Different nitrogen uptake patterns of plant and soil microorganisms in the forest-grassland transition zone on the Loess Plateau.

Introduction: It is unclear whether plants and microorganisms achieve niche complementarity by taking up different inorganic nitrogen (N) forms to alleviate N competition, particularly in N-limited regions.

Methods: This paper conducted a 15-day N tracer study (NHNO or NHNO) to quantitatively calculate the uptake rates of plants and microorganisms in four stands (pure L, pure Carrière, mixed -, and Weber ex Stechm grassland) in the forest-grassland transition zone on the Loess Plateau during the growing season. Among them, and can associated with arbuscular mycorrhizal and ectomycorrhizal, respectively.

Results: The results indicated that in the pure stand and preferred to take up NO , whereas in the pure stand preferred NH . Compared to pure stands, mixed afforestation decreased the NH and NO uptake rate of by 87% and 70%, respectively, but did not alter the N preference of plants. Plants and microorganisms differed in their N preferences in the pure stand, whereas this was not the case in the mixed stand. The proportional similarity index between and (0.90 ± 0.01) was higher than that between plants and microorganisms in forest stands, except for and microorganisms in the mixed stand (0.90 ± 0.02).

Discussion: Those results indicated that niche complementarity by preferring different N forms can alleviate N competition. This study helped to gain a deeper understanding of the plasticity of N uptake patterns by plants and microorganisms in the forest-grassland transition zone, and provides theoretical support for vegetation restoration during the implementation of the Grain for Green program on the Loess Plateau.