Aims In order to understand complex speciation, it is critically important to investigate the corresponding genetic divergence and lineage sorting between close species or taxa distributed in parapatric regions. Our aim was to outline the distribution of the maternally inherited chloroplast haplotypes of Hippophae gyantsensis and H. rhamnoides subsp. yunnanensis and construct their phylogeographic relationships. The former species occurs in central and west Tibet, while the latter is distributed in northwest Yunnan and west Sichuan. These taxa are distinguished by leaf shape, trichomes and fruits.
Methods We sequenced trnL-F and trnS-G DNA fragments for 109 trees of 14 populations from these two taxa.
Important findings A total of 11 chlorotypes were identified, seven in H. gyantsensis and six in H. rhamnoides subsp. yunnanensis, with two shared. Phylogenetic and Nested Clade Analysis analyses further suggested that the divergence of these haplotypes is highly inconsistent with morphological differentiation of the two taxa, suggesting complex maternal lineage sorting between them. These findings refute the previous systematic placements of H. gyantsensis within the genus. However, the available data could not distinguish between two alterative hypotheses regarding origin of this species: homoploid hybrid versus allopatric speciation. In addition, the unique haplotypes recovered in separate populations within each of two taxa suggest that multiple refugia might have maintained both across their distributional ranges during the Last Glacial Maximum.

Aims Our objective was to investigate the actual geographical distribution patterns and model the potential distribution ranges of five Caragana species, providing their distribution scenarios under future climate change.
Methods We collected spatial distribution data for five major Caragana species in the arid to semi-arid temperate regions of northern China and mapped their current distribution ranges using ArcGIS 9.0. Fifteen water and thermal indices of biological significance were chosen and calculated based on long-term climatic observations from weather stations. Using variance analysis, multiple comparison and factor analysis, we investigated the dominant driving factors for the geographical distribution differences of the five Caragana species. The potential distribution of five Caragana species under present climate and the impacts of future climate change on their patterns were simulated and predicted using software “DIVA-GIS” coupled BIOCLIM, a species distributional model.
Important findings Distributions of C. microphylla, C. intermedia and C. korshinskii occurred in a substitution pattern from east to west, then replacement by C. tibetica southwestward and C. stenophylla northwestward. Moisture especially humidity, was the dominant factor for C. microphylla and C. intermedia. Precipitation during the growing season and annual mean precipitation dominated the distributions of C. intermedia and C. korshinskii. Maximum summer temperature controlled the distribution of C. korshinskii and C. tibetica, and minimum winter temperature determined the ranges of C. korshinskii and C. stenophylla. Simulated present distributions matched actual distribution ranges. Under the future climate scenario with doubled CO₂ concentration, the five Caragana species all shifted northward and reduced their areas in China. Evaluation by ROC curve and Kappa statistic showed that BIOCLIM predicted accurately.

Aims Vegetation distributions are determined by diverse environmental conditions at different spatial scales. Our aim is to analyze the relationship between environmental factors and vegetation cover at different spatial scales.
Methods We obtained the distribution of NDVI in the Ordos Basin by mapping the remote sensing data (landsat5 TM). Using GIS software, we built a geo-database in the form of a thematic map and carried out spatial analysis to detect the relationship between the environment factors and NDVI at different spatial scales.
Important findings At the scale of the Ordos region, mean annual rainfall plays an important role in vegetation distribution and high-cover vegetation mainly occurs in geomorphology regions of diluvial and alluvial deposits. At the scale of the Kubuqi Desert, geohydrologic condition is one of the important factors contributing to the distribution of vegetation cover. In Mu-Us, the lithology of sublayer terrain greatly affects vegetation cover and distribution.

