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Global climate warming could affect the methane (CH4) and nitrous oxide (N2O) fluxes between soils and the atmosphere, but how CH4 and N2O fluxes respond to whole‐soil warming is unclear. Here, we for the first time investigated the effects of whole‐soil warming on CH4 and N2O fluxes in an alpine grassland ecosystem on the Tibetan Plateau, and also studied the effects of experimental warming on CH4 and N2O fluxes across terrestrial ecosystems through a global‐scale meta‐analysis. The whole‐soil warming (0–100 cm, +4°C) significantly elevated soil N2O emission by 101%, but had a minor effect on soil CH4 uptake. However, the meta‐analysis revealed that experimental warming did not significantly alter CH4 and N2O fluxes, and it may be that most field warming experiments could only heat the surface soils. Moreover, the warming‐induced higher plant litter and available N in soils may be the main reason for the higher N2O emission under whole‐soil warming in the alpine grassland. We need to pay more attention to the long‐term response of greenhouse gases (including CH4 and N2O fluxes) from different soil depths to whole‐soil warming over year‐round, which could help us more accurately assess and predict the ecosystem‐climate feedback under realistic warming scenarios in the future. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) decomposition can potentially feedback to climate change. However, the biotic, abiotic and inherent factors controlling the stability of soil carbon, and changes in these factors with soil depth, remain poorly understood. In this study, we combined a number of complementary methods to quantify the biological, thermal, chemical, molecular and isotopic indices of soil organic matter (SOM) stability along the soil profile (0–70 cm) in two contrasting alpine ecosystems (meadow and shrubland) on the Tibetan Plateau. Firstly, we conducted an aerobic lab–incubation experiment on root–free, sieved soils. The number of days to respire 5% of initial SOC, a biological index of SOM stability, decreased with soil depth. Moreover, the temperature at which half of SOM mass loss (TG–T50), a thermal index of SOM stability, increased with soil depth. Additionally, hot–water extractable organic carbon (HWEOC) per gram SOC, a chemical index of SOM stability, showed weak (meadow) and little (shrubland) declining trend with depth. Further, we used Fourier–transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) spectroscopy to characterize the molecular composition of SOM. The index of recalcitrance of FTIR spectra and the combined index of aliphaticity and aromaticity of NMR spectra both increased with depth, suggesting that the molecular composition of SOM was more complex with increasing depth. Finally, the isotopic values of SOM (13C and 15N) and the 14C–based SOC turnover time both increased with depth, indicating that the isotopic indices of SOM stability also increased with depth. Overall, our results suggest that the thermal, chemical, molecular and isotopic indices of SOM stability were mutually correlated and all showed increasing trend with increasing soil depth in the two alpine ecosystems, although the biological index (as measured by aerobic incubation of root–free sieved soils) showed the opposite results. • We used a number of techniques to characterize SOM stability along the soil profile in two alpine ecosystems on the Tibetan Plateau. • The biological index (as measured by aerobic incubation of root–free sieved soils) of SOM stability decreased with depth. • The chemical, thermal, molecular and isotopic indices of SOM stability all increased with depth. • We should interpret the biological index calculated from C mineralization rate of sieved root–free soils from lab–incubation studies with caution. • Combining biogeochemical, thermal, and spectroscopic evidences are imperative to explore SOM stability mechanisms. [ABSTRACT FROM AUTHOR]

The dynamics of multiple ecosystem functions (that is, multifunctionality) are closely associated with biodiversity, often show positive relationships, but the dynamics of the biodiversity multifunctionality relationship along soil profiles remain unclear. Eutrophication significantly affects biodiversity and soil functions, whereas the mechanisms underlying the impact of nitrogen addition on the biodiversity multifunctionality relationship are poorly understood. Here, we conducted a common garden experiment manipulating plant diversity and nitrogen addition to quantify the effects of biodiversity on soil multifunctionality in the topsoil and subsoil under different nitrogen addition levels. We showed that nitrogen addition had a minor impact on soil multifunctionality but weakened the positive biodiversity multifunctionality relationship. We also found that the positive plant diversity effect on soil multifunctionality decreased with soil depths, resulting in a weaker biodiversity multifunctionality relationship in the subsoil. The weak biodiversity multifunctionality relationship in the subsoil was caused by weakening the relationship between aboveground biomass and soil multifunctionality; nitrogen addition weakened the biodiversity multifunctionality relationship through the attenuation of the association of aboveground biomass and soil microbes with multifunctionality. Our study demonstrates that nitrogen addition undermines the biodiversity soil multifunctionality relationship and the relationship is weakened along the soil profiles, suggesting that Earth system models must represent these heterogeneous soil dynamics to accurately predict future feedbacks to global changes. • N addition weakens biodiversity soil multifunctionality (SMF) relationships (BMR). • Decrease in aboveground biomass (AGB) inputs leads to a weak BMR in the subsoil. • Weak associations of AGB and soil microbes with SMF weaken the BMR under N addition. [ABSTRACT FROM AUTHOR]