有机胶结形成土壤团聚体的机理及理论模型

土壤团聚体是土壤结构的基本单位,其组成和稳定性直接影响土壤肥力和农作物的生长,对于有机质含量高的黑土,有机胶结物质是形成土壤团聚体的主要因素。在综合有机胶结剂和土壤团聚体的研究的基础上,阐述了有机胶结物质的特性,土壤生物和植物根系在土壤团聚体形成中的作用,土壤团聚体形成的机理及理论模型。     

植物根系固坡抗蚀的效应与机理研究进展

植物根系对抵抗坡体浅层滑坡和表土侵蚀起着巨大的作用.植物根系通过增强土体的抗剪强度发挥固坡效应.目前有关植物根系固坡机理的模型较多,普遍接受的是Wu-Waldron模型.该模型表明,植物根系产生的土体抗剪强度的增量与根系的平均抗拉强度和根面积比成正比,应用该模型评价根系固坡效应的2个最重要因素是根系的平均抗拉强度和根面积比.研究发现,土壤抗侵蚀性随着植物根系数量的增加而提高,但未有一致的定量函数关系.植物根系提高土壤抗侵蚀性主要通过直径小于1mm的须根起作用.须根通过增加土壤水稳性团聚体的数量与粒径等作用来提高土壤的稳定性,以抵抗水流分散;须根还能有效地增强土壤渗透性,减少径流,从而达到减少土壤冲刷的目的.     

植物根系分泌物主要生态功能研究进展

根系分泌物在植物根系-土壤-微生物互作过程及其生态反馈机制中发挥重要作用。在植物根际复杂网络互作过程中, 根系分泌物被认为是“根际对话”的媒介, 其在调控植物适应微生境、缓解根际养分竞争及构建根际微生物群落结构方面意义重大。该文结合国内外该领域主要研究成果, 综述了根系分泌物对植物生长、土壤微生物特性及土壤养分循环的影响, 并展望了未来根系分泌物的研究方向。     

Research Advances in the Main Ecological Functions of Root Exudates

根系分泌物在植物根系-土壤-微生物互作过程及其生态反馈机制中发挥重要作用。在植物根际复杂网络互作过程中, 根系分泌物被认为是“根际对话”的媒介, 其在调控植物适应微生境、缓解根际养分竞争及构建根际微生物群落结构方面意义重大。该文结合国内外该领域主要研究成果, 综述了根系分泌物对植物生长、土壤微生物特性及土壤养分循环的影响, 并展望了未来根系分泌物的研究方向。     

消落区植物群落对土壤团聚体稳定性的影响研究进展

水位脉动、干湿交替是影响消落区植物群落分布和土壤稳定性的关键环境驱动力,消落区植物群落是影响土壤团聚体稳定的重要因素,研究消落区植物群落结构和功能性状对土壤团聚体稳定性的影响有助于预测消落区植物演替过程和揭示其对岸带稳定的影响机制。本文总结了国内外相关研究,综述了植物群落对干湿交替环境的响应,同时基于植物功能性状对干湿交替的响应重点阐述了其对土壤团聚体粒径稳定性的影响。未来研究应该重点关注根系构型性状和根际微生物性状对土壤团聚体的影响,并加强消落区不同胁迫强度和演替阶段植物群落组成、地上-地下性状对土壤团聚体稳定性的研究,进而探究水位脉动条件下植物群落对土壤团聚体稳定的影响机制,为消落区生态调节、生态恢复提供理论支撑。     

植物根系分泌物对土壤污染修复的作用及影响机理

生物修复是一种经济环保的土壤修复技术。根系分泌物是利用生物修复污染土壤过程中的关键物质,也是植物与土壤微生物进行物质交换和信息传递的重要载体,在植物响应污染物胁迫中扮演重要角色。研究植物根系分泌物对土壤污染修复的作用和影响机理,是深入理解植物和微生物环境适应机制的重要途径,对促进生物修复污染土壤有重要指导意义。从污染物胁迫对根系分泌物的影响、根系分泌物对土壤污染物环境行为的影响、根系分泌物在调控污染土壤中根际微生物群落结构和多样性中发挥的作用等几个方面综述了根系分泌物对土壤污染修复的影响及内在机制。研究结果表明,根系分泌物在降低重金属对植物的毒性、加速有机污染物降解等方面有非常重要的作用。根系分泌物对土壤微生物的丰度和多样性均有显著影响,其与根际微生物互作在土壤污染物的消减中发挥了重要的调控作用。在此基础上,提出了以往研究中的不足,并对污染物胁迫下根系分泌物未来研究的方向和趋势进行了展望。     

