Dryland forests account for 27% of the world’s forests and play a key role in global ecological balance and environmental protection. With the intensification of climate change, dryland forests are experiencing extensive decline, seriously restricting and even threatening local ecological security and the sustainable development of human society. However, a synthesis and comprehensive assessment of the research progress on the status and mechanisms of dryland forest decline on a global scale are still lacking. To fill this gap, we have systematically reviewed relevant literature to assess key concepts, characteristics, current status, influencing factors, and the formative mechanisms of dryland forest decline. We first synthesize key concepts and general characteristics of dryland forest decline. Then, we provide an overview of the current status of forest decline both in global and China’s drylands, and further discuss their variations among regions, forest types and tree species. Third, we discuss the processes of how natural (e.g., climate change, biological invasions, site conditions and natural disasters) and anthropogenic factors (e.g., anthropogenic disturbances and management measures) influence the decline of dryland forests. Finally, we discuss the formative mechanisms of forest decline at the individual scale (e.g., hydrodynamic failure hypothesis, carbon starvation hypothesis, biotic attack hypothesis and nutrient cycling hypothesis), the population scale, the community scale (e.g., competitive effects) and the ecosystem scale. We also highlight the interactions among these formative mechanisms and related research challenges to advance methodological innovations. Future research efforts should: (1) focus on the ecological mechanisms of dryland forest decline at larger scales; (2) collect long-term and high-quality data to enable the understanding of integrated effects of multiple factors on dryland forest decline; and (3) integrate multiple mechanisms to gain a comprehensive understanding of dryland forest decline. Overall, we have systematically reviewed the current status and mechanisms of dryland forest decline. This review will help enhance our understanding of the decline mechanisms and provide theoretical support for ecological restoration practices in drylands.

Alfalfa (Medicago sativa) is a globally important perennial leguminous forage, whose productivity and persistence are largely constrained by water availability. Xylem vessels, as the key structures responsible for long-distance water transport in plants, exhibit a classical trade-off between hydraulic efficiency and embolism resistance. Specifically, conduit structure and spatial configuration that enhance water transport efficiency are often associated with an increased risk of embolism, thereby reflecting a fundamental trade-off between “efficiency and safety”. Previous studies have mainly focused on single traits such as vessel diameter and density, whereas the spatial distribution of vessels at the tissue scale and its function have received less attention. In recent years, spatial point pattern analysis, particularly the Strauss-Hardcore point process model, has been increasingly applied to quantify the two-dimensional spatial arrangement of xylem vessels, providing a new approach into analyzing vessel spatial heterogeneity. This model characterizes vessel spatial configurations under physical exclusion and local interaction constraints using key parameters, including hard-core distance, interaction distance, and pairwise interaction strength. Accumulating evidence suggests that xylem vessel spatial patterns in alfalfa vary markedly among genotypes and environmental conditions, and are closely associated with hydraulic safety, water-use efficiency, and drought tolerance. This review synthesizes recent advances in the application of the Strauss-Hardcore model to studying xylem vessel spatial distribution in alfalfa. It also discusses the potential mechanism of vessel spatial configurations impacts on hydraulic trade-offs, further summarizing vessel network plasticity in response to drought, salinity, and nutrient availability. Furthermore, based on recent progress in the molecular regulation of vessel development, this review investigates possible correlation paths among environmental signal—anatomy—hydraulic function, with future directions integrating three-dimensional imaging and multi-omics approaches and the applications in ecological adaptation research.

Aims Germination timing determines the environmental conditions experienced after germination, holding significant adaptive significance. Plant populations can exhibit distinct patterns of germination timing along environmental gradients, and germination timing within populations responds to environmental change. Spartina alterniflora has rapidly expanded into temperate, subtropical, and tropical regions since it was introduced to China in 1979. At mid and high latitudes, it typically germinates in spring. However, populations along a latitudinal gradient have developed differentiated germination timing by adapting to local environmental conditions. Few studies have examined how seasonal germination characteristics vary among populations along the latitudinal gradient.

