Abstract
Alpine meadow ecosystem is among the highest soil carbon density and the most sensitive ecosystem to climate change. Partitioning autotrophic (Ra) and heterotrophic components (Rm) of ecosystem respiration (Re) is critical to evaluating climate change effects on ecosystem carbon cycling. Here we introduce a satellite-based method, combining MODerate resolution Imaging Spectroradiometer (MODIS) products, eddy covariance (EC) and chamber-based Re components measurements, for estimating carbon dynamics and partitioning of Re from 2009 to 2011 in a typical alpine meadow on the Tibetan Plateau. Six satellite-based gross primary production (GPP) models were employed and compared with GPP_EC, all of which appeared to well explain the temporal GPP_EC trends. However, MODIS versions 6 GPP product (GPP_MOD) and GPP estimation from vegetation photosynthesis model (GPP_VPM) provided the most reliable GPP estimation magnitudes with less than 10% of relative predictive error (RPE) compared to GPP_EC. Thus, they together with MODIS products and GPP_EC were used to estimate Re using the satellite-based method. All satellite-based Re estimations generated an alternative estimation of Re_EC with negligible root mean square errors (RMSEs, g C m−2 day−1) either in the growing season (0.12) or not (0.08). Moreover, chamber-based Re measurements showed that autotrophic contributions to Re (Ra/Re) could be effectively reflected by all these three satellite-based Re partitions. Results showed that the Ra contribution of Re were 27% (10–48%), 43% (22–59%) and 56% (33–76%) from 2009 to 2011, respectively, of which inter-annual variation is mainly attributed to soil water dynamics. This study showed annual temperature sensitivity of Ra (Q10,Ra) with an average of 5.20 was significantly higher than that of Q10,Rm (1.50), and also the inter-annual variation of Q10,Ra (4.14–7.31) was larger than Q10,Rm (1.42–1.60). Therefore, our results suggest that the response of Ra to temperature change is stronger than that of Rm in this alpine meadow.
Highlights
Gross primary production (GPP) is plant-driven carbon captures from atmosphere, and abundant organic carbon stores in the natural ecosystems [1,2], which forms the basis of all biosphere functions [3]
Annual average air temperature ranged from 2.3 ◦ C in 2011 to 3.4 ◦ C in 2009 with a mean value of 2.9 ◦ C, which was warmer than 50 year climate records mean (1.8 ◦ C)
Soil temperature was generally higher than air temperature by 4.0 ◦ C, and the difference was more pronounced during the growing season (Figure 3)
Summary
Gross primary production (GPP) is plant-driven carbon captures from atmosphere, and abundant organic carbon stores in the natural ecosystems [1,2], which forms the basis of all biosphere functions [3]. Response of Ra and Rm to temperature may exhibit different temperature sensitivity (Q10 ) [7], which is the key parameter of the climate–carbon feedback, usually expressed as the percentage of Re increase for a 10 ◦ C rise in temperature [8]. Climate–carbon feedback depends on whether Rm increases to warming are offset by corresponding increases in GPP [9]. This urges us to give a better understanding of the relative contribution of Ra and Rm components [10]. The average estimates generally mask considerable uncertainties arising from different ecosystems, estimating techniques and time scales [5]
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