土地利用方式对万木林土壤氨氧化微生物丰度的影响

以我国亚热带地区典型花岗岩发育酸性红壤为研究对象,选取福建建瓯万木林自然保护区封禁保护下5种自然植被和1种人工种植植被土壤,采用荧光实时定量PCR(Real-time PCR)技术测定了土壤氨氧化细菌(AOB)和氨氧化古菌(AOA)的群落丰度,采用15N稳定同位素成对标记和数值模型相结合的方法测定了土壤初级硝化速率。结果显示,长期封禁保护下的自然植被土壤pH低,土壤AOB数量偏低。人为种植和管理显著提高了土壤pH,促进了AOB的生长,其丰度比自然条件下提高了2个数量级,土壤初级硝化速率也显著提高,并与AOB数量存在显著的相关性,表明AOB是硝化作用的主要贡献者。5种自然植被条件下AOA的amoA基因拷贝数占泉古菌16S rRNA基因的比例都小于1%(0.01%～0.64%),在农业利用方式下上升到5.32%,表明并非所有泉古菌都具备氨氧化功能基因amoA,氮肥施用可能促进了氨氧化古菌的生长。

Abundances of ammonia-oxidizing prokaryotes and gross nitrification activities in forest soils under different vegetations in a natural reserve

In this study, the relative contribution of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to nitrification were investigated in acidic forested soils derived from granite in Wanmulin nature reserve, Jianou, Fujian Province of southern China. The abundances of AOA and AOB communities were determined by real-time quantitative polymerase chain reaction (qPCR), while gross nitrification activity was measured using 15N-pool enrichment technique in soils under five different vegetations over 600 years plantation one orange cultivation system. The results showed that soil pH, the abundance of AOB and gross nitrification rate were significantly lower in natural vegetation soil than those soil cultivated with orange plant. Furthermore, a significant correlation between the population size of soil AOB and soil gross nitrification activity suggested that AOB might dominate autotrophic nitrification in forested soil typical of the low-pH ecosystems, particularly in orange soil. The copy number ratio of archaeal amoA to crenarchaeota-specific 16S rRNA genes varied from 0.01% - 0.64% in all five natural vegetation soils while up to 5.32% in orange soil. The results indicated that not all archaea possessed ammonia-oxidizing functional gene of amoA and fertilization may facilitate AOA growth in soils cultivated with orange as well.