused on grazing or N enrichment alone. Few studies have combined these two factors to explore the role of plant resource stoichiometry (C:N:P ratios) in ecosystem multifunctionality (EMF) control. Here, we evaluated the direct and indirect effects of stocking rate (0, 2.7, 5.3, and 8.7 sheep ha− 1) and N addition rate (0, 5, 10, and 20 g N m− 2 yr− 1) on a range of ecosystem functions and EMF via changing plant diversity, soil pH and plant resource stoichiometry in a typical steppe on the Loess Plateau. Results We found that increasing stocking rate and interaction between grazing and N addition significantly decreased EMF, while increasing N addition rate significantly promoted EMF. Grazing decreased soil NH4⁺-N, soil NO3⁻-N, aboveground biomass, and plant C, N, and P pools, but increased soil total N and P at 8.7 and 5.3 sheep ha− 1, respectively. N addition increased soil NH4⁺-N, NO3⁻-N, and total P. Plant aboveground biomass, and plant C, N, and P pools increased at the lower N addition rate (≤ 5 g N m− 2 yr− 1) under grazing. The structural equation models indicated that (1) EMF was driven by the direct effects of grazing and the indirect effects of grazing on plant resource stoichiometry and soil pH; (2) EMF increased with increasing N addition rates, but such positive response of EMF to increasing N addition rates was alleviated at high levels of plant resource stoichiometry and diversity; and (3) the indirect effects of plant diversity induced by grazing and N addition had moderate effects on EMF via the variations of plant resource stoichiometry. Conclusions This study demonstrated grazing and N addition had contrasting effects on ecosystem multifunctionality in a typical steppe, and highlighted the capacity of plant diversity in balancing plant elements that serve as a key mechanism in the maintenance of EMF in response to intensive grazing y and N enrichment.
 
Article
Purpose Belowground carbon (C) allocation for nitrogen (N) acquisition plays a crucial role in determining primary productivity and plant competitiveness in legume-grass mixtures, but beyond modeling and qualitative assessments, this remains poorly understood, especially with regard to drought stress and interspecific interactions. Methods We grew a legume (Trifolium repens) and a grass (Lolium perenne) in monocultures and as a 50:50 mixture (with same plant density), at 70% and 50% soil water holding capacity representing non-drought and drought conditions, for 104 days in a growth chamber experiment. By using continuous ¹³CO2 labelling and ¹⁵N pulse soil-labelling, we analyzed how drought and interspecific interaction affected belowground C allocation (including root biomass, root respiration and rhizodeposition) and N acquisition through soil N uptake and biological N fixation. Results Drought increased belowground C allocation per unit of N acquisition in the legume, but not in the grass. Drought significantly reduced biological N fixation in the legume, so that the legume allocated relatively more C to take up soil N. Interspecific competition increased belowground C allocation per unit of N acquisition, which could be attributed to a reduction in biological N fixation by the legume and an increased abundance of the grass. Conclusions We highlight that drought and interspecific competition for N strongly alter C allocation towards biological N fixation and soil N uptake. Our measurements provide important process-based information to improve modeling drought effects on productivity and composition in legume-grass mixtures.
 
Mycorrhizal colonization measured as percentage of root length colonization and mycorrhizal parameters, and plant biomass for co-inoculated plants at 47 and 63 dpi harvests (n = 3). Statistical significance was determined with α = 0.05 using one-way ANOVA. Bars correspond to standard error. Different letters indicate different homogenous groups calculated by Tukey test. Myc: Rhizophagus irregularis; C.s.: Candida saitoana; T.p.: Tausonia pullulans; S.e.: Saccharomyces eubayanusm
Relative gene expression measured by RT-qPCR for mycorrhiza-related genes in roots of co-inoculated plants at 63 days post-inoculation (dpi) harvests. Each gene as a relative expression with respect to the single inoculation treatment with R. irregularis (Myc). Statistical significance was determined with α = 0.05 using one-way ANOVA. *: Kruskal–Wallis analysis. Different letters indicate different homogenous groups calculated by Tukey test for each variable. Myc: Rhizophagus irregularis; C.s.: Candida saitoana; T.p.: Tausonia pullulans, S.e.: Saccharomyces eubayanus. Studied genes: GinEF = R. irregularis elongation factor; D27 = tomato beta carotene isomerase d27; RAM1 = tomato GRAS transcription factor RAM1; PT4 = tomato mycorrhiza-inducible inorganic phosphate transporter 4
Endogenous abscisic acid (ABA), salicylic acid (SA), 12-OPDA and jasmonic acid (JA) contents in the roots of tomato plants with different inoculation treatment, harvested at 47 and 63 dpi (n = 3). Different letters indicate different homogenous groups calculated by Tukey test. Control: non-inoculated; Myc: Rhizophagus irregularis; S.e.: Saccharomyces eubayanus
Expression of defense-related genes PR1a and PinII in the roots of tomato plants with different inoculation treatment, harvested at 47 and 63 dpi. Each gene as a relative expression with respect to the single inoculation treatment with R. irregularis (Myc). Transcript levels were determined using RT-qPCR. Mean value (empty dot) and standard error (bar) for each treatment are shown. Expression was normalized with respect to the control non-inoculated plants, in which expression was designated as 1. *: Kruskal–Wallis analysis. Different letters indicate different homogenous groups calculated by Tukey test. Control: non-inoculated; Myc: Rhizophagus irregularis; S.e.: Saccharomyces eubayanus. Studied genes: PR1a = pathogenesis-related protein 1a; PinII = proteinase inhibitor II
Expression of genes related to jasmonic acid biosynthesis pathways in the roots of tomato plants with different inoculation treatment, harvested at 47 and 63 dpi. Each gene as a relative expression with respect to the single inoculation treatment with R. irregularis (Myc). Transcript levels were determined using RT-qPCR. Mean value (empty dot) and standard error (bar) for each treatment are shown. Expression is normalized with respect to the control non-inoculated plants, in which expression was designated as 1. *: Kruskal–Wallis analysis. Different letters indicate different homogenous groups calculated by the Tukey test. Control: non-inoculated; Myc: Rhizophagus irregularis; S.e.: Saccharomyces eubayanusMyc: Rhizophagus irregularis; S.e.: Saccharomyces eubayanus. Studied genes: LOXD = Lipoxygenase D; AOS1 = Allene oxide synthase 1; OPR3 = oxo-phytodienoic acid reductase 3
Article
Aims Many studies have reported beneficial effects of yeasts on the colonization and development of arbuscular mycorrhizae, thought a few studies have also shown neutral effects. All these studies have in common that the mechanism, by which yeasts and mycorrhizae interact, is little understood. Here, we explore how plant growth-promoting yeasts affect the colonization of tomato plants by beneficial mycorrhizal fungi. Methods We tested the influence of the soil yeasts Candida saitoana, Tausonia pullulans, and Saccharomyces eubayanus on colonization of tomato roots by the mycorrhizal fungus Rhizophagus irregularis. We analyzed mycorrhizal parameters and the expression pattern of mycorrhiza-specific genes. In plants co-inoculated with S. eubayanus and R. irregularis, we measured the root accumulation pattern of jasmonic acid, oxo-phytodienoic acid, abscisic acid and salicylic acid, and the expression of genes related to plant hormone signaling and metabolism. Results The three yeasts had distinct effects on mycorrhizal colonization: C. saitoana had no effect on mycorrhizal parameters, T. pullulans delayed mycorrhizal colonization at an early stage, and S. eubayanus slowed colonization down throughout the entire trial. In plants co-inoculated with S. eubayanus and R. irregularis, we observed a sustained increase in jasmonic acid and up-regulation of the JA biosynthesis related genes LOXD, OPR3, and AOS1. Conclusion Co-inoculation with yeast affected mycorrhizal colonization and altered the expression pattern of mycorrhizal and plant defense-related genes. In particular, the yeast S. eubayanus modified plant defense hormones such as jasmonic acid, which is linked to mycorrhizal-induced resistance in tomato plants.
 
