20 Sep 2022
20 Sep 2022
Status: this preprint is currently under review for the journal BG.

Phosphorus regulates fungal biomass production in a Norway spruce forest

Juan Pablo Almeida1, Lorenzo Menichetti2, Alf Ekblad3, Nicholas Rosenstock4, and Håkan Wallander1 Juan Pablo Almeida et al.
  • 1Lund University, Microbial Ecology, Dept of Biology, SE-223 62 Lund, Sweden
  • 2Sveriges Lantbruksuniversitet (SLU), Department of Ecology, Ulls Väg 17, Uppsala, Sweden
  • 3School of Science and Technology, Örebro University, SE- 701 82, Örebro, Sweden
  • 4Center for Environmental and Climate Research, Lund University, SE-22362 Lund, Sweden

Abstract. Ectomycorrhizal fungi (EMF) are important components of the soil microbial communities and EMF biomass can potentially increase carbon (C) stocks by accumulating in the soils as necromass and producing recalcitrant structures. EMF growth depends on the C allocated belowground by the host trees and the nutrient limitation on tree growth is expected to influence this allocation. Therefore, studying EMF production and understanding the factors that regulates it in natural soils is important to understand C cycling in forests.

Ingrowth meshbags are commonly used to estimate EMF production, but these measurements might not reflect the total EMF production since turnover rates of the hyphae are not considered. Here we estimated fungal production and turnover in response to P fertilization in a Norway spruce forest where nitrogen (N) deposition has resulted in phosphorus (P) limitation of plant production by using a combination of meshbags with different incubation periods and with Bayesian inferences. To test how localized patches of N and P influence EMF production and turnover we amended some bags with a nitrogen source (methylene urea) or P source (apatite). Additionally, the Bayesian model tested the effect of seasonality (time of meshbag harvesting) on fungal production and turnover.

We found that turnover of EMF and was not affected by P fertilization or meshbag amendment. P fertilization had a negative effect on EMF production in all the meshbag amendments suggesting a reduced belowground C allocation to the extramatrical mycelium under high P status. Apatite amendment significantly increased EMF biomass production in comparison with the pure quartz bags in the control plots but not in the P-fertilized plots. This indicates that P-rich patches enhance EMF production in P limited forests, but not when P is not limiting. Urea amendment had a general positive effect on EMF production, but this was significantly reduced by P fertilization, suggesting that a decrease in EMF production under high P status also will affect N foraging. Seasonality had a significant effect on fungal production and the differences registered between the treatments were higher during the warmer months and disappeared at the end of the growing season.

Many studies highlight the importance of N for regulating belowground C allocation to EMF in northern coniferous forests, but here we show that the P status of the forest can be equally important for belowground carbon allocation to EMF production in areas with high N deposition.

Juan Pablo Almeida et al.

Status: open (until 01 Nov 2022)

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Juan Pablo Almeida et al.

Juan Pablo Almeida et al.


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Short summary
In forests, trees allocate belowground a significant amount of carbon to support mycorrhizal symbiosis. In northern forests nitrogen normally regulates this allocation and consequently mycorrhizal fungi growth. In this study we demonstrate that in a conifer forest from Sweden, fungal growth is regulated by phosphorus instead of nitrogen. This is probably due to an increase in nitrogen depositions to soils caused by decades of human pollution that has alter the ecosystem nutrient regime.