草地早熟禾草坪土壤水分动态与根系生长分布

对草地早熟禾草坪土壤水分动态和根系生长发育状况进行研究,结果发现不同土壤层次水分变化有所不同,0～15cm变化最大,15～30cm次之,30cm以下土层水分变化不大;草地早熟禾的根系生长呈现双峰曲线模式,5月中旬和8月中下旬总根量处于峰值;其主体根系主要分布在0～30cm土层内,占总根量的85%以上;根重密度随土层深度呈指数衰减关系,0～30cm土层下降幅度较大,30cm以下土层根重密度相差不大;在0～30cm土层内不同层次根量占总根量的比例在不同时期亦有差异,春秋季节10～20cm和20～30cm土层内根量比例较大,说明此时期主体根系分布在较深的土层;综合分析认为草地早熟禾草坪主要利用土壤浅层水分,在降雨较少的春秋季节,根系较深,适宜深层灌溉,在降雨频繁的夏季,根系较浅,适宜浅层灌溉。     

干旱胁迫对花生根系生长发育和生理特性的影响

以花育17号和唐科8号两个花生品种为试验材料,在防雨棚栽培池内进行土柱栽培试验,研究了中度干旱胁迫和正常供水处理下花生生育后期根系形态发育特征和生理特性.结果表明: 唐科8号具有较发达的根系及较高的产量和抗旱系数,花育17号根系对干旱胁迫的适应性小于唐科8号.两品种根长密度、根系生物量均主要分布于0～40 cm土层中,但同一土层内两品种根系性状存在差异.与正常供水处理相比,干旱胁迫处理使花育17号各生育期总根长、根系总表面积和总体积均降低,而唐科8号除花针期显著降低外,其余生育期均明显升高;干旱胁迫增加了两品种20～40 cm土层内根系生物量、根系表面积和体积,而降低了40 cm以下土层内各根系性状;干旱胁迫处理使两品种饱果期40 cm以下土层内根系活力降低,且花育17号降低幅度高于唐科8号.干旱胁迫下两品种生育后期根系发育和生理特性的差异表明其根系在干旱胁迫下对水分吸收和利用存在差异.     

交替灌溉对山黧豆叶片气体交换和土壤水分以及产量指标的影响

改变土壤根系的分布以汲取深层土壤水分的能力是植物避免干旱的主要策略。山黧豆是一种抗逆性强的豆类作物,该研究通过起垄条播控制性沟灌的方式,设置传统灌溉(FI)、交替灌溉(PRD,灌水量减少50%)和不灌溉(NI)3种处理模式,探索不同灌溉模式对播种后不同时期山黧豆土壤水分、根系分布、叶片气体交换、水分利用效率和籽粒产量的影响。结果表明：(1)在FI、PRD和NI处理下,山黧豆的根系分别有89.8%、86.9%和84.9%生长在0~20 cm的表层土壤中;干旱胁迫使PRD和NI处理下深层土壤中根系的比例提高至13.05%和15.07%。(2)在整个生育期内,土壤干旱显著降低了山黧豆叶片的净光合速率、蒸腾速率和气孔导度;在种植后60 d时,PRD和NI处理下叶片的瞬时水分利用效率分别较FI处理显著提高了21.4%和14.9%。(3)干旱胁迫显著降低了山黧豆植株高度、第一豆荚高、平均结荚数和豆粒数以及地上部和根系的干重,但显著增加了根冠比;PRD处理对豆荚长度、豆荚重和每荚豆粒重没有显著影响;PRD和NI处理下山黧豆平均籽粒产量分别比FI处理显著降低了53%和63%。研究发现,在干旱胁迫条件下,山黧豆能够通过提高深层土壤中根系的比例、更多吸收深层土壤水分、显著增加根冠比以及显著提高生殖生长期叶片的瞬时水分利用效率,减轻干旱胁迫对自身生长的影响。该研究结果可为山黧豆在旱区推广种植提供理论依据。     

