低丘红壤复合农林系统光能竞争与生产力——以花生南酸枣间作为例

复合农林业 ,尤其是农林间作被设想为防治土壤退化 ,增进土壤肥力 ,提高农作物产量的策略[16～ 18] 。如何利用复合农林技术防治红壤退化 ,提高红壤生产力已成为红壤地区的研究热点[1～ 8] 。然而 ,生产者最关心的往往是农林间作中农作物的产量 ,在以往的农林间作技术研究中 ,有增产的报道[13] ,而更多的研究表明复合农林种植会造成农作物减产[3 ,4 ,6,10 ,12 ,15,19,2 0 ] 。农作物减产的原因可能是树木和农作物之间对光能、水分和养分等资源竞争作用所引起 ,更可能是其综合作用的结果[14 ] 。本文以前人推荐的花生 (Ａｒａｃｈｉｓｈｙｐ…     

农林复合系统种间关系研究进展

种间相互作用在很大程度上决定了农林复合系统的生产力和可持续性,理解种间相互作用是经营和管理农林复合系统的关键。地上部分相互作用主要包括复合系统组分对光的竞争与互利、小气候的改变对系统生产力的影响;地下部分相互作用主要包括复合系统组分对水分和养分资源的竞争与互利、固氮树种对系统生产力的影响以及化感作用。今后需加强不同立地条件下的不同农林复合系统种间关系的比较、农林复合系统组分的空间分布格局、化感作用以及农林复合系统种间关系模型等研究。     

农林复合系统中物种间水肥光竞争机理分析与评价

低丘红壤农林复合系统被认为能通过引入树木而利用土壤深层水分及防治水土流失,从而作为亚热带地区应对季节性干旱的有效利用方式。然而,复合也可引起光能、水分和养分的竞争,导致农作物减产。通过作物生长量的测定、利用多年监测的土壤水文数据、15N微区试验及光合有效辐射的测量,综合探讨了南酸枣-花生复合系统引起的物种间水肥光的变化;通过其交互作用形成的协同,竞争关系分析,较为全面地评价了农林复合系统水肥光竞争特征。研究表明：低丘红壤上南酸枣与花生复合,促进了南酸枣生长,却减小了20％～50％的花生产量和生物量。其原因不单是南酸枣遮荫引起复合花生光合有效辐射减弱,还与水、肥竞争有关。复合系统在旱季加大利用50～100cm土层土壤水分,从而缓冲了干旱造成的影响;但南酸枣与花生间作系统也存在着一定的水分竞争。复合使得南酸枣能够利用施于花生区及淋失到60cm深处的养分,提高了养分的利用率;但同时也导致养分的竞争并影响花生的生长。在花生产量、生物量受复合南酸枣竞争影响因子中,以光最大、养分其次、水分最小。农林复合系统水肥光交互作用因其组分类型与时空配置而异,需从生态、经济、社会效益方面对复合模式加以优化。     

三峡库区农林复合生态系统的效益评价

在对三峡库区农林复合生态系统大面积调查和定点测试的基础上,根据生态学原理和生态经济学原理,采用层次分析法（AH）,根据对农林复合生态系统的生物量和生产力,物质流,能量流,价值流,土地利用等系统研究的结果,对三峡库区分布面积较大的4种农林复合生态系统从经济效益,生态效益,社会效益及综合效益方面进行了评价,并与农田生态系统进行了对比研究。这一研究结果将为科学合理地利用三峡库区土地资源,生物资源和气候资源提供重要的科学依据,为保护和改善三峡库区的生态环境,解决农村移民就地安置部分的生态问题及提高农村的经济发展水平提供理论基础。     

碳同位素技术在森林生态系统碳循环研究中的应用

碳同位素技术对碳素在生态系统中的迁移动态具有很好的示踪作用,在生态学各领域研究中应用广泛。土壤、大气、植物是森林生态系统的重要碳库,植物是大气和土壤交换碳元素的重要介质。本文简要总结了碳同位素技术在研究碳元素在植物体内以及植物、土壤、大气碳库之间的迁移规律和生态学过程中的应用,展望了该技术在森林界面学中的应用前景。     

光能竞争对农林复合生态系统生产力的影响

农林复合生态系统是改善渭北黄土区脆弱生态环境、促进该区域经济发展的重要举措.以该区具有代表性的核桃(Juglans regia L.)、李子(Prunus salicina),绿豆(秦豆6号)、辣椒(陕椒981)农林复合模式为对象, 研究不同农林复合系统对光能分布、农作物生长、生产的影响.研究结果表明,不同复合模式下,玉米、辣椒的光合有效辐射、光合速率、生物量及产量均有不同程度的下降,且距树行愈近,影响愈大.叶片水势与玉米、辣椒的光合速率、地上部分生物量以及产量不相关或负相关.而10～20cm土壤含水量与绿豆的生物量和产量以及辣椒的地上部分生物量正相关.但绿豆、辣椒的生产量与其光合有效辐射呈显著正相关性,这说明,农林复合系统中光能竞争是导致间作绿豆、辣椒产量下降的主要原因.     

