根系间的相互作用——竞争与互利

植物根系间的相互作用分为竞争和互利两种形式 ,它是决定植物群落动态变化和群落结构的重要因素。根系间的竞争包括植株个体自身根系的竞争以及个体与个体根系间 (同种或异种 )的竞争两方面 ,前者的发生在农林系统中是不可避免的并且很难调控 ,后者可以分为种间植物根系的竞争和种内植物根系的竞争。还阐述了根系的竞争能力和与其密切相关的根系生长率、根组织的新陈代谢、植物的生长形式和根系的空间结构等植物特性 ,同时介绍了根系对水和养分的竞争机理、形式、影响以及竞争强度计算方法。接着具体分析包括根系错位在内的各种根系互利现象和相关机理。影响根系间相互作用的限制性因子有土壤营养的异质性、大气 CO2 浓度、地下草食生物、根系生产力和生物量、根系结构、形态和生理调节、土壤养分的扩散性以及植物间距等。随着科技的进步和各门学科的发展 ,未来根系的研究方向主要体现在结合实践优化农林系统中不同物种间的作用关系、预测根系竞争在全球气候变化下的发展规律、更新实验研究方法及手段研究作用机理等 3个方面。     

农林系统研究进展

综述了国内外农林系统的研究进展 ,介绍了农林系统的概念、产生背景和过程及主要的研究方向。从农林系统的结构和分类、农林系统小气候及系统效益评价等 3个方面对当前农林系统的研究现状进行了评述。重点从水分、温度、辐射、光照及人体舒适度等方面分析了农林系统小气候的研究状况 ;从化感作用和地下部分相互作用两个方面介绍了系统组分间的相互作用关系。同时指出农林系统类型较为单一、理论研究落后于实践、基础理论研究相对薄弱等研究中存在的问题。提出农林系统的研究应进一步加强多学科深层次、实质性的交流与合作 ,注重科研机构与生产基层的有机联系 ,加强理论基础研究 ,因地制宜地发展农林系统 ,更好地为生产实践服务。     

湿地植物生长模型的改进及其动态的计算机模拟分析

湿地植被的恢复与人工调控是恢复生态学研究的热点问题之一,建立湿地大型植物生长的控制模型。能为此提供一种理论模式。在湿地植物群落中,植物种间的相互作用关系较为复杂,在植物生长的不同阶段显现为互利、竞争或相互独立。基于此我们对Shukla提出的湿地植物生长模型进行了改进．建立了一种能够反映种间复杂作用机制(包括互利与竞争)的新模型。以植物的生物量为描述变量,用统计方法确定了模型参数,对实例进行了计算机模拟与数值分析．并研究了植物生长系统的稳定性。结果表明：①新模型能有效地描述湿地植物种间互利或竞争作用．优于只考虑种间竞争作用的Shukla模型;②对植物生长过程的计算机模拟结果和图像显示,在较低生物量水平上．种间显现互利关系;在较高生物量水平上．种间发生竞争作用,竞争的结局为一种植物占优势,而另一种植物趋于灭亡．这些与实际观测结果是一致的;③对系统进行了稳定性分析;④根据数值模拟结果,提出了湿地恢复的人工调控对策与建议。     

物种关系模式及其进化

主要介绍了种间相互作用的关系类型,包括中性作用,正相互作用（偏利、互利、原始协作）,负相互作用（竞争、捕食、寄生、偏害）,以及其进化意义。     

杨树-农作物复合系统中的化感作用

综述了植物化感作用的类型、作用机理、影响植物化感作用的因素,并从化感作用角度提出目前长江中下游主要农林复合系统(杨树-农作物)的研究方向,杨树与不同农作物种类配置研究;针对杨树主要害虫天牛进行生物防治的“相生植物”的筛选;杨树自毒作用以及对后续农作影响研究;杨树对土壤微生物区系和土壤酶活性的影响等。     

