Differences in Root Exudation Among Phosphorus‐Starved Genotypes of Maize and Green Gram and Its Relationship with Phosphorus Uptake

Abstract

Availability of phosphorus (P) in soil and its acquisition by plants is affected by the release of high and low molecular weight root exudates. A study was carried out to ascertain the qualitative and quantitative differences in root exudation among the genotypes of maize (Zea mays L.) and green gram (Vigna radiata L.) under P‐stress. Results showed that both inter‐ and intra‐species differences do exist among maize and green gram in terms of root exudation, P uptake, and shoot and root P content. In general, green gram, a legume crop, had greater root exudation compared to maize. However, the amino acid content of the total root exudates in maize was two‐fold as compared to green gram. The maize and green gram genotypes possessed genetic variability in root exudation. Irrespective of the species or genotypes, a positive relationship was found among P uptake rates, total root exudation, and shoot and root ³²P content. The amount of sugars and amino acid present in the root exudates of P‐starved seedlings also add to the variation in P uptake efficiency of genotypes.     

Root–shoot communication of field‐grown maize drought‐stressed at different rates as modified by atmospheric conditions

Maize is often grown in drought‐prone environments and, thus, drought resistance is an important trait. In order to minimize production losses, plants need to respond and adapt early and fast to moisture loss in the root zone. From experiments under controlled conditions, constituents of the xylem sap, such as the plant hormone abscisic acid (ABA), or xylem pH have long been recognized to act as signals in root–shoot communication. To investigate early signals of field‐grown maize under conditions of progressive drought, a field trial was set up in a field lysimeter for two consecutive years. Although the experimental set‐up was very similar in the two years, plant responses to moisture loss were significantly different in both, the cascade of events and the intensity of responses. The main difference between the two years was in atmospheric vapor‐pressure deficit (VPD), accelerating the drying rate of the soil in the second year. In contrast to observations during the first year, the sudden increase in VPD in the second year caused a strong, transient peak in xylem sap ABA concentration, but no change in xylem pH or leaf ABA concentration was observed. Whereas the water relations of the maize plants remained stable in the first year, they were severely unbalanced in the second. It is argued that the strong xylem‐ABA signal triggered a change from adaptation mechanisms to survival mechanisms. Modulations due to VPD of constituents of the signal cascade induced by drought are discussed with regard to possible resistance strategies, their initiation, and their modification by combining primary environmental signals.     

二氧化碳升高与干旱对植物生理、土壤碳及土壤酶活的影响

Global climate models have indicated high probability of drought occurrences in the coming future decades due to the impacts of climate change caused by a mass release of CO2.Thus,climate change regarding elevated ambient CO2 and drought may consequently affect the growth of crops.In this study,plant physiology,soil carbon,and soil enzyme activities were measured to investigate the impacts of elevated CO2 and drought stress on a Stagnic Anthrosol planted with soybean (Glycine max).Treatments of two CO2 levels,three soil moisture levels,and two soil cover types were established.The results indicated that elevated CO2 and drought stress significantly affected plant physiology.The inhibition of plant physiology by drought stress was mediated via prompted photosynthesis and water use efficiency under elevated CO2 conditions.Elevated CO2 resulted in a longer retention time of dissolved organic carbon (DOC) in soil,probably by improving the soil water effectiveness for organic decomposition and mineralization.Drought stress significantly decreased C:N ratio and microbial biomass carbon (MBC),but the interactive effects of drought stress and CO2 on them were not significant.Elevated CO2 induced an increase in invertase and catalase activities through stimulated plant root exudation.These results suggested that drought stress had significant negative impacts on plant physiology,soil carbon,and soil enzyme activities,whereas elevated CO2 and plant physiological feedbacks indirectly ameliorated these impacts.     

