Alleviation of P limitation makes tree roots competitive for N against microbes in a N-saturated conifer forest: A test through P fertilization and 15N labelling

Blanes, M. Carmen; Emmett, Bridget A. ORCID: https://orcid.org/0000-0002-2713-4389; Viñegla, Benjamín; Carreira, José A.. 2012 Alleviation of P limitation makes tree roots competitive for N against microbes in a N-saturated conifer forest: A test through P fertilization and 15N labelling. Soil Biology and Biochemistry, 48. 51-59. https://doi.org/10.1016/j.soilbio.2012.01.012

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Abstract/Summary

Chronic N deposition to forests may induce N saturation and stand decline, leading to reduced ecosystem N retention capacity, triggered by a shift from N limitation of trees to limitation by another nutrient. We conducted a 15N soil labelling experiment in non-fertilized and P-fertilized plots at two elevations in an N-saturated Mediterranean-fir (Abies pinsapo) forest in southern Spain which shows P limitation symptoms. Root-exclusion was applied to identify the relative contributions of roots (plus mycorrhizal fungi) uptake, and heterotrophic immobilization by free-living microbes, to N retention. Overall 15N recovery from the litter, 0–15-cm soil and root-uptake components was c.a. 35% higher in P-fertilized than in non-fertilized plots at both elevations. In non-fertilized plots, soil was the biggest sink for added 15N. Phosphorus fertilization increased the competitive ability of tree roots for soil N resulting in equal importance of the autotrophic (roots plus associated mycorhizal fungi) and heterotrophic (free-living microbes) components with respect to total 15N recovery in P-fertilized plots. Phosphorus addition increased litter and soil N immobilization only if roots had been excluded. By combining in situ fertilization, root-exclusion and isotope labelling we have demonstrated that reduced N retention capacity and dominance of soil microbial over plant immobilization in a N-saturated forest results from a shift from N to P limitation of trees, while alleviation of P limitation makes tree roots and associated mycorrhizal fungi competitive for N against free soil microorganisms.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1016/j.soilbio.2012.01.012
Programmes:	CEH Topics & Objectives 2009 - 2012 > Biogeochemistry
UKCEH and CEH Sections/Science Areas:	Emmett
ISSN:	0038-0717
Additional Keywords:	N saturation, N uptake, N/P relationships, P limitation and deficiency, P fertilization, plant-microbe competition, plant-soil interactions, vector analysis of foliar nutrients
NORA Subject Terms:	Ecology and Environment Agriculture and Soil Science
Date made live:	17 Jan 2013 15:06 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/20945

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