气候变化背景下农林复合系统碳汇功能研究进展

农林复合系统作为一种土地综合利用体系,可以有效吸收和固定CO₂、增加碳储量,在达到收获目的的同时,可有力减轻温室效应.农林复合系统对CO₂的调控作用,使人们认识到农林复合系统较单一作物系统有着明显优势,因此,深入了解不同农林复合系统的碳汇功能及其影响因素,对全球碳循环研究及碳收支准确评估具有重要意义.本文综述了农林复合系统的概念与分类,探讨了农林复合系统不同组分的碳固存潜力及其影响因子,得出不同区域、不同类型农林复合系统内植被的固碳速率相差很大(0.59～11.08 t C·hm^-2·a^-1),其主要受到气候因子和农林复合系统自身特性(物种组成、林木密度和林龄)的影响.农林复合系统内土壤的固碳潜力受到系统内树木和非树木成分输入的生物量多少和质量、土壤质地、土壤结构的影响.不同地区的任何一个农林复合系统的碳储量多少主要依赖于复合系统中各组分的结构和功能.针对目前的研究现状,指出应重点加强农林复合系统优化结构的碳汇功能研究,以及加强农林复合系统碳储量的时空分布格局及其固碳机制的长期研究.     

蕨类植物的化感作用及其对生物多样性的影响

植物化感作用是植物通过向环境中释放化学物质从而对同种植株和繁殖体或与其他植物之间产生的直接或间接、有益或有害的作用,它影响植物分布、群落形成与演化、作物间作等,与生物多样性保护以及农林和园艺生产实践关系密切,在国际上受到越来越多的关注。但国内这方面的研究起步相对较晚,研究范围有限,对蕨类植物化感作用的报道更少。本文系统介绍了蕨类植物化感作用的研究进展,包括蕨类植物种内的化感作用(即自毒效应)、常见的蕨类植物种间的化感作用(即孢子体对配子体的化感作用和配子体对配子体的化感作用)及蕨类植物对种子植物的化感作用(蕨类植物可通过化感作用与种子植物争夺更多的资源和生长空间)。还介绍了种子植物对蕨类植物的化感作用(主要表现为抑制作用)以及蕨类植物化感作用与动物侵食、微生物侵染的关系,研究发现昆虫侵食能增强或减弱蕨类植物的化感作用,微生物的活动可能增强某些蕨类植物的化感作用。本文从上述不同角度说明蕨类植物化感作用对生物多样性的影响,希望有助于促进我国学者对该领域的深入研究。     

渭北黄土区农林复合系统光能竞争与生产力

农林复合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.本文以该区具有代表性的核桃/李子与大豆(秦豆8号)/辣椒(陕椒981)农林复合模式为对象, 研究了复合系统内大豆、辣椒的光合作用、生长和产量等情况.结果表明:不同种植模式下,大豆、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.叶片水势与大豆、辣椒的光合速率、地上部分生物量以及产量呈不相关或负相关. 而10～20 cm土壤含水量与大豆的生物量和产量,以及辣椒的地上部分生物量呈正相关.大豆、辣椒产量与其光合有效辐射呈显著正相关.说明在农林复合系统中,光能竞争是导致间作大豆、辣椒产量下降的主要原因.     

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.     

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。     

Positive interactions among plants

Experimental evidence for positive interactions, or facilitation, among plants has increased markedly during the last 10 years. Experiments documenting facilitation have been conducted in many diverse ecological systems, which suggests that positive interactions may be fundamental processes in plant communities. Here, I review the evidence for facilitation, the mechanisms by which facilitation operates, and the effects facilitation has on community structure. Facilitative mechanisms may act simultaneously with resource competition or allelopathy, and the overall effect of one species on another may be the product of multiple, complex interactions. Positive interactions may also determine community spatial patterns, permit coexistence, enhance diversity and productivity, and drive community dynamics. Once viewed as anecdotal and idiosyncratic, facilitation is now contributing to a more complete understanding of community structure and dynamics.     