Laboratory and pilot trials setup. a Section view of box stratification. b Section view of the growing bed stratification. c Plant arrangement in laboratory scale boxes. d Plant arrangement in the pilot scale growing bed
Hyperaccumulator plants growing on P1 sewage sludge at the 12th week of culture
Trace metal accumulation in the shoot (aerial parts) of the four selected species. a As uptake in P. vittata.b Ni uptake in O. chalcidica. c Se uptake in A. bisulcatus. d Zn uptake in N. caerulescens. Data represent the average of 5 biological replicates ± SD. Small letters indicate significant differences in metal uptake among samples during weeks 7 to 16 according to ANOVA/Kruskal-Wallis followed by Tukey HSD/Dunn tests (p < 0.05). Data from weeks 7–15 represent trace metal concentration in young leaves, while the darker bar represents the average trace metal content in whole plant aerial biomass collected at week 16. Complete dataset (including root data) is available in Supplementary Table S3
Macronutrient and trace metal content in leachate. a Macronutrients (N (NH4⁺, NO3⁻), P, K, mg/l), b trace metals (As, Ni, Se, Zn, mg/l). Data represent the average of 5 biological replicates ± SD. Small letters indicate significant differences in the analysed parameters across weeks 1 to 13 according to ANOVA/Kruskal-Wallis followed by Tukey HSD/Dunn tests (p < 0.05). Data from weeks 14–16 were unavailable for lack of leachate. Complete dataset available in Supplementary Table S5
Article
Aims The present study aimed at: (i) verifying the suitability of pure sewage sludge (SS) as growing medium for the hyperaccumulator species ( Pteris vittata , Odontarrhena chalcidica, Astragalus bisulcatus and Noccaea caerulescens ); (ii) evaluating the removal of As, Ni, Se and Zn operated by the chosen species; (iii) estimating the potential metal yields (bio-ore production) and connected monetary rewards in a small-scale field experiment. Methods Hyperaccumulator plants were first tested under controlled conditions, on three different SS (P1, P2, P3) characterized by the presence of one or more contaminants among As, Ni, Se and Zn. P1 sludge was then chosen for a small-scale field experiment. Hyperaccumulator seedlings were transferred on SS and cultivated for 16 weeks before harvesting. Results All hyperaccumulator species grew healthy on P1 SS, with A. bisulcatus and O. chalcidica reaching an average biomass of 40.2 and 21.5 g DW/plant. Trace metal concentrations in aerial parts were: As ( P. vittata) 380 mg/kg DW, Ni ( O. chalcidica) 683 mg/kg DW, Se ( A. bisulcatus) 165 mg/kg DW, Zn ( N. caerulescens) 461 mg/kg DW. The total removal of As, Ni, Se and Zn from SS due to phytoextraction was 5.8, 19, 18, 29% respectively. Conclusions This study demonstrated that phytoextraction can be applied to SS for the removal contaminants while recovering valuable metals. Se and As were identified as the most promising target element, while Ni and Zn removal was poorly efficient under the present experimental conditions.
 
