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Title: Shifts in dominant tree mycorrhizal associations in response to anthropogenic impacts
Plant-fungal symbioses play critical roles in vegetation dynamics and nutrient cycling, modulating the impacts of global changes on ecosystem functioning. Here, we used forest inventory data consisting of more than 3 million trees to develop a spatially resolved “mycorrhizal tree map” of the contiguous United States. We show that abundances of the two dominant mycorrhizal tree groups—arbuscular mycorrhizal (AM) and ectomycorrhizal trees—are associated primarily with climate. Further, we show that anthropogenic influences, primarily nitrogen (N) deposition and fire suppression, in concert with climate change, have increased AM tree dominance during the past three decades in the eastern United States. Given that most AM-dominated forests in this region are underlain by soils with high N availability, our results suggest that the increasing abundance of AM trees has the potential to induce nutrient acceleration, with critical consequences for forest productivity, ecosystem carbon and nutrient retention, and feedbacks to climate change.  more » « less
Award ID(s):
1638702
NSF-PAR ID:
10191959
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Science Advances
Volume:
5
Issue:
4
ISSN:
2375-2548
Page Range / eLocation ID:
eaav6358
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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  5. Abstract Aim

    Trees associating with ectomycorrhizal (ECM) fungi typically occur in infertile soils and use nutrients more conservatively than arbuscular mycorrhizal (AM) trees. We hypothesized that ECM trees would have greater nutrient resorption (i.e., proportion of nutrients resorbed during leaf senescence) than AM trees.

    Location

    Global.

    Methods

    We synthesized nitrogen (N) and phosphorus (P) resorption data from 378 species from sub/tropical, temperate and boreal forests, including 43 studies where ECM and AM trees co‐occurred, and conducted a meta‐analysis. Additionally, we quantified N resorption in 45 plots varying in ECM‐AM tree abundances in the temperate deciduous forests of southern Indiana, USA.

    Results

    Overall, resorption patterns were driven primarily by mycorrhizal type, climate zone, and to a lesser degree, leaf habit. In the boreal forest, P resorption was 76% greater for ECM than AM trees (p < .05). In the sub/tropics, AM trees resorbed 30% more N than ECM trees. At the sites where AM and ECM trees co‐occurred, ECM trees resorbed more N in temperate forests (15% greater;p < .001) whereas AM trees tended to resorb more N in sub/tropical forests (by 29%;p = .08). Besides, deciduous ECM trees resorbed more N (10%) and P (15%) than deciduous AM trees, while evergreen ECM and AM trees did not differ. In the deciduous forests of Indiana, where ECM and AM trees co‐occurred, the relative abundance of ECM trees in a plot was positively correlated to plot‐scale N resorption (R2 = .25,p = .001), indicating greater nutrient conservatism with increasing ECM‐dominance.

    Main conclusions

    Our results indicate that mycorrhizal association – in addition to other factors – is correlated with the degree to which trees recycle nutrients, with the strongest effects occurring for N resorption by temperate deciduous trees.

     
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