Response Of Nutrient Disribution In Plant-soil System To Fire In A Typical Restored Grassland On The Loess Plateau

Loess Plateau, having the most serious environmental and ecological problem, was the ecotone of water and wind erosion and also the ecotone of agriculture and animal husbandry. Hence grassland would be of great importance in the ecological protection and economic development. Grassland, 30% of total area of the Loess Plateau, degraded seriously with arid environment and over-use. Enclosure, the best measures for the vegetation restoration on the Loess plateau, played an important role in solving the grassland degradation and the loss of water and soil. This research focused on the typical restored grassland. By analyzing the effect of fire to the distribution of plant-soil system, considering slope aspects and positions, we tried to reveal the general pattern of the nutrient distribution of plant-soil system and its responses to fire on the Loess Plateau. And then provided theories and technology for the understanding of the biogeochemistry within the restored ecosystem on the semi-arid area and the ecosystem adaptive management. Main conclusions were as followed:(1) Fire changed features of the restored grassland ecosystem, and accerated biogeochemical cycles of plant-soil system. After 10 monthes of fire, plants production, nutrients storage and soil carbon, nitrogen and phosphorus(organic carbon, total nitrogen, ammonium nitrogen and available phosphorus) increased, but vegetation cover, plants nutrients content, soil nitrate nitrogen and available phosphorus decreased. Total phosphorus showed no response to fire. The relationships among components of plant-soil system expressed differences after fire, and correlation between plant and soil nutrients showed decreasing after fire.(2) Topography(slope aspects and positions) performed effects on plant-soil system by influencing moisture, light and hotpower locally, and also interwened responses of plant-soil system within restored grassland to fire. Slope aspectsshowed effects on vegetation cover, biomass, nutrients content, nutrients storage and soil nutrients content. Slope postions significantly alterd soil nutreints content but little at plant.(3) Spatial heterogeneity(SH) could be influenced by fire and slope positions. Spatial heterogeneity(SH) of vegetation coverage and plant potassium content and storage expressed different responses when influenced by fire, compared between slope aspects. They were increasing and decreasing in shady and sunny slope, respectively. SH of communities biomass and plant carbon storage increased after fire. SH of plants carbon, nitrogen and phosphorus content and plants nitrogen and phosphorus storage decreased after fire. SH variations of soil nutrient content after fire were more complicated, slope aspect and soil layers would also influence them, and discrepant could be existed in different nutrient elements.Enclosure,as a control measure, had completed the restoration of natural vegetation of this area. But as the time gone by, lots of proplems has exposed. By analyzing effects of fire to restored grassland ecosystem, this research provided theories to the adaptive management of the restored grassland ecosystem. But lots work needed to do about effects of different fire regimes to restored grassland ecosystem and heterogeneity on different scales within restored grassland ecosystem.