Article
Aim As an environment friendly regulating factor, acetic acid (AA) plays an important role in linking basic physiological progresses and hormone signaling. Methods In this study, seedlings of Cunninghamia lanceolate collected from two different rainfall regions were used to explore the effects of exogenous AA. Results The results indicated that exogenous AA (200 mM) could eliminate drought-induced damages. The application of AA to soils could induce needle abscisic acid accumulation to decrease stomatal conductance and transpiration rate and further lead to the maintenance of needle water content and water use efficiency. Meanwhile, AA promotes the photosynthetic activity and photo-protection by increasing the contents of chlorophyll pigments and the activity of PSII reaction center. The alleviation of electrolyte leakage and malondialdehyde induced by drought, accompanied by the enhancement of the ROS scavenging system and osmotic regulation indicated that AA could protect cell membrane and eliminate oxidative toxicity. Additionally, this work further showed the provenance-specific responses to exogenous AA and demonstrated the feasibility of exogenous AA in larger pot experiments for woody plants. Conclusion Overall, our study provides evidence that exogenous AA can strengthen the ability of C. lanceolate seedlings against drought as a positive regulator. Therefore, the irrigation of appropriate doses of AA into soils can be an effective practice against drought for Chinese fir forests.
 
Article
Aims Peanut (Arachis hypogaea L.) straw decomposition and nutrient release (N, K, and P) processes were investigated using a 3-pool model (labile, intermediate, and resistant) to understand the determinant factors. Methods A two-year field experiment was carried out with a split-plot design: the main plot contained two irrigation regimes, while the subplot contained three peanut straw incorporation rates. A total of 216 nylon-mesh bags consisting of peanut straw were buried at a depth of 20 cm, and were removed at 6 winter wheat growth stages (overwintering, double ridge, jointing, flowering, grain filling, and maturity), and the nutrient release (N, P and K) from the peanut straw was measured. Results The decomposition dynamics of the labile and intermediate pools were similar in both years. The straw incorporation rate, rather than the irrigation regime, controlled the decomposition process, which increased with increased straw incorporation rates. At a high incorporation rate, the released N, P, and K from the peanut straw were approximately 39%, 30%, and 87% of the required regional fertilizer input for winter wheat, respectively. Furthermore, the N released from straw decomposition was strongly related to the released K as indicated by the stoichiometry ratio. The random forest model predicted that temperature, precipitation, and initial straw nutrients were the main drivers of peanut straw decomposition. Conclusions We determined the nutrient stoichiometry and release characteristics of peanut straw decomposition, and found that in comparison to irrigation, the straw incorporation rate exhibits a more profound effect on the peanut straw decomposition process. Graphical abstract
 
Soil properties (pH, TC: Soil total C content, TN: Soil total N content, IN: Inorganic N), microbial biomass C (MBC) and soil extracellular enzyme activities (BG: β-glucosidase; NAG: N-acetyl-β-glucosaminidase, Oxidase) along an altitudinal gradient on the northern slope of Changbai Mountain. Values are means of replicates (n = 4) and error bars are standard errors. Asterisks indicate significant differences between bulk soil and rhizosphere soil based on paired-samples t-tests (*P < 0.05, **P < 0.01)
Soil C mineralization rate (Cmin) and soil net N mineralization rate (Nmin) along an altitudinal gradient on the northern slope of Changbai Mountain. Values are means of replicates (n = 4) and error bars are standard errors. Asterisks indicate significant differences between bulk soil and rhizosphere soil based on paired-samples t-tests (*P < 0.05; **P < 0.01)
Relationships between soil C mineralization rate (Cmin) and soil net N mineralization rates (Nmin) in (a) rhizosphere soil and (b) bulk soil
Structural equation model (SEM) showing the multivariate effects of soil properties, microbial biomass C, and extracellular enzyme activities on C mineralization (Cmin) and net N mineralization (Nmin) rates in a) rhizosphere soil and b) bulk soil. Arrows indicate the hypothesized direct and indirect pathways. Orange arrows indicate positive relationships and blue arrows indicate negative relationships. Width of arrows represents the strength of the relationship. Double-layer rectangles represent the first component (PCA, principal component analysis) of soil properties (pH, TC: Soil total C, TN: Soil total N, IN: Inorganic N), microbial biomass C (MBC) and soil enzyme activities (BG: β-glucosidase; NAG: N-acetyl-β-glucosaminidase, Oxidase). The numbers next to arrows are standardized path coefficients. The solid arrows represent significant (†P < 0.1; *P < 0.05; **P < 0.01; ***P < 0.001) and the grey dashed arrows represent non-significant (P > 0.1) relationships. The proportion of variance explained (R²) appears alongside each response variable in the model. Goodness-of-fit statistics for the model: a) χ2 = 2.85, P = 0.09, df = 1, RMSEA = 0.22, CFI = 0.984, GFI = 0.976, ACI = 42.85; b) χ² = 1.39, P = 0.24, df = 1, RMSEA = 0.10, CFI = 0.997, GFI = 0.988, ACI = 41.39
Conceptual framework depicting potential mechanisms of the relationship between soil carbon mineralization (Cmin) and net N mineralization (Nmin) rates for bulk soil (left) and rhizosphere soil (right). Boxes represent the pools of soil organic matter (SOM) and soil microbes. The size of the boxes indicates the relative pool size between bulk and rhizosphere soil. Arrows show C and N fluxes from one pool to another. The thickness of the arrows indicates the magnitude of the flux. The red double-headed arrows indicate the interactions between Cmin and net Nmin. Words with question mark indicate there is no direct evidence to support them in the current study. MBC, microbial biomass carbon; Nimmobilization, N immobilization process; IN, cumulative inorganic N; CO2, cumulative microbial respiration. Further explanations are shown in the main text
Article
Aims Rhizosphere is a hotspot for soil C and N biogeochemical cycling in terrestrial ecosystems. However, the interaction between soil C and N mineralization remain poorly understood in the rhizosphere soils. This study aimed to identify interactions between soil C and N mineralization in rhizosphere soils and bulk soils at a large scale. Methods We used the “soil adhering to fine roots after shaking” method to collect paired rhizosphere soils and bulk soils along an altitudinal forest gradient. Soil C mineralization rates (Cmin) and net N mineralization rates (Nmin) were determined with laboratory incubation. Results We found a significantly positive relationship between Cmin and Nmin in the rhizosphere soils across sites, whereas Cmin was not correlated with Nmin in the bulk soils. Furthermore, soil properties, microbial biomass C (MBC) and extracellular enzyme activities showed substantial paths affecting Cmin and Nmin using structural equation model. The coupling of Cmin and Nmin in rhizosphere soils could be triggered by root-soil interactions, resulting in the higher level of MBC, total organic C of soil, total N of soil, and extracellular enzyme activities. By contrast, the decoupling of Cmin and Nmin in the bulk soils might be attributed to the lower level of MBC and extracellular enzyme activities. Conclusions Our results demonstrated that soil C and N mineralization coupled in the rhizosphere rather than in the bulk soils. These results suggest that the interaction between soil C and N cycling in rhizosphere are likely to differ from that in bulk soil.
 