干旱土壤中生物炭对黑麦草生长的促进机制

通过控制不同生物炭添加量和降水量,分析土壤理化性质及黑麦草(Lolium perenne L.)的各项生长指标,探究不同添加量的生物炭对缺水植物生长促进的直接与间接作用。结果表明:生物炭的添加可以提高土壤的田间持水率、土壤中速效磷的含量以及土壤的pH;干旱条件下,增加生物炭的用量能促进黑麦草植株的增高,但高剂量的生物炭抑制黑麦草的生长;生物炭加入并不能持续性的保持土壤中的水分,高浓度(>15%)的生物炭反而增大土壤中水分的流失,但由于生物炭中钾元素为植物对抗干旱提供了必要条件。适当添加生物炭(5%)可缓解黑麦草在缺水时生长发育受到的抑制作用,并促进黑麦草的根系生长以及保证较高的发芽率。土壤中添加生物炭对干旱条件下植物的生长有促进作用,有利于缓解植物受干旱胁迫的影响。     

Root-induced changes in the rhizosphere: Importance for the mineral nutrition of plants

Root-induced changes in the rhizosphere may affect mineral nutrition of plants in various ways. Examples for this are changes in rhizosphere pH in response to the source of nitrogen (NH₄-N versus NO₃-N), and iron and phosphorus deficiency. These pH changes can readily be demonstrated by infiltration of the soil with agar containing a pH indicator. The rhizosphere pH may be as much as 2 units higher or lower than the pH of the bulk soil. Also along the roots distinct differences in rhizosphere pH exist. In response to iron deficiency most plant species in their apical root zones increase the rate of H⁺ net excretion (acidification), the reducing capacity, the rate of Fe^III reduction and iron uptake. Also manganese reduction and uptake is increased several-fold, leading to high manganese concentrations in iron deficient plants. Low-molecular-weight root exudates may enhance mobilization of mineral nutrients in the rhizosphere. In response to iron deficiency, roots of grass species release non-proteinogenic amino acids (?phytosiderophores”?) which dissolve inorganic iron compounds by chelation of Fe^III and also mediate the plasma membrane transport of this chelated iron into the roots. A particular mechanism of mobilization of phosphorus in the rhizosphere exists in white lupin (Lupinus albus L.). In this species, phosphorus deficiency induces the formation of so-called proteoid roots. In these root zones sparingly soluble iron and aluminium phosphates are mobilized by the exudation of chelating substances (probably citrate), net excretion of H⁺ and increase in the reducing capacity. In mixed culture with white lupin, phosphorus uptake per unit root length of wheat (Triticum aestivum L.) plants from a soil low in available P is increased, indicating that wheat can take up phosphorus mobilized in the proteoid root zones of lupin. At the rhizoplane and in the root (root homogenates) of several plant species grown in different soils, of the total number of bacteria less than 1 % are N₂-fixing (diazotrophe) bacteria, mainly Enterobacter and Klebsiella. The proportion of the diazotroph bacteria is higher in the rhizosphere soil. This discrimination of diazotroph bacteria in the rhizosphere is increased with foliar application of combined nitrogen. Inoculation with the diazotroph bacteria Azospirillum increases root length and enhances formation of lateral roots and root hairs similarly as does application of auxin (IAA). Thus rhizosphere bacteria such as Azospirillum may affect mineral nutrition and plant growth indirectly rather than by supply of nitrogen.     

