Changes in hydraulic traits of nine vascular plants from different evolutionary lineages北大核心CSCD

Aims As vascular plants evolve from ferns to gymnosperms and angiosperms, their physiological structures and functions are assumed more adaptable to arid environment. Whether the three plant groups from early to late evolved lineages have improved their water transport and use efficiency has been studied on the basis of the morphological structure of leaf veins and stomata.Moreover, the water transportation rate was directly measured in the angiosperms. Therefore, we measured structural and functional traits related to water relations in all three plant groups simultaneously, to test the hypothesis on the evolutionary process of plant hydraulics. Methods We selected three species in each group grown in South China Botanical Garden, Guangzhou, China, including ferns (Dicranopteris pedata, Cyclosorus parasiticus and Blechnum orientale), gymnosperms (Podocarpus macrophyllus, Podocarpus nagi and Taxodium distichum) and angiosperms (Manglietia fordiana var. hainanensis, Sindora tonkinensis and Bauhinia purpurea). Important findings Sapwood and leaf specific hydraulic conductivities (KS and KL, respectively), and leaf conductance (Kleaf) significantly increased from ferns, gymnosperms to angiosperms. However, no significant trends were found in transpiration rate (E) and intrinsic water use efficiency. Meanwhile, neither the size and density of stomata nor wood density showed significant difference among three plant groups. The hydraulic functional traits (KS, KL and Kleaf) had significantly positive correlations with each other, but had no relationships with the two measured structural traits. Phylogenetic independent contrasts analyses showed that the coordination between KS and Kleaf, and between KS and E were independent of the phylogeny. Based on the nine vascular species, this study demonstrated that water transport related traits are improved as vascular plants evolved, and the co-evolution between water transport and transpiration traits were identified. For further study, it is necessary to consolidate our data with investigations of more detailed water-transport structures in more species from different evolutionary lineages. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

Responses of radial growth to temperature in Larix gmelinii of the da Hinggan Ling under climate warming北大核心CSCD

Aims The Da Hinggan Ling is amongst the areas in China susceptible to climate warming. The objective of this study is to determine the responses of radial growth to temperature variations in Larix gmelinii growing in different parts of the Da Hinggan Ling in the process of climate warming, by using dendrochronological techniques. Methods We collected tree-ring samples from the southern, the middle and the northern parts of the main Da Hinggan Ling, developed site-specific ring-width chronologies, and synthesized tree-ring indices of the southern, the middle and the northern parts of the study area according to the first principal component loading factors for each chronology. The relationships between radial growth in L. gmelinii and temperature variations were determined with correlation analysis, and the differences in the responses of radial growth to temperature variations among various parts were analyzed and compared with principle component analysis. Important findings There were notable discrepancies in the effects of temperature variations on radial growth in L. gmelinii between the southern and the northern parts of the study area (the middle part > the northern part > the southern part). In the southern part, the mean monthly temperature between the previous November and April of the current year had a significant relationship with tree-ring indices (p < 0.05). In the middle part, the mean monthly temperature during March and October of the current year had a significant relationship with tree-ring indices (p < 0.05), and so did the mean monthly temperature during June and August of the previous year (p < 0.05). The mean monthly temperature during April and May of the current year had a highly significant relationship with tree-ring indices in the northern part (p < 0.01). This study suggests that the warmer and drier regional climate condition caused by elevated temperature has resulted in that soil moisture becomes the main factor limiting the radial growth, and the relationship between tree growth and temperature variations signified with aggravated soil drought under climate warming. The productivity in L. gmelinii as reflected by basal area increment experienced a shift response from cold stress to water stress. In addition, the radial growth in L. gmelinii in the Da Hinggan Ling will likely to show a declining trend in the southern and the middle parts, and an increasing trend in the northern part, in response to rapid warming in the coming decades.     

