Land use pattern effects after 30 years of shifting cropland to fallow land on soil ammonia-oxidizer community

Abstract

Sympatric differentiation of ammonia-oxidizing archaea and bacteria may occur due to differences in ammonia availability during agricultural activities such as fertilization, which shift key biological drivers of soil nitrification processes. Restoring native habitat from intensive agricultural activities (e.g. converting cropland into fallow land) reduces fertilizer inputs, which has the potential to change active ammonia-oxidizers and thus nitrification rates. We incubated soils from fields under 30 years fallow and under continuous cropping to understand shifts in ammonia-oxidizers and nitrification processes. Thirty years of land fallow practices sharply decreased the abundance and activity of soil ammonia-oxidizing bacteria compared to continuous cropping. Nitrification in cropland was driven mainly by ammonia-oxidizing bacteria while ammonia-oxidizing archaea were the main drivers of nitrification in fallow soil. Conversion of cropland into fallow land shifted the dominant active ammonia-oxidizers from ammonia-oxidizing bacteria to archaea, and the low nitrification rates in fallow soil were caused by the lack of active ammonia-oxidizing bacteria rather than N substrate availability.