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, which seriously restricts or even threatens local ecological security and human social development. However, there is a lack of comprehensive assessment and analysis of the progress of research on the status and mechanisms of dryland forest decline on a global scale. Based on the extensive collection of relevant literature at home and abroad, we have systematically assessed and analyzed the concept, characteristics, current situation, influencing factors, and formation mechanisms of dryland forest decline. In terms of concepts and characteristics, we have summarized the concept, and the general characteristics of dryland forest decline. In terms of the current situation of forest decline, we have summarized the current situation of forest decline in global and Chinese dryland forests, and described the differences in dryland forest decline in regions, forest categories, and tree species. In terms of influencing factors, we have summed up the process of natural factors (climate change, biological invasions, site conditions, natural disasters) and anthropogenic factors (anthropogenic disturbances, anthropogenic management measures) influencing the decline of dryland forests. In terms of decline mechanisms, we have discussed the role of mechanisms at different scales (hydrodynamic failure hypothesis, carbon starvation hypothesis, biological attack hypothesis at individual scale; population-scale, community-scale like nutrient cycling, competitive effects; and ecosystem-scale) on dryland forest decline according to the research scales, and talked about the relationship between dryland forest decline mechanisms and the difficulties in the research. Based on these results, future research directions should focus on: (1) strengthening research on the ecological mechanisms of dryland forest decline at large scales; (2) strengthening the collection of long-term high-quality research data and systematically analyzing the integrated effects of multiple factors on dryland forest decline; and (3) strengthening integrated research on multiple mechanisms of dryland forest decline. We systematically reviews the current status and mechanisms of dryland forest decline, aiming to enhance the understanding of degradation mechanisms and provide theoretical support for ecological restoration practices in dryland.

Alfalfa (Medicago sativa L.) is a globally important perennial legume forage whose productivity and persistence are strongly constrained by water availability. Xylem vessels serve as the primary pathway for long-distance water transport, and their anatomical characteristics underpin the classical trade-off between hydraulic efficiency and embolism resistance. 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 functional significance 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 spatiial arrangement of xylem vessels, providing new insights into vessel spatial heterogeneity. This model characterizes vessel spatial configurations under physical exclusion and local interaction constraints using key parameters, including hard-core distance (h), interaction distance (R), and pairwise interaction strength (γ). Accumulating evidence suggests that xylem vessel spatial patterns in Alfalfa (Medicago sativa L.) 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 studies of xylem vessel spatial distribution in alfalfa, discusses the potential bet ween vessel spatial configurations and hydraulic trade-offs, and summarizes vessel network plasticity in response to drought, salinity, and nutrient availability. Furthermore, we highlight recent progress in the molecular regulation of vessel development and outline future directions integrating three-dimensional imaging and multi-omics approaches to better understand the ecological significance of xylem spatial organization.

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 (P < 0.05) and decreased spring germination percentage (P < 0.05), the proportion of winter-germinated significantly increased (P < 0.05), while the total germination percentage declined (P < 0.05). (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 (P < 0.001). 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 (P < 0.05). (3) As the temperature at sites of origin increased, the total germination percentage significantly decreased (P < 0.001), and the proportion of winter-germinated significantly increased (P < 0.001). 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 The objective of this study was to explore the initial response of leaf litter production and its carbon, nitrogen, and phosphorus restitution of Cunninghamia lanceolata plantation forests in the rain area of Western China to multiple levels of nitrogen addition. Methods A short-term N addition manipulation experiment with seven levels (0 kg·hm-2·a-1; 10 kg·hm-2·a-1; 20 kg·hm-2·a-1; 40 kg·hm-2·a-1; 80 kg·hm-2·a-1; 120 kg·hm-2·a-1; and 160 kg·hm-2·a-1) was conducted to examine the effects of N addition on leaf litter production, concentrations of leaf litter carbon (C), N, and phosphorus (P), as well as their return within C. lanceolata plantation forests located on the rain area of Western China. Important findings (1) The annual litterfall production of C. lanceolata ranged from 2595.88 to 3043.98 kg·hm-2·a-1, with a bimodal monthly dynamic pattern peaking in May and August. Low nitrogen additions (N10, N40) significantly promoted the withered leaf yield, but from N80 onwards, its promotion was significantly weakened until it turned to inhibition (N120, N160). (2) The mean annual C, N, and P contents of C. lanceolata litterfall were 313.89-498.12, 10.17-22.03, and 0.13-0.30 g·kg⁻¹, respectively. the carbon content of C. lanceolata withered leaves declined with the increase of the leaves of nitrogen addition, and the nitrogen and phosphorus contents showed the opposite trend. (3) The mean annual C, N, and P return of C. lanceolata litterfall ranged from 1032.91–1205.09, 43.61–36.85, and 0.50–0.61 kg·hm-2, respectively, and the carbon, nitrogen and phosphorus return was mainly regulated by yield. The short-term study showed that low N additions significantly increased the yield and carbon, nitrogen and phosphorus restitution of cedar plantation forests, while high N additions showed some negative effects, and 80 kg-N-hm-2-a-1 was the response threshold of N additions in C. lanceolata plantation forests in the West China rainforest area.

