Aims Exploring the characteristics of carbon source-sink has significant implications for guiding local governments in achieving its “dual carbon” goal. This study comprehensively assessed the dynamics of carbon emissions, terrestrial carbon sinks, the contribution of terrestrial carbon sinks in offsetting carbon emissions, and the impacts of clean energy production on the carbon emissions in Yunnan Province from 1981 to 2020, and further investigated the terrestrial carbon balance in the next four decades projected by coupled model intercomparison project phase 5 (CMIP5) earth system models under two climate scenarios.

Methods Two independent methods were used to estimate historical ecosystem carbon sinks in Yunnan Province. One was based on field observation data combined with empirical models, and the other was based on four terrestrial ecosystem models. The projections of future carbon balance in Yunnan Province were derived from five earth system models of CMIP5 under two scenarios (RCP4.5 and RCP8.5). Carbon emissions were estimated using the Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas Inventories, and China’s Provincial Guidelines for Greenhouse Gas Emission Inventory.

Important findings The results show that the terrestrial carbon sink in Yunnan Province varied between 12.41 and 31.22 Tg C·a^-1 over the past 40 years, with an average sink of 19.41 Tg C·a^-1. The highest ratio (247%) of ecosystem carbon sinks to carbon emissions (sink emission ratio) in Yunnan Province occurred during the period from 1981 to 1985, while the ratio has declined since then and reached its lowest value during the period of 2006-2010 followed by a slight increase after that. The ratio was 54% during the period of 2016-2020. The rise of the sink emission ratio in the past decade can be mainly attributed to the promotion of clean energy production, the increase in forest area, and the decrease in energy intensity. Large-scale deployment of clean energy in Yunnan Province has in general satisfied the energy needs of economic development, reducing the reliance of its economy on CO₂ emissions. Model projections indicated that under future climate change scenarios (RCP4.5 and RCP8.5), the net ecosystem productivity (NEP) in Yunnan Province during the 2020s and the 2030s may be lower than that during 2016-2020, while carbon sink may increase in the 2040s to 2050s. This study suggests that in the future, Yunnan Province should further develop clean energy programs, increase energy efficiency, and enhance ecosystem carbon sink to support both the achievement of carbon neutrality and regional high-quality development.

Aims The increases in drought intensity and frequency severely threaten structure and functioning of terrestrial ecosystems. To ensure the normal functioning of ecosystems under such scenarios, it is critically needed to understand the spatial-temporal characteristics of ecosystem productivity response and resilience under meteorological droughts.

Methods The intensity and frequency of meteorological droughts were quantified by standardized precipitation evapotranspiration index (SPEI) of the Hai River Basin (HRB). Net primary productivity (NPP) of natural ecosystems was estimated based on Carnegie-Ames-Stanford Approach (CASA). We quantitatively analyzed the relationship between NPP and SPEI, evaluated the drought risk of natural vegetation and the resilience of vegetation after drought.

Important findings (1) Both NPP and normalized differential vegetation index (NDVI) in the HRB showed significantly increasing trend. (2) The lagging time of NPP response to droughts follow an order of grassland and savanna < deciduous broadleaf forest and woody savanna < deciduous-evergreen mixed forest and closed shrubland. (3) Drought risk followed an order of grassland > closed shrubland > woody savanna > deciduous broadleaf forest > savanna > deciduous-evergreen mixed forest. (4) More than 75% of the vegetation in the HRB showed no continuous distinctly low NPP status one month after the droughts, indicating relatively strong resilience. The resilience of forests was stronger than shrub or herbaceous vegetation, which showed opposite temporal pattern within each growing season but shared similar increasing trend interannually. Response and resilience characteristics of NPP varied with vegetation types and drought intensity. Ecosystem stability of the HRB could be improved by adjusting the afforestation and grass restoration measures based on vegetation drought risk and resilience, optimizing vegetation structure, and enhancing species diversity.

Aims The dynamic monitoring of basin-scale land use and land cover changes and carbon stock estimation of the terrestrial ecosystem can provide suggestions for optimizing land utilization, enhancing terrestrial ecosystem carbon storage, and achieving the “dual carbon” objective.