H_2S对干旱胁迫下白三叶幼苗抗氧化防御能力的影响

以‘拉丁诺’白三叶(Trifolium repens cv.‘Ladino’)为试验材料,研究外源H2S处理对PEG6 000(聚乙二醇)模拟干旱胁迫下白三叶叶片相对含水量(RWC)、膜脂过氧化、活性氧成分、抗氧化酶、抗坏血酸-谷胱甘肽循环代谢和非酶抗氧化物质的影响,以揭示H_2S调控白三叶抗旱性的生理机制。结果显示:(1)0.2 mmol/L的外源NaHS(H_2S供体)能显著提高干旱胁迫下白三叶的叶片相对含水量,维持显著较低的电解质渗透率(EL)和丙二醛(MDA)含量。(2)与直接干旱胁迫相比,干旱胁迫下外源添加NaHS处理的白三叶叶片内超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性显著增强,抗坏血酸-谷胱甘肽循环代谢中关键酶抗坏血酸过氧化物酶(APX)、脱氢抗坏血酸还原酶(DHAR)、单脱水抗坏血酸还原酶(MDHAR)和谷胱甘肽还原酶(GR)活性及其抗氧化中间产物抗坏血酸(AsA)、谷胱甘肽(GSH)含量也显著提高。(3)叶片类黄酮、总酚和原花青素的含量在一定的胁迫时间范围内亦显著增加,并伴随着活性氧成分O_2~(-·)产生速率和H_2O_2水平降低。研究认为,外源H2S能通过促进干旱胁迫下白三叶体内的多重抗氧化防御能力来提高其幼苗的抗旱性。     

不同抗旱性花生品种的根系形态发育及其对干旱胁迫的响应

为明确不同抗旱性花生品种的根系形态发育特征,探讨其根系形态发育特征对不同土壤水分状况的响应机制,在防雨棚旱池内进行土柱栽培试验,研究抗旱型品种“花育22号”、“唐科8号”和干旱敏感型品种“花育23号”3个不同抗旱性花生品种根系形态发育特征及其对干旱胁迫的响应.结果表明:抗旱型品种根系较发达,具有较大的根系生物量、总根长、总根系表面积.干旱胁迫使抗旱型品种根系总表面积和体积增加,而干旱敏感型品种则相反.干旱胁迫显著增加抗旱型品种“花育22号”20 cm以下土层内根长密度分布比例及根系表面积和体积,但“唐科8号”相应根系性状仅在20-40 cm土层内增加;干旱胁迫使干旱敏感型品种“花育23号”40 cm以下土层内各根系性状升高,但未达显著水平且其深层土壤内各根系性状增加幅度小于“花育22号”.花生根系总长、总表面积及0-20 cm土层内根系性状与产量间呈显著或极显著正相关.土壤水分亏缺条件下,花生主要通过增加深层土壤内根长、根系表面积和体积等形态特性,优化空间分布构型,以调节植株对水分的利用.     

土壤干旱胁迫对黄栌叶片光合作用的影响

采用CIRAS-2型便携式光合作用系统,设置充足供水、轻度、中度和重度胁迫4种土壤水分处理,研究土壤干旱和强光胁迫对3年生黄栌苗木叶片光合作用的影响.结果表明:土壤干旱胁迫对黄栌叶片的光合性能参数影响显著,随着土壤水分胁迫的加剧,黄栌叶片的光合速率、蒸腾速率和光量子效率明显降低,光补偿点增高,水分利用效率在轻度水分胁迫(土壤相对含水量60%～65%)下最高;在强光(有效辐射强度1000～1800μmol.m-2.s-1)范围内,叶片光合速率和水分利用效率均较高,而对弱光的光能吸收和光量子效率较低,并随土壤水分胁迫加剧明显下降.     

干旱胁迫对不同烤烟品种根系生长和生理特性的影响

以抗旱型烤烟品种‘农大202'及一般型烤烟品种‘NC89'和‘K326'为材料,采用盆栽试验研究了干旱胁迫对根系生长和生理特性的影响,以明确各烟草品种的抗旱能力及其与根系生长和生理特性的关系.结果显示:严重干旱胁迫之后各烤烟品种根系鲜重、干重上升,而根系活力、根系吸收面积以及根系SOD和POD活性等根系生理指标则呈下降趋势.在干旱胁迫条件下,‘农大202'的根系总吸收面积、活跃吸收面积、根系活力、SOD活性和POD活性均显著高于两对照品种‘NC89'和‘K326',但其根系鲜重和干重等生物量并不具有太大的优势.研究表明,烟草的根系生长和生理特性对环境水分条件的响应存在明显的基因型差异;在干旱胁迫条件下, ‘农大202'根系能保持较高总吸收面积、活跃吸收面积、根系活力和保护酶活性,是其具有较强抗旱性的生理基础.     