Aims Biomass and leaf area index (LAI) are important parameters for indicating crop growth potential and photosynthetic productivity in wheat. Non-destructive, quick assessment of leaf dry weight and LAI is necessary for growth diagnosis and cultural regulation in wheat production. The objectives of this study were to determine the relationships of leaf dry weight and LAI to ground-based canopy hyperspectral reflectance and spectral parameters and to derive regression equations for monitoring leaf dry weight and LAI in winter wheat (Triticum aestivum) with hyperspectral remote sensing.
Methods Three field experiments were conducted with different wheat varieties and nitrogen levels for three growing seasons, and time-course measurements were taken on canopy hyperspectral reflectance and leaf dry weight and LAI during the experiments. Experiment one was conducted in 2005-2006 to construct a monitoring model with four N rates of 0, 90, 180 and 270 kg·hm^-2 using cultivars ‘Ningmai9’ and ‘Yumai34’ (low and high protein types, respectively). Experiment two was undertaken in 2004-2005 to construct a monitoring model with four N rates of 0, 75, 150 and 225 kg·hm^-2 using cultivars ‘Ningmai9’, ‘Yangmai12’ and ‘Yumai34’ (low, medium, high protein types, respectively). Experiment three was conducted in 2003-2004 to test a monitoring model with four N rates of 0, 75, 150, 225 and 300 kg·hm^-2 using cultivars ‘Ningmai9’, ‘Huaimai20’ and ‘Xuzhou26’ (low, medium, high protein types, respectively).
Important findings Leaf dry weight and LAI in wheat increased with increasing nitrogen rates and with significant differences between stages of growth. The dynamics of leaf dry weight and LAI during growth exhibited single peak patterns. The sensitive spectral bands were located mostly within red light and near infrared regions, with correlation coefficients <-0.60 in 590~710 nm and >0.69 in 745~1 130 nm. The regression analyses between existing vegetation indices and leaf dry weight and LAI revealed that some key spectral parameters could accurately estimate changes in leaf dry weight and LAI across a broad range of stages of growth, nitrogen levels and growing seasons, with unified spectral parameters for each growth parameter. Among them, regression models based on RVI (810, 560), FD755, GMI, SARVI (MSS) and TC3 produced better estimation of leaf dry weight and LAI. Testing of the monitoring models with an independent dataset indicated that the spectral indices of RVI (810, 560), GMI, SARVI (MSS), PSSRb, (R_750-800/R_695-740)-1, VOG2 and mSR705 gave accurate growth estimation under the experimental conditions. Overall, leaf dry weight and LAI in wheat could be monitored by key vegetation indices, with more reliable estimation from RVI (810, 560), GMI and SARVI (MSS).

Aims Our objective was to determine ecological mechanisms of plant community productivity performance based on study of effects of species diversity, species identity and fertility level on productivity.
Methods We carried out an experiment with combinations of three plant species (Elymus nutans, Roegneria nutans and Festuca sinensis) under three different fertility levels in an area of subalpine meadow in Hezuo County, Gansu Province, China. Using seeds collected in the area, we sowed seeds in monoculture with sowing densities of 20, 40 and 60 seeds·pot^-1, in mixtures with sowing densities of each pair of species of 20/20, 20/40 and 40/20 seeds·pot^-1 and in mixtures of all three species at a sowing density of 20/20/20 seeds·pot^-1. We fixed seedling density at half of the sowed density. The pots were fertilized with 0, 2.5 and 5.0 g of phosphorate ammonium at tillering and jointing stages. There were five replicates of each treatment. We regularly removed weeds by hand. Aboveground biomass in each pot was harvested, dried and measured by species by early October.
Important findings Under conditions of no-fertility and fertilizing 5.0 g diammonium phosphate per pot, aboveground biomass did not increase significantly with increasing species diversity; however, under condition of fertilizing 10.0 g diammonium phosphate per pot, aboveground biomass increased significantly with increasing species diversity. Compared with Festuca sinensis, both Elymus nutans and Roegneria nutans made larger contributions to community productivity. But the effects of different fertility levels and sowing density were not the same. Results suggest that effects of species diversity on productivity varied because of variation of soil fertility. Productivity of plant communities may be mainly influenced by species identity, in correspondence with resource use under the conditions of the habitat. The high productivity in the high fertility level was caused by species or species assembly, which can better adapt to the high soil fertilization, rather than by species diversity. Therefore, plant community productivity does not necessarily relate to plant species diversity, but relates to soil fertility level and species identity determined by the soil fertility.

Aims Cunninghamia lanceolata and Pinus massoniana forest ecosystems in subtropical China are important in national carbon budgets because of their large area and amount of carbon storage. Soil respiration is the second largest flux in the global carbon cycle, but the effect of these forest ecosystems on soil respiration is inadequately understood. Our objectives were to compare soil respiration rate, soil temperature, soil moisture and Q₁₀ value of the two communities and to evaluate relationships between soil respiration rates and environment factors.
Methods We examined seasonal variations of soil respiration using an infrared gas exchange analyzer (Li-Cor 6400-09) from January to December 2007 in Tianjiling National Forestry Park, Changsha. Soil temperature and moisture were measured at the same time at 5 cm depth. At the middle of January, April, July and October, we examined whole samples of root biomasses at 60 cm depth. We evaluated Q₁₀ values of soil respiration and correlations between soil respiration and environment factors.
Important findings The two communities had significantly different patterns in seasonal soil respiration processes. The two forests exhibited irregularly fluctuating curves during the study period with mean rates of soil respiration of 186.9 and 242.4 mg CO₂·m^-2·h^-1 in C. lanceolata and P. massoniana stands, respectively. Significant relationships were found between soil respiration rate and soil temperature in both communities and are best described by exponential equations. However, no significant relationships were found between soil respiration and soil moisture. Soil temperature and moisture could explain changes in soil respiration of 91.7% and 78.0% in the C. lanceolata community and 5.4% and 8.4%, in the P. massoniana community. The relationship between soil respiration rate (y) and soil temperature (t) is described by the regression equation: y=34.09e ^{0.081 5t} (R²=0.917, p<0.001), y=48.68e ^{0.075 4t} (R²=0.780 3, p<0.001). R ²=0.917, p<0.001. The Q₁₀ values in C. lanceolata and P. massoniana forests were 2.26 and 2.13, respectively, and tended to decrease when soil temperature increased from lower to higher scales. Seasonal patterns of soil respiration in these two forests were not only determined by soil temperature and soil moisture, but also by fine root mass and litter production.

