Environmental influences on carbon dioxide fluxes over three grassland ecosystems in China

Abstract

Abstract. This study compared carbon dioxide (CO 2 ) fluxes over three grassland ecosystems in China, including a temperate semiarid steppe in Inner Mongolia (NMG), an alpine shrub-meadow in Qinghai (HB), and an alpine meadowsteppe in Tibet (DX). Measurements were made in 2004 and 2005 using the eddy covariance technique. Objectives were to document the seasonality of the net ecosystem exchange of CO 2 (NEE) and its components, gross ecosystem photosynthesis (GEP), and ecosystem respiration (R eco ), and to examine how environmental factors affect the CO 2 exchange in these grassland ecosystems. The 2005 growing season (from May to September) was warmer than that of 2004 across the three sites, and precipitation in 2005 was less than that in 2004 at NMG and DX. The magnitude of CO 2 fluxes (daily and annual sums) was largest at HB, which also showed the highest temperature sensitivity of R eco among the three sites. A stepwise multiple regression analysis showed that the seasonal variation of GEP, R eco , and NEE of the alpine shrubmeadow was mainly controlled by air temperature, whereas leaf area index can likely explain the seasonal variation in GEP, R eco , and NEE of the temperate steppe. The CO 2 fluxes of the alpine meadow-steppe were jointly affected by soil moisture and air temperature. The alpine shrub-meadow acted as a net carbon sink over the two study years, whereas the temperate steppe and alpine meadow-steppe acted as net carbon sources. Both GEP and R eco were reduced by the summer and spring drought in 2005 at NMG and DX, respectively. The accumulated leaf area index during the growCorrespondence to: G. Yu (yugr@igsnrr.ac.cn) ing season (LAI sum ) played a key role in the interannual and intersite variation of annual GEP and R eco across the study sites and years, whereas soil moisture contributed most significantly to the variation in annual NEE. Because LAI sum was significantly correlated with soil moisture at a depth of 20 cm, we concluded that the available soil moisture other than annual precipitation was the most important factor controlling the variation in the CO 2 budgets of different grassland ecosystems in China.

Construction and progress of Chinese terrestrial ecosystem carbon, nitrogen and water fluxes coordinated observation

“…ChinaFLUX community modified several process-based models and remote sensing models, such as CEVSA (Cao et al, 2005;Gu et al, 2010), In-TEC , EALCO (Mi et al, 2007;Mi et al, 2009), and BEPS Ju et al, 2010), and VPM Wu et al, 2008). Meanwhile, many new models have been developed including AVIM2 (Ji et al, 2008;, CEVSA2 Gu et al, 2015), the evapo-transpiration model (Hu et al, 2013;Ren et al, 2005), a MODIS-based Photosynthetic Capacity Model , a remote sensing model for respiration ReRSM , and the statistical model GSM (Zheng et al, 2009;Zhu et al, 2014a). In addition, a Model-Data Fusion System (MDFS) has been developed based on a series of algorithms including the Markov-Chain Monte Carlo method, the Monte Carlo Simulated Annealing method, and the sobol' method Ren et al, 2012) to quantify and minimize the model uncertainty.…”

“…Temperate steppes and alpine meadows served as weak carbon sink (24±83, 45±59 g C m -2 yr -1 ). The grasslands in northern China probably served as a weak carbon source after disturbances, which differed substantially among ecosystems and years (Shi et al, 2006;Li et al, 2006;Fu et al, 2006Fu et al, , 2009Yu et al, 2013b).…”

“…At the same time, a series of important ecological phenomena and their controling mechanism were illustrated. For example, the 'light depress' at ecosystem scale in temperate and alpine grasslands (Fu et al, 2006(Fu et al, , 2009, the nonlinear response of ecosystem carbon flux to temperature variation , heterogeneous response of soil respiration to temperature Jia et al, 2013;Song et al, 2013), the spatio-temporal variation of ecosystem light use efficiency (Yuan et al, 2010;Zhang et al, 2006c;Wu et al, 2008), and the 'carbon pool' in mountain area (Yao et al, 2012). Such studies enhance the understanding of the biotic and abiotic controlling mechanism of ecosystem CO 2 flux across different temporal scales, and the response and adaptation of ecosystem flux to global change.…”

Biophysical effects on the interannual variation in carbon dioxide exchange of an alpine meadow on the Tibetan Plateau

“…Figure 10. Relationships between the annual GPP and precipitation (PPT) for this Lijiang site, the Haibei site (Kato et al, 2006;Fu et al, 2009), the Damxung site (Fu et al, 2009) and the semi-arid grassland sites (Fu et al, 2009;Du and Liu, 2013;Yang and Zhou, 2013).…”

“…Several studies of CO 2 exchange have been carried out on the Qinghai-Tibetan plateau, where the mean annual air temperature (T a ) is approximately 0 • C (Gu et al, 2003;Kato et al, 2006;Shi et al, 2006;Zhao et al, 2006). The daily CO 2 fluxes of the alpine meadow steppe in Damxung, Tibet were shown to be jointly affected by T a and soil moisture (Fu et al, 2009), while the daily CO 2 fluxes of an alpine shrubland at Haibei, Qinghai were found to be sensitive to T a . On an annual scale, the measurements at the Haibei alpine meadow revealed that the annual CO 2 uptake was increased by the earlier onset of the growing season, which was caused by higher T a (Kato et al, 2006).…”