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Soil pH has contrasting effects on gross and net nitrogen mineralizations in adjacent forest and grassland soils in central Alberta, Canada

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... Availability of labile C (used as an energy source for microbes) strongly affect soil N transformation and availability (Hart et al., 1994;Barnard et al., 2005a;Cabrera et al., 2005). Soil pH was found to directly regulate nitrification and mineralization rates (Cheng et al., 2013), primarily by affecting soil microbial composition and functions (Yang et al., 2018). Taken together, although the effects of an individual factor (climatic, plant, and soil) on soil N transformation are relatively well studied, the complex interaction among these factors in regulating N transformation rates in ecosystems across large spatial scales remains unclear (Eisenhauer et al., 2015;Wang et al., 2018). ...
... In the present study, soil pH was a direct driver contributing to the large variation in soil N transformation rates (Fig. 6). This finding was unsurprising given the dominant role of soil pH in SOM hydrolysis and integrated climate-microbe-plant inputs at large spatial scales (Cheng et al., 2013;Waldrop et al., 2017;Yang et al., 2018). Specifically, the decrease in soil potential N mineralization and ammonification rates with increasing soil pH (Figs. 6 and S4a, c) were attributed to the microbial immobilization of N (Curtin et al., 1998;Zhang et al., 2019b). ...
... Increased microbial demand for N with increasing soil pH would likely diminish soil N availability and subsequently decrease mineralization, as the N would be incorporated into microbial biomass (Booth et al., 2005;Cabrera et al., 2005). In contrast, the increase in the soil N nitrification rate with soil pH (Figs. 5, 6b and S4b) indicated that the nitrifying microbes could prefer less acidic or neutral soil environments, as reported in previous studies (Tietema et al., 1992;Cheng et al., 2013;Tian et al., Fig. 6. Structural equation modeling (SEM) analysis of the effects of climate (temperature and precipitation), biotic (plant N inputs and microbial biomass), and soil abiotic properties on potential N mineralization (a), nitrification (b), ammonification (c), and denitrification rates (d). ...
Article
The availability of soil inorganic nitrogen (N) is primarily regulated by the rates of soil N transformation, including mineralization, ammonification, nitrification, and denitrification, and are sensitive to climate, plant, and soil factors. However, the interactive effects among these factors regulating soil N transformation rates in ecosystems across large spatial scales remain unclear. Here, we investigated the spatial patterns of the potential N mineralization, nitrification, ammonification, and denitrification rates in relation to plant traits and soil edaphic conditions across a 600-km precipitation gradient in secondary grasslands of South China. The soil potential N mineralization and nitrification rates significantly increased with increasing precipitation. However, the soil potential N ammonification and denitrification rates did not significantly vary with precipitation. Moreover, the soil potential N nitrification and denitrification rates significantly increased with increasing soil pH, whereas the potential N mineralization and ammonification rates decreased with increasing soil pH. The soil potential N mineralization rate was positively correlated with soil labile N but negatively correlated with soil recalcitrant C and N contents. Our results revealed that changes in soil NH4⁺-N and pH along precipitation gradients primarily controlled the potential N mineralization, nitrification, and ammonification rates. In contrast, soil NO3⁻-N, soil pH, and plant N inputs predominantly regulated the potential N denitrification rate. Overall, our results reveal that soil N transformation varies along the precipitation gradient, and these results need to be considered when studying the effects of climate change on N cycling in grassland ecosystems across diverse environments.
... Additionally, reduced soil respiration due to acid rain can indirectly alter the soil system and influence the effects of elevated atmospheric CO 2 (Figs. 2 and 3). Acid rain possibly disrupts ecosystem services by cycling nutrients, leaching nutrients from plant foliage and soils, affecting soil microbial-root biomass, interfering with OM decomposition, and disrupting processes, such as organic mineralization, nitrification, and N fixation (Turner and Tingey, 1990;Aber et al., 1998;Kuzyakov and Larionova, 2005;Zhang et al., 2007;Lovett et al., 2009, Ling et al., 2010Cheng et al., 2013;Zhu et al., 2013;Chen et al., 2015;Liang et al., 2016). ...
... Thereby, soil microorganisms have a more robust response to soil environment changes than root systems, indicating that enhanced acid rain can change potential soil acidification sources. Acidic precipitation also alters soil mineralogy and nutrient cycling, affecting root and microbial health either positively or negatively (Lovett et al., 2009;Ling et al., 2010;Cheng et al., 2013;Zhu et al., 2013;Chen et al., 2015;Liang et al., 2016). However, H 2 CO 3 produced from elevated CO 2 (in the atmosphere and/or soil atmosphere) may not contribute to soil acidity at pH < 4.5 (Chen et al., 2015). ...
Article
Soil inorganic carbon (SIC) is the largest pool (≈950 Pg of soil carbonate + 1404 Pg of bicarbonate in groundwater; i.e., 1 Pg = 10¹⁵ g = 1 gigaton) of the global carbon cycle at a 100 cm depth, and it might be a significant carbon source and sink in arid and semi-arid regions. The knowledge of the impacts of changing climatic conditions on this important soil structural component is minimal. This review paper provides an inclusive compilation of the available information on potential natural and anthropogenic factors triggering soil acidification and weathering mechanisms under elevated CO2. Furthermore, the consequences of elevated atmospheric CO2 on the SIC pool, soil quality, and compromised ecosystem services have been explored. Soil water content and precipitation are critical factors that influence the effects of elevated CO2 in the SIC pool. Soil microbiological properties, respiration, depth, weathering, precipitation, acidity, and fertilization are emphasized here owing to the high degree of interrelationship between these factors on influencing overall soil quality. These phenomena are then outlined together with comments about possible short and long-term consequences in SIC stock.
... The increased vegetation cover and plant height from MD to G enhanced plant biomass, which directly affected the input of soil organic matter and indirectly altered the soil inorganic N pool (Zhou et al., 2009). The alkaline soil (MD: pH 7.62; G: pH 8.54; Table A.1) promoted soil nitrification, which can satisfy sandy plant growth as they mainly absorb the soil NO 3 − -N of inorganic N (Chen et al., 2013;Cheng et al., 2013). The increased SWC (the 64.8% increment from MD to G) and suitable T s are key factors that affect the soil inorganic N pool in desert regions (Li et al., 2018). ...
... Our previous study has demonstrated that the aboveground biomass and litter mass increased with the restoration of degraded vegetation (Zuo et al., 2015), which may indirectly affect soil N transformation (Rosenzweig et al., 2016). The microbial activity and alkaline soil can significantly stimulate the net nitrification rate (Cheng et al., 2013). Our result is in agreement with a previous study that reported increases in productivity stimulating the soil net N mineralization rate in a grassland ecosystem (Bardgett and Wardle, 2003). ...
Article
Vegetation restoration affects soil N cycling, which in turn strongly affects ecosystem functions, such as plant productivity and N availability. The soil N availability is a major limiting factor for restoring vegetation in semiarid grasslands and affects landscape evolution. However, few studies have focused on how landscape evolution caused by vegetation restoration affects soil N availability and transformation in semiarid sandy grasslands. Here, we conducted a 5-year field experiment from 2015 to 2019 to evaluate the growth season (May–August) changes in soil inorganic N pools and net N transformation rates along a landscape evolution gradient caused by vegetation restoration: mobile dunes, semi-fixed dunes, fixed dunes, and dune grasslands. We examined the relationship between climate factors, vegetation characteristics, soil properties, and soil net N transformation rates in different landscape types through multivariate analyses. The landscape type, sampling time, interannual variation, and their interactive effects significantly affected the soil inorganic N pool and net N transformation rate. Soil nitrate N concentration accounted for 68% of the total inorganic N, and soil nitrification dominated the soil N transformation during landscape evolution. Redundancy analysis revealed that the changes in net N nitrification and mineralization rates during the growing season were closely correlated with climate factors, vegetation characteristics, and soil properties. Variation partitioning analysis showed that the soil net N transformation rate during the growing season was mainly affected by soil properties, whereas soil net N transformation in August for all years was mainly affected by climate factors. These results suggest that soil N availability and transformation during landscape evolution caused by vegetation restoration were co-determined by climatic factors, vegetation characteristics, and soil properties. Therefore, long-term field monitoring should be considered to improve our exploration of soil N transformation changes and their underlying mechanisms in semiarid grassland ecosystems.
... Soil N mineralization rates are affected by climatic variables, soil microbial biomass, soil substrates, and edaphic properties (Dungait et al., 2012;Keuper et al., 2017;Li et al., 2019); however, studies regarding the main determinants of soil N mineralization have been inconsistent. For instance, some studies at local or regional scales found that surface-soil N mineralization was mainly explained by soil microbial biomass (Rustad et al., 2001;Li et al., 2019), whereas other studies have indicated that surface-soil N mineralization was determined by soil pH or soil C/N ratio (Cheng et al., 2013;Colman and Schimel 2013;Liu et al., 2016). In addition, the determinants of fungal and bacterial biomass and N mineralization at a regional scale differ among studies, which clearly hinders the inclusion of microbial processes in climate models. ...
... A negative relationship between SBD and soil N mineralization (Table S3) exists because soils with low SBD contain many large pores, which increase the their capacity to retain soil water and supply soil oxygen, thereby increasing soil microbial activity (De Neve and Hofman 2000). The strong and direct effects of soil environment on N mineralization rates even at the 0-100 cm soil sampling depth indicated that the soil environment was the primary determinant of soil N mineralization on the Mongolian Plateau (Cheng et al., 2013;Liu et al., 2016). All microbial biomass variables did not participate in determining soil N mineralization rates across all soil sampling depths, which were developed based on findings that soil microorganisms are probably important in soils, at least in surface soils (Rousk et al., 2016). ...
Article
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Direct evidence on how the determinants of soil microbial biomass and N mineralization differ with sampling depth and layer at a regional scale is lacking. We sampled 132 plots along aridity gradients on the Mongolian Plateau and determined the soil bacterial and fungal biomass and N mineralization rates at four soil sampling depths (0–20, 0–40, 0–60, and 0–100 cm) and layers (0–20, 20–40, 40–60, and 60–100 cm). We found that the determinants of microbial biomass and soil N mineralization differed among the four soil sampling depths or layers. At 0–20 cm, both bacterial and fungal biomasses were directly related to aridity and soil substrate quantity. Bacterial biomass was directly related to aridity and soil substrate quality at 0–100 cm soil depth and was directly related to aridity and plant substrate quantity in the 60–100 cm soil layer. Fungal biomass was directly related to aridity and the soil environment at 0–100 cm soil depth and in the 60–100 cm soil layer. The magnitude of these direct effects on microbial variables differed with soil depth and layer. For example, the direct effects of aridity (negative) and soil substrate quality (positive) on bacterial biomass increased with soil depth but not with soil layer. Soil N mineralization was directly associated with soil the environment and substrates across the four soil sampling depths, but was directly associated with soil substrates and plant quality across the four soil sampling layers. Our results provide the first regional-scale evidence that the determinants associated with soil microbial biomass and N mineralization depend on the sampling depth and layer. These findings indicate that studies based on surface soils may not accurately identify the determinants of microbial communities or ecosystem functions across the entire soil profile of drylands globally.
... Tea plants create an acidic soil environment due to their continuous acidification of the soil (USEPA, 2008). Soil nitrification rates have been demonstrated to be relatively low in acidic soils, and increase with increasing soil pH (Ste-Marie and Pare, 1999;Cheng et al., 2013). Thus, application of NH 4 +based fertilizers that are alkaline or can increase soil pH (such as through the hydrolysis of urea) would increase rates of nitrification and N 2 O emissions. ...
... Thus, NH 4 + substrate availability alone could not fully explain the change in nitrification rates following various NH 4 + -based N additions. Soil pH is another important factor controlling nitrification activity, and increasing pH often increases nitrification rate (Ste-Marie and Pare, 1999;Cheng et al., 2013). We also found that net nitrification rate was significantly positively elated to soil pH (Fig. 4a). ...
Article
Tea (Camellia sinensis L.) plants have an optimal pH range of 4.5–6.0, and prefer ammonium (NH4⁺) over nitrate (NO3⁻); strong soil acidification and nitrification are thus detrimental to their growth. Application of NH4⁺-based fertilizers can enhance nitrification and produce H⁺ that can inhibit nitrification. However, how soil acidification and nitrification are interactively affected by different NH4⁺-based fertilizers in tea plantations remains unclear. The objective of this research was to evaluate the effect of the application of different forms and rates of NH4⁺-based fertilizers on pH, net nitrification rates, and N2O and NO emissions in an acidic tea plantation soil. We conducted a 35-day aerobic incubation experiment using ammonium sulphate, urea and ammonium bicarbonate applied at 0, 100 or 200 mg N kg⁻¹ soil. Urea and ammonium bicarbonate significantly increased both soil pH and net nitrification rates, while ammonium sulphate did not affect soil pH but reduced net nitrification rates mainly due to the acidic nature of the fertilizer. We found that the effect of different NH4⁺-based nitrogen on soil nitrification depended on the impact of the fertilizers on soil pH, and nitrification played an important role in NO emissions, but not in N2O emissions. Overall, urea and ammonium bicarbonate application decoupled crop N preference and the form of N available in spite of increasing soil pH. We thus recommend the co-application of urease and nitrification inhibitors when urea is used as a fertilizer and nitrification inhibitors when ammonium bicarbonate is used as a fertilizer in tea plantations.
