【作者】 江小雷；

【导师】 王刚；

【作者基本信息】 兰州大学 ， 生态学， 2006， 博士

【摘要】 物种多样性对生态系统功能的影响是生态学领域所研究的核心科学问题之一。许多有关物种多样性-生态系统功能关系的观察、理论和实验研究都表明，在局域尺度范围内，植物种多样性对生态系统功能具有重要影响。然而，对于促成物种多样性-生态系统功能关系的潜在生态学机制却缺乏足够的了解。本实验利用两种不同类型的牧草——9种一年生牧草和10种多年生牧草，采用各物种单播及混播的方法，构建不同多样性梯度的人工草地实验群落，对物种多样性与生态系统功能(主要包括生产力、入侵性、水分利用)关系的短期关系格局及潜在作用机理进行了探讨。结果表明：(1)各物种单播的生产力差异显著，表明物种间在生长率、资源利用能力及功能特征方面存在较大差异。不同的群落其生产力随物种多样性的变化模式不同。在一年生群落中，物种多样性与群落生产力呈单峰格局关系，而在多年生群落中，物种多样性与群落生产力呈显著正相关关系。在两种群落中，物种多样性和物种成分都对系统生产力有显著影响。(2)不同的群落中，多样性与互补效应间关系较为复杂。在一年生群落中，4种互补效应指数分析均表明，虽然在部分混播群落中存在资源的互补性利用，但物种多样性与互补效应间不存在显著正相关关系，这说明在一年生植物群落中，物种间的相互关系较为复杂，不单纯表现为生态位互补效应。而在多年生群落中，混播群落中不仅程度不同地存在互补效应，而且，互补效应与物种多样性间呈显著正相关关系。同时还表明，不同的衡量指标反映出的资源互补性利强度有所不同。因此，在多样性-生态系统功能关系研究中，应同时应用多种方法，以免评价多样性效应时失之偏颇。(3)采用“分离添加效应”方法可将同一群落中的多样性净效应区分为取样效应和互补效应两个组成部分，并可对每部分的相对贡献做出定量估测。取样效应和生态位互补效应可同时对物种多样性-生态系统功能关系产生影响，但两种作用机理在不同的群落对物种多样性的变化有不同的响应。在一年生群落中，物种多样性与互补效应之间呈单峰曲线关系。而物种多样性与取样效应间呈显著的正相关关系，说明在一年生群落中，随着物种多样性的增加，特殊物种在群落中占优势地位，并对群落生产力的提高起主导作用。与之相反，在多年生群落中，互补效应与物种多样性间呈显著正相关关系，而取样效应与物种多样性间则线性关系不显著，进一步证明在多年生群落中，物种间对资源的互补性利用是群落生产力随多样性增加而提高的主要原因。(4)对于一年生植物群落而言，多样性的三种成分——物种多样性、功能群多样性及功能多样性对群落生产力的影响均表现出相同的趋势，但影响程度有所不同。物种多样性的变化对群落生产力没有显著影响，而功能群多样性和功能多样性的增加对群落生产力有显著影响，二者均对生产力的增加有促进作用，而且功能多样性对系统功能的影响程度更大。同时，混播群落中物种间在水分利用上也程度不同地存在互补作用。物种多样性，功能群多样性和功能多样性的增加均使土壤水分含量呈下降趋势，但在三种多样性成分中，只有功能多样性对土壤水分含量有显著影响。证明物种的功能特征而不是物种的数目，才对系统水分资源的利有实质性的影响。(5)平均而言，一年生群落的生产力和抗杂草入侵性能力均较多年生群落高。无论是一年生群落，还是多年生群落，随着物种多样性的增加，草地生产力均呈增加趋势。物种多样性和群落生产力均对杂草的入侵有显著的抑制作用。虽然两种群落在多样性—生产力—入侵性关系上表现为相同的格局，但在两种群落中，支配这种关系的作用机理却完全不同。在一年生群落中，物种多样性一群落生产力—杂草入侵关系受取样效应的支配，而在多年生群落中，物种多样性一群落生产力—杂草入侵性关系受互补效应的支配。表明，在不同的群落中，相同的生态现象其内在的作用机理可能不相同，因而在多样性-生态系统功能关系研究中，以某一特定的研究结果推论其他生态系统中二者间关系模式时，应持慎重态度。更多还原