Methods Based on the Landsat 5 TM and Landsat 8 OLI images from 1986 to 2022, this study employed random forest to obtain ten land use and land cover maps of the Songhua River Basin with high accuracy and conducted dynamic monitoring of land use and land cover change and its ecosystem carbon storage using an integrated valuation of ecosystem services and trade-offs (InVEST) model, Mann-Kendall tests, and Theil-Sen median trend analysis.

Important findings Results showed that farmland has the largest area in the basin, followed by forest land, grasslands, unused lands, water, construction land, sparse forest land, and shrub land. Among them, farmland, forest, and grassland are the dominant land use types in the study area. During the 1986-2022 period, the farmland expanded by 11 462.68 km² while forest land decreased by 18 567.21 km²; the construction land experienced the most significant change rate of 5.3% with an increased area of 3 505.82 km²; the change rate of the sparse forest is 4.7%, ranking second after construction land but having minimal impact on the overall basin due to limited area changes. The change rate of unused land was 4.5%, with an increased area of 5 385.43 km². There was evident spatial heterogeneity in the distribution of the terrestrial ecosystem carbon stocks within the Songhua River Basin, with high carbon stocks predominantly found in Da Hinggan Mountains and Xiao Hinggan Mountains as well as the Changbai Mountains. The median carbon stock values were observed in the Hinggan League, Songnen Plain, and Sanjiang Plain. In contrast, the areas with low carbon values were observed in Daqing and Baicheng. Over the 36 years, there was an overall decline in carbon storage within the basin, primarily concentrated in the regions initially characterized by high carbon stock values. However, the area with increased carbon stock is scattered in the basin. Notably, three recovery instances of ecosystem carbon stock occurred in 1994, 2002, and 2018 within the Songhua River Basin, all related to the changes in forest land. Based on ensuring no reduction of current forest land, it is recommended to expand forest land and continue implementing forestry projects to effectively prevent further depletion of terrestrial ecosystem carbon storage in the Songhua River Basin.

Aims Soil CH₄ and CO₂ fluxes, as key components of global carbon cycle, have a central role in mitigating and adapting to climate change. However, how soil CH₄ and CO₂ fluxes respond to climate warming and nitrogen (N) deposition during freeze-thaw cycles remain poorly understood.

Methods Here we investigated the effects of long-term (18 years) warming and N addition on soil CH₄ and CO₂ fluxes continuously during freeze-thaw cycles in a desert steppe of Nei Mongol used the SF-3500 multi-channel automatic soil gas flux measurement and control system from May 2021 to April 2022.

Important findings We found that warming, but not N addition, increased soil temperature. Warming and N addition did not change soil moisture. Annual cumulative CH₄ uptake flux ranged from 344 to 471 mg C·m^-2 in this desert steppe. Warming prolonged the duration of autumn freeze and increased soil cumulative CH₄ uptake flux, whereas N addition and warming plus N addition decreased CH₄ uptake during this period. On average, soil CH₄ uptake flux during the frozen winter period contributed to 8% of the annual total flux and no significant differences among different treatments. The contribution of soil CH₄ uptake during the spring thaw to annual total flux was 14%, and did not be changed by the warming and N addition treatments. Annual cumulative CO₂emission flux ranged from 101 to 106 g C·m^-2 in this desert steppe. Soil CO₂ emission flux during the autumn freeze period contributed most to non-growing season flux, and it tended to increase with warming and N addition. In particular, soil CO₂ flux shifted from emission to absorption during the frozen winter period. Both warming and warming plus N addition significantly increased CO₂ emission flux during the spring thaw. Overall, soil CO₂ flux during the non-growing season contributed to 9% of the annual total CO₂flux. Soil CH₄ absorption and soil CO₂emission were significantly correlated with soil temperature and moisture. Our results indicate that the desert steppe ecosystem acted as CH₄ uptake and CO₂ emission throughout the whole year, which help to understand the response, strength and direction of carbon source-sink under global change scenarios.