... Increased mineral N substrates with enhanced N deposition can promote N mineralization and nitrification (Niu et al., 2016). Meanwhile, N-induced soil acidification could limit N transformation processes by affecting microbial activities and N form as substrates (Pietri and Brookes, 2008;Cheng et al., 2013). Although meta-analysis showed that N deposition significantly increased N mineralization by 24.9% and nitrification by 153.9% , many variable results of impacts of N deposition on soil N transformations have been reported in individual studies, likely derived from the differences in local climatic conditions and soil properties. ...
... However, C/N ratios were not changed by N addition in this study and remained around 10, much lower than the critical value C/N ratio of ~25 for switching between N mineralization and immobilization processes, thus, falling into the range of C-limited microbial growth (Arunachalam et al., 1998;Zhu et al., 2015). In addition, although soil pH plays a critical role in N transformation by affecting microbial activities and mineral N forms (especially for NH x ) (Pietri and Brookes, 2008;Cheng et al., 2013), the studied alpine grassland soils are calcareous, with a strong acid-buffering capacity. Soil pH hardly changed with N addition, being similar in the control soils even after 11 years of 90 kg N ha − 1 yr − 1 additions. ...
... Under flooded conditions, the NO 3 --N produced by nitrification is more likely to cause runoff and leaching loss with the movement of paddy water (Chen et al., 2014;Liang et al., 2007). Thus, nitrification is the key process in regulating N loss in paddy fields (Cai et al., 2002).Nitrification rates are positively correlated with soil pH in the range from 4.8 to 8.5 (Cheng et al., 2013;Wang et al., 2019). Although nitrification activity in acidic soils is weaker than that in alkaline and neutral soils, soil pH usually increases to neutrality after flooding (Narteh & Sahrawat, 1999). ...
Article
Nitrogen (N) fertilizers are increasingly being used to meet crop demand for the expanding human population. However, historical N‐use efficiency (NUE) is low for rice paddy fields compared to upland ecosystems. This study aimed to investigate the fate of N fertilizer and compared NUE under different tillage regimes in a rice‐based agroecosystem. A long‐term field study of tillage regimes (i.e. flooded paddy field, conventional tillage and ridge tillage) and ¹⁵N isotope tracer methods (in situ and incubation) was used to determine N fertilizer fate and uptake. Nitrogen uptake by rice (which represents NUE) significantly differed between tillage regimes (p < .05). Nitrogen‐use efficiency was 31% of applied N fertilizer for ridge tillage, which was the highest among the three tillage regimes, while the lowest NUE occurred for conventional tillage (17%). The soil residual N for ridge tillage was significantly higher (21%), than for the flooded paddy field or conventional tillage. The total gaseous N loss was highest for ridge tillage (28%) and lowest for conventional tillage (17%). Ammonia (NH3) volatilization accounted for the largest proportion of gaseous loss from N fertilizer for all three tillage regimes. However, the largest loss of applied N was with water (runoff and leaching), where N loss accounted for 20% of applied N for ridge tillage but up to 54% for conventional tillage. Ridge tillage changed the soil micro‐topography and water regimes leading to better N conservation. Based on these results, adoption of ridge tillage should significantly improve NUE for rice paddy fields.
... Under the same conditions, AOA can immediately contribute to urea hydrolysis because of the high affinity of its ammonia monooxygenase (AMO) enzyme to NH 3 (Levy-Booth et al., 2014). In fact, the inorganic N soil form ) and soil pH are important factors, that can directly or indirectly regulate the abundance or the structure of the AOM communities (Aigle et al., 2019;Che et al., 2015;Cheng et al., 2013;Gubry-Rangin et al., 2018He et al., 2007;Lehtovirta-Morley et al., 2016;Levy-Booth et al., 2014;Nicol et al., 2008;Verhamme et al., 2011;Wang et al., 2018Wang et al., , 2011Wang et al., , 2019Yin et al., 2018;Ying et al., 2017;Zhalnina et al., 2015;Zhao et al., 2020). Furthermore, only the abundance of AOA is correlated with pH; in fact, AOA is more abundant than AOB when the conditions of low pH and low NH 4 + concentration are present (Wang et al., , 2011. ...
Article
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The incessant increase in the demand for food from the world population, which is occurring due to its continuous growth has, as a consequence, led to an increase in the use of fertilisers. Our work aims to analyse the application effect of various fungal strains with urea fertiliser on the structure and functions of bacterial communities, including ammonia-oxidising microorganisms (AOM) in different soil types. By analysing the abundance of ammonia-oxidising archaea (AOA) and bacteria (AOB), we observed that the application of urea fertiliser (UC) changed the soil microbial community, causing a disturbance in soil microorganisms diversity, whereas the addition of fungal strains to urea fertiliser (UA100; UA60) did not have a disordering effect compared to the Control soil (C). This indicates that the addition of fungal strains mitigated the adverse effects of urea on the soil environment. A similar effect was observed for the genes involved in the carbon cycle (bacterial carbon fixation, chitinase, and methanotrophic pathway genes). It was observed that the addition of fungi to the urea fertiliser had a positive effect, as the abundance of functional genes recorded in these treatments was the same as in the Control soil. From the diversity point of view, it is worth emphasizing that the diversity index changed after fungal organisms’ addition. We may also observe that the addition of fungal strains to urea protected or even improved the state of the soil macropores which are important for microbial communication in the soil environment. Furthermore, it may be concluded that to avoid a strong negative effect from the application of urea and the mitigation of its influence by fungal strains, we must consider the soil texture, pH, total carbon content, and soil organic matter including humic and fulvic acids.
... Nitrogen transformation and supply rates are closely related to plant growth and forest productivity (Kaye & Hart 1997;Yan et al. 2012;Duan et al. 2015). Nitrogen transformation rates and availability are affected by soil properties, such as soil temperature (Lang et al. 2010), pH (Cookson et al. 2007;Cheng et al. 2013), water content (Chen et al. 2011;Cheng et al. 2012), carbon (C) to N (C:N) ratio (Hart et al. 1994), and microbial and enzyme activities (Sinsabaugh et al. 1991;Burns et al. 2013). Vegetation cover also affects N availability as influenced by litter dynamics and N uptake by vegetation (Nadelhoffer et al. 1985;Kaye & Hart 1997). ...
... The different relationships between TN and soil pH might be concerned with the different pH range of the study area. Meanwhile, soil pH affected nitrogen content by influencing the growth and reproduction of soil microorganisms [41] or by affecting the nitrogen cycle process (nitrification and denitrification) [43]. ...
Article
Full-text available
Soil nitrogen in farmland ecosystems is affected by climate, soil physical and chemical properties and planting activities. To clarify the effects of these factors on soil nitrogen in sloping farmland quantitatively, the distribution of soil total nitrogen (TN) content, nitrate nitrogen (NO3-N) content and ammonium nitrogen (NH4-N) content at depth of 0–100 cm on 11 profiles of the Luanhe River Basin were analyzed. Meanwhile, soil physical and chemical properties, climatic factors and NDVI (Normalized Difference Vegetation Index) were used to construct a structural equation which reflected the influence mechanism of environmental factors on soil nitrogen concentration. The results showed that TN and NO3-N content decreased with the increase of soil depth in the Luanhe River Basin, while the variation of NH4-N content with soil depth was not obvious. Soil organic carbon (SOC) content, soil pH, soil area average particle size (SMD) and NDVI6 (NDVI of June) explained variation of TN content by 77.4%. SOC was the most important environmental factor contributing to the variation of TN content. NDVI5 (NDVI of May), annual average precipitation (MAP), soil pH and SOC explained 49.1% variation of NO3-N content. Among all environmental factors, only NDVI8 (NDVI of August) had significant correlation with soil NH4-N content, which explained the change of NH4-N content by 24.2%. The results showed that soil nitrogen content in the sloping farmland ecosystem was mainly affected by natural factors such as soil parent material and climate.
... Differences in nitrification rates from the two soils could be due to different soil properties. Taking soil initial pH for example, since it was lower in S1 than S2 (Table 1), the acid-sensitive nitrifiers rather than acid-tolerant nitrifiers in S1 may not adapt to the increasing pH circumstance at the initial incubation (Cheng et al. 2013;Nugroho et al. 2007), leading to a lag effect of pH stimulation of nitrification and lower nitrification rate than S2 (Table S1). ...
Article
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Background The size of lime material is vital for the efficiency of ameliorating soil acidity, thereby influencing soil biochemical processes. However, the effects of different sized lime material application on soil organic carbon (SOC) mineralization are yet to be elucidated. Therefore, a 35-day incubation experiment was conducted to determine the effects of three particle size fractions (0.5 to 0.25, 0.25 to 0.15, and < 0.15 mm) of dolomite on SOC mineralization of two acidic paddy soils. Results CO 2 emission was increased by 3–7%, 11–21%, and 32–49% for coarse-, medium-, and fine-sized dolomite treatments, respectively, compared to the control in both soils. They also well conformed to a first-order model in all treatments, and the estimated decomposition rate constant was significantly higher in the fine-sized treatment than that of other treatments ( P < 0.05), indicating that SOC turnover rate was dependent on the dolomite size. The finer particle sizes were characterized with higher efficiencies of modifying soil pH, consequently resulting in higher dissolved organic carbon contents and microbial biomass carbon, eventually leading to higher CO 2 emissions. Conclusions The results demonstrate that the size of dolomite is a key factor in regulating SOC mineralization in acidic paddy soils when dolomite is applied to manipulate soil pH.
... immobilization rates. There are fewer studies here than those reported in Table 1 because not all studies reported in Table 1 reported the background N deposition rate often stimulated by N addition (Norton 2008) while inhibited by soil acidification (Cheng et al. 2013). A previous review confirmed that when ambient N deposition was more than 5 kg N ha -1 yr -1 , soil pH decreased significantly with N addition (Tian and Niu 2015). ...
Article
Nitrogen (N) deposition can profoundly alter soil N transformation processes and the long-term productivity of forest ecosystems. The response of soil gross N transformations to N deposition in forest ecosystems has been well studied through simulated N addition experiments. Simulated N addition experiments are conducted under a wide range of background N deposition rates. However, it remains unclear whether the response of soil gross N transformation rates to simulated N addition is dependent on background N deposition rates. Here, we collate results from the literature in forest ecosystems, and found, for the first time, that the responses of gross rates of N mineralization, nitrification, and NO3− immobilization to experimental N addition changed from positive to negative with increasing background N deposition rates with the thresholds for such changes were 3.23, 6.02, 1.90 kg N ha− 1 yr− 1, respectively. Our results suggest that background N deposition rates shall be incorporated into ecosystem models to better predict forest ecosystem N cycling under future N deposition scenarios.
... The labile nutrients for the plants are influenced by soil pH (Zhao et al. 2012). Variety of root exudates, mainly carbohydrates, impacts the microbial diversity and structure as well as their population (Fierer and Jackson 2006;Pietri and Brookes 2009;Cheng et al. 2013b). In our experiment, soil pH slightly decreased under EO 3 which was possibly caused by release of organic acids in root exudates. ...
Article
Increasing concentrations of ground-level ozone (O3) exert significant impacts on the plants, but there is limited data for belowground processes. We studied the effects of long-term exposure of elevated O3 (EO3) on plant growth parameters (plant height and biomass) and biochemical parameters (nutrients, microbial biomass and enzymatic activities) of rhizospheric soil of leguminous tree species Leucaena leucocephala. L. leucocephala seedlings were grown under ambient O3 (AO3) and EO3 (+20 ppb above ambient) under Free Air Ozone Concentration Enrichment (O3-FACE) facility and changes in plant growth and their rhizospheric soil properties were studied during 6, 12, 18 and 24 months of EO3 exposure. L. leucocephala showed significant reductions in shoot length, root biomass, shoot biomass, leaf biomass and total biomass during 12, 18 and 24 months of exposure to EO3. Total nutrients in rhizospheric soil like carbon and phosphorus were significantly reduced after 24 months of EO3 exposure. Most of the available nutrients showed significant reduction after 6, 12 and 24 months of EO3 exposure. A significant decrease was apparent in microbial biomass carbon, nitrogen and phosphorus after 6, 12, 18 and 24 months of EO3 treatment. Significant reductions were observed in extracellular enzymatic activities (dehydrogenase, alkaline phosphatase, β-glycosidase, fluorescein diacetate, arylsulfatase, cellulase and protease) of soil after 6, 12 and 24 months of EO3 exposure. These results suggest that increasing O3 concentrations will directly impact L. leucocephala growth as well as have indirect impact on the nutrient contents (C, N, and P), microbial biomass and extracellular enzymatic activities of rhizospheric soil of L. leucocephala. Our results suggest that continuous increase in O3 concentrations will have serious implications for aboveground plant growth and belowground soil fertility in this region considered as O3 hotspot. Supplementary information: The online version contains supplementary material available at 10.1007/s13205-022-03215-1.