Article
Purpose Tackling the global carbon deficit through soil organic carbon (SOC) sequestration in agricultural systems has been a focal point in recent years. However, we still lack a comprehensive understanding of actual on-farm SOC sequestration potentials in order to derive effective strategies. Methods Therefore, we chose 21 study sites in North-Eastern Austria covering a wide range of relevant arable soil types and determined SOC pool sizes (0–35 cm soil depth) in pioneer versus conventional management systems in relation to permanently covered reference soils. We evaluated physico-chemical predictors of SOC stocks and SOC quality differences between systems using Fourier-transform infrared (FTIR) spectroscopy. Results Compared to conventional farming systems, SOC stocks were 14.3 Mg ha − 1 or 15.7% higher in pioneer farming systems, equaling a SOC sequestration rate of 0.56 Mg ha − 1 yr − 1 . Reference soils however showed approximately 30 and 50% higher SOC stocks than pioneer and conventional farming systems, respectively. Nitrogen and dissolved organic carbon stocks showed similar patterns. While pioneer systems could close the SOC storage deficit in coarse-textured soils, SOC stocks in medium- and fine-textured soils were still 30–40% lower compared to the reference soils. SOC quality, as inferred by FTIR spectra, differed between land-use systems, yet to a lesser extent between cropping systems. Conclusions Innovative pioneer management alleviates SOC storage. Actual realized on-farm storage potentials are rather similar to estimated SOC sequestration potentials derived from field experiments and models. The SOC sequestration potential is governed by soil physico-chemical parameters. More on-farm approaches are necessary to evaluate close-to-reality SOC sequestration potentials in pioneer agroecosystems.
 
Map of sampling locations in the Karkonosze. circle alpine heathlands, triangle acidic swards, white square subalpine scrubs, square subalpine tall forb community
Changes in mineral N concentration after 90 days of soil incubation (in relation to the initial value). Different lower case letters – indicate significant differences (Kruskal–Wallis Test). Bars represent median ± median absolute deviation (MAD)
PCA ordination of individual relevés based on environmental variables in relation to the first two axes. Symbols: circle alpine heathlands, triangle acidic swards, white square subalpine scrubs, square subalpine tall forb community. Abbreviations: N-NO3⁻ – soil nitrate nitrogen content, N-NH4⁺ – soil ammonium nitrogen concentration, DON – soil dissolved organic nitrogen, NO3⁻/NH4⁺ – quantitative ratio of soil nitrate nitrogen to ammonium nitrogen content after 90 days of laboratory incubation, C:N – soil total carbon to nitrogen ratio, CTot – soil total carbon, NTot – soil total nitrogen, N-MIN – soil total inorganic nitrogen after 4 months of incubation, pH – soil reaction, H – altitude a.s.l
Distance-based redundancy analysis (dbRDA) ordination relating environmental variables to plant community assemblage data, showing biplot projections for environmental variables. Analysis was performed on principal coordinate axes obtained from Bray–Curtis resemblance matrices of square-root transformed data. Projected environmental variables: soil pH; altitude a.s.l; soil total C – C tot; soil N-NH4⁺
Article
Aims The aim of the study was to investigate N biogeochemistry of four neighboring, high mountain plant communities and to identify main factors which drive variability among them. We hypothesized that the vegetation types differ in terms of N transformations, and that spatial differentiation of the communities and dominant growth form can reflect an existence of several N-environments along an elevational gradient. Methods Plant and soil N characteristics were studied in four vegetation types: heathland, scrub, sward and tall forb. Leaf nitrate reductase activity and total N were measured in the dominant species. Soil pH, total C, N, inorganic and dissolved organic N concentrations were measured. The soil net N mineralization rate was examined. Results The DistLM and PERMANOVA analyses revealed that variability among the vegetation types was driven primarily by elevation, soil N–NH 4 ⁺ , soil pH and soil total C. We identified three distinct N-environments along an elevational gradient. The “N-poor alpine” located at the highest altitudes, strongly N-limited and dominated by dwarf-shrub. The "N-mixed subalpine" located in the middle of the gradient and covered by scrub and sward. It was characterized by moderate N turnover rate. The "N-rich subalpine" occurred at lowest locations and was covered by subalpine tall forb community. It exhibited the highest dynamics of N transformations and was rich in inorganic N. Conclusion Three main N-environments were identified: N-poor alpine, N-mixed subalpine, N-rich subalpine. Variability among the vegetation types was driven primarily by elevation, soil N–NH 4 ⁺ , soil pH and soil total C.
 
