Experimental Warming Has Not Affected the Changes in Soil Organic Carbon During the Growing Season in an Alpine Meadow Ecosystem on the Qinghai-Tibet Plateau

Warming affects leaf light use efficiency and functional traits in alpine plants: evidence from a 4-year in-situ field experiment

Introduction

Light use efficiency (LUE) is a crucial determinant of plant productivity, while leaf functional traits directly affect ecosystem functions. However, it remains unclear how climate warming affects LUE and leaf functional traits of dominant species in alpine meadows.

Methods

We conducted a 4-year in-situ field warming experiment to investigate the eco-physiological characteristics for a dominant species (Elymus nutans) and a common species (Potentilla anserina) on the Tibetan Plateau. The leaf traits, photosynthesis and fluorescence characteristics were measured, along with the soil physical-chemical properties associated with the two species.

Results and discussions

Experimental warming increased the leaf LUE, maximum photochemical efficiency, non-photochemical quenching, relative water content and specific leaf area for both species. However, there was a decrease in leaf and soil element content. Different species exhibit varying adaptability to warming. Increasing temperature significantly increased the photosynthetic rate, stomatal conductance, transpiration rate, total water content, and specific leaf volume of E. nutans; however, all these traits exhibited an opposite trend in P. anserina. Warming has a direct negative impact on leaf LUE and an indirectly enhances LUE through its effects on leaf traits. The impact of warming on plant photosynthetic capacity is primarily mediated by soil nutrients and leaf traits. These results indicate that the two different species employ distinct adaptive strategies in response to climate change, which are related to their species-specific variations. Such changes can confer an adaptive advantage for plant to cope with environmental change and potentially lead to alterations to ecosystem structure and functioning.

Seasonal freeze-thaw characteristics of soil carbon pools under different vegetation restoration types on the Longzhong Loess Plateau

Soil carbon pools are important for maintaining the stability of the carbon cycle in terrestrial ecosystems and regulating climate change. However, it is not clear how soil carbon pools change under different vegetation restoration types at high altitudes during frequent seasonal freeze-thaws (FTs). Therefore, we studied the seasonal FT variability (before freezing, early stages of freezing, stable freeze stage, thawing stage) of soil organic carbon (SOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), and easily oxidized organic carbon (EOC) under three vegetation restoration types (Grassland, GL; Caragana korshinskii, CK; Xanthoceras sorbifolia, XS) on the Longzhong Loess Plateau region. We found that during the seasonal FT, the 0–40 cm SOC, MBC, DOC, and EOC contents were higher in XS vegetation than in GL and CK vegetation, but the sensitivity index of SOC was lower in XS vegetation (sensitivity index = 2.79 to 9.91). In the 0–40 cm soil layer, the seasonal FT process reduced the MBC content and increased the DOC content in the three vegetation soils. Meanwhile, DOC and EOC contents accumulated obviously in the stable freezing period and decreased significantly in the thawing period. We also found that the SOC, MBC, DOC, and EOC contents were higher in the surface soils (0–10 cm) than in the underlying soils (10–20 and 20–40 cm), while the sensitivity of the soil carbon pool fractions to seasonal FT processes differed considerably between soil depths. Redundancy analysis (RDA) showed that soil total nitrogen, temperature, total phosphorus, and soil water content were important environmental factors influencing soil carbon pool fractions during seasonal FT. This study suggested that in the Longzhong Loess Plateau region, soil MBC and DOC were more susceptible to seasonal FT phenomena and that the soil system of the Xanthoceras sorbifolia vegetation had a stronger soil C sequestration function during the seasonal FT process.