根际微生物群落介导植物磷胁迫应答与免疫调控的整合机制

植物与土壤微生物的长期互作过程中,逐渐演化形成了植物-微生物相互适应的协同调控机制。植物种类和根系分泌物可以影响根际微生物的群落结构,而根际微生物群落反过来也可以影响植物对土壤环境中生物和非生物胁迫的响应。植物磷饥饿(耐低磷)响应机制和抗病(免疫)机制研究在农业生产上都具有十分重要的意义。近年来的研究表明,植物根际微生物可以介导植物对营养物质识别(饥饿响应)和病原防御系统(免疫)分子机制的整合调控。本文综述了本领域研究的最新进展,详细解析了植物体内磷胁迫调控与免疫调控两个重要网络在根际微生物群落影响下发生的整合调控,探讨了植物体内分子应答与根际生态的互作机制,对开展作物耐低磷及抗病机制的研究和应用都具有重要意义。     

Rhizosphere microbiota assemblage associated with wild and cultivated soybeans grown in three types of soil suspensions

Soil microbial community composition is determined by the soil type and the plant species. By sequencing the V3-V4 region of the bacterial 16S rRNA gene amplicons, the current study assessed the bacterial community assemblage in rhizosphere and bulks soils of wild (Glycine soja) and cultivated (Glycine max) soybeans grown in the suspensions of three important soil types in China, including black, red and soda-saline-alkali soils. The alpha-diversity of the bacterial community in the rhizosphere was significantly higher than that of the bulk soils suggesting that bulk soil lacks plant nurturing effect under the current study conditions. Black and red soils were enriched with nitrifying and nitrogen-fixing bacteria but the soda-saline-alkali soil suspension had more denitrifying bacteria, which may reflect agronomic unsuitability of the latter. We also observed a high abundance of Bradyrhizobium and Pseudomonas, enriched cellulolytic bacteria, as well as a highly connected molecular ecological network in the G. soja rhizosphere soil. Taken all, the current study suggest that wild soybeans may have evolved to recruit beneficial microbes in its rhizosphere that can promote nutrients requisition, biostasis and disease-resistance, therefore ecologically more resilient than cultivated soybeans.     

不同磷水平下小麦蚕豆间作对根际有效磷及磷吸收的影响

【目的】探明不同磷水平下小麦–蚕豆间作对根际有效磷含量及作物磷吸收量的影响,提高磷肥利用率。【方法】2015—2016和2016—2017两季田间试验在云南农业大学试验基地耕作红壤上进行,供试小麦品种为云麦-52,蚕豆品种为玉溪大粒豆。设施P2O5 0 (P0)、45 (P45)和90 kg/hm^2 (P90)三个水平,和单作(M,包括小麦单作MW和蚕豆单作MF)和间作(I)两种种植模式。每季在小麦分蘖期、拔节期、抽穗期、灌浆期和成熟期,蚕豆分枝期、开花期、结荚期、籽粒膨大期、收获期采取根际土样测定有效磷含量。在小麦蚕豆收获期测定单、间作小麦、蚕豆产量,并测定作物地上部磷含量。计算土地当量比(LER)来衡量间作优势,并用磷肥农学利用率来反映磷肥的吸收效率。【结果】与单作相比,在P0、P45、P90水平下,2016年间作种植显著提高了小麦籽粒产量12.5%、21.7%和17.3%,2017年间作蚕豆产量较单作分别降低了16.8%、11.7%和8.2%。三个磷水平下,小麦–蚕豆间作具有产量优势,土地当量比(LER)为0.95~1.18。与常规施磷水平(P90)下的单作相比,小麦–蚕豆间作条件下,磷肥减施1/2 (P45)并未降低小麦和蚕豆产量。间作种植对小麦根际有效磷含量无显著影响(除2016年成熟期外),但2017年,在蚕豆分枝期、开花期、结荚期,间作则分别降低蚕豆根际有效磷含量20.8%、44.5%和18%。与P90单作相比,间作P45处理几乎不会降低小麦、蚕豆根际有效磷含量。小麦、蚕豆磷吸收量主要受磷水平的调控,种植模式对小麦和蚕豆磷的吸收量及磷肥农学利用率均没有影响。【结论】在本试验条件下,小麦–蚕豆间作提高了小麦籽粒产量,降低了蚕豆产量;间作种植主要是改变了蚕豆生育前期根际有效磷含量,但对作物的磷吸收量没有影响。小麦–蚕豆间作具有减施磷肥、维持作物产量和根际土壤有效磷的潜力。     