植物根构型的定量分析

植物根系具有锚定植株、吸收和运输土壤中的水分及养分、合成和贮藏营养物质等重要功能。根构型是根系在土壤中的空间造型和分布。对植物根构型进行定量分析, 有助于人们了解根系结构和根系功能在生态系统中的重要作用。本文对植物根构型的概念及其定量分析研究进展进行了概述, 并介绍了植物根构型的主要研究方法和定量分析技术。     

植物根构型的定量分析

植物根系具有锚定植株、吸收和运输土壤中的水分及养分、合成和贮藏营养物质等重要功能。根构型是根系在土壤中的空间造型和分布。对植物根构型进行定量分析,有助于人们了解根系结构和根系功能在生态系统中的重要作用。本文对植物根构型的概念及其定量分析研究进展进行了概述,并介绍了植物根构型的主要研究方法和定量分析技术。     

球囊霉素相关土壤蛋白与根系形态的相关性研究

球囊霉素相关土壤蛋白(GRSP)是丛枝菌根(AM)真菌菌丝分泌的糖蛋白,能够促进土壤团聚体的形成。多种因素影响GRSP的产量,植物根系形态是否通过碳素竞争机制影响GRSP产量目前尚不清楚。以Glomus mosseae的两个生态型菌株和红三叶草Trifolium repense为试材,通过砂培试验探讨宿主的根系形态与GRSP产量的相关性。发现接种AM真菌导致宿主细根的比例降低,粗根的比例增加,但对总根长和根表面积没有影响;侵染率和菌丝长度随着时间的延长而增加,菌株之间存在显著差异;接种AM真菌导致GRSP产量显著提高;GRSP产量与根系形态没有显著的相关性,但是与侵染率和菌丝长度显著相关。结果表明,尽管宿主根系形态建成和AM真菌都对碳素具有竞争关系,但是前者并没有抑制GRSP的形成,可能存在根系碳素分配的自调控机制。     

酸雨和根系去除对杉木和火力楠人工林土壤有机碳的影响

酸雨是我国严重的环境问题之一，近年来其类型逐渐由硫酸型(SAR)向混合型(MAR)和硝酸型(NAR)转变。根系不仅是土壤有机碳的来源，也在土壤团聚体形成过程中发挥重要作用。然而，酸雨类型的转变和根系去除如何影响森林土壤有机碳并不清楚。本研究在杉木和火力楠人工林中进行为期3年的不同类型酸雨(硫酸∶硝酸为4∶1、1∶1和1∶4)模拟并结合断根处理，分析土壤有机碳和理化性质的变化，并进行团聚体粒径分级及平均重量直径的测定。结果表明：根系去除使两林分土壤有机碳库分别显著降低16.7%和21.5%,使土壤惰性有机碳含量分别显著降低13.5%和20.0%;根系去除显著降低了火力楠土壤团聚体稳定性、大团聚体比例和有机碳含量，而对杉木林无显著影响。不同类型酸雨对杉木和火力楠人工林土壤有机碳库和土壤团聚体结构均无显著影响。综上，根系在土壤有机碳的稳定中起关键作用，且根系对有机碳稳定性的贡献因森林类型而异，而短期内不同类型酸雨对土壤有机碳的稳定性无显著影响。     

Variation in root system traits among African semi‐arid savanna grasses: Implications for drought tolerance

In arid to semi‐arid grasslands and savannas, plant growth, population dynamics, and productivity are consistently and strongly limited by soil water and nutrient availability. Adaptive traits of the root systems of grasses in these ecosystems are crucial to their ability to cope with strong water and/or nutrient limitation and the increasing drought stress associated with ecosystem degradation or projected climate change. We studied 18 grass species in semi‐arid savanna of the Kalahari region of Botswana to quantify interspecific variation in three important root system traits including root system architecture, rhizosheath thickness and mycorrhizal colonization. Drought‐tolerant species and shorter‐lived species showed greater rhizosheath thickness and fine root development but lower mycorrhizal colonization compared to later successional climax grasses and those characteristic of wetter sites. In addition, there was a significant positive correlation between root fibrousness index and rhizosheath thickness among species and a weak negative correlation between root fibrousness index and mycorrhizal colonization. These patterns suggest that an extensive fine root system and rhizosheath development may be important complementary traits of grasses coping with drought conditions, the former aiding in the acquisition of water by the grass plant and the latter aiding in water uptake and retention, and reducing water loss in the rhizosphere. Within species, both rhizosheath development and mycorrhizal colonization were significantly greater in a wet year than in a year with below‐average precipitation. The observed patterns suggest that the primary benefit of rhizosheath development in African savanna grasses is improved drought tolerance and that it is a plastic trait that can be adjusted annually to changing environmental conditions. The functioning of mycorrhizal symbiosis is likely to be relatively more important in infertile savannas where nutrient limitation is higher relative to water limitation.     

