黄土高原刺槐环境适应机制、成本与群落性状结构及功能变化

Black locust (Robinia pseudoacacia, BL) has become a pioneer species for vegetation restoration in Loess Plateau, and plays an important role in soil and water conservation and environmental improvement. However, the black locust has poorly developed in some sites or regions due to the high heterogeneity in environment conditions in Loess Plateau. These poorly developed trees are usually called “dwarf trees” with sparse understory vegetation and simple structure, and which cannot give full play to the expected ecosystem functions. How to prevent the development of these “dwarf trees” and communities with low functions, and improve the structure of existing poorly developed communities is still a big challenge for this region. This study, taking the whole Loess Plateau as the study area and using functional traits as a starting point, will investigate the functional traits and growth of black locust along two transect lines from the Southeast to Northwest on the Loess Plateau. Meanwhile, this study will investigate and compare the functional trait structure and ecosystem functions of black locust communities and native vegetation communities along two transect lines. The objectives of this study are 1) to analyze the response relationships between functional traits and growth of black locust along environmental gradient from Southeast to Northwest, and to detect the adaptation mechanism and adaptation cost of black locust in Loess Plateau; 2) to define the boundaries in environment and trait space of the formation of “dwarf trees”; 3) to compare the differences in trait structure and ecosystem functions between black locust communities and native communities along environmental gradient, and 4) to analyze the impact of black locust invasion on the trait structure and ecosystem functions, and 5) to detect the processes and mechanism of the development of the communities with low ecosystem functions. The result will provide supports for the vegetation restoration planning and management, and the transformation of the communities with low ecosystem functions in Loess Plateau.

刺槐是黄土高原地区植被恢复重建的先锋树种，在保持水土、改善环境方面发挥着重要作用。但因黄土高原地区环境的复杂性，一些立地环境下刺槐发育不良形成“小老树”，通常林下植被稀疏、结构简单、难以发挥预期的生态功能。如何避免这些低效人工植被的形成，并对现有低效植被进行改造以提升其功能，是该区恢复植被重建中亟待解决的关键科学技术问题。为此，项目试图以整个黄土高原为研究区，以植物功能性状为突破口，通过大尺度样线调查，结合控制试验，分析不同环境梯度下刺槐功能性状变化与生长速率的响应关系，阐明刺槐的环境适应机制与成本，明确“小老树”形成的环境与功能性状边界条件；比较刺槐人工群落与乡土植物群落的性状结构差异，分析不同环境梯度下刺槐对群落性状结构与系统功能的影响，揭示低效人工植被的形成过程与机制，为黄土高原人工植被恢复规划与管理提供依据，也为低效刺槐林分的改造提供技术支持。

项目针对黄土高原刺槐广泛种植中存在的“小老树”及其形成的低效林分问题，综合大尺度水热梯度调查、局部断面调查和控制实验，取得了一下主要研究进展：1）刺槐的功能性状随坡位和坡向呈规律性变化，并通过功能性状关系的权衡与协变的整体适应策略，形成不同的适应对策：在阳坡和下坡以生长组织投资为主，在阴坡和中上坡则着重于保守防御；2）刺槐适应环境是有成本的，如叶厚度增加一个单位，地径、总生物量、地上生物量和地下生物量分别减少0.515mm和1.124g、1.446g、0.968g；增加一个单位的比根长，地径、株高、冠幅 和总生物量分别减少0.222mm、0.287cm、0.492cm和0.511g；3）刺槐在草原和森林草原区，会引起林下物种数量的减少，物种多样性降低，但在森林区，刺槐种植后林下物种数量多且具有较高的物种多样性；4）刺槐林下植物群落和乡土植物群落的叶碳、叶氮、叶磷、比叶面积、叶组织密度等功能性状随植被带的变化规律一致，但刺槐林下植物群落叶碳含量、叶氮含量和比叶面积显著高于乡土植物群落，但功能多样性指数表现并不一致，刺槐在草原区会引起植物功能多样性的降低，导致林下植被较低的生物量生产，使得植被系统功能低下，但森林区引种刺槐则可提高植物群落功能多样性与系统功能；5）对土壤微生物多样性与群落结构的调查表明，刺槐种植对土壤微生物多样性与群落结构也会产生显著影响，在草原区，刺槐引入显著提高了土壤微生物的代谢活性和功能多样性，在森林草原区，其对土壤微生物代谢活性和功能多样性也有所提高，但在森林区的影响却显著低于乡土植物群落；6）在森林草原区和草原区，刺槐林下土壤细菌多样性大于或等于乡土植物群落，但真菌多样性低于乡土植物，在森林区则相反，刺槐林下土壤细菌多样性低于或等于乡土植物群落，但真菌多样性高于乡土植物群落。上述研究表明，刺槐对生态系统结构与功能的影响存在明显的梯度效应，这种梯度效应对于明确刺槐种植的适宜的边界条件和制定合理的建设方案具有重要意义。

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