Phosphorus acquisition and wheat growth are influenced by shoot phosphorus status and soil phosphorus distribution in a split‐root system

Root proliferation and greater uptake per unit of root in the nutrient‐rich zones are often considered to be compensatory responses. This study aimed to examine the influence of plant phosphorus (P) status and P distribution in the root zone on root P acquisition and root and shoot growth of wheat (Triticum aestivum L.) in a split‐root soil culture. One compartment (A) was supplied with either 4 or 14 mg P (kg soil)^–1, whereas the adjoining compartment (B) had 4 mg P kg^–1 with a vertical high‐P strip (44 mg kg^–1) at 90–110 mm from the plant. Three weeks after growing in the split‐root system, plants with 4 mg P kg^–1 (low‐P plants) started to show stimulatory root growth in the high‐P strip. Two weeks later, root dry weight and length density in the high‐P strip were significantly greater for the low‐P plants than for the plants with 14 mg P (kg soil)^–1. However, after 8 weeks of growth in the split‐root system, the two P treatments of compartment A had similar root growth in the high‐P strip of compartment B. The study also showed that shoot P concentrations in the low‐P plants were 0.6–0.8 mg g^–1 compared with 1.7–1.9 mg g^–1 in the 14 mg P kg^–1 plants after 3 and 5 weeks of growth, but were similar (1.1–1.4 mg g^–1) between the two plants by week 8. The low‐P plants had lower root P concentration in both compartments than those with 14 mg P kg^–1 throughout the three harvests. The findings may indicate that root proliferation and P acquisition under heterogeneous conditions are influenced by shoot P status (internal) and soil P distribution (external). There were no differences in the total root and shoot dry weight between the two P treatments at weeks 3 and 5 because enhanced root growth and P uptake in the high‐P strip by the low‐P plants were compensated by reduced root growth elsewhere. In contrast, total plant growth and total root and shoot P contents were greater in the 14 mg P kg^–1 soil than in the low‐P soil at week 8. The two P treatments did not affect the ratio of root to shoot dry weight with time. The results suggest that root proliferation and greater P uptake in the P‐enriched zone may meet the demand for P by P‐deficient plants only for a limited period of time.     

Drying method effects on extractable phosphorus levels in plant tissue

Abstract

The level of soluble tissue phosphorus (PO₄‐P) may be correlated with the plant P nutritional status, but the amount extracted depends upon dry matter losses or the amount of enzymatic or heat—induced hydrolysis of organic P compounds during sample drying.

Alfalfa (Medieago sativa L) and sugarbeet (Beta vulgaris L) plant parts grown under low and high soil P conditions, were freeze‐dried or oven‐dried at 40, 56, 70, or 100 C. Total K, P, and 0.35 N acetic‐acid‐soluble P (measured as PO ‐P) were determined. Dry matter losses were 0, 6.5, 3.6, 5.5, and 4.9 percent for the respective drying methods. The total‐P values, once corrected for dry matter losses, were not affected by the drying methods. The corrected PO₄‐P values were 0.15, 0.17, 0.16, 0.16, and 0.19 percent, while the (PO₄‐P)/P values were 0.63, 0.69, 0.67, 0.68, and 0.78 for each of the respective drying methods.

The potential utility of extractable PO₄‐P in describing the plants’ P nutritional status will depend upon rigorous sampledrying techniques. Freeze‐drying was the most satisfactory method tested, since it resulted in the least dry‐matter loss and least organic P hydrolysis.     

