Soil organic carbon (SOC) is an important carbon (C) pool in terrestrial ecosystems. Pant diversity can enhance SOC content in forests, grasslands, and agricultural ecosystems, and its potential effects on the composition and stability of SOC have aroused increasing interest. However, there is no systematic review of their underlying mechanisms. The present study therefore summarizes advances in research on the effects of plant diversity on the content, composition and stability of SOC and the underlying mechanism with the aim of providing a scientific basis for maximizing soil carbon and nitrogen (N) sequestration and mitigating global climate change through the promotion of plant diversity. Increasing plant diversity can increase the inputs of plant litter biomass into soils, enhance the quality of mixed litter (e.g., lower C:N), and promote the turnover and accumulation of SOC. It can also increase plant-derived C via root and litter inputs to soils, or increase microbe-derived C via enhanced microbial turnover. These processes can also increase soil particulate organic carbon (POC) and mineral associated organic carbon (MAOC) contents. In addition, increasing plant diversity can increase the stability of soil organic carbon by enhancing aggregate protection, changing mineral ion concentrations, and changing microbial community structure. Future studies are needed to investigate (1) how soil organic carbon content may be increased through integrated plant diversity and management options; (2) how the effects of plant diversity on soil organic carbon content and composition can be explored through long-term plant diversity field experiments in different ecosystems; (3) how the effects of plant diversity on soil organic carbon composition and stability can be examined using new experimental methods(e.g., isotope labeling); and (4) how the mechanisms underlying plant diversity effects on soil carbon content, composition and stability can be studied at different soil depths.

Soil microorganisms are key drivers of carbon (C) cycling in terrestrial ecosystems not only by facilitating soil organic C decomposition and CO₂ emission, but sequestering atmospheric CO₂ into soil organic C through microbial C fixation. Due to the ubiquitous presence of microorganisms in soils, microbial C fixation is vital for terrestrial ecosystem C cycle globally. In this paper, we explored the mechanisms and determinants of soil microbial C fixation based on data collections and analyses to address the following the three issues: 1) the pathways and processes of autotrophic microbial C fixation in soil; 2) the pathways and processes of heterotrophic microbial C fixation in soil; and 3) the impacts of soil properties, ecosystem types, and climate change (i.e., warming and precipitation change) on microbial C fixation. Overall, the paper provides insights into the dynamics of C fixation in terrestrial ecosystems which is helpful for better understanding the uncertainty of soil C pool in the relationship to microbial C fixation, and which also lays a theoretical foundation for advancing of C cycling models under climate change.

Aims The impact of global warming on soil freeze-thaw cycling in high-altitude area is increasing. However, the contribution of litter-derived carbon to various soil organic carbon fractions and its response to freeze-thaw cycling remains unclear.

Methods The study utilized an indoor simulated freeze-thaw cycling experiment and stable isotope tracing technique, using ¹³C-labeled Picea asperate litter (root, twig, leaf), to explore the contribution of litter-derived carbon to dissolved organic carbon (DOC), microbial biomass carbon (MBC), humus carbon (HC), particulate organic carbon (POC) and mineral associated organic carbon (MAOC) in soil under freeze-thaw cycles.

Important findings The results showed that: after 30 days of incubation, litter-derived carbon significantly contributed to soil POC and MBC, accounting for 13.1% and 9.0%, respectively. The contribution of litter to different soil organic carbon fractions varied among different organs, with roots exhibiting a significantly lower contribution rate to POC, MAOC, and HC compared to twigs and leaves. Under freeze-thaw cycles, litter carbon contributed more to soil DOC and MBC, while showing a lower contribution rate to soil POC, MAOC, and HC. Correlation analysis revealed a significant positive relationship between soil carbon acquisition-related activity enzymes and the contribution of litter-derived carbon to soil organic carbon. These findings indicate that freeze-thaw processes facilitate the accumulation of litter-derived carbon in active organic carbon fractions such as soil DOC and MBC, but inhibit the sequestration of plant-derived carbon in stable soil organic carbon during the initial litter decomposition period in subalpine forests. The research findings contribute to a deeper understanding of the contribution of forest litter return to soil organic carbon fractions, providing a scientific basis for the management and operation of soil carbon pools in subalpine forests under the backdrop of climate change.