Experimental comparison of competition and facilitation in alpine communities varying in productivity

Question. Competitive and facilitative interactions among plant species in different abiotic environments potentially link productivity, vegetation structure, species composition and functional diversity. We investigated these interactions among four alpine communities along an environmental productivity gradient in a generally harsh climate. We hypothesised that the importance of competition would be higher in more productive sites. Location. Mt. M. Khatipara (43°27′N, 41°41′E, altitude 2750 m), NW Caucasus, Russia. Communities ranged from low‐productivity alpine lichen heath (ALH) and snowbed communities (SBC), to intermediate productivity Festuca grassland (FVG), and high‐productivity Geranium‐Hedysarum meadow (GHM). Methods. We quantified the relative influence of competition and facilitation on community structure by expressing biomass of target species within each natural community proportionally to biomass of the species in a “null community” with experimental release from interspecific competition by removing all other species (for 6 years). An overall index of change in community composition due to interspecific interactions was calculated as the sum of absolute or proportional differences of the component species. Results. Species responses to neighbour removal ranged from positive to neutral. There was no evidence of facilitation among the selected dominant species. As expected, competition was generally most important in the most productive alpine community (GHM). The intermediate position for low‐productivity communities of stressful environments (ALH, SBC) and the last position of intermediately productive FVG were unexpected. Conclusions. Our results appear to support the Fretwell‐Oksanen hypothesis in that competition in communities of intermediate productivity was less intense than in low‐ or high‐productive communities. However, the zero net effect of competition and facilitation in FVG might be the result of abiotic stress due to strong sun exposure and high soil temperatures after neighbour removal. Thus, non‐linear relationships between soil fertility, productivity and different abiotic stresses may also determine the balance between competition and facilitation.     

不同根系分隔方式对栗和茶幼苗生长的影响

研究不同根系分隔方式对栗(Castanea mollissima)/茶(Camellia sinensis)间作地下部分相互作用和植物种间互作动态的影响, 探究根系互作对植株株高、基径和根系生长的影响, 可为栗/茶复合经营模式的可持续发展提供科学指导。该研究以栗/茶间作和相应单作为研究对象, 运用盆栽实验的根系分隔技术(塑料膜分隔、尼龙网分隔和不分隔), 分别利用logistic生长模型模拟栗和茶株高与基径生长动态过程, 利用幂函数研究株高-基径的异速生长关系, 并从细根发育角度分析地下部分相互作用对植物生长发育的影响。结果显示: 与单作茶相比, 间作茶塑料膜分隔方式地上部分、地下部分和总的干生物量以及根长、根表面积、根体积、分形丰度和直径为0.2-1.0 mm根的根长分别显著增加了357.1%、281.8%和345.2%以及74.3%、273.9%、244.8%、42.0%和382.4%。间作茶塑料膜分隔方式的株高渐进值比单作茶显著增加了30.9%, 尼龙网分隔方式的间作栗株高渐进值和基径渐进值比单作栗分别显著增加了21.9%和28.2%; 塑料膜分隔方式下间作茶株高达到最大增长速率的时间和间作栗的基径达到最大增长速率的时间比相应单作模式分别显著延迟了14和15天。不同处理中栗和茶的株高-基径异速生长均呈显著线性正相关关系, 且不分隔方式下间作栗和间作茶的株高-基径异速生长模型的斜率均表现为最小, 且均<1。结果表明, 栗和茶间作时, 栗地上部分通过遮阴促进茶幼苗侧根分枝数、细根根长和株高的生长来增加其干生物量累积, 但地下部分则表现为竞争作用, 且随着地下部分竞争作用的强度增加会逐渐抵消地上部分的促进作用, 最终植物种间相互作用表现为中性作用。     

