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Topsoil foraging - An architectural adaptation of plants to low phosphorus availability
Abstract
Low phosphorus availability is a primary constraint to plant productivity in many natural and agricultural ecosystems. Plants display a wide array of adaptive responses to low phosphorus availability that generally serve to enhance phosphorus mobility in the soil and increase its uptake. One set of adaptive responses is the alteration of root architecture to increase phosphorus acquisition from the soil at minimum metabolic cost. In a series of studies with the common bean, work in our laboratory has shown that architectural traits that enhance topsoil foraging appear to be particularly important for genotypic adaptation to low phosphorus soils (`phosphorus efficiency'). In particular, the gravitropic trajectory of basal roots, adventitious rooting, the dispersion of lateral roots, and the plasticity of these processes in response to phosphorus availability contribute to phosphorus efficiency in this species. These traits enhance the exploration and exploitation of shallow soil horizons, where phosphorus availability is greatest in many soils. Studies with computer models of root architecture show that root systems with enhanced topsoil foraging acquire phosphorus more efficiently than others of equivalent size. Comparisons of contrasting genotypes in controlled environments and in the field show that plants with better topsoil foraging have superior phosphorus acquisition and growth in low phosphorus soils. It appears that many architectural responses to phosphorus stress may be mediated by the plant hormone ethylene. Genetic mapping of these traits shows that they are quantitatively inherited but can be tagged with QTLs that can be used in plant breeding programs. New crop genotypes incorporating these traits have substantially improved yield in low phosphorus soils, and are being deployed in Africa and Latin America.
... An improved understanding of and consequent breeding for root and rhizosphere traits involved in efficient P acquisition is considered a key strategy for rendering agricultural production more sustainable (Bishopp and Lynch 2015;Oburger et al. 2022a, b). Plants increase P acquisition by (i) enhanced top soil exploration via increased lateral root growth (Lynch and Brown 2001) and/or in association with mycorrhizal fungi (Smith et al. 2003), as well as via (ii) increased soil mining driven by enhanced exudation of organic compounds ) and by nurturing beneficial rhizosphere-associated microbes (Richardson and Simpson 2011). While the importance of enhanced soil exploration has been repeatedly demonstrated (Lynch and Brown 2001;Wissuwa et al. 2020), the role of root exudation in improving P acquisition in rice is still not well understood. ...
... Plants increase P acquisition by (i) enhanced top soil exploration via increased lateral root growth (Lynch and Brown 2001) and/or in association with mycorrhizal fungi (Smith et al. 2003), as well as via (ii) increased soil mining driven by enhanced exudation of organic compounds ) and by nurturing beneficial rhizosphere-associated microbes (Richardson and Simpson 2011). While the importance of enhanced soil exploration has been repeatedly demonstrated (Lynch and Brown 2001;Wissuwa et al. 2020), the role of root exudation in improving P acquisition in rice is still not well understood. ...
... Previous studies have shown that a larger root system enhances soil P foraging and subsequent P acquisition (Lynch and Brown 2001;Reichert et al. 2022). A larger root system, including longer roots (total root length) and larger root surface area of P-efficient genotype DJ123 compared to Nerica4 (Fig. S1), confirms the important role of root system size in P foraging and it explains the detected higher P uptake of DJ123 under P deficiency (Fig. 1c). ...
Main conclusion
Rice exudation patterns changed in response to P deficiency. Higher exudation rates were associated with lower biomass production. Total carboxylate exudation rates mostly decreased under P-limiting conditions.
Abstract
Within the rhizosphere, root exudates are believed to play an important role in plant phosphorus (P) acquisition. This could be particularly beneficial in upland rice production where P is often limited. However, knowledge gaps remain on how P deficiency shapes quality and quantity of root exudation in upland rice genotypes. We therefore investigated growth, plant P uptake, and root exudation patterns of two rice genotypes differing in P efficiency in semi-hydroponics at two P levels (low P = 1 µM, adequate P = 100 µM). Root exudates were collected hydroponically 28 and 40 days after germination to analyze total carbon (C), carbohydrates, amino acids, phenolic compounds spectrophotometrically and carboxylates using a targeted LC–MS approach. Despite their reported role in P solubilization, we observed that carboxylate exudation rates per unit root surface area were not increased under P deficiency. In contrast, exudation rates of total C, carbohydrates, amino acids and phenolics were mostly enhanced in response to low P supply. Overall, higher exudation rates were associated with lower biomass production in the P-inefficient genotype Nerica4, whereas the larger root system with lower C investment (per unit root surface area) in root exudates of the P-efficient DJ123 allowed for better plant growth under P deficiency. Our results reveal new insights into genotype-specific resource allocation in rice under P-limiting conditions that warrant follow-up research including more genotypes.
... Phosphorus (P) availability is a major constraint to pearl millet productivity in many parts of West Africa as P availability in sandy soils of the Sahel is often below 2 mg kg À1 [9,10]. Furthermore, P is highly stratified in the soil and mostly found in superficial layers [11]. Therefore, P acquisition is highly dependent on the architecture of the root system [12]. ...
... Root system architecture, the spatiotemporal configuration of a root system, determines the ability of a plant to exploit soil resources [11,[13][14][15]. The pearl millet root system is characterized by a fast-growing primary root that rapidly colonizes deep soil horizons and by crown and lateral roots that begin to emerge 6 days after germination [16,17]. ...
... Altogether, this suggests that longer and denser root hairs could lead to improved tolerance to low-phosphorus conditions in pearl millet. As phosphorus is mainly present in the topsoil, shallow root systems have also been associated with better P acquisition [11,62,63]. We therefore simulated the impact of changes in crown root angles in pearl millet. ...
... The high flexibility of root configurations is a key strategy for plants to cope with drought, soil infertility, and other edaphic stresses [10]. For example, in P-deficient environments, plant roots expand the effective surface area for P uptake by increasing root length and surface area [11], lateral root spreading [12], and the formation of specialized roots (e.g., cluster roots) [13]. In water-stressed environments, plants increase roots in the deep soil to access water stored in deeper soil [14]. ...
... Due to the great potential in enhancing plant adaptation to different environmental stresses, considering root morphological configuration in future breeding work is important [57]. To optimize P, water, and N acquisition, the ideotype root architecture of 'topsoil foraging' and "Steep, Cheep, and Deep" were put forward by the group of Lynch [12,33,36], and have guided the development of maize, bean, and soybean cultivars with enhanced P, water, and N acquisition [58][59][60]. ...
Screening genotypes with optimal root traits presents a promising breeding strategy for enhancing adaptability to abiotic stresses and improving resource use efficiency. This study evaluated root traits of 100 winter wheat genotypes under four treatments: control (C), low phosphorus (LP), PEG-induced drought (D), and a combination of LP and drought (DLP), using a semi-hydroponic phenotyping platform. Significant variations in root traits were observed 65 days after transplanting, with over 80% of traits being significantly affected by drought, phosphorus, or their interactions. Biomass and phosphorus content decreased under LP and drought, while root length and diameter in deeper layers increased, especially under drought stress. Combined stress led to the most severe reductions in biomass, P-content, and leaf number. Phosphorus acquisition efficiency was positively correlated with root length but inversely related to stress tolerance. High heritability traits, such as root number, root length, maximum root depth, leaf number, and biomass, hold potential for breeding programs focused on environmental adaptation, resource efficiency, and yield improvement. The substantial genotypic variation in root morphology under stress conditions highlights the potential for breeding stress-resilient wheat genotypes. This finding lays a foundation for wheat-breeding initiatives aimed at developing genotypes better suited to prevailing environmental conditions.
... For example, mineral nitrogen mobility in soil water solution is greatly affected by drought (Plett et al. 2020). The direct impact of nutrient deficiency on RSA modifications (Gruber et al. 2013) in Arabidopsis (Giehl, Gruber, and Von Wirén 2014), phosphorus in common beans (Lynch and Brown 2001) or nitrogen in maize (Trachsel et al. 2013) is increasingly being studied. In maize, a modulation of root angles leads to improved nitrogen absorption (Trachsel et al. 2013). ...
... For immobile elements like phosphorus, potassium, iron and manganese, the plant tends to exhibit a dense root architecture with abundant branching and smaller roots, particularly in shallower soil layers (Desnos 2008;Koevoets et al. 2016). In general, according to Lynch and Brown (2001), plants adapt their root architecture by increasing root length and root surface area, allowing the acquisition of more mobile nutrients. Plants have developed strategies to enhance nutrient bioavailability during WS through modifications not only in root architecture but also in their functional capabilities. ...
In the context of climate change, associated with increasingly frequent water deficits and heat waves, there is an urgent need to maintain the performance of soybean, a leading legume crop worldwide, before its yield declines. The objective of this study was to explore which plant traits improve soybean tolerance to heat and/or water stress, with a focus on traits involved in plant architecture and nutrient uptake. For this purpose, two soybean genotypes were grown under controlled conditions in a high-throughput phenotyping platform where either optimal conditions, heat waves, water stress or both heat waves and water stresses were applied during the vegetative stage. By correlating architectural to functional traits, related to water, carbon allocation and nutrient absorption, we were able to explain the stress susceptibility level of the two genotypes. We have shown that water flow in the plant is central to the uptake and allocation of mineral elements in the plant, despite its modulation by stress and in a genotype-dependent manner. This cross-analysis of plant ecophysiology and plant nutrition under different stresses provides new information, especially on the importance of mineral elements in the different plant organs, and can inform future crop design, particularly under changing climatic conditions.
... Water and nitrate, being mobile, are invariably available more in deeper soil strata over time on account of evaporation and transpiration losses as well as leaching. However, phosphorus (immobile) and potassium (partially mobile) are more predominant in the topsoil [30]. Plants that produce comparable or higher yields under stress, are able to do so, mainly through acquisition of soil resources at reduced metabolic costs, by optimising the allometric shifts of resource allocation for growth, resource acquisition, and reproductive fitness [14]. ...
... Plants that produce comparable or higher yields under stress, are able to do so, mainly through acquisition of soil resources at reduced metabolic costs, by optimising the allometric shifts of resource allocation for growth, resource acquisition, and reproductive fitness [14]. With regard to functional role of root traits for resource capture, it is well evidenced that deeper root growth angle drives greater root depth and consequent improved performance under water and nitrogen constraints [31][32][33], whereas, shallower root growth angles are more advantageous for foraging topsoil P and K [15,30]. Deeper rooting helps in greater spatial root distribution at deeper soil layers and also promotes water uptake through hydraulic lift that drives up water in the day to be used by plants at night [34], with an additional benefit on nitrogen uptake [35]. ...
Root plasticity enables plants to adapt to spatial and temporal changes in soil resources. In this study, 40 common bean genotypes evaluated for two root and shoot traits under irrigated and water stress. Three genotypes WB-216, WB-N-2, and WB-966 with contrasting plasticity responses were used for in-depth study. Highest positive plasticity for most root traits was found in case of WB-N2 and WB-216, whereas, WB-966 had negative plasticity for all the traits recorded. In terms of spatial plasticity for root traits in three root length sections, WB-216 was positively plastic for root diameter with progressive decrease from top to bottom sections. WB-N2 had positive plasticity values for root diameter, root surface area and root volume. WB-966 had negative plasticity for all the traits. For WB-216, the root diameter increased under drought in S1 but was almost same in bottom sections. In case of WB-N2, there was increase in root diameter in S2 and S3, but for WB-966, root diameter decreased in all sections. Similar trend was observed in all three genotypes for root surface area and volume. We report that major drivers of spatial plasticity of root architectural traits are increased root diameter, surface area and volume at deeper layers.
... Colonized plants by AMF displays enhanced phosphorus (P) absorption, with nearly 80% of the plant's P uptake occurring at lower concentrations within the soil solution compared to non-mycorrhizal inoculated plants [39,40]. The AMF establishes an extraradical mycelium (ERM) network that efficiently explores the soil environment to acquire nutrients [41,42], facilitating access to more soluble phosphate forms [43,44] and enhancing plant nitrogen (N) uptake [45]. ...
