Ecophysiological Leaf Traits of Forty-Seven Woody Species under Long-Term Acclimation in a Botanical Garden.

Ex situ conservation plays an important role in the conservation and utilization of plant resources. In recent years, botanical gardens have greatly improved the ex situ conservation of plants, and research has mainly focused on morphological characteristics, reproduction technology, and conservation value. There are few studies on the ecophysiological traits of plants after conservation. Forty-seven plants that are frequently used in North China and were grown in the Beijing Botanic Garden were selected to measure their photosynthetic traits, light-use efficiency (LUE), water-use efficiency (WUE), specific leaf area (SLA), relative chlorophyll content (SPAD), and leaf water potential (φ). An analysis of variance showed that there were significant differences in the ecophysiological traits of the leaves of 47 woody species. The light saturation point (LSP), net photosynthetic rate at light saturation (Pnmax), φ, and SLA had significant differences among different plant life forms. The SLA and SPAD of leaves were significantly different among the families. The LUE of all species reached its maximum under a low light intensity, and species with a large difference between the light saturation point and light compensation point had larger Pnmax values. This research further adds to the understanding of the adaptation mechanisms of plants to the environment under the conditions of a botanical garden as well as the environmental fitness in a long-term ex situ domestication and then helps with scientifically setting up artificial management conditions.

Photoregulated Morphological Transformation of Spiropyran Derivatives Achieving the Tunability of Interfacial Hydrophilicity.

Regulation of self-assembly morphology is an effective strategy to obtain advanced functional materials with expected properties. However, achieving remarkable morphological transformation by light irradiation is still a challenge. Herein, three simple spiropyran derivatives (SP1, SP2, and SP3) are constructed, achieving different degrees of morphological transformation from nanospheres to hollow tadpole-like structures (SP3), tubular structures (SP2), and microsheets (SP1) after ultraviolet light irradiation. Interestingly, the hollow tadpole-like structures (SP3) can further extend to Y-shaped or T-shaped tubular morphology. In the process, SP1, SP2, and SP3 can be isomerized from a closed-ring form (hydrophobicity) to an open-ring form (hydrophilicity) in different degrees, interacting differently with methanol solvent molecules. The formation of hollow structures or microsheets along with the isomerization of spiropyran derivatives contributes to the adjustment of the hydrophilicity of the interface. Therefore, SP1, SP2, and SP3 with photoregulated morphological transformation show promising applications in tunable interface materials.

Simulating highly disturbed vegetation distribution: the case of China's Jing-Jin-Ji region.

BACKGROUND: Simulating vegetation distribution is an effective method for identifying vegetation distribution patterns and trends. The primary goal of this study was to determine the best simulation method for a vegetation in an area that is heavily affected by human disturbance. METHODS: We used climate, topographic, and spectral data as the input variables for four machine learning models (random forest (RF), decision tree (DT), support vector machine (SVM), and maximum likelihood classification (MLC)) on three vegetation classification units (vegetation group (I), vegetation type (II), and formation and subformation (III)) in Jing-Jin-Ji, one of China's most developed regions. We used a total of 2,789 vegetation points for model training and 974 vegetation points for model assessment. RESULTS: Our results showed that the RF method was the best of the four models, as it could effectively simulate vegetation distribution in all three classification units. The DT method could only simulate vegetation distribution in units I and II, while the other two models could not simulate vegetation distribution in any of the units. Kappa coefficients indicated that the DT and RF methods had more accurate predictions for units I and II than for unit III. The three vegetation classification units were most affected by six variables: three climate variables (annual mean temperature, mean diurnal range, and annual precipitation), one geospatial variable (slope), and two spectral variables (Mid-infrared ratio of winter vegetation index and brightness index of summer vegetation index). Variables Combination 7, including annual mean temperature, annual precipitation, mean diurnal range and precipitation of driest month, produced the highest simulation accuracy. CONCLUSIONS: We determined that the RF model was the most effective for simulating vegetation distribution in all classification units present in the Jing-Jin-Ji region. The RF model produced high accuracy vegetation distributions in classification units I and II, but relatively low accuracy in classification unit III. Four climate variables were sufficient for vegetation distribution simulation in such region.

A global meta-analysis of livestock grazing impacts on soil properties.

