Species distribution models (SDMs) have been extensively used in simulations of geographical distribution of animal and plant species during the past 20 years. Taking the simulation of plant species distribution as an example, we used both the digitized and library databases including the China National Knowledge Infrastructure (CNKI), the VIP Chinese Journal Database (VIP) and the Web of Science (WoS) to compile available literatures published from 2000 to 2018. The number of publications, SDMs used, target plant species, data sources, and the purpose of studies about using various SDMs to simulate plant species distribution in China was statistically investigated. In total 366 publications were collected. Further analysis and synthesis showed that the application of SDMs in simulating Chinese plant species distribution has developed rapidly since 2011, especially during the past five years. SDMs have been used in studies of ecology, Chinese traditional medicine, agriculture, and forestry. The Maximum Entropy Model (MaxEnt) is the most widely used model among 33 commonly used SDMs. A half of the studies use climate data only, and another half of the studies use both climate, soil and topography data. The source of both environmental data and plant distribution data are diverse, derived from international and domestic databases. In these studies, researchers have simulated the distribution of 562 plant species, in which 52.7% are woody species and 41.8% are herbaceous species, including a large number of Chinese medicinal plants, fruit trees, garden plants, and crops. Studies aim mainly on two aspects, i.e. the impact of climate change on plant species distribution and their predicted pattern in the past, present, and future climate scenarios, and the assessment of the potential distribution of plant species and biodiversity trends (including the risk of invasive species). In future studies, more attention should be paid to both the basic science on the modelling of potential distribution of plant species and the impact from climate change, and the applied science on the prediction of suitable distribution area of plant species in order to popularize their plantation. More applications of SDMs in multiple disciplines and in multiple industries such as ecology, forestry, crop science and Chinese traditional medicine should be further developed. Joint simulations and inter-comparisons using multiple plant species, more SDMs and multiple data sources of environmental data, as well as the development of new and mechanism SDMs are encouraged. The extension of model applications in new research fields is also needed.

Carbohydrates are important components of soil organic matter, which can be decomposed to different types of monosaccharides. Neutral monosaccharides in the soil are also called neutral sugars, including xylose, ribose, arabinose, glucose, galactose, mannose, fucose and rhamnose. Among them, plant-derived sugars mainly include pentoses, such as xylose and arabinose, while microbial-derived sugars mainly consist of hexoses including galactose, mannose, fucose and rhamnose. Generally, the ratios of hexoses to pentoses are used to evaluate the contribution of microbial- versus plant-derived sugars. Neutral sugars are the main carbon and energy resources for soil microorganisms and play a vital role in aggregates formation. In this study, we review studies about neutral sugars in soils over the past 30 years and compare different methods for neutral sugar analysis. Furthermore, we compare the distribution patterns and turnover of soil neutral sugars across diverse land-use regimes, different soil density and particle size fractions and their influencing factors. The lowest neutral sugar content is found in arable soils compared with other four land-use types (coniferous forests, deciduous forests, shrublands and grasslands) in terms of absolute and relative contents. No significant difference is observed for the (galactose + mannose)/‍(arabinose + xylose)(GM/AX) ratios across the five land-use regimes. Nevertheless, the ratio of (rhamnose + fucose)/(arabinose + xylose)(RF/AX) indicates that microbially derived neutral sugars are more abundant in the soils of grasslands than coniferous forests or farmlands. The heavy fraction is characterized by an enrichment of microbial neutral sugars but a lower content of total neutral sugars compared to the light fraction. Concerning the distribution of neutral sugars across different soil size fractions (or aggregates), the microbial-derived neutral sugars are more abundant in the clay fraction (or microaggregates). As for the factors affecting neutral sugar content and distribution, many studies have focused on the human disturbances like agriculture and grazing, while the influence of environmental factors such as temperature, precipitation is poorly investigated.

