Aimd gradual global warming and drying up, forest fires not only drive changes in the structure and function of forest ecosystems, but also affect the physiology and growth of trees. The thermal damage caused by forest fires can trigger a series of complicated physiological responses in trees. Revealing the response mechanisms of postfire tree physiology can guide the further understanding of the carbon–water relationship and how it influences the postfire growth recovery limitations of trees. Furthermore, the accuracy of tree mortality prediction after fires must be improved. Starting with a description of the pathways in which forest fires affect trees, this review elaborates on the damage caused by different forms of forest fires (canopy, surface, and ground fires) on various parts of trees (crowns, trunks, and roots). In particular, this review discusses the direct and indirect effects of forest fires on tree physiology and the tree physiology–abiotic/biotic interactions after fires. Cambium and phloem necrosis and xylem hydraulic dysfunction are the main response mechanisms of postfire tree physiology. The two physiological functional limitations—carbon starvation and hydraulic failure—caused by the two aforementioned mechanisms seriously affect the carbon–water relationship of trees, further influencing the growth recovery of trees or their delayed death after fires. The physiological mechanisms of trees after fires are also closely related to drought, insect attack, microbial invasion, and other factors. The quantitative analyses of forest fire intensity and the accurate judgment of the plant tissue death threshold are urgent tasks, and the interaction of tree physiology with the functional traits of trees and other factors after fires must be explored. Accurately evaluating the relationship between tree physiological mechanisms is crucial in fully understanding how forest fires affect the tree functional integrity of trees and contributes to the improvement of forest fire risk assessments and mortality model predictions. In the context of high-frequency and high-intensity forest fires driven by future climate warming and drying, a profound understanding of tree physiological responses can also enhance the study of the dynamics of postfire ecosystems and their interrelationships with climate factors.

The light response curve of photosynthetic electron flow is an important tool to investigate plant physiology and ecology. It can provide a theoretical basis for quantifying the absorption and transmission of light energy in primary reaction. In this paper, the mathematical characteristics, the advantages, and the potential weaknesses in practical application and research trends of the light response models of photosynthetic electron flow are reviewed and discussed. The primary reaction, which includes absorption of light energy, excitation and de-excitation of photosynthetic pigment molecules (including photochemical reaction, fluorescence emission and heat dissipation), and electron flow (J) steming from charge separation in the PSII reaction center caused by exciton resonance, is consisted by a series of complex physical and biochemical reactions. The classical and semi-mechanistic models of light response curve of photosynthetic electron flow are difficult to explain the dynamic down-regulation of PSII, light adaptation and light protection of algae and plant because they did not involve or only partly involved the primary reaction process. However, the mechanism model takes into account the important role of the physical parameters of the photosynthetic pigment molecule (e.g., the eign-absorption cross-section of light energy(?ik), the average lifetime of the molecule in the lowest excited state (?min), the energy level degeneracy of the molecule and the number of photosynthetic pigment molecules in the excited state (Nk)) in the whole primary reaction process, it can not only obtain the Jmax and PARsat of algae and plant, but also get some important physical parameters such as ?ik and ?min. Meanwhile also it can obtain the laws about light-response of the effective light energy absorption cross-section ( ) and of Nk. It may be the development direction of the mechanism model of photosynthetic electron flow response to light in the future when the mechanistic model was coupled with some environmental factors (e.g., temperature and CO2 concentration) and the relationship between light intensity and and Nk were determined.

Aims Nei Mongol is an important ecological security barrier in northern China, and the study of changes in its vegetation productivity is of great significance to the ecological security of the northern region. Methods Based on multi-source remote sensing data such as Eddy Covariance-Light Use Efficiency Gross Pri-mary Productivity (EC-LUE GPP) in Nei Mongol from 1982 to 2017, this paper uses trend analysis and correlation analysis to analyze the temporal and spatial variation characteristics of vegetation gross primary production (GPP) in Nei Mongol and its correlation with air temperature, precipitation and soil moisture. On this basis, multiple linear regression and residual analysis methods were used to decompose and quantify GPP under the influence of climate changes and human activities, divide different time periods to carry out its impact on vegetation GPP, and explore the impact of different vegetation types on the driving factors response. Important findings (1)Three meteorological elements showed good correlation with vegetation GPP, among which precipitation and soil moisture had higher correlations with GPP. (2)During the period 1982-1990, vegeta-tion GPP showed an insignificant fluctuation and increased, with an average annual increase of 1.8333 g C·m–2·a–1, and the remaining three time periods (1991-2000、2001-2010、2011-2017) showed an insignificant downward trend, with annual average decreases of 1.2967 g C·m–2·a–1、-0.2356 g C·m–2·a–1、3.6589 g C·m–2·a– 1. The areas with an overall downward trend accounted for 55% of the total area, and the other 45% showed a significant upward trend; (3)Except for the period from 2001 to 2010, climate changes played a decisive role in vegetation restoration in the other three time periods (1982-1990, 1991-2000, and 2011-2017), explaining 20%, 16% and 13% of veg-etation restoration, respectively; Human activities dominated vegetation degradation areas, with 13%, 19% and 20% explaining vegetation degradation, respectively. The research results can provide scientific reference for the implementation of ecological environmental protection and management policies and green and sustainable de-velopment in Nei Mongol.

