How climate and soil properties affect the abundances of nitrogen-cycling genes in nitrogen-treated ecosystems: a meta-analysis.

Purpose: The abundance of nitrogen (N)-cycling genes is frequently used to indicate N cycling and predict N₂O emissions. However, it remains difficult to clearly define how soil N-cycling genes in different ecosystems respond to anthropogenic N additions. Methods: We applied a meta-analysis approach to examine data about N-cycling genes (nifH, ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), nirK, nirS, and nosZ) in different ecosystems from 119 peer-reviewed articles. Results: In the ecosystems examined, the patterns of change in the abundances of the target genes, apart from AOA, varied considerably. This variation reflects the distinctive soil characteristics of ecosystems that develop when different forms of N are applied at different rates and over different durations. The nifH abundance decreased significantly, by 32.79%, in forests but did not change in grasslands and croplands. The AOB abundance increased in all three ecosystems, by 193.06% in grasslands, 73.26% in forests, and 151.86% in croplands, respectively. The denitrification gene abundances, namely the nirK, nirS, and nosZ, in croplands also increased significantly, by 60.74%, 47.42%, and 69.54%, respectively. Conclusion: In general, climate factors and long-term applications of organic N at high rates had significant effects on the gene abundances in different ecosystems, through their influence on soil properties. An enhanced understanding of how N additions influence the abundance of other N-cycling functional genes can help us improve our ability to model the populations and activities of microbial functional communities and predict N fluxes. [ABSTRACT FROM AUTHOR]