AimsIntensified human activities has resulted in more extreme droughts and high ground-level ozone (O₃) concentration during plant growing seasons. To clarify the combined effects of elevated O₃ (E-O₃) and drought on plants, we investigated the effects of elevated O₃, drought and their interaction on the accumulation and allocation of non-structural carbohydrates (TNC) in leaves and fine roots of poplar.
MethodsThe O₃-sensitive poplar ‘546’ (Populus deltoides cv. ‘55/56’ × P. deltoides cv. ‘Imperial’) saplings were exposed to two O₃ treatments (charcoal-filtered air (CF) and non-filtered ambient air (NF) + 40 nmol·mol^-1 O₃ (E-O₃)), and two watering treatments (control, well-watered and drought, reduced watering) using open-top chambers (OTC_S). The content of TNC and its components (glucose, fructose, sucrose, polysaccharides, total soluble sugars and starch) in leaves and fine roots were measured.
Important findings E-O₃ significantly decreased the content of starch and TNC, but increased the content of fructose, glucose and total soluble sugar in leaves. However, E-O₃ did not have significant effects on starch and soluble sugars in fine roots. In addition, drought significantly increased the content of fructose and polysaccharide, but decreased the content of sucrose in fine roots, although drought had no significant impacts on the content of starch and soluble sugars in leaves. There was significant interaction of O₃ and drought on the content of polysaccharides and total soluble sugar in leaves, as indicated by the significant increase by E-O₃ under well-watered irrigation, but no effects under drought. E-O₃ significantly increased the ratio of root to leaf in TNC content, but not under well water condition. In conclusion, E-O₃ affected the content of TNC and its components in leaves, while drought affected them in fine roots. From the response of TNC, moderate drought mitigates the negative effects of O₃ pollution on plants.

AimsAlpine desert, as the top part of the vertical vegetation spectrum of the Qinghai-Xizang Plateau, is widely distributed in the high altitude zones in the Qilian Mountains (QLM). Its distribution and growth conditions are different from the surrounding area. It is more sensitive to climate change but rarely being studied. In this study, we focused on the dynamic changes and spatiotemporal differences of the alpine desert belt in the QLM under the warming climates from the 1990s to the 2010s.
MethodsThe distribution changes in the alpine desert belt in the QLM during the past three decades were obtained from the thematic mapper and the operational land imager remote sensing digital images by using the decision tree classification and artificial visual interpretation. Spatiotemporal differences of the alpine desert distribution were studied by the overlay analysis. Meanwhile, the relationships between the changes and climates were explored using correlation analysis.
Important findings The results indicated that the alpine desert shrank gradually and lost its area by approximately 348.3 km²·a^-1 in the QLM with climate warming in the past 30 years. The amplitude of the shrinkage increased from east to west. However, its areas expanded in some sections. Collectively, the low boundary of the alpine desert belt moved upwards to higher altitudes at a velocity of 15 m per decade. The maximum upward-‌shifting amplitude lied in the western QLM, followed by the eastern and middle QLM. The vertical zonal shifting was modulated by topography-induced difference in local hydrothermal conditions. The distribution shifts in the alpine desert belt were mainly concentrated in the gentle slope regions. Because of the differences of hydrothermal background, the position shifts were greater in the sunny aspects than in the shady aspects in the eastern and middle QLM, while opposite in the western QLM. The differences in the hydrothermal conditions and regional topography led to the spatiotemporal change differences of the alpine desert distribution. The correlation between the normalized differential vegetation index and climate factors in the transition zone showed that temperature was the main factor affecting the dynamics and spatial differences of the alpine desert belt in the QLM, and climate warming facilitated the alpine meadow below the alpine desert belt by releasing the low temperature limitation on the vegetation growth.

AimsThe objective of this study was to determine the temporal stability of relationships between radial growth of Larix sibirica and climatic factors in Altay Mountains.
MethodsTree-ring samples were collected at high altitude (2 069 m) in Altay Mountains of Xinjiang, China. Residual chronologies (RES) were established by using the tree-ring width data. Growth-climate relationships were investigated by calculating the Pearson correlation coefficients between tree-ring width chronology and climatic factors. Moreover, the variations in radial growth in response to climatic factors were calculated by a moving correlation function with a 30-year time window using the DendroClim 2002 program.
Important findings Temperature in the early and middle growing seasons exerted the greatest control on the radial growth in Larix sibirica of the study region, with a significant negative correlation between the radial growth of trees and the air temperatures in the current April (mean minimum air temperature: r = -0.308, p < 0.05; mean air temperature: r = -0.324, p < 0.05; mean maximum air temperature: r = -0.330, p < 0.05), and a significant positive correlation between the radial growth and temperatures from June to July (mean minimum air temperature: r = 0.499, p < 0.01; mean air temperature: r = 0.456, p < 0.01; mean maximum air temperature: r = 0.431, p < 0.01). The radial growth in Larix sibirica exhibited divergent responses to temperature in April and from June to July. Specifically, with the changes in climate, the radial growth response sensitivity of trees showed a gradually increasing trend to drought caused by high temperature in current April, while the sensitivity to the temperature decreased initially and then increased from the current June to July. Our results show that the radial growth of Larix sibirica in Altay Mountains was sensitive to climatic factors, making it suitable to study the relationships between tree growth and climate change. Under climate change, our findings on divergent response of radial growth in Larix sibirica to climatic factors would provide a scientific basis for accurately reconstructing historical climate and predicting forest ecosystem dynamics based on tree-ring data.