Aims Priming effect (PE), as the change in the decomposition rate of soil organic carbon (SOC) caused by exogenous carbon (C) input, plays important roles in regulating the storage and dynamics of global SOC. Leaf litter and fine root are the main sources of SOC in forest ecosystems, which can significantly affect PE. In addition, increased soil nitrogen (N) availability caused by atmospheric N deposition also impacts PE. However, the differences between the PE induced by leaf litter and fine root differ and their response to increased soil N availability remain unclear.

Methods In this study, we conducted a 35-days incubation experiment by adding ¹³C-labelled leaf litter and fine root into Cunninghamia lanceolate soil. Leaf litter was covered on soil surface and fine root was mixed in the soils to simulate their natural field conditions. The amount and carbon isotope composition (δ¹³C) value of soil CO₂ were measured during the experiment, and soil nutrient contents and microbial community composition were also measured after incubation.

Important findings 1) Leaf litter addition promoted the SOC decomposition, that is, leaf litter induced a positive PE, with the magnitude of 1.69 mg C·kg^-1·d^-1, while fine root addition induced a negative PE with the magnitude of -1.26 mg C·kg^-1·d^-1. 2) N addition reduced the magnitude of positive PE induced by leaf litter addition by 38.7%, while it increased the magnitude of negative PE induced by fine root addition by 16.6%. 3) Leaf litter addition reduced fungi bacteria ratio by 22.9%, while adding fine root increased the fungal biomass by 30.8%. Furthermore, N addition increased the fungal bacterial ratio and the fungal biomass. Our results demonstrated the differences in the PE induced by leaf litter and fine root addition, and provided theoretical support for the prediction and management of SOC in forests under the scenario of increasing atmospheric N deposition.

Aims The reduction of snow cover may affect the organic matter turnover process in alpine forests by altering the surface hydrothermal environment and microbial activity, thereby affecting the synthesis and decomposition of soil humus.

Methods Focusing on the Abies fargesiivar. faxoniana fir forest in the subalpine region of western Sichuan, three snow cover treatments were set up in field: control (natural snow cover), snow cover reduction (50% snow cover removal), and snow cover removal (100% snow cover removal). The study investigated the effect of snow cover reduction/removal on soil extractable humic substance, humic acid, fulvic acid contents, and spectroscopic characteristics of humic substances. The study further explored the dynamic correlations between different snow cover treatments and soil humus based on dynamic monitoring of environmental factors and soil physicochemical properties.

Important findings The results showed that: (1) The snow cover reduction/removal treatment significantly reduced contents of soil extractable humic substance, humic acid, and fulvic acid. (2) Soil humification was low in all three snow cover treatments, with soil humic/fulvic acid values less than 1 and humic/extractable humic substance values less than 0.5. (3) Correlation analysis showed that total nitrogen content was negatively correlated with contents of soil extractable humic substance, humic acid, and fulvic acid. In summary, the snow cover reduction/removal treatments reduced soil humus content and affected the degree of soil humification. These results could facilitate an in-depth understanding of the formation of soil humus and the mechanisms of soil fertility maintenance in subalpine forests.

Aims The natural regeneration of Abies fargesiivar. faxoniana is crucial for the ecological restoration of natural secondary forests in the subalpine region of western Sichuan. The study of the key factors in the biomass accumulation and allocation of seedlings is helpful to understand the mechanism of regeneration. Therefore, our objective is to reveal the critical factors for the biomass accumulation of A. fargesiivar. faxoniana seedlings in the Betula albosinensis broadleaf forests (BB), B. albosinensis- A. fargesii var. faxoniana needleleaf-broadleaf forests (BA), and A. fargesii var. faxoniana primary forests (AP).

Methods We compared the biomass allocation patterns of A. fargesiivar. faxoniana seedlings in different forest types and investigated allometric relationships between different organs by a standardized major axis regression analysis. We revealed the relationships between seedlings’ biomass and habitat factors through a redundancy analysis followed by a quantitative decomposition of the contribution of influencing factors.