Arbuscular Mycorrhizal Fungi are used for soil fertility enhancements and stimulating plant growth in which they association with other organisms like terrestrial plants. Mycorrhizas create an association between fungi and the roots of plants. Therefore, the review was made to point out important fungal species involved in fungal plant interaction and their major roles in agriculture as well as ecosystem. 80% of plants form associations with mycorrhizal fungi. The fungal are used to use their different organs like chain, arbuscular, vesicle, supportive cells and spore to interact with the other plant/ plat's organ. The mycorrhizal fungi can be categorized into two principal classifications based on their anatomical interactions with the roots of host plants. Arbuscular Mycorrhizal and Ectomycorrhizal fungi utilize two distinct strategies for nutrient acquisition. The main categories of vesicular arbuscular mycorrhizal associations are linear or coiling and of ectomycorrhizal associations are epidermal or cortical. The rhizospheric and endophytic microbes promote plant growth as inoculated with crop. AM fungi as an obligate symbiont share a distinct feature called arbuscules as a site of nutrient exchanges between host and fungi. Arbuscules developed between cell wall and plasma membrane of root cortical cells and differentiated from plant plasma membrane by periarbuscular membrane. Arbuscular mycorrhizal fungi (AMF) play an indispensable role in augmenting plant nutrient acquisition, enhancing plant resilience and tolerance to various environmental stresses, improving soil fertility and structure, and providing numerous beneficial effects. AMF engage in interactions with other soil microorganisms, such as plant growth-promoting rhizobacteria, resulting in a synergistic effect that promotes plant growth and offers protection against pathogens associated with Rhizobia. Both AMF and Rhizobia utilize the same signaling pathways, which facilitate their association with host plants and enable nitrogen fixation within the soil ecosystem. A positive relationship has been established between AMF colonization and the diversity of soil microbial communities. Nitrogen-fixing rhizobia, mycorrhizal fungi, and root nodule symbioses typically exhibit synergistic interactions concerning infection rates and their effects on mineral nutrition and plant growth, thereby significantly enhancing the status of soil fertility, particularly with respect to soil quality characteristics.
... Underwater-deficient condition OsARF23 renders more developed RSA by controlling crown root growth direction for absorbing moisture in deep soil, thereby enhancing drought resistance and increasing rice yield (Uga et al. 2013). In comparison, in nutrient-deficient soil a prosperous shallow RSA is favorable for the acquisition of soil elements to lessen demand for fertilizers (Lynch and Brown 2001). Leaf angle is also important in cereal crop architecture. ...
... "SHAP" (SHapley Additive exPlanations) (Lundberg & Lee, 2017) was used to assist interpreting the results from XGBoost models. SHAP uses traditional Shapley values from game theory, and it has shown to be very successful in explaining the output of any ML model (Shrikumar et al., 2017;Štrumbelj & Kononenko, 2014). ...
Spatial adjustments are used to improve the estimate of plot seed yield across crops and geographies. Moving means (MM) and P‐Spline are examples of spatial adjustment methods used in plant breeding trials to deal with field heterogeneity. Within the trial, spatial variability primarily comes from soil feature gradients, such as nutrients, but a study of the importance of various soil factors including nutrients is lacking. We analyzed plant breeding progeny row (PR) and preliminary yield trial (PYT) data of a public soybean breeding program across 3 years consisting of 43,545 plots. We compared several spatial adjustment methods: unadjusted (as a control), MM adjustment, P‐spline adjustment, and a machine learning‐based method called XGBoost. XGBoost modeled soil features at: (a) the local field scale for each generation and per year, and (b) all inclusive field scale spanning all generations and years. We report the usefulness of spatial adjustments at both PR and PYT stages of field testing and additionally provide ways to utilize interpretability insights of soil features in spatial adjustments. Our work shows that using soil features for spatial adjustments increased the relative efficiency by 81%, reduced the similarity of selection by 30%, and reduced the Moran's I from 0.13 to 0.01 on average across all experiments. These results empower breeders to further refine selection criteria to make more accurate selections and select for macro‐ and micro‐nutrients stress tolerance.
... Moreover, most plants employ various mechanisms to enhance phosphate acquisition efficiency (PAE). These include increased density of lateral roots and root hairs at the expense of basal roots, widened angles between lateral roots and primary roots, enhanced solubilization at the soil surface, and improved interactions with beneficial microbes, among other strategies (Lynch and Brown 2001;Liu 2021;Han et al. 2022). Likewise, cellular and molecular stimuli of many crops are predisposed by such RSA adaptations under heterogeneous soil P profiles and regional deficiencies (Rogers and Benfey 2015;Ge et al. 2019;Maqbool et al. 2022). ...
Key message
We identified novel physiological and genetic responses to phosphorus starvation in sorghum diversity lines that augment current knowledge of breeding for climate-smart crops in Europe.
Abstract
Phosphorus (P) deficiency and finite P reserves for fertilizer production pose a threat to future global crop production. Understanding root system architecture (RSA) plasticity is central to breeding for P-efficient crops. Sorghum is regarded as a P-efficient and climate-smart crop with strong adaptability to different climatic regions of the world. Here we investigated early genetic responses of sorghum RSA to P deficiency in order to identified genotypes with interesting root phenotypes and responses under low P. A diverse set of sorghum lines (n = 285) was genotyped using DarTSeq generating 12,472 quality genome wide single-nucleotide polymorphisms. Root phenotyping was conducted in a paper-based hydroponic rhizotron system under controlled greenhouse conditions with low and optimal P nutrition, using 16 RSA traits to describe genetic and phenotypic variability at two time points. Genotypic and phenotypic P-response variations were observed for multiple root traits at 21 and 42 days after germination with high broad sense heritability (0.38–0.76). The classification of traits revealed four distinct sorghum RSA types, with genotypes clustering separately under both low and optimal P conditions, suggesting genetic control of root responses to P availability. Association studies identified quantitative trait loci in chromosomes Sb02, Sb03, Sb04, Sb06 and Sb09 linked with genes potentially involved in P transport and stress responses. The genetic dissection of key factors underlying RSA responses to P deficiency could enable early identification of P-efficient sorghum genotypes. Genotypes with interesting RSA traits for low P environments will be incorporated into current sorghum breeding programs for later growth stages and field-based evaluations.
... This suggests that wheat may have inherent tolerance mechanisms. Under P-limiting conditions, plants activate various adaptive mechanisms to enhance P uptake and utilization efficiency, thereby mitigating the negative effects of P stress [50,51]. Research has shown that plants under P stress increase root length and branching to improve P absorption efficiency [52,53]. ...
Wheat (Triticum aestivum L.) is a crucial cereal crop, contributing around 20% of global caloric intake. However, challenges such as diminishing arable land, water shortages, and climate change threaten wheat production, making yield enhancement crucial for global food security. The heading date (HD) is a critical factor influencing wheat’s growth cycle, harvest timing, climate adaptability, and yield. Understanding the genetic determinants of HD is essential for developing high-yield and stable wheat varieties. This study used a doubled haploid (DH) population from a cross between Jinmai 47 and Jinmai 84. QTL analysis of HD was performed under three phosphorus (P) treatments (low, medium, and normal) across six environments, using Wheat15K high-density SNP technology. The study identified 39 QTLs for HD, distributed across ten chromosomes, accounting for 2.39% to 29.52% of the phenotypic variance. Notably, five stable and major QTLs (Qhd.saw-3A.7, Qhd.saw-3A.8, Qhd.saw-3A.9, Qhd.saw-4A.4, and Qhd.saw-4D.3) were consistently detected across varying P conditions. The additive effects of these major QTLs showed that favorable alleles significantly delayed HD. There was a clear trend of increasing HD delay as the number of favorable alleles increased. Among them, Qhd.saw-3A.8, Qhd.saw-3A.9, and Qhd.saw-4D.3 were identified as novel QTLs with no prior reports of HD QTLs/genes in their respective intervals. Candidate gene analysis highlighted seven highly expressed genes related to Ca2+ transport, hormone signaling, glycosylation, and zinc finger proteins, likely involved in HD regulation. This research elucidates the genetic basis of wheat HD under P stress, providing critical insights for breeding high-yield, stable wheat varieties suited to low-P environments.
... The order of NLP from highest to lowest in the 0-30 cm layer is KS > BFS > FS > RYS, while the 0-60 cm layer shows a little difference, which is KS > BFS > RYS > FS. Figure 3C,D indicate that NaOH-Po and NaOH-Pi constitute a larger proportion of insoluble phosphorus; however, in RYS soil, Residual-P significantly exceeds other P fractions. These NLP variations suggest different distributions and deposition of insoluble phosphorus in various soil layers, possibly related to soil fertilization management, root structure, and microbial activity [37][38][39]. Phosphate deposition and release also relate to soil type and environment. In dry environments, longterm fertilization mainly increases organic phosphorus through phosphate precipitation, while in flooded environments, it reduces organic phosphorus, further transforming it into active phosphorus. ...
Effective phosphorus (P) management is crucial for optimal blueberry production. However, a comprehensive understanding of phosphorus distribution across soil depths and types after two decades of blueberry cultivation remains a challenge. This study examines pH, EC, SOC (soil organic carbon), Total N (total nitrogen), and phosphorus fractions in soils from Japanese blueberry fields that have been cultivated for over 20 years. The soils selected for this study represent typical soils from long-term blueberry-growing regions in Japan, ensuring the relevance of the findings to these key agricultural areas. Soil samples were gathered from depths of 0–30 cm and 30–60 cm, revealing significant variations in phosphorus content that are influenced by soil properties and fertilization history. Soil types such as KS (Kuroboku soils) and FS (Fluvic soils) show higher Total P accumulation in deeper layers, whereas BFS (Brown Forest soils) and RYS (Red-Yellow soils) accumulate more in shallower layers. Long-term cultivation has led to greater non-labile phosphorus (NLP) accumulation in shallower layers of KS, BFS, and FS soils, indicating strong phosphorus fixation. BFS soil also exhibits increased organic phosphorus (NaOH-Po) at deeper depths. NaOH-Po and NaHCO3-Po, through their interactions with EC and pH, critically modulate the transformation of NLP into labile phosphorus (LP), thereby influencing overall phosphorus and nitrogen dynamics in the soil. These findings underscore the importance of tailored phosphorus fertilization strategies based on blueberry field characteristics, providing a basis for low-input phosphorus fertilization approaches.
... The root distribution in the lower layer of topsoil is likely to contribute to drought avoidance during the early growth stage of rice. Generally, shallow RSA gives crops an advantage in phosphate uptake from topsoil in low-phosphate conditions of subsoil (Lynch and Brown, 2001;Lynch, 2011;Oo et al., 2020). Conversely, deep RSA benefits water uptake from the subsoil in drought conditions (Uga et al., 2013). ...
Background and Aims
Root system architecture (RSA) plays a key role in plant adaptation to drought because deep rooting enables better water uptake than shallow rooting under terminal drought. Understanding RSA during early plant development is essential for improving crop yields, as early drought can affect subsequent shoot growth. Herein, we demonstrate that root distribution in the topsoil significantly impacts shoot growth during the early stages of rice (Oryza sativa) development under drought, as assessed through three-dimensional (3D) image analysis.
Methods
We used 109 F12 recombinant inbred lines (RILs) obtained from a cross between shallow-rooting lowland rice and deep-rooting upland rice, representing a population with diverse RSA. We applied a moderate drought during the early development of rice grown in a plant pot (25 cm height) by stopping irrigation 14 days after sowing (DAS). Time-series RSA at 14, 21, and 28 DAS was visualized by X-ray computed tomography, and subsequently compared between drought and well-watered conditions. Following this analysis, we further investigated drought-avoidant RSA by testing 20 randomly selected RILs under drought conditions.
Key Results
We inferred the root location that most influences shoot growth using a hierarchical Bayes approach: the root segment depth, which positively impacted shoot growth, ranged between 1.7–3.4 cm under drought conditions and between 0.0–1.7 cm under well-watered conditions. Drought-avoidant RILs had a higher root density in the lower layers of the topsoil compared to the others.
Conclusions
Fine classification of soil layers using 3D image analysis revealed that increasing root density in the lower layers of the topsoil, rather than in the subsoil, is advantageous for drought avoidance during the early growth stage of rice.
... Hence, we selected the root morphology traits, root diameter and root surface area, which we previously showed were associated with P efficiency QTL in sorghum [13,16]. Topsoil foraging has been deemed to be an important adaptation to enhance P acquisition in low-P conditions in beans [37]. In sorghum, we previously saw that root architecture traits such as centroid, which measures the tendency of a root to grow and produce significant root biomass at different depths, were associated with allelic variation for SbPSTOL1 genes that were found to enhance P efficiency in sorghum [15]. ...
Background
On tropical regions, phosphorus (P) fixation onto aluminum and iron oxides in soil clays restricts P diffusion from the soil to the root surface, limiting crop yields. While increased root surface area favors P uptake under low-P availability, the relationship between the three-dimensional arrangement of the root system and P efficiency remains elusive. Here, we simultaneously assessed allelic effects of loci associated with a variety of root and P efficiency traits, in addition to grain yield under low-P availability, using multi-trait genome-wide association. We also set out to establish the relationship between root architectural traits assessed in hydroponics and in a low-P soil. Our goal was to better understand the influence of root morphology and architecture in sorghum performance under low-P availability.
Result
In general, the same alleles of associated SNPs increased root and P efficiency traits including grain yield in a low-P soil. We found that sorghum P efficiency relies on pleiotropic loci affecting root traits, which enhance grain yield under low-P availability. Root systems with enhanced surface area stemming from lateral root proliferation mostly up to 40 cm soil depth are important for sorghum adaptation to low-P soils, indicating that differences in root morphology leading to enhanced P uptake occur exactly in the soil layer where P is found at the highest concentration.