Rhizosheath formation and involvement in foxtail millet(Setaria italica) root growth under drought stress

The rhizosheath, a layer of soil particles that adheres firmly to the root surface by a combination of root hairs and mucilage, may improve tolerance to drought stress. Setaria italica(L.) P. Beauv.(foxtail millet), a member of the Poaceae family, is an important food and fodder crop in arid regions and forms a larger rhizosheath under drought conditions. Rhizosheath formation under drought conditions has been studied, but the regulation of root hair growth and rhizosheath size in response to soil moisture remains unclear. To address this question, in this study we monitored root hair growth and rhizosheath development in response to a gradual decline in soil moisture. Here, we determined that a soil moisture level of 10%–14%(w/w)stimulated greater rhizosheath production compared to other soil moisture levels. Root hair density and length also increased at this soil moisture level, which was validated by measurement of the expression of root hair-related genes.These findings contribute to our understanding of rhizosheath formation in response to soil water stress.     

准噶尔盆地南缘两种典型禾本科植物根鞘土壤微生物群落功能多样性

以准噶尔盆地南缘两种禾本科植物的根鞘与其外围土壤为研究对象,采用Biolog-ECO微平板检测法对土壤微生物群落功能多样性进行了研究。结果表明:两种植物根鞘土壤的有机质、全氮、速效氮和速效钾均高于根鞘外围土壤;两种禾本科植物根鞘土壤的微生物平均颜色变化率(AWCD)、香农多样性指数、均匀度指数、优势度指数和丰富度指数均高于根鞘外围土壤;两种植物根鞘土壤微生物主要利用的碳源类型为羧酸、糖类和聚合物,其中芨芨草根鞘微生物是以利用羧酸、糖类、聚合物和氨基酸类物质为主,羽毛针禾根鞘土壤微生物是以利用糖类、氨基酸和聚合物为主;微生物平均颜色变化率与Shannon多样性指数、均匀度指数、速效钾和全氮呈显著相关性,除了全钾以外,与其余的土壤理化指标均存在正相关性。总而言之,根鞘结构改善了微生物的生存环境,提高了土壤微生物群落功能多样性,从而增强了缓冲外界不利影响的能力。     

Plant litter chemistry alters the content and composition of organic carbon associated with soil mineral and aggregate fractions in invaded ecosystems

Through the input of disproportionate quantities of chemically distinct litter, invasive plants may potentially influence the fate of organic matter associated with soil mineral and aggregate fractions in some of the ecosystems they invade. Although context dependent, these native ecosystems subjected to prolonged invasion by exotic plants may be instrumental in distinguishing the role of plant–microbe–mineral interactions from the broader edaphic and climatic influences on the formation of soil organic matter (SOM). We hypothesized that the soils subjected to prolonged invasion by an exotic plant that input recalcitrant litter (Japanese knotweed, Polygonum cuspidatum) would have a greater proportion of plant‐derived carbon (C) in the aggregate fractions, as compared with that in adjacent soil inhabited by native vegetation that input labile litter, whereas the soils under an invader that input labile litter (kudzu, Pueraria lobata) would have a greater proportion of microbial‐derived C in the silt‐clay fraction, as compared with that in adjacent soils that receive recalcitrant litter. At the knotweed site, the higher C content in soils under P. cuspidatum, compared with noninvaded soils inhabited by grasses and forbs, was limited to the macroaggregate fraction, which was abundant in plant biomarkers. The noninvaded soils at this site had a higher abundance of lignins in mineral and microaggregate fractions and suberin in the macroaggregate fraction, partly because of the greater root density of the native species, which might have had an overriding influence on the chemistry of the above‐ground litter input. At the kudzu site, soils under P. lobata had lower C content across all size fractions at a 0–5 cm soil depth despite receiving similar amounts of Pinus litter. Contrary to our prediction, the noninvaded soils receiving recalcitrant Pinus litter had a similar abundance of plant biomarkers across both mineral and aggregate fractions, potentially because of the higher surface area of soil minerals at this site. The plant biomarkers were lower in the aggregate fractions of the P. lobata‐invaded soils, compared with noninvaded pine stands, potentially suggesting a microbial co‐metabolism of pine‐derived compounds. These results highlight the complex interactions among litter chemistry, soil biota, and minerals in mediating soil C storage in unmanaged ecosystems; these interactions are particularly important under global changes that may alter plant species composition and hence the quantity and chemistry of litter inputs in terrestrial ecosystems.     