DOES NITROGEN FERTILIZATION ENHANCE DROUGHT TOLERANCE IN SUNFLOWER? A REVIEW

Water stress is one of the major limitations to the agricultural productivity around the globe, particularly in warm, arid and semi-arid regions of the world. Sunflower (Helianthus annuus L.), being a crop with medium water requirements, has the ability to tolerate a short period of drought. However, water stress in the soil as well as inside the plant influences various physiological and biochemical processes. This may inhibit plant growth, decrease developmental activities of the cells and tissues and cause a variety of morphological, physiological and biochemical modifications. Nitrogen (N) is one of the most important mineral nutrients because of its numerous effects on plant growth and yield. A number of fundamental processes such as water and nutrient uptake, protein metabolism, photosynthesis, carbon partitioning, and enzyme and plant hormonal activities are regulated by N. These responses result in profound changes in growth rate, net photosynthate production, plant development, and yield. It is well documented that nutrient uptake of plants is inhibited in dry soils and with expected nutrient deficiencies the normal functioning of the plants is affected. Different strategies are being practiced in the world to cope with the problem of nutrient deficiency under water stress. Nitrogen application either through soil or through foliar feeding is an important strategy to alleviate the adverse effect of drought. Supplemental application of N as foliar fertilization to soil-applied fertilization is important in situation where nutrient supply through soil is limited. Some of the relevant work available about the effect of water stress and nutrient availability in sunflower is reviewed in this paper.     

Detection of Soil Organic Nitrogen in Xylem Sap Collected from Nonmycorrhizal Plants using an Immunological Technique

Phosphate buffer–extractable organic nitrogen (PEON) is considered to be a ubiquitous high-molecular-weightnitrogen (N) compound in soil and may be an important N source for some plant species. We examined whether nonmycorrhizal plants qing-geng-cai (Brassica rapa var. chinensis) and spinach (Spinacia oleracea L. cv. Atras) could uptake PEON from the soilusing animmunoassay that was previously developed from a PEON determination method using anti-PEON IgG. Xylem sap analysis of spinach using an enzyme-linked immune sorbent assay (ELISA) showed that this plant hadhigh capabilities to take up PEON from the soil. Spinach and qing-geng-cai exuded substantial amounts of oxalate or citrate under inorganic N-deficient conditions, indicating exudation of organic acids is probably involved in PEON mobilization. Further results of immunohistochemical localization of PEON in the root section of qing-geng-cai revealed that intact or at least a fraction of PEON absorbed by the epidermis passes through the cortex cell and intercellular space. Our findings indicated that some specific plants have the ability to mobilize PEON by root exudation and take up mineralizable organic N by endocytic invagination.     

Varied rates of mycorrhizal inoculum on growth and nutrient acquisition by barley grown with drought stress

Effectiveness of arbuscular mycorrhizal fungi (AMF) is crucial for maximum plant growth and acquisition of mineral nutrients under drought. The objective of this research was to determine effects of varied rates of AMF inoculum on plant growth and acquisition of phosphorus (P), zinc (Zn), copper (Cu), and manganese (Mn) by barley (Hordeum vulgare L. cv. SLB‐6) grown with and without drought stress (WS and nonWS). Plants inoculated with four inoculum rates [control (M₀), 120 (M₁), 240 (M₂), and360 (M₃) spores per 100 g dry soil] of Glomus mosseae were grown in a low P silty clay (Typic Xerochrept) soil (pH=8.0) mix in a greenhouse for 45 days. Root AMF colonization increased as inoculum rate increased in plants grown with WS and nonWS. Leaf area and shoot and root dry matter (DM) increased as inoculum rate increased up to M₂ regardless of soil moisture. Shoot concentrations of P, Cu, and Mn were generally higher for mycorrhizal (AMF) than for nonmycorrhizal (nonAMF) plants grown with both WS and nonWS. Shoot contents of P, Zn, Cu, and Mn were higher for AMF than for nonAMF plants grown with nonWS, and shoot contents of P were higher for AMF than for nonAMF plants with WS. For plants grown with WS and nonWS, contents of P, Zn, Cu, and Mn were generally higher for plants inoculated with M₂ compared to other rates of inoculum. The results of this study indicated that plant responses to root colonization with AMF were dependent on AMF rate and soil moisture. Based on enhancements in plant DM and mineral acquisition traits, M₂ inoculum was the most effective rate of inoculation for this AMF isolate.     

