Arbuscular mycorrhizal (AM) fungi are a group of soil-dwelling fungi that can form symbiotic associations with most terrestrial plants. The extraradical mycelium can colonize different plant roots in addition to hyphal fusion, thus form extensive arbuscular mycorrhizal networks (AMNs) underground. AMNs can transport and recycle water and nutrients including carbon, nitrogen, phosphorus among plants, recent evidences show that AMNs can also transfer defensive signals to neighboring plants when plants suffer environmental stresses, thus providing early warning to surrounding neighbors. However, the research on AMNs-mediated signal transfer is still in its infancy. Here, we firstly reviewed current research progresses in this research area, then proposed the unanswered questions that worth exploration in the future, including the possible pathways and mechanisms of signal transfer via AMNs among plants, the possible regulation of mycorrhizal symbionts by AMNs-mediated signal transfer, and the common techniques and their development used in the study of AMNs. Finally, we discussed about the possible ecological applications of AMNs such as filed crop protection.

Orchid is typical of mycorrhizal plants. Orchid mycorrhiza (OM), the symbiotic association between orchid roots and fungi, is unique to orchids. The nutrient sources of orchid mycorrhizal fungi (OMF) affect the lifestyle and nutrient levels of its host plants. Nitrogen (N) is the main limiting factor of plant growth. Orchids generally have higher tissue N levels compared to neighbor autotrophic plants, meaning N enrichment of plants. This paper reviewed the types and taxa of OMF, N nutrition characteristics of orchids, and N transfer mechanism in OM to provide a reference for the research on protection, regeneration, and sustainable utilization of orchid resources.

Aims The ecological mechanisms underlying species compositional differences among communities are crucial to understanding and predicting biodiversity changes. One of such mechanisms is the spatial structure independent of ground-level habitat (e.g., soil nutrients and topographic parameters). However, the primary drivers of this spatial structure are still unclear. Forest canopy structure can alter understory microclimates, which in turn influences the spatial structure and species compositional differences. We know little so far about such influence of the forest canopy structure. This gap has hindered our understanding of the ecological mechanisms underlying species compositional difference.

Methods The study was conducted in a 20 hm² evergreen broadleaf forest plot in the Tiantong region, Zhejiang Province, Eastern China. UVA-based LiDAR was used to estimate the high-precision forest canopy structure of the Tiantong plot. The redundancy analysis and the variance decomposition method were used to explore the relative importance of forest canopy structure and other potential factors on community species composition.

Important findings Our research showed that: (1) In the case of excluding the effect of canopy structure, the spatial structure independent of the ground-level habitat was one of the main contributors to the species compositional differences in the Tiantong plot. It explained 25.2%, 28.1%, and 8.0% of the variation in species composition at the scales of 100 m²,and 8.0% of the variation in species composition at the scales of 100 m² Our research showed that: (1) In the case of excluding the effect of canopy structure, the spatial structure independent of the ground-level habitat was one of the main contributors to the species compositional differences in the Tiantong plot. It explained 25.2%, 28.1%, and 8.0% of the variation in species composition at the scales of 100 m², 400 m²,400 m² 400 m², and 2 500 m²,and 2 500 m² and 2 500 m², respectively. (2) Including the effect of forest canopy structure significantly reduced the explanation power of the spatial structure by about 1/3 (26.2%-36.0%). (3) Among canopy structure factors, canopy height had the most significant influence on species composition, followed by internal canopy structure. With the increase of the plot scale, the effects of canopy height decreased while the impacts of internal canopy structure increased. In conclusion, our study demonstrated that canopy structure is one of the main drivers of spatial structure independent of ground-level habitat. Our results also clarify the relative importance of canopy height and internal canopy structure on species composition and provide new perspectives to understand the ecological mechanisms underlying species compositional differences among forest plant communities.

