Tropical rain forests are currently distributed in the southeastern Xizang, southern Yunnan, southern Guangxi, southern Taiwan, and Hainan Island in China. The ecological physiognomy, species composition and diversity of the tropical rain forests were reported in literatures, however with different terms for different regions of China, due partly to different methods, definitions and references used. In this review article, we summarize current research status and main questions on the phytosociological characteristics of the tropical rain forests in China, to provide information for further studies, protection and management. The lowland tropical rain forests in China belong to the northern marginal type of the southeastern Asian lowland rain forests, and share the similar community structure, physiognomy, and species diversity with other subtypes of the southeastern Asian lowland rain forests. Distributed in the northern edge of the monsoonal tropical zone, the lowland tropical rain forests in China are limited by seasonal drought and insufficient amount of heat, which is usually demanded by typical tropical rain forests, and therefore were given the name “tropical seasonal rain forest” by Chinese researchers. They are different from the typical humid or wet tropical rain forests in that they include a certain proportion of deciduous trees in canopy, less megaphanerophytes and epiphytes, but more lianas and microphyllous species in tree leaf sizes. The tropical rain forests in China show different floristic composition in different regions. Specifically, they contain less typical tropical floristic components, and show a transition to the tropical lower montane forests in southwestern China, and to the subtropical evergreen broad-leaved forests in south China. They show similar community structure and ecological physiognomy in Yunnan and Guangxi. Furthermore, the tropical seasonal rain forest in Yunnan contains dipterocarp trees and has the highest proportion of tropical Asian floristic components among the tropical rain forests in China and show the similar community structure characteristics as the lowland tropical rain forests in the Southeast Asia, although occurring on a higher altitude (up to 1 100 m above sea level, can reach up to 1 300 m in some certain areas). We further discuss the uncertainty and confusion in definition, classification and description of the tropical rain forests from literatures in different regions of China and propose to give a consolidated consideration on the definition and classification of the tropical rain forests in China.

Aims Ecosystem services such as carbon sequestration and climate regulation of wetland ecosystems are very important. Accurately assessing the carbon storage of natural reserves in the Yellow River Basin is helpful for carbon neutrality research and regional ecological protection and high-quality development.

Methods Based on field sampling and laboratory analysis, combined with remote sensing data, this study assessed carbon storage in the aboveground plant biomass and the top 50 cm soils of typical natural vegetation in Shaanxi Yellow River Wetland Provincial Nature Reserve. The total target area for assessment is 13 086.52 hm², accounting for 23.87% of the nature reserve.

Important findings The results showed that the aboveground carbon storage of the tall-grass vegetation was significantly higher than that of the short-grass vegetation and shrubland, and their carbon densities were 496.73, 23.45 and 138.38 g·m^-2, respectively; the carbon density of the soil at 0-50 cm was 7.15-11.98 kg·m^-2, and the soil carbon storage in the tall-grass vegetation area (5.02 × 10⁵ t) was significantly higher than that of the beach without vegetation (2.09 × 10⁵ t), the short-grass vegetation area (3.40 × 10⁵ t) and short-shrubland area (1.45 × 10⁵ t); finally, combining the aboveground carbon storage in plant biomass and the soil carbon storage in the top 50 cm, the total carbon storage is estimated around 1.22 × 10⁶ t for the natural vegetation area of Shaanxi Yellow River Wetland Provincial Nature Reserve, of which proportions of carbon storage were 17.13%, 27.95%, 12.13% and 42.79% for beaches, short-grass vegetation area, short-shrubland, and tall-grass vegetation area. These results can provide basic data for the protection and restoration of natural wetlands and the improvement of carbon sink function in the middle reaches of the Yellow River.

Aims Plant diversity is the basis for plant communities to maintain ecosystem stability. Despite the scarcity of vegetation, desert steppes play an irreplaceable ecological service function in terms of wind-break and sand- fixation, etc. However, how plant diversity in desert steppes responds to long-term extreme precipitation changes still remains poorly understood.

Methods Based on a long-term field experiment involving five precipitation treatments (50% reduction, 30% reduction, natural, 30% increase, and 50% increase) conducted in a desert steppe in Ningxia since 2014, the changing characteristics of plant biomass, species diversity and their relationships with soil properties were studied from May to October in 2020.