Cadmium fractions in an acid sandy soil and Cd in soil solution as affected by plant growth

In a previous experiment, plants were able to immobilize or solubilize Cadmium (Cd) in a sandy acid soil enriched with 40 μmol Cd kg^–1, because Cd solution concentration was decreased by maize (Zea mays) and sunflower (Helianthus annuus), and increased by flax (Linum usitatissimum L. ssp. usitatissimum) and spinach (Spinacia oleracea). It is assumed that the equilibrium with Cd fractions in the soil solid phase and the chemical form of Cd in the soil solution were affected. In the present study, the effect of the four plant species mentioned above on Cd binding in soil was investigated by means of a fractionation of soil Cd with a sequential extraction of seven steps. The seven fractions of Cd are operationally defined by the extraction sequence that follows the order of increasing acidity with extractants of different complexing and redox properties. In the unplanted soil, Cd was predominantly present in the exchangeable Fraction I (F. I) and easily mobilizable Fraction II (F. II) (64%). Significant concentrations of Cd were found in F. III (occluded in Mn oxides; 22%) and F. IV (organically bound; 10%). Fractions V (occluded in poorly crystalline Fe oxides), F. VI (occluded in well crystallized Fe oxides), and F. VII (residual fraction) amounted to less than 5% of the total soil Cd concentration. The plants changed the binding of Cd in soil in a different manner. All plants decreased F. I, but F. II was increased by maize and spinach, decreased by flax or remained unaffected by sunflower. Fraction III was not affected by maize and flax, but decreased by sunflower and spinach, and F. IV was not affected by sunflower and spinach, but was increased by maize and flax. These changes of Cd fractions were not related to the changes the plants had caused in total Cd or Cd²⁺ concentration of the soil solution. These results show that plant species differ in how they affect Cd binding to the soil solid phase, but this effect is not related to how they affect Cd in soil solution. The mechanisms by which plants affect the relationship between the soil solid and liquid phase are still unclear.     

野生大豆根系形态对局部磷供应的响应及其对磷吸收的贡献

通过土柱试验模拟局部供磷,定量评价了磷局部供应对野生大豆根系形态参数的影响以及这些根形态参数对植株磷吸收的贡献.磷局部供应明显改变了野生大豆的根形态,使总根长增加了80.5％,比根长增加了32.6％,根表面积扩大了70.7％,根直径减小了27.6％,植株对磷的吸收增加了43.2％,地上干重增加了72.0％;在所有的根形态参数中,总根长、根表面积和比根长对野生大豆植株磷吸收具有较大贡献,其中尤以比根长对植株磷吸收贡献最大,即在根长增加的同时,根直径减小能够明显提高野大豆根系对磷的吸收.结果表明,野生大豆对局部磷供应表现出高度的根系形态可塑性,通过局部养分供应优化根系空间分布和定向调控根系生长能显著提高植物对异质性土壤磷资源的获取能力.     

施磷对麦/玉/豆套作体系土壤磷素变化的影响

小麦/玉米/大豆带状套作是四川省丘陵低山区主要旱地作物生产体系,了解该体系磷养分变化对优化磷肥管理和促进可持续生产有重要意义。本研究通过连续3年(2011—2013年)田间定位试验,设置P0、P1、P2、P3和P4共5个磷(P2O5)水平(玉米带分别为0 kg·hm-2、37.5 kg·hm-2、75 kg·hm-2、112.5 kg·hm-2、150 kg·hm-2,小麦-大豆带分别为0 kg·hm-2、45 kg·hm-2、90 kg·hm-2、135 kg·hm-2、180 kg·hm-2),探讨该体系中土壤全磷、速效磷、水溶性磷的变化规律和速效磷的年际变化。结果表明:在麦/玉/豆套作体系中施磷165 kg(P2O5)·hm-2(玉米带75 kg·hm-2,小麦-大豆带90 kg·hm-2),可以满足体系作物对磷的需求,基本达到磷的表观平衡,维持土壤速效磷含量在20 mg·kg-1左右。3年后5个磷水平下体系耕层土壤(0~20 cm)全磷变化量分别为-0.024 g·kg-1·a-1、-0.016 g·kg-1·a-1、0.016 g·kg-1·a-1、0.11 g·kg-1·a-1、0.15 g·kg-1·a-1,速效磷变化量依次为-1.2 mg·kg-1·a-1、-0.9 mg·kg-1·a-1、0.2 mg·kg-1·a-1、2.0 mg·kg-1·a-1和2.7 mg·kg-1·a-1。通过线性平台函数的模拟,该体系中玉米、小麦、大豆产量的土壤速效磷临界值分别为16.5 mg·kg-1、12.6 mg·kg-1和8.8 mg·kg-1。当土壤全磷含量低于0.55 g·kg-1时,土壤全磷每增加0.1 g·kg-1,土壤速效磷增加1.70 mg·kg-1;当土壤全磷大于0.55 g·kg-1,全磷每增加0.1 g·kg-1,土壤速效磷增加6.49 mg·kg-1。当土壤速效磷含量在40 mg·kg-1以下时,速效磷每增加1 mg·kg-1,水溶性磷增加0.017 mg·kg-1。综上,在麦/玉/豆体系磷肥管理中应该维持土壤全磷含量低于0.55 g·kg-1,同时速效磷含量在20 mg·kg-1左右,这样既可以保证作物产量和系统生产力又不会产生较大的环境威胁。     