Aims As plants take up silicon (Si) from soil solutions and then form phytoliths, a little organic carbon (C) can be occluded, which is called phytolith-occluded C (PhytOC). Recently, PhytOC storage is recognized as one mechanism influencing C storage in terrestrial ecosystems. Elevated atmospheric nitrogen (N) deposition over the past few decades has profoundly affected C dynamics in forest ecosystems. However, limited study focused on increased exogenous N inputs effects on phytolith C sequestration in forests.

Methods Here, we designed an experiment with canopy N addition of 25 and 50 kg·hm⁻²·a⁻¹ (simplified as CN25 and CN50), respectively, and understory N addition of 25 and 50 kg·hm⁻²·a⁻¹ (simplified as UN25 and UN50), respectively, in a subtropical evergreen broadleaf forest, to explore the effects of atmospheric N deposition on PhytOC sequestration of dominant shrub, herb and soil in subtropical forest.

Important findings Our results showed that UN50 significantly increased PhytOC concentration in both plant leaves and litter. Exogenous N input can stimulate plant Si uptake, and thus promotes the phytolith C sequestration. However, only CN50 significantly increased PhytOC concentration in the soil, while as UN50 had a minor effect. This would be attributed to the inhibition of litter decomposition caused by UN50, thereby impeding phytolith release. Structural equation model showed that increased phosphorus (P) limitation, soil acidification, and alterations in litter decomposition rates caused by N addition affected PhytOC accumulation in leaves and soil. In summary, our results suggest that N deposition can promote the potential for PhytOC sequestration of understory plants and soil in subtropical forests.

Aims Fine root biomass is the basis for quantifying fine root dynamic characteristics, such as fine root turnover and nutrient return. The special karst habitat with high-rock outcrops and gravel soil indicates that the traditional root drilling method for measuring fine root biomass is time-consuming, labor-intensive, destructive, and difficult to achieve site-specific sampling, and the sample heterogeneity is large. Therefore, it is necessary to establish fine root biomass estimation models based on morphological characteristics to accurately estimate fine root biomass and its turnover rate.

Methods Five dominant tree species, Vitex kwangsiensis, Garcinia paucinervis, Streblus tonkinensis, Diospyros siderophylla, and Excentrodendron tonkinense in Nonggang National Nature Reserve, Guangxi, were selected to establish fine root biomass estimation models. Two types of fine root classification were defined as 1-3 orders and diameters ≤2 mm. Quantitative correlations between length and diameter, root surface area, and fine root biomass were established based on the collected data. Subsequently, the robustness and accuracy of different models were tested, and optimal fine root biomass estimation models were selected.

Important findings The results showed that: (1) fine root diameter, length, and surface area were significantly positively correlated with fine root biomass; thus, the fine root morphological characteristics can be used to construct the correlation equation with fine root biomass; and (2) the bivariate fine root biomass estimation model based on diameter and length is more accurate than that based on fine root surface area; (3) the optimal estimation models of fine root biomass are different among tree species, due to the differences in fine root diameter, specific root length, and root tissue density among tree species. The construction of a fine root biomass estimation model based on fine root morphological indicators is beneficial for converting the obtained fine root morphological data using visualization technology, such as micro-root canal in a fixed location, into biomass data. Moreover, it is also helpful to estimate the fine root turnover rate and nutrient return of special rock mountain habitats more accurately.

Aims In China, the typical desert plant Haloxylon persicum is only distributed in Gurbantünggüt Desert, Xinjiang, China. With the formation and expansion of the Quaternary desert, extensive migration and expansion events occurred. The study of the genetic pattern and migration path of the species is helpful to further understand the distribution and evolution of H. persicum.

