Abstract: The aim of this paper was to provide a reference for calculating the main root biomass and its spatial distribution law of the oasis farmland in the arid area and even the 3 northern shelterbelts. According to the selection of 2 lines-20 a-shelterbelt of Populus alba var. pyramidalis Bunge. in Dengkou, Ulan Buh Desert, Inner Mongolia, and based on the forest belt parameters, the root biomass of different soil layers were measured according to the size and depth of fixed soils. SPSS 18.0 statistical software was used to establish growth model to simulate the variation of main root biomass of different soil layers with diameter at breast height (DBH). And then 11 specific gravity model of the main root biomass were obtained by investigation and analysis in different soil layers. It was found that 87.11%~100% of the main root biomass distributed in 0~0.5 m and 0.5~1.0 m soil layer. And the biomass distribution ratio of the main root in 0~1.5 m soil layer was basically constant throughout the whole growing period and increased with the growth of DBH, only 1.5~2.0 m soil layer increased first and then decreased. When the average DBH reached 0.228 5 m and 0.363 0 m, there was the main root biomass distribution in 1.0~1.5 m and 1.5~2.0 m soil layer. According to the growth rate of 0.02 m DBH every year, after 11~18 a the vertical root system of poplar could grow down to 1.0~2.0 m soil layer. The spatial distribution structure and regularity of the main root biomass were as following: the main root biomass was mainly distributed in 0~1.5 m soil layer, accounting for over 97% of the main root biomass. As DBH reached a certain value, main root distributed in 1.5~2.0 m soil layer, and its biomass spatial distribution presented a near soil surface distribution potential. The reasons could be the desert monsoon climate + soil drought + low groundwater level, which caused the plant habitat drought, and plant root system streching to rich water resources. This was an adaptability evolution of plant to drought climate, and agricultural irrigation environment.

Key words: main root biomass, spatial distribution, farmland shelter, oasis, arid area

摘要： 绿洲农田防护林作为三北防护林的重要组成部分发挥着重要的固碳作用，其生物量直接决定碳储量的大小，尤其根生物量，而主根生物量是根生物量的主体部分，故探明干旱区绿洲农田防护林带主根生物量空间分布结构和规律，为干旱区乃至三北防护林修复过程根生物量的计算提供重要的指导价值。在内蒙古自治区乌兰布和沙漠磴口绿洲选择20 a、2行结构新疆杨农田防护林带，按径级、固定样方尺寸和深度测量不同土层主根生物量，利用SPSS 18.0统计软件建立生长模型，模拟主根生物量变化过程。通过调查分析得出新疆杨11个不同土层主根生物量及分配比例模型；发现0~0.5 m和0.5~1.0 m土层囊括了87.11%~100%的主根生物量，且主根生物量分配比例在生长过程中基本恒定；0~1.5 m土层主根生物量随胸径增长而增长，唯1.5~2.0 m土层有先增长后下降的趋势；1.0~1.5 m和1.5~2.0 m土层在林带平均胸径长到0.228 5 m和0.363 0 m时有主根生物量分布，按胸径年增0.02 m计算，到11~18 a时新疆杨的垂直根系才能向下生长到1.0~2.0 m土层。新疆杨农田防护林主根生物量空间分布结构及规律：主根生物量主要集中分布在0~1.5 m土层内，占主根97%以上的生物量；胸径达一定值时，1.5~2.0 m有主根分布；主根生物量空间分布呈近地表集中分布趋势。主根生物量近地表集中分布形成原因是：沙漠季风气候、土壤干旱和地下水位低造成植物生境干旱，植物根系生长向水性使其向水资源富集于地表灌溉水系和灌溉农田生长，是植物对干旱气候土壤和农业灌溉环境的一种适应性进化。

关键词: 主根生物量, 空间分布, 农田防护林, 绿洲, 干旱区