... This probably due to urea hydrolysis, in which 1 mol of H + is consumed for every 1 mol NH 4 + produced (CO (Rochette et al., 2013). Previous studies have shown that the rate of N mineralization increases with increasing pH levels between 4 and 8 (Högberg et al., 2007;Rousk et al., 2009;Cheng et al., 2013;Jiang et al., 2015). Consistently, we found that the potential N mineralization rate was positively correlated with pH because microbes prefer neutral or alkaline environments (Kader et al., 2013;Lin et al., 2016). ...
Article
Inputs of nitrogen (N) to peatlands in the form of fertilizers have rapidly increased due to the intensification of agricultural systems, impacting ecological processes, and the carbon storage function of peatland. However, detailed information on the impacts of long-termNinputs onthe individual steps of N transformation processes in peatland soils still needs to be fully understood.We investigated Nmineralization and nitrification rates aswell as nitrite dependent anaerobic methane oxidation (n-damo), anaerobic ammonium oxidation (anammox), denitrification, and dissimilatory nitrate reduction to ammonium(DNRA) in a peatland affected by Ninputs for >50 years, using isotope tracing technique and quantitative PCR. Based on the results, N inputs increased N mineralization and nitrification rates by 77 and 43%, respectively. Notably, the contributions of n-damo and anammox to N2 production were enhanced by 242 and 170%, accounting for 30 and 12%, respectively. The contributions of denitrification and DNRA to N2 production decreased by 27 and 52%, accounting for 48 and 10% of N2 production, respectively. Nitrifier abundance increased significantly, with AOA being the dominant prokaryote (from 696 to 1090 copies g−1), but AOB responded more strongly to N inputs (from 5 to 68 copies g−1). The N inputs also promoted the growth of ndamo and anammox bacteria, whose abundances increased by 3.7% (from 565 to 586 copies g−1) and 85.7% (from 305 to 567 copies g−1), respectively, while denitrifier abundance was significantly reduced, with nirK and nirS abundances decreasing by 58% (from738 to 308 copies g−1) and 50% (from218 to 109 copies g−1), respectively. Soil pH was the key environmental factor influencing N transformations. We show that n-damo plays important roles in N cycling in peatland subjected to N inputs, providing a scientific basis for improved peatlandmanagement.
... As described above, volcanic deposits may mitigate low soil pH, which may in turn enhance microbial growth (Rousk et al., 2009) and increase microbial biomass, resulting in increased N assimilation. Some studies have reported that increasing soil pH may relate to increased gross ammonium immobilization rates relative to gross N mineralization rates in forest soils (Cheng et al., 2013;Kooijman and Smit, 2009). Our results in organic soils also showed close associations among ammonium immobilization rate, pH, and microbial biomass N (Tables S1 and S3). ...
Article
Volcanic deposits increase soil organic carbon storage. However, little is known about the effect of volcanic deposits on forest soil nitrogen (N) dynamics and microbial communities. We explored gross and net N transformation rates and microbial community structure using a phospholipid fatty acid (PLFA) method across eight forests with soils derived from different parent material in Japan. Volcanic mineral soils had approximately three-fold greater total N and inorganic N contents and gross nitrification, ammonium immobilization, and nitrate immobilization rates that were one order of magnitude higher than in non-volcanic soils. Moreover, volcanic mineral soils had a 1.7-fold lower N turnover rate, which was estimated as net N mineralization rate per soil N. This was likely caused by a higher gross N immobilization rate, potentially due to the mineral traits of volcanic soils. Volcanic mineral soils had approximately four- and three-fold greater microbial biomass-N and bacterial PLFA contents, respectively, and the fungal:bacterial PLFA ratio was lower in volcanic mineral soils than in non-volcanic soils. Microbial community structure, analyzed using non-metric multidimensional scaling, was distinct between volcanic and non-volcanic soils, and was significantly affected by soil characteristics. This study demonstrates that aside from soil carbon storage, volcanic deposits are related to increases in soil N immobilization, N content, bacterial biomass, and N transformation rates in forest ecosystems.
... Under flooded conditions, the NO 3 --N produced by nitrification is more likely to cause runoff and leaching loss with the movement of paddy water (Chen et al., 2014;Liang et al., 2007). Thus, nitrification is the key process in regulating N loss in paddy fields (Cai et al., 2002).Nitrification rates are positively correlated with soil pH in the range from 4.8 to 8.5 (Cheng et al., 2013;Wang et al., 2019). Although nitrification activity in acidic soils is weaker than that in alkaline and neutral soils, soil pH usually increases to neutrality after flooding (Narteh & Sahrawat, 1999). ...
Article
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Nitrogen (N) fertilizers are increasingly being used to meet crop demand for the expanding human population. However, historical N-use efficiency (NUE) is low for rice paddy fields compared to upland ecosystems. This study aimed to investigate the fate of N fertilizer and compared NUE under different tillage regimes in a rice-based agroecosystem. A long-term field study of tillage regimes (i.e. flooded paddy field, conventional tillage and ridge tillage) and 15N isotope tracer methods (in situ and incubation) was used to determine N fertilizer fate and uptake. Nitrogen uptake by rice (which represents NUE) significantly differed between tillage regimes (p < .05). Nitrogen-use efficiency was 31% of applied N fertilizer for ridge tillage, which was the highest among the three tillage regimes, while the lowest NUE occurred for con-ventional tillage (17%). The soil residual N for ridge tillage was significantly higher (21%), than for the flooded paddy field or conventional tillage. The total gaseous N loss was highest for ridge tillage (28%) and lowest for conventional tillage (17%). Ammonia (NH3) volatilization accounted for the largest proportion of gaseous loss from N fertilizer for all three tillage regimes. However, the largest loss of applied N was with water (runoff and leaching), where N loss accounted for 20% of applied N for ridge tillage but up to 54% for conventional tillage. Ridge tillage changed the soil micro-topography and water regimes leading to better N conservation. Based on these results, adoption of ridge tillage should significantly improve NUE for rice paddy fields.
... Overall, the interactive effects of vermicompost and AM fungi on 15 N uptake by lettuce from wheat straw may be the result of 15 N mineralised from wheat straw by the vermicompost and the transfer from the HC to the plants by the hyphae (Fig. 5). Additionally, another mechanism of the interactive effects of vermicompost and AM fungi on 15 N uptake by lettuce from wheat straw may attribute to the increase of the mobility of soil 15 N-NH 4 + by decreasing soil pH (Andersson et al. 2000;Cheng et al. 2013). ...
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Aim Nitrogen (N) is an essential nutrient for plant growth. A modified up-down two-compartment system, with the addition of ¹⁵N-labelled wheat straw in the hyphal compartment (HC), was set up to investigate the effects of vermicompost and arbuscular mycorrhizal (AM) fungi on improving ¹⁵N mineralisation from wheat straw and uptake by lettuce. Methods Lettuce yield, the ¹⁵N contents of shoots and roots, the concentration of inorganic ¹⁵N in soil, the percentage of ¹⁵N transfer were measured, as well as soil organic matter content, soil aggregate-size distribution, hyphal length density and the soil bacterial community in the HC. Results Vermicompost can improve soil aggregation by replenishing organic matter, which can subsequently regulate the soil bacterial community and increase the relative abundance of N-cycling bacteria in the hyphosphere. Vermicompost enhanced ¹⁵N mineralisation from wheat straw by regulating the physical structure of the soil and the bacterial community but did not help transferring ¹⁵N to the plant alone. AM fungi hyphae could transfer ¹⁵N from the HC to the plant, which significantly increased shoot and root ¹⁵N uptake. Ultimately, the interaction between vermicompost and AM fungi increased the yield of lettuce by enhancing the uptake of N that was mineralised from crop residues. Conclusion Overall, the interaction between vermicompost and AM fungi may help lettuce to speed up ¹⁵N acqusition from crop residues via mineralization induced by vermicompost amendment and the transfer from soil to plant via AM fungi.
... The soil microbial biomass is sharply depressed by soil acidification at soil pH ≤ 5 Pietri & Brookes, 2008), and the transcript copies of ammonia-oxidizing bacteria decrease with soil pH decreasing from 6.9 to 4.9 (Nicol, Leininger, Schleper, & Prosser, 2008). Therefore, soil acidification remarkably impedes soil nitrification (Cheng et al., 2013). Soil nitrification in croplands may be weakened more severely than that of natural ecosystems. ...
Article
Soil nitrification, an important pathway of nitrogen transformation in ecosystems, produces soil nitrate that influences net primary productivity, while the by‐product of nitrification, nitrous oxide, is a significant green‐house gas. Although there have been many studies addressing the microbiology, physiology, and impacting environment factors of soil nitrification at local scales, there are very few studies on soil nitrification rate over large scales. We conducted a global synthesis on the patterns and controlling factors of soil nitrification rate normalized at 25°C by compiling 3140 observations from 186 published articles across terrestrial ecosystems. Soil nitrification rate tended to decrease with increasing latitude, especially in the north hemisphere, and varied largely with ecosystem types. The soil nitrification rate significantly increased with mean annual temperature, soil nitrogen content, microbial biomass carbon and nitrogen, soil ammonium, and soil pH, but decreased with soil carbon:nitrogen and carbon:nitrogen of microbial biomass. The total soil nitrogen content contributed the most to the variations of global soil nitrification rate (total coefficient = 0.29) in structural equation models. The microbial biomass nitrogen (total coefficient = 0.19) was nearly of equivalent importance relative to mean annual temperature (total coefficient = 0.25) and soil pH (total coefficient = 0.24) in determining soil nitrification rate, while soil nitrogen and pH influenced soil nitrification via changing soil microbial biomass nitrogen. Moreover, the emission of soil nitrous oxide was positively related to soil nitrification rate at a global scale. This synthesis will advance our current understanding on the mechanisms underlying large scale variations of soil nitrification and benefit the biogeochemical models in simulating global nitrogen cycling.
... Soil pH is one of the major factors affecting soil N transformation (Cheng et al., 2013). In this study, the results of the SEM analysis showed that pH indirectly affected SON pools through the activity of enzymes in soil. ...
Article
Soil soluble organic nitrogen (SON) is one of the most active components in soil nitrogen pools; however, limited information is available with regard to its driving factors, as well as their pathways and degrees of influence. In this study, structural equation modeling was used to analyze the driving factors, their significance, and pathways that affected SON dynamics in a waterlogged experiment of two typical paddy soils incubated for 80 d after green manure application. Soil pH, Eh, microbial biomass, enzyme activity, and SON dynamics were used to construct the structural equation model. Results showed that soil microbial biomass carbon (MBC), protease, glutamine, and initial organic matter (OM) directly and significantly affected soil SON with path coefficients corresponding to 0.405, 0.547, 0.523, and–0.623 (P < 0.01), respectively. Soil microbial biomass carbon and initial OM affected the SON dynamics indirectly through protease and glutamine activity. In addition, pH indirectly affected SON dynamics by glutamine activity. It is implied that soil MBC, protease, glutamine, and initial OM are the key factors affecting SON dynamics in the waterlogged paddy soils after green manure application. Our research indicated that structural equation modeling could provide an effective method to clearly recognize the impact, significance, and pathways of multiple factors on SON dynamics in paddy soils.
... Among all the amendments, lime application is the most effective agricultural practice for improving crop productivity by (i) substantially reducing soil acidity by neutralizing the excessive hydrogen ions in the soil solution, (ii) enhancing the availability of essential nutrients and reducing the availability of toxic elements, (iii) directly supplying several essential elements for crop production (e.g., calcium (Ca 2+ ) and magnesium (Mg 2+ ) as constituent elements in lime materials, and (vi) indirectly affecting nutrients transmission and uptake by plants through affecting soil microbial activity (Fageria and Baligar 2008;Eissa et al. 2013;Cheng et al. 2013;Fageria and Nascente 2014;Goulding 2016;Kunhikrishnan et al. 2016;Youssef and Eissa 2017). Numerous reports on the application of lime for the remediation of heavy metal-contaminated soils have been published (Simón et al. 2010;Hale et al. 2012;Chen et al. 2016;Cui et al. 2016). ...
