【作者】 白琰；

【导师】 王刚；

【作者基本信息】 兰州大学 ， 生态学， 2009， 博士

【摘要】 植物群落物种多样性形成与维持的机制即群落构建机制是当代生态学研究的核心论题。生态位理论主要用群落组分种的生态位分化即不同的物种占据不同的生态位来阐释这个问题。但由于所有植物在利用水、CO₂、光能、氮、磷、钾等资源时具有基本相同的方式，因而生态位理论并不能完全解释群落构建的机制。基于此，Hubbell提出了中性理论，其主要观点是：群落组分种都是生态等价的，各物种随机的生灭过程及迁移过程决定了局域群落的物种多样性；集合群落（metacommunity）水平上的种多样性是各物种个体扩散速率及物种形成（speciation）速率的函数。中性理论包含了生态位理论忽视的很多方面并在一定程度上解决了生态位理论在解释物种多样性时遇到的困难。但是由于假设所有物种的个体在生态学上都是等价的，并忽略生境异质性对群落构建的影响，也使中性理论遭到很多质疑。由此，近年来国际理论生态学界展开了关于群落构建机制阐释的生态位理论观点和中性理论观点之间的论争。本文针对此国际生态学前沿的论争，以甘南高寒草甸植被为研究对象，分别在局域（local）群落和集合群落两个水平上研究植物群落的构建机制。在局域群落中，以高寒草甸植物群落的重要组分种：鹅观草（Roegneria kamoj）、球花蓼（Polygonum sphaerostachyum）、洽草（Koeleria cristata）、嵩草（Kobresia myosuroides）、箭叶橐吾（Ligularia sagitata）和乳白香青（Anaphalis lacteal）为对象，通过施肥处理后光合能力以及群落结构的变化探讨α多样性的形成机制；在集合群落（metacommunity）水平上，通过对比两座相距180 m山坡上4个不同坡向样方间群落相似性与距离和环境梯度的相互关系，探讨β多样性的形成机制。本文实验研究的结果如下：1．鹅观草具有相对较高的光合水分利用率及较低的光合氮利用率，而球花蓼具有较高的光合氮利用率及较低的光合水分利用率。鹅观草的净光合速率与土壤氮含量呈正相关关系，其对于土壤水分含量变化的反应不明显，而对于土壤氮含量变化的反应明显。球花蓼的净光合速率与土壤水分含量呈正相关关系，其对于土壤水分含量变化的反应明显而对于土壤氮含量变化的反应不明显。鹅观草和球花蓼在资源利用方面的这些权衡（trade-off）有利于它们共存于波动的环境中。2．洽草、嵩草、球花蓼、箭叶橐吾和乳白香青的光合作用对于土壤氮磷比提高的反应不同：氮磷比的增加明显提高了嵩草，洽草和箭叶橐吾的净光合速率；中等程度的氮磷比一定程度上提高了乳白香青的净光合速率，但是高氮磷比条件下反而使得其净光合速率相对中等程度的氮磷比有所降低。对于所有氮磷比条件下的球花蓼来说，其净光合速率均与对照相比没有明显变化。在两年间的样方数据比较下，我们发现高氮磷比的洽草、嵩草较多的出现在高氮磷比土壤条件下的群落中，而低氮磷比的球花蓼较多的出现在低氮磷比的土壤中。不同物种对营养增添（nutrient enrichment）引起的土壤资源供应比率改变的响应差异性最终导致群落结构发生变化。3．通过对比相邻两座山坡上四个不同坡向的植物群落组成，我们发现在每个山坡上，各个相距8 m的样方间，沿着土壤水分梯度，群落相似性由南至北依次降低；而在相距180 m的不同山坡上位于相同位置的样方间的群落相似性却高于同一山坡不同位置样方间的群落相似性，对此，用扩散限制难以解释。不同山坡间、同一山坡内各样方间的群落相似性均与土壤水分含量表现出较高的线性关系。在实验所处的空间范围内（8-180 m），分离环境变化与距离变化的耦合关系后，环境梯度的作用随之显现。由上述，本文得出以下研究结论：1．对不同资源利用能力之间的权衡是生态位分化的基础，这在物种共存、群落构建过程中起着重要的作用。群落α多样性的形成机制仅用中性理论的随机生灭过程和迁移过程难以得到完满的解释。2．群落组分种对土壤营养增添（nutrient enrichment）的差异性响应是影响群落结构变化主导因子，因而从另一角度否证了中性理论关于群落组分种等价性的假定。3．扩散限制并不能完全解释β多样性的形成，在本研究所涉地域内，环境梯度才是引起群落结构变化的主要原因。更多还原