Important findings During the growing season, plant community biomass, Patrick richness index and Shannon-Wiener diversity index tended to increase first and then decrease, whereas no obvious regularities in Pielou evenness index and Simpson dominance index. Compared with the natural precipitation, the decreased precipitation had less effect on plant biomass and diversity, especially the 30% reduction in precipitation. In most cases, the increased precipitation stimulated the growth of Sophora alopecuroides, Stipa brevifloraand Pennisetum centrasiaticum,and thus increasing plant biomass. However, it did not significantly change plant diversity when precipitation increased, especially the 30% increase of precipitation. Plant biomass was significantly affected by soil urease activity, temperature, water content, pH, phosphatase activity and sucrase activity, while plant diversity was significantly affected by soil water content, electrical conductivity, and urease activity. In general, the results indicated that plants have high adaptability to moderate or even extreme drought in the research area under seven consecutive years of changing precipitation; moderately increasing precipitation increased soil water availability, enhanced exchangeable ion mobility, and stimulated enzyme activity, thereby promoting plant growth. However, the continuous increase of precipitation leaded to the increase of plant biomass and plant water consumption, resulting in the lack of soil water in the late growth season and then the early completion of the life cycle of some plants.

Aims Hainan gibbons (Nomascus hainanus) are amongst the most endangered primates in the world and only endemic to China. This study aims to determine the potential species richness patterns of the foraging plants for Hainan gibbons.

Methods Based on the data on actual distribution points of foraging plants for Hainan gibbons and the controlling environmental variables, the potential distribution of those foraging plants in Hainan Island was simulated by using the maximum entropy (MaxEnt) model. The foraging plants were classified according to the type of organs used by the Hainan gibbons, the occurrence of foraging in dry season vs in rainy season, and preference of foraging.

Important findings The results show that: (1) Altitude, slope and the annual air temperature range are important environmental factors affecting the potential distribution of the foraging plants, with the potential species richness for all categories of the foraging plants positively correlated with altitude and slope, and negatively with annual air temperature range. (2) In Hainan Island, ten counties and cities in the south are the areas with concentrated occurrence of the foraging plants. The potential species richness for plants foraged for fruits and leaves, plants that are foraged either in dry or rainy seasons, and plants that are used as preferential food sources are all greater in the south than in the north, but the potential species richness for plants foraged for flowers is greater in the middle part of the Island and smaller in the fourth. (3) The hotspots for potential species richness of the foraging plants cover about 25.50% of the Island. In Bawangling, except the plants foraged for fruits, members of families Moraceae and Lauraceae are the preferential food sources for the gibbons, the hotspots for potential species richness of all other categories of foraging plants accounted for more than 40.00% of the area. This study provides information on the potentially concentrated distributions and the potential hotspots of species richness for different categories of foraging plants for Hainan gibbons, which serves to guide the efforts on conservation and recovery of Hainan gibbon populations.

Aims Potaninia mongolica, as a remnant species of ancient monospecific genus distributed in the northwest desert area, belongs to the category of national secondary key protected plants in China. The present study aims to investigate the structure, intra- and interspecific relationships, as well as the adaptation strategies to the environment of different types of P. mongolica populations. In particular, the age structure, spatial distribution patterns, and spatial correlations between size classes of P. mongolica populations were analyzed.

Methods Potaninia mongolica population concentrated in the gravel land (referred to as the Alxa population) and distributed in sandy soil in the eastern marginalia of distribution area (referred to as Erdos population) were selected. Through the size structure analysis method, P. mongolica individuals were categorized into three size classes, namely class I: d ≤ 10 cm; class II: 10 cm < d ≤ 30 cm; and class III: d > 30 cm, where d stands for the cubic root of the product of crown length, crown width and plant height. Moreover, the age structure, spatial distribution patterns, and spatial correlations between size classes of the selected P. mongolicapopulations were analyzed using the Ripley’s K-function through spatial point pattern analysis.

Important findings Results of the study include: 1) The Alxa population of P. mongolica was dominated by class II plants, accounting for 69%, whereas class I plants accounting for only 5% of the total population. However, the Alxa population was observed to be stable because of asexual reproduction. On the other hand, for the Erdos population, the proportion of class II and III plants were similar, and no class I plants were observed, which resulted in limited population renewal by seed propagation. 2) The Alxa population was randomly distributed, with class I and II plants predominantly distributed in clusters at small and medium scales and randomly distributed at large scales. Nevertheless, the Erdos population was predominantly distributed in clusters, both in general and at all size scales, which was strongly related to interspecific competition. 3) There was a significant negative correlation between class III and I individuals of the Alxa population at small and medium scales, reflecting the inhibition effect of the senior individuals on the young individuals. However, class II and III plants of the Erdos population showed a positive association with increasing scale range, suggesting a positive interaction between mature age classes of P. mongolica.