贵州喀斯特山区人工草地-农田景观土壤温度界面季节性变化

景观界面是生态交错区的重要组成部分,在生态系统的结构、过程和功能中发挥了重要的作用。以贵州喀斯特山区人工草地-农田景观界面为研究对象,对界面表层土壤(0—20 cm)温度进行季节性监测;采用移动窗口法、野外测定和室内统计相结合,对以土壤温度为参数的界面宽度的大小进行了判定;对研究区3个功能区土壤温度进行比较分析。结果表明:贵州人工草地-农田景观界面四季表层土壤的平均温度分别为9.8,26.5,15.4℃和4.8℃;人工草地-农田景观春、夏、秋、冬四季土壤温度界面宽度随土壤温度的变化而变化,表现为由宽变窄的变化规律,分别为37,32,27 m和24 m,土壤温度界面在人工草地系统的影响域变化与总界面宽度保持一致。研究区四季农田功能区系统、人工草地-农田复合功能区系统和人工草地功能区系统的平均土壤温度为14.0,14.1℃和13.9℃,春季、夏季和冬季研究区3个功能区的土壤温度均呈极显著差异,秋季农田功能区系统与人工草地-农田复合功能区系统的土壤温度差异不显著,二者与草地功能区系统差异极显著。建议对研究区采用12—18 m的宽度进行草田间作,为丰富界面理论及"退耕还草"工程提供理论参考和实践措施。     

红壤坡地干旱季节地表-大气界面水分传输——以茶园为例

以红壤坡地茶园为研究对象 ,用波纹比——能量平衡法研究了红壤坡地干旱季节地表 -大气界面水热传输特性 ,结果表明 :在茶园稳定生态系统中 ,气象因素和表层土壤含水量是影响地表 -大气界面水热传输的重要因素。特别是在受旱条件下 ,土壤水分对地表 -大气界面水热传输起决定作用 ,土壤水分越小 ,潜热通量越小 ,显热通量越大 ,反之亦然。观测期间 ,棵间蒸发量占总蒸散量的 3 2 % ,因此通过减少田间土壤水分蒸发来提高农田水分利用效率大有可为     

森林根系分泌物生态学研究:问题与展望

植物根际过程与调控机理研究已成为当前土壤学最活跃、最敏感的研究领域,而根系分泌物作为根系-土壤-微生物界面物质能量交换和信息传递的重要媒介物质,是构成根际微生态系统活力与功能特征的内在驱动因素,是根际概念与根际过程存在的重要前提和基础。然而,由于传统的根际过程研究更强调以实际生产问题为导向,加之农作物生长周期较短、操作便利等诸多因素,以往对植物根系分泌物研究主要聚焦在农业生态系统,而有关根系分泌物在森林生态系统中的重要作用与调控机理研究甚少,认识相对零散和片段化。基于此,该文结合作者实际研究工作中的主要成果和该领域国际前沿动态,综述了森林根系分泌物的生态重要性,重点论述了目前森林根系分泌物生态学研究中存在的主要问题与不足,在此基础上展望了未来森林根系分泌物生态学研究中值得关注的重点方向和研究内容。     

Root exudates and their ecological consequences in forest ecosystems: Problems and perspective

植物根际过程与调控机理研究已成为当前土壤学最活跃、最敏感的研究领域, 而根系分泌物作为根系-土壤-微生物界面物质能量交换和信息传递的重要媒介物质, 是构成根际微生态系统活力与功能特征的内在驱动因素, 是根际概念与根际过程存在的重要前提和基础。然而, 由于传统的根际过程研究更强调以实际生产问题为导向, 加之农作物生长周期较短、操作便利等诸多因素, 以往对植物根系分泌物研究主要聚焦在农业生态系统, 而有关根系分泌物在森林生态系统中的重要作用与调控机理研究甚少, 认识相对零散和片段化。基于此, 该文结合作者实际研究工作中的主要成果和该领域国际前沿动态, 综述了森林根系分泌物的生态重要性, 重点论述了目前森林根系分泌物生态学研究中存在的主要问题与不足, 在此基础上展望了未来森林根系分泌物生态学研究中值得关注的重点方向和研究内容。     

Review: Current status and future prospects of associative nitrogen fixation in rice

