Biotic effects dominate the inter-annual variability in ecosystem carbon exchange in a Tibetan alpine meadow

Abstract

Aims The alpine meadow ecosystem in Tibet is fragile and sensitive, and its carbon sink function with respect to climate change has become a matter of widespread concern. Therefore, this study aims to clarify the inter-annual variations (IAVs) in the carbon fluxes in an alpine meadow and further quantify the contributions of the driving factors to the IAVs. Methods Based on seven years of flux data (2012–2018) and the corresponding climatic and biotic data, a set of look-up tables (LUTs) was used to separate and quantify the IAV sources. Furthermore, linear perturbation analyses were employed to quantify the contributions of each key factor. Important Findings During 2012–2018, the net ecosystem productivity (NEP), gross primary productivity (GPP) and ecosystem respiration (Re) of this alpine meadow were 3.31±26.90, 210.18±48.35 and 206.88±28.45 g C m –2 y –1, respectively, which indicate relatively large IAVs. When the contributions of climatic and biotic effects were distinguished and quantified, the dominant effects of biotic factors emerged. Additionally, negative interactions between climatic and biotic effects were detected. Among the climatic factors, only soil water content (SWC) contributed relatively more to the IAVs and played a role in regulating the interactions between climatic and biotic effects. These results suggest that biotic effects must be carefully considered to reduce the uncertainties associated with future carbon flux estimates.

Grazing decreases net ecosystem carbon exchange by decreasing shrub and semi-shrub biomass in a desert steppe

“…Although our finding of the positive correlation between productivity and NEE is consistent with many previous studies (Danielewska et al 2015;Xu et al 2022), we also found a positive correlation between aboveground biomass and NEE, primarily driven by shrubs and semi-shrubs and perennial forbs, which is consistent with previous work (Zhang et al 2023). Our finding that shrubs and semi-shrubs and perennial forbs were strongly influenced by grazing, while grasses were less so is consistent with the idea that shrubs and semi-shrubs and perennial forbs are more palatable and have higher nutritional value than grasses, mainly stipa breviflora , which are not preferred by livestock.…”

Soil Moisture Rather Than Atmospheric Dryness Dominates CO2 Uptake in an Alpine Steppe

“…There is a great variability in the NEP across alpine grassland ecosystems due to differences in the types of vegetation (Li et al., 2021). The magnitude of the NEP values of alpine steppes is generally similar to those of alpine shrubs (67–74.4 g C m −2 yr −1 ) (Li et al., 2016; Zhao et al., 2006), but lower than those of alpine wetlands (−120 to 187 g C m −2 yr −1 ) (Kang et al., 2014; Niu et al., 2017; Qi et al., 2021; Zhu et al., 2020) and alpine meadows (3.31–230 g C m −2 yr −1 ) (Kato et al., 2006; Sun et al., 2019; Wang, Jiquan, et al., 2018; Xu et al., 2022). Overall, seasonally or permanently inundated alpine wetlands have higher NEP values, followed by alpine meadows in the eastern–central TP, whereas the NEP is lowest on alpine steppes in the central–western TP.…”

“…Specifically, temperature is widely considered to be an important driver of the net CO 2 exchange in alpine wetlands (Kang et al., 2014; Niu et al., 2017; Qi et al., 2021; Zhu et al., 2020). Environmental controls on the net CO 2 uptake in alpine meadows include R n (Zhang et al., 2015), temperature (Kato et al., 2006; Saito et al., 2009; Sun et al., 2019) and the availability of water (Chen et al., 2019; Xu et al., 2022; Zhang, Zhang, et al., 2018). A recent study showed that the NEP of alpine ecosystems on the TP increased with increasing soil moisture content (Wang et al., 2021).…”

Grazing decreases net ecosystem carbon exchange by decreasing shrub and semi‐shrub biomass in a desert steppe

“…Our finding that NEE, ER, and GEP significantly decreased under heavy grazing intensity is consistent with previous results from desert steppe (Jin et al, 2023;Wang et al, 2023), in our case, due to a reduction in the aboveground biomass of plants (Figure 6, Figure S4), grazing livestock reduces the aboveground biomass through foraging, which reduces the effective photosynthetic area. Previous studies have also indicated that grazing reduced CO 2 exchange by reducing aboveground biomass (Danielewska et al, 2015;Ondier et al, 2021;Xu et al, 2022). Some studies have suggested that grazing appears to have little influence on the carbon budget of grassland ecosystems (Dai et al, 2014;Fang et al, 2010), although the NEE rate can be enhanced in the shortterm grazing due to the compensatory growth of plants, resulting in a negligible impact on the carbon balance.…”