Methods In this study, we collected seeds from nine populations along the latitudinal distribution range of S. alterniflora and sowed them in multiple common gardens across three different climate zones. Seed germination dates were continuously monitored to explore how seasonal germination characteristics responds to both the planting and seed source environmental conditions.

Important findings (1) As the latitude of common gardens decreased, winter temperatures significantly increased. Consequently, the germination window of S. alterniflora expanded from exclusively spring to both winter (earlier) and spring. Accompanied by increased winter germination percentage and decreased spring germination percentage, the proportion of winter-germinated significantly increased, while the total germination percentage declined. (2) Within each common garden, winter germination percentage did not change across populations along a latitudinal gradient; however, spring germination percentage decreased significantly with decreased latitude of origin. Specifically, in the mid-latitude and low-latitude common gardens, the proportion of winter-germinated showed a significant negative correlation with the latitude of origin. (3) As the temperature at sites of origin increased, the total germination percentage significantly decreased, and the proportion of winter-germinated significantly increased. Overall, both increased temperature of the planting environments and the source environments enhanced the likelihood of germinating in the current winter but reduced the total germination percentage, indicating that temperature is a key factor influencing the seasonal germination characteristics across latitudinal populations of S. alterniflora. These findings provide a scientific basis for predicting changes in the germination strategies of S. alterniflora along the latitudinal gradient under climate warming, which is crucial for forecasting shifts in the fitness and distribution range of S. alterniflora.

Aims This study aimed to explore the short-term effects of different nitrogen addition levels on leaf litter production and carbon (C), nitrogen (N), and phosphorus (P) returns in a Cunninghamia lanceolata plantation in the rainy area of Western China.

Methods We conducted a short-term N addition experiment with seven treatment levels (N0, N10, N20, N40, N80, N120, and N160, corresponding to 0, 10, 20, 40, 80, 120, and 160 kg·hm^-2·a^-1 N addition, respectively). The experiment was designed to examine the effects of N addition on leaf litter production, its C, N, and P contents, and their subsequent return in a C. lanceolata plantation in the rainy area of Western China.

Important findings (1) Annual leaf litter production of C. lanceolata ranged from 2 595.88 to 3 043.98 kg·hm^-2·a^-1 and exhibited a bimodal monthly pattern with peaks in May and August. N addition significantly influenced annual production, which followed a unimodal curve: initially increasing and then decreasing as N levels increased, with a response threshold at the N40 treatment. (2) Mean annual C, N, and P contents in leaf litter were 313.89-498.12 g·kg^-1, 10.17-22.03 g·kg^-1, and 0.13-0.30 g·kg^-1, respectively. C content decreased significantly at the N40 treatment. In contrast, N and P contents increased with rising N addition levels. (3) Mean annual C, N, and P returns from leaf litter ranged from 1 032.91-1 205.09 kg·hm^-2·a^-1, 36.85-43.61 kg·hm^-2·a^-1, and 0.50-0.61 kg·hm^-2·a^-1, respectively. These returns were primarily regulated by litter production and exhibited trends similar to production. This study indicates that 40 kg·hm^-2·a^-1 N addition treatment represents a critical response threshold for litter production in this region. Nitrogen addition within this threshold can effectively enhance leaf litter production and nutrient return in the C. lanceolata plantation. These findings provide an important reference for the adaptive management and scientific fertilization of regional C. lanceolata plantations under the context of nitrogen deposition.

Aims Increased atmospheric nitrogen (N) deposition leads to changes in the proportion of different forms of N inputted into forest ecosystems, but the response mechanisms of plants to different N-form sources and their resource trade-off strategies have not been clarified. The effects of N deposition on plant growth and development are still unclear, restricting the improvement of forest productivity based on the regulation of N forms. This study aimed to reveal the response of leaf traits and growth of temperate tree species to different forms of N addition and elucidate the adaptive strategies of plants to the heterogeneity of ammonium, nitrate, and organic N.

Methods We selected one-year-old seedlings of four common tree species in the temperate forests of Northeast China as the research objects, namely Betula platyphylla, Fraxinus mandshurica, Juglans mandshurica, and Quercus mongolica. We analyzed the effects of ammonium, nitrate, and organic N (glycine) additions and control (no N addition) on leaf traits of seedlings grown in pots over three growing seasons (2021-2023). At the end of the third growing season, changes in 11 indices, including leaf morphological traits, chemical traits, and biomass, were evaluated for their differences among N treatments and to investigate the relationship between leaf traits with sensitive plasticity in response to N treatments and growth.