Important findings The root biomass fraction (30.3%) and stem biomass fraction (43.3%) in the AP forest were significantly higher than that in the BA and BB forests. Correspondingly, leaf biomass fraction (26.4%) in the AP forest was significantly lower than that in the BA and BB forests. Seedlings in the BB forest showed an isometric relationship among three organs: roots, stems, and leaves. In the BA and AP forests, seedlings exhibited an isometric relationship between leaves and roots. In contrast, allometric relationships were observed between leaves and stems and between roots and stems. The annual biomass increment of seedlings was the highest in the western slope habitats compared to those on the northeast, north, and northwest slopes. The contribution rate of the slope aspect (20.9%) to seedling biomass accumulation and allocation surpassed that of altitude (18.1%), with substrate type (15.8%), moss cover density (11.7%) and thickness (7.7%), and canopy coverage (7.4%) ranking the top four among microhabitat factors. This study can assist in the management of Minjiang fir regeneration and the technical optimization of structures of secondary subalpine forests in western Sichuan.

Aims Vegetation map illustrates the vegetation types and their spatial distribution patterns of a given area, which is an important foundation for investigating fundamental ecology such as vegetation feature and biodiversity study, as well as applied ecology such as vegetation restoration and management. The aim of this research is to chart a high-resolution local vegetation map of Beishan Mountain in Jinhua, Zhejiang Province, a middle subtropical evergreen broadleaf forest region in eastern China.

Methods A digital vegetation map with very high spatial resolution at the 1:60 000 scale in a 65.5 km² area in the middle part of the southern slope of Beishan Mountain in Jinhua was produced, based on high-resolution of 1-4 m satellite (GF-2) remote sensing images and intensive field vegetation surveys of 3 774 sites and 24 plots. The Geographical Information System (ArcGIS) and remote sensing image processing software (ENVI) were further utilized to conduct the mapping.

Important findings 1) High-resolution remote sensing images and a large quantity of vegetation records characterized the vegetation pattern on the southern slope of Beishan Mountain in Jinhua. The vegetation was divided into 7 Vegetation Formation Groups, 22 Vegetation Formations, 25 Vegetation Subformations, 60 Alliance Groups, and 76 Alliances. 2) In the 65.5 km²area on the southern slope of Beishan Mountain in Jinhua, the vegetation coverage of mapping area is about 93.0%. Among these vegetation areas, forest (66.1%), agricultural vegetation (14.7%) and shrubland (10.5%) are the main three vegetation types. 3) The three widely distributed alliances are Pinus massoniana forest in an area of 10.6 km² and distributed below 900 m in altitude, Pinus massoniana - deciduous broadleaf mixed forest in an area of 7.4 km² and distributed between 108 and 946 m, and Schima superba forest in an area of 5.3 km² and distributed in 100-1 037 m. This is a case study of vegetation mapping at a big mapping scale. Such study can provide fundamental data for the high-resolution regional and national vegetation mappings at multiple scales, research of vegetation science, and vegetation service and management.

Aims The species-area relationship describes a fundamental pattern in community ecology, illustrating how species richness changes as the sampled area increases. It is a core issue in community ecology research. The island biogeography theory highlights a specific aspect of the species-area relationship known as the small island effect (SIE), which is a key component of the theoretical framework of island biogeography and biodiversity studies. Coastal islands represent a tangible and existing island system, yet there is relatively limited research on the SIE, especially concerning bryophytes.

Methods This study investigated the species composition of bryophytes on 43 coastal islands in the Xiangshan region of Zhejiang. We utilized four segmented regression models and two control models to examine the SIE across different bryophyte taxa. We compared the thresholds at which it occurs. Using generalized linear mixed-effect models and Mantel tests, we explored the impact of environmental factors, such as landscape characteristics and human disturbances, on bryophyte species richness on these maritime islands. Furthermore, we analyzed the response of different bryophyte taxa (liverworts, mosses, acrocarpous mosses, and pleurocarpous mosses) to environmental factors in these island environments.