Grazing effects on soil properties under different soil and environmental conditions across the globe are often controversial. Therefore, it is essential to evaluate the overall magnitude and direction of the grazing effects on soils. This global meta-analysis was conducted using the mixed model method to address the overall effects of grazing intensities (heavy, moderate, and light) on 15 soil properties based on 287 papers published globally from 2007 to 2019. Our findings showed that heavy grazing significantly increased the soil BD (11.3% relative un-grazing) and PR (52.5%) and reduced SOC (-10.8%), WC (-10.8%), NO3- (-23.5%), and MBC (-27.9%) at 0-10 cm depth, and reduced SOC (-22.5%) and TN (-19.9%) at 10-30 cm depth. Moderate grazing significantly increased the BD (7.5%), PR (46.0%), and P (18.9%) (0-10 cm), and increased pH (4.1%) and decreased SOC (-16.4%), TN (-10.6%), and P (-23.9%) (10-30 cm). Light grazing significantly increased the SOC (10.8%) and NH4+ (28.7%) (0-10 cm). Heavy grazing showed much higher mean probability (0.70) leading to overgrazing than the moderate (0.14) and light (0.10) grazing. These findings indicate that, globally, compared to un-grazing, heavy grazing significantly increased soil compaction and reduced SOC, NO3-, and soil moisture. Moderate grazing significantly increased soil compaction and alkalinity and reduced SOC and TN. Light grazing significantly increased SOC and NH4+. Cattle grazing impacts on soil compaction, SOC, TN, and available K were higher than sheep grazing, but lower for PR. Climate significantly impacted grazing effects on SOM, TN, available P, NH4+, EC, CEC, and PR. Heavy grazing can be more detrimental to soil quality based on BD, SOC, TN, C: N, WC, and K than moderate and light grazing. However, global grazing intensities did not significantly impact most of the 15 soil properties, and the grazing effects on them had insignificant changes over the years.

Evaluating physiological changes of grass and semishrub species with seasonality for understanding the process of shrub encroachment in semiarid grasslands.

Shrub encroachment occurs worldwide, especially in arid and semiarid grasslands. Changes in soil water in different layers affect the process of shrub encroachment. Understanding the biological and physiological responses of plant species to shrub encroachment is essential for explaining shrub encroachment. The dominant species in six typical plant communities changed from Stipa bungeana Trin. to Artemisia ordosica Krasch., representing different shrub-encroached grasslands. The gravimetric soil water content (SWC) and enzyme and osmotic adjustment compounds of the dominant species across shrub encroachment stages and growing seasons were measured to explain the shrub encroachment. Results showed that SWC decreased and then increased during the growing seasons. With the process of shrub encroachment, SWC first increased, then decreased. With increasing soil depth, SWC increased or decreased. Across seasons with decreasing SWC, enzyme activity decreased and then increased, and malondialdehyde content and osmotic adjustment compounds increased. With the process of shrub encroachment, enzyme activity, malondialdehyde content and osmotic adjustment compounds increased or decreased. The two dominant species (S. bungeana and A. ordosica) enhanced their drought resistance abilities by regulating their antioxidant systems and osmotic adjustment compounds when soil water in a specific layer was not over the threshold. We recommend increasing the clay content to increase the water holding capacity in the surface soil layer to restore the zonal vegetation of S. bungeana.

Changes in levels of enzymes and osmotic adjustment compounds in key species and their relevance to vegetation succession in abandoned croplands of a semiarid sandy region.

Reclamation of cropland from grassland is regarded as a main reason for grassland degradation; understanding succession from abandoned cropland to grassland is thus crucial for vegetation restoration in arid and semiarid areas. Soil becomes dry when cropland is reverted to grassland, and enzyme and osmotic adjustment compounds may help plants to adapt to a drying environment. Croplands that were abandoned in various years on the Ordos Plateau in China, were selected for the analysis of the dynamics of enzymes and osmotic adjustment compounds in plant species during vegetation succession. With increasing number of years since abandonment, levels of superoxide dismutase increased in Stipa bungeana, first decreased and then increased in Lespedeza davurica and Artemisia frigida, and fluctuated in Heteropappus altaicus. Levels of peroxidase and catalase in the four species fluctuated; levels of proline, soluble sugar, and soluble protein either decreased or first increased and then generally decreased. According to a drought resistance index, the drought resistance of the four species was ranked in descending order as follows: S. bungeana > A. frigida > H. altaicus > L. davurica. The drought resistance ability of the different species was closely linked with vegetation succession from communities dominated by annual and biennial species (with main accompanying species of L. davurica and H. altaicus) to communities dominated by perennial species (S. bungeana and A. frigida) when soil became dry owing to increasing evapotranspiration after cropland abandonment. The restoration of S. bungeana steppe after cropland abandonment on the Ordos Plateau is recommended both as high-quality forage and for environmental sustainability.

