Growth and phosphorus uptake of maize cultivated alone,in mixed culture with other crops or after incorporation of their residues

Intercropping or rotating of P‐efficient crop species which mobilize sparingly soluble P by their root exudates can have beneficial effects on growth and P uptake of P‐inefficient species. We aimed at studying the effect of intercropping or incorporating of crop residues of P‐efficient crops on the components of maize P‐uptake, i.e. the root‐system size and P influx (P‐uptake rate per unit root length). This was studied in 3 pot experiments in a low‐P sandy soil. In the first experiment, maize was intercropped with white lupine, sugar beet or oilseed rape, and with groundnut in the second experiment. In the third experiment, maize was grown after incorporating the crop residues of white lupine, sugar beet or oilseed rape. Maize growth and yield was strongly inhibited when intercropped with white lupine, sugar beet or oilseed rape, probably because of competition for nutrients. But with groundnut as the accompanying species, maize yield was increased by a factor of 3, mainly because of an enhanced P influx. Crop residues of oilseed rape and sugar beet increased the yield of maize by factors 2 and 1.6, respectively, because of a 3 and 2 times higher P uptake as compared to maize grown after maize without incorporation of crop residue. The reason for the higher maize P‐uptake after oilseed rape was an 11 times higher P influx as compared to maize without crop residues, and after sugar beet residues because of an enhanced root growth and a 4 times higher P influx. Lupine residues did not improve maize growth, mainly because of a low P influx, which was even less than that of maize grown without crop residues. The soil solution P concentration and calcium acetate lactate‐extractable P (CAL P) measured in this study did not reflect the P availability as indicated by the plants (P uptake, P influx). This indicates that other mechanisms such as P mobilization in the rhizosphere by root exudates or cell‐wall components were responsible for the increased P availability. These mechanisms need further investigation.     

Potassium efficiency mechanisms of wheat,barley, and sugar beet grown on a K fixing soil under controlled conditions

Plant species differ in their potassium (K) efficiency, but the mechanisms are not clearly documented and understood. Therefore, K efficiency of spring wheat, spring barley, and sugar beet was studied under controlled conditions on a K fixing sandy clay loam. The effect of four K concentrations in soil solution ranging from low (5 and 20 μM K) to high (2.65 and 10 mM K) on plant growth and K uptake was investigated at 3 harvest dates (14, 21, and 31 days after sowing). The following parameters were determined: shoot dry matter (DM), K concentration in shoot dry matter, root length (RL), root length/shoot weight ratio (RSR), shoot growth rate/average root length ratio (GR_s/aRL), K influx, and soil solution K concentrations. Wheat proved to have a higher agronomic K efficiency than barley and sugar beet, indicated by a greater relative yield under K‐deficient conditions. As compared to both cereals, sugar beet was characterized by higher K concentrations in the shoot dry matter, only 30—50 % of the root length, 15—30 % of the RSR and a 3 to 6 times higher GR_s/aRL. This means that the shoot of sugar beet had a 3 to 6 times higher K demand per unit root length. Even at low K concentrations in the soil solution, sugar beet had a 7 to 10 times higher K influx than the cereals, indicating that sugar beet was more effective in removing low available soil K. Wheat and barley were characterized by slow shoot growth, low internal K requirement, i.e. high K utilization efficiency, and high RSR, resulting in a low K demand per unit root length. At low soil K concentrations, both cereals increased K influx with age, an indication of adaptation to K deficiency. The mechanism of this adaptation merits closer investigation. Model calculations were performed to estimate the K concentration difference between the bulk soil and the root surface (ΔC_L) needed to drive the measured K influx. For the two cereals, the calculated ΔC_L was smaller than the K concentration in the soil solution, but for sugar beet, ΔC_L was up to seven times higher. This indicates that sugar beet was able to mobilize K in the rhizosphere, but the mechanisms responsible for this mobilization remain to be studied.     