【Abstract】 The biodiversity formation and maintenance mechanism of plant community isone of the most important key issues in the contemporary ecological research. Nichetheory had solved this problem to a certain degree. In a simple word, stablecoexistence between competing species requires them to occupy different niches.However, because all plants acquire water, CO₂, light, nitrogen, phosphorus, potassiumand a common set of minor mineral nutrients in a limited number of ways, nichecannot explain the mechanism of community construction.Neutral theory developed by Hubbell supposes that: species are ecologicallyequivalent, biodiversity in community relies on the randomness of births, deaths,migration, and immigration; at metacommunity level, regional biodiversity is thefunction of dispersal rate and speciation rate. Neutral theory includes many detailswhich are neglected by niche theory and resolves many problems which are difficult toexplain by niche theory. However, its assumption of species equivalence and theneglect of environmental effects have also raised considerable disagreement. Eachtheory has limitations that have been widely discussed. In accordance with thesediscusses in international ecological research, in this study, we analysed thecommunity construction mechanism at local community and metacommunity levelrespectively in an alpine meadow in Gannan.We measured the photosynthesis of Roegneria kamoj, Polygonumsphaerostachyum, Koeleria cristata, Kobresia myosuroides, Ligularia sagitata and Anaphalis lacteal under different soil status and investigated the variations ofcommunity composition after fertilizer to find out the mechanism ofαdiversityformation at local community level. At metacommunity level, we compared the effectsof distance and environmental gradient on the community similarity indexes of fourdifferent locations in two hills to seek the mechanism of D diversity formation. Theresults as follows:1. R. kamoji had relatively higher PWUE, but lower PNUE, making it a waterconservation species. In contrast, P. sphaerostachyum had very low PWUE, and higherPNUE, making it a nitrogen conservation species. The net photosynthetic rate of R.kamoji positive related to soil N content, and responded to the variations in soil watercontent insensitively but responded to the changes in soil N content sensitively; Thenet photosynthetic rate of P. sphaerostachyum positive related to soil water content,and responded to the variations in soil water content sensitively but responded to thechanges in soil N content insensitively. The trade-off of R. kamoji and P.sphaerostachyum between resource utilization promoted their coexisted in thecommunity under fluctuant environment.2. The photosynthesis of K. cristata, K. myosuroides, P. sphaerostachyum, L.sagitata and A. lacteal respond to the increase of soil N : P ratios differently: Naddition increased the photosynthetic assimilation rates of K. myosuroides, K. cristataand L. sagitata significantly; For A. lacteal, the photosynthetic assimilation rates onlyincreased at relatively lower nitrogen levels but significantly declined at highernitrogen levels; All additional N treated P. sphaerostachyum samples remainedconstant photosynthetic assimilation rates, which suggested that the additional Ntreatments had no significant effects on the photosynthesis of P. sphaerostachyum.Compared with their average cover in control plots, P. sphaerostachyum was reduced.A. lacteal was increased with 20 g Nm^-2 addition and reduced with 140 g Nm^-2addition. L. sagitata, K. myosuroides and K. cristata was increased. The results showed that species with the N : P ratios more close to soil supply ratios were predicted todominate in local communities. Species with inherently low N : P ratios （P.sphaerostachyum） is predicted to dominate in N-limited vegetation, and species withinherently high N : P ratios （K. myosuroides and K. cristata） are predicted to dominatein N-rich vegetation. Species are different in responding to nutrient enrichment, whichresults in the change of community structure finally.3. By comparing community composition of four positions in two neighbor hills,we found that community similarity indexes between plots decreased significantlyfrom South to North hillside in each hill; whereas no significant difference was foundbetween plots within the same topographic positions in two hills which were difficultto explain by dispersal limitation. Because there had a high community similarity inthe plots with same soil water content, it was possible to express the communitysimilarity as the liner function of the soil water content. As the distance between plotsin one hill was significantly shorter than it between hills, a consistent decrease incommunity similarity with distance which neutral theory predicts was not observed inthis experiment. The influence of environmental gradient should be assessed anddispersal limitation effects are not clear yet even at the scale of 8-180 m.From this study we have drawn the following conclusions:1. The trade-off between resource utilization is the foundation of nichedifferentiation, which is important in promoting species coexist and constructingcommunity. It is incomplete that explainsαdiversity only by randomness of births,deaths, migration, and immigration.2. The interspecific differences in responding to environmental disturbance arethe main factors lead to the change of community composition, which contraries to theassumption of neutral theory about species are ecological equivalent.3. Dispersal limitation cannot explain the formation ofβdiversity completely.Environment gradient, in the region involving in this study, is the main factor which results in the shift in community structure.更多还原