土壤水肥因子对胡杨幼苗生长权衡和木质化的影响

以当年生胡杨幼苗为材料,通过不同水平的水分和养分单因素控制盆栽试验,探讨土壤水肥因子对当年生胡杨幼苗生长权衡和木质化的影响,以明确胡杨生长过程中以及种子更新困难的原因和机理。结果表明:(1)当年生胡杨幼苗生长权衡主要体现在生物量的分配策略上,而主根长/高度没有显著差异。(2)在连续给水处理下,干旱胁迫使幼苗根冠比显著增加,土壤含水量15%处理的根冠比较含水量20%和30%处理分别显著增加了75%和93%;但干旱胁迫抑制了生物量的积累,含水量10%处理下生物量比15%、20%和30%处理分别显著减小53.4%、89.2%、78.6%;在断续给水处理下,随着干旱程度的增加幼苗根冠比显著增加,土壤含水量15%处理的根冠比较含水量20%和30%处理分别显著增加34%和38%;连续给水和断续给水两类干旱胁迫均能明显增加幼苗根系木质化程度。(3)土壤施加氮磷均显著增加幼苗根冠比和木质化,但过量的氮肥抑制根系生物量的积累。可见,胡杨幼苗对于水肥条件胁迫敏感性与生长权衡能力是胡杨林种子更新与种群维持的关键环节,调整立地土壤水肥环境对当年生胡杨幼苗的生长定居有重要的作用。     

陇东旱塬苹果根系分布规律及生理特性对地表覆盖的响应

为探明陇东旱塬区不同覆盖物对苹果园土壤理化性状、根系分布及根系生理活性的影响,以14年生苹果树为试材,采用土壤剖面分层取样法,调查根系空间分布,并对根系生物量、根长、表面积等进行分析,测定根系活力、抗氧化酶类、活性氧代谢等相关生理指标,同时测定不同深度土层土壤容重、孔隙度等.结果表明: 覆草可有效增大土壤含水量、孔隙度、有机质含量,增幅分别为2.7%～11.6%、3.2%～27.7%、5.1%～36.0%,但土壤容重降低,为清耕(CK)的88.7%～96.4%.CK根系主要分布在距树干30～120 cm范围内的0～60 cm深土层中;覆草、覆膜处理主要分布在距树干0～150 cm、0～60 cm水平范围内的0～100 cm深土层中,以20～40 cm根系最为密集;覆膜处理细根总量仅为CK的96.4%,根系水平分布范围较CK有所减小,0～60 cm内细根占根系总量的51.6%.不同覆盖处理显著增强0～80 cm土层根系活力及抗氧化酶活性,其中覆草处理根系活力为CK的111.3%～136.7%.综合分析根系生长分布与生理活性、土壤理化性状等,认为覆草处理是陇东旱塬区苹果园较为适宜的地表覆盖方式.     

土壤水分和磷营养对小麦根系生长生理特性的影响

采用小偃６号小麦品种,在模拟田间原状土容重的条件下土培,研究了土壤水分和磷营养对小麦根系生长生理特性的效应。结果表明：在土壤相对含水量为４０％─７０％范围内,土壤水分亏缺,小麦根系生长受到限制,根系比表面积（ＲＡ）、根呼吸速率（Ｒｐ）、根水势（Ｒψｗ）和叶片蒸腾强度（ＥＩ）明显降低,根系干物重（ＲＤＷ）减少;轻度干旱有利于根系的延伸生长;在土壤干旱条件下,磷营养可以提高根系ＲＡ,降低根系Ｒｐ,提高Ｒψｗ、增加叶面ＥＩ,促进根系延伸生长,扩大小麦根系对土壤深层水分的吸收和利用,进而促进地下部生长,提高ＲＤＷ。磷除作为一种营养物质促进作物根系生长发育外,在水分胁迫条件下,磷营养可明显改善植株体内的水分关系,增强对干旱缺水环境的适应能力,提高作物抗旱性。促进根系生长,提高水分利用的有效方法是根据土壤水分状况调节磷的用量。     

