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Contrasting effects of indigenous arbuscular mycorrhizal fungi on nitrogen absorption of C3 and C4 grasses: Evidence from microcosm and 15N labeling experiments

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Oct 25, 2023 version files 150.67 KB

Abstract

Background and aims

Nitrogen (N) captured by arbuscular mycorrhizal (AM) symbiosis is a major pathway in the N uptake of host plants.  However, the relative contribution of arbuscular mycorrhizal fungi (AMF) to N uptake in different plant functional types has not been well assessed.

Methods

Two dominant plant species in semiarid steppe ecosystems on the Mongolian plateau, i.e. Leymus chinensis (C3 grass) and Cleistogenes squarrosa (C4 grass), were selected in this study.  We conducted a greenhouse manipulation experiment using novel microcosms combined with 15N labeling techniques and investigated the effect of indigenous AMF on plant growth and quantified their relative contribution to N uptake under high and low levels of available soil N. 

Results

Indigenous AMF contribute more to N uptake in C3 grass than that in C4 grass, and mycorrhizal partners act as parasites for C4 plant growth.  For L. chinensis, indigenous AM symbiosis suppressed plant growth under low soil N but improved plant growth under high soil N conditions.  AMF contributed to c. 23% and 20% of the total plant N uptake under low and high soil N conditions, respectively.  For C. squarrosa, indigenous AM symbiosis consistently inhibited plant growth under both low and high soil N conditions, and the percent contributions of AMF to N uptake were only c. 9% and 7%, respectively.

Conclusions

Our results demonstrate that indigenous AM symbiosis plays a vital role in N uptake by host plants, even in the absence of a positive growth response.  AMF can modify the fitness of C3 and C4 grasses and thereby alter plant community composition and ecosystem N cycling, particularly under high N conditions.  Our study has important implications for improving global N cycling models in the face of increasing global N deposition.