Variations of root traits in three Xizang grassland communities along a precipitation gradient北大核心CSCD

Aims Root functional traits and their variations mediate coexistence and adaptive strategy of plant species. Yet, strong environmental constraints may induce convergence of root traits among different plant species. To study the variations of root traits and clarify the diverse adaptive strategies across plant species, we sampled three alpine grasslands along a precipitation gradient in the Xizang Plateau. Methods In three grassland communities along a precipitation gradient: Nagqu, Baingoin and Nyima from east to west of Xizang Plateau, we collected 22 coexisting plant species and measured three key root traits: 1st-order root diameter, 1st-order lateral root length and root branch intensity. Important findings The main results showed that: (1) the root of plants in the alpine grassland was generally thin, and the interspecific variation was also small (22.76%); (2) the root diameter of 86% plant species was in the range from 0.073 mm to 0.094 mm. Compared with the thick-root species, thin-root species had a higher root branching intensity, but shorter lateral root length. In addition, at community-level, plants mainly increased root diameter and lateral root length, but reduced root branching intensity to adapt to the decreasing precipitation; while at species-level, the plant species exhibited diverse adaptive strategies along the precipitation gradient. © Chinese Journal of Plant Ecology.     

Phenotypic plasticity and genetic differentiation of quantitative traits in genotypes of Leymus chinensis北大核心CSCD

Aims Adaptation mechanisms of plants to environment can be classified as genetic differentiation and phenotypic plasticity (environmental modification). The strategy and mechanism of plant adaptation is a hot topic in the field of evolutionary ecology. Leymus chinensis is one of constructive species in the Nei Mongol grassland. Particularly, Leymus chinensis is a rhizomatous and clonally reproductive grass, a genotype that can play an important role in the community. In this study, we aimed to (1) investigate the phenotypic plasticity of L. chinensis under different conditions, and (2) test the genetic differentiation and reaction norms (the relationship between the environment and the phenotype of an individual or a group of individuals) under four environmental conditions among different genotypes of L. chinensis. Methods Ten genotypes of L. chinensis were randomly selected. Under the control condition, we studied the effects of genotype, defoliation, drought and their interactions on 11 quantitative traits of growth (8 traits including photochemical efficiency of photosystem II, maximum net photosynthetic rate, transpiration rate, specific leaf area, relative growth rate, the number of tillers increased, aboveground and underground biomass growth), defense (total phenol concentration of leaf) and tolerance (non-structural carbohydrate content of root, root/shoot ratio) of L. chinensis. We studied the phenotypic plasticity, genetic differentiation and reaction norms mainly through tested the effect of environment and genotype on these traits. Important findings First, all 11 traits showed obvious phenotypic plasticity (i.e., significant effect of drought, defoliation and their interactions). The expression of 10 genotypes of L. chinensis was divergent under different environmental conditions. Interactions of genotype and environment significantly affected the maximum net photosynthetic rate, transpiration rate, specific leaf area, relative growth rate, total phenolic concentration of leaf, and total non-structural carbohydrate content of root. This indicated that the phenotypic plasticity of these five traits exhibited genetic differentiation. Second, the increase of number of tillers, belowground biomass and non-structural carbohydrate content of root did not show genetic differentiation under the same condition. The other eight traits showed significantly genetic differentiation, and the heritabilities (H2) of six traits related to growth were higher than 0.5. The leaf total phenol concentration and root/shoot ratio showed genetically differentiation only under the drought and defoliation condition, with the heritabilities being 0.145 and 0.201, respectively. These results explained why L. chinensis widely distributed in the Nei Mongol grassland, and provided genetic and environmental basis for related application and species conservation in this grassland ecosystem.     

