Permafrost and drought regulate vulnerability of Tibetan Plateau grasslands to warming

Abstract

The Tibetan Plateau has the largest expanse of high‐elevation permafrost in the world, and it is experiencing climate warming that may jeopardize the functioning of its alpine ecosystems. Many studies have focused on the effects of climate warming on vegetation production and diversity on the Plateau, but their disparate results have hindered a comprehensive, regional understanding. From a synthesis of twelve warming experiments across the Plateau, we found that warming increased aboveground net primary production (ANPP) and vegetation height at sites with permafrost, but ANPP decreased with warming at non‐permafrost sites. Aboveground net primary production responded more negatively to warming under drier conditions, due to both annual drought conditions and warming‐induced soil moisture loss. Decreases in species diversity with warming were also larger at sites with permafrost. These results support the emerging understanding that water plays a central role in the functioning of cold environments and suggest that as ecosystems cross a threshold from permafrost to non‐permafrost systems, ANPP will decrease across a greater proportion of the Tibetan Plateau. This study also highlights the future convergence of challenges from permafrost degradation and grassland desertification, requiring new collaborations among these currently distinct research and stakeholder groups.

Warming and land use change concurrently erode ecosystem services in Tibet

“…In addition to increasing air and soil temperatures, the warming treatment caused significant soil drying. The subsequent reduction in vegetation cover with warming and soil moisture loss is consistent with findings from other nonpermafrost sites in Tibet (Yang et al, 2018), as well as with correlations observed among increases in temperature, decreases in precipitation, and decreases in vegetation cover across central and western Tibet (Lehnert et al, 2016). The dual roles of temperature and water availability in controlling ecosystem structure are further supported by the temporal and spatial heterogeneity in environmental conditions across years of the experiment and across the landscape: intact meadows were predominantly located at cooler, moister sites around the landscape, and all experiment communities more closely resembled intact meadow composition in the coolest and wettest summer.…”

Plant community responses to warming modified by soil moisture in the Tibetan Plateau

“…Future warming in this region is predicted to be greater than the global average (Stocker et al 2013). Climate warming can change the moisture regime in the shallow active layer of permafrost areas, which, when combined with higher temperatures, may primarily affect ecosystem processes and individual plant species performance and plant community structure (Christensen et al 2003;Yang et al 2018).…”

“…On the Tibetan Plateau, a climate warming experiment increased above net primary production (ANPP) in an alpine mesic meadow but decreased ANPP in an alpine steppe with lower soil moisture (Ganjurjav et al 2016). Furthermore, across the whole Tibetan Plateau, the soil moisture regime has been shown to mediate ANPP response to warming (Yang et al 2018). A combined heating and watering experiment conducted in a moist alpine tundra habitat in North America increased ANPP (Winkler, Chapin, and Kueppers 2016).…”

Differential responses of carbon‐degrading enzyme activities to warming: Implications for soil respiration

“…The average global surface temperature is predicted to increase between 1 and 4°C by the end of the twenty‐first century (Collins & Knutti, ; O'neill et al., ). Rising temperatures have cascading impacts on ecosystem carbon (C) budgets, and these can cause both positive and negative C cycle–climate feedbacks (Carey et al., ; Chen, Sang, Zhang, & Hu, ; Chen, Zhou et al., ; Karhu et al., ; Paustian et al., ; Peñuelas et al., ; Yang et al., ). Soil respiration (SR) represents the largest C flux from soils to the atmosphere (Bradford et al., ; Tucker, Bell, Pendall, & Ogle, ) and is primarily driven by the microbial decomposition of soil organic matter (SOM).…”