Carbon cycling in temperate grassland under elevated temperature.

Anne B. Jansen‐Willems,Christoph Müller,Gary J. Lanigan,Ludger Grünhage

doi:10.1002/ece3.2210

Abstract

An increase in mean soil surface temperature has been observed over the last century, and it is predicted to further increase in the future. The effect of increased temperature on ecosystem carbon fluxes in a permanent temperate grassland was studied in a long‐term (6 years) field experiment, using multiple temperature increments induced by IR lamps. Ecosystem respiration (R‐eco) and net ecosystem exchange (NEE) were measured and modeled by a modified Lloyd and Taylor model including a soil moisture component for R‐eco (average R 2 of 0.78) and inclusion of a photosynthetic component based on temperature and radiation for NEE (R 2 = 0.65). Modeled NEE values ranged between 2.3 and 5.3 kg CO 2 m−2 year−1, depending on treatment. An increase of 2 or 3°C led to increased carbon losses, lowering the carbon storage potential by around 4 tonnes of C ha−1 year−1. The majority of significant NEE differences were found during night‐time compared to daytime. This suggests that during daytime the increased respiration could be offset by an increase in photosynthetic uptake. This was also supported by differences in δ 13C and δ 18O, indicating prolonged increased photosynthetic activity associated with the higher temperature treatments. However, this increase in photosynthesis was insufficient to counteract the 24 h increase in respiration, explaining the higher CO 2 emissions due to elevated temperature.

Highlights

Global mean surface temperature has increased by 0.6°C in the past century, and it is expected to increase by 1.5–4.5°C when the atmospheric CO2 concentration doubles (IPCC, 2013)
The effect of increased temperature on ecosystem carbon fluxes in a permanent temperate grassland was studied in a long-term (6 years) field experiment, using multiple temperature increments induced by IR lamps
Ecosystem respiration (R-eco) and net ecosystem exchange (NEE) were measured and modeled by a modified Lloyd and Taylor model including a soil moisture component for R-eco and inclusion of a photosynthetic component based on temperature and radiation for NEE (R2 = 0.65)

Summary

Introduction

Global mean surface temperature has increased by 0.6°C in the past century, and it is expected to increase by 1.5–4.5°C when the atmospheric CO2 concentration doubles (IPCC, 2013). If increased surface temperature results in higher CO2 emissions, a positive feedback loop could occur If an increased surface temperature leads to a net decrease in CO2 emissions, the current increase in atmospheric CO2 could be dampened. Due to the spatial variability and the climatic influence on the direction of change in net CO2 emissions, the need for small-scale studies, on the potential consequences of elevated soil and air temperatures across ecosystems at all latitudes and precipitations levels, has been proposed by several scientists (Rustad et al 2001; Aronson and McNulty 2009)

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