An invasive plant species may restrict its spread to only one type of habitat, or, after some time, may continue to spread into a different, often stressful, secondary, habitat. The question of whether evolution is required for an invasive species to spread from one habitat to another is currently hotly debated. In order for local adaptation to occur, genetic variation must be present within invasive populations. In this paper, I focus on the effect of habitat on the maintenance of genetic variation during the lag phase, the phase of population stability prior to expansion. Genetic diversity in invasive plant populations accumulates through multiple introductions, gene flow, mutation, and hybridization, but diversity is maintained by population level processes influencing effective population size (Ne). I show that when the plastic response to the environment results in little variation in reproductive output among indi-viduals, Ne is maximized and genetic variation is maintained. Established models of plant competition show that below-ground competition reduces the variation in reproductive output, whereas competition for light increases variation in reproductive output. The same environments that maintain high Ne also reduce the opportunity for selection and minimize the response to selection, and thus the effects of the environment are synchronized to prevent genetic purges. When the primary invasion habitat supports high Ne, conditions are ripe for local adaptation to a secondary habitat, particularly if the secondary habitat has high opportunity for selection. When the primary invasion habitat supports low Ne, genetic diversity is less likely to be sufficient for local adaptation to secondary habitat to occur.

As invasion science accepts that there is no single causal factor for biological invasion, the identification of groups of traits that are often associated, or “syndromes”, is a logical move forward. Invasion syndromes are proposed to identify suites of site conditions (biotic and environmental) that render a site vulnerable to invasion by different types of invaders. This paper proposed four invasion syndromes which relate invader attributes (competitive ability, niche construction, phenotypic plasticity, and phenological niche separation) to the biotic characteristics (biodiversity and enemies) and environmental conditions (resource abundance and fluctuation) of invaded sites. The four invasion syndromes described in this paper are a development of hypotheses of how the many factors that influence species invasion might be associated. Invasion Syndrome 1 proposes that sites with relatively high resource abundance and high diversity should be vulnerable to invasion by species with high competitive ability. Invasion Syndrome 2 hypothesizes that sites with relatively low resource abundance and low diversity should be vulnerable to invasion by species with niche construction ability. Invasion Syndrome 3 postulates that sites with moderate or fluctuating resources and moderate diversity should be vulnerable to invasion by species with high phenotypic plasticity. Invasion Syndrome 4 hypothesizes that species introduced into a site where it has phenological niche separation from natives will not have to contend with interference from the biotic community at a site (diversity or natural enemies) and may invade where ever site environmental conditions suit its life history. Further work is needed to support, contradict, or refine these hypotheses and almost certainly will identify more invasion syndromes.

This paper examines the hypothesis that non-native plant invasions are related to fluctuating resource availability as proposed by Davis et al. (2000). I measured relative functional responses of both invasive and native plants to changed resource availability due to nutrient enrichment and rainfall, and to increased disturbance. Data are presented from studies in two contrasting ecosystems. First is a series of glasshouse and field experiments on the invader Hieracium lepidulum and associated invasive and native species in subalpine temperate New Zealand. Second is a field study of invasive and native plant responses to altered disturbance regimes and rainfall from tropical savannas of north eastern Australia. Invaders responded differently from native species to changes in resource availability in both subalpine and tropical studies. However, invaders differed among themselves showing that different species exploit different functional niches to invade their respective habitats. These findings contribute to the contention that the fluctuating resource hypothesis does not provide a universal explanation for plant invasions. The diverse functional responses to increased resource availability among invaders in this and previous studies suggest that the cause of invasion depends on unique combinations of habitat and functional attributes of invaders and native assemblages. Such findings imply that universal predictions of what will happen under climate change scenarios across the globe will be difficult to make.

Exotic plant invasion is a growing concern in the conservation and management of indigenous arid land ecosystems. By creating areas of ameliorated microclimates and fertile soil below their canopies, perennial plants might influence exotic annual plant invasions. We conducted a quantitative literature review of studies that compared exotic annual plant abundance among native perennial plant species and interspace (open areas) microsites in North America’s Mojave Desert, where exotic plant invasion has corresponded with increasing extent of wildfire and broad-scale ecosystem transformation. Ten studies compared exotic annual plant abundance between interspaces and below a total of 36 native perennial species. These studies revealed that: (1) With few exceptions, most native perennial species supported a greater abundance of exotic annuals than interspaces, indicating overall facilitation of exotic species by native perennials. (2) Exotic species abundance varied by orders of magnitude among native perennial species, with some perennial species harboring amounts of exotics similar to interspaces. (3) Dis-tributions of dominant exotic species varied, where Bromus rubens displayed a greater affinity for below-perennial microsites than did Schismus spp. and Erodium cicutarium that often were most abundant in interspaces. Results suggest that the degree of facilitation of exotic plants warrants consideration when selecting native perennial spe-cies for revegetation and restoration projects.