盐度及种间相互作用对海三棱藨草、互花米草萌发及生长的影响

盐度和种间作用是影响湿地植物群落构建的关键因子。然而,已有研究主要集中于植物成体阶段,我们对生活史早期更新阶段的种间相互作用了解十分有限。崇明东滩国家级自然保护区是位于长江口的重要湿地,外来入侵植物互花米草对优势土著物种海三棱藨草的竞争排斥对当地生态系统造成了严重的负面影响。通过受控实验探讨了盐度及种间作用对海三棱藨草和互花米草种子萌发及生长的影响,以深入了解更新过程在盐沼湿地植物群落构建中的作用。结果表明,在培养皿中盐度对海三棱藨草的萌发有显著抑制作用,互花米草的萌发率受盐度影响不显著但萌发进程被延迟。混种处理对两者的萌发存在一定促进效应,且其作用强度受到盐度的调控。海三棱藨草与互花米草种子在萌发阶段的相互促进并非是通过化感作用实现的,可能是由于萌发过程对盐分的吸收减弱了盐胁迫的影响。盆栽条件下,两物种混种时的萌发及生长表现（高度、地上生物量）较单种时有所下降,但差异不显著。种间竞争受环境胁迫程度及生活史阶段的影响,竞争作用在胁迫较弱的淡水环境及生活史后期更强。盐沼湿地植物群落在形成早期受到盐度等环境因子的影响较大,不同植物对盐胁迫的响应是影响种群建成的主导因素,后期种间竞争的重要性不断增加,最终决定了植物群落的整体格局。     

Separation of allelopathy from resource competition using rice/barnyardgrass mixed-cultures

Plant-plant interference is the combined effect of allelopathy, resource competition, and many other factors. Separating allelopathy from resource competition is almost impossible in natural systems but it is important to evaluate the relative contribution of each of the two mechanisms on plant interference. Research on allelopathy in natural and cultivated plant communities has been hindered in the absence of a reliable method that can separate allelopathic effect from resource competition. In this paper, the interactions between allelopathic rice accession PI312777, non-allelopathic rice accession Lemont and barnyardgrass were explored respectively by using a target (rice)-neighbor (barnyardgrass) mixed-culture in hydroponic system. The relative competitive intensity (RCI), the relative neighbor effect (RNE) and the competitive ratio (CR) were used to quantify the intensity of competition between each of the two different potentially allelopathic rice accessions and barnyardgrass. Use of hydroponic culture system enabled us to exclude any uncontrolled factors that might operate in the soil and we were able to separate allelopathy from resource competition between each rice accession and barnyardgrass. The RCI and RNE values showed that the plant-plant interaction was positive (facilitation) for PI312777 but that was negative (competition) for Lemont and barnyardgrass in rice/barnyardgrass mixed-cultures. The CR values showed that one PI312777 plant was more competitive than 2 barnyardgrass plants. The allelopathic effects of PI312777 were much more intense than the resource competition in rice/barnyardgrass mixed cultures. The reverse was true for Lemont. These results demonstrate that the allelopathic effect of PI312777 was predominant in rice/barnyardgrass mixed-cultures. The most significant result of our study is the discovery of an experimental design, target-neighbor mixed-culture in combination with competition indices, can successfully separate allelopathic effects from competition.     

Changes in plant interactions along a gradient of environmental stress

A combination of competition and facilitation effects operating simultaneously among plant species appears to be the rule in nature, where these effects change along productivity gradients often in a non-proportional manner. We investigated changes in competition and facilitation between a leguminous shrub, Retama sphaerocarpa , and its associate understorey species along an environmental gradient in semi-arid southeast Spain. Our results show a change in the net balance of the interaction between the shrub and several of its associated species, from clearly positive in the water-stressed, infertile environment to neutral or even negative in the more fertile habitat. There was a weakening of facilitation along the fertility gradient as a consequence of improved abiotic conditions. Competition was the most intense for below-ground resources in the less fertile environment while total competition tended to increase towards the more productive end of the gradient. Changes in the balance of the interaction between and among different plant species along the gradient of stress were caused by a decline in facilitation rather than by a change in competition. As both competition intensity and facilitation change along gradients of resource availability, plant interactions are best viewed as dynamic relationships, the outcome of which depends on abiotic conditions.     

Allelopathic adaptation can cause competitive coexistence

The maintenance of plant diversity is often explained by the ecological and evolutionary consequences of resource competition. Recently, the importance of allelopathy for competitive interactions has been recognized. In spite of such interest in allelopathy, we have few theories for understanding how the allelopathy influences the ecological and evolutionary dynamics of competing species. Here, I study the coevolutionary dynamics of two competing species with allelopathy in an interspecific competition system, and show that adaptive trait dynamics can cause cyclic coexistence. In addition, very fast adaptation such as phenotypic plasticity is likely to stabilize the population cycles. The results suggest that adaptive changes in allelopathy can lead to cyclic coexistence of plant species even when their ecological characters are very similar and interspecific competition is stronger than intraspecific competition, which should destroy competitive coexistence in the absence of adaptation.     