Article
Lime application is the most effective agricultural practice for the reduction of cadmium (Cd) bioavailability in acid soils. This study was conducted to investigate the impact of continuous liming across five consecutive growing seasons on the remediation of Cd in acid paddy soils, as well as rice yield. Two rice cultivars, i.e., Zhuliangyou 819 and Xiangwanxian 12, were cultivated in Cd-contaminated paddy soil for five consecutive growing seasons from 2014 to 2018. The investigated lime levels were 0, 450, 900, 1350, 1800, 2250, 3000, and 3750 kg ha−1. Lime application significantly increased rice yield, soil pH, exchangeable soil Ca2+, and rice calcium (Ca) contents; besides, it reduced soil and rice Cd contents. The application of lime at the rate of 1350–2250 kg ha−1 significantly increased rice yield. Under continuous liming, rice yield obviously increased first and then decreased with the cumulative application of lime. The application of a cumulative lime amount of 18,000 kg ha−1 was identified as the critical transition point of soil pH, soil Cd, and rice Cd content. Application of lime up to or above 3000 kg ha−1 per season reduced Cd content in brown rice below 0.20 mg kg−1. The results suggest that the reduction in effective Cd content might be a result of the combined action of exchangeable soil Ca2+ and soil pH rather than being a direct effect of Ca2+. Therefore, acid Cd-contaminated paddy fields can realize the safe production of rice by the continuous application of an appropriate amount of lime.
... Most studies on the biodiversity-mineralization relationship have focused on net N mineralization and/or nitrification rates (Accoe et al. 2004;Fornara and Tilman 2009;Fornara et al. 2011;Rosenkranz et al. 2012;Mueller et al. 2013). However, net rates alone do not provide a process-based understanding of the N cycle (Hart et al. 1994;Verchot et al. 2002;Cheng et al. 2013), which requires the assessment of simultaneously occurring gross N transformations (Hatch et al. 2000;Paterson 2003;Bedard-Haughn et al. 2006;Müller et al. 2007;Cheng et al. 2014). Previous studies reported that increasing species richness increased net N mineralization rates (Rosenkranz et al. 2012;Mueller et al. 2013), as well as net nitrification rates (Scherer-Lorenzen et al. 2003;Mueller et al. 2013). ...
Article
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We conducted a 15N tracer experiment in laboratory microcosms with field-fresh soil samples from a biodiversity experiment to evaluate the relationship between grassland biodiversity and N cycling. To embrace the complexity of the N cycle, we determined N exchange between five soil N pools (labile and recalcitrant organic N, dissolved NH4+ and NO3− in soil solution, and exchangeable NH4+) and eight N transformations (gross N mineralization from labile and recalcitrant organic N, NH4+ immobilization into labile and recalcitrant organic N, autotrophic nitrification, heterotrophic nitrification, NO3− immobilization, adsorption of NH4+) expected in aerobic soils with the help of the N-cycle model Ntrace. We used grassland soil of the Jena Experiment, which includes plant mixtures with 1 to 60 species and 1 to 4 functional groups (legumes, grasses, tall herbs, small herbs). The 19 soil samples of one block of the Jena Experiment were labeled with either 15NH4+ or 15NO3- or both. In the presence of legumes, gross N mineralization and autotrophic nitrification increased significantly because of higher soil N concentrations in legume-containing plots and high microbial activity. Similarly, the presence of grasses significantly increased the soil NH4+ pool, gross N mineralization, and NH4+ immobilization, likely because of enhanced microbial biomass and activity by providing large amounts of rhizodeposits through their dense root systems. In our experiment, previously reported plant species richness effects on the N cycle, observed in a larger-scale field experiment within the Jena Experiment, were not seen. However, specific plant functional groups had a significant positive impact on the N cycling in the incubated soil samples.
... Agriculture, Ecosystems and Environment 301 (2020) 107021 predicting the NO 3 − −N and TN levels and loadings in the soil category. Numerous studies highlighted the importance of soil pH on the N transformation (Paavolainen et al., 2000;Cheng et al., 2013;Regehr et al., 2015), however, the pH was excluded in the soil category probably due to its small heterogeneity among the catchments (Table 1). Forest and agriculture were the two largest land use types in the catchments. ...
Article
Protecting and restoring riverine environmental quality requires a quantitative understanding between riverine nitrogen (N) and various determinants, however, it is still challenging in highly naturally-and-anthropogenically differentiated agricultural catchments. The study observed riverine ammonium-N (NH4⁺−N), nitrate-N (NO3⁻−N), and total-N (TN) in the eleven Chinese subtropical agricultural catchments, to develop predicting functions for riverine N concentrations and loadings through integrating the multiple stepwise linear regression (MLR) and variation partitioning analysis (VPA). The results suggested severe riverine N pollution in the catchments, with the observed TN concentrations of 1.23–4.24 mg N L⁻¹ and average annual TN loadings of 19.80 ± 24.72 kg N ha⁻¹ yr⁻¹. The mean annual flow-weighted N concentrations and loadings could be effectively predicted by the MLR (R² = 0.49−0.87, relative error = 4.1%–153.1%), using the explanatory variables in the catchment hydrogeographic characteristics (catchment area and topographic wetness index (Twi)), land use compositions (forest and agriculture areal percentages), soil properties (bulk density (BD) and total soil N content (TSN)), and socioeconomic (livestock densities) categories. The land use compositions had the largest relative independent contributions to all the flow-weighted N concentrations (78.46%–86.11%), showing the importance of land use compositions on riverine N levels. The socioeconomic conditions had the largest relative independent contributions to the NH4⁺−N (47.92%) and TN (40.74) loadings, due to the discharge animal excretions of rich NH4⁺−N and TN into stream systems. The land use category independently contributed to 82.24% of the explainability of the NO3⁻−N loadings, probably explained to the unique characteristics of NO3⁻−N loss under different land uses. Therefore, the study provided useful ideas and tools to environment managers and agencies for controlling riverine N pollution in the subtropical China.
... Obviously, soil pH alters nutrient availability through its effect on soil microbial community composition and soil biogeochemical processes (Falkengren-Grerup et al., 2006;Lambkin et al., 2011;Cheng et al., 2013). However, in the post−fire sites, soil pH itself is an indicator of habitat conditions that is regulated by topographical heterogeneity and the vegetation restoration process (YSF), as shown in Fig. 4a. ...
Article
Understanding the determinants of post–fire regeneration is critical for determining an appropriate restoration program following fire disturbances. However, studies addressing the drivers of post–fire regeneration of forests in monsoon climate are rare. This study explored the temporal and spatial variations of post–fire forest regeneration in the Central Yunnan Plateau of Southwest China, and disentangled the direct and indirect effects of the environmental factors via structural equation models (SEMs). We found that the overall post–fire regeneration density was generally greater for the habitat with higher values of elevation, pre–fire abundance, and soil pH. Post–fire regeneration was mainly composed of resprouts; seedlings were less relevant and appeared later. The SEM approach showed more variation of recruitment in resprouting (R2=0.66) than seeding (R2=0.33), and revealed different direct and indirect pathways. Resprouts were widely distributed, and significantly influenced by pre–fire abundance, elevation, soil pH, and years since the last fire. In contrast, seedlings preferentially occurred in infertile habitats, andweremainly influenced by topographic position and soil nutrients, showing distinct distribution from that of resprouts. Overall, forests under the subtropicalmonsoon climate in the Central Yunnan Plateau were resilient to fire mainly due to rapid post–fire resprouting. These findings indicate the complementary roles of resprouting and seeding in post- fire regeneration, and help to understand themechanisms that regulate post-fire plant regeneration in a spatially heterogeneous landscape. Our results should contribute to improving the post–fire management of forest ecosystems under the influence of a semi–humid monsoon climate.
... The negative effect of soil pH on soil δ 15 N in this study was probably due to the high 15 N discriminations in soils with low pH, as previous results have indicated that soil N mineralization via enzymes increased with declining soil pH (Sinsabaugh et al. 2008). In addition, fungi are generally favored compared to bacteria in soils of low pH (de Vries et al. 2006;Yi et al. 2013), which play key roles in the depolymerization of N-containing compounds due to its ability of spanning microsites and secreting exoenzymes (Schimel and Bennett 2004). Similar negative relationships has also been observed between soil C:N ratios and soil δ 15 N values in this study (Table 2), which could be due to the inhibitions of both soil N mineralization and nitrification rates in soils with low substrate quality (Booth and Stark 2005;Hirobe et al. 2003;Yang et al. 2013). ...
Article
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AimsSecondary grasslands reestablished after deforestation in subtropical and tropical regions greatly alter terrestrial carbon (C) and nitrogen (N) dynamics and their associated ecosystem functions. However, reliable evaluations of C and N dynamics in secondary grasslands across regional climatic gradient remain challenging.Methods We investigated natural 13C and 15N abundance in plants and soil as well as their associations with environmental factors (including climatic, plant and edaphic variables) from 20 sites across a 600 km climatic gradient in secondary grasslands of southern China.ResultsThe δ13C values in plants and soil declined with increasing mean annual precipitation (MAP) but increased as the mean annual temperature (MAT) increased. These changes were mostly attributed to the shift in plant functional group between C4 and C3. In contrast, increasing MAP and decreasing MAT had positive effects on soil δ15N values, which were mainly related to changes in edaphic factors, including soil pH, soil C and N content and soil C:N ratios.Conclusions Our findings indicate inverse patterns and different controls on soil δ13C and δ15N values along the climatic gradient, providing novel insights into the underlying mechanisms of ecosystem C and N dynamics in response to climate and vegetation change in secondary grasslands.
... Calcium can react with organic matter to form stable calcium humate [43], which is more difficult to break down for soil organisms, thereby leading to a decline in M Norg rate even when the content of soil organic matter (SOM) is high. Previous studies have found that the O NH4 rate is significantly positively related to pH in the soil [44,45]. Forest soil that has developed from basalt or granite in subtropical/tropical regions has a low pH (<4.5), which can inhibit the O NH4 rate [11,13]. ...
Article
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Evaluations of gross mineralization (MNorg) and nitrification (ONH4) can be used to evaluate the supply capacity of inorganic N, which is crucial in determining appropriate N fertilizer application. However, the relevant research for banana plantations to date is limited. In this study, natural forest and banana plantations with different cultivation ages (3, 7, 10, and 22 y) were chosen in a subtropical region, and the 15N dilution technique was used to determine the gross MNorg and ONH4 rates. The objective was to evaluate the effect of the conversion of natural forests to banana plantations on inorganic N supply capacity (MNorg + ONH4) and other relevant factors. Compared to other natural forests in tropical and subtropical regions reported on by previous studies, the natural forest in this study was characterized by a relatively low MNorg rate and a high ONH4 rate in the soil, resulting in the presence of inorganic N dominated by nitrate. Compared to the natural forest, 3 y banana cultivation increased the MNorg and ONH4 rates and inorganic N availability in the soil, but these rates were significantly reduced with prolonged banana cultivation. Furthermore, the mean residence times of ammonium and nitrate were shorter in the 3 y than in the 7, 10, and 22 y banana plantations, indicating a reduced turnover of ammonium and nitrate in soil subjected to long-term banana cultivation. In addition, the conversion of natural forest to banana plantation reduced the soil organic carbon (SOC), total N and calcium concentrations, as well as water holding capacity (WHC), cation exchangeable capacity (CEC), and pH, more obviously in soils subjected to long-term banana cultivation. The MNorg and ONH4 rates were significantly and positively related to the SOC and TN concentrations, as well as the WHC and CEC, suggesting that the decline in soil quality after long-term banana cultivation could significantly inhibit MNorg and ONH4 rates, thus reducing inorganic N supply and turnover. Increasing the amount of soil organic matter may be an effective measure for stimulating N cycling for long-term banana cultivation.
... However, saline-alkaline land spans 1170 million hectares worldwide (Hassani et al., 2020), and soil salinization (including salinity and pH) is an important factor affecting soil microbial communities and plant diversity (Salza et al., 2017;Rath et al., 2019;Zhao et al., 2020). High salinity inhibits microorganism growth in soil (Rath and Rousk, 2015;Yang et al., 2020), which in turn affects soil N mineralization and availability (Cheng et al., 2013) and further impacts plant growth. Hence, soil salinization could affect R s and its components by impacting microbial community and plant growth (Rath and Rousk, 2015;Yang et al., 2020;Zhao et al., 2020). ...
Article
The responses of soil total respiration (Rs ) and its components (soil autotrophic respiration (Ra ) and heterotro- phic respiration (Rh)) to nitrogen (N) deposition have been widely evaluated in non-saline-alkaline grasslands. However, their responses to N addition under drought and wet conditions, especially in saline-alkaline grasslands , remain unclear. A two-factorial experiment involving N addition and precipitation changes (decreased or increased 50% precipitation relative to ambient) was conducted in a saline-alkaline grassland of Northern China, while soil respiration was measured in different treatment plots during two growing seasons (2018, 2019). Results showed that the addition of N or changes in precipitation alone had no significant effect on R s , R a or R h in both years because root productivity and soil microbial biomass were not affected. However, N addition with increased precipitation synergistically augmented seasonal mean R s and R a by 25.7% and 46.8% in 2018, and by 42.4% and 89.3% in 2019, respectively, owing to the increase in plant productivity. The variation in R a primarily contributed to variation in R s , and the effect size of N addition on R s and R a were increased with precipitation. In addition, a structural equation model showed that the response of soil respiration to N addition and precipitation changes was regulated by soil salinization, in which the R a was regulated by soil based cations while R h was controlled by soil pH values. Our study highlights that N addition with increased precipitation preferentially affects plants rather than microorganisms, and that R h was not sensitive to N addition and precipitation changes in saline-alkaline grassland.
