宁夏干旱生态脆弱区土壤蒸发对季节性植被自适应性影响的研究

In view of the fact that the soil water carrying capacity is insufficient and vegetation growth is inhibited under the condition of drought and water shortage in the ecological fragile area of the arid zone in central Ningxia. With field and laboratory test， the evaporation threshold of soil water is researched under different soil moisture gradients. They are observed on soil water evaporation and soil water desorption process in arid area using micro-Lysimeter and soil column experiment. Seasonal vegetation transpiration is observed by barrel cultivation. The longitudinal and cross-sectional structures of the main roots and trunk of vegetation were observed by optical microscope, and the effects of soil evaporation on the adaptive growth of seasonal vegetation were analyzed on the different soil moisture stages. The effect of seasonal vegetation growth on soil water desorption are studied. The effect of soil water evaporation on the distribution of soil salinity was analyzed. The process is explored on salt accumulation in soil surface under different rainfall conditions. The seasonal vegetation growth law and time threshold of life support are studied on different soil water and salt conditions. By using the barrel cultivation experiment and the simulated precipitation process, the water supply threshold is calculated with the positive income of soil water. With meteorological data, this paper analyzes the possibility of natural precipitation to maintain seasonal vegetation water consumption in arid area. It will provide data support for improving soil evaporation under soil moisture control. It will provide data support and theoretical basis for the carrying capacity of soil moisture, water allocation and maintenance and restoration of ecological environment.

针对宁夏中部干旱带生态脆弱区土壤水承载能力不足、植被生长受抑制的情况，结合田间和室内模拟试验，寻求不同土壤水分梯度下土壤水蒸发阈值；采用微型蒸渗仪和土柱试验观测干旱区深层土壤水疏干过程及土壤蒸发量；利用桶栽法观测季节性植被蒸腾量，利用光学显微镜观测植被主根和主干的纵、横剖面结构，分析不同土壤水分阶段土壤蒸发对季节性植被自适应性生长的影响；探索季节性植被生长对土壤水疏干的影响规律；分析干旱条件下土壤水分蒸发对土壤盐分分布的影响，探讨不同降雨情况下土壤表层积盐过程，研究不同土壤水盐条件下季节性植被生长规律及生命维系的时间阈值；采用桶栽试验和模拟降水过程，推算土壤水正收入时补给水量阈值，结合气象资料，分析干旱区天然降水维系季节性植被耗水的可能性。研究成果以期为完善水分控制下的土壤蒸发理论提供数据支持；为客观评价生态脆弱区土壤水的承载能力、水量调配、生态环境维护与修复提供数据支撑与理论依据。

针对宁夏中部干旱带生态脆弱区土壤水承载能力不足、植被生长受抑制的情况，结合田间和室内模拟试验，进行了宁夏干旱生态脆弱区土壤蒸发对季节性植被自适应性影响研究。得到了以下结论：.1. 对生态脆弱区干旱条件下土壤水分蒸发阈值进行研究发现，枯水年水平，研究区裸地土壤年蒸发量为160.88mm，土壤水库年收入为-13.44mm；平水年水平，裸地土壤年蒸发量为171.44mm，其年收入为7.62mm，故可得到研究区裸地土壤水库水分收入阈值应介于160.88mm和171.44mm之间。在本项试验中，压砂地土壤水库水分均为正收入，依据试验设置的最小降雨量条件分析，压砂地土壤水库水分收入阈值应小于115.32mm。.2.对不同水盐条件对白茎盐生草根区土壤水盐动态变化及表层土微观结构的影响研究发现，研究区土壤水盐分布主要受降雨量的影响。土壤蒸发、入渗及植物生长均会影响土壤盐分的分布。研究区中土壤剖面全盐量总的变化趋势呈“S”型。特枯水年，白茎盐生草对土壤盐分的改善效果不明显，土层的盐分降幅为7.2%-86.5%；平水年，根区0-40cm土壤盐分降幅为2.16%-119.16%；特丰水年，根区0-40cm土壤盐分降幅为14.70%-41.61%。说明水分会影响白茎盐生草对根区土壤盐分的改善程度。.3.对表层土进行微观结构研究，发现盐含量对土壤微观结构会造成影响，土壤全盐量为10 g/kg时，有大量的不同形状的盐结晶析出，在土壤表面充当土壤骨架，影响土壤结构性能。降雨量少时，白茎盐生草根区土壤颗粒较疏松，孔隙多，盐结晶析出较少。.4.对干旱区天然降水维系季节性植被适应性生长耗水量分析时发现，白茎盐生草遭到胁迫时气孔会减小或关闭，气孔形状从长条形趋于圆润，气孔周围产生大量褶皱。平水年14 g/kg土壤含盐量对应的叶片出现气孔不能关闭的现象。白茎盐生草叶片和茎等肉质化器官均会聚集盐分，表皮细胞排列紧密，肉质化程度高的器官中含有大量的水分，其主要通过稀盐的方式以应对盐胁迫，水分不足时盐聚集现象愈加明显。