Plant community change mediated heterotrophic respiration increase explains soil organic carbon loss before moderate degradation of alpine meadow

Abstract

Alpine meadows on the Qinghai‐Tibet Plateau (QTP) store a huge amount of plant and soil carbon (C). The degradation of the alpine meadow has led to a significant loss of soil organic C (SOC), which endangers its weak C sink. The change in heterotrophic respiration was hypothesized as one of the primary biological processes for the SOC loss alongside the degradation of alpine meadow. However, little is known about how land degradation impacts Rh due to changes in plant communities and consequent labile organic C inputs. Rh, vegetation productivity, plant community composition, plant lignin concentration, leaf C/N, SOC, and soil labile C (SLC) were measured for alpine meadow grasslands with five degradation levels in 2 years. Our results showed that the SOC of the surface layer (0–10 cm) gradually decreased with land degradation. The plant lignin concentration and C/N ratio gradually increased with land degradation due to the proportion of sedges decreased while that of forbs increased, which consequently led to the soil C quality (SLC) increased before the moderate degradation level (MD) while significantly reduced in severe and very severe degradation levels (SD and VSD). The structural equation modeling result (SEM) revealed that the degradation‐induced change in soil C quality (SLC) due to an alteration in plant community composition relates to the Rh change with grassland degradation, and the Rh (C output) and aboveground biomass (AGB: C input) further mediated the loss of SOC alongside alpine meadow degradation. On average, Rh increased by 49% and 59% from the Intact to slight degradation level (SLD) and MD and reduced by 56% and 69% from MD to SD and VSD. The temperature sensitivity of Rh (Q10) was higher in the SLD (Q10 = 2.84) and MD (Q10 = 2.62) comparing with the Intact (Q10 = 2.58) respectively, but it was lower in SD (Q10 = 2.19) and VSD (Q10 = 1.65). AGB and belowground net primary productivity (BNPP) had no significant change until the MD, while reduced by 60%–90% in SD and VSD. Our results suggest that Rh and its Q10 change moderated by soil C quality alteration due to the plant community shifting could be one mechanism for the soil C loss before MD, but could not be the main pathway for the SOC loss at SD and VSD.

Degradation‐induced microbiome alterations may aggravate soil nutrient loss in subalpine meadows

“…On the one hand, soil microorganisms (e.g., diazotrophs, phosphate‐solubilizing bacteria, arbuscular mycorrhizal fungi, etc.) may aid in the restoration of degraded grasslands by improving plant resistance to environmental stresses (Ezawa & Saito, 2018; Lai et al, 2021; Pii et al, 2015; Singh, 2015). On the other hand, soil microbes such as nitrifying/denitrifying bacteria and plant pathogens may enhance grassland degradation by intensifying soil nutrient loss or plant diseases (Che et al, 2017; Lennon & Houlton, 2017).…”

Diversity characteristics and driving factors of soil protist communities in subalpine meadow at different degradation stages

“…作用 (Coban et al, 2022;Liu et al, 2023)。研究证实草 地退化可以通过改变土壤养分和植物特征来驱动 土壤微生物多样性和功能的变化 (Luo et al, 2020)。 与未退化草地相比, 退化草地土壤细菌和真菌群落 多样性、组成、生物网络和功能基因存在显著差异 (Li et al, 2016;Luo et al, 2020。土壤微生物群 落在草地退化过程中可能具有双重作用 (Xun et al, 2018;Coban et al, 2022)。一方面, 土壤微生物(如固 氮菌、溶磷菌、丛枝菌根真菌等)可通过提高植物对 环境胁迫的抗性来促进退化草地的恢复 (Ezawa & Saito, 2018;Lai et al, 2021)。另一方面, 土壤传播的 病原体会严重威胁植物的健康, 加剧草地退化 (Che et al, 2019;Zhang Q et al, 2022)…”