| Grazing is one of the most important ways of grassland utilization,which plays a key role in the economic development of pastoral areas.However,in recent decades,due to the influence of human and natural factors,the grassland has been degraded in a large area,and the availability of grassland has been greatly reduced.In order to alleviate the trend of grassland degradation,the government formulates some measures,such as selective enclosure and reducing grazing intensity to recover grassland ecosystem,which have achieved remarkable restoration effects.However,at present,the variation trends of vegetation,soil properties and microbial communities,and their interactions in the grassland under long-term enclosure are still unclear.In-depth understanding this question is very important for subsequent scientific application of enclosure to recover degraded grassland.Based on this,we selected the Leymus chinensis grassland(study site A),degraded grassland(study site B)and Stipa grandis grassland(study site C)in Xilin Gol League,Inner Mongolia,China,as the study sites,including long-term enclosed area and the slightly,moderately and severely degraded areas,respectively.We aim to explore the effects of long-term enclosure on vegetation,soil properties,and soil microbial characteristics,and their interaction.This work would provide theoretical basis and practical guidance for the restoration of degraded grassland in the future.The main research results are as follows:(1)Long-term enclosure promoted grassland vegetation restoration.In all sites,enclosure increased the number of grassland vegetation species,and the dominant species changed.The vegetation height,coverage rate,aboveground biomass,underground biomass and litter mass after enclosure were all higher than those of the degraded grassland.In the site A,compared with different degraded areas,the vegetation heights of the enclosed area increased by 47.82%～135.42%,the coverage rates increased by 23.40% ～ 93.33%,and the aboveground biomass increased by66.27%～95.88%,and the belowground biomass increased by 12.10%～55.29%,the litter mass increased by 1.09 ～ 91.37 times.In the site B,compared with different degraded areas,the vegetation heights of the enclosed area increased by 121.99%～151.26%,the coverage rates increased by 35.90%～ 130.43%,and the aboveground biomass increased by 140.16%～209.53%,and the belowground biomass increased by28.99%～116.67%,and the litter mass increased by 11.47～43.07 times.In the site C,compared with different degraded areas,the vegetation heights of the enclosed area increased by 97.90%～139.95%,the coverage rates increased by 18.18%～33.33%,and the aboveground biomass increased by 72.97%～132.60%,and the belowground biomass increased by 33.43% ～ 82.38%,and the litter mass increased by 15.97 ～151.21 times.In the site A and B,the shrub occurred after long-term enclosure.Compared with different degraded areas,shrub biomass in the site A after enclosure increased by 36.07～2113.00 times,and in the site B,it increased by 7.31～1185.50 times.Compared with the moderately degraded grassland,the gramineous biomass in the site A after enclosure increased by 497.74%.Compared with different degraded areas,the gramineous biomass in the site B after enclosure increased by 22.12% ～147.37%.Compared with different degraded areas,the gramineous biomass after enclosure in the site C increased by 74.07%～135.45%.The variation patterns of the diversity and evenness of grassland species were different after enclosure among different study sites.In the site A,the species diversity increased by 38.00%～95.28%,and the species evenness increased by 15.15% ～ 49.02%.In the site B,the species diversity decreased by 5.26% ～ 44.74%,and the species evenness decreased by30.43%～45.65%.However,in the site C,there was no significant difference in the species diversity and evenness between the enclosed area and different degraded areas.(2)Long-term enclosure improved soil texture and soil fertility.In the site A,compared with different degraded areas,the soil bulk densities after enclosure decreased by 15.66%～22.28%,the pH values decreased by 4.48%～9.77%,the soil water contents increased by 19.11%～32.65%,the organic matter contents increased by 43.69%～69.60%,the available nitrogen contents increased by 67.88%～130.79%,the total nitrogen contents increased by 52.38% ～ 100.00%,the total phosphorus contents increased by 46.67% ～ 83.33%,the phosphatase activities increased by26.61%～36.34%,and the sucrase activities increased by 18.77%～47.73%.In the site B,compared with different degraded areas,the soil bulk densities after enclosure decreased by 14.75%～17.89%,the pH values decreased by 2.24%～2.60%,the total potassium contents decreased by 2.41%～16.64%,the soil water contents increased by12.11%～40.59% and,the organic matter contents increased by 36.83%～83.40%,the available nitrogen contents increased by 95.98% ～ 156.97%,and the total nitrogen contents increased by 118.75%～169.23%.In the site C,compared with lightly and moderately degraded areas,the soil bulk densities after enclosure decreased by 12.16%and 12.67%,respectively,the pH values increased by 3.46% and 8.32%,respectively,and the soil water contents increased by 55.44% and 50.92%,respectively.In the site C,compared with different degraded areas,the organic matter contents after enclosure increased by 12.31% ～ 23.23%,the total nitrogen contents increased by 23.64% ～44.68%,and the total phosphorus contents increased by 4.35%～33.33%.In the site C,compared with the lightly and severely degraded areas,the available nitrogen contents after enclosure increased by 38.51% and 18.55%,respectively,while they were lower than those of the moderately degraded area,decreasing by 8.87%.The sucrase activities after enclosure increased by 15.88% compared with those of the mildly degraded area.However,compared with the moderately and severely degraded areas,they decrease by 18.99% and 64.45%,respectively.(3)There were no significant differences in the soil bacterial diversity and richness between the enclosed area and different degraded areas,but there were differences in the structure and composition of soil bacterial communities.Compared with different degraded areas,the absolute abundance of soil bacterial communities after enclosure increased by 49.62%～111.92% and 24.56%～76.99% in the site A and C,respectively;the absolute abundance of soil bacterial communities after enclosure reduced by 9.08% ～47.80% in the site B.In the site A,the absolute abundance of Phyla Eurycetes,Verrucoides,Trichospora,and Nitrocericoides increased significantly after enclosure,while in the site C,the absolute abundance of Phyla Trichospora and Verrucoides increased significantly after enclosure.Acidobacteria,Actinobacteria and Proteobacteria were the dominant phyla in the three study sites,and their absolute abundance accounted for more than 60% of the total absolute abundance.In particularly,the absolute abundance of GP6,Gemmatimonas,Gaiella and other genera of the enclosed areas increased compared with those of different degraded areas in the site A and C,but decreased in the site B.(4)According to Spearman correlation analysis,in the site A,the abundance of most soil bacteria phyla had significant correlations with vegetation and soil properties;in the site B and C,the abundance of most soil bacteria phyla had significant correlations with soil properties,but weak correlations with vegetation. |