Aims Steppe dominated by Stipa grandis and Leymus chinensis is the zonal vegetation in the temperate steppe region of China and eastern Eurasia. It has been heavily disturbed by overgrazing in China. Our objective was to investigate the spatial pattern of L. chinensis in a degraded community of steppe during restorative succession.
Methods We studied three fenced plots of degraded steppe in the Xilin Gole League, Inner Mongolia, China, which had been monitored by the Inner Mongolia Grassland Ecosystem Research Station, Chinese Academy of Sciences. We applied a new method of photography to measure the population pattern of L. chinensis, analyzing the point pattern, the area of “hole”, population territory area and territory density in different restorative succession stages.
Important findings During the process of restorative succession, the L. chinensis population increased, decreased and became stable. The population originally increased because colonization exceeded self-thinning. The decrease resulted primarily from interspecific competition and secondarily from intraspecific competition. The change of the hole was the result of the increase and decrease of L. chinensis, which led to the change of the pattern type. The distribution of Leymus chinensis was clumped at 0-4.85 m and random at 4.85-10 m in the sample plot fenced-off since 1983. It was clumped at 0-3.01 m, random at 3.01-3.37 m and regular at 3.37-10 m in the sample plot fenced-off since 1996. But it was clumped at 0-10 m in the seriously degraded community.

Aims Our objectives were to 1) explore variations of stand structure and spatial pattern after surface fire in Mongolian pine forest of the Hulun Buir sand region and 2) elucidate surface fire as a dynamic driving force in stand thinning and succession.
Methods Fire-killed and live trees were mapped in two 1-hm² plots one year postfire. Differences of fire intensities and stand structures were tested by the Kruskal-Wallis procedure, and spatial patterns were explored using the pair correlation function g(r).
Important findings Tree densities decreased greatly and basal areas were decreased slightly by surface fire with similar intensities. Fire-killed trees showed a nested, double-cluster, positively correlated pattern. Stems were aggregated spatially pre- and postfire; however, the ranges of significant scales were narrower postfire. Adults and saplings were independent or slightly negatively associated at small scales. We conclude that surface fire is an important driving force of stand thinning and variations in spatial pattern that influence succession to mature forest.

Aims Pinus massoniana and Schima superba are important coniferous and broad-leaved species, respectively, in timber plantations in the subtropical mountain area of China. Our aim was to elucidate the effects of competition on foraging behavior of these two species in a heterogeneous nutrient environment to provide scientifically based guidelines for mixed afforestation establishment in South China.
Methods We designed a pot experiment consisting of three treatments to evaluate effects of competion on seedling growth and foraging behavior of P. massoniana and S. superba. The treatments were single-, pure- and mixed-plantings under heterogeneous and homogeneous environments.
Important findings Compared with the homogeneous nutrient envionment, seedlings in the heterogeneous nutrient environment were taller, had greater dry matter accumulation and had more effective nutrient absorption with increased root proliferation in the nutrient-rich patches. In the heterogeneous environment, S. superba had better growth in mixed- than in single- and pure-plantings, and exhibited enhancement of root morphological and physiological plasticity in foraging patchy nutrients. Pinus massoniana in the mixed-planting also was taller, not only because of little change of root scale, sensitivity and precision but also increased nutrient absorption efficiency. However, intraspecific competition reduced root scale, sensitivity and root N, and P content and resulted in significantly decreased seedling height and dry matter accumulation. Schima superba was affected more markedly by intraspecific competition than P. massoniana in the heterogeneous environment. It is suggested that mixed-plantings can improve the growth of P. massoniana and S. superba and appropriate decrease of initial density or timely control of stand density can increase the productivity of pure plantations of the two species.