Vegetative and reproductive performance of maize to nitrogen and phosphorus fertilizers in Plinthic Acrisol and Gleyic Plinthic Acrisol

Soil specific maize response to N and P may provide guidelines for improving nutrient management. Three replicates of N and P fertilizer combinations (N₀P₀, N₀P₉₀, N₁₂₀P₀, and N₁₂₀P₉₀) were arranged in randomized complete block design on Plinthic Acrisol (PA) and Gleyic Plinthic Acrisol (GPA) in Ghana. Treatment effects on maize plant height and yield parameters were assessed. Plant height differed consistently with N₁₂₀P₉₀ > N₀P₉₀ > N₁₂₀P₀/N₀P₀ from 3 to 7?weeks after planting on the GPA. On the GPA, grain yield ranged from 1.20 to 2.40 t ha^?1 and increased by 10, 77 and 95% in the N₁₂₀P₀, N₀P₉₀ and N₁₂₀P₉₀, respectively. Residual effect of N₀P₉₀ and N₁₂₀P₉₀ increased maize yields on the GPA than on the PA. Rather than N, P was more critical to maize performance and should be externally supplied not exceeding the critical level of N₀P₆₀ (Plinthic Acrisol) and N₀P₉₀ (Gleyic Plinthic Acrisol) for optimum maize yield.     

不同施磷水平下 AM 真菌发育及其对玉米氮磷吸收的影响

【目的】不同丛枝菌根 (abuscular mycorrhizal,AM) 真菌菌种 (株) 因其分离地点及宿主的不同,其生理发育与生态功能差异显著,尤其是土壤养分状况对其影响更明显。研究不同土壤磷水平对 AM 真菌侵染宿主及生长发育繁殖的影响,以及不同 AM 真菌对玉米生长及氮磷吸收的影响,可以深化了解 AM 真菌与土壤磷的关系。 【方法】采用盆栽试验,以玉米为宿主植物,土壤灭菌后分别添加 0、50、200、500 mg/kg 4 个水平的磷营养 (P0、P50、P200、P500),并分别接种 6 种 AM 真菌,以不接种为对照。测定了 AM 真菌侵染率、丛枝丰度、孢子数、菌丝密度、玉米植株氮磷比 (N/P) 生态化学计量特征,讨论了不同土壤磷水平与 AM 真菌生长发育间的关系,以及 AM 真菌对玉米吸收利用氮、磷的影响。 【结果】在 P50 条件下,AM 真菌的侵染率、根内丛枝结构、根外生物量 (孢子数、菌丝密度) 显著高于不加磷 P0 和 P200 和 P500 处理,而且 AM 真菌侵染及生长发育指标在高磷水平时,显著下降。不同磷水平处理下,不同 AM 真菌对玉米的侵染能力及生物量存在明显差异。在 P0 和 P50 条件下,接种 G.m 处理侵染率达到 75%,菌丝密度达 240 m/g,显著高于其他五个 AM 真菌。AM 真菌 C.c、R.a、C.et 的菌根侵染状况及生物量次之,D.s、D.eb 最差。在高磷 P200 和 P500 条件下,仅有 F.m 真菌处理的侵染状况及生物量最高。在 P0、P50 水平下,接种 F.m、R.a、D.eb 显著降低了植株氮含量;在不加磷 (P0) 水平下,接种处理均显著促进了玉米植株中磷含量的提高,在 P50 水平下,F.m 植株磷含量显著高于不接种对照;在 P0、P50、P200 水平下,接种 AM 真菌处理降低了玉米植株中 N/P 比,且不同菌种间存在差异,接种真菌 F.m 处理的 N/P 比明显最低。 【结论】土壤添加低量磷 (50 mg/kg) 更适合 AM 真菌的侵染及生长发育,也利于菌根效应的发挥。侵染能力及效应以耐高磷菌种 F.m 最好,然后依次为 C.c、R.a、C.et。在适量磷条件下,接种 AM 真菌能够调节植株体 N/P 比达到平衡,改善植物营养状况,促进玉米生长。     

