Abstract
Plant–mycorrhizal interactions mediate plant nitrogen (N) limitation and can inform model projections of the duration and strength of the effect of increasing CO2 on plant growth. We present dendrochronological evidence of a positive, but context-dependent fertilization response of Quercus rubra L. to increasing ambient CO2 (iCO2) along a natural soil nutrient gradient in a mature temperate forest. We investigated this heterogeneous response by linking metagenomic measurements of ectomycorrhizal (ECM) fungal N-foraging traits and dendrochronological models of plant uptake of inorganic N and N bound in soil organic matter (N-SOM). N-SOM putatively enhanced tree growth under conditions of low inorganic N availability, soil conditions where ECM fungal communities possessed greater genomic potential to decay SOM and obtain N-SOM. These trees were fertilized by 38 years of iCO2. In contrast, trees occupying inorganic N rich soils hosted ECM fungal communities with reduced SOM decay capacity and exhibited neutral growth responses to iCO2. This study elucidates how the distribution of N-foraging traits among ECM fungal communities govern tree access to N-SOM and subsequent growth responses to iCO2.
Highlights
Plant–mycorrhizal interactions mediate plant nitrogen (N) limitation and can inform model projections of the duration and strength of the effect of increasing CO2 on plant growth
The largest relative responses occurred under conditions of low inorganic N availability, conditions where N bound in soil organic matter (N-soil organic matter (SOM)) is likely to contribute to tree growth; acquisition of N-SOM in these conditions is driven by the activity of specialized ECM fungal communities that are enriched in gene families associated with SOM decay
We present evidence suggesting that plant acquisition of N-SOM is contingent on the community N-foraging traits of ECM fungi and secondly that N-SOM contributes to a positive plant growth response to increasing ambient CO2 (iCO2)
Summary
Plant–mycorrhizal interactions mediate plant nitrogen (N) limitation and can inform model projections of the duration and strength of the effect of increasing CO2 on plant growth. We present dendrochronological evidence of a positive, but context-dependent fertilization response of Quercus rubra L. to increasing ambient CO2 (iCO2) along a natural soil nutrient gradient in a mature temperate forest We investigated this heterogeneous response by linking metagenomic measurements of ectomycorrhizal (ECM) fungal N-foraging traits and dendrochronological models of plant uptake of inorganic N and N bound in soil organic matter (N-SOM). The distribution of ECM taxa are subject to complex community assembly processes[43], we reason that trees associating with ECM communities with greater decay potential (i.e. occurring in inorganic N poor soils) exhibit the largest relativized fertilization response to iCO2 because both N-SOM and inorganic N contribute to tree growth (Fig. 1). Trees that primarily obtain inorganic N (i.e. occurring in inorganic N rich soils), exhibit a lower relativized growth response to iCO2 (Fig. 1)
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