Study sites and associated landscapes in wetland (CZ, GY and SX) and mountain (ZG, HT and ZQ) forests across subtropical areas in China. The black circle marked as CZ, GY, SX, ZG, HT and ZQ represents the sampling site at Chizhou, Gaoyou, Shaoxing, Zigui, Huitong and Zhaoqing, respectively
Isotopes (δ¹⁸O and δD) of groundwater, soil water and tree xylem water in wetland (a, b, c) and mountain (d, e, f) forests across subtropical China. LMWL is the local meteoric water line (Table 2). CZ, GY, SX, ZG, HT and ZQ represents the sampling site at Chizhou, Gaoyou, Shaoxing, Zigui, Huitong and Zhaoqing, respectively
Precipitation offset of soil water, tree xylem water and groundwater in six sites from wetland and mountain forests across subtropical China. Extents of water bars show 25th and 75th percentiles. CZ, GY, SX, ZG, HT and ZQ represents the sampling site at Chizhou, Gaoyou, Shaoxing, Zigui, Huitong and Zhaoqing, respectively. Different letters indicate significant differences (Duncan test, P < 0.05)
Article
Purpose Ecohydrological separation (ES) phenomenon, whereby two compartmentalized soil reservoirs supply either plant water uptake or stream/groundwater recharge, provides a novel mentality for hydrological model simulation and water resource management. However, it remains uncertain whether the ES phenomenon exists in subtropical forests, especially in different types of forests at the regional scale. Methods We employed stable hydrogen and oxygen isotopes (δD and δ¹⁸O) to explore the relationship between tree xylem water, soil water and groundwater in two types of forests (wetland and mountain forests, respectively) from six sites across subtropical China. Furthermore, we also calculated the precipitation offset and soil/xylem water δ source values to clarify whether the ES phenomenon exists in both wetland and mountain forests of subtropical China. Results δD and δ¹⁸O of tree xylem water were similar to that in soil water rather than groundwater across six subtropical forests. Ulteriorly, precipitation offsets showed a significant difference between soil/tree xylem water and groundwater, whether in mountain forests or wetland forests. In addition, soil and tree xylem water δD/δ¹⁸O source values were significantly higher than groundwater δD/δ¹⁸O in these forests. Conclusion Three lines of evidence indicated that the ES phenomenon existed in both wetland and mountain forests of subtropical China. The ES phenomenon should be further used to hydrological models for projecting runoff formation, surface water retention time and evaporation-transpiration partitioning in subtropical forests, which could largely improve the simulation accuracy.
 
a Soil temperature and (b) volumetric water content for ambient temperature and warmed plots at 5 cm depth from September 2019 to July 2021 (the data did not differ between new and old plots, and were thus pooled)
Potential extracellular enzyme activities in May and July in response to warming and plot age (unfertilized plots only; n = 10). P-values from the two-way ANOVA are provided in Tables 1, with significant effects displayed on the figure panels
Potential extracellular enzyme activities in May and July in response to nitrogen addition and plot age (ambient temperature plots only; n = 10). P-values from the two-way ANOVA are provided in Tables 1, with significant effects displayed on the figure panels
Potential extracellular enzyme activities in May and July in response to nitrogen addition and warming (old plots only; n = 10). P-values from the two-way ANOVA are provided in Tables 1, with significant effects displayed on the figure panels
Litter mass loss from (a) Bromus inermis leaves and (b) Cirsium arvense examined for (i) warming and plot age (ii) nitrogen addition and plot age and (iii) warming and nitrogen addition (old plot only). P-values from the two-way ANOVA are provided in Table 2, with significant effects displayed on the figure panels
Article
Purpose In long-term global change experiments, while cumulative treatment effects on soil and plant responses can emerge over time, comparisons between short and long-term responses can potentially be confounded with interannual variability in the environment. We added new nitrogen addition and warming plots to a pre-existing nitrogen and warming field experiment in a grass-dominated field to compare the short-term (1–2 year; new plots) versus long-term (14–15 year; old plots) treatment effects on soil microbial activity and plant litter decomposition, while controlling for the effects of interannual environmental variability. Methods We assessed microbial activity by assaying the potential activities of five soil extracellular enzymes: three hydrolase enzymes (N-acetyl-glucosaminidase, phosphatase and β-glucosidase) and two oxidase enzymes (phenol oxidase and peroxidase). We measured mass loss from litter bags to assess the decomposition of grass and forb litter. Results Warming interacted with plot age, with increased hydrolase activity in spring in response to warming only occurring in the long-term plots; increases in peroxidase activity with nitrogen addition in spring occurred for all plots. By summer, there were no significant interactions between the treatments and plot age for enzyme activity. Decreased decomposition with warming, observed for forb litter, only occurred in the long-term plots, but increased decomposition with nitrogen addition, observed for grass litter, occurred in both the long-term and short-term plots. Conclusions Our results confirm an intensification of treatment effects on enzyme activity and litter decomposition over time for warming, but no interactions with plot age for nitrogen addition.
 
Article
Purpose To provide useful knowledges for plantation management, we assessed how the transforming of the different ecosystem types to tree plantation may affect soil carbon (C), nitrogen (N), and phosphorus (P) concentrations and what are the driving factors of ecosystem transformation effects. Methods We synthesized 4262 pairwise observations collected from 366 peer-reviewed publications using meta-analysis method to assess the effects of ecosystem transformation to plantation on soil C, N, and P concentrations. Results We found that (1) ecosystem transformation effects on soil C, N, and P concentrations significantly varied with former ecosystem types, with positive effects of transforming croplands, deserts, and grasslands to plantations on total C (TC), soil organic C (SOC), dissolved organic C (DOC), total N (TN), and/or available N (AN), but negative effects of transforming primary and secondary forests to plantations on TC, SOC, TN, AN, and/or available P (AP); (2) the concentrations of soil dissolved organic N (DON), ammonium (NH4⁺), and nitrate (NO3–) were not affected by ecosystem transformation regardless of the former ecosystem types; and (3) ecosystem transformation effects were impacted by a variety of moderator variables, with climate, mycorrhizal association, stand age, and soil moisture and pH the most important ones. Conclusion Transforming croplands, deserts, and grasslands to plantations will increase soil C, N, and/or P concentrations, but transforming primary and secondary forests to plantations had opposite effects. Our results help to better understand ecosystem transformation effects on soil C and nutrient concentrations, and will be useful for guiding afforestation and sustainable plantation managements under global environment change scenario.
 
