母岩对华南天然林土壤有机碳密度的影响及其机制

Improved understanding of the controls of spatial variation in soil organic carbon (C) density is critical for the accurate estimation of soil organic C stock. Parent rock is well known as one of the five drivers of soil development; its influence on soil organic C density and the underlying mechanisms, however, are still poorly understood. Based on the results of a previous project on the estimation of national forest C stock in China, we selected a total of 128 representative natural evergreen-broadleaved forest plots in South China for the current project. We are planning to determine a series of parent rock properties (i.e., type, mineral composition, and the concentrations of iron (Fe), aluminum (Al), phosphorus (P) and carbonate) and physiochemical properties (i.e., particle size, pH, and Fe, Al, and P concentrations) of soils at different depths that are closely related to soil organic C sequestration. Our aim is to identify the spatial patterns of parent rock properties that are related to soil organic C sequestration and the difference in soil organic C density among parent rock types, in forest ecosystems in South China. By combining the parent rock properties that will be determined in this project with the measures of climate, vegetation, and topographic factors derived from the previous forest C stock project, we will quantify the relative influences of the parent rock, climate, and topographic factors on soil organic C density. We will also explore how the relative influences of the three groups of factors on soil organic C density change with soil depth. Meanwhile, we built a theoretical model of parent rock effect on soil organic C density, and we are planning to test this theoretical model using data collected in this project and a structural equation model analysis. By quantifying the relative importance of the different hypothetical pathways in the model, we will clarify the main mechanisms of parent rock effect on soil organic C density. Findings of this project will provide a sound theoretical basis for the accurate estimation of soil organic C stock in forest ecosystems at a regional scale.

揭示土壤有机碳密度的空间变异机理是准确估算土壤有机碳库的关键。母岩是影响土壤发育的五大因素之一，其如何影响土壤有机碳密度的空间变异及其作用机制尚不清楚。本项目基于前期全国森林碳库研究建立的森林样地数据库，拟选取华南地区的128个代表性天然常绿阔叶林样地为研究对象，测定分析与土壤有机碳固持相关的母岩特征（类型、矿物组成和铁、铝、磷、碳酸盐含量等）和不同土层土壤理化性质（颗粒组成、pH和铁、铝、磷含量等），阐明华南天然林下母岩特征的空间分布格局和不同类型母岩上发育土壤的有机碳密度差异。结合气候、植被和地形等资料，采用增强回归树方法，量化母岩、气候和地形等因素影响土壤有机碳密度的相对重要性及其随土壤深度的变化规律。构建母岩影响土壤有机碳密度的理论模型，采用结构方程模型进行检验，阐明不同影响途径的相对重要性，揭示其主要影响机制。研究成果将为准确评估地区尺度上的森林土壤有机碳库提供科学依据。

揭示土壤有机碳密度的空间变异机理是准确估算土壤有机碳库的关键。母岩是影响土壤发育的五大因素之一，其如何影响土壤有机碳密度的空间变异及其作用机制尚不清楚。..针对这一研究不足，本项目在广东、广西和福建三个华南地区省份建立56个代表性森林样点，每个样点选取了3个100m2样方，采集了0-20cm和20-40cm矿质土样334份，母岩样品241份和植物叶片样品273份。此外，我们还在局域、区域和全球尺度上开展了其他一些相关研究。主要研究结果如下：..(1) 华南地区主要存在安山岩、花岗岩、灰岩和砂页岩等8个类型母岩，母岩铝铁含量是预测森林土壤有机碳含量最重要的因子之一，支持了科学假设1：“母岩特征是影响华南天然林土壤有机碳密度的重要因素，其重要性同气候和地形特征等因素相当”。..(2) 土壤有机碳含量与其他土壤理化性质和母岩性质的关系整体上在0-20cm土壤中强于20-40cm土壤，但是土层间差异并不大，一定程度上支持了科学假设2：“母岩对深层土壤有机碳密度的影响大于对表层土壤有机碳密度的影响”。..(3) 土壤有机碳含量与土壤总磷含量关系最紧密，呈正相关关系，与土壤铁和铝含量也显著正相关，而且与土壤铝铁形态有关，验证了科学假说3：“母岩主要通过影响土壤颗粒组成、铁铝氧化物的含量和 pH 值影响土壤有机碳密度”。..(4) 母岩不同的两个海拔梯度上，母岩磷含量、土壤pH和颗粒组成等均显著不同，但是土壤有机碳含量却无明显差异，与区域尺度上结果不同。..(5) 全球尺度上，母岩类型和土壤有机碳和总磷含量关系密切，而且母岩类型可以通过影响土壤理化性质影响植物磷碳耦合关系。..上述研究结果表明，母岩是影响华南地区森林土壤有机碳的重要因素，可以通过作用于土壤磷、铝和铁含量和形态显著影响土壤有机碳含量。因此，我们在采用统计模型或者过程模型估算全球土壤有机碳库的时候应该考虑母岩因素，从而更准确可靠地模拟和预测全球变化背景下的土壤有机碳库。..在本项目资助下，已在Nature Communications、Ecology Letters和Catena等国际主流SCI期刊上发表论文10篇。