放牧与围栏内蒙古针茅草原土壤微生物生物量碳、氮变化及微生物群落结构PLFA分析

Analysis of Microbial Biomass C, N and Soil Microbial Community Structure of Stipa Steppes Using PLFA at Grazing and Fenced in Inner Mongolia , China

以内蒙古贝加尔针茅草原、大针茅草原和克氏针茅草原为研究对象,采用氯仿熏蒸法和磷脂脂肪酸（PLFA）分析方法研究了放牧与围栏条件下内蒙古针茅草原土壤微生物生物量和群落结构特征的变化情况。研究表明放牧与围栏草地土壤微生物生物量和群落结构差异显著。氯仿熏蒸法分析结果表明内蒙古针茅草原土壤微生物生物量碳的含量介于166.6-703.5mg·kg^-1之间,微生物生物量氮含量介于30.34-92.15mg·kg^-1之间,其中贝加尔针茅草原土壤微生物生物量碳、氮最高,大针茅草原次之,克氏针茅草原则最低。放牧条件下,贝加尔针茅草原、大针茅草原土壤微生物生物量碳、氮显著低于围栏草地,克氏针茅草原则无显著变化。PLFA分析结果显示,内蒙古针茅草原土壤微生物群落PLFAs种类、含量丰富,共检测出28种PLFA生物标记磷脂脂肪酸,并且以直链饱和脂肪酸和支链饱和脂肪酸为主,相对含量占总量的2/3左右,其中贝加尔针茅草原土壤微生物含量最丰富,其围栏样地土壤的PLFA含量达到27.3nmol·g-1,大针茅草原和克氏针茅草原依次降低。围栏条件下,各类型草原土壤细菌脂肪酸与总PLFA含量均显著高于放牧草地,真菌脂肪酸含量则因草原类型不同各有差异;放牧导致各类型草原革兰氏阳性细菌PLFAs/革兰氏阴性细菌PLFAs（GPPLFAs/GNPLFAs）比值显著降低,而除了克氏针茅草原,细菌PLFAs/真菌PLFAs比值则显著升高。PLFAs主成分分析表明,放牧和围栏处理对内蒙古针茅草原土壤微生物群落结构产生影响,且围栏处理的影响程度大于放牧处理。经相关分析表明,氯仿熏蒸法和PLFA分析方法之间有很好的一致性,且土壤微生物PLFAs与土壤有机质、全磷、硝态氮显著相关。

Soil microbial biomass and community structure were analyzed by using chloroform-fumigation extraction and phospholipid fatty aeid（PLFA） methods, based on 3 different Stipe types（Stipa baicalensis meadow steppe, Stipa grondis typical steppe, and Stipa krylovii typical steppe ） in Hulunbeier in Inner Mongolia. The results showed that there were significant differences in soil microbial biomass and community strueture at grazing and fenced steppes inside and outside fence. Soil microbial biomass carbon, nitrogen content ranged from 166.6 mg＂ kg-I to 703.5 mg.kg^-1, 30.34 mg. kg^-1 to 92.15mg.kg^-1, respectively. The analysis of Chloroform-fumigation extraction showed that the microbial biomass at Stipa baicalensis meadow steppe was largest, followed by Stipa grandis typical steppe, and the lowest was at Stipa krylovii typ- ical steppe. The microbial biomass at the fenced plots in Stipa baiccdensis meadow steppe and Stipa grandis typical steppe was signifieantly lower than that at the grazing plots, and there was no difference in Stipa krylovii typical steppe. The results of PLFAs displayed that Stipa communities in Inner Mongolia showed abundant speeies and quantity in soil microbial eomnmnities. Total 28 PLFAs biomarkers were detected in the soil samples, with saturated fatty acids and branched fatty acids accounting for 2/3, Stipa baicalensis meadow steppe had the highest content of fatty acid, being 27.3 nmol.g^-1. The bacteria PLFAs and total PLFAs in the fenced plots were much higher than those at the grazing plots. The changes of fungi PLFAs varied with different grassland types. Grazing decreased significantly the ratio of gram-positive bacteria PLFAs/gram-negative bacterium PLFAs （GP PLFAs/GN PLFAs） and remarkably increased the ratio of bacterial PLFAs/fungi PLFAs except at Stipa krylovii typical steppe. Principal component analysis（PCA） indicated that soil microbial community structure was influenced by dif- ferent regimes of grassland utilization, grazing 〉 exclosure. Correlation analysis of soil PLFAs content and soil nutrients showed that there ex- isted highly agreement between chloroform-fumigation extraction and pbospholipid fatty acid（PLFA ） methods, and soil microbial biomass had significant correlation with soil organic matter, total phospholipids and ammonium nitrogen.