Aims Populations are the basis for the formation and development of the structure and function of grassland ecosystems. However, long-term grazing accompanied by global climate change profoundly affects the growth and reproduction of populations. Stipa bungeana is a dominant species in typical steppe of the Loess Plateau and has a high ecological and economic value. Methods Therefore, this study was conducted to investigate the effects of grazing and nitrogen (N) addition on the growth of Stipa bungeana. It was based on the platform of a long-term rotational sheep grazing experiment in a typical steppe of the Loess Plateau, using a completely randomized split-plot experimental design with stocking rate (0, 2.7, 5.3, 8.7 sheep·hm–2) as the main factor and N addition levels (0, 5, 10, 20 g·m–2) as the secondary factor. Morphological traits, aboveground biomass, community status and the relationship between them in Stipa bungeana were used to investigate the effects of stocking rate, nitrogen (N) addition and their interaction. Important findings With the increase of stocking rate, the plant height, canopy diameter, tiller number, seedlings, aboveground biomass and ration of aboveground biomass showed a “single peak” curve trend, and the population density decreased. nitrogen (N) addition increased the plant height, canopy diameter, reproductive branch density, tiller number, aboveground biomass and ratio of aboveground biomass, the seedlings increased and then decreased with the increase of nitrogen (N) addition. The total effect of grazing on aboveground biomass and ratio of aboveground biomass was small compared with that of nitrogen (N) addition. In concrete terms, grazing had a direct negative effect on aboveground biomass and affected its ratio of aboveground biomass by regulating tiller number, population density and aboveground biomass. nitrogen (N) addition not only had a direct positive effect on aboveground biomass, but also had an indirect positive effect through plant height, reproductive branch density, and also had an impact on ratio of aboveground biomass through regulating population density, canopy diameter, tiller density and reproductive branch density. Overall, nitrogen (N) addition increased canopy diameter and reproductive branch density and grazing increased seeding, while the interaction of grazing and nitrogen (N) addition significantly affected reproductive branch density. Stipa bungeana had optimal aboveground biomass or community status at stocking rate of 4.10 sheep?hm-2 or 5.29 sheep?hm-2. The results indicated that grazing and nitrogen (N) addition regulated the aboveground biomass and community status of Stipa bungeana through influencing it's morphological characteristics, which provides a basis for the scientific management and sustainable development of grassland populations.

Aim Physiological responses at the leaf level are limited by the underlying anatomical structure, which has a deeper interpretation of plant physiological mechanisms. Quantitative analysis of the response of plant anatomy to human disturbance such as grazing in desert steppe is of great theoretical value to reveal the ecological adaptation mechanism of fragile ecosystem to harsh environment. Methods Beta In this study, the leaves of C. songorica, the dominant species in desert steppe under different grazing intensities (CK, LG, MG, HG) were used as experimental materials to make paraffin sections, and 13 anatomical indexes including protective tissue, vascular tissue and Kranz structure area related to photosynthesis were measured. Comparative analysis was made between different grazing intensities. Important findings The results showed that: (1) the cuticle thickness, as well as the ratio of cuticle thickness to leaf thickness first decreased and then increased with the increase of grazing intensity; (2) In terms of vascular tissue, the area of vascular bundle, vessel area and phloem area were firstly increased and then decreased with the increase of grazing intensity. The thickness of motor cells and xylem area first decreased and then increased with the increase of grazing intensity. Compared with control and moderately heavy grazing areas, the thickness of motor cells in lightly grazing areas decreased significantly (P<0.05). In terms of vascular tissue proportion, the ratio of xylem to vascular bundle area increased with the increase of grazing intensity, while the dominant vessel to vascular bundle area ratio decreased with the increase of grazing intensity. The phloem area increased first and then decreased with the increase of grazing intensity. Compared with the control area, the phloem area in the three grazing areas decreased significantly (P<0.05); (3) The area of Kranz structure increased with the increase of grazing intensity. Compared with the control area, the area of Kranz structure in the three grazing areas was significantly increased (P<0.05);