Effects of the supply levels and ratios of nitrogen and phosphorus on seed traits of Chenopodium glaucum北大核心CSCD

Aims Global nitrogen (N) deposition not only alters soil N and phosphorus (P) availability, but also changes their ratio. The levels and ratios of N and P supply and their interaction may simultaneously influence plant seed traits. However, so far there has been no experiments to distinguish these complex impacts on plant seed traits in the field. Methods A pot experiment with a factorial design of three levels and ratios of N and P supply was conducted in the Nei Mongol grassland to explore the effects of levels and ratios of N and P supply and their interaction on seed traits of Chenopodium glaucum. Important findings We found that the relative contribution (15%–24%) of N and P supply levels in affecting the N concentrations, P concentrations and germination rates of seeds was larger than that (3%–7%) of N:P supply ratios, whereas seed size was only significantly influenced by N:P. Simultaneously, seed N and P concentrations were impacted by the interaction of N and P supply levels and ratios. At the same N:P, decrease in nutrient supply levels increased seed N concentrations, P concentrations and germination rates. N:P supply ratios only had a significant effect on seed size and germination rates under low nutrient levels. Overall, these results indicate that different seed traits of C. glaucum show different sensitivities to N or P limitations, leading to adaptive and passive responses under different nutrient limitations. This study presents the the first field experiment to distinguish the effects of nutrient supply levels, ratios and their interactions on plant seed traits, which provides a new case study on the influences of global N deposition on future dynamics of plant population and community. © Chinese Journal of Plant Ecology.     

Dynamics in foliar litter decomposition for Pinus koraiensis and Quercus mongolica in a snow-depth manipulation experiment北大核心CSCD

Aims Changes in snowpack induced by climate change may alter water and heat regimes at the ground surface, thus influencing activities of decomposers and litter decomposition in snow-covered regions. However, effects of snow-depth changes on litter decomposition are unclear. Our objective was to characterize the decomposition dynamics of two contrasting tree species—Korean pine (Pinus koraiensis) and Mongolian oak (Quercus mongolica) in a snow-depth manipulation experiment. Methods The snow-depth manipulation experiment that included three treatments (i.e., snow-addition, snow-removal, and control) was conducted in a temperate Korean pine plantation in the Maoershan Forest Ecosystem Research Station, Northeast China. Air-dried foliar litter of the pine or oak (10 g litter per bag) was sealed in a nylon litterbag (15 cm × 20 cm). A total of 648 litterbags (3 plots × 3 treatments × 2 tree species × 3 replicates × 12 sampling dates) were placed evenly on the forest floor in October 2014. Three replicate litterbags per species were buried in each treatment plot and sampled 12 times (i.e., freezing onset stage, deep freezing stage, thawing stage, early, middle and late snow-free seasons) during the two-year period (2014–2016) to determine the temporal variation of the decomposition rate. Associated factors (i.e., mean temperature at litter layer, freeze-thaw cycle, available nitrogen and phosphorus at the organic layer) were measured simultaneously. Important findings Tree species, snow-depth treatment, decomposition stage, and the measured associated factors all influenced the decomposition rates of the foliar litter. The litter mass loss was 52.1%–54.5% for the pine, and 53.9%–59.1% for the oak during the two-year period. The decomposition coefficients for the litter of the two species were the highest in the snow-addition plot, and the lowest in the snow-removal plot. Moreover, the snow-depth manipulation dramatically changed the relative contribution of the mass loss (R ratio) during the snow-covered or snow-free seasons to the yearly total loss. Compared with the control, the snow-addition treatment increased the R ratio during the snow-covered season by 9.1% for the pine and 10.4% for the oak, while the snow-removal treatment increased the R ratio during the snow-free season by 10.4% and 12.7%, respectively. In conclusion, changes in snowpack induced by climate change may significantly affect the foliar decomposition in temperate forests, and also alter the relative contribution of the litter decomposition in the snow-covered and snow-free seasons to the yearly decomposition. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

Effects of dew on eco-physiological traits and leaf structures of Leymus chinensis and Agropyron cristatum grown under drought stress北大核心CSCD