Effect of phosphorus fertilizer application on the performance of maize/soybean intercrop in the southern Guinea savanna of Nigeria

Field experiments were conducted at the Teaching and Research Farm, Ladoke Akintola University of Technology, Ogbomoso, Nigeria in 2007 and 2008 to determine the effects of phosphorus fertilizer application on performance of intercropped maize and soybean. The experiments, arranged as a split plot in a randomized complete block design, replicated four times. A cropping system with sole maize, sole soybean and maize/soybean intercrop formed the main plot treatments while P rates with 0, 15 and 30 kg P₂O₅ ha^?1 were the subplot treatments. For both years, neither P fertilizer application nor cropping systems had a significant effect on maize grain yield. However, soybean grain yield was significantly higher (92.3% in 2007 and 44.5% in 2008) under sole cropping than under maize/soybean intercropping. On average, N fixed by soybean increased with the increase in P rate (from 51.8% without P to 60.5% with 30 P), but there was no significant difference in N fixed by sole soybean and soybean/maize intercrop. However, the interaction effect on N fixed between cropping systems and P rates was significant (P ≤ 0.05). N, P and K contents in maize grain were significantly higher (>100%) in intercropped maize than in sole maize. The cropping systems had no significant effect on post-harvest soil chemical characteristics. The land equivalent ratio was 1.52 in 2007 and 1.78 in 2008. The result shows that in utilizing legumes for N enrichment, the alleviation of P deficiency can enhance N₂-fixation by legumes. Furthermore, P replenishment in a maize/soybean intercrop may improve maize grain quality even though yield is not increased.     

Quantitative studies on the relationship between plowing into soil of clubbed roots of preceding crops caused by Plasmodiophora brassicae and disease severity in succeeding crops

The effect of the plowing of clubbed roots of cracifers on the population of Plasmodiophora brassicae in soil was quantitatively studied by measuring the number of resting spores produced in the diseased plants. Though the mean number of resting spores per diseased plant increased with the increase of the disease severity, it remained almost identical for the disease severity classified into category 3 among host species and cultivars tested. Mean number of resting spores per diseased plant ranged from 9.3 to 10.9 (log) regardless of the value of the disease index. When the number of resting spores in soil was calculated based on these data and plant cultivation methods, the values were equivalent to 4.8-6.4 resting spores g^-1soil (log)where clubroot disease occurred severely. The value of the disease index of Chinese cabbage plants grown in the pots where clubbed roots of initially grown plants had been plowed into soil (plowing plot) was higher than that in the pots where no plants had been grown (control plot) and where the clubbed roots of initial plants had been removed (removal plot). Though the number of resting spores of P. brassicae in soil decreased by 14% of the inocoKum concentration immediately after the inoculation, the number of spores after the first cultivation in the removal plot was similar to that in the control plot. On the other hand, the number of resting spores in the plowing plot increased significantly compared with that in the control plot. The plowing of clubbed roots into soil resulted in the increase of the population of P. brassicae and disease severity of clubroot in subsequent cultivation in the field. The results corresponded to the values estimated based on the number of resting spores in soil in relation to each value of the disease index.     