Aims Old trees not only record the climate and environment change information, but also witness the history of social changes. Understanding the history of growth change and disturbance of old trees is useful to accurately assess the health of old trees in the context of global warming and to develop conservation plans. Methods We used tree-ring ecology methods to analyze the disturbance history of the old tree (Pinus tabulaeformis) in the Xishan mountain of Beijing. Important findings There were five major growth suppression (1830–1837, 1855–1869, 1881–1891, 1920–1930 and 1960–2000) and release events (1820–1830, 1869–1881, 1909–1918, 1947–1959, 1960–1970 and 1980–1986). The response analysis of tree growth to climate factors and the historical data showed that drought events and subsequent climatic improvement were the main reasons for growth suppression and release events. Further studies showed that the average growth rate of old trees was 2.70 mm·a–1 before 1840, and then the growth gradually decreased. After 1980, there was an obvious growth suppression, and the annual average growth rate decreased to 0.38 mm·a–1. A stronger negative correlation between tree growth and temperature emerged after 1965, and a significant positive correlation emerged for Palmer Drought Severity Index (PDSI). These results suggest that the warming and drying trend in Beijing in recent years may further negatively affect old trees in the urban area. These results are helpful for further understanding the regularity of forest disturbance in Beijing area during historical period, and are of great significance for accurately assessing the health status of elderly trees under the background of climate change.

Species diversity is a crucial component of biodiversity. Changes in species diversity during forest succession directly affect ecosystem function and stability. Therefore, it is of significant importance to investigate the changes in species diversity and their influencing factors during forest succession for accurately predicting forest ecological processes and biodiversity patterns.The study focused on Betula platyphylla forest (early succession period), Betula platyphylla-Larix gmelinii mixed forest (middle succession period) and Larix gmelinii forest (late succession period) in the northern Da Hinggan Mountains as the research objects. The study employed a space instead of time to analyze the changes in species diversity during forest succession and explore the relationship between species diversity and envi-ronmental factors in cold temperate zone of China.The results demonstrated that: (1) Species richness and diversity significantly increased during forest succes-sion. Two indices including Margalef richness index and Shannon-Wiener index were 2.42 and 2.689 at the beginning of succession, and 5.90 and 3.432 at the end of succession. However, there was no significant dif-ference in the species Pielou evenness index. (2) During the forest succession process , the similarity of plant communities gradually decreased and the differences gradually increased.. The Jaccard index, Sorenson index and Bray-Curtis index all decreased. (3) During the forest succession process, soil pH, soil organic matter, total nitrogen, and total phosphorus significantly influnence the species diversity index. Specifically, total nitrogen and total phosphorus were the primary factors affecting species diversity in the pre-middle period of succession, while soil pH and soil organic matter were the dominate factors influencing species diversity in the later period of succession. (4) With the progression of succession, the influence of stand spatial structure on species diver-sity gradually increased. Angular scale and size ratio are the main spatial structure factors influencing species diversity during forest succession. Consequently, soil factors played a prominent role in species diversity during forest succession in the northern Da Hinggan Mountains, the driving effect of stand spatial structure on species diversity in the process of forest succession can not be ignored.

