Abstract
As heterotrophic respiration (RH) has great potential to increase atmospheric CO2 concentrations, it is important to understand warming effects on RH for a better prediction of carbon–climate feedbacks. However, it remains unclear how RH responds to warming in subtropical forests. Here, we carried out trenching alone and trenching with warming treatments to test the climate warming effect on RH in a subtropical forest in southwestern China. During the measurement period, warming increased annual soil temperature by 2.1 °C, and increased annual mean RH by 22.9%. Warming effect on soil temperature (WET) showed very similar pattern with warming effect on RH (WERH), decreasing yearly. Regression analyses suggest that WERH was controlled by WET and also regulated by the soil water content. These results showed that the decrease of WERH was not caused by acclimation to the warmer temperature, but was instead due to decrease of WET. We therefore suggest that global warming will accelerate soil carbon efflux to the atmosphere, regulated by the change in soil water content in subtropical forests.
Highlights
The subtropical evergreen broad-leaved forest in the Ailao Mountains in Yunnan of southwestern China has been considered a carbon sink[24], but the carbon sink strength is likely to be weakened by warming[25]
The factors T, W, and warming effect on T (WET) had a significant relationship with WERH (p < 0.0001), which meant WERH was affected by T, W, and WET
A 1 °C increase in T and a 1% decrease in W would reduce 0.98 and 0.79% of WERH, respectively; a 1 °C increase in WET would cause a 21.78% increase in WERH (Fig. 4)
Summary
The subtropical evergreen broad-leaved forest in the Ailao Mountains in Yunnan of southwestern China has been considered a carbon sink[24], but the carbon sink strength is likely to be weakened by warming[25]. A recent study showed that the mean annual air temperature increased by 0.36 °C per decade from 1983 to 2010, leading to an increasing trend of 0.31 °C per decade from 1986 to 2010 in the top 10 cm of soil in the subtropical forest[27]. Previous studies have shown that RH exhibited seasonal variation and had a significant positive relationship with soil temperature[28,29]. It remains unclear how soil warming affects RH in this subtropical forest. Based on mentioned studies above, we hypothesized that RH acclimated to continuous warming in this forest. We conducted ‘trenching alone’ and ‘trenching with warming’ treatments in this forest
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