Important findings All three forms of N additions were found to reduce leaf phosphorus (P) concentration and increase aboveground biomass, showing a “growth dilution effect” on P concentration due to rapid growth. Compared with control, the ammonium and nitrate additions did not have a significant effect on leaf N concentration, whereas glycine addition significantly increased leaf N concentration (+19%). Leaf N:P and C:P ratios showed sensitive plasticity to N addition (phenotype plasticity index ≥ 0.3), and interspecific differences increased under ammonium and nitrate treatments. The species with high N:P and C:P achieved greater biomass, indicating that species capable of more effective resource utilization had greater growth competition potential. The addition of N affected growth strategies of temperate tree species by regulating leaf chemical traits and stoichiometric ratios. Organic N (glycine) addition boosted N concentration without exacerbating interspecific differences and facilitated seedling acclimatization to N- and P-limited environments. These results provide a theoretical basis for understanding the response of temperate forest species to N addition and guidance for the selection of N fertilizer forms in plantation forests under the background of N depletion. It is recommended to prioritize the application of organic N to balance productivity enhancement and maintenance of community stability.

Aims Cloud and aerosol variations influence the total amount of solar radiation as well as the proportion of diffuse and direct radiation, which can potentially alter the microclimate of forest ecosystems. The clearness index (CI), a crucial parameter for assessing sky conditions, reflects changes in solar radiation. However, it remains unclear how clouds and aerosols impact the dynamics of carbon exchange in light-sensitive tropical montane rainforests.

Methods Based on carbon flux data and meteorological data during the wet (June to October) and dry (November to May) seasons of 2013-2017, we compare the difference in gross primary productivity (GPP), ecosystem respiration (ER), and net ecosystem productivity (NEP) under clear and cloudy conditions. The light response model was derived using a rectangular hyperbolic curve. Meanwhile, we utilized partial correlation analysis and a structural equation model to assess the influence of diffuse photosynthetically active radiation (PAR_f), direct photosynthetically active radiation (PAR_d), air temperature (T_a), vapor pressure deficit (VPD), and volumetric soil water content (VWC) on GPP, ER, and NEP.

Important findings Cloudy skies improve the efficiency in utilizing photosynthetically active radiation, with the canopy quantum efficiency (α) increased by 45%-88%. Additionally, cloudy skies enhanced canopy photosynthesis and net carbon uptake while reducing ER. GPP and NEP increased by 6%-8% and 17%-21%, while ER decreased by almost 2%. PAR_d decreased dramatically following the decline in CI, while PAR_fchanged only slightly. Since PAR_f directly enhanced NEP, it offset the suppression caused by the decline in total PAR. PAR_f and PAR_d are the major influencing factors of GPP, controlling its variation under clear and cloudy skies, respectively. T_a was the most controlling factor of ER, determining its variation under clear skies, while T_a, VPD, and VWC jointly controlled ER under cloudy skies. GPP and NEP peaked at moderate radiation (PAR = 1 300-2 000 μmol·m^-2·s^-1) and moderate CI (0.3-0.5), while ER was maximized at high radiation levels (PAR = 2 300 μmol·m^-2·s^-1) and comparatively high CI (>0.5). Overall, CI regulates both the quantity and quality of solar radiation. The net effects of diffuse radiation can compensate for the loss of total PAR quality, while intermediate levels of PAR and CI can enhance carbon exchange. This study emphasizes the crucial role of radiation and environmental effects induced by clouds and aerosols, offering insights for advancing our understanding of how tropical forests respond to climate change.

Aims To explore the characteristics of soil seed banks in typical shrub communities in Luoshan, Ningxia, and their relationship with aboveground vegetation. The study also evaluates the ecological restoration potential of soil seed banks and clarifies their role in vegetation restoration.