Methods In this study, the natural distribution data of H. persicum were combined with the trnS-trnG, trnV and ITS sequences of different geographic populations, GIS spatial analysis, species distribution modeling, GIS diffusion path analysis, haplotype network analysis (Network) and molecular analysis of variance (AMOVA) were integrated to investigate the spatial genetic variation pattern of 12 naturally distributed populations of H. persicum in Gurbantünggüt Desert, including 106 individuals. The Maximum Entropy Model (MaxEnt) was used to simulate the suitable distribution pattern of H. persicum in the Last Glacial Maximum and current climate. The analysis of population dynamics and dispersal paths during the late glacial period will help to understand the genetic variation pattern of H. persicum among different geographic populations in the Gurbantünggüt Desert.

Important findings The sequence length of trnS-trnG and trnV was 1 340 bp, and a total of 9 chloroplast DNA (cpDNA) haplotypes were defined. The sequence length of ITS1-ITS4 was 576 bp, and a total of 6 nuclear ribosomal DNA (nrDNA) haplotypes were defined. (2) The total genetic diversity (H_T) of the population was 0.862 (cpDNA) and 0.777 (nrDNA), which was significantly higher than the average genetic diversity (H_S) of the population (0.155 (cpDNA) and 0.217 (nrDNA)), and more than 76% of the genetic variation occurred in different sampled populations. (3) The mismatch distribution curve showed that H. persicum experienced recent population expansion, and the dispersal path analysis showed that H. persicumhad spread from west to east along the southern margin of Gurbantünggüt Desert since the Last Glacial Maximum, under the current climate period, H. persicum continues to spread westward along the southern margin of the desert, but the migration amplitude has obviously reduced. Haloxylon persicum population in Gurbantünggüt Desert has high genetic diversity and significant genetic differentiation among populations. Since the Last Glacial Maximum, H. persicum has exhibited a diffusion mode of migration along the edge of the desert. The southern edge of the Gurbantünggüt Desert is the most important diffusion path of Haloxylon persicum and an important channel connecting its east and west populations.

Aims Artificial vegetation, human planted and being that managed and influenced by human activities, is widely distributed all over the world, and its structure, process, pattern, and function are important topics in modern ecology. However, there are few studies on plant functional traits of artificial vegetation, which limit the understanding of artificial vegetation, especially agricultural vegetation. The aims of this study are to investigate key features of plant functional traits in main artificial vegetation types of Jinhua, Zhejiang, and to explore potential ways they have adapted to human disturbance.

Methods Above- and below-ground plant functional traits (leaf, twig or stem, and fine root) of eight dominant species in seven common artificial vegetation types in Jinhua, Zhejiang, were measured. Key characteristics of plant traits such as mean value, variability, correlation, and plant growth trade-offs were statistically analyzed. Combinations of above- and below-ground traits of different planted species were further analyzed by the principal component analysis to identify ecological strategies of these common planted species.

Important findings (1) Plant functional traits, and variation in artificial vegetation, exhibited different features. Woody plants had higher dry material content and tissue density in leaf, twig and fine root tissues, indicating stronger material storage capacity, whereas herbaceous plants had higher specific leaf area, specific root length and specific root area, facilitating quick access to resources. The ranges in the coefficient of variation (CV) of functional traits in woody, and then herbaceous plants were 8.80%-40.94% and 37.05%-61.60%, respectively. Furthermore, the CV for woody plants was generally smaller than that of herbaceous plants, indicating the latter were more sensitive to habitat changes. Species composition and the interaction between habitat and management, were the major factors affecting artificial vegetation traits. (2) Plant functional traits of different organs showed mostly positive and significant correlations, reflecting the synergy of artificial vegetation plant traits. (3) Different combinations of functional traits of species in different artificial vegetation types reflected various adaptation strategies. The leaf and fine root traits of peach (Amygdalus persica), with a larger specific leaf area, larger twig bark thickness, and smaller fine root diameter, showed the ability of quickly acquire resources, while camellia (Camellia japonica) tended to have greater leaf thickness, increased leaf mass per area and a coarser fine root component. This reflects a stronger substance accumulation and defense capacity. The orange (Citrus reticulata) however had intermediate trait values. The tea plant (Camellia sinensis) had flourishing fine roots to acquire more nutrients. Rice (Oryza sativa) and rape (Brassica napus) had stronger abilities to accumulate substance and to absorb nutrients because of their larger leaf thickness, greater specific leaf mass per area, and lower stem and fine root tissue densities. However the trait combinations of two artificial grassland species, Bermuda grass (Cynodon dactylon) and bluegrass (Poa annua) were in contrast with the above two crops. The study of plant functional traits, their trade-offs, and the various combinations of artificial vegetation from an ecological perspective, provide a scientific basis and new ideas for the management of anthropogenic ecosystems.