AimsQuantitative evaluation of the vegetation normalized differential vegetation index (NDVI) dynamics plays an important role in understanding of the characteristics of regional ecological environment change and realizing the harmonious and sustainable development between regional ecology and socio-economy.
MethodsThe study employed the supplementary trend analysis with MODIS-NDVI data, analyzed the spatio- temporal patterns of vegetation NDVI and the driving factors behind the changes in Xilin Gol during 2000-2015. Then, the ratio of the overlapped areas to the areas with significant NDVI changes was defined as the contribution rate.
Important findings 1) NDVI represented a slow vegetation increase trend and showed a “Northeast high and Southwest low” spatio-temporal pattern. The NDVI significantly increased area was twice of the area significantly reduced. 2) The vegetation NDVI showed a significant spatial heterogeneity under the dual effects of climate and human activities. In the area of NDVI significantly increased, climate factor accounted for 47.79% of the causes, and the precipitation and temperature make nearly equal contributions while the policies of grazing prohibition and balance management between grass and livestock is the most important human factor, accounting for 69.55% of the causes. 3) In the area of NDVI significantly reduced, climate factors accounted for 52.55% of the causes, in which precipitation was the main factor among all. Human activities accounted for 24.73% of the causes. 4) In the area of NDVI significantly increased, the impact of human activities is greater than that of climatic factors, and the coupling effect between them is prominent.

AimsSpatial heterogeneity of leaf area index (LAI) is very important for exploring the growth and spatial distributions of plants, as well as response strategy of plants to climate changes. Many previous studies have shown that biotic and abiotic factors had significant influences on spatial heterogeneity of LAI. However, few studies have been conducted to show the relative contributions of different influencing factors to the total variations of LAI. Our aim was to quantify the relative contributions of stand, soil and space factors to the total spatial variations of LAI in a spruce-fir valley forest in northeast China.
MethodsWe relied on a 9.12 hm ² (380 m × 240 m) spruce-fir valley forest plot in Xiao Hinggan Ling, China, which was divided into 228 subplots (20 m × 20 m). First, we measured LAI for each subplot by using the LAI-2200 plant canopy analyzer and then analyzed the spatial heterogeneity of LAI using geo-statistic methods (semivariogram and Kriging interpolation). Second, we measured 28 stand factors and 10 soil factors for each subplot, and quantified space factors using principal coordinates of neighbor matrices (PCNM). Finally, we quantified the relative contributions of stand, soil and space factors to the total spatial variations of LAI using the variance partitioning method.
Important findings The results showed that strong spatial autocorrelations of LAI values within 37 m distances in the spruce-fir valley forest, and the LAI presented different spatial patterns along distinct directions. The stand, soil and space factors totally explained 50.4% of the total spatial variations of LAI in the forest plot. The space factors explained greater spatial variations of LAI in relative to stand and soil factors, and solely explained 25.5% of the total spatial variations. The density of middle tree group (5 cm < diameter at breast height ≤ 10 cm) and basal area of major tree groups (including Abies nephrolepis and Picea spp.) were both significantly and positively correlated with LAI; and soil mass moisture content was significantly and negatively correlated with LAI. These results generally suggest that the spatial autocorrelation is more important than stand factor and soil factor for determining spatial heterogeneity of LAI of the spruce-fir valley forest in Xiao Hinggan Ling, China.