Aims Exploring the growth status and spatial distribution pattern of regenerated naturally young plants of Xinjiang wild apricot (Prunus armeniaca) population, which would provide a basis for protecting and artificially promoting the natural regeneration to this species.

Methods In this study, Daxigou (DXG) in Huocheng County, Xinghuagou (XHG) in Xinyuan County and Xiaomohu’ergou (XMHE) in Gongliu County were selected as the study sites. In order to fully understand the regeneration status of Prunus armeniaca population in the patchy, sparse and scattered habitats, forest understory, forest gap and forest glade were set sample plots in three study sites respectively. The distribution density, basal diameter, height and crown width of young plants were measured. The distribution type was determined by the method with 5 m × 5 m contiguous grid quadrats (7 aggregation indices). The aggregation intensity was calculated by point distribution pattern method.

Important findings The characteristics of natural regeneration young plants of Prunus armeniaca in Xinjiang were as follows: (1) The distribution density of XHG, DXG to XMHE was from high to low; the density in the forest gap is significantly higher than that in forest glade and forest understory. The average natural regeneration intensity of the population was 325 plants·hm^-2. (2) The basal diameter class of XMHE and DXG was significantly higher than that of XHG; and the one in the forest glade was significantly higher than that of forest understory and forest gap. The average basal diameter of natural regeneration of the population was about 1.7 cm. (3) The height of DXG and XMHE was significantly higher than that of XHG, and the one from the forest glade was significantly higher than that from forest understory and forest gap. The average height of natural regeneration of the population was 77.0 cm. (4) The crown breadth of DXG was significantly higher than that of XMHE and XHG, and the one in the forest glade was significantly higher than that of forest gap and understory. The average crown breadth of natural regeneration of the population was 38.7 cm. (5) There were 22 sample plots with young plants among all plots. In 5 m × 5 m quadrats, the proportions of aggregated, uniform and random distribution plots were 63.6%, 27.3% and 9.1% respectively. (6) In the point distribution pattern, the regeneration young plants were mostly aggregated in forest understory and forest glade. The aggregation intensity was the highest when the scale was 5-8 m, and it was mainly randomly distributed in the forest gap. When the scale was 1 m, the aggregation intensity was the highest, and its spatial pattern in different habitats was aggregated to random distribution. The results showed that both distribution area and habitat type could significantly affect the individual characteristics of young plants of wild apricot regeneration, and mixed forests types of DXG and XMHE were more conducive to the growth of young plants. The distribution number of regenerated young plants was seriously inhibited in forest understory. The forest gap was conducive to seed germination and planting, but the growth of young plants was hindered. The forest glade with condition was conducive to the growth and development of regenerated young plants. On the whole, the regeneration barriers of P. armeniacapopulation was obvious. The spatial distribution pattern of the existing regenerated young plants reflects the habitat change, survival stress, and grazing disturbance. In this context, more protective intervention should be enhanced to promote natural regeneration of P. armeniacapopulation.

Aims The contents of carbon (C), nitrogen (N) and phosphorus (P) in different plant organs and their ecological stoichiometric characteristics are important for understanding of the relationships among soil nutrients in their cycling process. The purpose of this study was to explore the variations of ecological stoichiometry of plant and soil C, N, and P in a jasmine (Jasminum sambac) plantation and their stoichiometric homeostasis under three different treatments.

Methods We set up three treatments: control, straw addition and biochar addition, and measured growth characteristic parameters of jasmine and C, N, P contents in different jasmine organs and in the soil and then analyzed their ecological stoichiometric characteristics.

Important findings Results showed that compared to the control, the straw addition treatment significantly increased the leaf biomass of jasmine by 73.33%, and decreased the soil salinity and soil temperature by 37.04% and 1.41%, respectively. Additionally, the biochar addition treatment significantly increased the plant height, leaf area, leaf and stem biomass of jasmine by 26.11%, 29.42%, 239.59% and 96.04%, while the soil density and soil temperature were significantly lower under the biochar addition treatment than under the control by 18.33% and 1.79%, respectively. Under different treatments, there was no significant difference in leaf or stem C content, or leaf N content. Root and soil C and N contents were significantly higher under biochar addition treatment than under straw addition and control treatments. The P contents of jasmine leaf, stem, root were in the order of biochar addition treatment > control treatment > straw addition treatment, while the soil P content was in the order of biochar addition treatment > straw addition treatment > control treatment. Compared with the control treatment, the biochar addition treatment decreased the C:P of leaf, stem, root and soil, and significantly decreased the N:P of jasmine leaf and stem, while increasing the N:P of root and soil. The overall internal stability of C, N, and P in different organs of jasmine was in the order of C > N > P, and the C:N, C:P and N:P were in the order of N:P > C:P > C:N. In summary, the application of biochar addition increased the absorption and assimilation of N and P by above-ground plants, and further promoted the C sequestration and homeostasis in the plant-soil system.