【Abstract】 The effects of species diversity on ecosystem functioning is one of the most important problems in ecological research. A number of observational, theoretical and experimental works lead to the conclusion that local plant species diversity can have important effect on ecosystem functioning. However, little is known about the ecological mechanisms behind these effects of species diversity. To investigate the relationship between plant species diversity and ecosystem functioning, mainly including productivity, invisibility and soil water use efficiency, in artificial grassland and underlying mechanisms control it in relative short-term, we established experimental communities containing monocultures and different diversity gradient using two different types of plant species--nine cultivated annual species and ten perennial species. The results indicated that:(1) Individual species differed significantly in their productivity, showing that they had significantly differences in growth rate, resource use ability, and functional traits. Two communities showed different patterns of diversity - productivity relationships. In annual communities, the relationship between species diversity and community productivity was unimodal. While in perennial communities, community productivity was positively correlated to species diversity. Otherwise, species diversity and species composition both had significantly effects on ecosystem productivity in two different communities.(2) The relationships between species diversity and complementarity are complex in two communities. In annual communities, the analysis of four complementary indices indicated that complementarity do exist in some mixtures, but there were no significant linear relationship between species diversity and complementary effect, and this suggested that the interspecies interactions are represented not only by complementary resource use, but also by other interaction, such as competitive effect. In perennial communities, however, complementary effects existed almost in all mixtures, and there are significantly linear correlations between species diversity and complementarity. Otherwise, the magnitudes of complementary resource use represented by four indices are different. This suggests that complementary resource use may operate mechanistically in driving the diversity effect in perennial communities. These results demonstrated that multiple measures should be used in order to approach proper conclusions in diversity-ecosystem functioning research.(3) By using "additive partitioning" method introduced by Loreau and Hector, the net effects of diversity generated by a combination of sampling effects and complementary effects can be separated, and their individual contributions can be estimated also. Sampling effect and complementary effect may simultaneously operate on how species diversity enhances ecosystem functioning, but these two components responded to increasing species diversity differently in two communities. In annual communities, the relationship between complementary effect and species diversity are unimodal, suggesting that as the increasing of species diversity, the increase of community productivity was not only caused by complementarity, but also by competition interactions. This led to the results that community productivity is not necessarily increased with increasing species diversity in annual communities. However, the sampling effect showed a positive correlation to species diversity, and this indicated that the species with particular traits, such as higher productivity and competitive ability, are likely to dominate community and have large impacts on ecosystem functioning in annual communities. In contrast with annual communities, however, complementary effects are positively correlated to species diversity, while sampling effects showed no relationships to species diversity. This provides another evidence that complementary resource use between species drives the positive relationships between diversity and productivity in perennial communities.(4) In annual communities, the effects of three components of diversity-plant species diversity, plant functional group diversity and plant functional diversity, on community productivity and soil water content all showed similar trend, but the importance they contributed are different. Multiple regression analyses showed that as the increase of functional group diversity and functional diversity, community productivity increased significantly, while species diversity showed no significant effect on productivity. Species diversity, functional group diversity and functional diversity all showed negative correlations to soil water content, but only functional diversity showed significant effects. These results suggested that, compared with species number, functional differences among species and the range of functional traits carried by plants species are the basis of biodiversity effects on ecosystem functioning. Thus, we can draw a conclusion that in our short-term experiment, these diversity effects of increasing functional group diversity or functional diversity were likely because species differing greatly in size, life form, phenology and capacity to capture and use efficiently resources in diverse communities can realize complementary resource use in the temporal, spatial, and biological ways.(5) On average, annual species performed better in productivity and invasion resistance than perennial species. A positive diversity-productivity relationship and negative diversity-invasibility and productivity-invasibility relationships emerged in two different communities. However, the mechanisms underlying are different in two communities. In the annual communities, the observed positive diversity-productivity and negative diversity - invasibility relationships are linked by the sampling effect. In the perennial communities, however, the mechanism responsible for these observed relationships are the complementary effect. These results demonstrated that identical mechanisms drive both diversity - productivity and diversity - invasibility relationships, and that because species in different communities (here, annual and perennial) may differ in their life history, biological and physiological traits, and may have different resource use style, and different interactions among them, mechanisms responsible for the same biological processes are likely different. Therefore, in the study of relationship between biodiversity and ecosystem functioning, cautious must be paid when extrapolates conclusions from one ecosystem to others.更多还原