森林土壤微生物与植物碳源的磷脂脂肪酸及其单体同位素研究

Mountain forest soil microbial communities and carbon source study by phospholipid fatty acid structure and compound-specific isotope analysis

森林生态系统的土壤微生物群落组成和活性,是影响生物地球化学循环、有机质代谢和土壤质量的关键因素。磷脂脂肪酸(PLFA)是一类可有效表征活体微生物群落结构的生物标志物,而其单体稳定碳同位素(δ^(13)C)水平对土壤微生物植物碳代谢具有独特的指示作用。本次研究以土壤PLFA为对象,分析了我国位处纬度梯度带上(24°N~47°N)的9个高山森林的土壤PLFA组成、丰度及其δ^(13)C水平,以此表征土壤细菌、真菌、革兰氏阳性菌和革兰氏阴性菌4种生物群落的生物量、微生物生物量、微生物的群落结构、植物碳源特征及其与环境因素的关系。土壤中PLFA总量为28.2~253μg/g,不同森林土壤中四类微生物群落PLFA含量和PLFA总量以及革兰氏阳性与阴性菌比值等指标存在显著差异(p<0.01)。处于相对高纬度–低海拔和相对低纬度–高海拔的森林土壤PLFA的组分相似,说明其微生物群落结构相似。土壤pH值、总有机碳(SOC)和总氮(TN)与土壤PLFA含量显著相关(p<0.01),年均温、土壤碳氮比和土壤温度是影响土壤微生物群落结构的主要因素(p<0.01),可见森林土壤微生物生物量主要由土壤性质决定,而微生物的群落结构受气候因素和土壤性质共同影响。森林土壤PLFA的单体δ^(13)C范围为−35‰~−17‰,整体上接近C_(3)植物,说明这些森林土壤中微生物的植物碳源主要来自C_(3)植物。四类微生物群落PLFA和PLFA总量的δ^(13)C与年均温、年降水量、土壤总有机碳、总氮显著相关(p<0.05),表明土壤微生物对植物碳源的选择可能受到气候因素和土壤肥力的共同影响。

Soil microbial structures and their activity in forest ecosystems plays a key role in soil biogeochemical cycles,soil organic matter metabolism,and soil quality.Phospholipid fatty acid(PLFA)is a biomarker of living microbial structure,and its natural stable carbon isotope abundance( δ^(13)C)is indicative of the microbial plant carbon sources.In this study,four microbial communities(bacteria,fungi,gram-positive bacteria,and gram-negative bacteria)as well as total microbial biomass,structures,plant carbon sources and their relationship with environmental factors were discussed based on the abundance,composition,and δ^(13)C of their representative PLFA in nine mountain forests distributed on a latitudinal gradient(24°N-47°N)in China.The total microbial biomass(28.2-253μg/g)was significantly different in the nine forests,as was the biomass of the four microbial communities and the ratio of gram-positive bacteria to gram-negative bacteria(GP/GN)(p<0.01).The principal components of PLFA in forests located at relatively high latitudes and low elevations are similar to those in forests located at relatively low latitudes and high elevations,indicating a similar microbial structure in these forests.Soil pH,soil organic carbon(SOC),and total nitrogen(TN)were significantly correlated with soil microbial biomass(p<0.01),while mean annual temperature(MAT),soil temperature,and the ratio of soil carbon and nitrogen were significantly correlated with the soil microbial structure(p<0.01).This indicates that the microbial biomass was mainly influenced by soil properties,but the microbial structure was determined in combination with climatic conditions.The δ^(13)C of soil microbes varied from −35‰ to −17‰,which was similar to that of C_(3) plants,indicating a principal C_(3) plant microbial carbon source in these forests.There was a significant relationship between the total and the four microbial δ^(13)C values and mean annual temperature,mean annual precipitation,soil organic carbon,and total nitrogen(p<0.05),suggesting that the choice of microbial plant carbon source is influenced by soil fertility and climatic conditions.