Aims The variation patterns and correlations of leaf functional traits have always been a key aspect in unraveling how plants respond to climate change. However, the similarities and differences in the variation and correlation of leaf structural traits and photosynthetic physiological characteristics among different growth types of broadleaf plants remain unclear. Methods This study focused on 18 dominant or common broadleaf plants in a mixed broadleaved-Korean pine (Pinus koraiensis) forest. We measured four structural traits (leaf area (LA), leaf thickness (LT), leaf dry matter content (LDMC) and leaf mass per area (LMA)) and four photosynthetic physiological traits (chlorophyll value (SPAD), intercellular CO2 concentration (Ci), stomatal conductance (Gs) and net photosynthetic rate (Pn)). We analyzed the variation and correlations of leaf structural traits and photosynthetic physiological traits among different growth types of broadleaf plants. Important findings The variation range of leaf functional traits was between 7.73% and 74.54%. Inter-specific variation was the main source of variation for LA and LT, while growth type drived the variation in Ci, SPAD, LDMC, and LMA. Gs and Pn variation mainly originate from intra-specific variation. There were significant differences in leaf functional traits among different growth types. Specifically, herbs showed significantly higher LA, LT, and Ci compared to shrubs and trees, while trees exhibited significantly higher LMA, LDMC, SPAD, Pn, and Gs compared to both shrubs and herbs (p < 0.05). There was a significant isometric relationship between Pn and LMA, LDMC among different growth types, with slopes greater than 1, while SPAD with LA, LT, LDMC, LMA, Ci with LT, LDMC, LMA showed slopes less than 1, indicating allometric growth relationships. Herbs adopted a resource-acquisitive strategy, while relatively, trees adopted a resource-conservative strategy, shrubs adopt an intermediate strategy between trees and herbs, possibly linked to the light conditions in the environments inhabited by different growth types of plants. The study of the variation and interactions between leaf structural traits and photosynthetic physiological characteristics is crucial for understanding resource acquisition and allocation mechanism in plants.

Aims Revealing the response patterns of soil bacterial community to changes in vegetation type during secondary succession can improve our understanding of the mechanisms that structure the above- and below-ground interactions in ecosystems. Methods To investigate how soil bacterial diversity, taxa network structure and biomarkers shift with vegetation succession, this study measured soil carbon, nitrogen and phosphorus contents, as well as soil bacterial communities across shrubland, deciduous broad-leaved forest and evergreen broad-leaved forests, representing the early- middle- and late-successional stages, respectively, on Dajinshan Island, Shanghai. Important findings Soil nutrient contents were significantly higher in evergreen broad-leaved forest than in deciduous broad-leaved forest. However, soil bacterial diversity was significantly higher in deciduous broad-leaved forest than in evergreen broad-leaved forest, while soil nutrient content and bacterial diversity were medium in deciduous shrubland. The correlation network nodes, density and complexity of soil bacteria were highest in deciduous broad-leaved forest, medium in deciduous shrub, and lowest in evergreen broad-leaved forest. The dominant soil bacteria in deciduous shrubland and broad-leaved forest was Rhizobiales and Burkholderiales, respectively, which belong to functional group of nitrogen-fixing. The dominant soil bacterial in evergreen broad-leaved forest were characterized by functional groups of pathogenicity and resistance such as Xanthomonadales and Thermogemmatisporales, and functional group associated with cellulose degradation such as Acidobacteriales. These results suggest that changes in plant species composition and soil nutrient availability during island vegetation succession can greatly reshape species diversity, community composition, interactive network structure and biomarkers of soil bacteria. In evergreen broad-leaved forest, lowered soil bacterial diversity, simplified bacterial network structure, and emerged biomarkers of functional groups of pathogenicity and resistance suggest a response of belowground to the degraded trend of aboveground in the studied climax forest.

The valley forest in the Ertix River basin is the germplasm bank of Salicaceae species and has important genetic diversity value of Altay Prefecture, Xinjiang Uygur Autonomous Region. It is of great significance for the protection and utilization of precious resources to study the distribution of plant species and vegetation types under the current human activities such as climate change, hydropower project and grazing. In this paper, 80 squares of 20 plots were investigated at 4–8 km intervals in the Burqin River, Haba River and Bilizik River, the constructive species, quantitative characteristics and diameter class structure of the community were analyzed, and the community types were classified. The results showed that, (1) 121 species, 34 families and 91 genera of plants were investigated in the main tributaries of the Irtysh River basin, with a large number of perennial herbaceous plants. (2) Betula pendula and Populus laurifolia were constructive species in Burjin River and Haba River, while Populus alba was constructive species in Bilizik River. Populus nigra, Populus × berolinensis var. jrtyschensis, and Populus canescens are associated species, while Salix alba is mainly distributed alone along the riparian edge and rarely mixed with poplar species. (3) The number of individuals of the dominant tree species Betula pendula reached the maximum at the middle elevation of the three tributaries, while the number of individuals of Populus laurifolia was smaller at the middle elevation. (4) The diameter class structure of tree layer species was greatly affected by grazing in summer, and the individuals of large diameter class were the most, and the number of saplings and seedlings were less. (5) The valley forest communities were divided into 6 formations and 26 associations.