Seed germination and seedling growth of five desert plants and their relevance to vegetation restoration.

Due to significant decreases in precipitation in northern China, knowledge of the response of seed germination and plant growth characteristics to key limiting factors is essential for vegetation restoration. We examined seed germination under different temperatures and water potentials, and we examined seedling growth under different amounts of water supply. Experiments were carried out in automatic temperature-, humidity-, and light-controlled growth chambers. Under low water potentials, the final germination percentages of four herbaceous species were high, while seed germination of the shrub species Caragana microphylla was significantly inhibited. Under the different water supply amounts, seedlings of Agropyron cristatum allocated more biomass to the root and had a higher growth rate than those of Elymus dahuricus and C. microphylla. In light of these results and drier environmental conditions (annual mean precipitation is 366 mm, which falling mainly between June and August), potential selections for revegetation of different landscapes include the following: A. cristatum for shifting sand dunes, the establishment of the pioneer species Agriophyllum squarrosum, C. microphylla for semifixed sand dunes, E. dahuricus for fixed sand dunes, and Melilotus suaveolens and Medicago sativa for cultivation.

Spatial variation in leaf nutrient traits of dominant desert riparian plant species in an arid inland river basin of China.

Understanding how patterns of leaf nutrient traits respond to groundwater depth is crucial for modeling the nutrient cycling of desert riparian ecosystems and forecasting the responses of ecosystems to global changes. In this study, we measured leaf nutrients along a transect across a groundwater depth gradient in the downstream Heihe River to explore the response of leaf nutrient traits to groundwater depth and soil properties. We found that leaf nutrient traits of dominant species showed different responses to groundwater depth gradient. Leaf C, leaf N, leaf P, and leaf K decreased significantly with groundwater depth, whereas patterns of leaf C/N and leaf N/P followed quadratic relationships with groundwater depth. Meanwhile, leaf C/P did not vary significantly along the groundwater depth gradient. Variations in leaf nutrient traits were associated with soil properties (e.g., soil bulk density, soil pH). Groundwater depth and soil pH jointly regulated the variation of leaf nutrient traits; however, groundwater depth explained the variation of leaf nutrient traits better than did soil pH. At the local scale in the typical desert riparian ecosystem, the dominant species was characterized by low leaf C, leaf N, and leaf P, but high leaf N/P and leaf C/P, indicating that desert riparian plants might be more limited by P than N in the growing season. Our observations will help to reveal specific adaptation patterns in relation to the groundwater depth gradient for dominant desert riparian species, provide insights into adaptive trends of leaf nutrient traits, and add information relevant to understanding the adaptive strategies of desert riparian forest vegetation to moisture gradients.

Response of Soil Surface Greenhouse Gas Fluxes to Crop Residue Removal and Cover Crops under a Corn-Soybean Rotation.

Excessive crop residue returned to the soil hinders farm operations, but residue removal can affect soil quality. In contrast, cover cropping can return additional residue to the soil and improve soils and environmental quality compared with no cover cropping. Residue and cover crop impacts on soil surface greenhouses gas (GHG) emissions are undetermined and site specific. Thus, the present study was conducted to investigate the impacts of corn ( L.) residue management and cover cropping on GHG fluxes. The fluxes were measured from 2013 to 2015 using static chamber under corn and soybean [ (L.) Merr.] rotation initiated in 2000 at Brookings, SD. Treatments included two residue management levels (residue returned [RR] and residue not returned [RNR]) and two cover cropping (cover crops [CC] and no cover crops [NCC]). Results showed that RR under corn and soybean phases significantly reduced cumulative CO fluxes (2681.3 kg ha in corn and 2419.8 kg ha in soybeans) compared with RNR (3331.0 kg ha in corn and 2755.0 kg ha in soybeans) in 2013. The RR emitted significantly less cumulative NO fluxes than RNR from both the phases in 2013 and 2014, but not in 2015. The CC treatment had significantly lower cumulative NO fluxes than the NCC for corn and soybean phases in 2013 and 2014. We conclude that crop residue retention and cover cropping can mitigate the GHG emissions compared with residue removal and no cover cropping.

Phylogeny, habitat together with biological and ecological factors can influence germination of 36 subalpine Rhododendron species from the eastern Tibetan Plateau.