Conclusion
Integrated QTLs detected in different mapping populations now provide a comprehensive molecular genetic framework for P efficiency studies in sorghum. This indicated extensive conservation of P efficiency QTL across populations and emphasized the terminal portion of chromosome 3 as an important region for P efficiency in sorghum. Increases in root surface area via enhancement of lateral root development is a relevant trait for sorghum low-P soil adaptation, impacting the overall architecture of the sorghum root system. In turn, particularly concerning the critical trait for water and nutrient uptake, root surface area, root system development in deeper soil layers does not occur at the expense of shallow rooting, which may be a key reason leading to the distinctive sorghum adaptation to tropical soils with multiple abiotic stresses including low P availability and drought.
... 벼, 보리, 수수, 밀 등 단자엽 식물 은 피트산의 80~90%를 종자의 호분층에 저장하나, 옥수수 는 예외적으로 약 10%의 피트산만 호분층에 축적하고 나머 지는 배아에 축적하는 것으로 알려져 있다 (Shi et al. 2003). 피 트산은 개화 후 수일 내에 식물체 내에서 합성이 시작되어 종자 발달 및 성숙기 동안 합성 및 축적이 지속되며, 벼에서 는 개화 후 10~25일 사이에 피트산 농도가 높아지는 것으로 알려져 있다 (Rasmussen et al. 2010;Silva et al. 2021 (Gu et al. 2016;Liu et al. 2013b;Lynch and Brown 2001;Zhao et al. 2004;Zhu et al. 2005 (Glassop et al. 2005;Grun et al. 2018;Schunmann et al. 2004 (Ai et al. 2009;Sun et al. 2012). (Paszkowski et al. 2002). ...
... This aligns with findings by Hill et al. [35], who reported increased root biomass production in pasture species under nutrient-scarce conditions. Such a response is often accompanied by modifications in root architecture, including enhanced root surface area through root hair development, and upregulation of nutrient transporter expression [36][37][38][39][40][41]. Moreover, Gojon et al. [42] and Lynch [43] suggest that nutrient limitations can also induce alterations in root growth pa erns. ...
Radiocesium (r-Cs) and radiostrontium (r-Sr) released from nuclear accidents (e.g., Chornobyl, Fukushima) and routine operations (reactors, reprocessing) pose environmental and health concerns. Their primary pathway to humans is through plant uptake and subsequent bioaccumulation within the food chain. While soil amendments with potassium (K) and calcium (Ca) are known to mitigate r-Cs and r-Sr uptake, respectively, the impact on plant growth remains unclear. This study investigates the effects of Cs and Sr on the growth of Holcus lanatus L. seedlings under hydroponic and soil conditions with varying Cs and Sr concentrations. Stable isotopes of Cs and Sr served as non-radioactive analogs. Seedling growth was assessed across a range of Cs and Sr concentrations (≤1 and ≥4 mg L⁻¹). The impact of the addition of K and Ca on Cs/Sr uptake in amended soils was also evaluated. Additionally, this study examined how Cs and Sr amendments affected the influx rates of other nutrients in H. lanatus. Higher Cs and Sr concentrations (≥4 mg L⁻¹) significantly inhibited seedling growth, while lower concentrations had no effect. Notably, H. lanatus exhibited moderate Cs tolerance and strong Sr tolerance. Furthermore, K and Ca supplementation in Cs/Sr-amended soils demonstrably reduced plant uptake of these elements. This study also observed alterations in the uptake rates of other nutrients within H. lanatus due to Cs/Sr addition. This study suggests that H. lanatus exhibits moderate tolerance to Cs and Sr contamination, potentially making it suitable for revegetation efforts in contaminated grasslands. Additionally, K and Ca amendments show promise as a strategy to mitigate plant uptake of these radioisotopes further. These findings contribute to the development of safer revitalization strategies for areas impacted by nuclear accidents.
... For example, white lupin forms cluster roots to cope with P deficiency stress (Lamont, 2003). P-deficient plants tend to increase the root/shoot ratio and root length by allocating more photosynthetic products to roots (Liao et al., 2001;Lynch and Brown, 2001). In low P alkaline soils, alfalfa (Medicago sativa L.) enhances rhizosphere acidification and carboxylate exudation (Fan et al., 2015;He et al., 2017;Wang et al., 2020). ...
Introduction
Phosphorus (P) fertilizer is critical to maintain a high yield and quality of alfalfa (Medicago sativa L.). There are several fertilizer types and soil types in China, and the application of a single type of P fertilizer may not be suitable for present-day alfalfa production.
Methods
In order to select the optimal combination of alfalfa and soil type and fertilizer type for improving P utilization efficiency. We conducted a greenhouse pot experiment, calcium superphosphate (SSP), diammonium phosphate (DAP), ammonium polyphosphate (APP), potassium dihydrogen phosphate (KP), and no-fertilizer control treatments were applied to alfalfa in sandy and saline-alkali soils. The response of alfalfa root morphology and rhizosphere processes to different P fertilizers was investigated.
Results and discussion
The results showed that shoot biomass of alfalfa was slightly higher in sandy soil than in saline–alkali soil. Shoot biomass of alfalfa increased by 223%-354% in sandy soil under P treatments compared with the control, and total root length increased significantly by 74% and 53% in DAP and SSP treatments, respectively. In saline–alkali soil, alfalfa shoot biomass was significantly increased by 229% and 275% in KP and DAP treatments, and total root length was increased by 109% only in DAP treatment. Net P uptake of alfalfa in DAP treatment was the highest in both soils, which were 0.73 and 0.54 mg plant⁻¹, respectively. Alfalfa shoot P concentration was significantly positively correlated with shoot and root biomass (P < 0.05, 0.01 or 0.001) whereas negatively correlated with acid phosphatase concentration (P < 0.05). Improvement of plant growth and P uptake induced by P fertilizer application was greater in sandy soil than in saline–alkali soil. DAP and KP was the most efficient P fertilizers in both sandy soil and saline–alkali soil.
... The availability of P in the soil is modified by changes promoted by the plants at the root-soil interface, mainly concentrated in the rhizosphere region. In response to low P availability, the plants developed mechanisms that increase the solubility of this nutrient, including modifications of root biomass production, organic acid exudation, and symbiotic association with microorganisms (Lynch & Brown, 2001;Watts-Williams et al., 2014;White & Hammond, 2008). These adaptations increase the uptake of P by the roots, as well as other nutrients, such as Zn (Arruda et al., 2016). ...
Background
Cotton productivity is commonly limited by the imbalanced nutritional status of phosphorus (P) and zinc (Zn) in Brazil. Evaluating the effect of the P–Zn interaction on nutrient availability in soil is crucial, as this interaction promotes plant adaptations that modify the availability of these nutrients in the rhizosphere. However, the influence of root growth on the P–Zn interaction and its adsorption in rhizosphere soil remains poorly understood.
Aim
We tested the interaction of P and Zn rates in two classes of soil cultivated with cotton. The aim of this investigation was to evaluate the P and Zn availability and adsorption capacity by rhizosphere soils cultivated with cotton plants subjected to P and Zn rates.
Methods
Cotton plants were grown under greenhouse conditions in two different soils (Entisol and Oxisol), with different P and Zn rates. Phosphorus fractionation and Zn sequential extraction were assessed in rhizosphere soil, while total P and Zn concentrations were measured in the shoot and roots.
Results
Soil type significantly affected the P–Zn availabilities on rhizosphere soils. Although increased P‐rates raised P‐soil availability on bulk and rhizosphere soils, cotton growth was not increased under low soil‐Zn availability. The labile inorganic P content was influenced by P and Zn rates just in Oxisol. In both soils, the Zn‐ Zn‐exchangeable content was decreased by P rates, while Zn bound to oxides increased.
Conclusions
Soil‐type effects on P–Zn interaction could have important implications for increasing cotton productivity. Increased cotton productivity by P application was only achieved with an adequate supply of Zn.
... DS restricts nutrient movement through diffusion and mass flow, impeding overall plant growth (Barber 1995). In response to DS, plants adapt by enhancing root length, surface area and modifying architecture to capture fewer mobile nutrients (Lynch and Brown 2011). Soil moisture deficit may reduce root growth, consequently limiting the uptake of less mobile nutrients like phosphorus. ...
Main conclusion
Pigeonpea has potential to foster sustainable agriculture and resilience in evolving climate change; understanding bio-physiological and molecular mechanisms of heat and drought stress tolerance is imperative to developing resilience cultivars.
Abstract
Pigeonpea is an important legume crop that has potential resilience in the face of evolving climate scenarios. However, compared to other legumes, there has been limited research on abiotic stress tolerance in pigeonpea, particularly towards drought stress (DS) and heat stress (HS). To address this gap, this review delves into the genetic, physiological, and molecular mechanisms that govern pigeonpea’s response to DS and HS. It emphasizes the need to understand how this crop combats these stresses and exhibits different types of tolerance and adaptation mechanisms through component traits. The current article provides a comprehensive overview of the complex interplay of factors contributing to the resilience of pigeonpea under adverse environmental conditions. Furthermore, the review synthesizes information on major breeding techniques, encompassing both conventional methods and modern molecular omics-assisted tools and techniques. It highlights the potential of genomics and phenomics tools and their pivotal role in enhancing adaptability and resilience in pigeonpea. Despite the progress made in genomics, phenomics and big data analytics, the complexity of drought and heat tolerance in pigeonpea necessitate continuous exploration at multi-omic levels. High-throughput phenotyping (HTP) is crucial for gaining insights into perplexed interactions among genotype, environment, and management practices (GxExM). Thus, integration of advanced technologies in breeding programs is critical for developing pigeonpea varieties that can withstand the challenges posed by climate change. This review is expected to serve as a valuable resource for researchers, providing a deeper understanding of the mechanisms underlying abiotic stress tolerance in pigeonpea and offering insights into modern breeding strategies that can contribute to the development of resilient varieties suited for changing environmental conditions.
... Soil integrity by erosion Every mineral nutrient [140] Transpiration driven mass flow Calcium, magnesium, silicon, nitrates and sulfates [140] Root growth P and K [141] Biological nitrogen fixation Loss of N [142] ...
Citation: Begna T (2024) Drought's Harmful Effect on Crops Production and its Mitigation Approaches. Asian J Plant Sci Vol:14 No:1: 313. Abstract The biggest and most significant issue that seriously affects global food security for people is drought. Among all the abiotic factors, drought is likely to have one of the most detrimental effects on soil organisms and plants. The most catastrophic abiotic stress that has severely affected crop productivity worldwide is drought. Crops are particularly prone to drought because it reduces the amount of water and nutrients available, both of which are essential for plant survival and growth. The main abiotic limitations in the current and future climate change scenarios is drought stress. The most detrimental abiotic factor is drought, which affects many molecular, biochemical, physiological, morphological and ecological aspects and processes during the whole growth and development process. Plants under prolonged drought stress have altered metabolic responses linked to growth and yield characteristics. One of the main issues with the current climate is drought, which is also one of the most serious abiotic stresses in many regions of the world. Drought is the single most important environmental stressor that negatively impacts crop productivity and quality worldwide. One of the main environmental variables influencing crop quality and productivity worldwide is drought. Drought stress diminishes a plant's capacity to yield by diminishing the size of its leaves, stem expansion and root multiplication inside the soil. It also messes with plant water interactions and lowers water-use efficiency. More than 50 years of climate change and population expansion have forced agriculture into environmentally marginal areas in drier parts of the world. This is projected to have a major impact on agricultural production, particularly in sub-Saharan Africa. Among abiotic factors, drought is the leading cause of crop yield loss worldwide. Drought is a major global issue that causes food shortages and makes it difficult for smallholder farmers to grow enough crops when rainfall is erratic and low. Crop plants have evolved a variety of morphological, physiological and biochemical mechanisms of adaptation to withstand drought stress. A plant, however, may display multiple coping mechanisms in response to drought stress. The mechanism(s) resulting in the least amount of yield loss during a drought are known as drought resistance. Some mechanisms of drought resistance include physiological factors, reduced transpiration, dehydration avoidance and drought escape. Utilizing high-yielding, drought-tolerant cultivars that are well adapted is crucial to maximizing production potential while lowering the risk of climate change for as long as possible. Climatic-smart agriculture is ultimately the only approach that can reduce the detrimental effects of climatic changes on crop adaptability before they have a significant influence on global crop production.
... Given that nutrient mobility in the soil matrix may differ by several orders of magnitude among essential nutrients (Lambers et al., 2008), warming-induced topsoil dryness and the resulting vertical mismatch between soil water and nutrients might have different effects on the availability of these nutrients for plants. Nutrients with limited mobility and diffusion rates in soil, such as phosphorus (P), are generally enriched in topsoil but easily immobilized in dry soil (Lynch & Brown, 2001). ...
1. Warming-induced soil drought, especially in topsoil, may enlarge the spatial mis-match between nutrients and water along the soil profile, which impedes the uptake of not only water but also nutrients by trees. Therefore, coordinating the acquisition of soil water and nutrients along the soil profile is an important strategy for trees to cope with global warming.
