桂西北喀斯特和非喀斯特森林土壤初级氮转化速率及其影响因素

研究土壤初级氮转化过程及其调控机制对评估生态系统供氮能力或氮流失潜力具有重要意义，然而目前针对喀斯特生态系统初级氮转化速率及其主控因素的研究非常有限。我们采用15N同位素稀释法研究了桂西北喀斯特和邻近非喀斯特森林0~10 cm、10~20 cm和20~40 cm三个土层初级氮转化速率，结合土壤理化性质和功能基因丰度分析了两个森林土壤初级氮转化速率的主控因素。结果表明：喀斯特森林土壤初级氮矿化速率、初级硝化速率、自养硝化速率和异养硝化速率均显著高于非喀斯特森林。喀斯特森林土壤自养硝化对初级硝化速率的贡献平均为75.04%，而非喀斯特森林自养硝化的贡献平均为28.51%。喀斯特森林土壤初级氮矿化、初级硝化和自养硝化速率随土层深度增加而下降，但非喀斯特森林仅土壤初级氮矿化速率随土层深度增加而下降。总体而言喀斯特和非喀斯特森林土壤初级氮转化速率存在显著差异，且全氮、微生物量是氮转化过程的主控因素，而功能基因的作用较小。

Soil gross nitrogen transformations and their influencing factors in karst and non-karst forests of Northwest Guangxi

Soil gross nitrogen (N) transformations and their controls are crucial for assessing soil N supply capacity or loss potential for terrestrial ecosystems. However, few studies have been conducted to explore soil gross N transformations and their controls for karst ecosystems. The current study determined soil gross N transformation rates for three mineral soil horizons, i.e., 0~10 cm, 10~20 cm and 20~40 cm using the 15N isotope dilution technique in a karst and an adjacent non-karst forests in northwest Guangxi. Soil physicochemical properties and functional gene abundances were measured as well to identify the factors influencing soil N transformations. Our results show that the rates of gross N mineralization, gross nitrification, autotrophic nitrification and heterotrophic nitrification were all significantly greater in the karst forest than in the non-karst forest. The averaged contribution of autotrophic nitrification to gross nitrification rate was 75.04% for the karst forest in comparison to a corresponding value of 28.51% in the non-karst forest. In the karst forest, rates of gross N mineralization, gross nitrification and autotrophic nitrification decreased as soil depth increased, whereas only soil gross N mineralization rate decreased with soil depth in the non-karst forest. Overall, there was significant difference in gross N transformations between the karst and non-karst forests with total N and microbial biomass being the more important controls relative to microbial functional genes.