Article
Aims In the finite element method, the mechanical behaviour of plant roots has been modelled by solid element or embedded beam element (EBE). However, the former is computationally expensive, whereas the latter is unable to capture the root pull–out failure mode. In this study, we modified the constitutive stress–strain relationship of an existing EBE to calculate uprooting resistance by considering the root–soil interfacial shearing and the strength decline as root pulls out. Methods We introduced an elasto–softening constitutive law to describe the root–soil interface interaction and an improved damage model to capture post–peak softening behaviour in EBE. We validated the EBE against three case studies. Finally, we conducted parametric analysis to study how root geometries, morphologies and soil saturation affect the uprooting response. Results Our new model captures the pre–peak uprooting behaviour up to the peak pull–out force (Pul). Root systems that failed by pull–out mode always had lower Pul than those that failed by breaking, irrespective of the root morphology. Reduction of soil effective stress following soil saturation always reduced Pul and could change the root failure mode, depending on the anchorage length and root–soil contact surface area. Conclusions Root–soil mechanical interaction and root failure mode, including pull–out and breakage, can now be modelled with more accuracy. We show the importance of considering soil moisture variation, which translates to variations in root reinforcement effects. The reinforcement effectiveness of deep–rooted systems can be halved, and the root failure mode can switch from breakage to pull–out, following soil saturation and reduction of soil effective stress.
 
Definition of the range of spheres influenced by root or by AM fungi in soil, forming the endosphere, rhizosphere, mycorrhizosphere and hyphosphere
The AM hyphae-mediated physical, chemical and biological changes and nutrient cycling in the hyphosphere. The lines with different colors on the left depict physical, chemical and biological processes at the hyphae-soil interface. Physical processes (red line) include soil aggregate formation and stabilization, physical weathering, acquisition, utilization and redistribution of soil water. Chemical processes (blue line) involve metal cation adsorption, nutrient depletion, acidification and oxidation–reduction. Biological processes (green line) include exudates, enzymes, small peptides and microorganisms. The cylinder in the centre depicts the hyphae and contains information on the internal carbon, nitrogen and phosphorus cycling mediated by transporters, permeases and metabolic pathways in the extraradical hyphae. The four zones on the right depict carbon, nitrogen and phosphorus cycling and their subsequent environmental consequences in the hyphosphere mediated by exudates of extraradical hyphae. These mycelial exudates contain low-molecular-weight compounds, such as glucose, fructose, oligosaccharides and amino acids, and they could serve as a C sources substrate or signalling molecules to stimulate growth and activity of AM fungi-associated bacteria. These bacteria are involved in decomposing organic matter through decomposing enzymes, and consequently release CO2. The N cycle in the hyphosphere is primarily controlled by microorganisms (saprotrophic fungi, bacteria, protists, etc.), and they are involved in transformation of inorganic and organic N forms by different pathways. The AM fungi-associated bacteria stimulated by mycelial exudates secrete phosphatase and organic acid anions to mobilize sparingly soluble inorganic and organic P, and consequently promote plant P uptake
The mesh-based microcosm for investigating AM hyphae-mediated ecological functions in the hyphosphere. (a) The in-growth tubes (10 cm in diameter, 6 cm in length), sealed with 30 μm mesh (permitting AM fungal hyphae but not roots to grow into) or 0.45 μm membrane (excluding both AM fungal hyphae and roots) at the two ends, were buried near the roots (in the layer 20–30 cm deep and 15 cm away from a maize plant) in the field to study the hyphosphere interaction effects (Zhang et al. 2018b). (b) Spatial separation of soil zones for root and hyphal growth and soil zones. The chamber has five compartments, a central one for root growth (including mycorrhizal structures) separated from the two adjacent ones by 30 μm mesh. The bulk soil compartments are separated from the hyphal compartments by 0.45 μm mesh. (c, d) Schematic diagram describing the underground ‘hyphae highway’ formed by mycorrhizal network of AM fungi. The phosphate-solubilizing bacteria can quickly migrate toward an organic P patch along the hyphae highway (Jiang et al. 2021; Sun et al. 2021)
Article
Background Most plants have a hyphosphere, the thin zone of soil around extraradical hyphae of arbuscular mycorrhizal (AM) fungi, which extends beyond the rhizosphere. This important interface has critical roles in plant mineral nutrition and water acquisition, biotic and abiotic stress resistance, mineral weathering, the formation of soil macroaggregates and aggregate stabilization, carbon (C) allocation to soils and interaction with soil microbes. Scope This review focuses on the hyphosphere of AM fungi and critically appraises the important findings related to the hyphosphere processes, including physical, chemical and biological properties and functions. We highlight ecological functions of AM fungal hyphae, which have profound impacts on global sustainability through biological cycling of nutrients, C sequestration in soil, release of greenhouse gas emissions from soil and the diversity and dynamics of the microbial community in the vicinity of the extraradical hyphae. Conclusions As a critical interface between AM fungi and soil, hyphosphere processes and their important ecological functions have begun to be understood and appreciated, and are now known to be implicit in important soil processes. Recent studies provide new insights into this crucial zone and highlight how the hyphosphere might be exploited as a nature-based solution, through understanding of interactions with the microbiome and the impacts on key processes governing resource availability, to increase sustainability of agriculture and minimize its environmental impact. Uncovering hyphosphere chemical and biological processes and their subsequent agricultural, ecological and environmental consequences is a critical research activity.
 