The combination of localized phosphorus and water supply indicates a high potential for savings of irrigation water and phosphorus fertilizer

Water and phosphorus (P) are often unevenly distributed in the soil profile, thus limiting water and P uptake and plant growth. A soil column and a split‐root experiment were conducted to quantify the effect of localized water and P supply on shoot growth, root morphology, specific P uptake (SPU), P‐use efficiency (PUE), and water‐use efficiency (WUE) of maize (Zea mays L.). Our results indicate that roots preferentially grow in the layer or compartment with both adequate water and P supply, subsequently stimulating SPU, PUE, and WUE, and enhancing shoot growth. Compared with the treatments in which both layers and compartments were supplied with adequate P and/or water, the growth of maize was maintained or minimally affected. SPU, PUE, and WUE were increased when both P and water were supplied in one layer or one compartment only. These findings show that normal plant growth with an adequate P uptake was achieved even if part of the roots were supplied with 2/3 (soil column experiment) and 1/2 (split‐root experiment) of the phosphorus and water supplied in the full‐phosphorus and full‐water treatment. Changes in root morphology under water stress conditions induced by the application of phosphorus and water in deeper soil layers or to a part of the roots may have substantial practical implications for agricultural production and environmental protection.     

Effect of defoliation on patterns of carbon exudation from Agrostis capillaris

Grassland ecosystems are important global sinks and sources of atmospheric carbon (C). In this study, we used an in‐situ ¹³CO₂ tracer approach to quantify differences in short‐term C exudation from defoliated and non‐defoliated Agrostis capillaris (L.) plants subjected to natural diurnal light and temperature regimes and rainfall events. Results showed: 1. There was no significant difference in overall carbon exudation from the plants as a result of defoliation; 2 . defoliation significantly increased exudation of recent photosynthate (i.e., ¹³C labeled); 3 . there was a distinct and statistically significant diurnal trend in C exudation with root C exudation increasing during the day and early evening and decreasing during the night and early morning. The importance of light/temperature and defoliation as drivers of patterns of root C exudation and the contribution of recent assimilate C to atmosphere‐plant‐soil carbon flow are discussed.     

Effects of drought stress on photosynthesis,rhizosphere respiration,and fine‐root characteristics of beech saplings: A rhizotron field study

Soil drought influences the C turnover as well as the fine‐root system of tree saplings. Particularly during the period of establishment, the susceptibility to drought stress of saplings is increased because of incompletely developed root systems and reduced access to soil water. Here, we subjected beech saplings (Fagus sylvatica L.) to different levels of drought stress. Beech saplings were planted in rhizotrons, which were installed in the soil of a Norway spruce forest before bud burst. Soil moisture was manipulated in the following year during May to September. We measured photosynthetic net CO₂ uptake, volume production of fine roots, and rhizosphere respiration during the growing season. Biometric parameters of the fine‐root system, biomass, and nonstructural carbohydrates were analyzed upon harvest in October. Photosynthesis and rhizosphere respiration decreased with increasing drought‐stress dose (cumulated soil water potential), and cumulative rhizosphere respiration was significantly negatively correlated with drought‐stress dose. Fine‐root length and volume production were highest at moderate soil drought, but decreased at severe soil drought. The proportion of fine‐roots diameter < 0.2 mm and the root‐to‐shoot ratio increased whereas the live‐to‐dead ratio of fine roots decreased with increasing drought‐stress dose. We conclude that the belowground C allocation as well as the relative water‐uptake efficiency of beech saplings is increased under drought.     

Influence of AM fungi,inorganic phosphorus and irrigation regimes on plant water relations and soil physical properties in okra (Abelmoschus esculentus L.) – pea (Pisum sativum L.) cropping system in Himalayan acid alfisol