Methods In this study, six typical shrub community sample plots were set up in Luoshan Nature Reserve of Ningxia, and the method of field investigation and sampling and germination experiment was adopted.

Important findings The study found that a total of 82 plant species belonging to 31 families and 64 genera were recorded in the aboveground vegetation of 6 typical shrub groups. The life form of the species is mainly composed of perennial herbs, followed by shrubs, and the proportion of annual plants is relatively low. The species richness of the Ostryopsis davidiana community is the highest and the distribution is relatively uniform, while the species richness of the Convolvulus tragacanthoides community is the lowest and the distribution is uneven. There are a total of 43 plant species in the soil seed banks of 6 typical shrub communities, belonging to 17 families and 35 genera. The life forms of these plants are mainly perennial herbs. The density range of soil seed banks for 6 plant communities is (1 033.33 ± 57.74)-(7 000.00 ± 200.00) grains·m^-2. The soil seed density is highest in the community of Buddleja alternifolia, and lowest in the community of Convolvulus tragacanthoides. Most of the seeds in each plant community are concentrated in the 0-10cm soil layer. As the soil layer deepens, the density and number of species in the soil seed bank of each plant community show a decreasing trend. Overall, the species diversity index of the Ostryopsis davidiana and Buddleja alternifolia communities is the highest, while the Convolvulus tragacanthoides community is the lowest. The aboveground vegetation of six typical shrub communities is higher in terms of plant species and quantity than in the soil seed banks, and the uneven distribution of plant species in the soil seed bank is more pronounced than in the aboveground vegetation. The similarity between aboveground vegetation and soil seed bank in various plant communities is relatively low, with a similarity index range of 0.286-0.444. The evaluation of the ecological restoration potential of soil seed banks shows that the ecological restoration potential of the Ostryopsis davidianacommunity is strong, while the ecological restoration potential of the other five typical shrub communities is moderate. Overall, although soil seed banks provide a certain source of seeds in vegetation restoration, relying solely on natural seed banks is not sufficient to fully meet the ecological restoration needs. In the actual production process, corresponding restoration measures need to be adopted based on the characteristics of different plant communities, and moderate human regulation should be carried out to promote community succession in the direction of progress or increasing biomass.

Aims The current study aims to investigate the diversity patterns of naturally regenerated understory trees in different exotic plantations in Mt. Jianfeng of the Hainan Tropical Rainforest National Park, China, and to identify main factors underlying such patterns.

Methods We established a total of 173 plots (20 m × 20 m) in Mt. Jianfeng in a range of stand types, including three exotic plantations (Eucalyptus urophylla, Acacia mangium, and Pinus caribaea) and natural lowland tropical rainforest. In each plot, we identified all woody plant individuals with a diameter at breast height (DBH) of ≥ 1 cm to species, recorded their DBH, and measured a range of environmental variables considered potentially relevant to species diversity patterns. We applied non-parametric tests (Kruskal-Wallis and Dunn’s tests) to compare stem density, basal area, and species richness across stand types, separately for three DBH classes. For each stand type, we additionally identified dominant and indicator species based on importance value, and Indicator Species Analysis (ISA), respectively. We further used similarity analysis and nonmetric multidimensional scaling (NMDS) to assess variations in community composition among stand types, and used permutation tests to assess the relevance of numerous environmental factors to such variations.

Important findings Among all stand types studied, E. urophylla plantations had the lowest species understory tree richness (30 species·400 m^-2) but the highest stem density (392 individuals·400 m^-2). In contrast, the understory tree species richness (47 and 42 species·400 m^-2, respectively) and stem density (291 and 262 individuals·400 m^-2, respectively) of A. mangium and P. caribaea plantations did not differ significantly from those of natural forest (54 species·400 m^-2 and 214 individuals·400 m^-2). The naturally regenerated understory trees of all three types of plantations generally lacked large-diameter individuals (DBH ≥ 10 cm). The understory of E. urophylla plantations was dominated by Alchornea rugosa, whereas Acacia mangium and P. caribaea plantations had no particularly dominant species. Community composition differed significantly among stand types and particularly between any type of plantation and natural forest, with E. urophylla plantations showing the lowest similarity to natural forests. For all types of plantations studied, the main environmental factors explaining their compositional differences with natural forests included soil pH, soil total nitrogen content, soil total phosphorus content, soil available phosphorus content, available potassium content, altitude, stand age, and basal area of the tree species planted. For exotic plantations in the Hainan Tropical Rainforest National Park, future management should optimize stand structure, and promote the growth and regeneration of small-diameter individuals of native species to facilitate their transition into larger-size classes. Given variations in natural regeneration among plantation types, tailored restoration strategies should be developed for each plantation type.

