| Based on a nine-year fertilization and water addition filed experiment conducted in Duolun Restoration Ecological Research Station of Chinese Academy of Sciences, we investigated soil physical and chemical properties, soil microbial community, and soil microbial biomass and enzyme activities under the nitrogen (N), phosphorus (P), and water addition. The co-variation of structure and function of soil microbial community and environmental factors was examined under precipitation enhancement, and N and P addition. The results showed that soil physical and chemical properties were significantly changed under water and nutrients addition. Soil available N concentration significantly increased, while soil pH value decreased with increasing N addition gradient. Both soil microbial biomass and respiration rate were significantly depressed under treatments with10or15g kg-1m-2yr-1N addition. Soil NO3--N concentration significantly decreased with water addition, while soil microbial biomass and respiration rate increased herein.Soil cellulose (CBH) and N-acetyl-β-D-glucosaminida.se (NAG) activities were increased, while β-Glucosidase (BG) and protease activities (PRO) were decreased under N addition. Precipitation increment decreased cellulose activity, while increased β-glucosidase activity. Phosphorus addition decreased the activity of soil phosphomonoesterase, but increased the activity of β-glucosidase.By using the16S-rDNA-DGGE, we found that soil bacterial community composition was significantly changed by water and N addition. Bacterial richness (R), Shannon-Wiener diversity index (H), and Evenness index (J) were significantly increased under water addition. No significantly affected of N addition on indexes of soil bacteria a-diversity. By using PLFA method, we found that N addition reduced the relative abundance of soil fungi, but increased the relative abundance of soil bacteria, and this decreased the ratio of fungi to vbacteria in soil. The relative abundances of soil fungi, arbuscular mycorrhizal fungi, and anaerobic bacteria were significantly increased with water addition. The relative abundance of soil arbuscular mycorrhizal fungi was decreased, while that of soil actinomycetes was increased with P addition. The results of microbial community structure of redundancy analysis showed that soil pH, microbial biomass, and microbial respiration were the main driving factors that influencing soil microbial community under water and N addition. Soil available N and dissolved organic carbon were also the main environmental factors affecting the soil microbial communities.The relationship between microbial community function and structure was analyzed by using Mantel test. The results showed that microbial function and structure co-varied with water and fertilizer treatment. Soil bacteria was significantly and positively correlated with NAG activity, and soil fungi was significantly and positively correlated with BG activity.The result abtained in this study will help us to understand the pattern and functional stability of grassland ecosystem bioversity under the projected global climate change conditions. It suggests that water and fertilizer addition hoped to accelerate the recovery of plant cover and improve ecosystem service function in the degraded grassland ecosystem in northern China. |