The reproductive stages of the life cycle are crucial in explaining the distribution patterns of plant species because of their extreme vulnerability to environmental conditions. Despite reported evidence that seed germination is related to habitat macroclimatic characteristics, such as mean annual temperature, the effect of this trait in controlling plant species distribution has not yet been systematically and quantitatively evaluated. To learn whether seed germination can predict species distribution along altitude gradients, we examined germination data of 36 Rhododendron species in southeastern Tibet originating from contrasting altitudes, habitats, plant heights, seed masses, and phylogenies. Germination varied significantly with altitude, habitat, plant height, and phylogeny and was higher in the light than in the dark. Germination percentage was highest at 10:20°C in the light and 15:25°C in the dark. As altitude increased, germination percentages first rose and then decreased, being highest at 3,500-4,000 m. Germination percentage and rate were highest on rocky slopes, increasing as seed mass and plant height rose. Variations in germination percentage and rate were not significant at subgenera, section, and subsection levels, but they were significant at species level. The results suggested that the relationship between germination and altitude may provide insights into species distribution patterns. Further, germination patterns are a result of long-term evolution as well as taxonomic constraints.

Community Characteristics and Leaf Stoichiometric Traits of Desert Ecosystems Regulated by Precipitation and Soil in an Arid Area of China.

Precipitation is a key environmental factor determining plant community structure and function. Knowledge of how community characteristics and leaf stoichiometric traits respond to variation in precipitation is crucial for assessing the effects of global changes on terrestrial ecosystems. In this study, we measured community characteristics, leaf stoichiometric traits, and soil properties along a precipitation gradient (35-209 mm) in a desert ecosystem of Northwest China to explore the drivers of these factors. With increasing precipitation, species richness, aboveground biomass, community coverage, foliage projective cover (FPC), and leaf area index (LAI) all significantly increased, while community height decreased. The hyperarid desert plants were characterized by lower leaf carbon (C) and nitrogen/phosphorus (N/P) levels, and stable N and P, and these parameters did not change significantly with precipitation. The growth of desert plants was limited more by N than P. Soil properties, rather than precipitation, were the main drivers of desert plant leaf stoichiometric traits, whereas precipitation made the biggest contribution to vegetation structure and function. These results test the importance of precipitation in regulating plant community structure and composition together with soil properties, and provide further insights into the adaptive strategy of communities at regional scale in response to global climate change.

Alpine vegetation phenology dynamic over 16years and its covariation with climate in a semi-arid region of China.

Vegetation phenology is a sensitive indicator of ecosystem response to climate change, and plays an important role in the terrestrial biosphere. Improving our understanding of alpine vegetation phenology dynamics and the correlation with climate and grazing is crucial for high mountains in arid areas subject to climatic warming. Using a time series of SPOT Normalized Difference Vegetation Index (NDVI) data from 1998 to 2013, the start of the growing season (SOS), end of the growing season (EOS), growing season length (GSL), and maximum NDVI (MNDVI) were extracted using a threshold-based method for six vegetation groups in the Heihe River headwaters. Spatial and temporal patterns of SOS, EOS, GSL, MNDVI, and correlations with climatic factors and livestock production were analyzed. The MNDVI increased significantly in 58% of the study region, whereas SOS, EOS, and GSL changed significantly in <5% of the region. The MNDVI in five vegetation groups increased significantly by a range from 0.045 to 0.075. No significant correlation between SOS and EOS was observed in any vegetation group. The SOS and GSL were highly correlated with temperature in May and April-May, whereas MNDVI was correlated with temperature in August and July-August. The EOS of different vegetation groups was correlated with different climatic variables. Maximum and minimum temperature, accumulated temperature, and effective accumulated temperature showed stronger correlations with phenological metrics compared with those of mean temperature, and should receive greater attention in phenology modeling in the future. Meat and milk production were significantly correlated with the MNDVI of scrub, steppe, and meadow. Although the MNDVI increased in recent years, ongoing monitoring for rangeland degradation is recommended.

Comparison modeling for alpine vegetation distribution in an arid area.