Aims Xizang is one of the most sensitive regions to global climate change, and bryophytes are sensitive indicator plants to environmental change. This study investigates the relationship between morphological traits and environmental factors such as climate, soil, and vegetation of Didymodon constrictus, which is widely distributed in Xizang. It analyzes the response strategies of bryophytes to environmental changes, providing reference for revealing the response mechanisms of bryophytes to environmental changes and formulating protection strategies for bryophytes in Xizang.

Methods Specimens were collected from Xizang from 2007 to 2015, and valid specimens of D. constrictus with a certain spatial distance were confirmed. Six mature plants were selected from each specimen and the morphological traits of plant height, leaves and related cells were measured. Pearson and redundancy analysis methods were used to analyze their relationships with the environmental conditions.

Important findings With the altitude increases, the plants become shorter, the leaves tend to be ovoid and the cell walls thicken. As the air temperature rises and precipitation is abundant, the plants become taller, the leaves are elongated, the midribs are short, and the cell wall are thinner. When solar radiation increases, the angle of leaf inclination on the stem decreases. The results also showed that the environmental factors that have a significant impact on the growth of D. constrictus, including annual mean air temperature, annual precipitation, and solar radiation. The response of plant height, area of leaf, and angle of leaf to environmental changes is relatively sensitive, while at the cellular level, area of leaf cell and cell wall thickness are preferred as measurement indicators. We consider that plant height, leaf area and leaf inclination are more sensitive to environmental changes, while leaf cell area and cell wall thickness are preferred as measures at the cellular level. In summary, the various morphological traits of moss plants are closely related and moss plants respond synergistically to environmental changes through combined changes.

Aims Understanding on how nitrogen uptake of plants is influenced by soil conditions and plant traits is crucial. Elucidating the nitrogen preferences of different plants and their interactions with soil properties and root traits, can enhance our understanding of plant nitrogen acquisition strategies. This knowledge can provide a theoretical basis for designing mixed-species plantation construction for arid and semi-arid region of northern China, like the Bashang region of Hebei Province.

Methods In Kangbao County, Zhangjiakou City, China, the tree species Ulmus pumila, Populus simonii, Caragana korshinskii, and Lycium barbarum were selected. The ¹⁵N isotope tracing technique was employed to quantify nitrogen uptake rates and preferences for different forms (nitrate, ammonium, and glycine) by these plants. Correlations among nitrogen uptake rates, root morphology, architecture, and chemistry, and soil characteristics were analyzed.

Important findings Lycium barbarum roots exhibited an uptake preference for nitrate with a contribution of 46.05%, followed by glycine and ammonium. For P. simonii, U. pumila, and C. korshinskii, the contributions of each form of nitrogen to total nitrogen uptake showed ammonium (44.91%-68.68%) > glycine (22.63%-45.11%) > nitrate (8.69%-9.98%). The nitrate uptake rate was significantly negatively correlated with root diameter and tissue density, but positively correlated with specific root length and specific surface area. This indicate that roots with smaller diameter, lower tissue density, larger specific root length, and greater specific surface area had higher nitrate uptake rate. Root branching intensity was positively correlated with the uptake rate of glycine and total nitrogen, suggesting that the roots with higher branching intensity take up organic and inorganic nitrogen more efficiently. Furthermore, there was a significant negative correlation between root nitrogen content and ammonium as well as glycine or total nitrogen uptake rate; implying that roots with lower nitrogen content displayed higher nitrogen uptake rate. The observed differences in the nitrogen uptake patterns among four species were influenced not only by soil nitrogen content but also by various morphological, architectural, and chemical traits of the roots. Based on the plant nitrogen uptake preference and relationships with root structural traits and soil fertility, it is necessary to minimize the interspecific competition of plants and maximize the use of nutrients in nutrient poor environment. Therefore, we recommended to construct a mixed-species shelterbelt such as tree-shrub combination (P. simonii - L. barbarum, U. pumila - L. barbarum) or shrub-shrub combination (C. korshinskii - L. barbarum), or to replant shrubs under the pure P. simonii or U. pumila plantations. These research results provide valuable insights for the constructing mixed-species shelterbelts in Bashang region of Hebei Province.

