Effect Of Forest Gap On Soil Microbial Community Structure And Enzyme Activity Under Pinus Tabulaeformis Plantation

Forest gap is an important driving force of forest natural regeneration and environmental change,which plays an important role in dynamic succession and ecological function optimization of forest ecosystem.The formation of forest gap will cause the change of illumination,temperature,humidity and vegetation composition,and soil microbial community structure and the activity of enzyme will be changed,thus affecting the soil nutrient cycling and transformation of the forestland then the regeneration of the seedlings will be influenced indirectly.At present,the researches about the forest gap mainly be focused on the effect of the restoration and succession of plants and the microenvironment after the formation of forest gap,but the changes of soil microbial community structure,nutrient characteristics and the activity of enzyme under the forest gap are researched rarely.Pinus tabulaeformis is one of the excellent afforesting species in Loess Plateau,because of its drought-resistant functions in soil and water conservation.The regeneration of P.tabulaeformis plantation in Loess Plateau occurred under the forest gap primarily.This study was based on 3 kinds of forest gaps?large,medium and small?of P.tabulaeformis plantation in Loess Plateau as the research object,using phospholipids fatty acid?PLFA?technique to research the difference between microbial population structure of litter layer and topsoil under different size forest gaps,analyzing the effect of forest gap area on soil nutrient characteristics and the enzyme activity.The research results show that:?1?The soil nutrient characteristics of P.tabulaeformis plantation were closely related to the forest gap area.The nutrient content in litter layer was significantly higher than which in topsoil.In the litter layer and topsoil,soil pH,total organic carbon?TOC?,total nitrogen?TN?,ammonium nitrogen?NH₄⁺-N?,microbial biomass nitrogen?MBN?reached top under the medium forest gap.In the topsoil,the content of microbial biomass carbon?MBC?was the highest under the medium forest gap,but that was the highest under the small gap and the lowest under the middle gap in the litter layer.?2?The forest gap area affected the microbial community structure of P.tabulaeformis plantation significantly.In the litter layer,the content of BPLFA under forest gap was significantly higher than that under the forest.The contents of G⁺PLFA and G^-PLFA were high under the middle forest gap and the large gap.The content of FPLFA was the highest under the small gap.In the topsoil,the BPLFA content was the highest under the big gap.The contents of G⁺PLFA and G^-PLFA under the middle forest gap were significantly higher than those in middle,small gap and undergrowth.The FPLFA content decreased with the increase of the forest gap area,and the contents of soil FPLFA in the undergrowth and small gaps were significantly higher than those under the middle and large gaps.?3?The litter layer of P.tabulaeformis plantation was greater influenced by gap than topsoil layer.In the litter layer,the activities of?-glucoside,cellulase and protease under the middle and large gaps were significantly higher than which under the undergrowth.In the topsoil,the forest gap area had a huge effect on the activity of alkaline phosphatase,and the activity of alkaline phosphatase was the highest under the medium forest gap.?4?There were correlations during soil microbial community structure,the activity of enzyme and nutrient characteristics.The contents of bacteria,Gram-positive bacteria and negative bacteria PLFA were significantly correlated with soil pH in the litter layer.The fungi PLFA content was significantly positively correlated with microbial biomass carbon,and negatively correlated with available P.The contents of Gram-positive bacteria and negative bacteria PLFA were significantly correlated with ammonium nitrogen,pH and microbial biomass nitrogen.The fungi PLFA content was significantly negatively correlated with microbial biomass nitrogen and pH.?5?The medium forest gap?90-290 m²?could effectively improve the soil environment of micro-ecological of P.tabulaeformis plantation in the Loess Plateau.