施氮对不同有机碳水平桉树林土壤微生物群落碳代谢的影响

土壤微生物群落碳代谢功能既受土壤氮素水平的影响,也与土壤有机碳水平密切相关,但二者如何共同影响土壤微生物群落碳代谢功能的研究尚不多见。以我国南方广泛种植的桉树林为对象,采用野外控制实验比较研究了4种施氮处理(对照:0kg/hm2,低氮:84.2 kg/hm2,中氮:166.8 kg/hm2,高氮:333.7 kg/hm2)对有机碳水平差异显著的两桉树林样地土壤微生物群落碳代谢功能的影响,结果表明:(1)两种有机碳水平桉树林土壤微生物群落碳代谢强度和代谢碳源丰富度显著不同,高有机碳水平桉树林土壤微生物群落碳代谢强度和代谢碳源丰富度显著高于低有机碳水平桉树林(P0.01);(2)施氮显著改变了桉树林土壤微生物群落的碳代谢强度和代谢碳源丰富度(P0.05),随着施氮水平的升高,土壤微生物群落碳代谢强度和代谢碳源丰富度均呈现先增加后降低的变化规律,但是高、低有机碳水平桉树林土壤微生物群落碳代谢强度和代谢碳源丰富度对施氮梯度的响应各不相同,高、低有机碳水平桉树林的土壤微生物群落碳代谢指标分别在中氮、低氮处理中达到最高值;(3)施氮影响土壤微生物群落代谢的碳源类型主要是碳水化合物类、氨基酸类和羧酸类,土壤微生物生物量是影响土壤微生物碳代谢强度和代谢碳源丰富度的重要因素。由此可知,施氮对土壤微生物碳代谢功能影响,也与土壤本底中有机碳水平的调节有关,所以在研究土壤微生物群落对施氮等条件的响应时,不能忽略土壤中有机碳水平。

Effects of nitrogen application on carbon metabolism of soil microbial communities in eucalyptus plantations with different levels of soil organic carbon

Soil microorganisms are involved in the turnover of soil nitrogen and other soil nutrients.. Nitrogen and carbon, two basic elements utilized by soil microbial communities, directly influence the structure and function of these communities. However, few studies have focused on the combined effects of nitrogen application and soil organic carbon level on soil microbial communities. In this study, we conducted field experiments with four different nitrogen applications (control, CK): 0 kg/hm²; low application nitrogen level, LN:84.2 kg/hm²; middle application nitrogen level, MN: 166.8 kg/hm²; high application nitrogen level, HN: 333.7 kg/hm²) in two Eucalyptus plantation sites with significantly different soil organic carbon levels (low organic carbon site, LC and high organic carbon site, HC) in Guangxi, southern China. We identified the compound effects of nitrogen application level and soil organic carbon level on soil microbial function by using the BIOLOG method. The results showed that (1) carbon metabolism of soil microbial communities responds positively to soil organic carbon levels. Carbon metabolism intensity and richness of soil microbial communities in HC sites were significantly higher than those in LC sites (P< 0.01). (2) Carbon metabolism of soil microbial communities was significantly influenced by the nitrogen application level (P< 0.05). With the increase in nitrogen level, carbon metabolism intensity and richness of soil microbial communities increased gradually and then decreased gradually. However, carbon metabolism intensity and richness of soil microbial communities in Eucalyptus plantations with different soil organic carbon levels had significantly different responses to nitrogen application. The maximum carbon metabolism intensity and richness of soil microbial communities were observed in the HC site with MN application; this was also observed in the LC site with the LN level. The interactive effects of nitrogen application level and soil organic carbon level on soil carbon metabolism is significant (P <0.01). (3) The main metabolized carbon sources of soil microbial communities, which differentiated the responses of soil microbial carbon function according to nitrogen application level, were carbohydrates, amino acids, and carboxylic acids. Carbon in the soil microbial biomass was positively correlated with carbon metabolism intensity and richness index of soil microbial communities. Our results suggest that not only nitrogen levels but also soil organic carbon levels influence soil microorganism carbon source utilization, and soil organic carbon level cannot be neglected in analyzing the effects of nitrogen application level on soil microorganism community metabolism.