Aims Increased atmospheric nitrogen (N) deposition leads to changes in the proportion of different forms of N input in 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, stoichiometric ratios, and biomass, were evaluated for their differences among N treatments and to investigate the relationship between leaf traits with sensitive plasticity in response to nitrogen treatments and growth. Important findings All three forms of N additions were found to reduce leaf 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 (PPI≥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 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 (PARf), direct photosynthetically active radiation (PARd), air temperature (Ta), 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%. PARd decreased dramatically following the decline in CI, while PARf changed only slightly. Since PARf directly enhanced NEP, it offset the suppression caused by the decline in total PAR. PARf and PARd are the major influencing factors of GPP, controlling its variation under clear and cloudy skies, respectively. Ta was the most controlling factor of ER, determining its variation under clear skies, while Ta, VPD, and VWC jointly controlled ER under cloudy skies. GPP and NEP peaked at moderate radiation (PAR=1 300–2 000μmol·m-2·s-1) and moderate CI (=0.3–0.5), while ER was maximized at high radiation levels (PAR=2 300μmol·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 The aim of this study is 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 Province, and the method of field investigation and sampling and germination experiment was adopted. Important finding A study found that a total of 82 plant species belonging to 31 families and 64 genera were counted in the aboveground vegetation of 6 typical shrub groups. The life form of the species is mainly composed of perennial herbaceous plants, followed by shrubs, and the proportion of annual plants is relatively low; The species richness of the tiger hazelnut community is the highest and the distribution is relatively uniform, while the species richness of the thorn spiral flower community is the lowest and the distribution is uneven. There are a total of 43 plant species in the soil seed bank 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 1033.33 ± 57.74 (grains/m2) -7000.00 ± 200 (grains/m2). The soil seed density is highest in the community of mutual leaved drunken fish grass, and lowest in the community of spiny spiral flowers; 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 tiger hazelnut and mutual leaved drunken fish grass communities is the highest, while the thorn spiral flower community is the lowest. The vegetation on the ground of six typical shrub groups is higher in terms of plant species and quantity than in the soil seed bank, and the uneven distribution of plant species in the soil seed bank is more pronounced than in the above ground vegetation. The similarity between aboveground vegetation and soil seed banks 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 tiger hazelnut community 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 Investigating the species diversity of naturally regenerated understory vegetation in different exotic plantations within the National Park of Hainan Tropical Rainforest, and identifiy the dominant factors affecting variation in species composition. Methods A total of 173 plots (20×20 m) were established in Mt.Jianfengling section of National Park of Hainan Tropical Rainforest, including three exotic plantation types (Eucalyptus urophylla, Acacia mangium, and Pinus caribaea) and natural tropical lowland rainforests. In each plot, all woody individuals with a diameter at breast height (DBH)≥1cm were surveyed and environmental variables were sampled. The non-parametric tests (Kruskal-Wallis and Dunn’s test) were applied to compare stem density, basal area, and species richness across three DBH classes. Dominant species were identified based on importance value, and indicator species were identified using Indicator Species Analysis (ISA). Variation in species composition among forest types were examined by using similarity analysis and nonmetric multidimensional scaling (NMDS). Permutation tests were conducted to assess the effects of different varied environmental factors on variation in community composition. Important findings Eucalyptus urophylla plantations had the lowest species richness (30 ±1 species) but the highest stem density (392 ±13 individuals). In contrast, the species richness (47±1 and 42±1 species) and stem density (291±16 and 262±12 individuals) of A. mangium and P. caribaea plantations did not differ significantly from those of natural forests (54±3 species, 214±31 individuals). Naturally regenerated vegetation understory of plantations generally lacked large-diameter individuals (DBH≥10 cm). The understorey of E. urophylla plantations was dominated by Alchornea rugosa, whereas A. mangium and P. caribaea plantations had no particularly dominant species. Species composition differed significantly among forest types: E. urophylla plantations showed the lowest similarity to natural forests, while A. mangium and P. caribaea plantations exhibited greater similarity but still differed notably from natural forests. Soil pH, total nitrogen, total available phosphorus, available potassium, elevation, stand age, and basal area of planted species were the main environmental drivers to determine species composition . Conclusion For exotic species plantations in the National Park of Hainan Tropical Rainforest, future management should prioritize optimizing stand structure and promoting the growth and succession of small diameter individuals of native species to facilitate their transition into larger size classes. Given the variation in natural regeneration among plantation types, specific restoration strategies should be developed for each forest type.