Aims The study of the pattern of biomass variations and their drivers along environmental gradients commonly contributes to the understanding of plant’s adaptability to environmental changes, further explains the spatial differences in vegetation and ecosystem processes. We investigated the biomass latitudinal patterns of plant communities and its components and revealed the quantitative relationships of biomass with climatic, soil and community structure as well as species diversity.

Methods In order to analyze the variation patterns of biomass along the latitude gradient and the drivers, we set up a total of 101 plots (4 m × 6 m) across nine region along latitude in the arid valley of southwest China (23.23°-32.26° N), to investigate biomass and species composition of plant communities and its components.

Important findings In the arid valley, the average biomass of community was (17.05 ± 1.09) t·hm^-2, of which the average biomass of shrub, herb and litter were (11.51 ± 1.03), (2.11 ± 0.21) and (3.41 ± 0.34) t·hm^-2, respectively, with each of them accounting for 60.2%, 15.6%, and 24.1% of the community biomass. With the increase of latitude, community biomass increased significantly. Shrub biomass and their proportion also increased significantly, herb biomass and their proportion remained consistent, whereas litter biomass decreased significantly. The changes of shrub dominance and abundance were the main internal factor for vegetation biomass variation along the latitude gradient. Additionally, compared with soil factors, climatic factors had a more significant impact on the biomass changes of communities and its components.

Aims In order to explore the important ecological function of moss in forest ecosystems in the southeast Xizang and provide a theoretical basis for the influence of forest disturbance on forest surface vegetation, the diversity and biomass characteristics of ground moss per unit area in different habitats in the Sygera Mountain of southeast Xizang.

Methods We collected the surface moss in the Sygera Mountain of the southeast Xizang as the investigation object, and selected 7 sample plots with similar forest stand, slope direction, slope and terrain composition, with each plot size of 100 m × 100 m. We took canopy gap of each sample plot as the center, and three different habitats (canopy gap, forest edge and understory) were selected in four directions to set 50 cm × 50 cm quadrats, with 12 quadrats for each sample plot and 168 quadrats in total. Moss survey and collection were carried out in each quadrat.

Important findings (1) 24 families, 63 genera and 110 species of moss were found in the study area, in which there were 8 dominant families, which were Pottiaceae, Dicranaceae, Polytrichaceae, Mniaceae, Bryaceae, Grimmiaceae, Brachytheciaceae and Hypnaceae. There were obvious distribution rules of different moss families, such as Dicranaceae and Bryaceae were widely distributed at all elevations, and Polytrichaceae, Bryaceae and Mniaceae were distributed at altitudes from 3 700 to 4 300 m. Most of Pottiaceae were distributed over 4 300 m. (2) The habitat of canopy gap was more complex than those of forest edge and understory and it interfered with moss composition and community structure, in which the moss community had the most species and the most complex structure. However, the moss community in understory had the least species and the simplest structure. The biomass of ground moss was the highest in the gap, followed by the edge and the lowest in the understory. (3) The biomass of ground moss was not only affected by species composition, coverage, body shape and community structure, but also resulted from the interaction of many factors rather than any one single factor.

Aims The mountainous region on the east side of the Qingzang Plateau is a biodiversity hotspot and a refuge for many plants during the ice age. The unique topography allows geographic isolation to play an important role in shaping population genetic patterns. The white birch (Betula platyphylla) population located on the eastern side of the Qingzang Plateau shows a fragmented distribution, which is isolated by valleys, mountains, and rivers, and the genetic pattern is still unclear.

Methods We used 11 pairs of nuclear microsatellite molecular markers to analyze the genetic diversity and structure of 13 birch populations located in the eastern mountainous area of the Qingzang Plateau.