Present investigation studied plant water relations and soil physical properties through AM fungi (Glomus mosseae) to mitigate drought stress in Himalayan acid Alfisol having low water retentivity. Experimentation was carried out at Palampur, India during 2009–2011 in okra–pea cropping system in randomized block design (RBD) replicated thrice with 14 treatments comprising arbuscular mycorrhizal (AM) fungi, varying phosphorus nutrition and irrigation regimes at 40 and 80% available water holding capacity. Integrated use of AM fungi at varying phosphorus (P) levels and irrigation regimes led to significantly higher relative leaf water content (3% each) in okra and pea besides significantly higher xylem water potential (27%) in pea over non-AM fungi counterparts. AM fungi enhanced water-use-efficiency in okra (5–17%) and pea (12–35%) over non–AM fungi counterparts. AM fungi also improved water holding capacity (5–6%) and mean weight diameter of soil particles (4–9%) over non–AM fungi counterparts; but, had nominal or no effect on bulk density. Mycorrhizal plants maintained higher tissue water content imparting greater drought resistance to plants over non–mycorrhizal plants at moisture stress. It is inferred that integrated application of AM fungi and P at varying irrigation regimes improved the plant water relations vis-à-vis drought resistance, crop productivity, WUE, soil aggregation and water holding capacity in okra–pea sequence in Himalayan acid Alfisol.     

Potassium deficiency impedes elevated carbon dioxide‐induced biomass enhancement in well watered or drought‐stressed bread wheat

Potassium (K) deficiency reduces photosynthesis and biomass production of crop plants and also renders them vulnerable to drought stress, whereas elevated carbon dioxide (CO₂) has a positive effect on photosynthesis and yield and ameliorates the adverse effects of drought stress. This study aimed to characterize the physiological responses of wheat (Triticum aestivum L.) stressed with K deficiency under elevated CO₂ and drought conditions. Increased biomass production caused by elevated CO₂ as a consequence of increased photosynthesis and water use efficiency was absent in young K‐deficient wheat plants. Shoot K concentration was negatively affected by elevated CO₂ particularly under K‐deficient conditions, whereas K content per plant was greatest in plants supplied with adequate K and adequate water. Specific leaf weight was increased as a consequence of carbohydrate accumulation in the source leaves of K‐deficient plants particularly under elevated CO₂ and drought stress. Potassium deficiency clearly impeded the impact of elevated CO₂ in both well watered as well as drought‐stressed plants. Adequate K fertilization is a prerequisite for efficient harvesting of atmospheric CO₂ through increased photosynthesis, decreased transpiration, and increased biomass production under changing atmospheric CO₂ and soil moisture conditions.     

Ethylene evolution and ammonium accumulation by tomato plants under water and salinity stresses. Part II

Foliar wilting, epinasty, abscission, chlorosis, and necrosis are common symptoms in plants affected by water and salinity stresses. Ethylene evolution and ammonium accumulation frequently accompany the expression of the symptoms of stresses from various origins. These symptoms and physiological phenomena have been associated with other environmental stresses, such as ammonium toxicity. Intact and excised tomato plants (Lycopersicon esculentum Mill. ‘Heinz 1350’ and neglecta‐1) were subjected to stresses of waterlogging, water‐deficit, or saline conditions (NaCl or CaCl₂). In soil culture in the greenhouse, tomato plants subjected to waterlogging developed epinasty and chlorosis and had increased ethylene evolution and ammonium accumulation. The application of aminooxyacetic acid (AOA) ameliorated the symptoms and reduced ethylene evolution and ammonium accumulation. Tomato subjected to drought developed chlorosis and had enhanced ammonium accumulation, but no increased ethylene evolution was observed. The chlorotic and necrotic symptoms were observed for plants receiving NaCl or CaCl₂. Application of ammonium nutrition or water stress aggravated the development of toxic symptoms. Ammonium accumulation and ethylene evolution were enhanced with intact plants or excised seedlings under these stresses. Application of AOA through stems of excised seedlings suppressed the enhancement. ‘Heinz 1350’ receiving CaCl₂ accumulated more Ca⁺⁺ and had higher ethylene evolution than those receiving NaCl or the neglecta‐1 receiving CaCl₂. Neglecta‐1 accumulated more Na⁺ with the NaCl treatment and had higher ethylene evolution than ‘Heinz 1350’. The results indicate that environmental stresses stimulate ammonium accumulation and initiate ethylene evolution, which may function in development of stress induced symptoms.     