Aims Floral longevity is assumed to reflect a balance between the benefit of increased pollination success and the cost of flower maintenance. Hedychium is the only large genus distributed from the tropics to high elevations in the Zingiberaceae. Members of this genus vary greatly in floral longevity. The floral longevity of H. villosum var. villosum is 5 days, which is much longer than other sympatric gingers. Our objective was to assess the effects of floral longevity on male and female fitness of H. villosum var. villosum through manipulated experiments.
Methods We reduced the functional floral longevity for female function by clipping stigmas and measured the fruit-set of different treatments to test whether long flowering duration increased female fitness. We compared the pollen grain number of flowers in different stages to determine if long floral longevity benefited pollen dispersal.
Important findings Fruit-set increased with increased female functional duration. Flowers with functional floral longevity of 1 day had only 1.85% ± 1.59% fruit-set, which was significantly lower than 20.96% ± 4.13% fruit-set of control flowers with natural longevity. Mean pollen grain number was similar in unopened flowers and flowers 1 day after anthesis, but less in flowers 2, 3 and 4 days after anthesis. These results indicate that long floral longevity is advantageous to both female and male fitness in H. villosum var. villosum. Long floral longevity may contribute to exploring new habitats and spreading toward high elevation areas from tropical areas in the Zingiberaceae.

Aims Resource allocation plays a central role in linking life history evolution and functional plant ecology. Stipa species are widely distributed in the Inner Mongolia grassland of China; however, their resource allocation patterns are not well addressed. We selected three Stipa species, S. krylovii, S. grandis and S. baicalensis and examined their reproductive allocation patterns at four organizational levels. We focused on two specific questions: 1) do these Stipa species exhibit similar or different reproductive allocation patterns at the same organizational level and 2) which step of biomass reproductive allocation is limiting the plant performance of each species?
Methods We conducted this experiment in three sites dominated by S. krylovii, S. grandis and S. baicalensis, respectively, in Inner Mongolia grassland in 2007. At each site we investigated the density, height and biomass of reproductive tillers and vegetative tillers of each species in ten quadrats (1 m×1 m). We randomly sampled 50 reproductive tillers of each species and analyzed reproductive allocation at different organizational levels.
Important findings Three Stipa species exhibited significant divergence in reproductive allocations at different organizational levels. At the bunch level, S. krylovii and S. grandis allocated more biomass to reproductive tillers than S. baicalensis. At the reproductive tiller level, S. krylovii allocated less biomass to reproductive tillers than S. grandis and S. baicalensis. At the spike level, S. grandis and S. krylovii allocated about 60% and 50% biomass to diaspore, respectively, while S. baicalensis allocated about 40% biomass to diaspores. At the diaspore level, S. grandis and S. krylovii allocated about 70% and S. baicalensis allocated about 90% biomass to fertilized diaspores. Despite these differences, the fraction of fertilized diaspore biomass in bunch biomass exhibited convergence. The species had different bottlenecks in reproductive allocation. Stipa grandis and S. krylovii were limited by the allocation of biomass from reproductive tillers to spikes, while S. baicalensis was limited by the allocation of biomass from bunch to reproductive tiller or by the allocation from spike to diaspores. Our experiment suggests these species have developed different life history strategies.

Aims Dry matter partitioning is the basis of external quality formation of ornamental plants. Nitrogen is the important nutrient affecting dry matter partitioning of plants. Our aim was to quantitatively investigate the effects of nitrogen on dry matter partitioning of standard cut chrysanthemum (Dendranthema morifolium ‘Shenma’) grown in a solar greenhouse.
Methods We conducted our experiments using different planting dates and different levels of nitrogen application rates in a solar greenhouse in Beijing, China during October 2005 and July 2006. The integrated photo-thermal index, the product of thermal effectiveness, photosynthetically active radiation (PAR) and day length (PTEP), was used to describe changes of the partitioning indices of leaf, stem and flower with development stages. Effects of the accumulated leaf nitrogen content at bud-showing stage on the dynamics of the partitioning indices of leaf, stem and flower were quantified based on experimental data. Based on these quantitative relationships, we developed a model for predicting the effects of nitrogen on dry matter partitioning. Independent experimental data were used to validate the model.
Important findings The seasonal maximum accumulated leaf nitrogen content occurred at the bud- showing stage, and the optimal value at this stage is 1.62 g·m^-2. Based on the 1:1 line, the coefficients of determination (R²) between the simulated and measured dry weight of stem, leaf and flower were 0.96, 0.97 and 0.94, respectively, and the relative prediction errors (RSE) between the simulated and measured dry weight of stem, leaf and flower were 8.26%, 5.76% and 3.70%, respectively. The model we developed can satisfactorily predict dry weight of stem, leaf and flower using greenhouse air temperature, radiation, day length and the accumulated leaf nitrogen content at the bud-showing stage as inputs; hence, it can be used for the optimization of nitrogen management for standard cut chrysanthemum ‘Shenma’ production in solar greenhouse.

