极端干旱地区胡杨林根系分布的非线性分析

依据2006年5—7月在极端干旱区额济纳旗的实测资料，对胡杨林的根系分布特征进行了分析与研究，期望对全面认识胡杨根系、根系吸水及胡杨SPAC系统进一步的研究提供有力的试验依据和理论支持.该文将根系分为输运根系（d02 cm）和吸水根系（d≤02 cm）.输运根系的分布存在分形现象，根系土壤水分的变化对胡杨输运根系的分布有着直接影响.分析过程引入了土壤含水率期望的概念，当土壤含水率期望的平均值为25.03 cm·g/g时，输运根系分布的分维值为2.000 7；当土壤含水率期望的平均值为55.95 cm·g/g 时，输运根系分布的分维值为1.627 5.即当土壤含水率期望值较低时，输运根系分布的分维值较大；当土壤含水率期望值较高时，输运根系分布的分维值较小.对于吸水根系，该文建立了根长密度在垂直和水平方向的一维分布函数以及二维分布函数.采用指数函数对吸水根系的根长密度分布函数进行拟合，拟合函数与实测数据的R2分别为:0.89、0.68、0.73和0.69，说明胡杨吸水根系根长密度的分布基本符合指数衰减规律. 

Nonlinear analysis of root distribution of Populus euphratica forests in the extremely arid region-Ejina, Inner Mongolia in northern China

Quantification of root distribution contributes an improved understanding of chemical fluxes in the vadose zone to both ecological and hydrological studies. Based on the data observed at Ejina Banner, Inner Mongolia of northern China, from May to July of 2006, root distribution of Populus euphratica forests was analyzed. Root system was divided into coarse root system (d>0.2 cm) and fine root system (d≤0.2 cm). The content and method of research were different between two root systems: 1) for coarse root system, using fractal theory, the authors researched the relations between root distribution of P. euphratica and soil moisture. And a new definition, expectation of soil moisture content, was introduced. When the mean value of expectation of soil moisture content was 25.03 cm·g/g, the fractal dimension of coarse roots was 2.000 7, and when it was 55.95 cm·g/g, then the fractal dimension was 1.627 5, ie the larger the expectation of soil moisture content was, the smaller the fractal dimension of coarse root distribution was, vice versa. 2) For fine root system, one dimension (including the vertical and horizontal radial direction) and two dimension function of root length density (RLD) were simulated. All the functions of RLD were simulated by exponent function, and R2 was 0.89，0.68, 0.73 and 0.69,respectively. It shows that the RLD of fine root system of P. euphratica is accorded with exponent distribution on the whole.