... Application of lime can neutralize excessive hydrogen ions in the soil solution (Bolan et al., 2003) and increase the availability of P, K and S (Li et al., 2018). Besides, liming improves nutrient use efficiency (Fageria and Nascente, 2014) and intensifies microbial activity for nutrient transformations (Cheng et al., 2013). In other districts, soil pH is mostly favorable for K availability. ...
Article
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Potassium (K) availability to crops and their response to K fertilization depend largely on K-bearing clay minerals in soil and their interactions with other soil properties. In the present study, we used data from existing literature on K in agricultural soils of Bangladesh. The dominant group of K-bearing minerals in soils of Bangladesh is mica-smectite and mica-chlorite existing in about 40% of the cropped area of the country. The second most dominant groups are mica-vermiculite-kaolinite, kaolinite-mica, mica-kaolinite-vermiculite~suite and mica-kaolinite-vermiculite found in around 43% of the soils. Exchangeable K in soil, the most important indicator of K availability to crops, varies greatly in the country, ranging from 0.04 to 1.54 cmol kg-1 , the frequency of the lower values being relatively high. Potassium fixation from added fertilizer is likely to occur in soils of 47 out of 64 districts of Bangladesh. An assessment based on neural networking specified pH, organic carbon content, clay fraction, moisture at field capacity and cation exchange capacity as the most important soil properties regulating K availability to crops. Rice responded positively to applied K fertilizer when nitrogen (N) availability was not limiting. Optimization of K fertilizer rates and proper K management are imperative for sustainable crop production in the country.
... This may increase the gross NH 4 + production. Furthermore, the increase in the gross NO 3 − production with increasing pH may be explained by pH-dependent alterations in the activity of acid-sensitive nitrifying bacteria (Cheng et al. 2013;Tang et al. 2021). ...
Article
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Purpose Soil acidification influences competitive N uptake between plants and microorganisms. The mechanisms by which soil acidification affects competition between maize and microorganisms for organic N must be determined to understand N cycling and adjust the forms and levels of N fertilisation. Methods The uptake of glycine, mineral N after glycine decomposition, and NH4⁺ by maize and microorganisms was investigated using ¹³C and ¹⁵N labelling. Microbial community composition biomarkers were analysed using phospholipid fatty acid (PLFA) analysis. Mineralisation of organic N was monitored via CO2 production, and gross NH4⁺/NO3⁻ production and consumption was assessed using ¹⁵N pool dilution. Results Soil acidification (pH from 7.6 to 5.1) increased the intact glycine uptake by maize roots (from 0.7 to 2.4% of added ¹⁵N) but decreased its uptake by microorganisms (from 32 to 2.4% of added ¹⁵N). Soil acidification altered the microbial community composition: the PLFA of arbuscular mycorrhizal fungi and anaerobes decreased by 6- and 1.5-fold, respectively. Soil acidification reduced the decomposition rates of proteins, peptides, and amino acids as indicated by the CO2 release. This corresponded to a gross NH4⁺ production increase by 1.3-fold and a gross NO3⁻ production decrease by 97%, compared with soil at pH 7.1. Conclusions Acidification led to decreased microbial biomass, shift in the microbial community, and the strong decrease (10–15-fold) in amino acid uptake by microorganisms, and was beneficial to maize plants, which assimilated 2.4% of the N added as glycine. However, these quantities of N are insufficient for a substantial increase in the N nutrition of the plants.
... Different lower-case letters represent significant differences among root exudate (RE) treatments. mineralization increased with increases of soil pH (Cheng et al., 2013). In our study, we found a significant increase of soil pH after adding organic acids, regardless of organic acids concentration, while carbohydrates did not change the soil pH (Fig. 1). ...
Article
Nitrogen (N) availability is a primary constraint to plant productivity, especially in marginal lands with inherently low fertility. Root exudates change with plant nutrient status, and are expected to affect the microbially-mediated N transformations (gross N mineralization vs N fixation) in low fertility soil (low soil organic matter). To explore this possibility, we sampled soils from two monoculture switchgrass (var. Cave-In-Rock) plot with and without N addition at two marginal land sites in Michigan, USA. In a two-week lab incubation, we quantified the effect of different root exudates on gross N mineralization and N fixation by adding simulated root exudates (carbohydrates, organic acids) at a rate of 100 μg C g⁻¹ day⁻¹. On average, adding carbohydrates to low fertility soil increased the soil respiration by 254%, the dissolved organic carbon (DOC) by 366% and reduced dissolved organic N (DON) by 40%. In contrast, soils receiving organic acids had 159% more soil respiration, 163% higher DOC concentration and the DON concentration increased by 49%. Analysis of the C recovery in measured pools revealed that root exudates C inputs were nearly equivalent to the DOC, microbial biomass carbon (MBC), and soil respiration in sandy soil, but only 45–74% of the root exudate C was recovered in these pools in the sandy loam soil. This suggests that root exudate C may be adsorbed to mineral particles in the sandy loam soil. Soil treated with organic acids had higher gross N mineralization and N immobilization rates than soil with carbohydrates addition. Adding carbohydrates significantly increased the free-living N fixation rates, compared to organic acid addition. Changes in soil pH, and DON induced by root exudate addition had strong association with N transformation rates and N availability. Gross N mineralization produced more plant-available N than N fixation, as evidenced by higher inorganic N concentration in soils receiving organic acids than carbohydrates. By quantifying how different root exudates affect the contribution of N mineralization and N fixation to the plant-available N pool in low fertility soils, this study enhances our understanding of the “C for N” exchange in the plant rhizosphere.
... Plot treated with PM were resulted the highest fruit length (cm), fruit girth (cm) which ultimately increased the individual fruit weight (g) of okra. Organic amendment and liming might be influence both transformation and uptake of nutrient by plant in acidic soil, ultimately better biomass production and photosynthates accumulation [5], [11]. ...
Article
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Integrated Nutrient Management (INM) is a novel strategy to achieve sustainable crop production in degraded soils through judicious and balanced plant nutrients utilization. Sole application of chemical fertilizers in crop production causes soil and environmental pollution. The present study was designed to assess the effects of application of organic manures conjointly with chemical fertilizers on growth and yield of okra in acid soil. The experiment was consisted of four treatments viz. T0 [Control], T1 [Recommended dose of chemical fertilizers (RDF)], T2 [Dolomite (D) @ 1t ha-1 + RDF], T3 [Poultry manure (PM) @ 3t ha-1 + RDF], T3 [Cow dung (CD) @ 5t ha-1 + RDF] with six replications in a randomized complete block design. The results indicated that the use of PM with RDF showed better performance in the growth and yield attributes of okra. Compared with others plots, the highest plant height (114.10 cm), fresh weight plant-1 (591.58 g) and dry weight plant-1 (86.73 g) were observed in the PM-treated plot. Similarly, the highest number of fruits plant-1 (20.33) and fruit yield (13.58 t ha-1) were also found in PM-treated plants. Therefore, under acidic soil conditions, organic and inorganic fertilization may have a significant positive impact on the growth and yield of Okra.
... Soil pH had a relatively weaker effect on potential GNM through influencing microbial biomass. Several studies have shown that soil pH significantly influenced SOM mineralization, due to its effects on microbial growth, community structure and activity (Cheng et al., 2013;Hogberg et al., 2007;Rousk et al., 2009;Zhalnina et al., 2015;Zhou et al., 2017). Despite a negative relationship between climate and potential GNM (Fig. 4), climatic variables only exhibited an indirect influence on potential GNM mainly through soil pH (Fig. 5). ...
Article
Nitrogen (N) mineralization in soils generally controls biological N availability in terrestrial ecosystems. As the pivotal first step in the overall N mineralization process, gross N mineralization (GNM, defined as the production of ammonium from microbial mineralization of organic N) is inherently coupled with microbial mineralization of soil organic carbon (C) which is commonly referred to as microbial respiration (MR), and that has often been used as a proxy of C availability. However, the pattern of GNM and its underlying mechanisms at a regional scale, and its linkage with MR remain unclear. By analyzing 100 soil samples collected across different forest types along a 3800 km long north-south transect in eastern China, we simultaneously measured the potential GNM using a ¹⁵N pool dilution method and MR using a dynamic CO2 trapping technique. We conducted a structural equation model (SEM) to examine the interactive effects of climate, soil pH, microbial substrate availability, and microbial biomass on potential GNM along the forest transect. Furthermore, we conducted a non-linear regression analysis between potential GNM and MR. We found that both potential GNM and MR varied largely, from 0.55 to 16.14 mg N kg⁻¹ soil d⁻¹ and from 3.64 to 24.30 mg C kg⁻¹ soil d⁻¹, respectively, but were not significantly affected by forest type. The SEM analysis showed that 51% of the variation in potential GNM was explained, with microbial substrate availability being the most important influencing factor. There was a positive non-linear relationship between potential GNM and MR (R² = 0.52, P < 0.0001). Notably, MR alone exerted a comparable role in explaining the variation in potential GNM compared to the interactive effects between multiple factors used in the SEM. Our findings confirm the dominant control of C availability to microbes on potential GNM, and necessitate the incorporation of MR for better modeling GNM in forest soils.
... There is also evidence that soil Ca is increasing over time (up to 500%) in some areas where current intensive forest production methods have been applied (McMahon et al. 2019). Application of Ca in the form of Ca carbonate (CaCO 3 , commonly referred to as lime) increases soil pH, which affects other soil nutrient availability and may address soil deficiencies (Fageria et al. 2002, Cheng et al. 2013. High levels of soil organic matter will reduce the direct impact of lime application on pH because soil organic matter provides negatively charged sites that bind to H + in the soil, resulting in a more acidic soil solution (Fageria and Baligar 2008). ...
Article
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Calcium (Ca) is a critical plant nutrient typically applied at the time of planting in intensive Eucalyptus plantations in South America. At two sites in Colombia, we examined (1) calcium source by comparing growth after application of 100 kg ha−1 elemental Ca as lime or as pelletized highly reactive calcium fertilizer (HRCF) compared to a no application control, and (2) Ca rate by applying 0, 100, 200, and 400 kg ha−1 elemental Ca as HRCF with the addition of nitrogen, phosphorus, potassium, sulfur, and boron (NPKSB). We assessed height, diameter, and volume after 12 and 24 months. There were no growth differences from Ca source at the 100 kg ha−1 rate. We found increased volume after 24 months at the “Popayan” site with 200 and 400 kg ha−1 Ca HRCF+NPKSB treatments (112 and 113 m3 ha−1, respectively) compared to control (92 m3 ha−1), a 22% increase. In contrast, volume did not differ after 24 months at the “Darien” site, ranging from 114 m3 ha−1 in the 0 kg ha−1 Ca HRCF+NPKSB treatment to 98 m3 ha−1 in the control. Differences in response are likely due to soil characteristics, such as organic matter, emphasizing the importance of identifying site-specific nutrient deficiencies. Study Implications: Operational applications may be over- or under-applying calcium carbonate in Eucalyptus plantations in South America. In the first two years of a seven-year rotation located in volcanic soils in Colombia, we found that one site with more organic matter at a greater depth did not need Ca additions, whereas the other site required greater than current operational applications to optimize productivity. Ca application rate trials across a gradient of soil conditions could establish critical values and improve recommendations of appropriate Ca application rates and emphasize the importance of understanding site-specific soil conditions to produce effective fertilization regimes.
... The initial NH 4 + -N contents of the HW, CF, P1, and P2 groups in Alisols were 53.0, 90.2, 71.3, and 73.2 mg·kg −1 , respectively, which were all significantly higher than the control group (2.9 mg·kg −1 ). Soil pH is an important factor in controlling nitrification activity; increasing pH often increases the rate of nitrification [36,37]. The NH 4 + -N soil content was still high after 10 days, which may be because the acidic soil environment inhibited the nitrification rate of Alisols. ...
Article
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Replacing chemical fertilizers with human waste for vegetable planting is a traditional, economical, and environmentally friendly waste resource utilization strategy. However, whether the human waste substitute strategy can improve soil fertility and increase crop yield and quality compared to the simple application of chemical fertilizers is still unclear, especially under acidic and alkaline soil conditions. In this study, we studied the effects of different ratios of human waste (urine and feces) to chemical fertilizer on the crop yield, crop quality, soil fertility, and soil chemical parameters in alkaline Cambisols and acidic Alisols cultivated with water spinach (Ipomoea aquatica Forssk.). The application variants of human waste and chemical fertilizer were as follows: (i) Control, no fertilization (CK), (ii) human waste application (HW), (iii) chemical fertilizer application (CF), (iv) 1/3 human waste to chemical fertilizer (P1), and (v) 2/3 human waste to chemical fertilizer (P2). Human waste application increased the total nitrogen, available phosphorus, available potassium, organic matter, NO3−-N, and conductivity in soil, enhanced soil enzyme activity, slowed down soil acidification, and increased the yield, soluble sugar, and vitamin C contents of the water spinach while reducing its nitrate content. Our findings indicate that human waste substitution improved soil fertility while reducing the potential risks of soil acidification, salinization, and human exposure to nitrates. These findings may be applied to increase vegetable production and quality, improve the soil environment, and increase the utilization of human waste as a valuable resource.
