Nutrient availability as the key regulator of global forest carbon balance

Abstract

Forests strongly aect climate through the exchange of large amounts of atmospheric CO2 (ref. 1). The main drivers of spatial variability in net ecosystem production (NEP) on a global scale are, however, poorly known. As increasing nutrient availability increases the production of biomass per unit of photosynthesis2 and reduces heterotrophic3 respiration in forests, we expected nutrients to determine carbon sequestration in forests. Our synthesis study of 92 forests in dierent climate zones revealed that nutrient availability indeed plays a crucial role in determining NEP and ecosystem carbon-use eciency (CUEe; that is, the ratio of NEP to gross primary production (GPP)). Forests with high GPP exhibited high NEP only in nutrient-rich forests (CUEe D 33 4%; mean s.e.m.). In nutrient-poor forests, a much larger proportion of GPP was released through ecosystem respiration, resulting in lower CUEe (6 4%). Our finding that nutrient availability exerts a stronger control on NEP than on carbon input (GPP) conflicts with assumptions of nearly all global coupled carbon cycle–climate models, which assume that carbon inputs through photosynthesis drive biomass production and carbon sequestration. An improved global understanding of nutrient availability would therefore greatly improve carbon cycle modelling and should become a critical focus for future research

Stand age and species richness dampen interannual variation of ecosystem-level photosynthetic capacity

“…Part of the dataset (36 sites) was complemented with soil nutrient availability classes derived from literature 17 . For each site, nutrient availability was computed using site-level specific information about the following variables: carbon, nitrogen and phosphorus concentrations of soil and/or leaves, soil type, soil texture, soil C/N ratio, and soil pH.…”

“…The sites were eventually classified in three classes: low, medium and high nutrient availability. Afterwards the classification was approved by the site principal investigators 17 .…”

“…In this study we brought together a wide range of data: ecosystem---atmosphere CO 2 fluxes measured at eddy covariance flux sites, information about climate (temperature, precipitation, and water availability index (WAI)), species richness, stand age, and plant traits, derived from field campaigns, and information about forest structure derived from satellite data for each of the selected sites; finally, data about nutrient availability was derived from the literature 17 . Sites were selected according to the availability of eddy covariance flux measurements for at least 4 years, information about stand age, canopy cover, canopy height, and species abundance.…”

“…In this study, we used measurements of ecosystem-level fluxes, and climate variables (temperature, precipitation, and water availability), species richness, stand age, forest structure (canopy cover, height, and LAI), and soil properties (nutrient availability 17 ) derived from satellite data, in situ observations and the literature (see the Methods).…”

Microbial community structure mediates response of soil C decomposition to litter addition and warming

“…Maintaining or increasing global soil C stocks is desirable for soil function and agricultural productivity, but also as a climate change mitigation strategy (Lal, 2004). Despite intensive research on these topics, there is no consensus as to how climate change, largely through the effects of warming temperatures, nitrogen availability, and plant productivity, will impact soil and litter decomposition and ecosystem carbon stocks (Curtis and Wang, 1998;Neff et al, 2002;Mack et al, 2004;Pregitzer et al, 2008;Fernandez-Martínez et al, 2014).…”