Soil as a mediator in plant‐plant interactions in a semi‐arid community

Abstract. Competition and facilitation may occur simultaneously in plant communities, and the prevalence of either process depends on abiotic conditions. Here we attempt a community‐wide approach in the analysis of plant interactions, exploring whether in a semi‐arid environment positive or negative interactions predominate and whether there are differences among co‐occurring shrub species. Most shrubs in our plot exerted significant effects on their understorey communities, ranging from negative to positive. We found a clear case of interference and another case where the effect was neutral, but facilitation predominated and the biomass of annuals under most shrubs in our community was larger than in gaps. Effects on soil water and fertility were revealed as the primary source of facilitation; the build‐up of soil organic matter changed soil physical properties and improved soil water relations. Facilitation by shrubs involved decoupling of soil temperature and moisture. Sheltering from direct radiation had an effect on productivity, but significant differences in understorey biomass did not parallel understorey light environment. A positive balance of the interaction among plants, essentially mediated by changes in soil properties, is the predominant outcome of plant interactions in this semi‐arid community.     

Responses of native and non-native Mojave Desert winter annuals to soil disturbance and water additions

Habitat modification (i.e., disturbance) and resource availability have been identified as possible mechanisms that may influence the invasibility of plant communities. In the Mojave Desert, habitat disturbance has increased dramatically over the last 50 years due to increased human activities. Additionally, water availability is considered to be a main limiting resource for plant production. To elucidate the effects of soil disturbance and water availability on plant invasions, we created experimental patches where we varied the levels of soil disturbance and water availability in a fully crossed factorial experiment at five replicated field sites, and documented responses of native and non-native winter annuals. The treatments did not significantly affect the density (seedlings m⁻²) of the non-native forb, Brassica tournefortii. However, the relationship between silique production and plant height differed among treatments, with greater silique production in disturbed plots. In contrast to Brassica, density of the non-native Schismus spp. increased in soil disturbed and watered plots, and was greatest in disturbed plots during 2009 (the second year of the study). Species composition of the native annual community was not affected by treatments in 2008 but was influenced by treatments in 2009. The native forb Eriophyllum sp. was most dense on water-addition plots, while density of Chaenactis freemontii was highest in disturbed plots. Results illustrate that habitat invasibility in arid systems can be influenced by dynamics in disturbance regimes and water availability, and suggest that invasiveness can differ between non-native annual species and among native annuals in habitats undergoing changing disturbance and precipitation regimes. Understanding the mechanistic relationships between water availability and non-native plant responses will be important for understanding the effects of shifting precipitation and vegetation patterns under predicted climate change in arid ecosystems.     

Formation and Stabilization of Rhizosheaths of Zea mays L. (Effect of Soil Water Content)

Field observations have shown that rhizosheaths of grasses formed under dry conditions are larger, more coherent, and more strongly bound to the roots than those formed in wet soils. We have quantified these effects in a model system in which corn (Zea mays L.) primary roots were grown through a 30-cm-deep prepared soil profile that consisted of a central, horizontal, "dry" (9% water content) or "wet" (20% water content) layer (4 cm thick) sandwiched between damp soil (15-17% water content). Rhizosheaths formed in dry layers were 5 times the volume of the subtending root. In wet layers, rhizosheaths were only 1.5 times the root volume. Fractions of the rhizosheath soil were removed from individual roots by three successive treatments; sonication, hot water, and abrasion. Sonication removed 50 and 90% of the soil from rhizosheaths formed in dry and wet soils, respectively. After the heat treatment, 35% of the soil still adhered to those root portions where rhizosheaths had developed in dry soil, compared with 2% where sheaths had formed in wet soil. Root hairs were 4.5 times more abundant and were more distorted on portions of roots from dry layers than from wet layers. Drier soil enhanced adhesiveness of rhizosheath mucilages and stimulated the formation of root hairs; both effects stabilize the rhizosheath. Extensive and stable rhizosheaths may function in nutrient acquisition in dry soils.     