田间矿化水灌溉下小麦和甜菜的离子区隔化

通过田间灌溉试验,研究了矿化水灌溉下小麦和甜菜对离子的选择吸收及其区隔化.随着灌溉水中NaCl含量的增加,小麦茎、鞘、叶、颖的离子吸收的选择系数SK,Na逐渐降低,而根和籽粒的SK, Na逐渐增加.小麦和甜菜各器官的离子吸收的选择系数SCl、Na都随灌溉水中NaCl含量的增加而逐渐降低.小麦地上部各器官的SK, Na;SCl, Na都大于根;而甜菜叶的SK, Na大于根, SCl , Na在二者之中的差异不大,由于K+的再转移和分配,甜菜枯叶的Na/K大于叶.小麦和甜菜对离子的选择吸收和运输使Na 和Cl主要分布于对生长和产量影响最小的部分,即小麦的茎和鞘,甜菜的枯叶.     

Manganese efficiency and maganese‐uptake kinetics of raya (Brassica juncea), wheat (Triticum aestivum), and oat (Avena sativa) grown in nutrient solution and soil

Manganese (Mn) deficiency is reported worldwide and often decreases crop yield. However, plant species differ in their susceptibility to Mn deficiency. Poaceae are often inefficient, whereas Brassicaceae seem to be efficient in Mn uptake. The objective of this paper was to determine the relevance of Mn‐uptake kinetics, root‐system size, and Mn mobilization for differences in Mn efficiency of wheat, oat, and raya. To determine Mn‐uptake kinetics, wheat (Triticum aestivum L. cv. PBW 343), raya (Brassica juncea L. cv. RLM 619), and oat (Avena sativa L. cv. Aragon) were grown in a growth chamber together in complete nutrient solution having an average Mn concentration of 90, 180, 360, 910, and 2270 nmol L^–1. For determining Mn efficiency of the three species in soil, the plants were grown for 22 d in pots filled with 3 kg of a loamy soil low in Mn availability (pH (CaCl₂) 7.4; DTPA‐extractable Mn: 3.5 mg (kg soil)^–1). The soil was fertilized with 0, 1, 2, 4, and 8 mmol Mn (kg soil)^–1 resulting in Mn soil‐solution concentrations ranging from 40 to 90 nmol L^–1, hence lower than in the solution experiment. In order to determine Mn soil‐solution concentration close to the root surface, the root length density was increased by growing two plants of raya and four plants of wheat in only 250 mL soil columns for 25 d. In solution culture at high concentrations, raya showed a higher Mn uptake compared to wheat and oat. However, at low Mn supply, all three species were comparably Mn‐efficient, i.e., plant growth was similar, and also the uptake was similar. In soil, the highest yield was achieved for raya in the unfertilized treatment whereas the Poaceae needed at least a fertilization of 1 mmol Mn (kg soil)^–1. The Poaceae showed a yield reduction of about 40% in the unfertilized treatment. Manganese concentration in the shoot dry weight was always higher in raya than in wheat or oat. This was due to a higher Mn uptake whereas relative shoot‐growth rate and root‐to‐shoot ratio were similar among the species. The higher Mn uptake of raya in soil was in contradiction to the comparable Mn‐uptake kinetics of the three crops at low Mn concentration in solution. This points to plant differences in their ability to affect Mn availability in the rhizosphere. In the bulk soil, all the crops decreased Mn solution concentration, but this effect was somewhat less for raya. But in the rhizosphere, raya increased Mn soil‐solution concentration significantly to 58 nmol L^–1, as compared to 37 nmol L^–1 of the unplanted control soil. In contrast, wheat showed a Mn solution concentration of 25 nmol L^–1 which was not significantly different from the control. The results indicate that differences in Mn efficiency among the crops studied are related to their ability to affect the solubility of Mn in the rhizosphere.     

Phosphatversorgung von Sommerweizen (Triticum aestivum L.) in Mischkultur mit Weißer Lupine (Lupinus albus L.)

