北方农牧交错区沙漠化的生物过程研究

通过对不同土地利用/覆盖下4种类型沙漠化土地的土壤与植被特征、变化规律、动因和互动关系的调查研究,结果表明土地沙漠化导致了土壤环境和植被的明显退化。其中严重沙漠化农田和非沙漠化农田相比,土壤有机质含量、速效氮、生长季土壤含水量分别下降66.2%、69.0%、74.8%,地温由21.5 ℃上升到22.4 ℃,其中干旱期严重沙漠化农田土壤含水量仅为23%,已无法满足作物生长需要。土壤环境恶化首先威胁土壤微生物和土壤动物的生存,使土壤微生物和动物数量分别下降95.0%和75.9%,酶活力下降39.5%~ 90.6%。同时植物多样性、种的饱和度和初级生产力大幅度下降,如严重沙漠化草地和非沙漠化草地相比,3项指标分别下降85.5%~883%,87.5%~ 950%和80.6%~ 967%,植被开始发生逆向演替,群落优势种不断更替,最终形成耐牧耐风沙的沙生植物群聚。旱作农田虽采取了施肥、中耕等管理措施,但光合转化效率和初级生产力还是下降了567%和574%。这一过程因其动因不同可分为植被退化(如放牧)引起的土地沙漠化和裸露地表风沙流活动直接导致的土地沙漠化(如农田风蚀和流沙迁移),前者是植被先行退化进而影响到土壤环境,其过程较为缓慢,后者是土壤环境首先恶化进而导致植。

Study on Bio-processes in Desertification in Northern Agro-Pasture Interzone

Features of soil environment and vegetation in four types of desertified land were investigated and their changes laws and causes and mutual relation were analyzed. Results showed: desertification caused a rapid deterioration of soil environment and vegetation, of which soil organic matter and quick-acting N and water content declined by 66.2%, 69.0%, 74.8% respectively, and soil temperature raised by 0.9 ℃ in seriously desertified land compared with no desertified land, specially soil water content is 2.3% in dry period and can not meet the needs for crop growth. The plant diversity decreased by 85.5%~88.3%,saturation index of plant spices dropped from 20~40 n·m^-2 to 1~5 n·m^-2,primary productivity declined by 80.6%~96.7% in seriously deteriorated grassland compared with normal grassland. Meanwhile, contrary succession displayed and dominant spices changed in the vegetation. Though management measures as fertilizing and inter-tilling were practiced, photosynthetic efficiency and biomass decreased by 56.7% and 57.4% in dry cropland. Desertification process caused by vegetation deterioration was slower than that by wind drifting sand.