Mapping and modeling vegetation distribution are fundamental topics in vegetation ecology. With the rise of powerful new statistical techniques and GIS tools, the development of predictive vegetation distribution models has increased rapidly. However, modeling alpine vegetation with high accuracy in arid areas is still a challenge because of the complexity and heterogeneity of the environment. Here, we used a set of 70 variables from ASTER GDEM, WorldClim, and Landsat-8 OLI (land surface albedo and spectral vegetation indices) data with decision tree (DT), maximum likelihood classification (MLC), and random forest (RF) models to discriminate the eight vegetation groups and 19 vegetation formations in the upper reaches of the Heihe River Basin in the Qilian Mountains, northwest China. The combination of variables clearly discriminated vegetation groups but failed to discriminate vegetation formations. Different variable combinations performed differently in each type of model, but the most consistently important parameter in alpine vegetation modeling was elevation. The best RF model was more accurate for vegetation modeling compared with the DT and MLC models for this alpine region, with an overall accuracy of 75 % and a kappa coefficient of 0.64 verified against field point data and an overall accuracy of 65 % and a kappa of 0.52 verified against vegetation map data. The accuracy of regional vegetation modeling differed depending on the variable combinations and models, resulting in different classifications for specific vegetation groups.

Modeling the impacts of temperature and precipitation changes on soil CO2 fluxes from a Switchgrass stand recently converted from cropland.

Switchgrass (Panicum virgatum L.) is a perennial C4 grass native to North America and successfully adapted to diverse environmental conditions. It offers the potential to reduce soil surface carbon dioxide (CO2) fluxes and mitigate climate change. However, information on how these CO2 fluxes respond to changing climate is still lacking. In this study, CO2 fluxes were monitored continuously from 2011 through 2014 using high frequency measurements from Switchgrass land seeded in 2008 on an experimental site that has been previously used for soybean (Glycine max L.) in South Dakota, USA. DAYCENT, a process-based model, was used to simulate CO2 fluxes. An improved methodology CPTE [Combining Parameter estimation (PEST) with "Trial and Error" method] was used to calibrate DAYCENT. The calibrated DAYCENT model was used for simulating future CO2 emissions based on different climate change scenarios. This study showed that: (i) the measured soil CO2 fluxes from Switchgrass land were higher for 2012 which was a drought year, and these fluxes when simulated using DAYCENT for long-term (2015-2070) provided a pattern of polynomial curve; (ii) the simulated CO2 fluxes provided different patterns with temperature and precipitation changes in a long-term, (iii) the future CO2 fluxes from Switchgrass land under different changing climate scenarios were not significantly different, therefore, it can be concluded that Switchgrass grown for longer durations could reduce changes in CO2 fluxes from soil as a result of temperature and precipitation changes to some extent.

Seed germination of seven desert plants and implications for vegetation restoration.

Germination cues reflect the conditions under which a species is likely to succeed in recruitment. Therefore, knowledge of the seed germination characteristics of key plant species in desertified areas is essential for restoration. The aims of this study were to evaluate the seed germination responses of seven native species, and to explore the implications for vegetation restoration. Seeds of seven desert species were sown in Petri dishes and subjected to various temperature and light conditions. The seeds germinated well at day/night temperatures of 25/15 °C and 30/20 °C but poorly at 35/25 °C. Seeds germinated best in the dark, and final germination percentages of all species were strongly inhibited at a photon irradiance of 1000 µmol m(-2) s(-1) Based on these results and the environmental conditions of their natural habitat, Agropyron cristatum and Artemisia halodendron are best adapted to shifting sand dunes: Elymus dahuricus, Caragana korshinskii and C. microphylla for semi-fixed sand dunes: and Medicago sativa and Melilotus suaveolen for fixed sand dunes. If seeds are sown in early May, they will likely be buried in sand, and the precipitation and temperature conditions will be suitable for seedling survival.

Evaluating the impacts of landscape positions and nitrogen fertilizer rates on dissolved organic carbon on switchgrass land seeded on marginally yielding cropland.

Dissolved organic carbon (DOC) through leaching into the soils is another mechanism of net C loss. It plays an important role in impacting the environment and impacted by soil and crop management practices. However, little is known about the impacts of landscape positions and nitrogen (N) fertilizer rates on DOC leaching in switchgrass (Panicum virgatum L.). This experimental design included three N fertilizer rates [0 (low); 56 (medium); 112 (high) kg N ha(-1)] and three landscape positions (shoulder, backslope and footslope). Daily average DOC contents at backslope were significantly lower than that at shoulder and footslope. The DOC contents from the plots that received medium N rate were also significantly lower than the plots that received low N rates. The interactions of landscape and N rates on DOC contents were different in every year from 2009 to 2014, however, no significant consistent trend of DOC contents was observed over time. Annual average DOC contents from the plots managed with low N rate were higher than those with high N rate. These contents at the footslope were higher than that at the shoulder position. Data show that there is a moderate positive relationship between the total average DOC contents and the total average switchgrass biomass yields. Overall, the DOC contents from leachate in the switchgrass land were significantly influenced by landscape positions and N rates. The N fertilization reduced DOC leaching contents in switchgrass field. The switchgrass could retain soil and environment sustainability to some extent. These findings will assist in understanding the mechanism of changes in DOC contents with various parameters in the natural environment and crop management systems. However, use of long-term data might help to better assess the effects of above factors on DOC leaching contents and loss in the switchgrass field in the future.

