Abstract
N and P are essential macronutrients for all organisms. How shifts in the availability of N or P affect fungal communities in temperate forests is not well understood. Here, we conducted a factorial P × N fertilization experiment to disentangle the effects of nutrient availability on soil-residing, root-associated, and ectomycorrhizal fungi in beech (Fagus sylvatica) forests differing in P availability. We tested the hypotheses that in P-poor forests, P fertilization leads to enhanced fungal diversity in soil and roots, resulting in enhanced P nutrition of beech, and that N fertilization aggravates P shortages, shifting the fungal communities toward nitrophilic species. In response to fertilizer treatments (1 × 50 kg ha−1 P and 5 × 30 kg ha−1 N within 2 years), the labile P fractions increased in soil and roots, regardless of plant-available P in soil. Root total P decreased in response to N fertilization and root total P increased in response to P addition at the low P site. Ectomycorrhizal species richness was unaffected by fertilizer treatments, but the relative abundances of ectomycorrhizal fungi increased in response to P or N addition. At the taxon level, fungal assemblages were unaffected by fertilizer treatments, but at the order level, different response patterns for saprotrophic fungi among soil and ectomycorrhizal fungi on roots were found. Boletales increased in response to P, and Russulales decreased under N + P addition. Our results suggest that trait conservatism in related species afforded resistance of the resident mycobiome composition to nutritional imbalances.
Highlights
Nitrogen (N) and phosphorus (P) are essential nutrients that determine plant growth and productivity in many terrestrial ecosystems (Elser et al 2007; Vitousek et al 2010).The main natural sources of N and P are biological N fixation from atmospheric N2 for N and rock weathering for P (Augusto et al 2017; Wardle, 2004)
We studied the richness, diversity, and taxonomic composition of ectomycorrhizal fungi (EMF) living in symbioses with root tips and conducted Illumina sequencing of whole, root-associated fungal (RAF), and soil-associated fungal (SAF) assemblages in beech forest plots fertilized with either P, N, or P + N and untreated plots (Fagus sylvatica L.)
In P-fertilized forest soils with higher availabilities of Plab, the fine root P tot concentrations were only higher in the low-P site (LP) forest, whereas Ptot in fine roots in the high-P site (HP) and medium-P site (MP) forests were unaffected compared with the controls (Fig. 2a–c)
Summary
Nitrogen (N) and phosphorus (P) are essential nutrients that determine plant growth and productivity in many terrestrial ecosystems (Elser et al 2007; Vitousek et al 2010). The main natural sources of N and P are biological N fixation from atmospheric N2 for N and rock weathering for P (Augusto et al 2017; Wardle, 2004). Forests are often naturally N-limited (Vitousek et al 2010). Anthropogenic N deposition can change the nutrient regime and affect the P demand of forest ecosystems (Vitousek et al 2010). N deposition into forest ecosystems has increased primary production in N-limited forest ecosystems (Du and De Vries, 2018; Schulte-Uebbing and De Vries, 2018). Increasing N:P ratios in plant tissues have been suggested to indicate that many European forest ecosystems are transitioning from N to P limitation (Jonard et al 2015; Peñuelas et al 2013)
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