Root Respiration,Photosynthesis and Grain Yield of Two Spring Wheat in Response to Soil Drying

The effects of soil water regime and wheat cultivar, differing in drought tolerance with respect to root respiration and grain yield, were investigated in a greenhouse experiment. Two spring wheat (Triticum aestivum) cultivars, a drought sensitive (Longchun 8139-2) and drought tolerant (Dingxi 24) were grown in PVC tubes (120 cm in length and 10 cm in diameter) under an automatic rain-shelter. Plants were subjected to three soil moisture regimes: (1) well-watered control (85% field water capacity, FWC); (2) moderate drought stress (50% FWC) and (3) severe drought stress (30% FWC). The aim was to study the influence of root respiration on grain yield under soil drying conditions. In the experiment, severe drought stress significantly (p < 0.05) reduced shoot and root biomass, photosynthesis and root respiration rate for both cultivars, but the extent of the decreases was greater for Dingxi 24 compared to that for Longchun 8139-2. Compared with Dingxi 24, 0.04 and 0.07 mg glucose m⁻² s⁻¹ of additional energy, equivalent to 0.78 and 1.43 J m⁻² s⁻¹, was used for water absorption by Longchun 8139-2 under moderate and severe drought stress, respectively. Although the grain yield of both cultivars decreased with declining soil moisture, loss was greater in Longchun 8139-2 than in Dingxi 24, especially under severe drought stress. The drought tolerance cultivar (Dingxi 24), had a higher biomass and metabolic activity under severe drought stress compared to the sensitive cultivar (Longchun 8139-2), which resulted in further limitation of grain yield. Results show that root respiration, carbohydrates allocation (root:shoot ratio) and grain yield were closely related to soil water status and wheat cultivar. Reductions in root respiration and root biomass under severe soil drying can improve drought tolerant wheat growth and physiological activity during soil drying and improve grain yield, and hence should be advantageous over a drought sensitive cultivar in arid regions.     

Physiological and morphological traits associated with adaptation of lucerne (Medicago sativa) to severely drought‐stressed and to irrigated environments

Adaptation to severe drought and to irrigated cropping can both contribute to increased water use efficiency of lucerne, but knowledge on the relevant adaptive traits is limited. Five cultivars featuring contrasting adaptive responses for 3‐year forage yield across 10 agricultural environments of the western Mediterranean basin were currently studied, to identify physiological and morphological traits associated with specific and wide‐adaptation responses. The landraces Mamuntanas, Demnat 203 and Erfoud 1, and the varieties SARDI 10 and Prosementi, were grown in replicated metal containers (55 cm long × 12 cm wide × 75 cm deep; 21 plants per container) under irrigation (weekly restoring soil field capacity) and under moderate and severe drought stress (implying decreased irrigation for 30 days followed by withheld irrigation for 33 and 58 days, respectively). Cultivar post‐stress survival reflected the known cultivar adaptation to drought‐prone agricultural environments. Demnat 203, specifically adapted to irrigated, frequently mown environments, displayed higher amounts of starch, soluble proteins and total nitrogen in the crown and the root under irrigation. This was due to outstanding organ size and, for starch, higher concentrations. Mamuntanas, specifically adapted to drought‐prone environments, exhibited high water‐soluble carbohydrate concentration in storage organs under severe stress, along with a water‐conservation strategy implying less water used in initial drought‐stress phases due to limited early root development that resulted in more water available under severe stress. Drought‐tolerant germplasm also displayed lower wilting under early stress, more plants with green tissues under severe stress, and more stems per plant in stress or favourable conditions. Multivariate patterns of cultivar variation for physiological and morphological traits were strictly associated with cultivar variation for adaptation pattern. Our results highlighted the difficulty to combine some traits of environment‐specific adaptive value into a unique widely adapted variety, supporting the selection of varieties specifically adapted to irrigated or severely drought‐prone environments.     