Phosphorus nutrition of spring wheat (Triticum aestivum L.) in mixed culture with white lupin (Lupinus albus L.). Spring wheat (Triticum aestivum L. ?Schirokko”?) and white lupin (Lupinus albus L.) were grown in mixed culture in Mitscherlich pots with 20 kg of soil in a green house. The soil used was a B_t of a Parabraunerde-Pseudogley from loess low in available P and limed from pH 4.6 to pH 6.5. Phosphorus was added as phosphate rock. In half of the pots cylinders of stainless steel screen prevented intertwining of the roots of the plant species. Independent of P addition, white lupin had higher dry matter production and P uptake than wheat, even although wheat had thinner roots and higher root densities than lupin, factors which favour the utilization of soil and fertilizer P. The higher P efficiency of white lupin was due to higher P uptake rates per unit root length mainly through mobilization of P especially in the rhizosphere of the proteoid roots. When the roots of the two species were allowed to intertwine, shoot dry matter production of wheat was nearly double because of improved tillering. Higher P concentrations and a more than 2-fold higher P uptake indicated that the increase in dry matter production of wheat was due to improved P nutrition. Nitrogen concentrations, however, remained unaffected at sufficient levels. An increased P uptake rate per unit root length was responsible for the better utilization of P by wheat, rather than the increase in total root length, due to the extended root volume. White lupin was able to mobilize P in the rhizosphere in excess of its own requirements. Thus mobilized P may be available to less P-efficient plants grown in mixed culture.     

The effects of potassium fertilization on water‐use efficiency in crop plants

The supplies of water and nitrogen to a plant during its critical stages of growth are the main factors that define crop yield. A crop experiences irregular water deficits during its life cycle in rain‐fed agriculture. An effective anti‐stress‐oriented approach therefore ought to focus on increasing the units of water productivity. The main objective of this conceptual review is to confirm that adequate K management can be used as an important tool to alleviate the negative effects of water deficit on plant growth, yield‐component formation, and yield. The French and Schultz approach of using the water‐limited yield (WLY) was modified in this review into a graphical form and was used to discriminate between yield fractions that depended on the volume of transpired water from those that were induced by K fertilizer. By using this method, it was possible to demonstrate the extent of several crop (winter wheat, spring triticale, maize, sugar beet) responses to the K supply. Yield increases resulting from K application mostly appeared under conditions of mild water deficit. As described for sugar beet, finding the critical period of crop K sensitivity is a decisive step in understanding its impact on water‐use efficiency. It has been shown that an insufficient supply of K during crucial stages in the yield formation of cereals (wheat, spring triticale), maize, and sugar beet coincides with a depressed development in the yield components. The application of K fertilizer to plants is a simple agronomic practice used to increase crop tolerance to a temporary water shortage. It may be that the improvement of a plant's access to K during mild water‐deficiency stress will increase water uptake by the root cells, which in turn increases their osmotic potential and thereby allows extension growth. This growth in turn promotes access to other mineral elements (including nitrogen) and water, which favor plant growth and yield.     

The acquisition of phosphate by higher plants: Effect of carboxylate release by the roots. A critical review.

Phosphorus is one of the most limiting macronutrients for plant productivity in agriculture worldwide. The main reasons are the limited rock phosphate reserves and the high affinity of phosphate (P) to the soil solid phase, restricting the P availability to the plant roots. Plants can adapt to soils low in available P by changing morphological or/and physiological root features. Morphological changes include the formation of longer root hairs and a higher root : shoot ratio both parameters increasing the root surface which provides the shoot with P. This may be successful if the P availability in soil, i.e., the P concentration of the soil solution is not extremely low (> 1–2 µM P). If the P concentration of the soil solution is lower, the diffusive flux to the root surface will be very low and may not satisfy the P demand of the shoots. Under these conditions plants have developed strategies to increase the rhizosphere soil solution concentration by secreting mobilizing agents. The most effective way of P mobilization is the release of di‐ and tricarboxylic acid anions, especially oxalate and citrate. Citrate can accumulate in the rhizosphere up to concentrations up to 80 µmol g^?1 soil. Cluster root formation is an efficient way of carboxylate accumulation in the cluster root rhizosphere improving P mobilization. Cluster roots strongly improve the acquisition of the mobilized P. Considering a single root, around 80–90% of the mobilized P diffuses away from the root. From the rhizosphere of cluster roots, most of the mobilized P is taken up by the cluster roots. Both, the strong accumulation of carboxylates in and the effective P uptake from the cluster‐root rhizosphere are the basis of the unique ability of P acquisition by cluster root‐forming plants. Plants that do not form cluster roots, e.g., red clover, can also accumulate carboxylates in the rhizosphere. Red clover accumulates high quantities of citrate in the rhizosphere soil. Model calculations show that the release of citrate by red clover roots and its accumulation in the rhizosphere strongly improve P acquisition by this plant species in various soils. Similar results are obtained with alfalfa. In sugar beet, oxalate release can strongly contribute to P acquisition. In summary, P acquisition can be strongly improved by the release of carboxylates and should be taken as a challenge for basic and applied research.     