Aims: To investigate the effects of dew on plants, we conducted the experiment to determine the physiological characteristics and leaf structures of Leymus chinensis and Agropyron cristatum in response to increasing dew under drought stress. Methods: Four treatments (no dew, three times dew and five times dew per week under drought stress, and well-watering) were designed to examine leaf relative water content, water potential, net photosynthetic rate, water use efficiency, biomass, and leaf structures of L. chinensis and A. cristatum. Important findings: There was a significant increase in the relative water content and water potential by simulated dew increase for two plants species under drought stress (p < 0.05). For A. cristatum, simulated dew increase significantly enhanced the net photosynthetic rate, stomatal conductance, and transpiration rate of plants under drought stress (p < 0.05). On the other hand, there was no significant difference in the stomatal conductance and transpiration rate for L. chinensis among treatments. Simulated dew increase improved the aboveground biomass and root biomass of two species. The ratio of yellow leaves to the total leaves was decreased by simulated dew increase for two species. Dew increase also protected leaf structures against the drought stress, suggesting that the dew increase can slow down the death process of leaves resulted from drought stress. Therefore, the study demonstrated that dew increased the available water for the leaves of L. chinensis and A. cristatum grown in the drought stress and thus had positive effects on the photosynthesis, water physiology and plant development.     

Diversity and evolution of samara in angiosperm北大核心CSCD

Samara (winged fruit) can be dispersed easily by wind and may be a crucial factor for angiosperm spread and diversification. In a narrow sense, a samara is an indehiscent dry fruit with wing(s) developed from fruit pericarp, while in a broad sense samaras also include all winged fruits with wings developed from both pericarp and peri-anth or bracts. According to the wing shape and growth patterns of samaras, we divided samaras into six types, i.e. single-winged, lanceolate-winged, rib-winged, sepal-winged, bract-winged, and perigynous samaras. Perigynous samaras can be further classified into two forms, i.e. round-winged and butterfly-winged samaras. Accordingly, the aerodynamic behavior of samaras can be classified into five types, autogyro, rolling autogyro, undulator, helicopter, and tumbler. The rib-winged and round-winged samaras can be found in Laurales, a basal angiosperm, and may represent the primitive type of early samaras. In the derived clades, samaras evolved enlarged but unequal wings and decreased wing loading (the ratio of fruit weight to wing size), which is likely an adaptation to gentle wind and secondary dispersal through water or ground wind. The wings of some samaras (such as sepal-winged and bract-winged samaras) may have multiple functions including wind dispersal, physical defense for the seeds, and adjust seed germination strategy. The pantropical family Malpighiaceae is extraordinarily rich in samara types, which is likely related to its multiple inter-continent dispersal in history, which is known as “Malpighiaceae Route”. Therefore, Malpighiaceae can be used as a model system for the studies on samara adaptation and evolution. We identified the following issues that deserve further examination in future studies using both ecological and evo-devo methods: 1) the adaption of different types of samaras in dispersal processes, 2) the molecular and developmental mechanism of sepal- and bract-wings, and 3) the evolution of samara types and their effects on angiosperm diversification. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

Leaf surface traits: overlooked determinants of birch resistance to herbivores and foliar micro-fungi?

Previous studies on the mechanisms of birch resistance to herbivores and foliar micro-fungi (both pathogenic and endophytic) have focused mainly on the role of internal leaf chemistry. In the present study, we examined genetic correlations between leaf surface traits (glandular trichome density and total concentrations of surface flavonoid aglycones) and occurrence of three species of foliar micro-fungi, one pathogenic rust (Melampsoridium betulinum) and two endophytic fungi (Fusicladium sp. and Melanconium sp.), and performance of autumnal moth larvae (Epirrita autumnata) in two birch species, Betula pubescens ssp. czerepanovii and B. pendula. The performance of autumnal moth larvae on B. pubescens ssp. czerepanovii was negatively correlated with density of glandular trichomes (RGR: r=–0.855; pupal mass: r=–0.709). In addition, rust infection was negatively correlated with trichome density in B. pendula (r=–0.675) and with epicuticular flavonoid aglycones in B. pubescens ssp. czerepanovii (r=–0.855). The frequency of the endophytic fungus Fusicladium sp., was related to epicuticular flavonoid aglycones (r=–0.782), while another endophytic fungus, Melanconium sp., showed no associations with any of the studied variables in B. pubescens ssp. czerepanovii. Our results indicate that leaf surface traits may be at least as important determinants of herbivore performance and micro-fungi abundance in birch as leaf internal chemistry.     