Aims It is often assumed that trees near the high-elevation tree limit fall short in photosynthate (source limitation). Alternatively, low temperature may restrict carbon investment (growth, sink limitation). The content of mobile nonstructural carbohydrates (NSC) in tissues is considered as a measure of the carbon source-sink balance. Our objective was to test source vs. sink limitation. We compared late-season NSC concentrations in leaves and branches of Betula ermanii across elevational gradients from the subalpine forest interior to tree line on the north slope of Changbai Mountain, China.
Methods We sampling the leaves and branches of B. ermanii on August 25, 2007. The NSC (including dissolubility total sugar, sucrose, and fructose) concentration was measured using a modified anthrone method; the perchloric acid method was used for starch concentration measure.
Important findings The NSC (including starch) concentrations in branches increased significantly with elevation, while there were no significant trend in leaves. The ratio of starch to sugar decreased with elevation in branches and leaves. The overall elevational trends of the NSC revealed no depletion of carbon reserves near the tree limit, suggesting that sink limitation predominates across this treeline ecotone community.

Aims Our aims were to reveal the effects of acid rain stress on photosynthesis of three angiosperms (Parakmeria lotungensi, Lithocarpus glaber and Carya cathayensis) of different evolutionary ages, test the hypothesis that species with longer evolutionary time have higher adaptability and interpret results in terms of vegetation reconstruction in regions with severe acid rain.
Methods Three simulated acid rain treatments were randomly applied to the species: severe acid rain (pH 2.5), moderate acid rain (pH 4.0) and control (pH 5.6). The light response curves were determined in April 2007.
Important findings Under different acid rain treatments, maximum net photosynthetic rate (P_nmax) of P. lotungensi was in the order of pH 2.5 > pH 4.0 > pH 5.6, while that of L. glaber was pH 5.6 > pH 4.0 > pH 2.5 and there were no significant differences for C. cathayensis. In the control, the order of P_nmax was L. glaber > P. lotungensi > C. cathayensis. However, in the treatments with pH ≤ 4.0, the order was P. lotungensi > L. glaber > C. cathayensis. Therefore, P. lotungensi has higher photosynthetic capacity and higher adaptability than the other two species under acid rain stress. Compared with the other two species, P. lotungensi is a more favorable species for vegetation reconstruction in regions with severe acid rain.

Aims Camptotheca acuminate is a common tree species in southern and eastern China. It is planted widely as a virescence species and is cultivated as an officinal species, because its seed, leaf and stem can be used to distill camptothecin, which is used to treat cancer. Our objective was to examine C. acuminate’s resistance to waterlogging.
Methods One-year seedlings of C. acuminata were grown in pots in a greenhouse in January, and we implemented four treatments in May: CK (common soil water content), A (water level 10 cm under soil surface), B (water level equal with soil surface) and C (water level 4 cm above soil surface). Treatments lasted 21 days, and indexes of lenticels, root growth, root vigor, POD, SOD, MDA and LDH were determined at different times after treatment.
Important findings Root growth was better in A and CK treatments, and roots gradually died in B and C treatments. Comparatively, root vigor was higher in A and decreased gradually under B and C with treatment time. Many lenticels were observed on the stem under B and C, but not under CK and A. The POD and SOD activity of leaves of A treatment were higher during treatment, but increased and then decreased under B and C treatments. The production rate of O₂^-·, H₂O₂ content and MDA content of leaves of A, B and C treatments increased gradually with treatment time, but was higher under C and B treatments. The LDH activity of roots in A, B and C treatments was lower early in treatment, but increased significantly late in treatment. We conclude that C. acuminata grows well in lightly waterlogged sites, but not in waterlogged and flooded sites.