Nitrogen supply to cereals and sugar beet by mass flow and diffusion on a silty loam soil

In a four-year field study the nitrogen supply by mass flow and diffusion to cereals (spring wheat, winter barley, winter wheat) and sugar beet was investigated on a silty loam soil. The rates of water withdrawal, N mass flow and N diffusion were determined as a function of soil depth and time. The contribution to the N supply to roots by mass flow was 15–33% and mainly confined to the topsoil layer. The N supply by diffusion plays with 67–85% the dominant role, particularly in deeper rootzone layers. During periods of high N uptake, the N inflow (per unit root length and time) ranges between 0.26–2.07 μmol/(m · d) at various rootzone layers for cereal, and between 3.80–8.98 μmol/(m · d) for sugar beet, respectively. As a consequence of the high proportion of diffusion supply, at harvest the whole rootzone was largely depleted of nitrate. Thus, nitrate leaching losses during winter were small, the average nitrate concentration of the yearly groundwater recharge being only 7.9 mg N/l. Additionally, some results on supply of K, Ca, Mg and Cl for spring wheat and sugar beet are given. Diffusion supply prevails for K, and in the case of sugar beet for Mg and Cl also. Mass flow of Ca exceeded uptake considerably.     

Impact of water availability on root growth of sugar beet varieties

On average, sugar beet yield in the UK is reduced by 10% due to water limitation. The root system of a plant is responsible for water uptake and hence an extensive root system is crucial to mitigate drought stress. There might be varietal differences when it comes to plant root system architecture but so far none have been reported in sugar beet. This study shows the results of 2 years of field experiments, examining the rooting patterns and overall plant growth of sugar beet under both rainfed and irrigated conditions. In the first year, three varieties were assessed, and in the second year, five varieties. No significant yield differences were found between the rainfed and irrigated treatments, which is likely due to the applied drought stress only being mild in both years. There were, however, significant varietal differences in plant growth and rooting patterns in rainfed plants which were most distinct when plants were subjected to mild drought stress. Varietal differences observed might indicate the possibility of breeding for certain root traits to mitigate drought stress in sugar beet in the future.     

集约化互作体系植物根系高效获取土壤养分的策略与机制

【目的】植物根系的形态与生理变化是植物从土壤中高效获取养分资源的重要机制,由相同物种或不同物种组成的互作体系中植物根系对养分的吸收利用受相邻植物竞争的强烈影响,阐明互作体系不同竞争条件下植物根系获取养分的策略并揭示其作用机制,这是基于根系觅食行为探讨养分高效利用的根际调控途径与技术措施的重要理论基础。主要进展根系属性的互补性有利于降低根系间对养分的竞争。根系构型的互补性,例如深根系与浅根系植物互作,促进个体植株对土壤剖面不同深度养分的吸收利用;由根系可塑性介导的水平方向上根系空间分布的互补性,提高了植物根系对同一土层不同空间位点土壤养分的挖掘;个体植株根系形态属性与相邻植物根际生理过程的互补性促进根系对不同形态养分的利用。互作体系根系获取养分的策略具有高度互补性,这有助于提高整个作物系统的养分利用效率,进而提高生产力。根系空间生态位的分离 (包括垂直与水平方向) 以及根际生物化学特征生态位的分离,是驱动互作体系根系高效获取养分资源的主要机制。合理的根层调控可以提高植物根系挖掘土壤养分的能力;优化互作体系物种的搭配能充分发挥根的互作效能,提高养分利用的生物潜力。问题与展望今后应进一步针对集约化高投入作物体系,通过管理根层养分供应和物种间的互作效应,强化根际养分信号的调控作用,调节根系形态与生理特性,降低种间竞争,增强种间互利,以最大化根系和根际的生物学潜力,提高养分利用效率和作物产量,为实现以节肥增效为核心的可持续集约化作物生产提供重要的调控策略与途径。     

