Terrestrial N cycling associated with climate and plant‐specific N preferences: a review.

The dramatic increase in anthropogenic reactive nitrogen (Nr) from agricultural activities negatively affects the environment. An additional challenge is to ensure food security while at the same time keeping the environmental impact to a minimum to prevent negative feedback effects on climate. To date, however, few studies have addressed the direct connection between soil N transformations, forms of N, species‐specific N preferences and climate, despite the fact that the fate of N and soil N biochemical cycling are known to be intimately linked. In this paper we review the connections between soil N transformation, species‐specific N preferences and climate, and explore how N‐use efficiency may be enhanced while minimizing the environmental effect. Gross rates of N mineralization and immobilization govern the amount of available N in soil, especially in natural ecosystems, while nitrification plays a central role in regulating the NO₃⁻ to NH₄⁺ ratio. Plant species prefer either NH₄⁺‐N or NO₃⁻‐N, depending on the NO₃⁻‐N to NH₄⁺‐N ratio in their habitat. Thus, plant N uptake could be optimized (i.e. Nr losses reduced) if species‐specific N preferences are maintained by matching N sources applied with prevailing soil‐specific N transformations. Therefore, whether N management practices can optimize N‐use efficiencies hinges on the coupling of soil N transformation with climate and species‐specific N preferences. Highlights: We review the inherent connections between the soil N cycle, plant N preference and climate. Nitrification plays a central role in regulating the NO₃⁻ to NH₄⁺ ratio in soil and soil solution. Soil N transformations regulate the composition of hydrological N export. Plant N uptake can be optimized if soil N cycle is well matched with plant N preference. [ABSTRACT FROM AUTHOR]