Lignite‐derived humic substances modulate pepper and soil‐biota growth under water deficit stress

Organic matter‐derived soil amendments containing humic substances (HS) have a functional role to improve plant growth and soil quality, but their response to water deficit stress is less reported, particularly in vegetable crops. This study assessed the impact of lignite‐derived HS on biota growth and evaluated their potential mitigative effects under water deficit stress in growth chamber and greenhouse environments. Bell pepper (Capsicum annuum L. cv. Revolution) plants were grown in sandy and clay soil previously mixed with lignite‐derived HS and subjected to four irrigation levels (20%, 40%, 60%, and 80%) based on soil water‐holding capacity. Plant growth traits, soil chemical properties, and microbial populations were measured and analyzed. HS increased plant root development and soil bacteria population in moderate and no stress conditions (60%, 80%). Physiologically, HS rapidly decreased leaf stomatal conductance and transpiration after imposing severe or mild stress (20%, 40%). The results indicate that HS transiently ameliorated plants exposed to water stress by reducing moisture loss. In addition, due to their capacity to improve plant root growth, soil nutrient cycling and microbial activity, application of HS might have long‐term benefits in agricultural systems.     

Exudation of organic anions by roots of cabbage,carrot, and potato as influenced by environmental factors and plant age

A previous study demonstrated that cabbage was P efficient compared to carrot and potato. However, calculating plant P uptake by a mechanistic simulation model based on P transport by diffusion and mass flow, P uptake of roots according to the Michaelis‐Menten kinetics, and morphological root characteristics including root hairs, revealed that these parameters could explain only 2/5 of the total P uptake of cabbage, but 4/5 of that of carrot and potato (Dechassa et al., 2003). Therefore, it was hypothesized that a higher root exudation of organic anions may enhance P mobilization and hence P uptake of cabbage. The objective of this research was to determine root exudation of organic anions by the three species, and to investigate the influence of plant age and dark/light period on organic‐anion exudation by cabbage. Experiments were conducted in a growth chamber in nutrient solution with or without P. Organic anions were determined in root exudates and in root tissue. With cabbage and potato, P deficiency induced exudation of citrate and succinate, respectively. Citrate‐exudation rate of P‐deficient cabbage plants was correlated with accumulation of citrate in root tissue. In contrast, high succinate‐exudation rates in potato were not correlated with an increased concentration in root tissue. For carrot, no change was observed in the exudation of any of the organic anions in response to P deficiency. The results also showed that succinate‐ and citrate‐exudation rates of cabbage roots increased with increased plant age. There was also a significant increase in exudation rates of organic anions of cabbage roots during the light period of the day. It was concluded that cabbage had the ability to exude large amounts of citrate in response to P deficiency by which it can additionally enhance its P‐uptake efficiency, whereas carrot and potato showed little evidence of possessing such a mechanism.     

Water stress and mycorrhizal isolate effects on growth and nutrient acquisition of wheat

Arbuscular mycorrhizal (AM) colonized plants often have greater tolerance to drought than nonmycorrhizal (nonAM) plants. Wheat (Triticum durum Desf.), whose roots were colonized with Glomus mosseae (Gms) and G. monosporum (Gmn), were grown in a greenhouse to determine effects of water stress (WS) on shoot and root dry matter (DM), root length (RL), and shoot phosphorus (P), zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe) concentrations and contents. Mycorrhizal colonization was higher in well‐watered (nonWS) plants colonized with both AM isolates than WS plants, and Gms had greater colonization than Gmn under both soil moisture conditions. Shoot and root DM were higher in AM than in nonAM plants irrespective of soil moisture, and Gms plants had higher shoot but not root DM than Gmn plants grown under either soil moisture condition. Total RL of AM plants was greater than nonAM plants, but was consistently lower for plants grown with WS than with nonWS. The AM plants had similar shoot P and Mn concentrations as nonAM plants, but contents were higher in AM than in nonAM plants. The AM plants had higher shoot Zn, Cu, and Fe concentrations and contents than nonAM plants. The Gms plants grown under nonWS generally had higher nutrient contents than Gmn plants, but nutrient contents were similar for both Gms and Gmn plants grown under WS. The results demonstrated a positive relationship between enhanced growth and AM root colonization for plants grown under nonWS and WS.     