Are lianas more drought-tolerant than trees? A test for the role of hydraulic architecture and other stem and leaf traits

Lianas are an important component of Neotropical forests, where evidence suggests that they are increasing in abundance and biomass. Lianas are especially abundant in seasonally dry tropical forests, and as such it has been hypothesized that they are better adapted to drought, or that they are at an advantage under the higher light conditions in these forests. However, the physiological and morphological characteristics that allow lianas to capitalize more on seasonal forest conditions compared to trees are poorly understood. Here, we evaluate how saplings of 21 tree and liana species from a seasonal tropical forest in Panama differ in cavitation resistance (P ₅₀) and maximum hydraulic conductivity (K _h), and how saplings of 24 tree and liana species differ in four photosynthetic leaf traits (e.g., maximum assimilation and stomatal conductance) and six morphological leaf and stem traits (e.g., wood density, maximum vessel length, and specific leaf area). At the sapling stage, lianas had a lower cavitation resistance than trees, implying lower drought tolerance, and they tended to have a higher potential hydraulic conductivity. In contrast to studies focusing on adult trees and lianas, we found no clear differences in morphological and photosynthetic traits between the life forms. Possibly, lianas and trees are functionally different at later ontogenetic stages, with lianas having deeper root systems than trees, or experience their main growth advantage during wet periods, when they are less vulnerable to cavitation and can achieve high conductivity. This study shows, however, that the hydraulic characteristics and functional traits that we examined do not explain differences in liana and tree distributions in seasonal forests.     

Effects of nitrogen addition on photosynthetic characteristics of Leymus chinensis in the temperate grassland of Nei Mongol,China北大核心CSCD

Aims The increased atmospheric nitrogen (N) deposition due to human activity and climate change greatly causes grassland ecosystems shifting from being naturally N-limited to N-eutrophic or N-saturated, and further affecting the growth of grass species. The aims of this study are: 1) to evaluate the effects of different N addition levels on morphology and photosynthetic characteristics of Leymus chinensis; 2) to determine the critical N level to facilitate L. chinensis growth. Methods We conducted a different N addition levels experiment in dominant species in the temperate steppe of Nei Mongol. The aboveground biomass, morphological and leaf physiological traits, pigment contents, chlorophyll a fluorescence parameters and biochemical parameters of L. chinensis were investigated. Important findings Our results showed that aboveground biomass first increased and then decreased with the increased N, having the highest values at the 10 g N·m-2·a?1 treatment, but the 25 g N·m-2·a?1 still significantly increased the aboveground biomass relative to 0 g N·m-2·a?1. Leymus chinensis accommodate low N situation through allocating less N to carboxylation system and decreasing leaf mass per area (LMA) in order to get more light energy. Moderate N addition captured more light energy through increasing total chlorophyll (Chl) contents and decreasing the ratio of Chl a/b. Moderate N addition increased LMA, carboxylation efficiency, maximum car boxylation rate (Vcmax), maximum electron transport rate (Jmax) and decreased Jmax/Vcmax, thus allocating more N to carboxylation system to enhance carboxylation capability. Moreover, the photochemical activity of PSII was increased through higher effective quantum yield of PSII photochemistry, electron transport rate and photochemical quenching coefficient. Excessive N addition had negative effects on physiological variables of L. chinensis due to lower carboxylation capability and photochemical activity of PSII, further leading to decreased net photosynthetic rate, whereas increased non-photochemical quenching coefficient and carotenoids played the role in the dissipation of excess excitation energy. Overall, moderate N addition facilitated the photosynthetic characteristics of dominant species, but excessive N addition inhibited photosynthetic characteristics. The most appropriate N addition for the growth of L. chinensis was 5-10 g N·m-2·a?1 in the temperate steppe of Nei Mongol, China.     