Important findings Our study documented 209 bryophyte species belonging to 46 families and 85 genera across the 43 coastal islands in the Xiangshan region. All bryophytes taxa exhibited the SIE, with the double-breakpoint model identified as the optimal model. The area thresholds ranged from 0.098 to 4.419 km², with mosses showing higher thresholds than liverworts, and acrocarpous mosses higher than pleurocarpous mosses. Moreover, the richness of bryophytes increased with the island area, habitat richness, shape index, coastline length, population size, and traffic frequency, while it decreased with increasing isolation. Habitat richness was identified as the primary factor influencing bryophytes richness. Generally, taxa with lower resource requirements and higher dispersal abilities (such as mosses) exhibited lower SIE area thresholds. Larger islands with greater distances from the mainland, characterized by lower vegetation cover and habitat richness, were less suitable for the growth of pleurocarpous mosses, resulting in lower SIE area thresholds than acrocarpous mosses. Therefore, the conservation of habitat diversity is crucial for maintaining species diversity.

Aims Differences in herbivory among plant species can greatly affect the functioning of forest ecosystems. However, little is known about the main drivers causing interspecific differences in herbivore damage among tree species. The growth-defence trade-off hypothesis posits that the intrinsic growth rate of plant species governs resource allocation between defense and growth, thereby shaping interspecific variation in herbivory. However, the validity of this hypothesis is extensively debated, especially in highly species-rich subtropical forests.

Methods We quantified leaf herbivore damage in 27 native tree species in a tree species diversity experiment conducted in subtropical China. We measured 12 leaf traits associated with insect palatability and relative growth rates of 27 tree species. Using a combination of phylogenetic multivariate analyses, we assessed trade-offs between leaf traits and the relative effect of these traits on leaf herbivore damage.

Important findings We found 1) neither phylogenetic principal component analysis nor hierarchical cluster analysis supported the idea that species displayed one-dimensional trade-off; 2) Conventional strategies, such as content of condensed tannins, are not strongly involved as a defence against herbivores; 3) No significant trade-off between plant intrinsic growth rate and chemical defence traits for the 27 studied tree species. Our results do not support arguments for growth-defense trade-off hypothesis. Rather, plants exhibit a range of combinations of leaf traits. We suggest this lack of a one-dimensional trade-off may be adaptive, resulting from selective pressure to adopt a different combination of defences to coexisting species.

Aims Acer pictumsubsp. mono is a main accompanying tree species in broadleaf Korean pine (Pinus koraiensis) forests, and plays an important role in the structure and function of broadleaf Korean pine forests. Studying the variation in functional traits of leaves, branches, and roots of Acer pictumsubsp. mono at different life-history stages is of great significance for understanding intra species variation in plant traits, and strategies for plant resource acquisition and allocation.

Methods This article focused on the seedling, sapling, and adult trees of A. pictumsubsp. mono in the broadleaf Korean pine forests of Liangshui National Nature Reserve located in Heilongjiang. Twelve physiological and morphological traits of leaves, branches, and roots were measured, and chemometric traits such as carbon (C), nitrogen (N), and phosphorus (P) contents of different plant organs were analyzed. We then explored the influence of different life history stages on the variation of leaf, branch, and root traits, and the trait-trait correlations.

Important findings (1) With the development of plant life history, leaf thickness, branch tissue density, root diameter, leaf N content, and C contents of leaves, branches, and roots increased significantly, whereas specific leaf area, net photosynthetic rate, and specific root length decreased significantly. Additionally, intraspecific variation of each trait varied in different life history stages. (2) Correlations among traits of leaves and branches were significants, yet in fine roots, only specific root length was correlated with chemical traits. (3) Leaf N content, net photosynthetic rate, and photosynthetic products increased with the development of plant life history. Leaves varied from a “slow investment-return” type to a “fast investment-return” type. Moreover, the metabolic capacity such as branch water content, and the ability of resource acquisition of fine roots decreased. Both branches and roots transitioned from a “resource acquisition” type to a “resource conservation” type.

Aims Stem photosynthesis plays a crucial role in maintaining the carbon balance in plants. By exploring the impact of stem photosynthesis on hydraulic traits and leaf gas exchange in desert woody plants during a long period of drought, we aimed to gain deeper insights into the remarkable drought resistance capabilities of these plants in extreme environments.

Methods Aluminum foil was used to shade the stems of two-year-old Calligonum arborescensseedlings planted in 15-L pots at the beginning of the 2022 growing season under the rain shelter of Fukang desert station. The stems of a control group were exposed to normal light levels. After 0, 15 and 30 d of drought, the stem/leaf photosynthesis rate, hydraulic parameters, and non-structural carbohydrates (NSC) contents were measured in the shading and control groups.

