森林生物量的根冠分配特征及其影响因子分析

Biomass allocation between root and shoot and its impact factors of forest ecosystems

根冠比(shoot ratio,RS)通常用来描述植物同化产物在地上(茎、枝叶)和地下部分(根)的分配比例,受到生物因子和环境因子的共同影响和制约,是陆地生态系统模型中同化产物分配模块的重要参数.根冠比是一个动态参数,而目前多采用经验性常数,影响了模型对生态系统碳储量及碳分配的客观评估.本文利用全国森林生态系统的生物量及其环境因子数据集分析了根冠比的变化特征,阐明了根冠比对土壤质地和气候变量等影响因子的响应趋势.结果表明:我国森林生态系统的根冠比中值为0.23,根冠比在森林生态系统内部数值变化较大;随着土壤质地由黏土至壤土、砂土的变化,根冠比变大;落叶针叶林的根冠比最大,常绿针叶林次之,而常绿阔叶林和落叶阔叶林根冠比最小;总体上根冠比表现出与多年平均降水、多年平均气温和干旱度系数等变量显著负相关;次生林的根冠比与降水、温度、干旱度系数等显著负相关,原始林与人工林关系不明显;不同植被功能型和土壤质地的森林,根冠比对气候变量的响应关系不同,证明森林的受影响程度、植被功能型和土壤类型等改变着根冠比对气候变量的响应特征.

Shoot ratio(RS)is usually used to describe the distribution ratio of plant assimilates on the ground(stems,branches and leaves)and underground parts(roots).It is influenced and restricted by both biological factors and environmental factors,and is an important parameter of assimilates distribution module in terrestrial ecosystem models.The root-cap ratio is a dynamic parameter,but the empirical constant is often used at present,which affects the objective evaluation of ecosystem carbon storage and carbon distribution by the model.In this paper,the change characteristics of root shoot ratio were analyzed by using the biomass of national forest ecosystem and its environmental factor data set,and the response trends of root shoot ratio to soil texture and climate variables were illustrated.The results showed that the median value of root:shoot ratio for forests was 0.23.The range of root:shoot ratio was considerably wide across different forest groups.As the soil texture changing from clay→loam→sand,root:shoot ratio became bigger.The root shoot ratio of deciduous coniferous forest was the largest,followed by evergreen coniferous forest,and the root-canopy ratio of evergreen broad-leaved forest and deciduous broad-leaved forest was the smallest.Overall,root:shoot ratio was negatively correlated to mean annual precipitation(MAP),mean annual temperature(MAT)and the aridity index(ET/PET).The root shoot ratio of secondary forest was negatively correlated with precipitation,temperature and dryness coefficient,but the relationship between primary forest and plantation forest was not obvious.For forests with different vegetation functions and soil textures,the root shoot ratio has different response relations to climate variables,which proves that the degree of forest impact,vegetation functions and soil types,etc.change the response characteristics of root shoot ratio to climate variables.