休牧对贝加尔针茅草原土壤微生物群落功能多样性的影响

采用Biolog-Eco微平板技术和氯仿熏蒸浸提法,以自由放牧地(zero rest grazing, RG₀)为对照,研究了休牧不同年限(RG_3a、RG_6a和RG_9a)贝加尔针茅草原土壤微生物群落功能多样性及土壤微生物量的变化。结果表明,休牧后贝加尔针茅草原土壤微生物群落代谢活性显著升高。反映土壤微生物活性的平均颜色变化率(AWCD)呈以下变化趋势:RG_6a>RG_9a>RG_3a>RG₀。RG_6a和RG_9a样地AWCD值差异不显著(P>0.05),但均显著高于RG₀样地(P<0.05),RG_3a与RG₀样地差异不显著(P>0.05)。休牧不同年限贝加尔针茅草原土壤微生物群落Shannon-Wiener物种丰富度指数(H)、Shannon-Wiener物种均匀度指数(E)和Simpson优势度指数(D)均为RG_9a最高,其中RG_9a样地H值与其他样地差异显著(P<0.05);不同处理E值差异不显著(P＞0.05),RG_9a样地D值与RG₀差异显著(P<0.05)。主成分分析结果表明,RG₀,RG_3a和RG_6a样地土壤微生物群落碳源利用方式及代谢功能相似,而RG_9a样地土壤微生物群落具有不同的碳源利用方式和代谢功能。对不同碳源的分析结果表明,糖类、氨基酸类、脂类为土壤微生物利用的主要碳源。随休牧年限的增加,土壤微生物量呈增加趋势。RG_9a土壤微生物量碳、微生物量氮(soil microbial biomass C, N)含量均最高,分别为590.20和72.86 mg/kg。相关分析表明,AWCD值与土壤微生物H值呈显著正相关(P<0.05),与D值呈极显著正相关(P<0.01);H值与D值呈极显著正相关(P<0.01)。H值、D值均与土壤微生物量碳(SMBC)呈显著正相关(P<0.05);H值与土壤微生物量氮(SMBN)呈显著正相关(P<0.05)。由此可知,休牧使草原土壤微生物代谢功能增强,土壤微生物繁殖快、数量大,从而促进土壤微生物量碳、氮含量的增加。

Effect of rest-grazing on soil microbial community functional diversity in Stipa baicalensis steppe

The changes in soil microbial community functional diversity and microbial biomass under different rest-grazing years (RG_3a, RG_6a and RG_9a) in Stipa baicalensis steppe were investigated and compared with zero rest grazing grassland (RG₀) using the Biolog-ECO micro-plate technique and chloroform fumigation extraction method. The soil microbial metabolic activity significantly increased after rest grazing. The average well color development (AWCD), which represented soil microbial metabolic activity, followed the order of RG_6a>RG_9a>RG_3a>RG₀. The AWCD of RG_6a and RG_9a showed no significant difference, but both were significantly higher than that of RG₀ (P<0.05). RG_3a had no significant difference from RG₀ (P>0.05). The RG_9a had the highest Shannon index (H), substrate evenness (E) and Simpson’s dominance (D) of soil microbial community. The Shannon index (H) of RG_9a was significantly (P<0.05) different from those under other treatments. Substrate evenness (E) was not significantly different from each other; Simpson’s Dominance (D) of RG_9a was not significantly different from those of RG_3a and RG_6a, but significantly different from RG₀. Principal component analysis (PCA) showed that the RG₀, RG_3a and RG_6a had a similar carbon source utilization mode and the metabolic function differed from that of RG_9a. The carbon sources most used by soil microorganisms were carbohydrates, amino acids, and lipids. Soil microbial biomass increased gradually with more rest grazing years. RG_9a had the highest soil microbial biomass C (590.20 mg/kg) and soil microbial biomass N (72.86 mg/kg). Correlation analysis indicated that the AWCD had a significantly (P<0.05) positive correlation with the Shannon index (H) and a highly significantly (P<0.01) positive correlation with Simpson’s dominance (D). The Shannon index had a highly significantly (P<0.01) positive correlation with the Simpson’s dominance (D). The Shannon index (H) and Simpson’s dominance (D) both showed a significantly (P<0.05) positive correlation with soil microbial biomass C and there was also a significantly (P<0.05) positive correlation between the Shannon index (H) and soil microbial biomass N (P<0.05). Therefore, rest grazing enhanced the soil microbial metabolic function which was beneficial to the reproduction of soil microorganisms, thereby promoting an increase of soil microbial biomass carbon and nitrogen content.