Aims The existence of dry valleys in the Three Parallel Rivers Area causes the interruption of vegetation belts, i.e., the "vegetation inversion" phenomenon, making it necessary to conduct a refined extraction of the vegetation vertical belts in this region. Despite extensive discussions on the vegetation distribution in this area, existing studies are often limited by data precision and extraction methods, failing to fully reveal the refined characteristics of vegetation vertical belts. Methods Based on the DEM-NDVI algorithm, combined with Landsat 8 OLI image data and NASADEM data, this study carried out a refined extraction of the vegetation vertical belts in the dry valleys of the Three Parallel Rivers area, and verified the accuracy of the algorithm to update the vegetation vertical belts in this region. Important findings 1)The spatial distribution characteristics of vegetation vertical belts at three different sections were determined, and the NDVI threshold values for the upper limits of each vegetation vertical belt at the north section were 0.61, 0.43, 0.10, at the middle section were 0.78、0.46、0.07、-0.05, and at the south section were 0.78、0.55、0.43；2)The width of the subtropical dry valley shrub-grassland belt, which serves as the base belt, gradually increased from the south section's 795m to the north section's 1161m. The width of the forest belt, which is the dominant vertical belt in the Three Parallel Rivers area, showed the opposite trend, gradually decreasing from south to north. The width and distribution area of the subalpine cold temperate shrub meadow belt and the alpine cold temperate sparse cushion vegetation belt in the study area were relatively narrow and small；3)The minimum altitude error of vegetation vertical zone extracted by DEM-NDVI algorithm is 3m, and the maximum altitude error is 43m, indicating high accuracy.This study provides basic data support and a reliable method for related fields, contributing to the advancement of research on mountain vegetation vertical belts.

Abstract 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 determinethe 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 the Tibetan 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. Important findings The main findings are that temperature is the main factor affecting the 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 all 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 days, while there was no significant difference in the 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 Tibetan Plateau and the construction of phenological models.