Biological sources of nutrients are gaining importance over the chemical and organic sources from the standpoint of environmental safety and quality, and sustainable agriculture. The nutrient input for a growing rice crop can largely be met by promoting the activities of physiologically diverse microorganisms in the aerobic, anaerobic and interface zones in the ecologically important flooded soils. Associative bacteria contribute from 10 to 80 kg N per hectare per cropping season depending upon the ecosystem, cultural practices and rice variety grown. In addition to N contribution, these bacterial associations can improve the nutrient transformations and contribute to plant growth-promoting effects. Current improved agronomic and crop production management systems greatly affect the contributions of biological sources to the overall soil nutrient status. Azospirillum and other associative bacterial systems have been intensively researched using various evaluation techniques to understand the diazotrophic rhizocoenosis. Researches clearly indicate that these associations are governed by several soil, water, nutrient, agrochemical, plant genotype and other biological factors. Considerable efforts have been made so far in selecting efficient bacterial strains as inoculants and identifying host genotypes which support maximum nitrogenase activity in addition to other beneficial traits of effective associative relationships. Knowledge gained so far on how the N2-fixing system in rice functions suggests the need for providing optimum management practices to ensure greater contribution from the plant-microbe associations. Holistic approaches integrating technological developments and achievements in biological sciences could lead to crop improvement. Research on extending nitrogen-fixing symbiosis to rice using molecular and genetic approaches is underway, albeit at a slow pace. The need for further fine-tuning and developing management practices, innovative approaches to improve rice-bacterial systems and the strategies to sustain the benefits from associative diazotrophy are discussed.     

The role of eutrophication in the biological control of water hyacinth, <Emphasis Type="Italic">Eichhornia crassipes</Emphasis>, in South Africa

South Africa has some of the most eutrophic aquatic systems in the world, as a result of the adoption of an unnecessarily high 1 mg l⁻¹ phosphorus (P) standard for all water treatment works in the 1970 s. The floating aquatic macrophyte, water hyacinth (Eichhornia crassipes (Mart.) Solms (Pontederiaceae)), has taken advantage of these nutrient rich systems, becoming highly invasive and damaging. Despite the implementation of a biological control programme in South Africa, water hyacinth remains the worst aquatic weed. A meta-analysis of published and unpublished laboratory studies that investigated the combined effect of P and nitrogen (N) water nutrient concentration and control agent herbivory showed that water nutrient status was more important than herbivory in water hyacinth growth. Analysis of long-term field data collected monthly from 14 sites around South Africa between 2004 and 2005 supported these findings. Therefore the first step in any water hyacinth control programme should be to reduce the nutrient status of the water body.     

Nutrient stress gradient in the bottom 5 cm of fast ice, McMurdo Sound, Antarctica

One-centimeter-scale vertical sampling of fast ice from McMurdo Sound, Antarctica reveals evidence of progressive nutrient limitation with distance above the ice/water interface. Over the bottom 6 cm photosynthetically active radiation increases by between 1.8 and 3 times, C:N increases from 6.8 to 19.8 and δ¹³C increases from −18 to −12. Fatty acid composition also changes with a consistent decline in polyunsaturated fatty acids and a rise in saturated fatty acids. These factors all suggest severe and progressive nutrient limitation with distance from the ice/water interface. Accepted: 5 September 1998     

Testing experimentally the effect of soil resource mobility on plant competition

Aims The volume of soil beyond a plant's roots from which that plant is able to acquire a particular nutrient depends upon the mobility of that nutrient in the soil. For this reason it has been hypothesized that the strength of competitive interactions between plants vary with soil nutrient mobility. We aimed to provide an experimental test of this hypothesis.Methods We devised two experimental systems to investigate specifically the effect of nutrient transport rates upon intraspecific competition. In the first, the exchange of rhizosphere water and dissolved nutrients between two connected pots, each containing one plant, was manipulated by alternately raising and lowering the pots. In the second experiment, the roots systems of two competing plants were separated by partitions of differing porosity, thereby varying the plants' access to water and nutrients in the other plant′s rhizosphere. In this second experiment, we also applied varying amounts of nutrients to test whether higher nutrient input would reduce competition when competition for light is avoided, and applied different water levels to affect nutrient concentrations without changing nutrient supply.Important findings In both experiments, lower mobility reduced competitive effects on plant biomass and on relative growth rate (RGR), as hypothesized. In the second experiment, however, competition was more intense under high nutrient input, suggesting that low nutrient supply rates reduced the strength of the superior competitor. Competitive effects on RGR were only evident under the low water level, suggesting that under lower nutrient concentrations, competitive effects might be less pronounced. Taken together, our results provide the first direct experimental evidence that a reduction in nutrient mobility can reduce the intensity of competition between plants.     