Aims Increasing global N deposition will lead to severe damage to bryophytes due to their sensitivity to N deposition. Our objective is to examine the responses of three species of bryophytes, widely distributed in South China, to simulated N deposition.
Methods Four N addition treatments (Control, 20, 40 and 60 kg N·hm^-2) in three replicates were established for Reboulia hemisphaerica, Hypnum plumaeforme, and Pogonatum cirratum subsp. fuscatum. The N additions were divided into four applications.
Important findings With N addition treatments in the range of 0-60 kg N·hm ^-2 for H. plumaeforme, photosynthesis, concentrations of starch, soluble sugars, total N and soluble proteins all increased with increasing N addition. Inducible nitrate reductase activity (NRA) of H. plumaeforme at control conditions was very high, indicating its N-limited situation. K ⁺ leakage of H. plumaeforme increased at 20 kg N·hm ^-2 treatment, but did not further increase at higher N addition concentrations. Most of the physiological indices of P. cirratum subsp. fuscatum showed similar trends within an N treatment of 0-40 kg N·hm ^-2, but showed opposite trends at >40 kg N·hm ^-2. Inducible NRA of P. cirratum subsp. fuscatum at the control condition was 2.20 µg N·g ^-1 FW·h^-1, but decreased dramatically when treated with N. Its K⁺ leakage only increased significantly at the 60 kg N·hm^-2 N addition treatment. Soluble sugars and soluble proteins of R. hemisphaerica were not significantly different at different N treatments, but photosynthesis and the starch concentration were lower at 20 and 40 kg N·hm ^-2treatments than at control and 60 kg N·hm^-2 treatments, while the total N concentration changed inversely. The inducible and constituted NRA of R. hemisphaerica were both very low for all treatments, indicating its restricted ability to utilize nitrates. K ⁺ leakage of R. hemisphaerica increased significantly only at an N addition of 60 kg N·hm ^-2.

Aims Xylem hydraulic structure of water transport plays a key role in plants’ distribution, resistance to stress, etc. However, the current “flushing method” for studying characteristics of xylem hydraulic structure takes different solutions as the flushing solution, which may lead to different values of xylem hydraulic conductivity and cavitation resistance ability.
Methods We used deionized water (pH=7), the solution of 10 mmol·L^-1 oxalic acid (pH=2) and 30 mmol·L^-1 KCl (pH=7) as flush solutions to measure the hydraulic characteristics of tress of Populus tomentosa and Pinus tabulaeformis, which are the specific conductivities (Ks), leaf specific conductivities (Kl), xylem vulnerability curves and cavitation resistance ability (Ψ₅₀) .
Important findings Compared with deionized water, oxalic acid and KCl as flushing solutions led to higher xylem hydraulic conductivities (Ks, Kl) in both species. With KCl flushing, the cavitation resistance abilities (-Ψ₅₀) slightly increased in P. tomentosa and significantly increased (p<0.01) in P. tabulaeformis. However, oxalic acid led an increase in cavitation resistance in P. tomentosa but a significant decrease (p<0.01) in P. tabulaeformis. Furthermore, there was no significant linear correlation between xylem hydraulic conductivity and cavitation resistance ability for both species, measured under the same flush solution. The hydraulic conductivity with different tress length (in a range of 5-20 cm) showed that the hydraulic conductivity was stable with trees length in P. tomentosa, but greatly increased with tress length in P. tabulaeformis. Different flush solutions have different effects on xylem hydraulic structure. Furthermore, the hydraulic conductivities and cavitation resistance abilities measured with different flush solutions show a species-specific response. Thus, dynamic adjustment of components and concentration of sap in xylem conduit may facilitate a flexible response of plant hydraulic structure to changing environmental conditions.

Aims As a universal, common feature in arid and semi-arid regions, biological crusts can affect soil surface properties which may relate to seed dispersal, germination and establishment of vascular plants. Numerous studies have addressed aspects of the influence of crusts on vascular plants; however, the interaction between crusts and vascular plants is controversial. Our objective was to examine effects of biological crusts on seed germination of desert vascular plants with different seed morphologies in Gurbantunggut Desert, China.
Methods Gurbantunggut Desert, the largest fixed and semi-fixed desert in China, has well-developed biological crusts. We conducted a series of shadow experiments to examine the effects of biological crusts on seed germination of Haloxylon persicum, Ephedra distachya, Ceratocarpus arenaarius, Malcolmia africana and Lappula semiglabra.
Important findings The effects of biological crusts on germination were variable under both moist and dry conditions. The presence of crusts significantly reduced germination of Ceratocarpus arenaarius and Malcolmia africana compared with surfaces from which the crusts had been removed, but there was no significant effect on germination of the other species under dry conditions. Under moist conditions, seed germination of Haloxylon persicum, Ceratocarpus arenaarius and Lappula semiglabra was significantly lower on crust than on the surface devoided of crust, and there was no significant effect for Ephedra distachya and Malcolmia africana. In general, biological crusts affected the germination of some vascular plants, but whether the effect was negative or positive depended on water condition and biological characteristics of the seeds.