... Soil pH is generally affected by land use change. It has been documented that pH is one of the primary regulators of organic matter cycling in soil (Cheng et al., 2013). A study of two broadleaf woodland sites at Rothamsted Each soil layer is represented by a different color. 1 to 5 stands for soil layers ranging from 0 to 10 cm (upper) to 40-50 cm (deepest), with each layer having a thickness of 10 cm. ...
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How to reduce the rising carbon (C) in the atmosphere by enhancing forest soil C-holding capacity requires further research. Forest density via thinning has long been studied for this reason. However, how changes in density affect soil C sequestration is still uncertain for many other factors also affect soil C in open forest ecosystems. To measure the effect of thinning on soil organic carbon (SOC) stock relative to other contributing factors, we selected 12 25 × 25 m plots, and applied a series of thinning treatments: CK (control plots; 2173 ± 12 trees ha⁻¹, which was how all plots started), LT (light thinning; 1834 ± 12 trees ha⁻¹), MT (moderate thinning; 1418 ± 7 trees ha⁻¹) and HT (heavy thinning; 1089 ± 13 trees ha⁻¹). We measured the SOC stocks (kg C m⁻²) for 11 seasons crossing three years. In addition, soils of the four treatment plots (0–50 cm soil depth, 5 layers, 10 cm per layer) were collected once per season, and then the samples were incubated for 56 days before measuring their cumulate mineralized carbon (CMC). The temperature at 10 cm underground was measured every 60 min throughout two years. The active carbon (DOC (dissolved organic C) and MBC (microbial biomass C)) stocks were also measured. We found that soil in MT plots held more C overall, with more active carbon per unit of SOC. Soil temperatures were affected by the thinning as well as the C and N (nitrogen) stock. Soil temperatures and C, N stock alike rose from CK levels and peaked in MT, before decreasing in HT. However, SOC mineralization rate (mineralized-C) was reduced in MT across seasons, and mineralized-C varied seasonally. Soil C and N stocks were enhanced in MT plots, partly due to the increased soil temperatures and the reduced mineralized-C.
... Plants' transformation and absorption of nutrients can both be influenced by liming [70,71] and, additionally, nutrient use efficiency [72]. The use of lime and organic manure amendment considerably increased the content and absorption of macronutrients in both rice and maize, according to our findings. ...
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Acid soil is a hindrance to agricultural productivity and a threat to food and environmental security. Research was carried out to assess the impact of lime and organic manure (OM) amendments on yield and nutrient uptake by using the T. Aman-Maize-Fallow cropping pattern in acid soils. The experiment was set up in an RCBD design and used nine treatments and three replications. The treatments, comprising of various doses of lime, OM (cow dung and poultry manure), and a lime-OM combination, were applied to the first crop, T. Aman (Binadhan 7), and in the next crop, maize (BARI Hybrid Maize-9), the residual impacts of the treatments were assessed. Results demonstrate that the highest grain yield, 4.84 t ha−1 (13.61% increase over control) was recorded for T. Aman and 8.38 t ha−1 (58.71% increase over control) for maize, was achieved when dololime was applied in combination with poultry manure. The total rice equivalent yield increase over the control ranged from 20.5% to 66.1%. The application of lime with cow dung or poultry manure considerably enhanced N, P, K, and S content and uptake in both crops, compared to the control. Thus, it may be inferred that using dololime in association with poultry manure can increase crop productivity in acid soils.
... However, before setting soil pH as a disaggregation factor, more understanding of its effect on the N cycle processes is required. Indeed, soil pH influences different steps of the N cycle, such as N mineralisation rate (Fu et al., 1987;Cheng et al., 2013), nitrifier communities (Nicol et al., 2008), denitrifiers' enzymes (Liu et al., 2014;Žurovec et al., 2021), and the overall outcome on the balance of N 2 O emissions remains unclear (ŠImek and Cooper, 2002). A wider range of soil pH should be assessed in EF 3PRP studies in order to help in understanding its effect on N 2 O, in interaction with other factors (López-Aizpún et al., 2020). ...
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Excreta deposition onto pasture, range and paddocks (PRP) by grazing ruminant constitute a source of nitrous oxide (N2O), a potent greenhouse gas (GHG). These emissions must be reported in national GHG inventories, and their estimation is based on the application of an emission factor, EF3PRP (proportion of nitrogen (N) deposited to the soil through ruminant excreta, which is emitted as N2O). Depending on local data available, countries use various EF3PRPs and approaches to estimate N2O emissions from grazing ruminant excreta. Based on ten case study countries, this review aims to highlight the uncertainties around the methods used to account for these emissions in their national GHG inventories, and to discuss the efforts undertaken for considering factors of variation in the calculation of emissions. Without any local experimental data, 2006 the IPCC default (Tier 1) EF3PRPs are still widely applied although the default values were revised in 2019. Some countries have developed country-specific (Tier 2) EF3PRP based on local field studies. The accuracy of estimation can be improved through the disaggregation of EF3PRP or the application of models; two approaches including factors of variation. While a disaggregation of EF3PRP by excreta type is already well adopted, a disaggregation by other factors such as season of excreta deposition is more difficult to implement. Empirical models are a potential method of considering factors of variation in the establishment of EF3PRP. Disaggregation and modelling requires availability of sufficient experimental and activity data, hence why only few countries have currently adopted such approaches. Replication of field studies under various conditions, combined with meta-analysis of experimental data, can help in the exploration of influencing factors, as long as appropriate metadata is recorded. Overall, despite standard IPCC methodologies for calculating GHG emissions, large uncertainties and differences between individual countries' accounting remain to be addressed.
... The highest GNM rate was noted in slightly acidic soils (pH 6.1-6.5; Figure S5c), which are ideal for soil microbes, because in this soil plants grow well and produce more root exudates as an available C source for survival and reproduction of microbes (Msimbira & Smith, 2020). Furthermore, although a few studies suggested that GNM is stimulated by increasing soil pH (Cheng et al., 2013;Zhao et al., 2018) due to the increase in soil organic matter solubility (Curtin et al., 1998), we found that GNM significantly decreased when soil pH was >8.0, and the lowest GNM was recorded in strongly alkaline soils ( Figure S5c). This may be due to higher pH reduced the activities of the enzymes that directly regulated GNM. ...
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Soil gross nitrogen (N) mineralization (GNM), a key microbial process in the global N cycle, is mainly controlled by climate and soil properties. This study provides for the first time a comprehensive analysis of the role of soil physicochemical properties and climate and their interactions with soil microbial biomass (MB) in controlling GNM globally. Through a meta‐analysis of 970 observations from 337 published papers from various ecosystems, we found that GNM was positively correlated with MB, total carbon, total N and precipitation, and negatively correlated with bulk density (BD) and soil pH. Our multivariate analysis and structural equation modelling revealed that GNM is driven by MB and dominantly influenced by BD and precipitation. The higher total N accelerates GNM via increasing MB. The decrease in BD stimulates GNM via increasing total N and MB, whereas higher precipitation stimulates GNM via increasing total N. Moreover, the GNM varies with ecosystem type, being greater in forests and grasslands with high total carbon and MB contents and low BD and pH compared to croplands. The highest GNM was observed in tropical wet soils that receive high precipitation, which increases the supply of soil substrate (total N) to microbes. Our findings suggest that anthropogenic activities that affect soil microbial population size, BD, soil substrate availability, or soil pH may interact with changes in precipitation regime and land use to influence GNM, which may ultimately affect ecosystem productivity and N loss to the environment.
... Liming can also influence both transformation and uptake of nutrients by plants [49,50] and, additionally, nutrient use efficiency [34]. It is widely accepted that liming can neutralize excessive acidic ions in the soil including proton ions and other acidic mineral cations (e.g., Al 3+ ), while simultaneously supplying basic cations to the root zones e.g., Ca 2+ and Mg 2+ [51]. ...
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Soil acidity is a major problem when it comes to improving crop productivity and nutrient uptake. This experiment was therefore conducted at a farmer’s field—Nalitabari Upazila under AEZ 22 (northern and eastern Piedmont plains) to evaluate the effects of lime and organic manure (OM) amendment on crop productivity and nutrient uptake of the wheat–mungbean–T. Aman cropping pattern in acidic soils of northern and eastern Piedmont plains. The experiment was laid out in a randomized complete block design with three replications. There were nine treatments applied, varying doses of lime (dololime at the rate of 1 and 2 t ha−1), OM (cow dung at the rate of 5 t ha−1, poultry manure at the rate of 3 t ha−1) and a lime–OM combination to the first crop; T. Aman and its residual effects were evaluated in the succeeding second crop, wheat, and the third crop, mungbean. Results demonstrate that application of lime and organic manure to soil had significant effects on the first crop. However, the effects of lime and organic manure were more pronounced in the second and third crops. The increase in grain yield over control ranged from 0.24 to 13.44% in BINA dhan7. However, it varied from 10.14 to 54.38% in BARI Gom30 and 40 to 161.67% in BARI Mung6. The straw yields of the crops also followed a similar trend. The N, P, K, and S uptake by grain and straw of T. Aman, wheat, and mungbean were influenced significantly by the combined application of lime and organic manure. Sole or combined application of lime and manure amendment significantly improved nutrient availability and soil quality. Therefore, application of lime in combination with manure can be practiced for uplifting the crop productivity and improving soil quality in acidic Piedmont soils of northern and eastern Piedmont plains.
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Agricultural practices can lead to fluctuations in soil pH and salinity, likely affecting soil nutrient cycling. Compost addition may reduce the impact of these stresses, leading to more stable and resilient systems. We tested nitrogen (N) and carbon (C) cycling responses to the imposition and relief of an acute stress in an agricultural soil, and whether these responses were moderated by compost. In greenhouse pots, we mixed soil with elemental sulfur (S) and compost in a complete 2-way factorial design and incubated at ambient temperatures. Sulfur induced strong acidity and mild salinity stress. After 70 d, stress was partially alleviated by leaching with liquid lime. We took samples 21 and 42 d after S addition and one week after alleviation, measured enzyme activity, microbial biomass, and soluble organic C and N, and performed N and C cycle assays by incubating subsamples with and without ground legume residues to stimulate mineralization and microbial growth. Net N mineralization increased in response to the applied stress, and declined after alleviation. Conversely, stress reduced most C cycling indicators and inhibited nitrification. Stress limited microbial growth more than respiration. Unexpectedly, compost additions to the stressed soils consistently stimulated net N mineralization compared to stressed soils without compost. Compost thus exacerbated rather than buffered the effects of stress on net N mineralization. Compost addition did not affect microbial growth or respiration in any treatment, or how any C cycle parameter responded to stress. The decoupled C and N responses suggest that the localized stresses associated with intensive agriculture may have important implications for C and N turnover in these systems, and warrant further study. Additionally, they demonstrate that biogeochemical processes should be evaluated concurrently when accessing the effect of stressors in soil systems.
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Using a structural equation model (SEM), this paper investigates the response of soil nitrogen content of five typical grasslands in the middle line countries of China’s “Belt and Road” initiative to the changes of climate variables, soil pH value, and normalized vegetation index, and employs the principal component analysis method to determine the spatial variation characteristics and influencing factors of nitrogen reserves in different grasslands. Pontiac grassland (PS), Middle East grassland (MES), Kazakh grassland (KS), Kazakh forest grassland (KFS), and Kazakh semi-desert grassland (KFS) are the five grasslands in the research region (KSD). The results indicated that (1) the nitrogen reserves of the five grassland soils (0–100 cm) in the research area were 7.49 Pg, or approximately 5.7 percent of the total world nitrogen reserves. The sum of the five grasslands’ 0–30 cm and 0–50 cm N reserves accounted for 36.3 percent and 63.1 percent, respectively, of the total 0–100 cm N reserves. The density of nitrogen in the soil (0–100 cm) varied significantly between grasslands, ranging from 1.47 to 3.87 kg/m2, with an average of 3.10 kg/m2. (2) PCA analysis revealed a substantial positive correlation between soil N and MAP (p < 0.01), a negative correlation between soil N and Srad (p < 0.01), and a high degree of similarity between the three grassland samples, KFS, KS, and KSD. (3) The decision tree algorithm determined that MAP had the most relative importance for changes in soil nitrogen content in PS, MES, and KFS, whereas Srad had the greatest relative importance for changes in soil nitrogen content in KS and KSD. The pH showed the least proportional impact for variations in soil N concentration in all five grasslands. (4) Different factors influence the change in soil N content across diverse grasslands. The principal positive driving factor of soil N content in KS and KSD is Srad, with loads of −0.39 and −0.44, respectively. The principal negative driving factor of soil N content in PS and MES is Map, with loads of 0.38 and 0.2, respectively. In the SEM model of soil nitrogen content in KFS, no environmental variables had a significant effect on N content, and the model’s R2 value was 0.08, indicating an average fit.