紫色土施用磷酸盐肥料对玉米铜毒害的缓解

A pot experiment was conducted to evaluate the effects of phosphorus fertilizer in inhibiting the copper toxicity to maize(Zea mays L.) in neutral purple soil. Results indicated that the growth of the shoot and roots of maize plant was obviously reduced by copper and the height and biomass were significantly negatively correlated to the application levels of copper (r = -0.899^**~-0.994^**) at no P and low P (100 mg kg^-1). However, the maize biomass was relatively increased and the high Cu (100 and 200 mg kg^-1) induced toxicity of maize was greatly alleviated in all treatments with medium P (300 mg kg^-1 ) and high P (500 mg kg^-1). To maintain the normal growth of maize plant (≥3.68 g pot^-1), the critical application rates of phosphorus fertilizer should be 160, 210, 300 and 500 mg P kg^-1 at 10, 50, 100 and 200 mg Cu kg^-1 levels of the soil, respectively. The increases in polyphenol oxidase and catalase activities in maize leaf and dehydrogenase activity in roots by phosphorus fertilizer were in the order of medium P>high P>low P>no P. Activities of polyphenol oxidase and catalase were significantly positively correlated to the application levels of copper (r =0.892^**~0.924^**), whereas that of dehydrogenase was just reverse (r = -0.966^**) at no P. Medium and high P repressed the influence of copper on activities of three enzymes. Phosphorus fertilizer reduced the copper concentrations of maize roots and leaf and the change ranges of the P/Cu ratio of maize roots and the P/Cu, N/Cu and K/Cu ratios of maize leaf. The three ratios of maize leaf were 256^**71.5, 2643^**839 and 1133^**440 at normal growth of maize plant, respectively. Soil available Cu could be markedly cut down by application of phosphorus fertilizer, especiallly at high phosphorus level.     

Root growth and nutrient element status of creeping bentgrass cultivars differing in heat tolerance as influenced by supraoptimal shoot and root temperatures

This study was designed to determine and compare root growth and nutritional responses of creeping bentgrass cultivars that differ in heat tolerance to differential, supraoptimal, shoot and root temperatures. Shoots and roots of ‘Penncross’ (heat sensitive) and ‘L‐93’ (heat tolerant) were exposed to four air/soil temperature regimes (20/20°C‐control, 20/35°C, 35/20°C, and 35/35°C) in water baths and growth chambers. Exposing roots to supraoptimal root temperature (35°C) while maintaining shoots at normal temperature (20°C) or particularly at 35°C reduced root fresh weight, root number, and contents of nitrogen (N), phosphorus (P), and potassium (K) in shoots and roots and accelerated root death for both cultivars. High root temperature had greater detrimental effects on root growth and nutrient element accumulation than high shoot temperature for both cultivars. A low root temperature at supraoptimal shoot temperature improved root growth, reduced root mortality; and increased N, P, and K contents in shoots and roots. Among the three nutrient elements, K was the most sensitive to changes in root temperature. L‐93 generally maintained higher fresh weight and number of roots and higher N, P, and K contents in shoots and roots, particularly K in roots, under high root (20/35°C) or shoot/root (35/35°C) temperatures. The results indicated that root growth and nutrient element accumulation, particularly of K, played an important role in creeping bentgrass tolerance to heat stress imposed on shoots by high air temperature or to roots by high soil temperatures. The enhanced root growth and nutrient element relations with a low root temperature at supraoptimal ambient temperatures could lead to the improved shoot growth in cool‐season grasses observed under these conditions.     

Influence of extreme K:Na ratios and high substrate salinity on plant metabolism of crops differing in salt tolerance

Mineral regulation of two soybean varieties Jackson and Lee was investigated in long term water culture experiments using saline solutions. The effects of extreme K:Na ratios using chloride and sulfate as counterions were studied in the early stages of salinity.

The growth rates of both varieties were not affected by salinization. A K⁺ stimulated, intensive acropetal Cl^‐ translocation was observed in the salt sensitive variety Jackson. The varieties did not differ in Na⁺ translocation and in the suppression of Ca²⁺ and Mg²⁺ in the leaves. But the effect of the nature of salinization indicates already differences in Na uptake and translocation of the cultivars.

