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Abstract
Soil respiration (R S) represents a large terrestrial source of CO2 to the atmosphere. Global change drivers such as climate warming and nitrogen deposition are expected to alter the terrestrial carbon cycle with likely consequences for R S and its components, autotrophic (R A) and heterotrophic respiration (R H). Here we investigate the impacts of a 3°C soil warming treatment and a 50 kg ha−1 y−1 nitrogen addition treatment on R S, R H and their respective seasonal temperature responses in an experimental tussock grassland. Average respiration in untreated soils was 0.96±0.09 μmol m−2 s−1 over the course of the experiment. Soil warming and nitrogen addition increased R S by 41% and 12% respectively. These treatment effects were additive under combined warming and nitrogen addition. Warming increased R H by 37% while nitrogen addition had no effect. Warming and nitrogen addition affected the seasonal temperature response of R S by increasing the basal rate of respiration (R 10) by 14% and 20% respectively. There was no significant interaction between treatments for R 10. The treatments had no impact on activation energy (E 0). The seasonal temperature response of R H was not affected by either warming or nitrogen addition. These results suggest that the additional CO2 emissions from New Zealand tussock grassland soils as a result of warming-enhanced R S constitute a potential positive feedback to rising atmospheric CO2 concentration.
Highlights
Soils contain a pool of carbon approximately double that stored in terrestrial biomass [1]
Both RS and RH were sensitive to soil water content, with a reduction in respiration rate observed below 0.2 m3 m23 soil water content
The average (6 SE) soil respiration rate measured in the control plots over the course of this study was 0.9660.09 mmol m22 s21
Summary
Soils contain a pool of carbon approximately double that stored in terrestrial biomass [1]. Soil respiration (RS), the primary pathway for return of soil carbon to the atmosphere, is increasing globally by 0.1 Pg C y21 at present [2]. Several notable examples have shown the effect of warming on RS to be only transient [7,8] Mechanisms for this acclimation of RS to prolonged warming include depletion of labile carbon substrates [8,9,10], changes to the microbial community structure [7,11], physiological acclimation of soil microbes [12], reduction in root biomass [13] and reduction in the specific root respiration rate [14]. Acclimation of soil respiration may limit potential soil carbon loss as a result of climate warming
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