Important findings Our main results showed that: (1) Stem photosynthetic rate of C. arborescens ranged from 1.0 to 2.0 μmol·m^-2·s^-1, and was not significantly affected by the duration of the drought. Stem photosynthetic rates were 1.42, 1.28 and 1.21 μmol·m^-2·s^-1 after 0, 15 and 30 d of drought, respectively. (2) The specific hydraulic conductivity, leaf/stem water content, leaf water potential, and leaf photosynthetic rate decreased significantly over the dry period in the shading group but declined more slowly in the control group. (3) After 15 d without water, the percentage loss of conductivity, was significantly reduced in the control seedlings and the NSC contents of leaf and stem were significantly increased. Following 30 d of drought, the number and cross-sectional area of embolized vessels decreased significantly, by 33.8% and 22.8%, respectively, in the control seedlings. (4) In the same drought duration, leaf photosynthetic rate in the control group was significantly higher than that of the shading group, increasing 2.3 and 3.2 μmol·m^-2·s^-1 after 15 and 30 d of drought, respectively. Our results indicate that stem photosynthesis can improve the drought resistance of desert plants and provide a theoretical foundation for understanding the strategies and mechanisms used by desert plants to survive under drought conditions, which are important when considering projected climate change scenarios.

Aims Variation in leaf colour is natural in bamboo, and the leaf colour variation of Pseudosasa japonicaf. akebonosuji is a typical representative. The mechanism of colour variation can be resolved by studying the photosynthetic properties of different leaf colours.

Methods The photosynthetic pigment content, the relative content of chlorophyll (Chl) synthesis precursors, photosystem activities and photosynthetic effect differences of leaves with different leaf colours were determined by ultraviolet spectrophotometer, high-performance liquid chromatography and continuous excitation fluorescence to elucidate the physiological mechanism of leaf colour variation of P. japonicaf. akebonosuji.

Important findings (1) There were significant differences in photosynthetic pigment content between the all-green and mosaic leaves of P. japonica f. akebonosuji. The mosaic leaves’s chl a/b value was significantly lower than the all-green leaves, while the carotenoid/Chl a+b value was substantially higher than all-green leaves. (2) The chlorophyll biosynthetic precursor substance, Coprogen III, was significantly higher in albino and striped albino leaves than in green leaves. At the same time, the content of protoporphyrin IX decreased sharply, resulting in significant reductions in Chl a and Chl b content. (3) The net photosynthetic rate and apparent quantum yield of striped leaves were significantly lower than in green leaves, and there was no photosynthetic effect in all-albino leaves. (4) Using all-green leaves as a control, the overall performance of photosystem II in mosaic leaves was lower than that of green leaves. The proportion of fluorescence intensity at J-step (F_j)in F₀ - F_p (F₀, minimal fluorescence intensity; F_p, fluorescence intencity at P-step) amplitude of chlorophyll value of green leaves was significantly lower than that of albino and re-greened leaves. There was no significant difference with striped green leaves, indicating that PSII receptor side performance was consistent on green and striped green leaves, but re-greened leaves did not fully recover to the level of green leaves. (5) The light absorption at 820 nm of mosaic leaves and re-greened leaves was lesser than that of green leaves. During the re-greening of albino leaves, the maximum redox capacity of photosystem I (PSI) (ΔI/I_o) values increased significantly. They gradually returned to the level of stable green leaves, indicating that the redox capacity of chlorophyll I (P700) was low. The oxidative capacity of albino leaves after re-greening was not significantly different from that of green leaves. (6) The change in coordination between PSI and PSII (Φ_PSI/PSII) in albino leaves was significantly lower than in green leaves, and the coordination of PSI/PSII deteriorated, with PSII decreasing more than PSI. PSII mainly triggered the weakening of the photosystem performance of re-greened leaves. The mosaic leaves a Chl a-deficient mutation caused by reduced chlorophyll content and Chl a/b value, and a sharp reduction in protoporphyrin IX content impairs chlorophyll synthesis. Therefore, the whole plant always retains the mosaic leaves, and the photosynthetic capacity and utilization efficiency are lower than green leaves. There are physiological differences in photosynthesis between the different leaf colours.