Aims Seed germination is a crucial plant life history stage related to seedling establishment, survival, fitness and life history expression. Our objectives were to determine: 1) seed germination characteristics of common woody species from the eastern Qinghai-Tibet Plateau and 2) whether differences in seed germination among species are related to seed size, dispersal mode, and mother plant altitude and habitat.
Methods We surveyed seed germination of 61 species under an alternating temperature regime (20 °C/5 °C; 12 h light/dark). We used one-way ANOVA to determine the effects of seed size, dispersal mode, altitude and habitat on final germination percentage and initial germination time, the least significant difference test (LSD) to survey the extent of differences in final germination percentage and initial germination time among dispersal categories and correlation analysis to determine the relationship between seed size and germination.
Important findings Final germination percentages of the species displayed a skewed bimodal distribution, and this implies that dormancy and low and/or continuous germination are the main germination strategies to escape adverse factors. Variances in final germination percentages and initial germination time among species were largely dependent upon dispersal mode, but a few were influenced by seed size, habitat and altitude. Wind-dispersed seeds had higher mean germination percentage (60.6%) and earlier initial germination time (9 d) than those of vertebrate-dispersed (23.4%, 23 d) and unassisted-dispersal seeds (29.5%, 17 d). Findings indicate intrinsic association between life-history characteristics such as seed germination and dispersal mode.

Aims Tripterygium wilfordii is a highly valuable traditional Chinese medicinal plant. Celastrol, an active compound of T. wilfordii, has recently received attention from pharmaceutical researchers due to its medicinal value. Environmental stress may promote the formation and accumulation of secondary metabolites of medicinal plants. Our objective was to investigate whether mild environmental stress increased the content of Celastrol in T. wilfordii.
Methods Orthogonal comparison of mild stress treatments of water, sunlight and N content were performed on the seedlings of T. wilfordii in the greenhouse. The content of Celastrol was determined by High Performance Liquid Chromatography (HPLC).
Important findings Celastrol was mainly produced in the seedling root and was increased 10.8%, 14.4% and 13.0% under the three different stress treatments, respectively. Therefore, mild stress treatment improves the synthesis and accumulation of Celastrol.

Aims Schrenk spruce (Picea schrenkiana) forest is an important zonal vegetation in Tianshan Mountain, northwestern China. In addition to being an important timber resource, P. schrenkiana has important soil and water conservation functions and makes up 98.6% of the total stand volume in the region. Schrenk spruce forest exhibits slow growth, regeneration obstacles, declining productivity and confusing size and age structure. Our aims were to 1) compare autotoxicities of three organic fractions from leaves and 2) identify autotoxins from leaves. Findings could improve understanding the mechanisms of P. schrenkiana autotoxicity.
Methods Fresh leaves were extracted with water and partitioned against diethyl ether, ethyl acetate and n-butanol sequentially. We tested the three organic fractions for inhibitory activity, using germination rate, vigor and index as germination parameters and radicle and plumule elongation and weight (wet and dry) change of seedlings as seedling growth parameters. We investigated the chemical nature of the three fractions using GC-MS-MS and NMR. The chemicals in the samples were estimated on the basis of ion-molecular messenger of MS-MS spectral of samples and MS-MS user library spectra of pure reference compounds. These findings were confirmed by comparing the retention time and mass spectral in the GC-MS-MS of samples with those of reference standards under the same conditions.
Important findings The diethyl ether fraction exhibited the strongest phytotoxicity, reducing seed germination at low concentration (IC₅₀ = 5.84 mg·ml^-1), and n-butanol had the weakest effect (IC₅₀ > 10.00 mg·ml^-1). The diethyl ether fraction had a significant inhibitory effect on seedling growth at a concentration of 1.25 mg·ml^-1, whereas, the n-butanol fraction at 1.25 mg·ml^-1 stimulated it and at 2.5 mg·ml^-1 inhibited it. Seventeen secondary metabolites were identified and quantified in the three fractions, including 2-keto-4a-methyl-8-methoxy-2,3,4,4a,5,6,11,12-ocahydro chrysene in the diethyl ether fraction (this metabolite had been found but not previously reported as an allelochemical). When we used identified components to prepare synthetic mixtures, it showed the same inhibitory effect on seed germination and seedling growth as did the three fractions.

