Soil-moisture dynamics and tree-water status in a Picea crassifolia forest, Qilian Mountains, China  

作　　者：Hu Liu Lin Li SiJia Wang QiYue Yang WenZhi Zhao 

机构地区：[1]Linze Inland River Basin Research Station,Chinese Ecosystem Research Network,Lanzhou,Gansu 730000,China [2]Key Laboratory of Ecohydrology of Inland River Basin,Northwest Institute of Eco-Environment and Resources,Chinese Academy of Sciences,Lanzhou,Gansu 730000,China [3]University of Chinese Academy of Sciences,Beijing 100029,China

出　　处：《Research in Cold and Arid Regions》2020年第1期34-46,共13页寒旱区科学（英文版）

基　　金：supported by the West Light Foundation of the Chinese Academy of Sciences(awarded to Dr.Hu Liu in 2018);the Youth Innovation Promotion Association of the Chinese Academy of Sciences(awarded to Dr.Hu Liu in 2016)

摘　　要：Landscapes of the mountainous regions in northwestern China comprise a unique pattern of vegetation,consisting of a mosaic of grassland and shrub-forest.Forests generally self-organize into ordered structures and coalesce into blocks on north-facing slopes or stripes along southeast-facing slopes,with Picea crassifolia being the most representative and dominant tree species.We investigated the tree-water status and soil-moisture dynamics at a forest site(Guantan)of the Qilian Mountains in northwest China.The 30-minute-interval measurements of tree-sap flow during the growing season of 2008 are presented,and the potential functional relations between tree transpiration and environmental factors are evaluated.Soil moisture and solar energy were identified as the most influential factors,explaining more than 70%of the variance in sap flow.Based on field measurements obtained at the forest site,a stochastic model of soil-moisture dynamics was tested;and the steady-state probability density functions(PDFs)of the long-term soil-moisture dynamics and static tree-water stress were estimated using the validated model and parameters.We found that the model reproduced measured soil moisture well,despite all the simplifying assumptions.The generated PDF of long-term soil moisture was relatively open,with middle to low average values;and the calculated density of the static tree-water stress at the forest site was largely concentrated between 0 and 0.6,suggesting a moderate water-stress situation in most cases.We argue that both water and energy are limiting factors for vegetation at the forest site.In addition,the tradeoff between reduced evapotranspiration(ET)from limited solar energy and increased soil-moisture availability may create a stressed but tolerable environment and,in turn,produce a relatively constant ecological niche favorable to Picea crassifolia growth.Landscapes of the mountainous regions in northwestern China comprise a unique pattern of vegetation, consisting of a mosaic of grassland and shrub-forest. Forests generally self-organize into ordered structures and coalesce into blocks on north-facing slopes or stripes along southeast-facing slopes, with Picea crassifolia being the most representative and dominant tree species. We investigated the tree-water status and soil-moisture dynamics at a forest site(Guantan) of the Qilian Mountains in northwest China. The 30-minute-interval measurements of tree-sap flow during the growing season of 2008 are presented, and the potential functional relations between tree transpiration and environmental factors are evaluated.Soil moisture and solar energy were identified as the most influential factors, explaining more than 70% of the variance in sap flow. Based on field measurements obtained at the forest site, a stochastic model of soil-moisture dynamics was tested; and the steady-state probability density functions(PDFs) of the long-term soil-moisture dynamics and static tree-water stress were estimated using the validated model and parameters. We found that the model reproduced measured soil moisture well, despite all the simplifying assumptions. The generated PDF of long-term soil moisture was relatively open, with middle to low average values; and the calculated density of the static tree-water stress at the forest site was largely concentrated between 0 and 0.6, suggesting a moderate water-stress situation in most cases. We argue that both water and energy are limiting factors for vegetation at the forest site. In addition, the tradeoff between reduced evapotranspiration(ET) from limited solar energy and increased soil-moisture availability may create a stressed but tolerable environment and, in turn,produce a relatively constant ecological niche favorable to Picea crassifolia growth.

关 键 词：sap flow soil moisture stochastic modeling semiarid alpine ecosystem 

分 类 号：S714[农业科学—林学]