2. This study examined soil depth-related changes in nutrient concentrations, bio-mass and morphology of fine roots in a Chinese fir plantation after 3 years of large-scale manipulative soil warming.
3. Soil warming (ambient +4°C) increased fine root nitrogen (N) concentrations but decreased fine root phosphorus (P) concentrations across soil depths. Warming did not affect total fine root biomass and its vertical distribution. At the 0-10 cm depth, warming increased specific root length (SRL), specific root area (SRA), fine root diameter (RD) and root length density (RLD) but reduced root tissue density (RTD). In the 40-60 cm layer, warming reduced RD, SRL and RLD while increasing RTD mainly for roots of the 1-2 mm diameter class.
4. Synthesis. We concluded that roots of Chinese fir plantations could adapt to warming-induced moderate water stress through contrasting depth-related root morphological adjustments, probably to optimize the acquisition of both soil water and nutrients. The results of this study are crucial for understanding the adaptation strategies of subtropical forests under future climate conditions.
... In several crop species, genetic variation in lateral root growth angle is associated with rooting depth as in common bean and maize, shallow growth angles enhances top soil foraging and acquisition of top soil resources such as phosphorus [19,20,21,22]. In common bean, wheat, sorghum and rice, steep growth angles enhances subsoil foraging and water acquisition under terminal drought [23,24,25,26]. ...
The three land races viz. land races -1 (Lal Kada), land races -2 (Futiyu) and land races -3 (Kala Rata) were sown in organic media to investigate the uptake of nitrogen in the form of amino acid as substitute for inorganic nitrogenous fertilizers in their seedlings.The four concentrations (50%, 75%, 100% and 125%) of amino acid mixture (glycine, glutamic acid and aspartic acid) were applied to growing media and the roots architectural responses of 21 days of old seedlings were measured with the help of 2-D imaging software Ez-Rhizo after scanning of roots. Among four concentrations (50%, 75%, 100% and 125%) of amino acid mixture, the 100% amino acid mixture showed higher number of lateral roots, sum of lateral root length per seedling, lateral root angles, total root system size, mean lateral root length, lateral root density, nitrogen content in leaves and roots, root biomass and shoot biomass as compared to other percentage (50%, 75% and 125%) of amino acid mixtures. Moreover, land races -1 was found more responsive to amino acid mixture among the three land races.
... Root shovelomics has been used to select varieties with different root structures, and further experiments showed that the nutrient and water use efficiency of these varieties were different (Zhan et al. 2015, Trachse et al. 2013. This shallow root structure phene is beneficial under fertile conditions, when nutrients are mainly derived from the decomposition of organic matter on the soil surface, or when phosphorus or potassium (mainly present in topsoil) is restricted (Lynch 2013, Lynch andBrown 2001). Research shows that genotypes with both large root hairs and shallow roots had higher phosphorus acquisition efficiency and greater biomass accumulation than short-haired, deep-rooted phenotypes (Miguel et al. 2015). ...
Root phenes are associated with the absorptive efficiency of water and fertilizers. However, there are few reports on the genetic variation and stability of peanut ( Arachis hypogaea L.) root architecture under different environments. In this study, the diversity, variance and stability of root phenes of 89 peanut varieties were investigated with shovelomics (high throughput phenotyping of root system architecture) for two years in both field and laboratory experiments. The root phenes of these peanut genotypes presented rich diversity; for example, the value of total root length (TRL) ranged from 347.84 cm to 1013.80 cm in the field in 2018, and from 55.14 cm to 206.22 cm in the laboratory tests. The root phenes of different genotypes varied differently; for example, the coefficient of variation (CV) of TRL ranged from 24.0 to 83.5 across the two‐year field test. Field and laboratory evaluations were highly correlated, especially on lateral root density (LRD) and root angle (RA), and the quadrant graph analysis of LRD and RA implied that 69.7% of the roots belong to the same type. These not only further reflect root phenes stability through different environment but also demonstrate that some root phenes identified at early stage can indicate their status at later growth stage. In addition, root phenes showed a strong correlation with shoot growth, especially root dry weight (RDW), TRL and（nodule number）NN. Thus, laboratory tests in combination with field shovelomics can efficiently screen and select genotypes with contrasting root phenes to optimize water and nutrient management.
... Roots, as the primary organs for detecting drought signals, play a pivotal role in plant anchoring and in the uptake, storage, and transport of water and nutrients [9,10]. Root system architecture (RSA) plays a critical role in soil resource acquisition, plant growth, and crop performance [11,12] and has been hailed as the second green revolution in crop improvement [13]. RSA exhibit extensive phenotypic and genetic diversity [14,15]. ...
Background
Root system architecture (RSA) exhibits significant genetic variability and is closely associated with drought tolerance. However, the evaluation of drought-tolerant cotton cultivars based on RSA in the field conditions is still underexplored.
Results
So, this study conducted a comprehensive analysis of drought tolerance based on physiological and morphological traits (i.e., aboveground and RSA, and yield) within a rain-out shelter, with two water treatments: well-watered (75 ± 5% soil relative water content) and drought stress (50 ± 5% soil relative water content). The results showed that principal component analysis identified six principal components, including highlighting the importance of root traits and canopy parameters in influencing drought tolerance. Moreover, the systematic cluster analysis was used to classify 80 cultivars into 5 categories, including drought-tolerant cultivars, relatively drought-tolerant cultivars, intermediate cultivars, relatively drought-sensitive cultivars, and drought-sensitive cultivars. Further validation of the drought tolerance index showed that the yield drought tolerance index and biomass drought tolerance index of the drought-tolerant cultivars were 8.97 and 5.05 times higher than those of the drought-sensitive cultivars, respectively.
Conclusions
The RSA of drought-tolerant cultivars was characterised by a significant increase in average length-all lateral roots, a significant decrease in average lateral root emergence angle and a moderate root/shoot ratio. In contrast, the drought-sensitive cultivars showed a significant decrease in average length-all lateral roots and a significant increase in both average lateral root emergence angle and root/shoot ratio. It is therefore more comprehensive and accurate to assess field crop drought tolerance by considering root performance.
... This has led to a global focus on research related to crop roots (Epstein, 2004;Sugden et al., 2004;Trumbore and Gaudinski, 2003). The root system architecture (RSA) is a crucial aspect of the root system that influences soil resource acquisition and plant growth (Lynch, 2013;Lynch and Brown, 2001). Root system architecture encompasses root length, diameter, and density, among others (Lynch and Brown, 2012). ...
Context: Root system architecture (RSA) plays an important role in soil water uptake and plant growth. However, there is a lack of understanding regarding the connection between the changes in RSA characteristics under drought stress in cotton plants and their drought tolerance and yield. Objectives: This study aims to evaluate the RSA variations in different drought-tolerant cotton cultivars under drought stress, and to assess the correlation between RSA, drought tolerance, and yield. Methods: Three drought-tolerant cotton cultivars and three drought-sensitive cotton cultivars were grown in a field equipped with rain shelters to prevent interference from rainfall. Drought stress was initiated at the three-leaf stage, maintaining the soil relative water content at 50 ± 5%, while control plants were irrigated normally at 75 ± 5% soil water content. Multiple parameters, including leaf water potential, relative water content, seed cotton yield, and RSA traits, were assessed. Results: Notable variations in drought tolerance were observed among different cultivars when exposed to drought stress. Specifically, drought-tolerant cultivars exhibited a 34% increase in the average length of all lateral roots and a 15% increase in maximum root depth under drought stress. In contrast, seed cotton yield experienced a reduction of 22.34% in such conditions. Interestingly, there were significant differences in several RSA traits under drought stress, which were not evident under well-watered. Leaf water potential and relative water content were positively correlated with specific root length, dry root weight, average length of all lateral roots and maximum depth, and negatively correlated with average lateral root emergence angle and width/depth ratio. These results underscore the close association between RSA traits and plant drought tolerance. There was also a strong correlation between the seed cotton yield and RSA traits. Specifically, seed cotton yield increased linearly with specific root length, average lengths of lateral roots, and maximum depth, but decreased linearly with root tissue density, and average lateral root emergence angle and width/depth ratio. Conclusions: Optimizing RSA improves drought tolerance and reduces yield loss in drought-tolerant cotton cul-tivars. Understanding of the role of RSA in plant adaptation to drought stress is important for selecting and developing high-yielding cultivars with superior drought tolerance. Significance: This knowledge holds great significance in improving cotton resilience and facilitating adapting to abiotic stress through genetic improvement or agronomic measures.
... The drought conditions limit the movement of these nutrients via diffusion and mass which leads to retarded plant growth. Plants increase the length and surface area of roots and change their architecture in order to capture the less mobile nutrients (Lynch and Brown 2001). The soil moisture deficit at times reduces the growth of the roots and, hence, reducing the uptake of the less mobile nutrients such as phosphorus (Garg 2003). ...
Globally, climate change has a negative impact on food security, particularly in developing nations where a growing population is battling food and nutritional insecurity. It is anticipated that there will be a 10% increase of dry land areas worldwide, along with increased climate variability and extreme weather events (drought and heat stress). Pearl millet is a resilient and climate-smart nutricereal, ideal for areas vulnerable to drought and heat stress. It is a water saving, drought tolerant, and climate change complaint crop. In spite of these unique features, the yields of pearl millet are very low due to lack of optimum production practices under changing climate conditions. A better understanding on the impact of climate change on crop productivity and possible adaptation strategies to mitigate these effects is needed to increase its productivity. Many pearl millet crop simulation models are in use to simulate crop growth and development in response to management decisions. However, recent advances in modeling enabled to simulate the effect of climate change on crop yields and predict adaptation strategies to mitigate these adverse effects. These models assist the researchers, stakeholders. and policy makers to address and adapt to the current and future climate changes.
... gradient (i.e. high diameter and high SRL) may have even occurred at local sites involving broader aspect of the root system architecture, such as nutrient foraging through vertical soil stratification (Lynch & Brown, 2001;Duan et al., 2020). This was particularly striking between two co-occurring species in low-P site: Tapirira guinanensis developed thin and highly branched roots in the topsoil, while Aspidosperma spruceanum produced thick, poorly branched roots in the mineral horizon, despite displaying a similar mean AM colonization (i.e. ...
Soil phosphorus (P) is a growth‐limiting nutrient in tropical ecosystems, driving diverse P‐acquisition strategies among plants. Particularly, mining for inorganic P through phosphomonoesterase (PME) activity is essential, given the substantial proportion of organic P in soils. Yet, the relationship between PME activity and other nutrient‐acquisition root traits remains unclear.
We measured root PME activity and commonly measured root traits, including root diameter, specific root length (SRL), root tissue density (RTD), and nitrogen concentration ([N]) in 18 co‐occurring species across soils with varying P availability to better understand trees response to P supply.
Root [N] and RTD were inversely related, and that axis was not clearly related to soil P supply. Both traits, however, correlated positively and negatively with PME activity, which responded strongly to P supply. Conversely, root diameter was inversely related to SRL, but this axis was not related to P supply.
This pattern suggests that limiting similarity influenced variation along the diameter–SRL axis, explaining local trait diversity. Meanwhile, variation along the root [N]–RTD axis might best reflect environmental filtering. Overall, P availability indicator traits such as PME activity and root hairs only tended to be associated with these axes, highlighting limitations of these axes in describing convergent adaptations at local sites.
... Phosphorus deficiency is a limiting factor for plant growth, and a limited amount of plant-available soil phosphorous leads to severe yield losses [44]. Phosphorus deficiency causes a decrease in the number of primary roots and an increase in lateral root density and length [45][46][47][48]. Alfin-like transcription factor AL6 pure mutants produced shorter root hairs under phosphorus deficiency conditions, probably caused by altered expression of its downstream target genes. ...
Alfin-like (AL) proteins are an important class of transcription factor (TF) widely distributed in eukaryotes and play vital roles in many aspects of plant growth and development. AL proteins contain an Alfin-like domain and a specific PHD-finger structure domain at the N-terminus and C-terminus, respectively. The PHD domain can bind to a specific (C/A) CAC element in the promoter region and affect plant growth and development by regulating the expression of functional genes. This review describes a variety of AL transcription factors that have been isolated and characterized in Arabidopsis thaliana, Brassica rapa, Zea mays, Brassica oleracea, Solanum lycopersicum, Populus trichocarpa, Pyrus bretschenedri, Malus domestica, and other species. These studies have focused mainly on plant growth and development, different abiotic stress responses, different hormonal stress responses, and stress responses after exposure to pathogenic bacteria. However, studies on the molecular functional mechanisms of Alfin-like transcription factors and the interactions between different signaling pathways are rare. In this review, we performed phylogenetic analysis, cluster analysis, and motif analysis based on A. thaliana sequences. We summarize the structural characteristics of AL transcription factors in different plant species and the diverse functions of AL transcription factors in plant development and stress regulation responses. The aim of this study was to provide a reference for further application of the functions and mechanisms of action of the AL protein family in plants.