Aims The presence of dry valleys in the Three-Parallel-Rivers area, located on the southeastern margin of the Qingzang Plateau, has led to a phenomenon of “inverted” vegetation distribution. To better understand the local ecosystem, information of vegetation vertical belt is critical. Although existing studies have extensively explored vegetation patterns in the area, they are often limited by data resolution and extraction methods and have not fully revealed the detailed characteristics of the inverted vegetation belts.

Methods Here, a refined extraction of vegetation vertical belts in the dry valleys of the Three-Parallel-Rivers area was conducted using the Digital Elevation Model (DEM)-Normalized Difference Vegetation Index (NDVI) algorithm, in combination with Landsat 8 OLI imagery and NASADEM data. The accuracy of the algorithm was verified to enable an updated classification of vegetation belts in the area.

Important findings 1) The spatial distribution characteristics of vegetation vertical belts were identified in three different sections. The NDVI upper-limit threshold values for the vegetation belt in the northern, middle and southern sections were (0.61, 0.43, 0.10), (0.78, 0.46, 0.07, -0.05) and (0.78, 0.55, 0.43), respectively. 2) The width of the subtropical dry valley shrub-grassland belt, which serves as the base belt, gradually increased from 795 m in the southern section to 1 161 m in the northern section. In contrast, the forest belt, which represents the dominant vegetation zone in the area, showed the opposite trend, gradually narrowing from south to north. The subalpine cold temperate shrub meadow belt and the alpine cold temperate sparse cushion vegetation belt were relatively narrow and had small distribution areas. 3) The elevation error of vegetation belt extraction using the DEM-NDVI algorithm ranged from a minimum of 3 m to a maximum of 43 m, indicating high accuracy.

Aims Previous studies on the impact of climate change on plant phenology were mostly based on constant warming. However, under natural conditions, climate change shows seasonal and diurnal asymmetry. A few studies based on remote sensing or long-term observations showed that the response of plant phenology to asymmetric warming is inconsistent with that to constant warming. However, due to the limitations of remote sensing and statistical methods, these research conclusions are still uncertain, and ground-based control experiments are needed to accurately determine the impact characterize of asymmetric warming on plant phenology.

Methods An infrared automatic temperature warming experiments (2023-2024) was carried out in the typical development area of the alpine meadow in Nagqu, the heart of Qingzang Plateau. Three common plants were selected, including the early-flowering plant Potentilla multifida, the mid- and late-flowering plants Stipa purpurea and Leontopodium pusillum, to simulate the characteristics of diurnal and seasonal asymmetric climate warming and constant warming field control experiments, while coupling the water increase factor, to investigate the effects of asymmetric warming and water addition on the first flowering phenology of the three species.

Important findings The main findings are that temperature is the main factor affecting the first flowering phenology of alpine meadows, while water has no significant effect. Among them, early flowering plant Potentilla multifida, is more sensitive to warming. The mid- to late-flowering plant Stipa purpurea had no significant response to warming. There is no significant difference in the effects of diurnal asymmetric and symmetrical warming on the flowering phenology of three species. A comparison between seasonal asymmetric and symmetric warming revealed that seasonal asymmetric warming significantly advanced the first flowering day of Leontopodium pusillum by about 4-7 d, while there was no significant difference in the first flowering phenology of the other two plants. This may indicate that asymmetric warming (especially day and night) does not change the chilling and accumulated temperature processes of plants. Our research results provide empirical data and theoretical guidance for the implementation of future warming experiments on the Qingzang Plateau and the construction of phenological models.