The avoidance of Cl^‐, but also of Ha⁺, in connection with influences of the resulting ionic imbalance on metabolic pathways are probably the most causative factors for the different tolerance to salinity of the two soybean varieties.     

Effect of nitrogen forms on reduction of manganese oxides in an Oxisol by plant root exudates

Reductive dissolution of soil manganese (Mn) oxides increases potential toxicity of Mn²⁺ to plants. In order to examine the effect of nitrogen forms on reduction of Mn oxides in rhizosphere soil, a rhizobox experiment was employed to investigate the reduction of Mn oxides due to the growth of soybean and maize in an Oxisol with various contents of NO₃^–-N and NH₄⁺-N and a total N of 200 mg kg^?1. The results showed that exchangeable Mn²⁺ in rhizosphere soil was 9.6–32.7 mg kg^?1 higher than that in bulk soil after cultivation of soybean and maize for 80 days, which suggested that plant root exudates increased reduction of soil Mn oxides. Application of ammonium-N promoted reduction of Mn oxides in rhizosphere soil compared to application of nitrate and nitrate together with ammonium. Soybean cultivation led to a higher reduction in soil Mn oxides than maize cultivation. Application of single ammonium enhanced Mn uptake by the plants and led to more Mn accumulating in plant leaves, especially for soybean. Therefore, application of ammonium-based fertilizer can promote reduction of soil Mn oxides, while application of nitrate-based fertilizer can inhibit reduction of soil Mn oxides and thus reduce Mn²⁺ toxicity to plants.     

The diagnosis of nitrogen deficiency in wheat by means of a critical nitrate concentration in stem bases

Abstract

Stem bases from wheat plants in a glasshouse pot experiment conducted under varying nitrogen and two water regimes, were analysed for nitrate (NO₃) concentration. The concentration of NO₃ at three stages of growth i.e. tillering, jointing and anthesis were related both to rates of applied nitrogen and to shoot dry matter yield at time of sampling. Plotted against rate of increasing nitrogen application, the response curve of NO₃ concentration in wheat stem bases was sigmoidal. The level of nitrogen application at which NO₃ began to accumulate in the plants was the supply at which plants reached maximum dry matter yield. The concentration of NO₃ at which plant yield was 90% of maximum dry matter was taken as the critical level. This concentration was around 1000 ppm NO₃‐N at all stages. Compared with plants supplied with unlimited water, plants under moderate water stress accumulated relatively more NO₃ but had a similar critical NO₃ concentration.

Maximum grain yield was obtained from plants which stayed above the critical level throughout the growing season.     

玉米/大豆和玉米/甘薯模式下玉米干物质积累与分配差异及氮肥的调控效应

【目的】西南山地玉米区是我国第三大玉米主产区,但单产比全国低近750 kg/hm2。由于该区特殊的气候条件,玉米以多熟间套种植为主,如何利用多熟种植中各作物的间套优势和茬口特性,寻求提高本区玉米产量的新途径,是农业科技工作者研究的热点。本文在四川的两个玉米主产区,通过四年的田间小区试验,对比研究了西南玉米主要的两种套作模式—玉米/大豆和玉米/甘薯模式下玉米干物质积累分配、转运差异及施氮量对其的调控效应,以探讨种植模式和氮肥管理的增产效应。【方法】2008年设置玉米/大豆和玉米/甘薯两个套种田间试验,分析比较两种模式玉米干物质积累、分配和转运的差异;2009 2010年在前一年的基础上分带轮作,即玉米分别种在大豆或甘薯茬上,分析套作和轮作效应对玉米干物质积累的影响;2011年,在前三年的基础上,采用小区套微区的方式,研究两种模式下不同施氮水平(N0、N90、N180、N270、N360)对玉米干物质积累和转运的调控。【结果】1)在玉米/大豆模式下,玉米干物质积累量从蜡熟期开始显著高于玉米/甘薯模式,茎鞘输出率也显著高于玉米/甘薯模式,最终产量增加2.4%3.2%,但差异未达显著水平;2)分带轮作后,从拔节期开始,玉米/大豆模式下玉米干物质积累量就显著高于玉米/甘薯模式,到成熟期两套种模式下玉米单株干物质积累两试验点平均相差达26.8 g,茎秆向籽粒的输出率和贡献率也显著高于玉米/甘薯模式,收获指数玉米/大豆模式平均较玉米/甘薯模式提高3.9%,最终玉米/大豆模式下玉米产量较玉米/甘薯模式增幅加大,两年两个试验点分别增加了7.4%和14.4%;3)氮肥对两种模式下玉米干物质积累分配和产量的调控效应显著,玉米/大豆模式下,玉米以施氮180kg/hm2处理,而玉米/甘薯模式下270 kg/hm2处理与同一模式下其他氮素水平相比,增加了光合产物的积累,提高了干物质增长速率,延长了灌浆持续天数,有利于茎鞘和叶片的干物质向籽粒转移,显著提高收获指数,进而提高玉米的增产潜能,玉米/大豆模式下低氮处理(0 180 kg/hm2)对玉米的增产效应比较明显,在高施氮水平(270360 kg/hm2)下两种模式间玉米产量差异不显著。【结论】西南丘陵旱地应选择玉米与大豆套作,采用分带轮作种植方式,既有利于提高玉米产量,又可避免大豆的连作障碍;且氮肥管理措施应因种植模式不同而有所差异,在中高等肥力条件下,与大豆套作玉米施氮180 kg/hm2,与甘薯套作施氮应提高至270 kg/hm2。     

