Changes of Soil Ecosystem in Karst Mountain Areas Under the Impact of Different Vegetations
LI Yang-Bing~(1,2),GAO Ming~1,Shao Jing-An~1,XIE De-Ti~1,Wei Chao-Fu~1 (1.Resources and Environment College,Southwest Agricultural University,Chongqing 400716;2.College of Geography and Biology Science,Guizhou Normal University,Guiyang,Guizhou 550001)
In this study some typical karst mountainous regions in Chongqing were selected to discuss the essential characteristics of soil degradation during vegetation change processes.The results showed that:(1) After the vegetation turned into secondary vegetation or man-made vegetation,or reclamation,soils would be degraded in physical properties in the karst mountainous environment.Compared with the abandoned field,shrub-grassland,secondary forest and natural forest,in the surface soil layer of sloping cropland,the contents of 2 mm-sized (water-)stable aggregates dropped obviously to(52.1%,24.7%,29.9%,22.8%,) and those of(1mm-) to(0.05 mm-)sized particles increased,but those of 0.05mm-to 0.001mm-sized particles decreased,demonstrating apparent sandification;in slopping cropland soils,the capillary and aeration porosities,long-term soil water-retention and water-supplying capacities and soil resistance against drought were reduced as well,and their field water-holding capacity accounts for 79.3% of that of the forest land soils.(2) The contents of soil organic matter and total nitrogen are controlled completely by vegetation type and land-use intensity.The contents of SOM(soil organic matter) in sloping cropland are lower than in woodland and grassland.After the land was converted for forest and pasture,the contents of SOM would increase steadily,though this trend of increasing is rather slow in the early days when over-reclamation is stopped and the land is converted for forest and pasture.The contents of SOM in man-made woodland and secondary forestland are still lower than in natural forestland.(3) Herbaceous species increase and woody plants species decrease with increasing land use intensity,therefore,the soil seed banks degrade more seriously.With the process of evolution from abandoned field,shrub-grassland to secondary forestland,the ecological dominance will be reduced and the Richness index and diversity index will increase in soil seed banks.Based on the above research results,it is suggested that land degradation in the karst ecosystem is essentially characterized by the degradation of soil functions that are served as water banks,nutrient banks and soil seed banks,and the degradation rates of these three banks are different.