Fractal analysis on root systems of rice plants in response to drought stress

A fractal analytical method was used to examine the developmental responses of root systems in upland rice genotype CT9993-5-10-1-M (japonica) and lowland genotype IR62266-42-6-2 (indica) (abbreviated as CT9993 and IR62266, respectively) to soil water stress. The root systems were grown for one month in root boxes with 25 cm in length, 2 cm in width and 40 cm in depth, which were filled with soil. The root systems were sampled by following the needle-pinboard method, and then spread on the transparent plastic films with nets after carefully washing out the soils. The two-dimensional images of root systems were digitized by using a scanner. The digitized images were used for analysis based on fractal geometry with the box-counting method. The reductions in shoot dry weight, photosynthesis rate and transpiration rate of IR62266 by soil drought were greater than those of CT9993. The change of fractal parameters in response to soil moisture conditions differed between the two rice genotypes. The values of fractal abundance (FA) and fractal dimension (FD) in well-watered IR62266 plants were larger than in CT9993. The value of FA of IR62266 was decreased more by drought stress than that of CT9993, indicating that the volume of soils explored by the whole root systems of CT9993 was maintained or less decreased under drought stress in comparison to IR62266. Moreover, the values of FD tended to increase in CT9993 while it tended to decrease in IR62266 in response to drought. These root responses detected by the fractal analysis in CT9993 may be advantageous for its extracting more water from drying soils, which explains its better growth under drought-stressed condition.     

Inoculation with arbuscular mycorrhizal fungi enhances growth of Litchi chinensis Sonn. trees after propagation by air-layering

This study investigated the patterns of root growth and water uptake of maize (Zea mays L.) and cowpea (Vigna unguiculata (L.) Walp) grown in a mixture under greenhouse conditions. The plants were grown in root boxes for 5 weeks under 2 watering regimes; fully irrigated and water stress conditions, followed by a 5-day drying cycle imposed during the 6th week of growth. Water uptake patterns were analysed during the drying cycle. The two-dimensional distribution of the roots of both plants in the boxes was determined immediately at the end of the drying cycle. Under well-irrigated conditions, the roots of the component plants grew profusely into all sections of the root box and intermingled considerably. Water stress resulted in the decline of root growth of maize and cowpea but the root:shoot ratios of maize and cowpea were not affected, suggesting that there was no significant effect of water stress on root:shoot partitioning. However, water stress affected the biomass distribution between fine and coarse roots in cowpea. About 64% by weight of cowpea roots under water stress were coarse whereas as against 48% under well-irrigated conditions. Furthermore, water stress generally restricted the lateral extent of the roots of both maize and cowpea with a tendency of clumping together of the root systems and a reduced degree of intermingling. Thus, the extent of mixing of the root systems was apparently controlled by the availability of soil water. Water uptake from the well-irrigated soil in the root boxes was initially restricted to the sections directly below the base of each plant. Although roots of both plants were present in almost all sections of the root box, all the sections did not contribute simultaneously to water uptake by each plant. Water uptake was delayed from the middle intermingled zones. In effect, uptake patterns did not relate generally to the root distribution. The tendency was for the component plants to initially `avoid' water uptake from zones of intense intermingling or competition.     

Root System Dynamics of Miscanthus × giganteus and Panicum virgatum in Response to Rainfed and Irrigated Conditions in California

Miscanthus (Miscanthus × giganteus) and switchgrass (Panicum virgatum) are large perennial grass bioenergy crops in the USA and Europe. Despite much research into their agronomic potential, few studies have examined in situ root growth dynamics under irrigation and soil water deficits, particularly as they relate to shoot performance. We grew miscanthus and switchgrass in outdoor mesocosms under irrigated and rainfed conditions and assessed the spatial distribution and abundance of roots using minirhizotron images and whole root system sampling. Despite surviving an extended period of drought, shoot and root biomass, root length density, numbers of culms, and culm height were reduced in both species under rainfed (dry) conditions. However, rainfed switchgrass far outperformed rainfed miscanthus in all shoot and root growth metrics. The rainfed (drought) treatment reduced switchgrass and miscanthus whole plant biomass by 83 and 98 %, culm production by 67 and 90 %, and root length density by 67 and 94 % compared to irrigated plants, respectively. Root nitrogen concentration was higher for miscanthus (3-fold) and switchgrass (4-fold) in the rainfed treatment compared to irrigated plants and did not significantly differ between species. Unlike miscanthus, switchgrass grew roots continuously into regions of available soil moisture as surface soil layers grew increasingly dry, indicating a drought avoidance strategy. Our study suggests that switchgrass is more likely to tolerate drought by mining deep wet soils, while miscanthus relies on shallow rhizome production to tolerate dry soils.     