AimsAs a dominant understory layer, shrubs is important in the material turnover and nutrient circulation of forested ecosystems. It is essential to explore stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) of the shrubs and their driving factors, including microenvironments and soil nutrients.
MethodsThe leaves, branches, roots of the shrubs and the soils they rooted were sampled from seven dominant forest types of Qinghai, China, and the tissue contents of C, N and P were examined. One-way ANOVA was used to explored the difference of the shrubs and the soils among the forest types using, respectively. Redundancy analysis (RDA) was used to analyze the effects of soils and environmental factors on the stoichiometric characteristics of C, N and P of shrubs.
Important findings Our results showed that there were no significant differences in the P content and C:P of the leaves, branches and roots among all the seven dominant forest types, while the N content and N:P of shrubs in the Populus davidiana, Sabina chinensis and Picea asperata forests were significantly higher than those in Betula platyphylla, Populus tomentosa, Betula albosinensis and Picea wilsonii forests, while the C:N ratios were the other way around. The shrubs in Sabina chinensis forest were limited by the soil P content, but that in the other six forest types was limited by the soil N content. The contents of soil organic C (SOC) and soil total N (TN) were significantly different among the seven forest types, while the soil total P (TP) was not. Correlation analysis showed that the N content, the C:N and N:P of understory shrub tissues (leaves, branches and roots) were significantly correlated with soil TN content, soil C:N and N:P, while tissue P contents and the C:P ratios were correlated with soil TP contents. Redundancy analysis (RDA) showed that the stoichiometric characteristics of C, N and P the understory shrub layer were synthetically affected by soils and environmental factors, of which the soil C:N, altitude, mean annual temperature and mean annual precipitation were the main influence factors.

AimsThe grassland in southwestern China is mainly warm and tropical grass and shrub grassland, accounting for approximately one-tenth of the national grassland area. Analysis of the relationship between shrub coverage and the grassland carbon pool and its composition is of great significance for accurately assessing carbon storage in the southwestern grassland, which grassland is still in the secondary succession stage.
MethodsIn a field investigation, 41 representative plots of different geomorphic types in southwestern China were divided into three types according to shrub coverage: no shrub grassland community (shrub coverage is 0), low shrub coverage grassland community (shrub coverage is 0-10%) and high shrub coverage grassland community (shrub coverage is 10%-30%). Carbon density was calculated by measuring the aboveground and underground biomass and litter biomass of grassland communities at different shrub coverage levels, as well as plant and soil carbon content.
Important findings The results showed that with increasing shrub coverage and species richness in grasslands, the ecosystem vegetation carbon density increased from 0.304 kg·m ^-2 to 1.574 kg·m ^-2, and the roots and litter carbon density also showed growth trends. The soil carbon density increased from 7.215 kg·m ^-2 to 9.735 kg·m ^-2, and the ecosystem carbon density increased from 7.519 kg·m ^-2 to 11.309 kg·m ^-2, with increasing shrub coverage. Regarding the composition of the grassland carbon pool, the soil carbon pool of the low shrub coverage grassland accounted for the smallest proportion of the ecosystem carbon pool. In summary, the increase in shrub coverage changes the composition of the grassland ecosystem carbon pool and leads to an increase in the amount of ecosystem carbon. Therefore, when estimating the grassland ecosystem carbon pool, it is necessary to overall plan for and take into account the changes in grassland shrub coverage in southern China.

AimsPrevious studies have shown that Dendrobium plants form a specific symbiotic relationship with fungi at differentiation stages during natural seed germination. In order to explore the evolution and adaptation of this symbiotic relationship in interspecific hybrid progenies, this study was to understand whether the strong specificity with symbiotic fungi during seedling formation and differentiation was also an important factor limiting the formation of hybrid progenies in Dendrobium, and the relationship between hybrid progenies of orchids and symbiotic fungi during seed germination stage.
MethodsThe effects of fungi on germination of interspecific hybrid seeds of D. officinale and D. tortile were studied using the highly specific fungi strains Tulasnella SSCDO-5 and Epulorhiza FDd1, which can effectively promote seed germination and seedling formation in D. officinale and D. devonianum, respectively.
Important findings The results showed that both SSCDO-5 and FDd1 strains could effectively promote the protocorm and seedling formation of hybrid seeds after 68 days incubation with no significant difference. The SSCDO-5 strain from D. officinale did not show any advantages, and the seedling formation rate of hybrid was lower than that of FDd1 strain from D. devonianum. The seedling formation rate incubation with SSCDO-5 strain was (22.13 ± 6.62)% while with FDd1 strain was (29.53 ± 5.51)%. The specificity of SSCDO-5 strain with D. officinale at seedling formation and development stage was not inherited or expressed in hybrid progenies, indicating that hybridization broke the symbiotic relationship of this specificity, which enabled hybrid progenies to establish new symbiotic relationship with different fungi. Our results do not support the hypothesis that the specificity of symbiotic fungi is an important limiting factor for the formation of hybrid progenies in Dendrobium. We speculate that the symbiotic relationship between Dendrobium plants and fungi during seedling differentiation and development is formed and established in the process of adapting to specific ecological environment.