Drought stress and plant ecotype drive microbiome recruitment in switchgrass rhizosheath

The rhizosheath, a layer of soil grains that adheres firmly to roots, is beneficial for plant growth and adaptation to drought environments. Switchgrass is a perennial C4 grass which can form contact rhizosheath under drought conditions. In this study, we characterized the microbiomes of four different rhizocompartments of two switchgrass ecotypes (Alamo and Kanlow) grown under drought or well-watered conditions via 16S ribosomal RNA amplicon sequencing. These four rhizocompartments, the bulk soil, rhizosheath soil, rhizoplane, and root endosphere, harbored both distinct and overlapping microbial communities. The root compartments (rhizoplane and root endosphere) displayed low-complexity communities dominated by Proteobacteria and Firmicutes. Compared to bulk soil, Cyanobacteria and Bacteroidetes were selectively enriched, while Proteobacteria and Firmicutes were selectively depleted, in rhizosheath soil. Taxa from Proteobacteria or Firmicutes were specifically selected in Alamo or Kanlow rhizosheath soil. Following drought stress, Citrobacter and Acinetobacter were further enriched in rhizosheath soil, suggesting that rhizosheath microbiome assembly is driven by drought stress. Additionally, the ecotype-specific recruitment of rhizosheath microbiome reveals their differences in drought stress responses. Collectively, these results shed light on rhizosheath microbiome recruitment in switchgrass and lay the foundation for the improvement of drought tolerance in switchgrass by regulating the rhizosheath microbiome.     

干旱半干旱草地生态系统与土壤水分关系研究进展

研究干旱半干旱草地生态系统与土壤水分关系和相互作用机理对于揭示草地生态系统稳定性及其水土关键要素的变化过程具有重要意义。从不同界面、不同尺度综述了草地生态系统对土壤水分的影响及草地生态系统的响应与适应机制,总结了草地生态系统与土壤水分关系模型研究的相关进展,并分析了气候变化对草地生态系统和土壤水分关系的影响。草地生态系统通过影响水文过程和生态过程来影响土壤水分,土壤水分在植物生长发育、形态、生理生态过程、种间关系、群落组成和结构以及草地生态系统功能等方面对草地生态系统产生影响;充分揭示草地生态系统-土壤水分相互作用机理是模型研究的关键;气候变化对草地生态系统植物与土壤水分关系具有重要影响。今后应加强以下研究:1)开展草地不同优势种和植物功能型与土壤水分关系的研究,找出能反映植物对土壤水分响应的性状指标,阈值响应点及适应机制;2)注重对不同时间和空间尺度上的转换和比较;3)加强个体、群体和生态系统尺度草地植物生长模型的研究及其与土壤-植被-大气水分传输模型的耦合;4)加强草地生态系统与土壤水分关系对气候变化响应的研究。     

Formation of aggregates by plant roots in homogenised soils

The influence of root growth and water regime on the formation of aggregates was studied in modified minirhizotrons under controlled conditions. Two soils, a black earth (67% clay) and a red-brown earth (19% clay) were ground and forced through a 0.5 mm sieve. Ryegrass, pea and wheat were grown for fifteen wetting and drying (wd) cycles for 5 months. Another set of minirhizotrons was not planted and served as a control. Measurements of aggregate size distribution (ASD), aggregate tensile strength (ATS), aggregate stability (AS), aggregate bulk density (ABD) and organic carbon (OC) were made on single aggregates of the 2–4 mm fraction. The results showed that aggregates of the black earth which has a high clay content and shrink/swell properties had more smaller aggregates with higher ATS, AS and ABD than those from the red-brown earth. It was also found that for both soils: (1) w/d cycles and higher root length density (RLD) increased the proportions of smaller aggregates and aggregate strength; (2) differences in the ability of the plant species to influence aggregation was evident and seemed to be related to the RLD. The RLD was in the order ryegrass > wheat > pea. Mechanisms likely to be involved in processes of aggregate formation and stabilization are discussed. They include cracking of soil due to tensile stresses generated during drying of a shrinking soil; changes in pore water pressure within the soil mass caused by water uptake by plant roots generating effective stresses; and biological processes associated with plant roots and root exudates.