Comparison of methods for detecting vulnerability of xylem embolism in Robinia pseudoacacia北大核心CSCD

Aims The vulnerability of xylem embolism is one of the key physiological factors that are related to plant mortality. Vulnerability curves are typically used for determining the vulnerability of xylem embolism. However, the shapes of vulnerability curves vary with the methods of assessment, especially in plant species with long xylem vessels. This study aims to investigate the feasibility of using different methods for establishment of vulnerability curves. Methods Robinia pseudoacacia branches, with long xylem vessels, were used as plant materials for comparison of three different methods in establishing vulnerability curves, including bench top dehydration, Cochard Cavitron centrifugation and Sperry centrifugation. In the Sperry centrifugation method, rotors of two different sizes were used to test the ‘open vessel artifact’ hypothesis. Important findings The vulnerability curve established by the bench top dehydration method displayed an “s” shape, while both the Cochard Cavitron centrifugation and Sperry centrifugation methods produced “r” shape curves. Vulnerability curves derived from the bench top dehydration method and the centrifugation methods were significantly different. Using the Sperry centrifugation method, the R. pseudoacacia branch samples in the 14.4 cm rotor had a higher proportion of open vessels, while the embolic vulnerability curves established on the 27.4 cm and 14.4 cm long stem segments were similar, indicating that the Sperry centrifugation method does not produce “open vessel artifact”. © Chinese Journal of Plant Ecology.     

Response of vegetation and soil carbon accumulation rate for China's mature forest on climate change北大核心CSCD

Aims This study aims to evaluate the impacts of future climate change on vegetation and soil carbon accumulation rate in China's forests. Methods The vegetation and soil carbon storage were predicted by the atmosphere-vegetation interaction model (AVIM2) based on B2 climate change scenario during the period of 1981 2040. This study focused on mature forests in China and the forested area maintained constant over the study period. The carbon accumulation rate in year t is defined as the carbon storage of year t minus that of year t 1. Important findings Under B2 climate change scenario, mean air temperature in China's forested area was projected to rise from 7.8 °C in 1981 to 9.0 °C in 2040. The total vegetation carbon storage was then estimated to increase from 8.56 Pg C in 1981 to 9.79 Pg C in 2040, meanwhile total vegetation carbon accumulation rate was estimated to fluctuate between 0.054 0.076 Pg C•a1, with the average of 0.022 Pg C•a1. The total soil carbon storage was estimated to increase from 30.2 Pg C in 1981 to 30.72 Pg C in 2040, and total soil carbon accumulation rate was estimated to vary in the range of 0.035 0.072 Pg C•a1, with the mean of 0.010 Pg C•a1. The response of vegetation and soil carbon accumulation rate to climate change had significant spatial difference in China although the two time series did not show significant trend over the study period. Our results also showed warming was not in favor of forest carbon accumulation, so in the northeastern and southeastern forested area, especially in the Changbai Mountain, with highest temperature increase in the future, the vegetation and soil carbon accumulation rate were estimated to decrease greatly. However, in the southern of southwestern forested area and other forested area, with relatively less temperature increase, the vegetation and soil carbon accumulation rate was estimated to increase in the future.     

Spatio-temporal characteristics of evapotranspiration and water use efficiency in grasslands of Xinjiang北大核心CSCD