Important findings A total of 114 alleles were detected in 412 individuals, and we found a high level of overall genetic diversity (expected heterozygosity (H_E) = 0.579; observed heterozygosity (H_O) = 0.555), a medium level of genetic differentiation (genetic differentiation coefficient (F_st) = 0.127), and a large pairwise genetic distance between groups (F_st = 0.017-0.319). The genetic distance was significantly positively correlated with geographic distance. The cluster analysis divides all individuals into two groups, bounded by the Yalong River Canyon. The population on the west side has lower genetic diversity and greater genetic differentiation than the population on the east side. This study shows that the geographic isolation caused by the unique topography on the eastern side of the Qingzang Plateau has profoundly affected the genetic diversity and genetic structure of white birch. The marginal populations located in the Yunnan area have already faced the risk of reduced genetic diversity and should be given priority protection.

Aims The variations in population structure and the quantitative dynamics of plants are a reflection of the local ecology and environment. Hippophae tibetana is a dwarf shrub, and a pioneer species of vegetation succession which is peculiar to the alpine region of the Qingzang Plateau. It has excellent water and soil conservation effects and good ecological adaptability to high-altitude environments. However, little research has been made into the changes in the population structure and dynamics at different altitudes. Such an understanding is important to understanding the ecological strategy of H. tibetana adaptation to alpine habitats. The Qilian Mountains in the northeastern margin of the Qingzang Plateau contain degraded alpine grassland and are ecologically fragile. It is thought that the irregularly distributed native species, H. tibetana, plays an important role in water conservation at 2 700-3 300 m in this region.

Methods The structure, dynamics, life span and morphological characteristics of H. tibetana populations distributed at three altitudes (2 868, 3 012, and 3 244 m) in Tianzhu Zangzu Autonomous County, Qilian Mountains were studied and quantified, establishing static life tables and population survival curves. This quantitative analysis of the population dynamics was used to try to determine future population development trends.

Important findings We found: 1) The plant height, basal diameter and crown width of H. tibetana decreased with elevation. The age structures of all populations at the three altitudes were roughly spindle-shaped, with abundant mature individuals but few seedlings and few old plants. Populations were found to be stable. 2) The survival curves of all populations tended to approach the Deevey-II type, and the survivability was greatest at low altitude, medium at middle altitude, and lowest at high-altitude. The mortality and disappearance rates were both high, ranking from highest to lowest with high-altitude > low-altitude > middle-altitude. Seedlings were proportionally more abundant at the middle and high altitudes. Life expectancy was greatest at middle-altitude > low-altitude > high-altitude. 3) The dynamic index (V′_pi) of each altitude population was close to 0, indicating that all populations were stable, and the maximum of probability under random disturbance (P_max) of the middle altitude population was the smallest, indicating that the middle-altitude populations were the most resiliant to random interference. The middle altitude was the most suitable for the growth of H. tibetana. 4) The proportion of seedlings in all populations is likely to decrease, while the proportion of mature and old plants will increase over the next 2, 4 and 6 age classes of time. Any decline in the total populations at the three altitudes is likely due to the lack of young individuals, interspecific and intraspecific competition, and environmental stress. These findings will enable us to predict future growth and death of H. tibetana populations and provide a reliable theoretical foundation for the protection of natural forests in this region. This will be important to the future management of these alpine environments as global climate warming makes its impact.

Aims The flowering phenology and floral trait of plants reflect their adaptation to the habitat, which is the result of long-term adaptation and evolution to the surrounding biological and abiotic environment. The aim of this study is to explore the differences of flowering and pollination processes of individuals with different gender phenotypes in Lilium concolor var. megalanthum populations between Gushantun wetland with low human disturbance and Jinchuan wetland with strong human disturbance.

Methods Lilium concolor var. megalanthum is a plant with two different gender phenotypes (male individuals and hermaphroditic individuals) in wild population. Lilium concolor var. megalanthum in Gushantun wetland and Jinchuan wetland were used as study materials. We compared the flowering phenology, the floral trait and the visiting behaviors of pollinators of two gender phenotypes of L. concolor var. megalanthum between these two habitats.

