Nitrogen ion form and spatio-temporal variation in root distribution mediate nitrogen effects on lifespan of ectomycorrhizal roots
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Background and Aims
Absorptive roots active in soil resource uptake are often intimately associated with mycorrhizal fungi, yet it remains unclear how nitrogen (N) loading affects lifespan of absorptive roots associating with ectomycorrhizal (ECM) fungi.
Through a three-year minirhizotron experiment, we investigated the responses of ECM lifespan to different rates of N addition and examined the roles of N ion form, rooting depth, seasonal root cohort, and ECM morphotype in mediating the N effects on ECM lifespan in a slash pine (Pinus elliottii) forest in subtropical China.
High rates of NH4Cl significantly decreased foliar P concentrations and increased foliar N:P ratios, and mean ECM lifespan was negatively correlated to foliar P concentration. N additions generally increased the lifespan of most ectomycorrhizas, but the specific differences were context dependent. N rates and forms exerted significant positive effects on ECM lifespan with stronger effects occurring at high N rates and under ammonium N addition. N additions extended lifespan of ectomycorrhizas in shallower soil and born in spring and autumn, but shortened lifespan of ectomycorrhizas in deeper soil and born in summer and winter. N additions reduced lifespan of dichotomous ectomycorrhizas, but increased lifespan of coralloid ectomycorrhizas.
The increased ECM lifespan in response to N additions may primarily be driven by the persistent and aggravated P limitation to plants. Our findings highlight the importance of environmental contexts in controlling ECM lifespan and the need to consider potential differences among mycorrhizal morphotypes when studying N—lifespan relationships of absorptive roots in the context of N deposition.
KeywordsAbsorptive roots Ectomycorrhizas Median lifespan Morphotype Nitrogen deposition
This research is financially supported by the grants from the National Natural Science Foundation of China (No. 31130009), the National Key Research and Development Plan (No. 2016YFD06000202), and the Key Frontier Science Program of Chinese Academy of Sciences (QYJ-DQ098). The authors acknowledge the contributions of the anonymous reviewers.
Compliance with ethical standards
Conflict of interest
The authors declare no conflict of interest.
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