Stand Productivity And Soil Microbial Community In A Black Locust Plantation In Sub-humid Loess Region In Response To Precipitation Reduction

Changes in rainfall patterns caused by global climate change are having a huge impact on various ecosystems,especially forest ecosystems located in semi-arid and humid areas will face the threat of reduced rainfall.The Loess Plateau is the region with the most serious soil erosion in China.Artificial vegetation construction is an important measure for ecological restoration and soil and water conservation in this area.Robinia pseudoacacia is the most typical plantation tree species in the region with the largest planting area.Therefore,exploring the changing characteristics of the soil environment and productivity of the R.pseudoacacia plantation ecosystem under the reduced rainfall environment,and revealing its internal response mechanism,not only helps to explore the relationship between the various elements of the ecosystem and its mechanism of action,to predict the context of global change The evolution trend of the ecosystem has important theoretical and practical significance for the rational construction and management of the artificial ecosystem.In this study,the R.pseudoacacia plantation located in the gully region of the semi-humid loess plateau was used as the research object.By setting a 30% reduction in rainfall input treatment and using the plot with normal rainfall as control,the soil environment and forest productivity in the second year of treatment were investigated.The characteristics and mechanism of the change,particularly the characteristics and changing trend of forest soil microbial community,were analyzed.The main results are as follows:(1)There was no significant difference between the forest soil temperature and the control plot,but the soil moisture content of the forest plot was significantly lower than that of the control plot,indicating that continuous reduction of rainfall input had a significant impact on the forest soil moisture content.Different soil layers have different responses to rainfall reduction.Although the surface soil(0-10cm)is highly sensitive to rainfall events,the reduction in soil moisture caused by reduced rainfall input is most evident in the30-50 cm soil layer.(2)Short-term rainfall reduction did not have a significant impact on the biomass of the artificial locust forest layer,but significantly reduced the annual production of the arbor layer.The total above-ground productivity of the forest tree layer in the second year of rainfall reduction was 8.272t/ha,which was significantly lower than the control plot.The aboveground productivity of the tree layer is still the same(12.253t/ha).The decrease inrainfall input significantly reduced the annual production of fine roots in artificial R.pseudoacacia forests,a decrease of 9.67%.The growth of fine roots in different soil layers responded differently to the reduction in rainfall.40 cm soil layer,which may be related to the treatment period.(3)The reduction of short-term rainfall has no significant effect on the total annual yield of forest litter,but it has a certain impact on the monthly dynamics of litter volume,which may be related to the high sensitivity of the rain reduction treatment plot to short-term drought.The litter decomposition coefficient(0.50)of the rain reduction treatment plot was smaller than that of the control plot(0.67),indicating that reducing the rainfall input reduced the litter decomposition rate.However,the nutrient release pattern of litter was not changed.The release of organic carbon showed a direct release pattern,and the release of nitrogen showed an enrichment first,and then release pattern.(4)The reduction of short-term rainfall did not change the main community types and diversity of soil microbes in the artificial R.pseudoacacia forest,but the average relative abundance values of the flora in the treatment and control plots in the non-growth season and the growth season are different,indicating that changes in the external environment will Screen strains with more adaptability.It is speculated that with the extension of treatment time,the possibility of affecting the composition of soil microbial community will increase.The bacterial diversity index is different between the growing season and the non-growth season,but there is no difference between the fungi,indicating that the seasonal change has a more obvious effect on the bacterial diversity,and the fungal community is more tolerant to environmental changes,and its community High structural stability.