Article
Increasing inputs of nitrogen (N) fertilizer greatly affect the functionality of farmland carbon (C) and N cycling. Soil contain various C and N fractions that have diverse chemical and physical characteristics, and they can be used as sensitive evaluation indicators for the change in soil C and N content; however, N application's effects on the deep soil layer N and C fractions of the North China Plain remain unclear. Therefore, we investigated the changes in content, percentage, and sensitivity of N and C fractions under four N fertilization application rates at the upper 200 cm soil layer since 2012. N and C fractions in soil layers respond differently to N enrichment. For grain yield, soil organic carbon (SOC), and total nitrogen (TN) contents, the sensitivity index (SI) of N fractions were the highest at N applications of 180 and 240 kg ha⁻¹. SOC and TN are most active in the 0–20 cm soil layer. The SI of most C fractions in the topsoil layer were not the highest, and the SI of the N fractions was higher in the middle soil layer. Obvious leaching during the application of 300 kg ha⁻¹ of N fertilizer was indicated by the nitrate content. Under the experimental conditions, the 180 and 240 kg N ha⁻¹ applications proved to be the best for stabilization of C and N and improved crop productivity. This article is protected by copyright. All rights reserved.
Article
Nitrogen-based fertilizer applications have an effect on nitrification and nitrifying microorganisms in acidic soils of agricultural and forest lands. However, the effect of different nitrogen (N) fertilizers on nitrification and nitrifying microorganisms in acidic Ultisols of the subtropical regions are not well studied. Here, we investigated the effect of ammonium sulfate and urea applications on nitrification and nitrifying microorganisms in acidic Ultisols of Jinyun Mountain. The abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) amoA genes were quantitatively analyzed by real-time PCR. Our results indicated that there was a significant difference in soil pH among treatments and the maximum pH value (pH = 4.93) was recorded in urea addition due to the hydrolysis of urea. Similarly, significant differences in the content of NH4⁺-N and NO3⁻-N were observed among treatments. The result also revealed that urea addition had higher ammonium and nitrate than that of ammonium sulfate, and stimulated nitrification in acidic Ultisols, whereas nitrification was not stimulated by the application of ammonium sulfate. The net nitrification rate at the end of the experiment for control, ammonium sulfate, and urea treatment were −0.005, −0.003 and 0.004 mg N kg⁻¹ soil day⁻¹ respectively. Besides, the addition of urea significantly increased the AOA and AOB abundance. The abundance of AOA amoA gene was greater than AOB in all treatments. However, the ratio of AOA to AOB was lower in soils with ammonium sulfate and urea addition compared to control. This implies that N addition greatly stimulates AOB rather than AOA abundance. Therefore, AOB may be responsible for the higher nitrification potential in the urea added soil. In conclusion, urea addition significantly increased the content of ammonium, soil pH, AOA and AOB abundance, and stimulates nitrification. AOB may play a significant role in nitrification process in urea added acidic Ultisols.
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In order to better understand factors affecting greenhouse gas (GHG) emissions in Canadian agroforestry systems, we conducted a laboratory incubation study to assess N2O, CO2 and CH4 emissions from soils in response to land use (forestland vs. cropland) and agroforestry system type (hedgerow vs. shelterbelt) in central Alberta, Canada. Emissions of N2O were lower in soils from forestland than cropland, and forest soils acted as a net sink of atmospheric CH4 while cropland soils were weak sources of CH4. However, the forest soil had higher CO2 emission rates than the cropland soil within both agroforestry systems. Soil CH4 oxidation was higher in soil from hedgerow (consisted of natural forest vegetation) than from shelterbelt system (planted forest vegetation), while the former also had lower N2O emissions. Overall, soil CO2 emissions were significantly higher from hedgerow than from shelterbelt systems. Emissions of N2O were positively related with gross nitrification rates and soil pH, and negatively related with gross N immobilization rates. The CO2 emissions were positively related with water‐soluble organic C contents, while CH4 emissions were positively related with clay content, but negatively with gross N immobilization rates and soil organic C content. The global warming potential was higher in forestland soil than in cropland soil within agroforestry systems, and higher in forestland soil of the hedgerow compared to that in shelterbelts. Our results suggest that we need to select land uses or agroforestry systems that have a higher potential of mitigating GHG emissions from soils. This study assessed the N2O, CO2 and CH4 emissions from soils in response to land use (forestland vs. cropland) and agroforestry system type (hedgerow vs. shelterbelt) through a laboratory incubation experiment. We found that the global warming potential was higher in forestland soil than in cropland soil within agroforestry systems, and higher in forestland soil of the hedgerow compared to that in shelterbelts. Our results suggest that we need to select land uses or agroforestry systems that have a higher potential of mitigating GHG emissions from soils.
Chapter
The concept of “circular bioeconomy” has garnered more scholarly attention with emphasis on the economy, environment, and resources. In this chapter, the role of biochar in improving circular bioeconomy is discussed. Biochar produced from biowastes is an effective method for helping solve the environmental pollution caused by these wastes. Meanwhile, valuable products such as biochar, bio-oil, and gases can be recovered through pyrolysis technologies, which bring both economic and environmental benefits. Biochars can have different characteristics based on their original feedstocks and pyrolysis conditions. Further application of biochar in the water and soil environment is a promising method to increase the efficiency of the circular bioeconomy. Specifically, biochar containing specific properties can help with the recovery of water and nutrient resources from aqueous environments. For example, biochar application in soils can improve the soil quality and crop yield via the effects of biochar on soil water-holding capacity, nutrients recycling, and microbial communities in soils. Contaminated soils can be purified of toxic substances after the application of biochar, and this leads to less toxic outcomes for the environment and human health. Additionally, the application of biochar in soils also plays an important role in climate change mitigation via carbon sequestration and curtailing greenhouse gas emissions. In short, biochar technology can bring several advantages to the circular bioeconomy.
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Nitrogen is an essential component in forest ecosystem nutrient cycling. Nitrogen fractions, such as dissolved nitrogen, ammonium, nitrate, and microbial biomass nitrogen, are sensitive indicators of soil nitrogen pools which affect soil fertility and nutrient cycling. However, the responses of nitrogen fractions in forest soils to organic mulching are less well understood. The rhizosphere is an important micro-region that must be considered to better understand element cycling between plants and the soil. A field investigation was carried out on the effect of mulching soil in a 15-year-old Ligustrum lucidum urban plantation. Changes in total nitrogen and nitrogen fractions in rhizosphere and bulk soil in the topsoil (upper 20 cm) and in the subsoil (20–40 cm) were evaluated following different levels of mulching, in addition to nitrogen contents in fine roots, leaves, and organic mulch. The relationships between nitrogen fractions and other measured variables were analysed. Organic mulching had no significant effect on most nitrogen fractions except for the rhizosphere microbial biomass nitrogen (MBN), and the thinnest (5 cm) mulching layer showed greater effects than other treatments. Rhizosphere MBN was more sensitive to mulching compared to bulk soil, and was more affected by soil environmental changes. Season and soil depth had more pronounced effects on nitrogen fractions than mulching. Total nitrogen and dissolved nitrogen were correlated to soil phosphorus, whereas other nitrogen fractions were strongly affected by soil physical properties (temperature, water content, bulk density). Mulching also decreased leaf nitrogen content, which was more related to soil nitrogen fractions (except for MBN) than nitrogen contents in either fine roots or organic mulch. Frequent applications of small quantities of organic mulch contribute to nitrogen transformation and utilization in urban forests.
Article
Potassium (K) fertilizer plays an important role in increasing crop yield, quality, and nitrogen use efficiency. However, little is known about its environmental impacts, such as its effects on emissions of the greenhouse gas nitrous oxide (N2O). A nitrogen-15 (¹⁵N) tracer laboratory experiment was therefore performed in an acidic agricultural soil in the suburbs of Wuhan, central China, to determine the effects of K fertilizer on N2O emissions and nitrification/denitrification product ratios under N fertilization. During 15-d incubation periods with a fixed initial N concentration (80 mg kg⁻¹), K application increased average N2O emission rates significantly (1.6–10.8-fold) compared to the control treatment. N2O emissions derived from nitrification and denitrification both increased in K-treated soil, and denitrification contributed more to the increase; its contribution ratio rose from 32% without K fertilizer to 53% with 300 mg kg⁻¹ of K applied. The increase in N2O emissions under K fertilization is probably due to an increase in the activity of denitrifying microorganisms and acid-resistant nitrifying microorganisms caused by higher K⁺ concentrations and lower soil pH. Combined treatment with potassium chloride (KCl) and N fertilizer produced lower N2O emissions than combined treatment with potassium sulfate (K2SO4) and N fertilizer during 15-d incubation periods. Our results imply that there are significant interaction effects between N fertilizers and K fertilizers on N2O emissions. In particular, combining N fertilizers with fertilizers that reduce soil acidity or contain Cl or K ions may significantly affect agricultural N2O emissions.
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Little information is available on soil N cycling in the grasslands of the Qinghai-Tibet plateau under different grazing regimes, which is required to evaluate management practices with respect to soil N availability and dynamics. In this study, a ¹⁵N-labeled (¹⁵NH4NO3 and NH4¹⁵NO3) incubation experiment was conducted to investigate gross N transformation rates in soils of the southeast region of the Qinghai-Tibet plateau (China) under no grazing, continuous grazing and grazing rest conditions. Compared with no grazing, continuous grazing significantly reduced the rates of mineralization, microbial NH4⁺ immobilization, autotrophic nitrification and NO3⁻ consumption, but increased the ratio of autotrophic nitrification to microbial NH4⁺ immobilization and the ratio of the rates of total NO3⁻ production to total NO3⁻ consumption. This indicated that continuous grazing greatly decreased both the inorganic N supply capacity and N turnover but increased the NO3⁻ production potential of the soil. By contrast, mineralization and microbial NH4⁺ immobilization rates did not significantly differ in the soils of the grazing rest and no grazing treatments, suggesting that a higher soil inorganic N supply capacity is maintained by grazing rest than by continuous grazing. In addition, grazing rest stimulated NO3⁻ turnover, by increasing the rates of autotrophic nitrification, microbial NO3⁻ immobilization and dissimilatory NO3⁻ reduction to NH4⁺. Taken together, our study suggests that the most effective management practice for the sustainable utilization of local grasslands is a regime based on grazing rest, as it improved physicochemical and biological properties, which in turn increases N supply and N turnover.
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Context The yield and quality of Leymus chinensis, a major forage resource with high nutritional value, is strongly affected by chemical fertiliser application. Aims Comprehensive estimation of the effects of different fertilisation practices on the yield and quality of L. chinensis. Methods In this study, we conducted a meta-analysis using 206 valid datasets extracted from 10 studies on L. chinensis growth responses to chemical fertilisation in China. Key results Yield increases resulting from fertilisation were higher on alkaline soil with a pH >7.0 and aeolian soil with a coarse texture. Forage yield and quality were also associated with the fertiliser combinations and the fertiliser types. Compared with no fertiliser treatment, the yield increase was higher under NP (NPK) fertiliser application (74.7%; P < 0.05) than N or P fertiliser alone. Application of NP (NPK) fertiliser significantly increased the crude protein content, while N fertiliser reduced the crude fiber content and increased the crude fat content. Moreover, the combined application of macro-and micronutrient fertilisers resulted in a substantial increase in yield and quality. The optimal benefits of fertilisation were achieved in aeolian soil with a pH of 7.9–9.5. Conclusions Reasonable selection of fertilisers should therefore, be implemented to ensure high-yielding, high-quality L. chinensis based on local soil conditions in different regions. Implications The results of this study provide essential information for the formulation of reasonable fertilisation regimes and sustainable production of L. chinensis.
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Photosynthetic “least‐cost” theory posits that the optimal trait combination for a given environment is that where the summed costs of photosynthetic water and nutrient acquisition/use are minimised. The effects of soil water and nutrient availability on photosynthesis should be stronger as climate‐related costs for both resources increase. Two independent datasets of photosynthetic traits, Globamax (1509 species, 288 sites) and Glob13C (3645 species, 594 sites), were used to quantify biophysical and biochemical limitations of photosynthesis and the key variable Ci/Ca (CO2 drawdown during photosynthesis). Climate and soil variables were associated with both datasets. The biochemical photosynthetic capacity was higher on alkaline soils. This effect was strongest at more arid sites, where water unit‐costs are presumably higher. Higher values of soil silt and depth increased Ci/Ca, likely by providing greater H2O supply, alleviating biophysical photosynthetic limitation when soil water is scarce. Climate is important in controlling the optimal balance of H2O and N costs for photosynthesis, but soil properties change these costs, both directly and indirectly. In total, soil properties modify the climate‐demand driven predictions of Ci/Ca by up to 30% at a global scale.
