School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China; Forest Ecosystem Research and Observation Station in Putuo Island, Zhoushan, Zhejiang 316100, China; Tiantong National Forest Ecosystem Observation and Research Station, Ningbo 315114, Zhejiang, China.
Centre for Environment and Sustainability, Chalmers University of Technology, 412 96 Göteborg, Sweden.
Sci Total Environ. 2017 Nov 15;598:38-48. doi: 10.1016/j.scitotenv.2017.04.131. Epub 2017 Apr 25.
The biodiversity - aboveground biomass relationship has been intensively studied in recent decades. However, no consensus has been arrived to consider the interplay of species diversity, and intraspecific and interspecific tree size variation in driving aboveground biomass, after accounting for the effects of plot size heterogeneity, soil fertility and stand quality in natural forest including agroforests. We tested the full, partial and no mediations effects of species diversity, and intraspecific and interspecific tree size variation on aboveground biomass by employing structural equation models (SEMs) using data from 45 homegarden agroforestry systems in Sri Lanka. The full mediation effect of either species diversity or intraspecific and interspecific tree size variation was rejected, while the partial and no mediation effects were accepted. In the no mediation SEM, homegarden size had the strongest negative direct effect (β=-0.49) on aboveground biomass (R=0.65), followed by strong positive direct effect of intraspecific tree size variation (β=0.32), species diversity (β=0.29) and interspecific tree size variation (β=0.28). Soil fertility had a negative direct effect on interspecific tree size variation (β=-0.31). Stand quality had a significant positive total effect on aboveground biomass (β=0.28), but homegarden size had a significant negative total effect (β=-0.62), while soil fertility had a non-significant total effect on aboveground biomass. Similar to the no mediation SEM, the partial mediation SEMs had explained almost similar variation in aboveground biomass because species diversity, and intraspecific and interspecific tree size variation had non-significant indirect effects on aboveground biomass via each other. Our results strongly suggest that a multilayered tree canopy structure, due to high intraspecific and interspecific tree size variation, increases light capture and efficient utilization of resources among component species, and hence, support the niche complementarity mechanism via plant-plant interactions.
生物多样性-地上生物量关系在最近几十年得到了深入研究。然而，在考虑到自然林（包括 agroforests）中斑块大小异质性、土壤肥力和林分质量的影响后，对于物种多样性、种内和种间树木大小变化在驱动地上生物量方面的相互作用，尚未达成共识。我们利用来自斯里兰卡 45 个家庭园艺 agroforestry 系统的数据，通过结构方程模型（SEMs）测试了物种多样性、种内和种间树木大小变化对地上生物量的完全、部分和无介导效应。物种多样性或种内和种间树木大小变化的完全介导效应被拒绝，而部分和无介导效应被接受。在无介导 SEM 中，家庭园艺大小对地上生物量的直接负效应最强（β=-0.49）（R=0.65），其次是种内树木大小变化（β=0.32）、物种多样性（β=0.29）和种间树木大小变化（β=0.28）的强烈正直接效应。土壤肥力对种间树木大小变化有负直接效应（β=-0.31）。林分质量对地上生物量有显著的正总效应（β=0.28），但家庭园艺大小有显著的负总效应（β=-0.62），而土壤肥力对地上生物量有非显著的总效应。与无介导 SEM 类似，部分介导 SEM 也解释了地上生物量几乎相似的变化，因为物种多样性、种内和种间树木大小变化通过彼此对地上生物量没有显著的间接效应。我们的结果强烈表明，由于种内和种间树木大小变化较大，多层次的树冠结构增加了各组成物种的光捕获和资源的有效利用，从而通过植物-植物相互作用支持生态位互补机制。
