Abstract
Soil respiration represents the second largest carbon flux, next to photosynthesis of the terrestrial biosphere, and thus plays a dual role in regional and global carbon cycles. However, soil respiration in Asian monsoon forests with high rainfall has rarely been studied. In this study, we continuously measured soil respiration using a 12-channel automated chamber system in a 61-year-old Japanese cedar forest in central Taiwan with annual rainfall greater than 2500 mm. A 4-year (2011–2014) continuous half-hourly dataset was used to quantify the influences of soil temperature and moisture, especially rainfall events, on both total soil respiration (Rs) and heterotrophic respiration (Rh). The annual mean Rs was approximately 10.8 t C ha−1 (ranging from 10.7 to 10.9) t C ha−1, with Rh contributing approximately 74.6% (ranging from 71.7% to 80.2%). Large seasonal variations in both Rs and Rh were primarily controlled by soil temperature. Over 45.8% of total annual rainfall amounts were provided by strong rainfall events (over 50 mm), and over 40% of rainfall events occurred during summers between 2012 and 2014. These strong rainfall events caused rainwater to enter soil pores and cover the soil surface, which resulted in limited soil microorganism activity and, consequently, restricted CO2 production. The mean Q10 values were 2.38 (ranging from 1.77 to 2.65) and 2.02 (ranging from 1.71 to 2.34) for Rs and Rh, respectively. The Q10 values in this study, which were lower than in global forest ecosystems, may imply that the interannual Rs values observed in this study that were caused by high rainfall were less temperature-dependent than the Rs levels in global forest ecosystems. Both Rs and Rh were negatively correlated with soil moisture, which indicated that the soil moisture levels in the studied forest were usually under saturated conditions. These results also provide the lack of data for respiration in the Asian monsoon region under high-rainfall conditions.
Highlights
Forest ecosystems significantly impact the global carbon cycle and serve as carbon sinks for the atmosphere [1]
Previous reports have explained the interannual variability in Rs as being due to spring soil temperatures or summer rainfall and soil moisture [15], the inconsistency of the results suggests that the cause of interannual Rs variability may depend on climate
Soil moisture varied between 14.8% and 46.9%, with peaks generally occurring on days with high rainfall
Summary
Forest ecosystems significantly impact the global carbon cycle and serve as carbon sinks for the atmosphere [1]. The amount of biomass stored in forest ecosystems is estimated to be approximately 80% of the global terrestrial biomass [2]. Global forests contain approximately 1146 Pg of carbon, which represents 69% of the total carbon stored in forest soil and litter [3]. Greenhouse gas release rates of forest soil affect global climate change. Soil carbon cycling processes have received much attention from ecological scientists and policy makers because of their possibility of influencing the soil carbon cycle through land use management. Accounting for forest carbon to clarify the response of carbon cycles to control mechanisms and to climate change is necessary to predict carbon magnitudes and identify possible mitigation and adaptation methods. Rs generally has a positive relationship with soil temperature and can be described by a simple exponential function [12,17,18,19,20,21] and by the exponential “Q10 ”
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