Important findings The results showed that the initial flowering stage, peak flowering stage and final flowering stage of its population in less disturbance site were earlier than those in disturbance site. The pollen viability of male individuals of it in less disturbance site was higher than that in disturbance site at the beginning of flowering. While the overall change trend of pollen viability of hermaphroditic individuals of it between two habitats were the same. The nectar content of male individuals of it in less disturbance site was higher at the beginning of flowering and then decreased slowly, while it increased first and began to decline after 48 h slowly in disturbance site. The nectar content of hermaphroditic individuals of it in less disturbance site began to decrease after 24 h, while it began to decrease after 48 h in disturbance site. The peak time of sugar secretion of both male and hermaphroditic individuals of it in less disturbance site was later than that in disturbance site. Stigma receptivity of it in both habitats has always maintained a high level. The main pollinators of it in two habitats were Apis cerana, Everes argiades and Argyronome laodice. The visiting frequency of Apis cerana and Everes argiades to L. concolor var. megalanthum in less disturbance site was significantly lower than that in disturbance site, but the visiting frequency of Argyronome laodice was significantly higher than that in disturbance site. Among the three pollinator species, Apis cerana had the highest flower visiting efficiency, and Everes argiades and Argyronome laodice played supplementary pollination role. The variation of flowering phenology and floral trait between the two habitats are related to the local microclimate and the number of pollinators. This difference is the result of the evolution of L. concolor var. megalanthum over a long period of time.

Aims The plant absorptive roots function to absorb water and nutrients. Investigations of anatomical traits of the roots are to understanding environmental adaptations of plant species. Ferns in tropical and subtropical regions are abundant and of important ecological and economic values. However, the anatomical traits of the absorptive roots of ferns are not fully comprehended.

Methods We investigated anatomical traits of absorptive roots for 26 fern species from four typical tropical/ subtropical forests by analyzing inter-specific differences in the traits across the species to explain the influence of phylogeny and climate. In addition, we compiled relevant root traits of subtropical angiosperm tree species and temperate fern species from literature to explore the trait differences among the groups.

Important findings (1) We found significant differences in eight root anatomical traits among the 26 fern species, with coefficient of variation ranging from 20.61% to 41.75%. (2) Root traits showed no significant phylogeny signal except in cortex thickness (CT), indicating little affection from phylogeny. However, climate might exert significant impacts on root traits, i.e., root diameter (RD) and CT significantly increased with decreasing precipitation of the driest month (quarter). (3) As RD decreases, the subtropical angiosperm woody plants showed a significant decrease in the ratio of CT to stele diameter (SD), but fern had an opposite pattern. Compared to temperate ferns, the tropical and subtropical ferns had higher RD, CT, and tracheid diameter (TD).

Aims In the lower subtropical region of China, there are large areas of single-species plantations. These plantations have simple community structure and thus are sensitive to climate change. Under the background of regional climate drying, the eco-physiological strategies of these afforestation species and their response to seasonal drought should be investigated.

Methods We selected ten tree species that are commonly planted in this region including six native species and four exotic species. Based on measurements of the mean growth rate, hydraulic traits, and economics traits, we analyzed the trait-growth correlations within each species and compared the differences in hydraulic safety margin and stomatal safety margin among species.

Important findings (1) The growth rate was significantly and positively correlated with hydraulic conductivity, but not with the economic traits, such as wood density, specific leaf area, and hydraulic safety-related traits. (2) There was no significant trade-off between hydraulic efficiency and safety. Two of the exotic tree species, Acacia crassicarpa and Eucalyptus grandis × urophylla, showed both high hydraulic conductivity and great cavitation resistance. (3) There were significant differences in hydraulic safety margin and stomatal safety margin among the tested species. During the dry season, Acacia auriculiformis, Castanopsis hystrix, Mytilaria laosensis and Cinnamomum burmannii would suffer from higher risks of hydraulic failure than the other species. We suggest that tree hydraulic traits should be included into the index system of ecological monitoring of subtropical plantations, which can provide important references for sustainable management of these plantations.