As the greatest repository of carbon on the planet’s surface, soil contains twice as much of the element as the atmosphere and two to three times more than all living things combined. A living, breathing natural object comprises solids, liquids, and gases in the soil. It acts as a home and food source for all living things, has water-filtering qualities, recycles waste, and may be used as a building material. However, our main focus will be on soil nutrition because of its vital functions in retaining water and nutrients for plant growth while also giving plants structural stability. Odisha’s tropical climate, deltaic and coastal areas, and geological development all contribute to the production of various soil types. In Odisha, eight major soil types may be divided into groups: red, red, yellow, black, laterite, deltaic alluvial, coastal saline, brown forest, and mixed red and black. This chapter includes a brief overview of Odisha’s soil nutrition, additional readily available geomaterials, common natural risks, the use of soils in various applications, the state-built structures, and a case study of soil data collected from several districts. This chapter’s material also addresses soil health and its application, giving readers a comprehensive overview of soil functionality and the state of soil conservation in Odisha. The scientific advancements, present knowledge, and outlook for future soil nutrient management practices in the agriculture industry are highlighted in this paper. The biological, chemical, and physical characteristics of soil critical to long-term, sustainable agricultural productivity with little negative environmental effect in various sections of Odisha are covered in this book chapter.
Climate changes are perceived globally due to human activities leading to severe food and water insecurity at regional and global levels. The primary reason for climate change is the accelerating trend of emission of greenhouse gases by the industry, agriculture, forestry and other land uses, transport, and energy sectors. The maximum and minimum temperatures and extreme precipitation events in South Asia are rising with high temporal and spatial variabilities. These changes have affected soil fertility and moisture status, degrading agricultural land productivity. Changes in CO2 concentration and temperature in the atmosphere and intensity and frequency of precipitation would positively and negatively impact soil nutrient dynamics and nutrient uptake by plants depending on the context. Climate change impacts affecting thermal and hydraulic conductivity of soil, inputs and outputs of organic carbon to soil, dynamics of soil organic carbon pools, and microbial transformations would serve as the key determinants of nutrient and moisture availability to support crop growth. Therefore, urgent actions must be taken at local and regional levels to mitigate the negative consequences of climate change on the availability of soil nutrients and moisture targeting to improve agricultural production and productivity and thereby ensure continuous assurance of food security. Thus, this chapter discussed aspects related to management of nutrients and soil moisture in the context of climate change.
Phosphorus (P), an essential macronutrient, is crucial for plant growth and development. However, available inorganic phosphate (Pi) is often scarce in soil, and its limited mobility exacerbates P deficiency in plants. Plants have developed complex mechanisms to adapt to Pi-limited soils. The root, the primary interface of the plant with soil, plays an essential role in plant adaptation to Pi-limited soil environments. Root system architecture significantly influences Pi acquisition via the dynamic modulation of primary root and/or crown root length, lateral root proliferation and length, root hair development, and root growth angle in response to Pi availability. This review focuses on the physiological, anatomical, and molecular mechanisms underpinning changes in root development in response to Pi starvation in cereals, mainly focusing on the model monocot plant rice (Oryza sativa). We also review recent efforts to modify root architecture to enhance P uptake efficiency in crops and propose future research directions aimed at the genetic improvement of Pi uptake and use efficiency in crops based on root system architecture.
Global wheat production is expected to be negatively impacted by climate variability and change. In the meantime, the global demand for wheat is expected to increase by 26% by the mid-century to feed the growing population, which will require an annual increase of global wheat production by 2%. Thus, wheat yield performance must be improved to ensure food security for a growing human population amid production constraints due to diminishing resources, land loss and climate change. In this chapter, we discussed two approaches to face the shortage in wheat production and fulfil the existed demand worldwide. Breading for more resilient wheat cultivars to face biotic (viruses, fungi, and insects) and abiotic (heat, drought and salinity) stresses, as well as sustainably increase wheat production are the two suggested approaches to globally reduce wheat production-consumption gap. Globally, breeding programs for resilient wheat cultivars have been implemented and identified genetic resistance against biotic stress in wheat. Furthermore, breeding efforts have been successful to develop resilient wheat cultivars through studying genetic mechanism caused by abiotic stresses and modifying it to develop resistant cultivars. Breeding for improved root system of wheat was also done to improve water and nutrients uptake. With respect to the second approach, namely sustainably increase wheat production, increasing nutrients (nitrogen, phosphorus and potassium) use efficiency should be implemented, as well as reducing the reliance on chemical fertilizer by application of organic fertilizer, wheat rotating with legume crops, and implementing wheat intercropping system with legume crops were also reviewed. Moreover, increasing water use efficiency and water productivity can also conducted to sustainably increase wheat production through improving cultivation method and using more efficient irrigation system. Inclusion of legume crops in wheat-based cropping can lead to increase water use efficiency and water productivity. These practices will increase wheat production and, in the meantime, it will achieve the sustainable use of soil and water resources.
The mechanisms by which low light accelerates starch macromolecules degradation by auxin and gibberellin
(GA) in geophytes during sprouting remain largely unknown. This study investigated these mechanisms in
saffron, grown under low light (50 μmol m-2 s-1) and optimal light (200 μmol m-2 s-1) during the sprouting
phase. Low light reduced starch concentration in corms by 34.0 % and increased significantly sucrose levels in
corms, leaves, and leaf sheaths by 19.2 %, 9.8 %, and 134.5 %, respectively. This was associated with a 33.3 %
increase in GA3 level and enhanced auxin signaling. Leaves synthesized IAA under low light, which was transported
to the corms to promote GA synthesis, facilitating starch degradation through a 228.7 % increase in
amylase activity. Exogenous applications of GA and IAA, as well as the use of their synthesis or transport inhibitors,
confirmed the synergistic role of these phytohormones in starch metabolism. The unigenes associated
with GA biosynthesis and auxin signaling were upregulated under low light, highlighting the IAA-GA module role
in starch degradation. Moreover, increased respiration rate and invertase activity, crucial for ATP biosynthesis
and the tricarboxylic acid cycle, were consistent with the upregulation of related unigenes, suggesting that auxin
signaling accelerates starch degradation by promoting energy metabolism. Upregulated of auxin signaling
(CsSAUR32) and starch metabolism (CsSnRK1) genes under low light suggests that auxin directly regulate starch
degradation in saffron corms. This study elucidates that low light modulates auxin and GA interactions to
accelerate starch degradation in saffron corms during sprouting, offering insights for optimizing agricultural
practices under suboptimal light conditions.
Modern agriculture’s goal of improving crop resource acquisition efficiency relies on the intricate relationship between the root system and the soil. Root and rhizosphere traits play a critical role in the efficient use of nutrients and water, especially under dynamic environments. This review emphasizes a holistic perspective, challenging the conventional separation of nutrient and water uptake processes and the necessity for an integrated approach. Anticipating climate change-induced increase in the likelihood of extreme weather events that result in fluctuations in soil moisture and nutrient availability, the study explores the adaptive potential of root and rhizosphere traits to mitigate stress. We emphasize the significance of root and rhizosphere characteristics that enable crops to rapidly respond to varying resource availabilities (i.e. the presence of water and mobile nutrients in the root zone) and their accessibility (i.e. the possibility to transport resources to the root surface). These traits encompass for example root hairs, mucilage and extracellular polymeric substance (EPS) exudation, rhizosheath formation and the expression of nutrient and water transporters. Moreover, we recognize the challenge of balancing carbon investments, especially under stress, where optimized traits must consider carbon-efficient strategies. To advance our understanding, the review calls for well-designed field experiments, recognizing the limitations of controlled environments. Non-destructive methods such as mini rhizotron assessments and in-situ stable isotope techniques, in combination with destructive approaches such as root exudation analysis, are proposed for assessing root and rhizosphere traits. The integration of modeling, experimentation, and plant breeding is essential for developing resilient crop genotypes capable of adapting to evolving resource limitation.
Plant growth is directly related to growth and establishment of root system. A developed root system of any plants determines the water uptake capacity as well as the strength of roots to held and utilize the nutrients present in soil. Under different stress conditions such as drought and low nutrient availability the highly developed root system has a major role to access mobile and immobile resources which are present in soil. A proper established root system absorbs water and nutrients faster as compared to less developed root system. Highly established root system has more capability to go deeper inside the soil as compared to less developed root system. Under these different aspects of root system architecture like role of root system, function and utilization capacity of different roots types, effect of genetic and climatic factors, some constraints and their solutions with stress tolerance and opportunities in genetic improvements are reviewed after considering the proper availability of water and nutrients provided to the crop.
Phosphorus is an essential macro-nutrient that often limits plant productivity in agricultural soils, particularly in
alkaline-calcareous soils. In these soils, phosphorus availability is primarily controlled by sorption and precipitation reactions. This paper critically reviews and synthesizes the principal strategies through which rhizosphere
processes modulate phosphorus bioavailability in such typical soils, providing a valuable resource for researchers
and practitioners on the current state of knowledge. The review also emphasizes the importance of rhizosphere
processes and their applications in developing sustainable farming practices. It focuses on recent advancements
in root exudation, anatomical and molecular mechanisms, and their interactions with key agricultural practices.
Furthermore, it synthesizes and discusses cutting-edge rhizosphere research, pinpointing opportunities for future
explorations. Several knowledge gaps were identified. For instance, there is a paucity of information regarding
the trade-offs between root morphological and physiological traits (e.g., root exudates) in response to phosphorus deficiency. Additionally, metabolomics needs to be integrated to unravel the molecular mechanisms
involved in rhizosphere interactions. Further research is also required to identify specific plant and microbial
traits that contribute to rhizosphere acidification in calcareous soils.
This chapter provides an overview of how the stable isotope composition of oxygen bond to phosphorus, δ ( ¹⁸ O) PO4 , in phosphate can be used to investigate P cycling in the soil–plant continuum. In recent years, several books and articles about different aspects of P cycling have been published. This chapter provides summary information about P cycling in the soil–plant continuum focusing on the current methods in P research. It also provides an overview of the pitfalls of the δ ( ¹⁸ O) PO4 method, especially regarding sampling and sample handling. The chapter concludes with the way forward and prospects of the δ ( ¹⁸ O) PO4 method to investigate P cycling in the soil–plant continuum.
Phosphorus is indispensable for plant growth and development, with its status crucial for determining crop productivity. Plants have evolved various biochemical, morphological, and developmental responses to thrive under conditions of low P availability, as inorganic phosphate (Pi), the primary form of P uptake, is often insoluble in soils. Over the past 25 years, extensive research has focused on understanding these responses, collectively forming the Pi starvation response system. This effort has not only expanded our knowledge of strategies to cope with Pi starvation (PS) but also confirmed their adaptive significance. Moreover, it has identified and characterized numerous components of the intricate regulatory network governing P homeostasis. This review emphasizes recent advances in PS signaling, particularly highlighting the physiological importance of local PS signaling in inhibiting primary root growth and uncovering the role of TORC1 signaling in this process. Additionally, advancements in understanding shoot-root Pi allocation and a novel technique for studying Pi distribution in plants are discussed. Furthermore, emerging data on the regulation of plant-microorganism interactions by the PS regulatory system, crosstalk between the signaling pathways of phosphate starvation, phytohormones and immunity, and recent studies on natural variation in Pi homeostasis are addressed.
This extensive book chapter examines the intricate correlation between plant stress and agriculture, emphasizing the diverse challenges presented by both abiotic and biotic stressors on crop productivity, quality, and global food security. The growing population and climate change-induced adversities have led to an urgent need for sustainable stress-tolerant crops. The integration of advanced biotechnological techniques, precision breeding, and ecological insights has facilitated the development of crops equipped to withstand various stressors, thereby transforming the landscape of stress-tolerant agriculture. Moreover, the investigation of plant growth–promoting fungi (PGPF) as a solution presents a promising avenue for enhancing plant growth, nutrient acquisition, and stress resilience through symbiotic interactions. PGPF have the potential to revolutionize agricultural practices, reduce reliance on agrochemicals, and bolster crop resilience in the face of environmental fluctuations, thus offering a sustainable pathway to address the challenges posed by changing climates and limited resources. This review illuminates the complex interplay between plants, microorganisms, and their environment, highlighting the significance of innovative strategies to ensure sustainable agricultural development in the future.
Introduction
Plant responses to drought stress are influenced by various factors, including the lateral root angle (LRA), stomatal regulation, canopy temperature, transpiration rate and yield. However, there is a lack of research that quantifies their interactions, especially among different cotton varieties.
Methods
This experiment included two water treatments: well-watered (75 ± 5% soil relative water content) and drought stress (50 ± 5% soil relative water content) starting from the three-leaf growth stage.