Aims: Xinjiang is located in the hinterland of the Eurasian arid areas, with grasslands widely distributed. Grasslands in Xinjiang provide significant economic and ecological benefits. However, research on evapotranspiration (ET) and water use efficiency (WUE) of the grasslands is still relatively weak. This study aimed to explore the spatio-temporal characteristics on ET and WUE in the grasslands of Xinjiang in the context of climate change. Methods: The Biome-BGC model was used to determine the spatio-temporal characteristics of ET and WUE of the grasslands over the period 1979-2012 across different seasons, areas and grassland types in Xinjiang. Important findings: The average annual ET in the grasslands of Xinjiang was estimated at 245.7 mm, with interannual variations generally consistent with that of precipitation. Overall, the value of ET was lower than that of precipitation. The higher values of ET mainly distributed in the Tianshan Mountains, Altai Mountains, Altun Mountains and the low mountain areas on the northern slope of Kunlun Mountains. The lower values of ET mainly distributed in the highland areas of Kunlun Mountains and the desert plains. Over the period 1979-2012, average annual ET was 183.2 mm in the grasslands of southern Xinjiang, 357.9 mm in the grasslands of the Tianshan Mountains, and 221.3 mm in grasslands of northern Xinjiang. In winter, ET in grasslands of northern Xinjiang was slightly higher than that of Tianshan Mountains. Average annual ET ranked among grassland types as: mid-mountain meadow < swamp meadow < typical grassland < desert grassland < alpine meadow < saline meadow. The highest ET value occurred in summer, and the lowest ET value occurred in winter, with ET in spring being slightly higher than that in autumn. The higher WUE values mainly distributed in the areas of Tianshan Mountains and Altai Mountains. The lower WUE values mainly distributed in the highland areas of Kunlun Mountains and part of the desert plains. The average annual WUE in the grasslands of Xinjiang was 0.56 g kg-1, with the seasonal values of 0.43 g kg-1 in spring, 0.60 g kg-1 in summer, and 0.48 g kg-1 in autumn, respectively. Over the period 1979-2012, the values of WUE displayed significant regional differences: the average values were 0.73 g kg-1 in northern Xinjiang, 0.26 g kg-1 in southern Xinjiang, and 0.69 g kg-1 in Tianshan Mountains. There were also significant differences in WUE among grassland types. The values of WUE ranked in the order of mid-mountain meadow < typical grassland < swamp meadow < saline meadow < alpine meadow < desert grassland.     

Nonlinear responses of productivity and diversity of alpine meadow communities to degradation北大核心CSCD

Aims The alpine meadow degradation could have profound effects on the grassland productivity. The aim of our study is to clarify the dynamic response of community productivity and species diversity in the process of alpine meadow degradation. Methods In the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Northern Tibetan Grassland Ecosystem Research Station (Nagqu station), we conducted stages experiments with multiple degradation levels: control, mild degraded meadow, moderate degraded meadow, severe degraded meadow and serious sandy meadow. Important findings The response of aboveground biomass to alpine meadow degradation showed a linear or nonlinear increased response patterns, but the belowground biomass and total biomass decreased nonlinearly. As observed in measurement of aboveground biomass, Margalef index, Simpson index, Shannon-Wiener index and Pielou evenness index also exhibit a nonlinear increased response to degradation. The results of structural equation models showed that belowground biomass has a positive relationship with soil carbon content (p < 0.05) and volume water content (p < 0.1). However, soil nutrient and soil physical properties had no significant impact on aboveground biomass (p < 0.1). Compared with soil physical properties, soil nutrition is an important factor influencing the diversity index. In our study, the nonlinear responses of productivity and diversity of alpine meadow were described by using the multiple levels of degradation in space. The results suggested that aboveground productivity cannot interpret the degree of degradation of alpine meadow, and by contrast, alpine meadow degradation should be measured by the change of plant functional groups, such as edible grasses and poisonous forbs. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

Characteristics and underlying mechanisms of plant deep soil water uptake and utilization: Implication for the cultivation of plantation trees北大核心CSCD