Aims The root nodules of leguminous plants are the site of biological nitrogen fixation by rhizobia, and nodules also harbor diverse endophytes, which play important roles in plant growth and nutrient status. However, how root nodule endophytes respond to nitrogen input and the associations of endophyte composition with plant ecological stoichiometric characteristics remain largely unkown.

Methods We planted Arachis hypogaea‘Qicai’ in a field experiment with three levels of nitrogen treatment (N0: 0 kg·hm^-2, N1: 140 kg·hm^-2, N2: 280 kg·hm^-2). We also quantified the structures of endophyte communities and the contents of carbon (C), nitrogen (N) and phosphorus (P) in leaves, then the endophytic functions were predicted by PICRUST 2 software.

Important findings The results showed that endophytes are extremely diverse, with a total of 546 families and 1 049 genera. Among them, Bradyrhizobium accounted for 27.83% in relative abundance, while other genera accounted for more than 70%. The average proportion of Burkkholderia-Caballeronia-Paraburkholderia and Enterobacter was more than 10%. Nitrogen application decreased the diversity of endophytes and shifted the community composition, and the relative abundance of microorganisms from Bradyrhizobium, Enterobacter, Kosakonia and Pantoea increased significantly, while those from Allorhizobium-Neorhizobium-Pararhizobium- Rhizobium, Mesorhizobium, Mycobacterium and Burkholderia-Caballeronia-Paraburkholderia were significantly decreased. The relative abundance of part of genera was closely correlated with the stoichiometric characteristics of the plants. The results of co-occurrence network analysis show that some modules are significantly correlated with the contents and stoichiometric characteristics of C, N, and P in the leaves. Meanwhile, the results of PICRUSt 2 functional prediction show that the functions of microbial C, N, and P metabolic enzymes are significantly correlated with the contents and stoichiometric characteristics of C, N, and P in leaves, indicating that there is a close association of the microbial community structure with the contents and balance of plant nutrients. In summary, our study shows that the composition of endophytes in the root nodules of the Arachis hypogaea‘Qicai’ is extremely diverse, and the community structures and functions are sensitive to nitrogen addition. In future studies, the functions of nitrogen-tolerant and sensitive endophytes can be further explored through microbial isolation and synthetic microbial community techniques.

Leymus chinensis alliance, one of the most widely distributed communities in China’s temperate steppe, is a grassland vegetation type with the highest utilization value for animal husbandry. Investigating the distribution and community characteristics of Leymus chinensis formations can provide data for the management and restoration of natural grasslands. In this study, we investigated the characteristics of L. chinensis communities of 46 sites in Nei Mongol, including species composition, ecological characteristics, and community classification of L. chinensis alliance. A total of 187 vascular species, belonging to 109 genera and 37 families, were recorded. Asteraceae was the family with the most species, while Artemisia was the genus with the most species. Perennial herbs were the dominant life form, accounting for 71.66% of the total species. Xerophyte dominated the communities, accounting for 67.38% of the total species. The geographic composition of the system was dominated by the Eastern Palearctic species, followed by the Central Asian species. The L. chinensis alliance could be divided into 8 association groups, including Leymus chinensis - tussock, Leymus chinensis - semi-shrubby, Leymus chinensis - rhizome, Leymus chinensis - Carex, Leymus chinensis - annual/biennial, Shrub - Leymus chinensis, Leymus chinensis - bulbiferous herb and Leymus chinensis - forb and 26 associations.