根区交替控制灌溉条件下玉米根系吸水规律

为了阐明根区交替控制灌溉(CRDAI)条件下玉米根系吸水规律,通过田间试验,在沟灌垄植模式下采用根区交替控制灌溉研究玉米根区不同点位(沟位、坡位和垄位)的根长密度(RLD)及根系吸水动态。研究表明,根区土壤水分的干湿交替引起玉米RLD的空间动态变化,在垄位两侧不对称分布,并存在层间差异;土壤水分和RLD是根区交替控制灌溉下根系吸水速率的主要限制因素。在同一土层,根系吸水贡献率以垄位最大,沟位最低;玉米营养生长阶段,10—30 cm土层的根系吸水速率最大;玉米生殖生长阶段,20—70 cm为根系吸水速率最大的土层,根系吸水贡献率为43.21%—55.48%。研究阐明了交替控制灌溉下根系吸水与土壤水分、RLD间相互作用的动态规律,对控制灌溉下水分调控机理研究具有理论意义。     

Shoot and root physiological responses to localized zones of soil moisture in cultivated and wild lettuce (Lactuca spp.)

Cultivated crisphead lettuce (Lactuca sativa L.) has a shallower root system than its wild relative, Lactuca serriola L. The effects of localized soil water, at depth, on plant water relations, gas exchange and root distribution were examined in the two species using soil columns with the soil hydraulic-ally separated into two layers, at (0–20 cm and 20–81) cm, but permitting root growth between the layers. Three treatments were imposed on 7-week-old plants, and maintained for 4 weeks: (i) watering, both layers to field capacity; (ii) drying the upper layer while watering the lower layer to field capacity, and (iii) drying both layers. Drying only 0–20 cm of soil had no effect on leaf water status, net photosynthesis, stomatal conductance or biomass production in L. serriola compared to a well-watered control, but caused a short-term reduction (10 d) in leaf water status and photosynthesis in L. sativa that reduced final shoot production. The different responses may be explained by differences in root distribution. Just before the treatments commenced, L. serriola had 50% of total root length at 20–80 cm compared to 35% in L. sativa. Allocation of total biomass to roots in L. serriola was approximately double that in L. sativa. The wild species could provide germplasm for cultivated lettuces to extract more soil water from depth, which may improve irrigation efficiency.     

Enhancing drought tolerance in C(4) crops

Adaptation to abiotic stresses is a quantitative trait controlled by many different genes. Enhancing the tolerance of crop plants to abiotic stresses such as drought has therefore proved to be somewhat elusive in terms of plant breeding. While many C(4) species have significant agronomic importance, most of the research effort on improving drought tolerance has focused on maize. Ideally, drought tolerance has to be achieved without penalties in yield potential. Possibilities for success in this regard are highlighted by studies on maize hybrids performed over the last 70 years that have demonstrated that yield potential and enhanced stress tolerance are associated traits. However, while our understanding of the molecular mechanisms that enable plants to tolerate drought has increased considerably in recent years, there have been relatively few applications of DNA marker technologies in practical C(4) breeding programmes for improved stress tolerance. Moreover, until recently, targeted approaches to drought tolerance have concentrated largely on shoot parameters, particularly those associated with photosynthesis and stay green phenotypes, rather than on root traits such as soil moisture capture for transpiration, root architecture, and improvement of effective use of water. These root traits are now increasingly considered as important targets for yield improvement in C(4) plants under drought stress. Similarly, the molecular mechanisms underpinning heterosis have considerable potential for exploitation in enhancing drought stress tolerance. While current evidence points to the crucial importance of root traits in drought tolerance in C(4) plants, shoot traits may also be important in maintaining high yields during drought.