Article
Aims Potato starch wastewater contains higher contents of essential nutrients, which can be fertilizer to help crop growth. However, the effects of fermented potato fertilizer on soil ecology and microbial community structure have not yet been elucidated. This study aimed to investigate the shifts of active ammonia oxidation microbial communities under different fertilization in a typical soil in North China. Methods The different levels of fermented potato fertilizer without or with chemical fertilizer were designed by field experiment. Results The results showed that applying fermented potato fertilizer could significantly increase crop yields by 165–399% compared to Control. The content of available soil nutrients and the activity of saccharase and cellulase were increased when fermented potato fertilizer was applied, and the combination fertilizers further increased the content of Olsen-P by 145.6–166.7%, NO3⁻ by 15.2–81.1%, Total C by 13.8–14%, and Total N by 27.2–34.7% compared with fermented potato fertilizer (PW) treatments. In addition the fermented potato fertilizer significantly stimulated the diversity of soil microbial community and increased the differentiation and stability of soil microbial networks in deep soils. Finally, the change of niche of soil Comammox (COM), ammonia-oxidizing archaea (AOA), and ammonia-oxidizing bacteria (AOB) were found after PW treatments. It showed a significant positive correlation between AOA and COM (r = 0.79, P < 0.01), AOB and NOB (r = 0.7, P < 0.05) instead of theoretically the competitive relationship between AOA and COM. Conclusions One of the reasons crop yield increase is that fermented potato fertilizer can modulate soil nitrification strategy bychanging the niche of soil functional microorganisms to increase fast-acting nutrients and increase crop yield. Graphical abstract
 
Bias representation: number of studies and replicates by a) each spectral region, b) absolute latitude of the field sites of the studies, c) ecosystem type; d) climatic zone (see ESM Appendix-5 for more details about the climate classification); e) decay period (months), f) litter habit, g) litter form and h) biome type. The climate are: Tropical climate (Tropi.); Dry climate; Temperate climate (Tempe.); Continental climate (Conti.); Polar climate. The biomes are: Boreal forests / Taiga (BF); Deserts and xeric shrublands (DXS); Mediterranean Forests, Woodlands and Scrub (MF); Montane grasslands and shrublands (MG); Temperate broadleaf and mixed forests (TB); Temperate grasslands, savannas and shrublands (TG); Tropical and subtropical moist broadleaf forests (TSB). The repilcates are not repeated measures, but represent the number of independent treatments (e.g. field sites) of one species
Locations of the experimental sites of the studies considered in the meta-analysis divided according to the World Wildlife Fund (WWF) biome classification (see Online Resource 6)
Effects of exclusion of a) the full spectrum, b) blue light, c) UV-A radiation, d) UV-B radiation and e) UV radiation on litter mass loss according to categories of climate, ecosystem, decay period, habit and litter form. Average effect size (log response ratio) and 95% CI are shown. Numbers in parenthesis represent the number of replicates
Article
• Background and aim: Wherever sunlight reaches litter, there is potential for photodegradation to contribute to decomposition. Although recent studies have weighed the contribution of short wavelength visible and ultraviolet (UV) radiation as drivers of photodegradation, the relative importance of each spectral region across biomes and plant communities remains uncertain. • Methods: We performed a systematic meta-analysis of studies that assessed photodegradation through spectrally selective attenuation of solar radiation, by synthesizing 30 published studies using field incubations of leaf litter from 110 plant species under ambient sunlight. • Results: Globally, the full spectrum of sunlight significantly increased litter mass loss by 15.3% ± 1% across all studies compared to darkness. Blue light alone was responsible for most of this increase in mass loss (13.8% ± 1%), whereas neither UV radiation nor its individual constituents UV-B and UV-A radiation had significant effects at the global scale, being only important in specific environments. These waveband-dependent effects were modulated by climate and ecosystem type. Among initial litter traits, carbon content, lignin content, lignin to nitrogen ratio and SLA positively correlated with the rate of photodegradation. Global coverage of biomes and spectral regions was uneven across the meta-analysis potentially biasing the results, but also indicating where research in lacking. • Conclusions: Across studies attenuating spectral regions of sunlight, our meta-analysis confirms that photodegradation is a significant driver of decomposition, but this effect is highly dependent on the spectral region considered. Blue light was the predominant driver of photodegradation across biomes rather than UV radiation.
 
Article
Background and aims It is demonstrated that intercropping improves soil fertility, but its effect on deep soil is still unclear. The major objective of this study was to determine the distribution of arbuscular mycorrhizal fungi (AMF) and soil aggregates and their interrelationship across soil depths in intercropping systems. Methods A three-year positioning experiment based on a two-factor experimental design at two N application levels (N0 and N2) and different cropping systems (maize/soybean intercropping and corresponding monocultures) was started in 2017. Soil samples were collected from 0–15 cm and 15–30 cm for analyzing soil aggregates and from 0–15 cm, 15–30 cm, 30–5 cm, and 45–60 cm for determining the AMF composition. Results It was observed that intercropping improved the macro-aggregate (> 5 mm) content at 0–15 cm and 15–30 cm depths for maize soil and only 0–15 cm depth for soybean soil without N treatment. The application of N decreased the macro-aggregate content in the intercropping soil at 0–15 cm and 15–30 cm depths. Moreover, intercropping significantly improved the AMF diversity of maize and soybean soils across soil depths, while the application of N reduced the AMF diversity of soil across depths. Conclusions The structural equation modeling analysis indicated that the intercropping system influenced the stability of soil aggregates and promoted the formation of large aggregates by altering soil nutrients and the diversity of AMF. The results further revealed the reasons behind soil fertility improvement by adopting crop diversification.
 
