Passive and active ecological restoration strategies for abandoned farmland leads to shifts in potential soil nitrogen loss by denitrification and soil denitrifying microbes

Abstract Ecological restorations of abandoned farmland have been performed in degraded ecosystems with the goal of increasing ecosystem sustainability. The environmental benefits of ecological restoration can at least be partially neutralized by enhanced nitrogen (N) loss and potential nitrous oxide (N 2 O) emissions via denitrification. However, few studies have focussed on comparative analysis of the contributions of ecological restoration strategies to soil denitrifying microbes, particularly in arid and semiarid degraded ecosystems, where N is often the limiting nutrient. In this study, artificial afforestation (artificial forest sites) and natural revegetation (grassland sites) of abandoned farmland have an enhanced effect on reducing potential denitrification rates (PDR) compared with farmland sites and orchard sites, leading to lower N losses and potential N 2 O emissions. Combined analyses indicated that the greatest differences in microbial abundance, species richness, and diversity were observed among different ecological restoration strategies. The abundance, richness, and diversities of denitrifying microbes ( nirS , nirK , and nosZ genes) were decreased by natural revegetation and artificial afforestation, leading to attenuated denitrifying activity responsible for the reduced PDR. Notably, the abundance and diversity of denitrifying microbes were dominant variables that explained the changes in PDR (up to 0.96). Overall, our results contribute to a better understanding of the feedback of denitrifying microorganisms to ecological restoration strategies and how these microorganisms collaboratively contribute to N loss and potential N 2 O emissions in arid and semiarid degraded ecosystems.