Results
The results revealed that different LRA varieties show genetic variation under drought stress. Among them, varieties with smaller root angles show greater drought tolerance. Varieties with smaller LRAs had significantly increased stomatal opening by 15% to 43%, transpiration rate by 61.24% and 62.00%, aboveground biomass by 54% to 64%, and increased seed cotton yield by 76% to 79%, and decreased canopy temperature by 9% to 12% under drought stress compared to the larger LRAs. Varieties with smaller LRAs had less yield loss under drought stress, which may be due to enhanced access to deeper soil water, compensating for heightened stomatal opening and elevated transpiration rates. The increase in transpiration rate promotes heat dissipation from leaves, thereby reducing leaf temperature and protecting leaves from damage.
Discussion
Demonstrating the advantages conferred by the development of a smaller LRA under drought stress conditions holds value in enhancing cotton’s resilience and promoting its sustainable adaptation to abiotic stressors.
In addition to being a crucial component of plant growth, phosphorus (P) is also important for preserving thesustainability of the environment. The accessibility of phosphorus in soil, its vital importance for plant roots, and thewider environmental effects of managing it are all covered in this abstract. The intricate interaction of multiple elements,including soil pH, biological material content, and microbial activity, determines the availability of phosphorus in soil. Itis essential to comprehend and maximize phosphorus availability to guarantee a sufficient supply of nutrients to plantroots. Plants absorb phosphorus mostly in the form of phosphate ions (H2PO4). A deficiency of phosphorus in the soilcan cause stunted growth, lower agricultural yields, and general plant health problems. Plants have developed severaltactics to improve their uptake of phosphorus, such as the exudation of organic acids from their roots and as well assymbiotic relationships with mycorrhizae fungus. These adaptations demonstrate how important phosphorus is to plantlife and ecological health.
Shade avoidance syndrome (SAS) is triggered by a low ratio of red (R) to far‐red (FR) light (R/FR ratio), which is caused by neighbor detection and/or canopy shade. In order to compete for the limited light, plants elongate hypocotyls and petioles by deactivating phytochrome B (phyB), a major R light photoreceptor, thus releasing its inhibition of the growth‐promoting transcription factors PHYTOCHROME‐INTERACTING FACTORs. Under natural conditions, plants must cope with abiotic stresses such as drought, soil salinity, and extreme temperatures, and biotic stresses such as pathogens and pests. Plants have evolved sophisticated mechanisms to simultaneously deal with multiple environmental stresses. In this review, we will summarize recent major advances in our understanding of how plants coordinately respond to shade and environmental stresses, and will also discuss the important questions for future research. A deep understanding of how plants synergistically respond to shade together with abiotic and biotic stresses will facilitate the design and breeding of new crop varieties with enhanced tolerance to high‐density planting and environmental stresses.
This study assessed the effect of Bacillus megaterium on seedling growth of Glycyrrhiza uralensis Fisch. under control and phosphorus (P) deficiency conditions. The results showed that P deficiency improved 1) G. uralensis root growth, 2) superoxide dismutase, catalase, and peroxidase activities, 3) inorganic P, starch, and soluble sugar contents in roots, 4) dissipated energy flux per reaction center, trapped energy flux per reaction center, and absorption flux per reaction center, and 5) net photosynthetic rate, stomatal conductance, transpiration rate, maximum fluorescence intensity after dark adaptation, and variable fluorescence. However, P deficiency significantly decreased chlorophyll and carotenoid contents in G. uralensis, but enhanced chlorophyll and carotenoid contents in B. megaterium. Our findings on the regulatory mechanisms of B. megaterium in response to P starvation hold promise for improving the success of G. uralensis cultivation. Keywords: Bacillus megaterium; Glycyrrhiza uralensis Fisch; Phosphorus deficiency; Chlorophyll fluorescence; Antioxidant enzymes superoxide; Non-structural carbohydrate
Increasing nutrient uptake and use efficiency in plants can contribute to improved crop yields and reduce the demand for fertilizers in crop production. In this study, we characterized a rice mutant, 88n which showed long roots under low nitrogen (N) or phosphorus (P) conditions. Low expression levels of N transporter genes were observed in 88n root, and total N concentration in 88n shoots were decreased, however, C concentrations and shoot dry weight in 88n were comparable to that in WT. Therefore, 88n showed high nitrogen utilization efficiency (NUtE). mRNA accumulation of Pi transporter genes was higher in 88n roots, and Pi concentration and uptake activity were higher in 88n than in WT. Therefore, 88n also showed high phosphorus uptake efficiency (PUpE). Molecular genetic analysis revealed that the causal gene of 88n phenotypes was OsbZIP1, a monocot-specific ortholog of the A. thaliana bZIP transcription factor HY5. Similar to the hy5 mutant, chlorophyll content in roots was decreased and root angle was shallower in 88n than in WT. Finally, we tested the yield of 88n in paddy fields over 3 years because 88n mutant plants showed higher PUpE and NUtE activity and different root architecture at the seedling stage. 88n showed large panicles and increased panicle weight/plant. Taken together, a mutation in OsbZIP1 could contribute to improved crop yields.
Inundation that gives rise to soil flooding, or more complete submergence, is the most common environmental cause of oxygen deprivation for vascular plants. Species differ considerably in their susceptibility to the stress. Tolerance can vary from only a few hours to many days or weeks depending on species, the organs directly affected, stage of development, and external conditions such as temperature. Mechanisms that underlie short-and long-term tolerance to external anaerobic conditions are reviewed. For roots, these include metabolic adaptations such as avoidance of self poisoning and cytoplasmic acidosis, maintenance of adequate supplies of energy and sugar, modifications to gene expression and metabolic acclimation to tissue anoxia by previous exposure to partial oxygen shortage. Morphological escape mechanisms based on aerenchyma development and internal aeration pathways are emphasised. Shoots are often less susceptible to oxygen deficiency than roots. Their mechanisms of tolerance can include metabolic adaptations and developmentally passive tolerance such as that seen in overwintering rhizomes of many wetland species. Escape mechanisms for shoots are based on active and, sometimes, increasingly rapid shoot extension in the presence or absence of oxygen, and formation of replacement roots through adventitious rooting at the shoot base. Systemic signalling between roots and shoots integrates root and shoot physiology and limits indirect damage to shoot tissues by soil flooding. The review is completed by an assessment of prospects for future research.
Phosphorus deficiency is a major yield limiting constraint in wheat cultivation on acid soils. The plant factors that influence P uptake efficiency (PUPE) are mainly associated with root characteristics. This study was conducted to analyze the genotypic differences and relationships between PUPE, root length density (RLD), colonization by vesicular arbuscular and arbuscular mycorrhizal (V)AM fungi and root excretion of phosphatases in a P-deficient Andisol in the Central Mexican Highlands. Forty-two semidwarf spring-bread-wheat (Triticum aestivum L.) geno-types from CIMMYT were grown without (−P) and with P fertilization (+P), and subsequently in subsets of 30 and 22 genotypes in replicated field trials over 2 and 3 years, respectively. Acid phosphatase activity at the root surface (APASE) was analyzed in accompanying greenhouse experiments in nutrient solution. In this environment, PUPE contributed more than P utilization efficiency, in one experiment almost completely, to the variation of grain yield among genotypes. Late-flowering genotypes were higher yielding, because the postanthesis period of wheat was extended due to the cold weather at the end of the crop cycles, and postanthesis P uptake accounted for 40–45% of total P uptake. PUPE was positively correlated with the numbers of days to anthesis (at −P r=0.57 and at +P r=0.73). The RLD in the upper soil layer (0–20 cm) of the wheat germplasm tested ranged from 0.5 to 2.4 cm cm −3 at –P and 0.7 to 7.7 at +P. RLD was the most important root trait for improved P absorption, and it was positively genetically correlated with PUPE (at –P r=0.42 and at +P r=0.63) and the number of spikes m −2 (at –P r=0.58 and at +P r=0.36). RLD in the upper soil layer was more important with P fertilizer application. Without P fertilization, root proliferation in the deeper soil profile secured access to residual, native P in the deeper soil layer. (V)AM-colonisation and APASE were to a lesser degree correlated with PUPE. Among genoptypes, the level of (V)AM-colonisation ranged from 14 to 32% of the RLD in the upper soil layer, and APASE from 0.5 to 1.1 nmol s −1 plant −1 10 −2 .
Sitka spruce [Picea sitchensis (Bong.) Carr.] plants were grown under controlled conditions in specially designed boxes in which the plagiogravitropic lateral roots grew out from moist peat into an air space at one side. In one treatment the air was saturated with water vapour. In the other a linear horizontal gradient of water vapour pressure was maintained between the vertical peat surface and a porous membrane made from black cloth. Near the peat surface the vapour pressure gradient was equivalent to a soil water-potential gradient of about 0.48 MPa mm−1.
The angles of the roots before and after emergence from the peat were measured in different planes. In the saturated air treatment there was no significant change of angle after emergence but roots which emerged into the air with the humidity gradient grew more slowly and showed a marked change of direction. This deflection had two components; there was some tendency for the roots to be attracted to the moist peat surface (hydrotropism), and there was also a downward component (gravitropism). Mean deviation from the angle of emergence which would have resulted from a hydrotropic response alone was 58°, while deviation from the true gravitropic position was only 31°. Therefore under the conditions of the experiment the gravitropic response was considerably stronger than the hydrotropic one.
The implications of these results are discussed for the growth of roots in soils, where water potential gradients generally do not seem to be sufficient to cause hydroptropic curvature. However, there was an enhanced gravitropic response of the tips of lateral roots subject to water stress and this may help control the orientation of roots near the soil surface.
This book is intended for a wide range of individuals, including scientists, students and informed laypersons who are interested in agricultural biotechnology, alternative agriculture, bioremediation of the environment and decreasing our reliance on pesticides and fungicides. It will deal primarily with understanding, at a biochemical and molecular biological level, how certain free living bacteria are able to promote plant growth; symbiotic bacteria such as Rhizobia will be mentioned only briefly. The assumption underlying the entire endeavour will be that a more profound understanding of these fundamental mechanisms will eventually permit scientists to manipulate these bacteria and use them more efficiently as a regular component of agricultural and/or horticultural practice. Therefore, while all the topics are discussed in as comprehensive a manner as possible, the book emphasizes a critical overview of the field rather than a mere compendium of data.
Phosphorus deficiency is a major yield limiting constraint in wheat cultivation on acid soils. The plant factors that influence
P uptake efficiency (PUPE) are mainly associated with root characteristics. This study was conducted to analyze the genotypic
differences and relationships between PUPE, root length density (RLD), colonization by vesicular arbuscular and arbuscular
mycorrhizal (V)AM fungi and root excretion of phosphatases in a P-deficient Andisol in the Central Mexican Highlands. Forty-two
semidwarf spring-bread-wheat (Triticum aestivumL.) genotypes from CIMMYT were grown without (−P) and with P fertilization (+P), and subsequently in subsets of 30 and 22
genotypes in replicated field trials over 2 and 3 years, respectively. Acid phosphatase activity at the root surface (APASE)
was analyzed in accompanying greenhouse experiments in nutrient solution. In this environment, PUPE contributed more than
P utilization efficiency, in one experiment almost completely, to the variation of grain yield among genotypes. Late-flowering
genotypes were higher yielding, because the postanthesis period of wheat was extended due to the cold weather at the end of
the crop cycles, and postanthesis P uptake accounted for 40–45% of total P uptake. PUPE was positively correlated with the
numbers of days to anthesis (at −P r=0.57 and at +P r=0.73). The RLD in the upper soil layer (0–20 cm) of the wheat germplasm
tested ranged from 0.5 to 2.4 cm cm-3 at –P and 0.7 to 7.7 at +P. RLD was the most important root trait for improved P absorption, and it was positively genetically
correlated with PUPE (at –P r=0.42 and at +P r=0.63) and the number of spikes m-2 (at –P r=0.58 and at +P r=0.36). RLD in the upper soil layer was more important with P fertilizer application. Without P
fertilization, root proliferation in the deeper soil profile secured access to residual, native P in the deeper soil layer.
(V)AM-colonisation and APASE were to a lesser degree correlated with PUPE. Among genoptypes, the level of (V)AM-colonisation
ranged from 14 to 32% of the RLD in the upper soil layer, and APASE from 0.5 to 1.1 nmol s-1 plant-1 10-2.
Roots represent a considerable carbon cost for plants. Furthermore, plants vary considerably in how carbon is expended for belowground processes. One attribute that varies widely among species is the investment of root biomass in the production of root length. Relatively thin roots have a high specific root length (SRL) or length: dry weight ratio. Since water and nutrient uptake is based more upon root length than mass, one might conclude that species of high SRL invest their root biomass more efficiently than species of low SRL. This, however, ignores many other functional attributes of roots that may permit coarse lateral roots to be more adaptive than fine lateral roots under certain environmental conditions. In leaves, studies on the relationship of structure and function suggest that evergreen plants with greater leaf longevity commonly have thicker leaves, lower photosynthetic capacity, and lower respiration rates than deciduous plants. These kinds of relationships may also be true for thick roots (low SRL). Limited evidence suggests that species of high SRL tend to have greater plasticity in root growth, greater physiological capacity for water and nutrient uptake, but less root longevity and less mycorrhizal dependency than species of low SRL. More study is needed before the physiological traits associated with variation in length-biomass ratio are understood.