Experimental set-up of split root ¹⁵N-labelling technique. The labelling compartment (LabC), where the ¹⁵N-urea was added, contained sand (orange) and transfer compartment (TraC) and receiving compartment (RecC) contained soil (brown). |Part (a) shows the two-compartment set-up used. Clover roots were split across the LabC and TraC and grass roots were all in the TraC. Part (b) shows the three-compartment set-up used, with clover roots split evenly between the LabC and TraC, and ryegrass roots split evenly between TraC and RecC for the clover to ryegrass experiment. For the ryegrass to clover experiment, ryegrass roots were split between the LabC and TraC, and clover roots between TraC and RecC. Diagram is not to scale
The proportion of nitrogen in (a) receiver plant, (b) soil and (c) soil protein pool derived from the donor plant via N transfer (NdftR). Values are mean ± SE (n = 4). Lower case letters indicate if there are significant differences between the treatments determined via a one-way ANOVA and multiple pairwise comparisons (p < 0.05)
Mass of individual AAs exuded from clover (black) and ryegrass (grey) roots. Values are mean ± SE (n = 4) and are corrected for recovery rates of AA standards from sand (Table S7)
The N transfer (NdftR) pathways in a model clover-ryegrass system as affected by management (simulated grazing by defoliation, N fertiliser application or shoot residue decomposition) and presence of soil organisms (weevils, mycorrhiza). The bidirectional N transfer at 100 h was determined via the three-compartment experiment. All values are mean ± SE (n = 4)
Article
Purpose Nitrogen (N) transfer from white clover ( Trifolium repens cv.) to ryegrass ( Lolium perenne cv.) has the potential to meet ryegrass N requirements. This study aimed to quantify N transfer in a mixed pasture and investigate the influence of the microbial community and land management on N transfer. Methods Split root ¹⁵ N-labelling of clover quantified N transfer to ryegrass via exudation, microbial assimilation, decomposition, defoliation and soil biota. Incorporation into the microbial protein pool was determined using compound-specific ¹⁵ N-stable isotope probing approaches. Results N transfer to ryegrass and soil microbial protein in the model system was relatively small, with one-third arising from root exudation. N transfer to ryegrass increased with no microbial competition but soil microbes also increased N transfer via shoot decomposition. Addition of mycorrhizal fungi did not alter N transfer, due to the source-sink nature of this pathway, whilst weevil grazing on roots decreased microbial N transfer. N transfer was bidirectional, and comparable on a short-term scale. Conclusions N transfer was low in a model young pasture established from soil from a permanent grassland with long-term N fertilisation. Root exudation and decomposition were major N transfer pathways. N transfer was influenced by soil biota (weevils, mycorrhizae) and land management (e.g. grazing). Previous land management and the role of the microbial community in N transfer must be considered when determining the potential for N transfer to ryegrass.
 
Article
Aims Plant phosphorus (P) recovery of applied P (PF) is a critical factor for seed production in soybeans [Glycine max (L.) Merr.], but the quantitative effect of nitrogen (N) application (NF) on P-recovery is not established. This study aimed to model the relationship between P-uptake (PA) and PF in soybeans under varying NF conditions. Methods Pot experiments were conducted using nodulated [Lee( +)] and non-nodulated [Lee(–)] soybeans under multiple levels of basal-dressed PF and top-dressed NF from the full-bloom to the beginning-maturity stages. Results PA at each NF was represented by a function of PF as a straight-line with a positive-slope and an intercept of soil P (PS) connecting with a ceiling-line due to plant P-uptake capacity. The apparent crop recovery efficiency of PF [RE = (PA – PS) / PF] at the slope-phase asymptotically increased with NF. As a result, PA was represented by the single-function PF × RE, which consisted of a 1:1 slope and a ceiling across different NF rates. Seed weights increased with NA for both nodulation types, but the responses of seed yield to PA in Lee(–) differed due to NA. PA asymptotically increased the maximum NA and N fixation by nodulation, and was approximated by the N quantitative model. Conclusion PA can be represented as a function of PF by excluding P retained in soils, which is influenced by NF and the capacity for P uptake. Accordingly, P uptake affects seed production via N uptake, which is determined by fertilizer, soil, and fixed N.
 
Article
Purpose Partial rootzone drying (PRD) typically alternates the dry and irrigated parts of the rootzone, but how plant physiology and soil evaporation respond to this alternation are poorly understood. Methods Dwarf tomatoes were grown in small split pots comprising two 250 cm³ compartments and fully irrigated (WW: 100% ETc) or subjected to three deficit irrigation treatments (75% ETc): homogeneous rootzone drying (HRD; irrigation evenly distributed); fixed PRD (PRD-F, irrigation applied to one fixed compartment); alternated PRD (PRD-A: as PRD-F but alternating the irrigated compartment every three days). Stem diameter and evapotranspiration were monitored during alternation cycles. The day after alternating the irrigated side of the root system, whole-plant gas exchange and leaf water potential were measured following step increments of vapour pressure deficit. Results Alternation did not affect stem diameter contractions or evapotranspiration, which were lower in HRD than in the two PRD treatments. However, soil evaporation was higher in HRD and PRD-A after alternation than in PRD-F. Following alternation, higher soil evaporation was counteracted by decreased transpiration compared with fixed PRD, despite similar overall soil water content. VPD increments did not change this pattern. Conclusion Irrigation placement determined soil moisture distribution, which in turn affected soil evaporation and whole plant gas exchange. Optimising the frequency of PRD alternation to maximise water savings while ensuring productive water use needs to consider how soil moisture distribution affects both soil evaporation and plant water use.
 
Top-cited authors
Hans Lambers
  • University of Western Australia and China Agricultural University
Thom W Kuyper
  • Wageningen University & Research
Johannes Lehmann
  • Cornell University
Matthias C Rillig
  • Freie Universität Berlin
Michael D Cramer
  • University of Cape Town