Effect of root morphological traits on zinc efficiency in Iranian bread wheat genotypes

Zinc (Zn) has a vast number of functions in plant metabolism, the lack of which had dramatic effects on growth and yield of plants. Plants have morphological and biochemical responses to enhance mineral solubility in the soil and facilitate uptake, such as root plasticity, secretion processes and symbioses. Root architecture modification is an important plant response to nutrient availability. The aim of this study was to identify root morphological reactions to Zn efficiency in Iranian bread wheat genotypes. Soil and solution cultures were used to survey Zn efficiency. In soil culture, six and seven genotypes with high and low Zn contents were selected among 110 Iranian bread wheat genotypes, respectively. The solution culture experiments were set up in a completely randomized block design and plants fed with Johnson’s grass solution. All traits were assessed at 30 and 60 DAPs (days after planting). Our results showed a significant difference between two groups of efficient and inefficient genotypes only at 60 DAP, and Zn-efficient genotypes showed 1.63-, 1.50-, 1.69- and 1.92-fold increases in root diameter, surface area density, shoot and root dry weight, respectively, compared to inefficient genotypes. In contrast, Zn-inefficient genotypes had 1.20- and 2.62-fold more root length and fineness, respectively, than efficient genotypes. The positive significant correlations were observed between shoot and Zn uptake as well as root dry weight and Zn uptake at both stages. Furthermore, shoot and root dry weight showed a significant correlation with root fineness, diameter and surface area density at both stages. The path analysis showed indirect effects on Zn uptake through root traits. Our results showed that roots have a major role in Zn efficiency. Therefore, the better growth and greater Zn uptake in efficient genotypes, compared to inefficient ones, can be attributed to greater root diameter and surface area density, and lower root fineness in these genotypes.     

Efficiency of Potassium Fertilization and Salicylic Acid on Yield and Nutrient Accumulation of Sugar Beet Grown on Saline Soil

Rising soil salinity has been a major problem in the soils of Egypt in recent decades. Potassium fertilization and salicylic acid (SA) play an important role in promoting plants to tolerate salt stress and increased the yield of sugar beet crop. A field experiment on sugar beet (Beta vulgaris L.) grown on saline soil was carried out during 2014 growing season in Port Said Governorate, Egypt, to study the effect of potassium fertilization of the soil at applications of 0, 100, 150, and 200 kg potassium (K) ha^?1 and foliar spray of SA by solution of 1000 mg L^?1, twice (1200 L ha^?1 each time) on yield and nutrient uptake. Application of 200 kg K ha^?1 in combination with salicylic foliar spray gave the highest root length, root diameter, shoot and root yield, sucrose, juice purity percentage, gross sugar yield, and white possible extractable sugar, nitrogen (N), phosphorus (P), and potassium (K) content, and uptake of sugar beet. The highest increase in sucrose (20%) as well as white possible extractable sugar (184%) was obtained by 200 kg K ha^?1 in combination with salicylic foliar spray compared with untreated soil with potassium fertilization and without salicylic foliar spray.     