Effects of Competition and Facilitation on Species Assemblage in Two Types of Tropical Cloud Forest

Competition and facilitation between tree individuals are two kinds of non-random processes influencing the structure and functioning of forest communities, but how these two plant-plant interactions change along gradient of resources or environments remains very much a matter of debate. We developed a null model to test the size-distance regression, and assessed the effects of competition and facilitation (including interspecific interactions, intraspecific interactions and overall species interactions) on each adult tree species assemblage [diameter at breast height (dbh) ≥5 cm] across two types of tropical cloud forest with different environmental and resource regimes. The null model test revealed that 17% to 27% tree species had positive dbh-distance correlations while 11% to 19% tree species showed negative dbh-distance correlations within these two forest types, indicating that both competition and facilitation processes existed during the community assembly. The importance of competition for heterospecific species, and the intensity of competition for both heterospecific and overall species increased from high to low resources for all the shared species spanning the two forests. The importance of facilitation for conspecific and overall species, as well as that the intensity of facilitation for both heterospecific and conspecific species increased with increasing low air temperature stress for all the shared species spanning the two forests. Our results show that both competition and facilitation processes simultaneously affect parts of species assemblage in the tropical cloud forests. Moreover, the fact that nearly 50% species assemblage is not detected with our approaches suggest that tree species in these tropical forest systems are assembled with multiple ecological processes, and that there is a need to explore the processes other than the two biotic interactions in further researches.     

Interspecific interactions in phytophagous insects revisited: a quantitative assessment of competition theory

The importance of interspecific competition is a highly controversial and unresolved issue for community ecology in general, and for phytophagous insects in particular. Recent advancements, however, in our understanding of indirect (plant- and enemy-mediated) interactions challenge the historical paradigms of competition. Thus, in the context of this rapidly developing field, we re-evaluate the evidence for interspecific competition in phytophagous insects using a meta-analysis of published studies. Our analysis is specifically designed to test the assumptions underlying traditional competition theory, namely that competitive interactions are symmetrical, necessitate spatial and temporal co-occurrence, and increase in intensity as the density, phylogenetic similarity, and niche overlap of competing species increase. Despite finding frequent evidence for competition, we found very little evidence that plant-feeding insects conform to theoretical predictions for interspecific competition. Interactions were highly asymmetrical, similar in magnitude within vs. between feeding guilds (chewers vs. sap-feeders), and were unaffected by the quantity of resources removed (% defoliation). There was mixed support for the effects of phylogeny, spatial/temporal separation, and the relative strength of intra- vs. interspecific competition. Clearly, a new paradigm that accounts for indirect interactions and facilitation is required to describe how interspecific competition contributes to the organization of phytophagous insect communities, and perhaps to other plant and animal communities as well.     

灰飞虱与褐飞虱种内和种间密度效应比较

在人工气候室内比较研究了灰飞虱和褐飞虱在汕优63和秀水11上的种内和种间密度效应对其主要生物学参数的影响,结果表明两种稻飞虱均存在显著的种内竞争,主要表现为随着密度增加,若虫发育历期延长、若虫羽化率下降、雌成虫寿命缩短、每雌产卵量下降。种内密度效应与稻飞虱种类和寄主品种有显著互作关系,灰飞虱种内竞争较褐飞虱明显,二者在适宜寄主上种内竞争更为明显。同时,两种稻飞虱存在着显著的种间密度效应,主要表现为异种存在时的促进作用,即异种共存时若虫历期缩短、若虫羽化率提高、雌虫寿命延长、每雌产卵量增加。种间密度效应也与稻飞虱种类和寄主品种有显著互作关系,两种共存对灰飞虱的有利作用显著大于对褐飞虱的有利作用,在欠适宜寄主上种间互利效应更为明显。最后,本文对稻飞虱种内和种间密度效应的机制和进化意义进行了讨论。