Aims In order to accurately assess the impact of drought events on the function of forest carbon sinks, this paper explores the occurrence and persistence of the drought legacy effect at different altitude gradients based on tree radial growth data. Methods In this paper, we take Picea schrenkiana as the dominant tree species in the Ili River Basin in the western Tianshan Mountains of Xinjiang, quantify the drought legacy effect of Picea schrenkiana at different elevations (2100, 2300 and 2500 m a.s.l.) by using ARIMA.We compared and analysed the differences in the duration and degree of the drought legacy effect of Picea schrenkiana at different altitudes, and revealed the changing law of the drought legacy effect of Picea schrenkiana at different altitudes and its driving factors. Important findings The results showed that (1) the radial growth of Picea schrenkiana at all three elevations was significantly positively correlated with the precipitation and PDSI of last year's growing season, suggesting that drought stress strongly limited the radial growth of trees. (2) With the increase of elevation, the duration of drought legacy decreased. The drought legacy effect of Picea schrenkiana existed for 2 years at low elevation, but only existed for 1 year at middle and high elevation. The recovery and resilience of Picea schrenkiana to drought events at low elevation were lower than those at medium and high elevation（P＜0.05）..(3) The effect of drought legacy and the cumulative drought legacy are low elevation＞middle elevation＞high elevation,and the drought legacy effect of each elevation was the greatest in the first year after the end of drought.After several drought disturbances, the cumulative drought legacy effect and the percentage of trees with drought legacy effect showed a tendency of decreasing and then increasing.Therefore, the recovery and resilience of trees to drought events and the frequency of droughts are all important factors that contribute to the elevation differences of the Picea schrenkiana drought legacy in western Tianshan.

Aims Frequent drought events have significantly influenced the growth and survival of plants. 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 investigated the antioxidants, osmotic 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 antioxidant and osmotic regulation systems and photosynthesis of alpine plants. Important findings Our results showed that: Overall, the response of plant leaf antioxidants to seasonal droughts was not significant, 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 the plant 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 (36-45%). There is a synergistic mechanism among the systems, and the osmotic regulation - antioxidant system shows a significant correlation (proline content and SOD: r = -0.19**;) Soluble protein and POD: r = 0.128*), specific leaf area was negatively correlated with CAT activity (r = -0.14*), leaf dry matter was positively correlated with proline content (r = 0.18**), and N/P was negatively correlated with SOD (r =-0.18**). It is worth noting that photosynthesis and defense metabolism show a seasonally dependent trade-off: Under spring drought, the net photosynthetic rate (Pn) is negatively correlated with POD and CAT (r = -0.41*, -0.35*), and during autumn drought, Pn is significantly negatively correlated with proline (r = -0.39*), 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 interaction of 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 cannot 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 A. ordosica, a typical sandy plant in desert areas, was used as the research object. Four rainfall gradients 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) A. 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 (β=0.78 and 0.90, respectively) substantially counteracted the indirect photosynthetic inhibition effects (β=-0.87 and -0.27), revealing this species' survival strategy of actively modulating carbohydrates’ allocation through the non-photosynthetic pathways under drought stress.

Aims Analyze the characteristics of water source and hydrological ecological status of coniferous and broad-leaved pure plantation and mixed plantation in different seasons under the temperate semi-humid and semi-arid climatic conditions, and to investigate the water utilization strategy of vegetation in different types and the distribution and competition mechanism of water, so as to provide theoretical basis for the optimization and regulation of forest structure in the process of ecological restoration of the mountainous areas of Beijing, and then accelerate the restoration process of the plantation and the ecosystems. Methods In this study, we selected pure and mixed plantations of representative species of Pinus tabuliformis and Quercus variabilis in Beijing mountain area as research objects. We collected precipitation, soil samples from 0-100 cm, and samples of the xylem of P. tabuliformis and Q. variabilis, and analyzed the characteristics and dynamic changes of their δ2H and δ18O. The MixSIAR model was employed to calculate the relative contribution of each water source to the plants and Levins index and the similarity proportion index was employed to calculate the hydrological ecological niche breadth and overlap. Simultaneously, the study monitored atmospheric temperature, humidity, water content of soil, and root distribution to analyze the changes in tree water sources and their hydrological ecological niches. Important findings In the dry season (March to May), pure plantations of P. tabuliformis and Q. variabilis as well as mixed plantations of Q. variabilis mainly utilized the shallow soil water (0-40 cm); while mixed forests of P. tabuliformis mainly utilized the deep soil water (60-100 cm). In the first part of the rainy season (June to July), P. tabuliformis and Q. variabilis in pure and mixed plantations mainly utilized the middle-deep soil water. In the later part of the rainy season (August to September), P. tabuliformis and Q. variabilis in pure and mixed plantations both shifted to mainly utilize the shallow soil water (0-40 cm). During the whole study, the widths of the hydrological ecological niches of P. tabuliformis and Q. variabilis in pure plantation were both less than those in mixed plantation, and the width of the hydrological ecological niches of Q. variabilis in pure plantation and mixed plantation was slightly greater than that of P. tabuliformis. The over-lapping degree of the hydrological ecological niches of Q. variabilis and P. tabuliformis was lower in the dry season (March to May) compared in rainy season (June to September), and P. tabuliformis and Q. variabilis responded to drought stress by separating the time and space of water use, niche separation, to weaken the competition for water.

