Abstract
Savanna ecosystems play a crucial role in the global carbon cycle. However, there is a gap in our understanding of carbon fluxes in the savanna ecosystems of Southeast Asia. In this study, the eddy covariance technique (EC) and the biometric-based method (BM) were used to determine carbon exchange in a savanna ecosystem in Southwest China. The BM-based net ecosystem production (NEP) was 0.96 tC ha−1 yr−1. The EC-based estimates of the average annual gross primary productivity (GPP), ecosystem respiration (Reco), and net ecosystem carbon exchange (NEE) were 6.84, 5.54, and −1.30 tC ha−1 yr−1, respectively, from May 2013 to December 2015, indicating that this savanna ecosystem acted as an appreciable carbon sink. The ecosystem was more efficient during the wet season than the dry season, so that it represented a small carbon sink of 0.16 tC ha−1 yr−1 in the dry season and a considerable carbon sink of 1.14 tC ha−1 yr−1 in the wet season. However, it is noteworthy that the carbon sink capacity may decline in the future under rising temperatures and decreasing rainfall. Consequently, further studies should assess how environmental factors and climate change will influence carbon-water fluxes.
Highlights
Studies, most savanna ecosystems are appreciable carbon sinks[10,12,19,21,22,23]
Understanding the state of carbon sequestration and seasonal fluctuation is beneficial, for understanding the important role of savannas in the global carbon cycles and predicting future carbon exchanges under climate change[5], and for developing policies or management practices to protect similar ecosystems that would likely be more sensitive to climate change
The wind rose for a whole year (2015) of observations (Fig. 1) shows that the prevailing wind directions at the study site are ESE and SE, and the wind speed mainly lies in the range 2–7 m s−1 (Fig. 1a), while the footprint shows that most (90%) of the carbon fluxes measured by the eddy covariance (EC) system are in an area within 500 m of the flux tower (Fig. 1b)
Summary
Studies, most savanna ecosystems are appreciable carbon sinks[10,12,19,21,22,23]. Some are carbon neutral or marginal carbon sources[9,13,24] and show considerable seasonal fluctuations[8,9,10,13,25,26,27,28] due to variations and uncertainties in rainfall, water availability, solar radiation, temperature, terrain, nutrients, fire, and human activity[4,11,29,30,31,32], while others are carbon sources[13,33,34]. We had no idea of the net ecosystem carbon exchange (NEE) of this typical savanna ecosystem and its variations, whether diurnal or seasonal. Understanding the state of carbon sequestration and seasonal fluctuation is beneficial, for understanding the important role of savannas in the global carbon cycles and predicting future carbon exchanges under climate change[5], and for developing policies or management practices to protect similar ecosystems that would likely be more sensitive to climate change. The main objectives of this study are: 1) to quantify the gross primary productivity (GPP), ecosystem respiration (Reco), and NEE to determine whether this region is a carbon sink or source; 2) to understand the diurnal and seasonal variation in carbon fluxes; and 3) to explore carbon uptake responses to climate change
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