Aims Caragana korshinskii is the dominant species in the hilly area of northwest Shanxi, which plays very important roles in maintaining community species diversity, ecosystem stability and soil environment restoration.

Methods In order to investigate the stoichiometric characteristics of carbon (C), nitrogen (N), phosphorus (P) in the ecosystem of C. korshinskii artificial forest with different ages and their effects on leaf photosynthesis, the plant leaves and soil of C. korshinskii artificial forest with different ages (0, 6, 12, 18, 40, and 50 years) were collected. The variations of C, N, P stoichiometry in plant leaves and soil were analyzed.

Important findings With the increase of plantation time, the contents of C and N in the leaves of C. korshinskii increased significantly, while the contents of P increased firstly and then decreased. The contents of C, N and P in the leaves ranged from 434.14-452.26, 15.72-28.11 and 1.32-1.95 g·kg^-1, the contents of C and N in leaves reached the maximum value after 50 years of plantation, while the content of P in leaves reached the maximum value after 18 years of plantation. Leaf C:N increased first and then decreased, and reached the maximum in 18 years, while N:P increased significantly and reached the maximum in 50 years. The photosynthetic pigments (chlorophyll a, chlorophyll b, carotenoid and total chlorophyll) contents of leaves decreased significantly with increasing time of plantation, and leaf C and N contents had a significant effect on the changes of photosynthetic pigments contents. Soil water content increased first and then decreased with increasing time of plantation in the 0 -20 cm soil depth, and decreased significantly after 18 years of plantation. Soil organic carbon (SOC) and total nitrogen (STN) contents in the 0-20 cm soil depth profile increased with increasing time, and soil total phosphorus (STP) contents had no significant change with time. Soil C:N, C:P and N:P increased with the increase of forest age. Soil water content of C. korshinskii was significantly positively correlated with SOC and STN contents, and SOC and STN contents were also significantly positively correlated. The N and P contents of C. korshinskii leaves were significantly positively correlated. Leaf C and N contents were significantly positively correlated with SOC, STN and STP contents, and negatively correlated with soil water content. Leaf stoichiometric ratio was significantly positively correlated with corresponding soil stoichiometric ratio. The results of this study are of guiding significance to systematically understand the nutrient changes of artificial C. korshinskii forest ecosystem and to regulate and manage forest nutrients.

Aims Exploring intraspecific variations of plant functional traits with abandoned years and the relevant driving factors will deepen our understanding about the vegetation recovery of abandoned lands and thus guide our agricultural management.

Methods Using the method of substitution of space for time, we set up 42 plots in four types of habitat, i.e., field margin, abandoned grassland, shrub-grassland and forest which represents community succession along a chronosequence of vegetation restoration in Sitang town, Lingui District of Guilin in the middle reaches of Lijiang River watershed. We investigated change of intraspecific variation of five functional traits (i.e., leaf mass per area, leaf dry matter content, leaf nitrogen (N) content, leaf phosphorus (P) content and plant height) for four common herbaceous species (Imperata cylindrica, Paspalum distichum, Bidens pilosa and Alternanthera philoxeroides) with abandoned years. We also investigated the effects of soil properties and woody plant coverage on the intraspecific variation of functional traits.

Important findings With the increase of abandoned years, soil N and P content decreased significantly, soil N:P increased first and then decreased, and the woody plant coverage increased significantly. Leaf N content of I. cylindrica increased significantly, while leaf P content decreased significantly with the increase of abandoned years. This is because leaf N content decreased significantly and leaf P content increased significantly with the increase of soil P content. Leaf mass per area and leaf dry matter content of P. distichum increased significantly and plant height decreased significantly with the increase of abandoned years. Plant height of B. pilosa decreased significantly with the increase of abandoned years, because plant height of B. pilosa decreased significantly with the increase of woody plant coverage. Leaf mass per area of A. philoxeroides decreased significantly with the increase of abandoned years, because leaf mass per area of A. philoxeroides increased significantly with the increase of soil N:P. In sum, the intraspecific changes of plant functional traits are caused by the changes of soil physical and chemical properties and woody plant coverage with abandoned years.