灌溉制度对膜下滴灌甜菜产量及水分利用效率的影响

为制定新疆合理的甜菜膜下滴灌制度,设置3个灌水次数(8、9和10次)和2个灌水定额(45和60mm)两因素全组合试验,于2016—2017年在新疆玛纳斯县农科院甜菜改良中心开展田间试验。结果表明,灌水次数增加时甜菜叶面积指数与产量增加,含糖率降低,对甜菜的水分利用效率、耗水量无明显影响(P0.05),甜菜叶绿素值随灌水次数与定额增加呈下降趋势;在灌水次数与定额交互作用下,灌水8次时由于土壤相对含水率低于50%,甜菜会减产;当灌水9次,灌水定额为45 mm时,增加15 mm灌水定额土壤相对含水率达50%以上,此时甜菜增产7.4%～7.7%,糖产增加9.4%～9.7%;而继续增加灌水次数时,会导致甜菜含糖率降低而降低糖产。因此针对新疆膜下滴灌甜菜以60 mm灌水定额灌水9次为宜,可获得高产与糖产,较传统新疆膜下滴灌甜菜制度节水10%。该研究对指导新疆膜下滴灌甜菜灌溉制度具有一定意义。     

Assessment of Arsenic and Selenium Concentration with Chlorophyll Contents of Sugar Beet (Beta vulgaris var.saccharifera) and Wheat (Triticum aestivum) Exposed to Municipal Sewage Sludge Doses

The present study was conducted to assess the suitability of sewage sludge amendment in soil for Beta vulgaris var. saccharifera (sugar beet) and Triticum aestivum (wheat) by evaluating the arsenic and selenium accumulation and physiological responses of plants grown at 10%, 25%, and 50% sewage sludge amendment rate. Sewage sludge amendment was modified by the physicochemical properties of soil, thus increasing the availability of heavy metals in the soil and consequently with higher accumulation in plant parts. The chlorophyll contents increased after the sewage sludge treatments except for 50%. The sewage sludge amendment led to a significant increase in arsenic and selenium concentrations of the soil. The heavy metal accumulation in the soil after the treatments did not exceed the limits for the land application of sewage sludge recommended by the US Environmental Protection Agency. The increased concentration of heavy metals in the soil due to the sewage sludge amendment led to increases in heavy metal uptake in the leaves and root concentrations of arsenic and selenium in plants as compared to those grown on unamended soil. Accumulation was more in roots than shoots and leaves for most of the heavy metals. Concentrations of arsenic and selenium were more than the permissible limits of national standards in the edible portion of sugar beet and wheat grown on different sewage sludge amendments ratios. The study concludes that the sewage sludge amendment in the soil for growing sugar beet and wheat may not be a good option due to risk of contamination of arsenic and selenium.     

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.     

Phosphorus Influx and Root‐Shoot Relations as Indicators of Phosphorus Efficiency of Different Crops

Abstract

The large variation in phosphorus acquisition efficiency of different crops provides opportunities for screening crop species that perform well on low phosphorus (P) soil. To explain the differences in P efficiency of winter maize (Zea mays L.), wheat (Triticum aestivum L.), and chickpea (Cicer arietinum L.), a green house pot experiment was conducted by using P‐deficient Typic ustochrept loamy sand soil (0.5 M NaHCO₃‐extractable P 4.9 mg kg^?1, pH 7.5, and organic carbon 2.7 g kg^?1) treated with 0, 30, and 60 mg P kg^?1 soil. Under P deficiency conditions, winter maize produced 76% of its maximum shoot dry weight (SDW) with 0.2% P in shoot, whereas chickpea and wheat produced about 30% of their maximum SDW with more than 0.25% P in shoot. Root length (RL) of winter maize, wheat, and chickpea were 83, 48, and 19% of their maximum RL, respectively. Considering relative shoot yield as a measure of efficiency, winter maize was more P efficient than wheat and chickpea. Winter maize had lower RL/SDW ratio than that of wheat, but it was more P efficient because it could maintain 2.2 times higher P influx even under P deficiency conditions. In addition, winter maize had low internal P requirement and 3.3 times higher shoot demand (i.e., higher amount of shoot produced per cm of root per second). Even though chickpea had 1.2 times higher P influx than winter maize, it was less P efficient because of few roots (i.e., less RL per unit SDW). Nutrient uptake model (NST 3.0) calculations satisfactorily predicted P influxes by all the three crops under sufficient P supply conditions (C_Li 48 µM), and the calculated values of P influx were 81–99% of the measured values. However, in no‐P treatment (C_Li 3.9 µM), under prediction of measured P influx indicated the importance of root exudates and/or mycorrhizae that increase P solubility in the rhizosphere. Sensitivity analysis showed that in low P soils, the initial soil solution P concentration (C_Li) was the most sensitive factor controlling P influx in all the three crops.     