Interactions between drought stress and vesicular-arbuscular mycorrhiza on the growth of Faidherbia albida (syn. Acacia albida) and Acacia nilotica in sterile and non-sterile soils

Summary Faidherbia albida (syn. Acacia albida) (Del.) A. Chev. and Acacia nilotica (L.) Willd. were grown for 18 weeks in sterile and non-sterile soils inoculated with Glomus clarum (Nicolson and Schenck). During this period, drought stress was imposed for the last 10 (F. albida) or 12 weeks (A. nilotica) at 2-week intervals. A greater number of leaves abscissed in drought-stressed mycorrhizal plants of A. nilotica than drought-stressed non-mycorrhizal and unstressed plants. In F. albida, the number of abscissed leaves was few and similar for all treatments. At the end of the drought stress, inoculation with vesicular-arbuscular mycorrhizal (VAM) fungi in sterile soil increased the plant biomass of the two tree species compared to the control plants. In non-sterile soil, the mycorrhizal growth response of introduced G. clarum equalled the effect of indigenous VAM fungi. There were significant interactions between the mycorrhizal and drought stress treatments and between the mycorrhizal and soil treatments for plant biomass and P uptake in F. albida. The absence of these interactions except for that between the mycorrhizal and soil treatments in A. nilotica indicates that the increased plant biomass and nutrient uptake cannot be attributed directly to a mycorrhizal contribution to drought tolerance. F. albida tolerated the drought stress by producing long tap roots and similar weights of dry matter in shoots and roots. Whereas A. nilotica tolerated the drought stress by developing larger root systems able to explore a greater volume of soil, in addition to leaf abscission, for a favourable internal water status. The introduction of G. clarum increased nodulation by A. nilotica under unstressed conditions, but at the expense of a reduced P uptake in sterile soil.     

磷与水分互作的根土界面效应及其高效利用机制研究进展

【目的】磷与水分利用率低是制约作物生产的重要因子。磷必须在水分的作用下通过根土界面才能被作物吸收利用,磷和水分在根土界面的互作效应是影响其高效利用的关键环节。本文以根际为核心,重点综述了磷与水分在根土界面的互作机制,并剖析了通过强化根土界面磷与水分的协同,提高农田水肥资源利用效率的根际调控途径。[主要进展]根系的形态和生理变化深刻影响磷和水分的有效性,而根系生长和根际过程依赖于植物的营养和水分供应状况,作物根层适宜的水分和养分供应水平能最大化根系和根际过程的效率,从而促进作物对磷与水资源的高效利用。作物根系除了能对根层土壤中磷和水分的系统供应做出响应外,也对局部磷和水分的变化产生形态和生理上的反应。根系响应磷和水分的表型可塑性与植物激素的调控作用密切相关。ABA、乙烯、NO均参与磷和水分互作的调控过程,质外体pH在调控植物抵抗水分胁迫过程中具有重要作用,并与植物的营养状况密切相关。[展望]深入理解根土界面水与磷互作的协同过程及其调控机制是提高集约化作物体系水分和磷利用效率的关键。未来的研究方向与重点包括:进一步揭示磷和水分互作与激素信号途径之间的关系,探明农田生态系统中磷与水分互作的根土界面效应及其高效利用的协同机制,建立不同种植条件下水肥资源高效利用的根际调控途径,为通过根系、根际的定向调控,发挥其生物学潜力,提高集约化农田水肥资源的利用效率提供科学依据。