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Elevational variation in plant growing environment drives diversification of photosynthetic capacity, however, the mechanism behind this reaction is poorly understood. We measured leaf gas exchange, chlorophyll fluorescence, anatomical characteristics, and biochemical traits of Salvia przewalskii at elevations ranging from 2400 m to 3400 m above sea level (a.s.l) on the eastern Qinghai-Tibetan Plateau, China. We found that photosynthetic capacity showed an initial increase and then a decrease with rising elevation, and the best state observed at 2800 m a.s.l. Environmental factors indirectly regulated photosynthetic capacity by affecting stomatal conductance (g s ), mesophyll conductance (g m ), maximum velocity of carboxylation (V c max ), and maximum capacity for photosynthetic electron transport (J max ). The average temperature (T) and total precipitation (P) during the growing season had the highest contribution to the variation of photosynthetic capacity of S. przewalskii in subalpine areas, which were 25% and 24%, respectively. Photosynthetic capacity was mainly affected by diffusional limitations (71%-89%), and mesophyll limitation (l m ) played a leading role. The variation of g m was attributed to the effects of environmental factors on the volume fraction of intercellular air space (f ias ), the thickness of cell wall (T cw ), the surface of mesophyll cells and chloroplasts exposed to intercellular airspace (S m , S c ), and plasma membrane intrinsic protein (PIPs, PIP1, PIP2), independent of carbonic anhydrase (CA). Optimization of leaf tissue structure and adaptive physiological responses enabled plants to efficiently cope with variable climate conditions of high-elevation areas, and the while maintaining high levels of carbon assimilation., Competing Interests: Declaration of competing interest The authors assert that we have no financial or other non-financial interests that could influence the reported in this paper., (Copyright © 2024 Elsevier Masson SAS. All rights reserved.)

Elucidating the mechanisms that control the leaf stable carbon isotope values (δ 13 C leaf ) is the prerequisite for the widespread application of δ 13 C leaf . However, the competing effects of physiological and environmental factors on δ 13 C leaf variations of the different plant functional types (PFTs) have not been disentangled, and the corresponding mechanisms remain unclear. Based on large-scale δ 13 C leaf measurements on the eastern Qinghai-Tibetan Plateau, the relative contributions and regulatory pathways of leaf functional traits (LFTs) and climatic factors to δ 13 C leaf variations of the different PFTs were investigated. We found that δ 13 C leaf of the different PFTs was correlated with annual mean precipitation negatively, but not a simple linear relationship with annual mean temperature and varied by PFTs. Leaf nitrogen content per unit area and leaf mass per area (correlated with δ 13 C leaf positively) had more substantial effects on the δ 13 C leaf variations of the different PFTs than other LFTs. The relative contributions of LFTs to the δ 13 C leaf variations were greater than that of climatic factors, and the direct and indirect effects of climatic factors on δ 13 C leaf variations varied by PFTs. Our findings provide new insights into understanding key drivers of δ 13 C leaf variations at the PFT level on a regional scale., Competing Interests: Declaration of competing interest The authors assert that we have no financial or other non-financial interests that could influence the reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Mycorrhizal fungi can form symbiotic associations with tree species, which not only play an important role in plant survival and growth, but also in soil carbon (C) and nitrogen (N) cycling. However, the understanding of differences in soil C and N cycling patterns among forests with different mycorrhizal types is still incomplete. In order to determine the similarities and differences of soil C and N cycling patterns in different mycorrhizal forest types, three primary forests dominated by ectomycorrhizal (EcM), arbuscular mycorrhizal (AM) and ericoid mycorrhizal (ErM) trees respectively were studied on the eastern Qinghai-Tibetan Plateau. Indicators associated with soil C and N cycling, including leaf litter quality, soil C and N contents, soil C and N fluxes, and soil microbial biomass C and N contents were measured in each mycorrhizal type forest. The results showed that leaf litter quality was significantly lower with high C:N ratio and lignin: N ratio in ErM forest than that in AM and EcM forests. Soil CO 2 flux (508.25 ± 65.51 mg m -2 h -1 ) in AM forest was significantly higher than that in EcM forest (387.18 ± 56.19 mg m -2 h -1 ) and ErM forest (177.87 ± 58.40 mg m -2 h -1 ). Furthermore, soil inorganic N content was higher in the AM forest than that in EcM and ErM forests. Soil net N mineralization rate (-0.02 ± 0.03 mg kg -1 d -1 ) was lower in ErM forest than that in EcM and AM forests. We speculated that AM and EcM forests were relatively characterized by rapid soil C cycling comparing to ErM forest. The soil N cycling in EcM and ErM forests were lower, implying they were 'organic' N nutrition patterns, and the pattern in ErM forest was more obvious., Competing Interests: The authors declare there are no competing interests., (©2022 Zhang et al.)