Effects of the Dry–Wet Hydrological Shift on Dissolved Organic Carbon Dynamics and Fate Across Stream–Riparian Interface in a Mediterranean Catchment

Abstract The stream–riparian interface, characterized by a dynamic and complex hydrology, is an important control point for nutrient fluxes and processing between terrestrial and aquatic systems. Predicted alterations in the discharge regime in Mediterranean climate regions make it necessary to understand the effects of abrupt hydrological transition between dry and wet conditions on the transport and fate of dissolved organic carbon (DOC) across the stream–riparian interface. In this study, the concentrations and fate of total DOC (TDOC) and a subset of four molecular weight fractions (<1 kDa, 1–10 kDa, 10–100 kDa, >100 kDa) were investigated in stream water and riparian groundwater during autumn of 2003 and 2004. The two study periods were characterized by contrasting antecedent hydrological conditions: the streamflow was interrupted in summer 2003 but was permanent in summer 2004. Comparison of the two study periods indicates that an abrupt dry–wet hydrological transition amplifies the water exchange across the stream–riparian interface and favors retention of up to 57% of the TDOC that flows across the interface. Furthermore, the efficiency of DOC retention across the stream-riparian interface also varies greatly depending on DOC molecular size. More than 70% of DOC fractions higher than 10 kDa were retained, whereas the smaller fraction (less than 1 kDa) was nearly conserved. Consequently, our study helps to clarify the effects of extreme hydrological events on DOC transport in running waters in Mediterranean regions.     

Towards optimum permeability reduction in porous media using biofilm growth simulations

While biological clogging of porous systems can be problematic in numerous processes (e.g., microbial enhanced oil recovery—MEOR), it is targeted during bio‐barrier formation to control sub‐surface pollution plumes in ground water. In this simulation study, constant pressure drop (CPD) and constant volumetric flow rate (CVF) operational modes for nutrient provision for biofilm growth in a porous system are considered with respect to optimum (minimum energy requirement for nutrient provision) permeability reduction for bio‐barrier applications. Biofilm growth is simulated using a Lattice‐Boltzmann (LB) simulation platform complemented with an individual‐based biofilm model (IbM). A biomass detachment technique has been included using a fast marching level set (FMLS) method that models the propagation of the biofilm–liquid interface with a speed proportional to the adjacent velocity shear field. The porous medium permeability reduction is simulated for both operational modes using a range of biofilm strengths. For stronger biofilms, less biomass deposition and energy input are required to reduce the system permeability during CPD operation, whereas CVF is more efficient at reducing the permeability of systems containing weaker biofilms. Biotechnol. Bioeng. 2009;103: 767–779. © 2009 Wiley Periodicals, Inc.     

A tracer study for assessing the interactions between hydraulic retention time and transport processes in a wetland system for nutrient removal

In this study, a new-generation subsurface upflow wetland (SUW) system packed with the unique sorption media was introduced for nutrient removal. To explore the interface between hydraulic and environmental performance, a tracer study was carried out in concert with a transport model to collectively provide hydraulic retention time (7.1 days) and compelling evidence of pollutant fate and transport processes. Research findings indicate that our pollution-control media demonstrate smooth nutrient removal efficiencies across different sampling port locations given the appropriate size distribution conversant with the anticipated hydraulic patterns and layered structure among the sorption media components. The sizable capacity for nutrient removal in this bioprocess confirms that SUW is a promising substitute for an extension of traditional on-site wastewater treatment systems.     

Plant species natural abundances are determined by their growth and modification of soil resources in monoculture

Plant and Soil - Although modelling of water and nutrient uptake by root systems has advanced considerably in recent years, steep local gradients of nutrient concentration near the root-soil...     

Water Supply Changes N and P Conservation in a Perennial Grass Leymus chinensis

Changes in precipitation can influence soil water and nutrient availability, and thus affect plant nutrient conservation strategies. Better understanding of how nutrient conservation changes with variations in water availability is crucial for predicting the potential influence of global climate change on plant nutrient-use strategy. Here, green-leaf nitrogen (N) and phosphorus (P) concentrations, N- and P-resorption proficiency (the terminal N and P concentration in senescent leaves, NRP and PRP, respectively), and N- and P-resorption efficiency (the proportional N and P withdrawn from senescent leaves prior to abscission, NRE and PRE, respectively) of Leymus chinensis (Trin.) Tzvel., a typical perennial grass species in northern China, were examined along a water supply gradient to explore how plant nutrient conservation responds to water change. Increasing water supply at low levels (< 9000 mL/year) increased NRP, PRP and PRE, but decreased green-leaf N concentration. It did not significantly affect green-leaf P concentration or NRE. By contrast, all N and P conservation indicators were not significantly influenced at high water supply levels (> 9000 mL/year). These results indicated that changes in water availability at low levels could affect leaf-level nutrient characteristics, especially for the species in semiarid ecosystems. Therefore, global changes in precipitation may pose effects on plant nutrient economy, and thus on nutrient cycling in the plant-soil systems.