Growth and rhizosphere P pools of legume–wheat rotations at low P supply

Legume pre-crops may increase P uptake of the following wheat, but the mechanisms behind this effect are unclear. A rotation study was carried out to assess the concentrations of rhizosphere P pools of three grain legumes and wheat (phase 1) and their effects on P uptake and P pools in the rhizosphere of the following wheat (phase 2). Faba bean, chickpea, white lupin and wheat were grown for 10 weeks in a loamy sand soil with low P availability. The following wheat was grown in the pre-crop soil with and without addition of pre-crop residues. Among the pre-crops, white lupin had the strongest effect on the P pools; it depleted the labile P pools, resin P and NaHCO₃-Pi and also the less labile P pools, NaOH-Pi and residual P; whereas the concentration of NaHCO₃-Po was higher than that in the rhizosphere of the other pre-crops. White lupin had a smaller biomass compared to faba bean which depleted the P pools to a lesser extent. Phosphorus uptake of the following wheat was greatest in white lupin pre-crop soil. Chickpea increased P uptake of the following wheat when residues were added. In the presence of residues, wheat after legumes depleted labile P pools to a greater extent than wheat after wheat, but this coincided with greater P uptake only in wheat after chickpea and white lupin, which may be explained by the small root biomass of wheat after faba bean. The results show that the greater P uptake of the following wheat induced by pre-crops may be due to two mechanisms: P mobilisation (white lupin) or P addition with legume residues (chickpea). This study further showed that P uptake by a crop is only partly a function of the depletion of P in the rhizosphere; another important factor is the ability to exploit a large soil volume.     

作物对盐分的吸收及其盐害的预测预报

通过温室和田间试验,研究小麦和甜菜在盐胁迫下的生长及其对盐分的吸收。结果表明,小麦耐热略低于甜菜,Ｎａ＾＋抑制小麦和甜菜对Ｋ＾＋和Ｃａ＾２＋的吸收,小麦和甜菜的相对干物质重与土壤含盐量的关系符合Ｍａａｓ－Ｈｏｆｆｍａｎ模型,小麦和甜菜叶Ｎａ＾＋含量与土壤含盐量呈显著正相关,且与干物质重的关系也符合Ｍａａｓ－Ｈｏｆｆｍａｎ模型,文中提出了利用作物叶的Ｎａ＾＋含量与相对干物质重之间的Ｍａａｓ－Ｈｏｆｆ     

植物对不同形态磷响应特征研究进展

磷是植物生长发育所必需的大量营养元素之一,参与植物体内许多重要化合物的合成与代谢。土壤中磷素具有多种形态,且不同形态磷的植物有效性差异较大;植物在不同形态磷环境下,体内会形成相应的适应性机制。植物吸收积累磷通常与根形态、根系分泌物、体内磷转运等因素有关,受到特异基因表达的调控。了解植物对磷的吸收积累特性是筛选磷高效植物或磷富集植物的前提,也是充分利用土壤磷素资源、修复磷过剩环境的关键。根据国内外研究现状,本文从磷素吸收积累、根系形态特征、磷酸酶与植酸酶的变化以及磷营养高效的分子机制,综述了植物对不同形态磷的响应特征,并对未来该领域的研究进行了展望。     

小麦对钾高效吸收的根系形态学和生理学特征

用 6个小麦品种作为试验材料 ,研究了钾效率不同小麦的根系形态学和生理学特征 ,以及对K+吸收的动力学参数。结果表明 ,高效吸收钾的品种根系长、半径小、吸收面积大、Km小、Imax大。低效低响型品种京核 1号的最小临界浓度值 (Cmin)小。根系形态学和生理学特征可以作为筛选高效吸钾小麦品种的参考指标。K+吸收的动力学参数可以作为钾高效吸收和低响型小麦品种的筛选指标 ,最好的筛选指标是将根系形态和生理特性相结合。根系分泌H+的能力与K+的吸收无明显相关。