芦苇克隆整合对石油污染湿地土壤微生物群落结构和生物量的影响

克隆植物形体相连的无性个体(分株)之间可以进行水分、养分和光合产物的传递和共享,并且这种克隆整合可以显著提高分株对环境胁迫的耐受能力,从而可能进一步影响分株周围的土壤微生物群落结构和生物量。尽管国内外已经开展了大量有关克隆整合对分株耐受胁迫能力影响的研究,但克隆整合对土壤微生物群落结构和生物量影响的研究却十分缺乏。以黄河三角洲芦苇(Phragmites australis)湿地生态系统为研究对象,将直径60 cm的圆形样方进行三个水平的石油添加处理(不添加石油或每年添加5 mm或10 mm厚的石油),同时通过切断或不切断样方内外芦苇根状茎的连接来控制克隆整合的有无。实验连续开展了两年(2014—2015年),每年8月份在样方内进行土壤样品取样,在实验室内采用磷酸脂肪酸(PLFA)法测定土壤微生物总量及主要微生物类群含量,并测定土壤微生物生物量碳和氮含量。取样时间显著影响土壤微生物PLFA总量、微生物碳和氮含量,这3个变量在2015年均显著高于2014年。石油添加在2015年显著增加了土壤微生物PLFA总量,但在2014年却无显著效应;同时,石油添加在2014年降低了土壤微生物碳和氮含量,而在2015年却增加了其含量。然而,无论在2014年还是2015年,芦苇的克隆整合对土壤微生物PLFA含量、微生物碳和氮含量均没有显著影响。土壤微生物PLFA总量与土壤微生物碳和氮含量呈正相关关系。这些结果表明,石油污染可以显著影响湿地土壤微生物动态,但克隆整合却无显著效应。

Effects of clonal integration of Phragmites australis on the composition and biomass of soil microbial communities in a wetland contaminated by crude oil

Connected asexual individuals (ramets) of clonal plants can transport and share resources such as water, nutrients, and photosynthates. Such clonal integration can enhance the capacity of ramets to tolerate environmental stresses, and thus may further affect the composition and biomass of soil microbial communities around the ramets. Although a large number of studies have examined the effects of clonal integration on the capacities of clonal plants to withstand stresses, very few have tested its influence on soil microbial communities. In a Phragmites australis wetland in the Yellow River Delta in China, we added 0, 5, and 10 mm crude oil per year to circular plots of 60 cm in diameter. In half of the plots, we severed the rhizome connections between the ramets of P. australis inside and outside the plots to prevent clonal integration, whereas the rhizome connections were kept intact in the other half to allow integration. The experiment lasted for two years from 2014 to 2015. We sampled soil in each plot in August, and measured the phospholipid fatty acids (PLFAs) of soil microbes and the carbon and nitrogen concentrations of the soil microbial biomass. Sampling time had a significant effect on total soil microbial PLFAs, carbon, and nitrogen, and these three variables were all higher in 2015 than in 2014. Crude oil addition significantly increased total PLFAs of soil microbes in 2015, but had little effect in 2014. Furthermore, crude oil addition resulted in a decrease in soil microbial carbon and nitrogen in 2014, but an increase in 2015. Clonal integration had no significant effect on soil microbial PLFAs, carbon, or nitrogen in either 2014 or 2015. Total soil microbial PLFAs were significantly positively related to soil microbial carbon and nitrogen. Therefore, crude oil contamination in wetlands can significantly affect the dynamics of soil microbes, whereas physiological integration of clonal plants may not.