Aims To accurately assess the impact of drought events on the function of forest carbon sinks, this study aims to assess the occurrence and persistence of the drought legacy effect across varying elevation gradients based on tree radial growth data.

Methods We selected Picea schrenkiana, a dominant conifer species in the Ili River Basin of the western Tianshan Mountains, Xinjiang, and quantified drought legacy effects on radial growth across three elevations (2 100, 2 300, and 2 500 m) using autoregressive integrated moving average (ARIMA) modeling. We compared the duration and magnitude of drought legacy effects in P. schrenkiana at different elevations and identified key drivers underlying this variation.

Important findings The results showed that (1) the radial growth of P. schrenkiana across all three elevations exhibited a significant positive correlation with the precipitation and Palmer Drought Severity Index (PDSI) of previous growing season, suggesting that drought stress strongly limited the radial growth of trees. (2) As elevation increased, the duration of drought legacy decreased. The drought legacy effect of P. schrenkiana persisted for 2 years at low elevation, but only for 1 year at middle and high elevation. The recovery and resilience of P. schrenkianato drought events at low elevation were lower than those at middle and high elevation. (3) The effect of drought legacy and the cumulative drought legacy followed the order: low elevation > middle elevation > high elevation, and the drought legacy effect of each elevation was greatest in the first year after the end of drought. After several drought disturbances, the cumulative drought legacy effect and the percentage of trees affected by drought legacy showed a pattern of initially decreasing and then increasing. Therefore, the recovery and resilience of trees to drought events as well as the frequency of droughts are all important factors contribute to the elevation-dependent variation in the P. schrenkiana drought legacy effect in the western Tianshan Mountains.

Aims Frequent drought events significantly influence plants’ growth and survival. However, it is not yet clear how the physiological and ecological characteristics of different alpine plants respond to droughts in different seasons.

Methods Based on a simulated seasonal drought experiment, this study quantified the antioxidants, osmo regulation substances, functional traits, and photosynthetic parameters of the leaves of eight typical alpine plants, and analyzed the effects of drought in different seasons on the antioxidants, osmo regulation system and photosynthesis of alpine plants.

Important findings Overall, we observed no significant response of plant leaf antioxidants to seasonal droughts, but interspecific differences were evident. Poa crymophila adapted to seasonal drought primarily through increased catalase (CAT) and peroxidase (POD) activities, whereas Stipa aliena and Carex przewalskii relied more on superoxide dismutase (SOD) activity (-25%-38%). Autumn drought increased the content of malondialdehyde (MDA) (32%-35%), while growing season drought significantly enhanced CAT activity (122%-161%). Plant leaf osmoregulatory substances responded significantly to seasonal droughts, with interspecific variations. The soluble protein content in the leaves of Poa crymophila increased by 73% under summer drought. Potentilla saundersiana increased by 47% during the drought of the growing season. The contents of proline and soluble sugar are sensitive to autumn drought and decrease by 36%-45%. The osmotic regulation-antioxidant system shows a significant positive correlation (proline content was negatively correlated with SOD activity; soluble protein content was positively correlated with POD activity), specific leaf area was negatively correlated with CAT activity, leaf dry matter content was positively correlated with proline content, and nitrogen to phosphorus ratio was negatively correlated with SOD activity. It is worth noting that photosynthesis and defense metabolism show a seasonally dependent trade-off: Under spring drought, the net photosynthetic rate (P_n) is negatively correlated with POD and CAT activities, and during autumn drought, P_n is significantly negatively correlated with proline content, revealing the seasonal dependence of resource allocation. This study proposed the framework of “seasonally specific defense strategies”, revealing the regulatory pathways by which alpine plants respond to seasonal drought through the synergistic changes in functional traits and physiological metabolic dynamics, providing a theoretical basis for the adaptive management of alpine grassland ecosystems under climate change.

Aims Exploring the interactions between non-structural carbohydrates (NSC) allocation patterns and photosynthetic properties of different age classes of Artemisia ordosica under drought stress can not only reveal the evolution of drought-resistant strategies during individual plant development but also provide theoretical support for predicting the dynamics of desert vegetation and formulating differentiated ecological restoration strategies in the context of climate change.

