Long-term increases in soil carbon due to ecosystem fertilization by atmospheric nitrogen deposition demonstrated by regional-scale modelling and observations

E Tipping,A Lilly,M A Sutton,G J D Kirk,A J Dore,J A C Davies,P A Henrys,S J Tomlinson,U Dragosits,E J Carnell

doi:10.1038/s41598-017-02002-w

Abstract

Fertilization of nitrogen (N)-limited ecosystems by anthropogenic atmospheric nitrogen deposition (Ndep) may promote CO2 removal from the atmosphere, thereby buffering human effects on global radiative forcing. We used the biogeochemical ecosystem model N14CP, which considers interactions among C (carbon), N and P (phosphorus), driven by a new reconstruction of historical Ndep, to assess the responses of soil organic carbon (SOC) stocks in British semi-natural landscapes to anthropogenic change. We calculate that increased net primary production due to Ndep has enhanced detrital inputs of C to soils, causing an average increase of 1.2 kgCm−2 (c. 10%) in soil SOC over the period 1750–2010. The simulation results are consistent with observed changes in topsoil SOC concentration in the late 20th Century, derived from sample-resample measurements at nearly 2000 field sites. More than half (57%) of the additional topsoil SOC is predicted to have a short turnover time (c. 20 years), and will therefore be sensitive to future changes in Ndep. The results are the first to validate model predictions of Ndep effects against observations of SOC at a regional field scale. They demonstrate the importance of long-term macronutrient interactions and the transitory nature of soil responses in the terrestrial C cycle.

Highlights

Soil organic matter (SOM) is a key ecosystem component, both as a store of carbon that can exchange with the atmosphere thereby affecting climate[1], and because of its key soil functional roles in water and heat retention, nutrient cycling, and sorption of contaminants[2]
From an analysis of model performance, it can be shown that uncertainty in these soil organic carbon (SOC) increases arises primarily from uncertainty in nitrogen deposition (Ndep), and it is reasonable to assume an error of c. 30% in the estimated values
The average calculated ratio of SOC gained to Ndep for all the soils considered over the entire period was 8.2 gCgN−1, at the lower end of the range suggested by de Vries et al.[10]

Summary

Introduction

Soil organic matter (SOM) is a key ecosystem component, both as a store of carbon that can exchange with the atmosphere thereby affecting climate[1], and because of its key soil functional roles in water and heat retention, nutrient cycling, and sorption of contaminants[2]. To explore possible long-term and widespread SOC response to Ndep in both forest and non-forest ecosystems, we conducted a combined modelling and data analysis of the soils of British semi-natural ecosystems comprising broadleaf woodland, unimproved grasslands, and shrublands, which account for a total area of 6.8 × 104 km[2], i.e. 32.5% of Great Britain (Fig. 1). The modelling was done by combining the ecosystem model N14CP13 with a new high-resolution spatio-temporal Ndep dataset covering the period since 1750, produced through atmospheric emission, transport and deposition modelling

Methods

Results

Conclusion