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The relationship between soil respiration (SR) and microbial community structure (MCS) is relevant to changes in forest soil ecosystem stability and chemical cycling under acid rain. Simulated acid rain treatments of pH 4.5 (control), 4.0, 3.25 and 2.5 were applied to two forest stands in the Three Gorges Reservoir Area of Jinyun Mountain, Chongqing. We used phospholipid fatty acid (PLFA) analysis to observe the MCS in the 0–10 cm soil layer and measured SR in situ from January 2016 to December 2017. Additionally, we determined the effects of soil properties on the MCS and SR. Acid rain simulation significantly increased the fungal PLFA abundance and decreased the bacterial PLFA abundance in the mixed coniferous and broad-leaved forest (CF). However, in the evergreen broad-leaved forest (BF), the abundance of bacterial and fungal PLFAs did not differ significantly among treatments. Redundancy analysis (RDA) showed that significant changes in the MSC were mainly due to the C/N ratio, hydrolysable N content, content, fine root biomass and sucrase activity. Acid rain simulation in the CF and BF significantly inhibited SR, but the SR sensitivity to simulated acid rain differed among forests. In 2017, the annual mean SR in the CF under the pH 4.0, 3.25 and 2.5 treatments decreased significantly by 6.1%, 19.2% and 28.9%, but in the BF, SR decreased significantly by 25.6% only under pH 2.5. The structural equation model showed that the relationship between the MCS and the variation in SR was closer and more direct than that with soil nutrients. The microbial community structure was an important factor driving the response of soil respiration to acid rain.
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Thoroughly updated and now in full color, the 15th edition of this market leading text brings the exciting field of soils to life. Explore this new edition to find: A comprehensive approach to soils with a focus on six major ecological roles of soil including growth of plants, climate change, recycling function, biodiversity, water, and soil properties and behavior. New full-color illustrations and the use of color throughout the text highlights the new and refined figures and illustrations to help make the study of soils more efficient, engaging, and relevant. Updated with the latest advances, concepts, and applications including hundreds of key references. New coverage of cutting edge soil science. Examples include coverage of the pedosphere concept, new insights into humus and soil carbon accumulation, subaqueous soils, soil effects on human health, principles and practice of organic farming, urban and human engineered soils, new understandings of the nitrogen cycle, water-saving irrigation techniques, hydraulic redistribution, soil food-web ecology, disease suppressive soils, soil microbial genomics, soil interactions with global climate change, digital soil maps, and many others Applications boxes and case study vignettes bring important soils topics to life. Examples include “Subaqueous Soils—Underwater Pedogenesis,” “Practical Applications of Unsaturated Water Flow in Contrasting Layers,” “Soil Microbiology in the Molecular Age,” and "Where have All the Humics Gone?” Calculations and practical numerical problems boxes help students explore and understand detailed calculations and practical numerical problems. Examples include “Calculating Lime Needs Based on pH Buffering,” “Leaching Requirement for Saline Soils,” "Toward a Global Soil Information System,” “Calculation of Nitrogen Mineralization,” and “Calculation of Percent Pore Space in Soils.”
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Abstract In Fennoscandian boreal forests, soil pH and N supply generally increase downhill as a result of water transport of base cations and N, respectively. Simultaneously, forest productivity increases, the understory changes from ericaceous dwarf shrubs to tall herbs; in the soil, fungi decrease whereas bacteria increase. The composition of the soil microbial community is mainly thought to be controlled by the pH and C-to-N ratio of the substrate. However, the latter also determines the N supply to plants, the plant community composition, and should also affect plant allocation of C below ground to roots and a major functional group of microbes, mycorrhizal fungi. We used phospholipid fatty acids (PLFAs) to analyze the potential importance of mycorrhizal fungi by comparing the microbial community composition in a tree-girdling experiment, where tree belowground C allocation was terminated, and in a long-term (34 years) N loading experiment, with the shifts across a natural pH and N supply gradient. Both tree girdling and N loading caused a decline of ca. 45% of the fungal biomarker PLFA 18:2ω6,9, suggesting a common mechanism, i.e., that N loading caused a decrease in the C supply to ectomycorrhizal fungi just as tree girdling did. The total abundance of bacterial PLFAs did not respond to tree girdling or to N loading, in which cases the pH (of the mor layer) did not change appreciably, but bacterial PLFAs increased considerably when pH increased across the natural gradient. Fungal biomass was high only in acid soil (pH < 4.1) with a high C-to-N ratio (>38). According to a principal component analysis, the soil C-to-N ratio was as good as predictor of microbial community structure as pH. Our study thus indicated the soil C-to-N ratio, and the response of trees to this ratio, as important factors that together with soil pH influence soil microbial community composition.
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Potential nitrogen mineralization and nitrification were measured in soils from a primary successional sequence developed on sand dunes and from a secondary successional sequence on old fields. Potential nitrogen mineralization in soils from the primary sere increased through the first five stages and then leveled off. Nitrogen mineralization was relatively constant in soils from the secondary sere, except that the highest rates were observed in the oldest site. Nitrification was very closely correlated with nitrogen mineralization in soils from both the primary and secondary seres. Only one site had both substantial nitrogen mineralization and low nitrification. The results of this study do not support the hypothesis that nitrification is progressively inhibited in the course of ecological succession.
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Although acid soils are common in forest ecosystems, and there is documented evidence of pH influencing transformations of organic matter in soil, there are surprisingly few studies on the influence of soil pH on the chemical structure of physically fractionated soil organic matter (SOM). The aim of this study was to characterize the influence of pH on the chemical and physical processes involved in SOM stabilization. Forest soils of different pH (4.4 and 7.8) sampled from two long-term experiments at Rothamsted Research (UK) were physically fractionated. The free light fraction (FLF), the intra-aggregate light fraction and the fine silt and clay (S + C, <25 mu m) were characterized using elemental, isotopic (delta C-13), thermogravimetric, differential thermal, diffuse reflectance infrared Fourier transform spectroscopy and high-resolution magic angle spinning H-1 nuclear magnetic resonance analyses. The quantitative distribution of carbon (C) between SOM fractions differed between the two soils. Carbon contents in the light fractions from the acid soil were significantly greater than in those of the alkaline soil. In contrast, in S + C fractions, C content was greater in the alkaline soil. FLF from the acid soil was characterized by a greater C:N ratio, smaller delta C-13 and greater content of thermo-labile compounds compared with FLF from the alkaline soil. In contrast, there was only a weak effect of soil pH on the chemical composition of the organic matter in S + C fractions. Irrespective of soil pH, these latter fractions contained mainly aliphatic compounds such as carbohydrates, carboxylic acid, amide and peptide derivates. This suggested that physical mechanisms, involving the interactions between SOM and mineral surfaces, are of greater importance than the presence of chemically recalcitrant species in protecting SOM associated with the finest soil fractions.
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Investigations to analyze the nature of nitrification in acid soils were carried out in the laboratory using 2 soil types from a tea field. The optimum temperature for the nitrification activity in these soils was 25°C and the activity was inhibited above 35°C, suggesting that the nitrifying bacteria became adapted to the soil conditions. The optimum NH4 -N concentrations for nitrification ranged between 20 and 200 mg N/100 g of soil and the activity decreased at a concentration above 300 mg N. The effect of acidity on nitrification was studied by using soil samples amended with various amounts of CaCO3. Although the pattern of NO2¯ production changed, the rate of ammonia oxidation was not influenced by the addition of CaCO3. The nitrification activity was completely inhibited by the addition of nitrapyrin or acetylene. These results suggest that acid-tolerant or acidophilic autotrophic nitrification occurs in acid tea soils in Japan.
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Previous studies have examined the effects of soil osmotic potential (Ψs) on net rates of mineralization and nitrification. Because net rates represent the difference between gross production and consumption processes, it is unclear which process is being affected. We used an 15N isotopic dilution method to evaluate the effects of Ψs on gross rates of nitrification, ammonification, NH+4 assimilation, and NO-3 assimilation, and net rates of nitrous oxide production in a Penoyer sandy loam at field capacity. To avoid creating specific ion toxicities that normally do not occur in this soil, we used a chemical equilibrium model to predict how solute concentrations in the soil solution change during evapo-concentration; then we used solutions containing these mixtures of solutes to create individual Ψs treatments. A nitrification potential assay was also performed to determine the effect of Ψs on nitrification rates at high substrate concentrations. In soil slurries with elevated NH+4 concentration (1110 μM), nitrification rates declined exponentially with reduced Ψs (increased salt concentration); however, in soil samples incubated at field capacity without added NH+4 (9.7 μM, or 2 mg N kg -1), the gross nitrification rate was independent of Ψs. The differential response between slurries and soil at field capacity was attributed to differences in NH+4 concentrations, and indicated that the effects of Ψs were secondary to NH+4 concentrations in controlling nitrification rates. Nitrification rates in slurries declined more when a single salt (K2SO4) was used than when the mixture of salts that more closely approximated the solute composition predicted to occur in the field was used to lower Ψs. This suggests that nitrifying bacteria are capable of adapting to specific ion toxicities. Gross rates of ammonification declined exponentially with decreased Ψs between 0 and -500 kPa but were independent of Ψs at potentials of -500 to -1750 kPa. Rates of microbial assimilation of NO-3 exceeded NH+4 assimilation by a factor of 4, indicating that under NH+4 limited conditions substantial NO-3 assimilation can occur. Microbial assimilation of both NH+4 and NO-3 declined exponentially with decreased Ψs, and were insignificant at <-1500 kPa Ψs. Because NO-3 assimilation declined more rapidly than gross nitrification, net nitrification rates actually increased with declining Ψs. Rates of nitrous oxide (N2O) production were also inversely correlated with Ψs. Our results indicate that in previous studies, measurement of net rates, use of inappropriate salts, and addition of substrate may have resulted in over-estimation of the adverse effects of low Ψs on rates of N-transformations.
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Results from the pioneering research on the interactions between pH and denitrification in soil from the 1950s to the present are reviewed, the changing perceptions of this complex relationship are discussed, and the current status of the subject is assessed. Facets of this relationship that are analysed in detail include the direct or indirect influence of pH on overall denitrification rates in soils, changes in the composition of gaseous products that depend on pH, methods for measuring the process, the concept of an optimum pH for denitrification, and the adaptation of microbial denitrifying communities to acidic environments. The main conclusions to be drawn are as follows. Total gaseous emissions to the atmosphere (N2O, NO and N2) have repeatedly been shown to be less in acidic than in neutral or slightly alkaline soils. This may be attributable to smaller amounts of organic carbon and mineral nitrogen available to the denitrifying population under acid conditions rather than a direct effect of low pH on denitrification enzymes. Numerous laboratory and field studies have demonstrated that the ratio N2O:N2 is increased when the pH of soils is reduced. The relation between soil pH and potential denitrification as determined by various incubation methods remains unclear, results being influenced both by original conditions in soil samples and by unknown changes during incubation. The concept of an optimum pH for denitrification has been frequently proposed, but such a term has little or no meaning without reference to specific attributes of the process.
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The isotope dilution method was here applied to intact soil cores so that the effects of soil mixing were avoided. Soil cores were injected with solutions of either 15NH4+ or 15NO3-; gross mineralization rates were calculated from the decline in 15N enrichment of the NH4+ pool during a 24-h incubation; gross nitrification rates were calculated from the decline in 15N enrichment of the NO3- pool; gross rates of NH4+ and NO3- consumption were calculated from disappearance of the 15N label. The assumptions required for application of this method to intact cores are evaluated. The method provides a powerful tool for measuring gross rates of microbial transformations of soil nitrogen in intact soil cores. -from Authors
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Summary • Soil microorganisms are considered C-limited, while plant productivity is frequently N-limited. Large stores of organic C in boreal forest soils are attributed to negative effects of low temperature, soil acidity and plant residue recalcitrance upon microbial activity. • We examined microbial activity, biomass and community composition along a natural 90-m-long soil N supply gradient, where plant species composition varies profoundly, forest productivity three-fold and soil pH by three units. • There was, however, no significant variation in soil respiration in the field across the gradient. Neither did microbial biomass C determined by fumigation-extraction vary, while other estimates of activity and biomass showed a weak increase with increasing N supply and soil pH. Simultaneously, a phospholipid fatty acid attributed mainly to mycorrhizal fungi declined drastically, while bacterial biomass increased. • We hypothesize that low N supply and plant productivity, and hence low litter C supply to saprotrophs is associated with a high plant C supply to mycorrhizal fungi, while the reverse occurs under high N supply. This should mean that effects of N availability on C supply to these functional groups of microbes acts in opposing directions.
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The effect of chlorides and sulphates of sodium, potassium, calcium, and magnesium, added at 01.% to 2.0% sodium chloride-equivalent (soil basis), on nitrogen mineralization and nitrification during incubation (3 weeks, 30C) of soil was studied. For the chloride series the critical level for virtually complete suppression of nitrification was between 0.5% and 1.0% of the added salts. Nitrogen mineralization was reduced only where 1–2% of salts were added. In the sulphate series nitrogen mineralization and nitrification were reduced to a fair extent only by the 2% level of sodium sulphate, the other sulphates having little or no effect on these processes. At some levels the sulphates and chlorides of all cations, except sodium, resulted in a small but significant increase in nitrogen mineralization.