Methods Artemisia ordosica, a typical sandy plant in desert areas, was used as the research object. Four rainfall levels were set up through a field precipitation control experiment to simulate the normal (natural precipitation); mild drought (30% rainfall reduction); moderate drought (50% rainfall reduction); and extreme drought (70% rainfall reduction) conditions for A. ordosica. Based on its morphological characteristics, we classified the age classes of A. ordosica (low, medium, and high) and measured the photosynthesis-related parameters as well as the NSC content in leaves and twigs of plants from these different age classes.

Important findings Our main results showed that: (1) Mild drought did not affect photosynthetic carbon assimilation in A. ordosica, while moderate and extreme drought significantly suppressed it. (2) Artemisia ordosica dynamically replenishes photosynthetic losses through organ-specific partitioning of NSC. Twigs rapidly responded to mild drought stress through significant soluble sugar accumulation and starch depletion. During moderate to extreme drought conditions, twig starch reserves recovered substantially while leaf soluble sugars maintained accumulation, with osmotic regulation sustained through starch hydrolysis. (3) Structural equation modeling (SEM) analysis demonstrated that drought’s direct positive effects on twig and leaf NSC substantially counteracted the indirect photosynthetic inhibition effects, revealing this species’ survival strategy of actively modulating carbohydrates’ allocation through the non-photosynthetic pathways under drought stress.

Aims This study aims to analyze the characteristics of water sources and hydrological niche of coniferous pure plantations, broadleaf pure plantations, and mixed plantations across seasons under temperate semi-humid and semi-arid climatic conditions, and to investigate the water utilization strategy of different forest types, including water distribution and competition mechanisms, and thus, to provide a theoretical basis for optimizing forest structure during ecological restoration mountainous areas of Beijing, thereby accelerating the restoration of plantations.

Methods In this study, we selected pure and mixed plantations of representative species of Pinus tabuliformis and Quercus variabilis in Beijing mountainous regions. We collected precipitation, soil samples (0-100 cm), and xylem samples of P. tabuliformis and Q. variabilis, and analyzed the characteristics and dynamic changes of their hydrogen and oxygen stable isotopes composition (δ²H and δ¹⁸O). The MixSIAR model was employed to quantify the relative contributions of each water source to the plants, and the Levins index and the similarity proportion index was employed to assess the hydrological niche breadth and overlap. Concurrent environmental monitoring included atmospheric temperature, humidity, soil water content, and root distribution patterns to evaluate tree water source variations and associated niche differentiation.

Important findings During the dry season (March to May), pure stands of P. tabuliformis and Q. variabilis as well as Q. variabilis in mixed plantations, primarily utilized shallow soil water (0-40 cm); whereas P. tabuliformis in mixed plantations relied mainly on deep soil water (60-100 cm). In the early rainy season (June to July), P. tabuliformis and Q. variabilis in pure and mixed plantations mainly utilized middle-deep soil water. In the late rainy season (August to September), P. tabuliformis and Q. variabilis in pure and mixed plantations both shifted to mainly utilize shallow soil water (0-40 cm). During the whole study period, the hydrological niche widths of P. tabuliformis and Q. variabilis in pure plantations were lower than those in mixed plantations, and the niche widths of Q. variabilis in pure plantations and mixed plantations was slightly greater than that of P. tabuliformis. Notably, niche overlap between Q. variabilis and P. tabuliformis was lower in the dry season (March to May) compared to the rainy season (June to September), and temporal and spatial segregation of water use serves as a drought adaptation strategy to minimize interspecific water competition between P. tabuliformis and Q. variabilis.

Aims The type of photosynthetic pathway is an important driver for the divergence of growth rate among species, which may indirectly affect carbon assimilation capacity through water transport. However, there is still a lack of direct evidence as to whether divergence in growth rates among photosynthetic pathway types correlates to differences in hydraulic architecture.

Methods We used nine windbreak afforestation tree species from two photosynthetic pathway types (C₃ and C₄) as research objects, and determined parameters such as growth rate, hydraulic efficiency and vulnerability curves to analyze the correlations between plant growth rate and hydraulic traits with different photosynthetic pathways.

