Comparative Microbial Nitrogen Functional Gene Abundances in the Topsoil vs. Subsoil of Three Grassland Habitats in Northern China.

The microbial groups of nitrogen fixers, ammonia oxidizers, and denitrifiers play vital roles in driving the nitrogen cycle in grassland ecosystems. However, the understanding of the abundance and distribution of these functional microorganisms as well as their driving factors were limited mainly to topsoil. In this study, the abundances of nitrogen functional genes (NFGs) involved in nitrogen fixation (), ammonia oxidation (), and denitrification (, , and ) were investigated in both topsoil (0-10 cm, soil layer with concentrated root) and subsoil (30-40 cm, soil layer with spare root) of three grassland habitats in northern China.

Importance of matching soil N transformations, crop N form preference, and climate to enhance crop yield and reducing N loss.

The preferential uptake of nitrogen (N) by plant species is generally considered to be tightly associated with soil N transformation characteristics and climatic conditions. In the present study, the yield, N recovery, and N balance of wheat (an NO-preferring crop) and rice (an NH-preferring crop) planted in two sites with significantly different soil N transformations and precipitation were compared to test the connections among soil N transformations, species-specific N preferences, crop yield, N use efficiency (NUE), N loss, and climate. Nitrogen recoveries of N applied as either an NH or NO based fertilizer in crops and soil were determined, and N losses were calculated using the N balance.