Safflower yields and water use efficiency as affected by irrigation at different soil moisture depletion levels and plant population density under arid conditions

A field experiment was carried out over two years to investigate the effects of an irrigation regime and its interaction with plant density on yield, yield components and water use efficiency (WUE) of safflower Giza 1 cv. The experiment was laid out in randomized complete block design with split plot arrangement with three replications. There were three available soil moisture depletion levels (ASMD) under this study (I₁:50% of ASMD, I₂:65% of ASMD and I₃:80% of ASMD), which were kept in main plots and three plant population densities (D₁: 10, D₂: 20 and D₃: 40 plants m^?2), which were randomized in sub-plots. Significant interaction effects between irrigation regime and plant population density were detected for seed and oil yields, 1000-seed weight and seed weight plant^?1 as well as WUE. The highest seed and oil yields were found for D₂I₁. Meanwhile, the highest WUE was found for D₂I₁ or D₂I₂. Based on these results, the combination of an irrigation rate of 50% of ASMD at a density of 20 plants m^?2 when irrigation water supplies are sufficient or a rate of 65% of ASMD at the same plant density when irrigation water are limited, are recommended for planting safflower under similar soil and climatic conditions.     

Effects of P fertilization level on phosphorus uptake and agronomic traits under deficit irrigation in winter wheat (T. aestivum L.)

Abstract

Enhancing the phosphorus (P) use efficiency is critical for the sustainable cultivation of winter wheat. In this study, we investigated the effects of P fertilization level on plant P-uptake and agronomic traits under deficit irrigation, by using two wheat cultivars sharing contrasting water responses (i.e., Jimai 585 and Shimai 22). The high P level treatment (P120) improved plant biomass and P accumulation at each growth stage, grain yields, P remobilization amount to grain (PRA), P remobilization rate (PRR), and P contribution rate (PRR) of the cultivars with respect to the low P treatments (i.e., P90 and P60). Compared with Jimai 585, a cultivar acclimated to affluent water, the drought tolerant cultivar Shimai 22 exhibited similar behaviors on plant biomass, P-associated traits at each stage, and agronomic traits at maturity under P120. However, Shimai 22 was more improvement on P-associated and agronomic traits than Jimai 585 under P60 and P90. P contents were increased whereas moisture contents decreased in soil profile treated by P120 with respect to those by P60. Meanwhile, the soil profile cultivated by Shimai 22 displayed reduced moisture and P contents under P deprivation (i.e., P90 and P60) respect to that by Jimai 585, suggesting the contribution of more consumption of soil P and water storage to improved agronomic traits of Shimai 22. Together, our investigation suggested that suitable P input management positively mediates plant P-associated traits and grain formation capacity under deficit irrigation by improving supply and internal translocation of P across tissues in winter wheat plants.