Important findings (1) Growth rates in plant height and basal diameter were significantly and positively correlated with xylem hydraulic conductivity, and growth rates of C₄ plants were affected by hydraulic conductivity to a greater extent than those of C₃ plants. (2) C₃ plants adopted trade-off between growth rates in plant height and basal diameter and hydraulic safety, while C₄ plants coordinated efficient hydraulic conductivity and embolism resistance, thus leading to fast growth. (3) Photosynthetic pathway types regulated the relationship between hydraulic efficiency and safety of tree species, showing that C₃ and C₄ plants adopted the strategies of trade-off and decoupling, respectively. (4) The hydraulic margin differed significantly among the nine tree species, which were all negative values. The study showed that hydraulic efficiency could predict the growth of tree species, and C₄ plants (Haloxylon ammodendron and Calligonum mongolicum) had both strong resistance to embolism and high growth rate, which could be used as the main silvicultural species for sand fixation forests.

Aims Numerous simulation experiments have shown that increased atmospheric acid deposition leads to enhanced soil microbial phosphorus limitation. However, there is a lack of in-depth analysis of how acid deposition affects microbial element limitation around industrial acid emission sources, especially in areas with severe soil salinity-alkalinity.

Methods Taking three power plants in the Ningdong Energy and Chemical Industry Base as the monitoring sites, this paper analyzed soil enzyme ecological stoichiometry and explored the microbial element limitation and its influencing factors around industrial acid element sources.

Important findings The results showed that the ranges of carbon-acquiring enzyme activity (C_E), nitrogen-acquiring enzyme activity (N_E), phosphorus-acquiring enzyme activity (P_E), ln C_E:N_E, ln C_E:P_E, and ln N_E:P_E were 3.31-59.92 nmol·g^-1·h^-1, 4.24-125.95 nmol·g^-1·h^-1, 3.62-189.46 nmol·g^-1·h^-1, 0.48-1.47, 0.32-1.41, and 0.56-1.18, respectively. Nitrogen and sulfur deposition did not affect the enzyme vector angle and length. Ca²⁺ and K⁺ deposition can positively affect the vector length either directly or indirectly by influencing soil physiochemical properties (electrical conductivity, available phosphorus content, Na⁺ content, Mg²⁺ content, etc.), plant traits (total phosphorus content and N:P), and microbial characteristics (biomass carbon and nitrogen content). Ca²⁺ and Na⁺ deposition indirectly positively affected the vector angle by influencing soil physiochemical properties and plant traits. In summary, microbes are mainly limited by phosphorus content in the study area; nitrogen and sulfur deposition did not alter microbial element limitation. In contrast, base cation deposition could enhance microbial carbon and phosphorus limitation by aggregating soil salt stress, reducing soil phosphorus availability, and triggering phosphorus competition between plants and microbes.

This study compares different methods for measuring inflorescence area in the Fabaceae (subfamily Papilionoideae), with the aim of providing methodological guidelines for research on plant functional traits and reproductive strategies. Five species of Papilionoideae were examined, and three measuring methods (fully unfolded area, column area, and projected area) were compared in terms of their differences and their correlations with carbon economics and physiological traits. The main findings are: (1) Inflorescence areas obtained by different methods followed the order: fully unfolded area > column area ≈ projected area. Linear regression revealed significant positive correlations across all pairs of area types. The conversion equations are: projected area (cm²) = 0.20 × fully unfolded area (cm²); projected area (cm²) = 0.67 × column area (cm²); column area (cm²) = 0.27 × fully unfolded area (cm²). (2) Both fully unfolded area and projected area showed significant positive correlations with inflorescence dry mass and total respiration rate, whereas column area was not significantly correlated with inflorescence dry mass, total transpiration rate, or total respiration rate. Projected inflorescence area can be measured easily and rapidly using image-based methods, making it a convenient and highly repeatable indicator. We therefore propose projected area as a standard measure for quantifying inflorescence area. By establishing conversion relationships among area indices and verifying the effectiveness of projected area in reflecting carbon investment and metabolic activity in reproductive organs, this study provides a practical approach for building trait databases and conducting comparative ecological analyses.