Root water uptake is an essential part of tree water relations and plays a crucial role in tree physiological activities. Water resource in deep soil is relatively abundant and can provide plenty of water to trees to guarantee their survival and healthy growth during dry seasons. Thus, a good comprehension of the characteristics and underlying mechanisms of deep soil water uptake and utilization by trees will deepen the understanding of the interaction between trees and the environment, tree survival and growth strategies, coexistence and competition among different species, etc. This knowledge is important in establishing green cultivation schemes for plantations, which depend less on the external water resources input and avoid the adverse effects on the water ecological environment. From existing studies, the characteristics and underlying mechanisms of deep water uptake and utilization by trees are reviewed. Firstly, the definition of deep roots and deep soil is discussed, and 1 m depth is recommended as the average (reference) definition standard in main forest vegetation types except the boreal forest. The reasons for the formation of deep tree roots around the globe were also determined. Secondly, the observed deep soil water uptake characteristics of trees and their influencing factors are summarized. Then, from the aspects of the adjustment of deep root traits and the coordination of hydraulic traits of different organs, the mechanisms of deep water uptake by trees are discussed. For example, the spatial, temporal and efficiency adjustment strategies of deep roots can be used to facilitate the absorption of deep soil water. Finally, some implications of deep soil water uptake for the cultivation of plantations are proposed, such as “for water management in plantations, trees should be induced to moderately utilize some deep soil water and an appropriate irrigation frequency should be selected”, “appropriate mixed planting of different tree species can facilitate the buffering effect of deep soil water storage”, “developing techniques of selecting trees for thinning based on the water uptake depths of different species”, etc. Deficiencies of existing studies and some future research directions were also pointed out. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All Rights Reserved.     

Effects of exotic-native species relationship on naturalization and invasion of exotic plant species北大核心CSCD

Aims: Darwin's naturalization conundrum describes the paradox that the relationship of exotic species to native residents could either promote or hinder invasion success through opposing mechanisms: niche pre-adaptation or competitive interactions. Previous Darwin's naturalization studies have showed invasion success could vary at stages, sites, and spatial and phylogenetic scales. Our objective was to assess the effects of exotic-native species relationship on invasion process of exotic plant species in China, where related research is still lacking. Methods: Generalized linear mixed models were used to examine relationship between exotic-native species relationship and performance of exotic species at different spatial scale (provincial, municipal and community) and invasion stages (naturalization, dispersal and invasion). At community scale, we measured environmental factors of communities we investigated to control the effect of habitat heterogeneity among them. Important findings: At the provincial and municipal scales, exotic species closely related to native flora were more likely to be naturalized and distributed, which is more consistent with the expectation of the pre-adaptation hypothesis. On the community scale, the exotic-native species relationship was not related to establishment and abundance of exotic species in the community. The results suggested that exotic species did not strongly compete with their close native relatives in communities, but were better adapted to areas where their close relatives had lived. Considering their high potential of naturalization and invasion, special attention should be paid to those exotic species that closely related to the native flora in the management of invasive species. © Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

Comparative genomic and protein sequence analyses of the chemotaxis system of Azorhizobium caulinodans北大核心CSCD

［Objective］ Azorhizobium caulinodans ORS571 can fix nitrogen not only as a free-living organism and an associative-symbiotic bacterium by colonizing the root surface of non-leguminous plants, but also as a symbiotic bacterium by interacting with leguminous plant Sesbania rostrata.Due to its ability to grow and fix nitrogen under three conditions, A.caulinodans uses sophisticated chemotaxis signal transduction systems to transform environmental cues into corresponding behavioral responses.Chemotaxis appears crucial for the growth of A.caulinodansin complicated environment and the construction of associative relationship with the plant.However, little is known about the chemotactic pathway of A.caulinodans.Thus, our study aimed to compare the chemotaxis-like genes of A.caulinodans with those of well-studied species.［Methods］ NCBI protein BLAST was used for searching sequence similarity with default parameter values against the genomes of A.caulinodans.HMMER3, based on Pfam database, was used for comparative analyses of methyl-accepting chemotaxis protein （MCP）.［Results］ There was a major chemotaxis cluster in A.caulinodans and the CheR methylated MCPs independently of pentapeptide motif.There were 43 MCP homologs containing diverse signal-sensing architectures in A.caulinodans.In addition,cytoplasmic domains of these MCPs were all composed of 38 heptad repeats.［Conclusion］ Despite the extremely high homology presented between the chemotactic system of A.caulinodans and those of well-studied species, A.caulinodans shows its own unique characteristics.The classification of these chemotactic pathways by comparative genomics enables us to better understand how A.caulinodansresponds to changes in environment via exquisite signal transductions in chemotaxis system.