Aims The type of photosynthetic pathway is an important driver of growth rate divergence between species, and its differences may indirectly affect carbon assimilation capacity through water transport. However, there is still a lack of direct evidence as to whether photosynthetic pathway types diverge in growth rates due to dif-ferences in hydraulic structure. Methods We used nine windbreak afforestation tree species of two photosynthetic pathway types (C₃ and C₄) as research subjects, and measured parameters such as growth rate, hydraulic efficiency and vulnerability curve to analyse the correlation between the growth rate and hydraulic traits of plants with different photosynthetic pathways. Important findings (1) Plant height and basal diameter growth rates were significantly and positively corre-lated with xylem hydraulic conductivity, and growth rates of C₄ plants were more affected by hydraulic con-ductivity than those of C₃ plants. (2) C₃ plants adopted trade-off between plant height and basal diameter growth rate and hydraulic safety, while C₄ plants achieved synergy between efficient hydraulic conductivity and em-bolism resistance. (3) Photosynthetic pathway types regulated the relationship between hydraulic efficiency and security of tree species.C₃ and C₄ plants respectively adopted the strategies of trade-off and decoupling. (4) The interspecific differences in the hydraulic safety boundaries of the nine tree species were significant,and all the hydraulic safety boundaries were 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 could lead to the increase of phosphorus limitation of soil microbes. 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 emission 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), lnC:N_E, lnC:P_E, and lnN:P_E were 3.31~59.92 nmol·g^⁻1, 4.24~125.95 nmol·g^⁻1, 3.62~189.46 nmol·g^⁻1, 0.48~1.47, 0.32~1.41, and 0.56~1.18. Nitrogen and sulfur deposition did not affect the enzyme vector length and angle (p > 0.05). Ca²⁺ and K⁺ deposition positively influenced the vector length (p < 0.05) by a direct approach or by indirect approaches, soil physiochemical properties (electrical conductivity, available phosphorus, Na⁺, Mg²⁺, etc.), plant traits (total phosphorus and N:P) and microbial characteristics (biomass carbon and nitrogen). Ca²⁺ and Na⁺ deposition positively influenced the vector angle (p < 0.01) by affecting soil physiochemical properties and plant traits. In summary, microbes are mainly limited by phosphorus in the study area; nitrogen and sulfur deposition does 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.

Aims This study compares different inflorescence area measurement methods in Fabaceae (subfamily Papilionoideae), aiming to provide methodological references for studies on plant functional traits and reproductive strategies.
Methods Five species of Papilionoideae were selected as research subjects, and the differences among three measurement methods—fully unfolded area, column area, and projected area—were measured and analyzed, along with their correlations with carbon economics and physiological indicators.
Important findings The results demonstrate that: (1) Inflorescence areas obtained by different measurement methods is in the order of fully unfolded area > column area ≈ projected area. Linear regression reveals a significant positive correlation between any two types of areas (p < 0.001). The conversion equation for different areas is: 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 show significant positive correlations with inflorescence dry weight (p < 0.001; p = 0.006) and total respiration rate (p < 0.001; p = 0.006), whereas column area exhibits no significant correlation with inflorescence dry weight, total transpiration rate, or total respiration rate (p > 0.05). Projected inflorescence area can be measured easily and quickly using image-based methods, making it a convenient and highly repeatable indicator. We therefore recommend projected area as the preferred standard for quantifying inflorescence area. By establishing the conversion relationships between different area indices and verifying the effectiveness of projected area in representing carbon investment and metabolic activity in reproductive organs, this study provides a viable pathway for building trait databases and conducting comparative ecological analyses.