Although ethylene is known to be involved in plant response to a number of biotic and abiotic stresses, relatively little is known concerning its role in nutritional stress arising from nutrient deficiency or mineral toxicity. There is clear evidence for involvement of ethylene in the symbiosis between Rhizobium and legumes, and in the ‘Strategy 1’ response to Fe deficiency. Ethylene may also be generated during tissue necrosis induced by severe toxicities and deficiencies. Metal toxicity may generate ethylene through oxidative stress. Evidence for a more general role for ethylene in regulating plant responses to macronutrient deficiency is suggestive but incomplete. Few studies have addressed this interaction, and most published reports are difficult to interpret because of the unrealistic way that nutrient treatments were imposed. Deficiency of N and P appear to interact with ethylene production and sensitivity. A role for ethylene in mediating adaptive responses to P stress is suggested by the fact that P stress can induce a variety of morphological changes in root systems that are also affected by ethylene, such as gravitropism, aerenchyma formation, and root hair development. Other adaptive responses include senescence or abscission of plant parts which cannot be supported by the plant. Ethylene and other plant hormones may be involved in mediating the stress signal to generate these responses. Although existing literature is inconclusive, we speculate that ethylene may play an important role in mediating the morphological and physiological plasticity of plant responses to nutrient patches in time and space, and especially root responses to P stress.
We have observed that low soil phosphorus availability alters the gravitropic response of basal roots in common bean (Phaseolus vulgaris L.), resulting in a shallower root system. In this study we use a geometric model to test the hypotheses that a shallower root system is a positive adaptive response to low soil P availability by (1) concentrating root foraging in surface soil horizons, which generally have the highest P availability, and (2) reducing spatial competition for P among roots of the same plant. The growth of nine root systems contrasting in gravitropic response over 320 h was simulated in SimRoot, a dynamic three-dimensional geometric model of root growth and architecture. Phosphorus acquisition and inter-root competition were estimated with Depzone, a program that dynamically models nutrient diffusion to roots. Shallower root systems had greater P acquisition per unit carbon cost than deeper root systems, especially in older root systems. This was due to greater inter-root competition in deeper root systems, as measured by the volume of overlapping P depletion zones. Inter-root competition for P was a significant fraction of total soil P depletion, and increased with increasing values of the P diffusion coefficient (De), with root age, and with increasing root gravitropism. In heterogenous soil having greater P availability in surface horizons, shallower root systems had greater P acquisition than deeper root systems, because of less inter-root competition as well as increased root foraging in the topsoil. Root P acquisition predicted by SimRoot was validated against values for bean P uptake in the field, with an r
2 between observed and predicted values of 0.75. Our results support the hypothesis that altered gravitropic sensitivity in P-stressed roots, resulting in a shallower root system, is a positive adaptive response to low P availability by reducing inter-root competition within the same plant and by concentrating root activity in soil domains with the greatest P availability.
Root gravitropism may be an important element of plant response to phosphorus availability because it determines root foraging in fertile topsoil horizons, and thereby phosphorus acquisition. In this study we seek to test this hypothesis in both two dimensional paper growth pouch and three-dimensional solid media of sand and soil cultures. Five common bean (Phaseolus vulgaris L.) genotypes with contrasting adaptation to low phosphorus availability were evaluated in growth pouches over 6 days of growth, and in sand culture and soil culture over 4 weeks of growth. In all three media, phosphorus availability regulated the gravitropic response of basal roots in a genotype-dependent manner. In pouches, sand, and soil, the phosphorus-inefficient genotype DOR 364 had deeper roots with phosphorus stress, whereas the phosphorus-efficient genotype G19833 responded to phosphorus stress by producing shallower roots. Genotypes were most responsive to phosphorus stress in sand culture, where relative root allocation to the 0–3- and 3–6-cm horizons increased 50% with phosphorus stress, and varied 300% (3–6 cm) to 500% (0–3 cm) among genotypes. Our results indicate that (1) phosphorus availability regulates root gravitropic growth in both paper and solid media, (2) responses observed in young seedlings continue throughout vegetative growth, (3) the response of root gravitropism to phosphorus availability varies among genotypes, and (4) genotypic adaptation to low phosphorus availability is correlated with the ability to allocate roots to shallow soil horizons under phosphorus stress.
Accumulation of the gaseous plant hormone ethylene is very important for the induction of several responses of plants to flooding. However, little is known about the role of this gas in the formation of flooding-induced adventitious roots. Formation of adventitious roots in Rumex species is an adaptation of these plants to flooded soil conditions. The large air-spaces in these roots enables diffusion of gases between shoot and roots.
Application of ethylene to non-flooded Rumex plants resulted in the formation of adventitious roots. In R. palustris Sm. shoot elongation and epinasty were also observed. The number of roots in R. thyrsiflorus Fingerh. was much lower than in R. palustris, which corresponds with the inherent difference in root forming capacity between these two species. Ethylene concentrations of 1.5–2μI I− 1 induced a maximum number of roots in both species.
Quantification of ethylene escaping from root systems of Rumex plants that were de-submerged after a 24 h submergence period showed that average ethylene concentrations in submerged roots reached 1.8 and 9.1 μl I−1 in R. palustris and R. thyrsiflorus, respectively. Inhibition of ethylene production in R. palustris by L-α-(2-aminoethoxyvinyl)-glycine (AVG) or α-aminobutyric acid (AIB) decreased the number of adventitious roots induced by flooding, indicating that high ethylene concentrations may be a prerequisite for the flooding-induced formation of adventitious roots in Rumex species.
Plants respond strongly to environmental heterogeneity, particularly below ground, where spectacular root proliferations in nutrient-rich patches may occur. Such 'foraging' responses apparently maximize nutrient uptake and are now prominent in plant ecological theory. Proliferations in nitrogen-rich patches are difficult to explain adaptively, however. The high mobility of soil nitrate should limit the contribution of proliferation to N capture. Many experiments on isolated plants show only a weak relation between proliferation and N uptake. We show that N capture is associated strongly with proliferation during interspecific competition for finite, locally available, mixed N sources, precisely the conditions under which N becomes available to plants on generally infertile soils. This explains why N-induced root proliferation is an important resource-capture mechanism in N-limited plant communities and suggests that increasing proliferation by crop breeding or genetic manipulation will have a limited impact on N capture by well-fertilized monocultures.
The development of plant root systems is sensitive to the availability and distribution of nutrients within the soil. For
example, lateral roots proliferate preferentially within nitrate (NO3
–)-rich soil patches. A NO3
−-inducible Arabidopsis gene (ANR1), was identified that encodes a member of the MADS box family of transcription factors. Transgenic plants in whichANR1 was repressed had an altered sensitivity to NO3
– and no longer responded to NO3
–-rich zones by lateral root proliferation, indicating that ANR1 is a key determinant of developmental plasticity in Arabidopsis roots.
The roots of most plants are colonized by symbiotic fungi to form mycorrhiza, which play a critical role in the capture of nutrients from the soil and therefore in plant nutrition. Mycorrhizal Symbiosis is recognized as the definitive work in this area. Since the last edition was published there have been major advances in the field, particularly in the area of molecular biology, and the new edition has been fully revised and updated to incorporate these exciting new developments. . Over 50% new material . Includes expanded color plate section . Covers all aspects of mycorrhiza . Presents new taxonomy . Discusses the impact of proteomics and genomics on research in this area.
An understanding of the mineral nutrition of plants is of fundamental importance in both basic and applied plant sciences. The Second Edition of this book retains the aim of the first in presenting the principles of mineral nutrition in the light of current advances. This volume retains the structure of the first edition, being divided into two parts: Nutritional Physiology and Soil-Plant Relationships. In Part I, more emphasis has been placed on root-shoot interactions, stress physiology, water relations, and functions of micronutrients. In view of the worldwide increasing interest in plant-soil interactions, Part II has been considerably altered and extended, particularly on the effects of external and interal factors on root growth and chapter 15 on the root-soil interface. The second edition will be invaluable to both advanced students and researchers.
Gregor Mendel (1866) conducted the first genetic analysis of common beans. Mendel studied the inheritance of growth habit, and pod color and shape in a progeny between P. vulgaris and P. nanus (= P. vulgaris, bush type) in order to confirm his findings with peas. Unfortunately, further studies on the inheritance of flower and seed coat color were hampered by his use of interspecific hybrids between P. nanus and P. multiflorus (= P. coccineus), which are now known to yield aberrant ratios. Later, Shaw and Norton (1918) used intraspecific crosses and determined that pigmentation and pigmentation patterns of the seed coat are controlled by multiple independent factors. A few years later Sax (1923) began to identify the multiple components that determine the inheritance of these traits. A single factor was identified as responsible for pigmentation, while two linked factors were identified to control mottling; this appears to be the first report of linkage in beans. Furthermore, Sax (1923) was the first to report linkage between a Mendelian character (seed coat pigmentation) and a QTL (for seed size). Although the common bean was used as experimental material at the inception of genetics, its genetic characterization has lagged behind that of many other crop species.
Bean (Phaseolus vulgaris L.) is a staple food in Latin America and is frequently grown by small farmers on acid infertile soils. Average yields are very low (±500 kg ha-1) when compared to those in temperate zones (1500 kg ha-1). On acid, infertile soils, the main limiting factor for bean production is low available phosphorus. These soils have a high P-fixing capacity, so additional P from fertilizers is soon unavailable. Furthermore, the residual effect of P fertilizer is practically nil. P fertilizer is expensive and many farmers cannot afford to apply it. Other soil constraints (e.g. pH, Al toxicity, and low organic matter) impede P use efficiency and response to applied P. Also, fertilizer management influences the response of beans to P application.
Differential yield response of beans in the field and in the greenhouse to P fertilization has been observed, but poor correlation is found as to dry matter production, leaf area index, P content in the tissue, and P uptake by the plant. Screening techniques for controlled environments do not give satisfactory results when tested in the field. The difficulties of these methods proposed the simple field screening method but the efficiency gain is small. Some other potential mechanisms for screening are discussed.
Ethylene in Plant Biology, Second Edition provides a definitive survey of what is currently known about this structurally simplest of all plant growth regulators. This volume contains all new material plus a bibliographic guide to the complete literature of this field. Progress in molecular biology and biotechnology as well as biochemistry, plant physiology, development, regulation, and environmental aspects is covered in nine chapters co-authored by three eminent authorities in plant ethylene research. This volume is the modern text reference for all researchers and students of ethylene in plant and agricultural science. Key Features * Completely updated * Concise, readable style for students and professional * Contains an extensive bibliographic guide to the original literature * Well illustrated with diagrams and photographs * Thorough coverage of: * ethylene and ethephon roles and effects * stress ethylene * biosynthesis of ethylene * molecular biology of ethylene * action of ethylene * agricultural uses of ethylene.
The effects on elongation of applying a continuous flow of ethylene in moist air to the roots of intact seedlings of rice (Oryza sativa L. cv. «IR 20»), white mustard (Sinapis alba L.) and tomato (Lycopersicon esculentumMill., CV's «Ailsa Craig», «Moneymaker» and «Diageotropica») were studied in relation to their rates of endogenous ethylene production.
Variation in root system architecture among plants and its ecological correlates are discussed. The need to quantify costs and benefits of different root system architectures is emphasized. The components of root system architecture are magnitude, topology, angle of branching and radial angle, link lengths and link radii. The costs of root systems are affected by all of these angles. Root systems perform two primary functions for plants: anchorage and resource acquisition. Both depend on architectural charcteristics. Architecture appears to be a component of the underlying morphological plan or strategy of many plants, and plasticity in architecture is discussed. -from Author
Nutrient-efficient crops have an important role in modern agriculture. In the low-input systems that characterize most of world agriculture, nutrient-efficient crops improve crop productivity. In high-input systems of the developed world, nutrient-efficient crops are valuable in reducing pollution of surface and ground water resources from intense fertilization. Recent developments in molecular biology, root biology, rhizosphere interactions, and modeling present new opportunities for the understanding and improvement of crop nutrient efficiency. The degree and extent of nutritional limitations to crop productivity, and the economic and ecological liabilities of intensive fertilization, are such that eventually nutrient-efficient crops will be an important part of integrated nutrient management of cropping systems.