Detailed information on the spatial and temporal variation of soil respiration and controlling factors in different terrestrial ecosystems is critical for understanding the ecosystem carbon budget and the response of soils to global climate change. Despite the importance of this topic, knowledge is limited, and key processes and mechanism need clarification. We reviewed recent research advances in the spatial and temporal variation of soil respiration, driving mechanisms and simulation. Environmental and biotic factors play key roles in regulating the temporal variations of soil respiration. Soil respiration also exhibits high levels of spatial heterogeneity, especially across small spatial scales at different time scales. The heterogeneity of vegetation cover, root distribution, major environmental factors and soil properties contributes to the spatial variation of soil respiration. Biotic factors have also been shown to have an effect on soil respiration. However, empirical models of soil respiration typically use soil temperature, soil moisture and their interaction for large-scale soil respiration estimates. Thus, significant errors may result from these models when changes in other biotic factors can confound the temperature or moisture dependence of soil respiration. Therefore, in order to accurately estimate soil respiration in target ecosystems, we must be able to account for its small-scale spatial variation and address the influence of biotic factors in explaining the variation of soil respiration at different temporal scales. Besides climatic variables, it is necessary to incorporate additional factors (biotic factors or soil properties) into these empirical models for accurately evaluating soil respiration.

Three photosynthetic pathways are used by plants: C₃, which most plants use, C₄ and crassulacean acid metabolism (CAM). C₃ is the ancestral pathway, with C₄ and CAM representing recently diverged forms. We conclude that the variation and evolution of photosynthetic pathway of C₃ and C₄ are adaptations to environmental stresses. First, we discuss the evolutional future of photosynthetic pathways. It has been suggested that low atmosphere CO₂, enhanced temperatures, drought and salinity are external drivers of C₄ photosynthetic evolution. Second, we analyze the possibility of evolution from C₃ to C₄. The polyphyletic evolution of the C₄ pathway suggests that the transition from C₃ to C₄ was relatively simple. This suggestion is supported by the observation that both C₃ and C₄ plants possess inherent plasticity in their photosynthetic characteristics. The stress causing the shift from C₃ to C₄ was involved in the environmental regulation of plants, and the C₄ pathway in C₃ plants evolved as an adaptation. The environmental stresses may have involved plant capacities for survivorship and competition in arid areas. Third, we present a simplistic model of the main phases of C₄ photosynthetic evolution and discuss the variation and evolution of C₃ and C₄ photosynthetic carbon assimilating pathways. Evolution was not directly to C₄ photosynthesis, so each step had to be stable, beginning with numerous preconditions needed for an evolutionary lineage to begin evolving C₄ characteristics. A current complication of C₄ photosynthetic evolution is global climate change and human manipulation of the biosphere. It is possible that C₄ photosynthesis can be used to resist adversity and increase the yield of C₃ crops. In conclusion, study of the evolution of photosynthetic pathway in plants provided insight into the photosynthetic physiology of plants under stress and provided new theory to reconstruct vegetation, enhance crop yield, and explain adaptation of C₃ species in arid areas.

Intrafloral stamen differentiations have adaptive significances and possible effects on plant reproduction strategies and mating patterns. Intrafloral stamen differentiations, in which stamens in a flower differ distinctly in shape, size or color of filament and/or anther and normally in function, can be classified into five main types: filament differentiation (e.g., filament length differentiation), anther differentiation (e.g., differentiation in pollen viability and anther color or size), differentiation in growth pattern of stamens (e.g., some stamens grow fused and others separately), differentiations in stamen movement (e.g., stamens move at different time and are in different dehiscence stages and different spatial position), and staminodes (i.e., some stamens have lost the function of producing viable pollen and normally have a different shape). Heteranthery, which is mostly found in enantiostylous species with mirror-image flowers, is a special type of stamen differentiation in which filament length, anther size and color, and pollen viability all are so differentiated that the two kinds of stamens show different functions: feeding stamens (normally sterile, but provide nutrients that attract and feed pollinators) and pollinating stamens (produce viable pollen). In some special types of complex breeding systems such as heterostyly and enantiostyly, intrafloral stamen differentiations are also present and differentiation modes often differ among individuals. Intrafloral stamen differentiations cause various spatial positions of anthers in a single flower, which can affect the herkogamy (spatial separation of female and male organs) and dichogamy (temporal separation of female and male functions), and the modes and foraging activities of pollinators can also be greatly affected. Consequently, plant mating patterns such as levels of selfing and sexual interferences are modified. Stamen differentiation can increase plant fitness through presenting pollen in many small doses in differentiated stamens, which can greatly enhance pollen output in plants receiving many pollinator visits, as suggested by pollen presentation theory. So, intrafloral stamen differentiations can be seen as a kind of pollen packaging and dispensing mechanism. Some adaptive significances of stamen differentiations have been recognized, but specific functions of some types (e.g., monodynamous stamens, differentiations in stamen movement time and/or mode, and trimorphic differentiation of stamen in Commelinaceae and some plants of Fabaceae) need further illumination.