Aims The variability of climatic conditions and complexity of underlying surface conditions in the humid regions of southern China have brought difficulties to the measurement and estimation of evapotranspiration. Tree transpiration is the key component of forest evapotranspiration. The monitoring and measurement of sap flow has become the main method to determine transpiration. Cunninghamia lanceolata forest as a representative vegetation in the source area of Xinʼanjiang River, is crucial to soil and water conservation and climate regulation in the area.

Methods In order to investigate the controlling mechanism of environmental factors on the change of the sap flow rate (J_s) during the growing season of C. lanceolata (April to September 2020), the J_s of C. lanceolata were monitored by the sap flow measurement system and environmental observations and soil water content were measured by the meteorological gradient tower in the source area.

Important findings The J_s of C. lanceolatahad obvious seasonal variations with the largest in August and the lowest in May. Among the environmental factors, net solar radiation (R_n) and vapor pressure deficit (VPD) were the strongest factors correlating with J_s. The results of principal component analysis indicated that the variance contribution rates of the first principal component were 59.1% and 57.9% at the hourly and daily scales, respectively. Furthermore, VPD and R_n played a major role in the first principal component and were the main environmental factors affecting the change of the sap flow rate of C. lanceolata in the study area. During the observation period, the maximum J_s occurred earlier than the maximum VPD by approximately (20 ± 3) min and occurred later than the maximum R_n by approximately (100 ± 5) min. The changes in soil water content caused by rainfall in the growing season of C. lanceolata did not significantly affect the sap flow, while the sap flows under different weather conditions varied significantly: J_s was higher and mainly showed a unimodal change with early start and late end in sunny days, but showed a multimodal change with late start and early end in rainy days.

Aims Understanding the effect of tourism disturbances on soil microbial diversity and community structure is necessary for the restoration and management of environmental resources in tourist areas. Therefore, we conducted a field survey in Beijing Songshan National Nature Reserve, to reveal the effect of different tourism disturbance intensity on soil microorganisms in a Pinus tabuliformis forest.

Methods Three intensity groups, high disturbance (HD), low disturbance (LD) and no disturbance (ND), were conducted in the P. tabuliformis forest. We investigated microhabitat conditions and measured soil physicochemical properties. Next generation sequencing technique was used to determine the diversity and community structure of soil microorganisms. Then, we evaluated the impact of tourism disturbance intensity on soil microorganisms.

Important findings 1) HD significantly reduced soil fungal alpha diversity, and LD significantly reduced soil fungal phylogenetic diversity. Soil fungal diversity showed a decreasing trend, and soil bacterial diversity showed an increasing trend with increasing disturbance intensity. 2) For soil fungal community structure, the dominant phylum of three intensity groups were Basidiomycota and Ascomycota. HD disturbance significantly affected the relative abundance of Ascomycota, but had no effect on Basidiomycota, LD had no effect on both of them. LEfSe analysis showed that indicators of ND were Pseudogymnoascus and three species (Oidiodendron griseum, Acrodontium hydnicola, Metacordyceps chlamydosporia); indicator of HD was Clavariaceae; there was no indicator in LD. 3) For bacterial community structure, the dominant phylum of three intensity groups were Proteobacteria, Actinobacteria and Acidobacteria, but HD and LD had no effect on them. LEfSe showed that indicators of ND accounted for 82.05% of total indicators, and the most indicative ones were Gaiellales and Solirubrobacterales; indicators of HD accounted for 17.95% of total indicators, they mainly manifested as pathogenic indicator bacteria and bacterial groups related to human activities, the most indicative ones were Flavobacteriia and one genus of Verrucomicrobia; there was no indicator in LD. 4) Partial Least Squares Path Modeling (PLS-PM) found disturbance intensity significantly impacted microhabitat and alpha diversity of soil fungi. Redundancy analysis showed that soil and microhabitat condition explained 71.35% and 74.47% of variations in community structure of fungi and bacteria under different intensity group, respectively. Tree diameter at breast height, herb cover and litter cover were the main factors that altered fungal and bacterial community structure. In conclusion, tourism disturbance significantly reduced alpha diversity and impacted community structure of soil microbiota in the P. tabuliformis forest, and the degree of influence associated with disturbance intensity and the kind of microorganisms. Moreover, the impact was also controlled by microhabitat and soil physical and chemical properties. Therefore, future attentions should be paid to the restoration of microhabitats and soil conditions in tourism areas.