Remobilization of P from vegetative tissues can be an important source of grain P in common bean (Phaseolus vulgaris L.). Yet, data on the extent of remobilization of P from roots is scarce. We measured P remobilization from roots and leaves and examined the influence of P nutrition on remobilization patterns and tissue longevity. A split-root system was used to expose a portion of the root system (compartment roots) to low-P treatments independently from those imposed on the main root system. Phosphorus content of retained leaves, abscised leaves, stems, pods, seeds, and roots were observed over time. Leaf remobilization supplied over half of the pod plus seed P. Flux analysis suggested that leaf remobilization occurred earlier in low-P than it did in high-P plants. Root P content of compartment roots did not decrease with ontogeny. We compared remobilization patterns of root P in low-P and high-P plants in a short-term experiment using 32P applied to roots grown in either low-P or high-P compartments. Compartment roots retained over 80% of absorbed 32P almost all cases. The exception was roots of high-P plants grown in a high-P compartment, which retained only 20% of absorbed 32P. Together these results indicate common bean roots retain P when soil P levels are low. This behavior is in contrast to that of leaves and stems which remobilize P to the grain at both low and high levels of soil P fertility.
The effect of available P in subsoil on plant uptake of P from surface soil layers and consequently on fertilizer recommendations is largely unknown. Our objective was to determine how much P may be removed by crops from subsurface soil layers and how the subsurface P level influences crop drawdown of P from the surface layer. Soil columns were prepared that contained all four possible combinations of low or high P levels in the surface soil and low or high P levels in the subsurface layer. The soil used was a Farnum fine sandy loam (fine-loamy, mixed, thermic Pachic Argiustoll). Phosphorus removal was monitored by growing hybrid sorghum-sudangrass [Sorghum bicolor (L.) Moench cv. ‘Honey Chow’] 84 days with an intermediate harvest after 35 days. Compared to when both the surface and subsurface layers had low P levels, P uptake increased when either or both layers had high P levels. Root growth and morphology responded to the P level of the soil layers. For all conditions, P uptake demonstrated a high correlation (R²=0.94) to an accessibility factor defined as the product of the available P level and root length summed for both soil layers. Comparing ratios of crop P removal to the change in soil test showed that P drawdown from the surface layer was reduced when the P-supplying capacity of the subsurface layer was high. We concluded that available P in the subsurface layer can supply P to the crop, especially if the surface layer cannot supply sufficient P to meet crop demand. These results suggest that subsoil fertility should be considered in evaluating P available to crops and in estimating crop drawdown of available P.
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1 This paper demonstrates the role played by plant hormones in linking environmental signals with plant responses. It concentrates on two strategies for a sessile organism as a plant to cope with changing environmental conditions: life cycle timing and phenotypic adjustment. 2 The significance of abscisic acid and gibberellins for dormancy and germination, respectively, is discussed in relation to life cycle timing. Cytokinins are presented in relation to a possible role in carbon allocation. The gaseous plant hormone ethylene is discussed in relation to its involvement in wind- and water-induced changes in shoot growth. 3 Evidence for the role played by plant hormones in developmental processes and plastic responses comes from only a very few plant species. It will be a task for ecologists to come to a more generalized understanding of the involvement of plant hormones in ecological processes by applying the existing knowledge to a much wider range of species.
Soybean [Glycine max (L.) Merr.] acclimation to flooding has been investigated at biochemical and physiological levels, but long-term acclimation to flooding may be associated with morphological changes. Supplementing legumes with nitrate ameliorates flooding stress, compared with plants dependent on N2 fixation. Two experiments evaluated morphological and anatomical changes induced by flooding for plants relying on N2 fixation or supplemented with nitrate. An additional experiment assessed the role of aerenchyma in flooding acclimation by blocking aerenchyma formation with silver. Flooding soybean for 21 d with nutrient solution without N increased biomass allocation to roots. No aerenchyma was observed in roots of non-flooded plants; however, it was abundant in roots of flooded plants. Porosity measurements of root and stem-base tissues indicated that 10 to 15% of the volume was gas filled in flooded plants, while gas-filled volume was negligible in the non-flooded controls. Flooding in the presence of nitrate decreased aerenchyma and increased adventitious roots, compared with plants flooded with nutrient solution without N. Increased growth under flooding of nitrate-supplemented plants, therefore, was not directly associated with increased root porosity. For flooded plants dependent on N2 fixation, silver prevented aerenchyma and adventitious root development and decreased biomass accumulation and N2 fixation by approximately one-half compared with plants flooded in the absence of silver. These results indicate that acclimation to flooding in soybean involves preferential allocation of photosynthates to development of porous adventitious roots and that aerenchyma formation for soybean relying on N2 fixation is critical for acclimation to flooding.
Published data for the most widely used bioassays for auxins as. well as other auxin-induced responses, have been analyzed to determine whether the response is ultrasensitive, hyperbolic or subsensitive, i.e. whether the change from 10 to 90% of maximal response requires less than, equal to or more than an 81-fold increase in external auxin concentration. Auxin-dependent callus growth is most often ultrasensitive. Other responses, including the curvature of Avena coleoptiles, may show simple Mi-chaelis-Menten kinetics. In the majority of cases, however, the response is sub-sensitive, often very markedly so. The finding of subsensitive responses is consistent with the proposal by A. J. Trewavas that plant development is regulated by changes in the sensitivity to plant growth substances.
Detailed data for subsensitive dose responses, particularly auxin-induced inhibition of root growth, can often be precisely represented by bi- or multiphasic isotherms, with the phases separated by sharp transitions. The relationship to auxin uptake and the relationship, if any, between carriers and receptors for auxins remain to be elucidated.
Low phosphorus availability stimulates root hair elongation in many plants, which may have adaptive significance in soil phosphorus acquisition. We investigated the effect of low phosphorus on the elongation of Arabidopsis thaliana root hairs. Arabidopsis thaliana plants were grown in plant culture containing high (1000 mmol m−3) or low (1 mmol m−3) phosphorus concentrations, and root hair elongation was analysed by image analysis. After 15d of growth, low-phosphorus plants developed root hairs averaging 0.9 mm in length while high-phosphorus plants of the same age developed root hairs averaging 0.3 mm in length. Increased root hair length in low-phosphorus plants was a result of both increased growth duration and increased growth rate. Root hair length decreased logarithmically in response to increasing phosphorus concentration. Local changes in phosphorus availability influenced root hair growth regardless of the phosphorus status of the plant. Low phosphorus stimulated root hair elongation in the hairless axr2 mutant, exogenously applied IAA stimulated root hair elongation in wild-type high-phosphorus plants and the auxin antagonist CM PA inhibited root hair elongation in low-phosphorus plants. These results indicate that auxin may be involved in the low-phosphorus response in root hairs.
The involvement of ethylene in root architectural responses to phosphorus availability was investigated in common bean (Phaseolus vulgaris L.) plants grown with sufficient and deficient phosphorus. Although phosphorus deficiency reduced root mass and lateral root number, main root length was unchanged by phosphorus treatment. This resulted in decreased lateral root density in phosphorus-deficient plants. The possible involvement of ethylene in growth responses to phosphorus deficiency was investigated by inhibiting endogenous ethylene production with amino-ethoxyvinylglycine (AVG) and aerating the root system with various concentrations of ethylene. Phosphorus deficiency doubled the root-to-shoot ratio, an effect which was suppressed by AVG and partially restored by exogenous ethylene. AVG increased lateral root density in phosphorus- deficient plants but reduced it in phosphorus-sufficient plants. These responses could be reversed by exogenous ethylene, suggesting ethylene involvement in the regulation of main root extension and lateral root spacing. Phosphorus-deficient roots produced twice as much ethylene per g dry matter as phosphorus-sufficient roots. Enhanced ethylene production and altered ethylene sensitivity in phosphorus-deficient plants may be responsible for root responses to phosphorus deficiency.
We investigated whether the capacities of Lolium perenne L. and Poa pratensis L. roots to proliferate locally and to alter local nitrogen (N) inflows in a decomposing organic matter patch were important in their capture of N when grown together. In the presence of a patch, plants of both species were significantly heavier and contained more N. Root length and weight densities increased in the patch, but specific root length was unaltered. Although both species proliferated roots in the patch, L. perenne produced greater root length densities than P. pratensis, and also captured more N from the patch. Indeed, total N uptake from the patch was related to root length density within the patch. N inflows (rate of N uptake per unit root length) in the patch were no faster than in the whole root system for both species. Under the conditions of this study, root proliferation in an organic patch was more important for N capture from the patch than alterations in N inflows. Local proliferation of roots may be a key factor in interspecific competition for non-uniformly distributed supplies of N in natural habitats, so resolving the previous uncertainty as to the ‘adaptive’ nature of root proliferation.
The paper examines some of the physical and chemical properties of a deep red friable clay profile (Nitosol) developed in the Kenya highlands over trachyte. This soil is widely planted to coffee. The profile is remarkable for the depth and uniformity of the B horizon and for its stable microaggregation. Despite a clay content of 50–60% throughout the deep solum, the soil feels and handles like a loam.
Work with radioactive phosphorus on samples from the profile and from nearby experimental plots under coffee showed that the activity, and the amounts, of surface phosphate fractions decreased in the order Fe-P, Al-P and Ca-P, but the order of decrease of specific surface activity was Al-P, Fe-P, Ca-P. The relative availabilities of these forms is discussed.
Low phosphorus availability is often a primary constraint to plant productivity in native soils. Here we test the hypothesis that root carbon costs are a primary limitation to plant growth in low P soils by assessing the effect of P availability and mycorrhizal infection on whole plant C budgets in common bean (Phaseolus vulgaris L.). Plants were grown in solid-phase-buffered silica sand providing a constant supply of low (1 μm) or moderate (10 μm) P. Carbon budgets were determined weekly during the vegetative growth phase. Mycorrhizal infection in low-P plants increased the root specific P absorption rate, but a concurrent increase in root respiration consumed the increased net C gain resulting from greater P uptake. The energy content of mycorrhizal and non-mycorrhizal roots was similar. We propose that the increase in root respiration in mycorrhizal roots was mainly due to increased maintenance and growth respiration of the fungal tissue. Plants grown with low P availability expended a significantly larger fraction of their total daily C budget on below-ground respiration at days 21, 28 and 35 after planting (29–40%) compared with plants grown with moderate P supply (18–25%). Relatively greater below-ground respiration in low P plants was mainly a result of their increased root∶shoot ratio, although specific assimilation rate was reduced significantly at days 21 and 28 after planting. Specific root respiration was reduced over time by low P availability, by up to 40%. This reduction in specific root respiration was due to a reduction in ion uptake respiration and growth respiration, whereas maintenance respiration was increased in low-P plants. Our results support the hypothesis that root C costs are a primary limitation to plant growth in low-P soils.
Adventitious rooting in Rumex plants, in which the root systems were in hypoxic conditions, differed considerably between two species. R. palustris , a species from frequently flooded river forelands, developed a large number of adventitious roots during hypoxia, whereas adventitious root formation was poor in R. thyrsiflorus , a species from seldom flooded dykes and river dunes. Adventitious rooting could also be evoked in aerated plants of both species by application of auxin (1‐naphthaleneacetic acid or indoleacetic acid) to the leaves. The response to auxin was dose‐dependent, but even high auxin doses could not stimulate R. thyrsiflorus to produce as many adventitious roots as R. palustris . Consequently, the difference between the species in the amount of adventitious root formation was probably genetically determined, and not a result of a different response to auxin.
A prerequisite for hypoxia‐induced adventitious root formation is the basipetal transport of auxin within the shoot, as specific inhibition of this transport by N‐1‐naphthylphthalamic acid severely decreased the number of roots in hypoxia‐treated plants. It is suggested that hypoxia of the root system causes stagnation of auxin transport in the root system. This can lead to an accumulation of auxin at the base of the shoot rosette, resulting in adventitious root formation.
SimRoot, a geometric simulation model of plant root systems, is described. This model employs a data structure titled the Extensible Tree, which is well suited to the type of data required to model root systems. As implemented on Silicon Graphics workstations, the data structure and visualization code provides for continuous viewing of the simulated root system during growth. SimRoot differs from existing models in the explicit treatment of spatial heterogeneity of physiological processes in the root system, and by inclusion of a kinematic treatment of root axes. Examples are provided of the utility of the model in estimating the fractal geometry of simulated root systems in 1, 2, and 3 dimensional space. We envision continued development of the model to incorporate competition from neighboring root systems, linkage with crop simulation models to simulate root-shoot interactions, explicit treatment of soil heterogeneity, and plasticity of root responses to soil factors such as presence of mycorrhizal associations.
Recent work on root distribution, growth angles and gravitropic responses in Japanese cultivars of winter wheat are reviewed. Vertical distribution of roots, which influences the environmental stress tolerance of plants, was observed in the 12 Japanese cultivars in the field. The root depth index (RDI: the depth at which 50% of the root length has been reached) differed among the cultivars at the stem elongation stage. Since the RDI was closely related to the growth angle of seminal roots obtained in a pot experiment, it was assumed that growth angle is useful for predicting vertical root distribution among wheat genotypes. Gravitropic responses of the primary seminal root of 133 Japanese wheat cultivars assessed by measuring the growth angle in agar medium, were larger in the northern Japanese cultivars and smaller in the southern ones. It was also found that the geographical variation resulted from the wheat breeding process, i.e. genotypes with limited gravitropic responses of roots had been selected in the southern part of Japan where excessive soil moisture is one of the most serious problems.