Distribution of three congeneric shrub species along an aridity gradient is related to seed germination and seedling emergence.

Environmental tolerance of a species has been shown to correlate positively with its geographical range. On the Ordos Plateau, three Caragana species are distributed sequentially along the precipitation gradient. We hypothesized that this geographical distribution pattern is related to environmental tolerances of the three Caragana species during seed germination and seedling emergence stages. To test this hypothesis, we examined seed germination under different temperature, light and water potentials, and monitored seedling emergence for seeds buried at eight sand depths and given different amounts of water. Seeds of C. korshinskii germinated to high percentages at 5 : 15 to 25 : 35 °C in both light and darkness, while those of C. intermedia and C. microphylla did so only at 15 : 25 and 25 : 35 °C, respectively. Nearly 30 % of the C. korshinskii seeds germinated at -1.4 MPa at 20 and 25 °C, while no seeds of the other two species did so. Under the same treatments, seedling emergence percentages of C. korshinskii were higher than those of the other two species. The rank order of tolerance to drought and sand burial of the three species is C. korshinskii > C. intermedia > C. microphylla. The amount of precipitation and sand burial depth appear to be the main selective forces responsible for the geographical distribution of these species.

Meta-analysis of gene expression signatures reveals hidden links among diverse biological processes in Arabidopsis.

The model plant Arabidopsis has been well-studied using high-throughput genomics technologies, which usually generate lists of differentially expressed genes under various conditions. Our group recently collected 1065 gene lists from 397 gene expression studies as a knowledgebase for pathway analysis. Here we systematically analyzed these gene lists by computing overlaps in all-vs.-all comparisons. We identified 16,261 statistically significant overlaps, represented by an undirected network in which nodes correspond to gene lists and edges indicate significant overlaps. The network highlights the correlation across the gene expression signatures of the diverse biological processes. We also partitioned the main network into 20 sub-networks, representing groups of highly similar expression signatures. These are common sets of genes that were co-regulated under different treatments or conditions and are often related to specific biological themes. Overall, our result suggests that diverse gene expression signatures are highly interconnected in a modular fashion.

Geographic variation in seed traits within and among forty-two species of Rhododendron (Ericaceae) on the Tibetan plateau: relationships with altitude, habitat, plant height, and phylogeny.

Seed mass and morphology are plant life history traits that influence seed dispersal ability, seeding establishment success, and population distribution pattern. Southeastern Tibet is a diversity center for Rhododendron species, which are distributed from a few hundred meters to 5500 m above sea level. We examined intra- and interspecific variation in seed mass and morphology in relation to altitude, habitat, plant height, and phylogeny. Seed mass decreased significantly with the increasing altitude and increased significantly with increasing plant height among populations of the same species. Seed mass differed significantly among species and subsections, but not among sections and subgenera. Seed length, width, surface area, and wing length were significantly negative correlated with altitude and significantly positive correlated with plant height. Further, these traits differed significantly among habitats and varied among species and subsection, but not among sections and subgenera. Species at low elevation had larger seeds with larger wings, and seeds became smaller and the wings of seeds tended to be smaller with the increasing altitude. Morphology of the seed varied from flat round to long cylindrical with increasing altitude. We suggest that seed mass and morphology have evolved as a result of both long-term adaptation and constraints of the taxonomic group over their long evolutionary history.

Organic matter and water addition enhance soil respiration in an arid region.

Climate change is generally predicted to increase net primary production, which could lead to additional C input to soil. In arid central Asia, precipitation has increased and is predicted to increase further. To assess the combined effects of these changes on soil CO2 efflux in arid land, a two factorial manipulation experiment in the shrubland of an arid region in northwest China was conducted. The experiment used a nested design with fresh organic matter and water as the two controlled parameters. It was found that both fresh organic matter and water enhanced soil respiration, and there was a synergistic effect of these two treatments on soil respiration increase. Water addition not only enhanced soil C emission, but also regulated soil C sequestration by fresh organic matter addition. The results indicated that the soil CO2 flux of the shrubland is likely to increase with climate change, and precipitation played a dominant role in regulating soil C balance in the shrubland of an arid region.