The invasion of nonnative plants is considered one of the main threats to the structure and function of North American ecosystems. Moreover, they can alter ecosystem processes and reduce biodiversity. In arid and semi-arid region of North America, the species of European annual grass Bromus tectorum L. is an outstanding example of these problems, which not only increase the fire density and change the fire regime, but replace native communities. Therefore, there are amount of researches on B. tectorum, including resource acquisition, water use efficiency and growth. Whereas the relevant research on the morphology of diaspore is scare. Diaspores have a fundamental role in seed germination and seedling establishment. Besides, as an important link between different generations, diaspores have a vital significance on individual reproduction and population extension. Hence, diaspores under selection for studying have an important implication. This study compares differences in seed mor-phology for Bromus tectorum collected from the United States, Kazakhstan, and Xinjiang of China. The following indices of B. tectorum diaspores were analyzed: size, thickness of covering layers, and micromorphological characteristics of the base, middle and transition area of diaspores as well as of the awn. Micromorphology of the lemma and the cross-section of the diaspore were observed by scanning electron microscopy. Results showed that thickness of the lemma and the palea of diaspores from B. tectorum-infested grasslands in the United States were reduced (P<0.05), likely because of environmental influences. This reduction facilitated the germination of diaspores and lowered the resistance of B. tectorum to adverse environmental conditions. The length of the awn also increased significantly (P<0.05), which helped in dispersal and anchoring of diaspores. Therefore, B. tectorum adapted ecologically to its new environment in the United States by strengthening its establishment ability. However, the defense capability of B. tectorum decreased. These results fit the evolution of increased competitive ability hypothesis (EICA) of invasive species. Analysis of various cells on the lemma revealed that prickle densities and col-lapsed, long epidermal cells were easily influenced by environmental factors such as temperature and moisture because of the physiologic function of these structures on silicon accumulation. However, the form and the position of silica cells, which were not greatly influenced by environmental factors, might be genetically controlled. Studying these structures at the microscopic level helps define the relationship between the diaspore and its environment. This study has a reference value for future studies on B. tectorum.

Aerial parts of Xanthium italicum in an air tight container greatly inhibited root elongation of radish, implying that this invasive plant could release biologically active volatile organic compounds (VOCs) into the environment to affect other plants’ growth. This phenomenon was further studied by evaluating the phytotoxic effects of X. italicum essential oil against two dicot plants, amaranth (Amaranthus mangostanus L.) and lettuce (Lectuca sativa L.), and two monocot plants, wheat (Triticum aestivum Linn) and ryegrass (Lolium multiforum), and analyzing the chemical composition of the oil. Among the 4 test species, amaranth was the most sensitive plant, 0.5µl/mL essential oil application resulted in a 50% reduction on root elongation, and 2.5 µl/mL essential oil almost completely inhibited its seedling growth. Wheat was the least sensitive species, whose root growth was reduced to 36% of control by 5 µl/mL essential oil. The essential oil exerted moderate inhibitory effect on both lettuce and ryegrass. Compared to a commercial herbicide–Harness, X. italicum oil exhibited stronger phytotoxicity on amaranth, lettuce and wheat, but weaker activity on ryegrass. The chemical composition of the essential oil isolated by hydrodistillation from the aerial parts of X. italicum Moretti was analyzed by GC/MS. Thirty two compounds were identified, representing 94.89% of total oil, which was found to be rich in monoterpene hydrocarbons (60.71%). The main constituents of the oil were limonene (51.61%), germacrene B (6.98%), δ-cadinol (5.94%), β-pinene (5.23%), α-caryophyllene (5.1%) and bornyl acetate (3.15%). Bioassay revealed the dominant constituent–limonene, was unlikely the responsible phytotoxic compound due to its low biological activity; rather, there might be other oil constituent(s) that either act alone, or work together, and possibly assisted by synergistic effect, to display the phyto-toxic activity. Our results suggested that X. italicum might produce allelopathic VOCs to facilitate its invasion success. This is the first report on the phytotoxic activity and the chemical composition of the essential oil of X. italicum Moretti from China.

Clarifying the persistence time of seedlings of dominant species under continual drought will help us understand responses of ecosystems to global climate change and improve revegetation efforts. Drought tolerance of four dominant psammophytic shrub species occurring in different environments was studied in the semi-arid areas of Inner Mongolian grasslands. Seedlings of Hedysarum laeve, Caragana korshinskii, Artemisia sphaerocephala and Artemisia ordosica were grown under four air temperature regimes (night/day: 12.5/22.5°C, 15/25°C, 17.5/27.5°C and 20/30°C) within climate (air temperature and humidity) controlled, naturally lit glasshouses with a night/day relative humidity of 70%/50%. Pots were watered to field capacity for each temperature treatment. Soil water condition was monitored by weighting each pot every day using an electronic balance. Date of seedling death for each treatment was recorded and the dead plants were harvested. Plant dry weights were determined after oven drying at 80°C for 3 days. Two Artemisia species had higher growth rates than H. laeve and C. korshinskii, and the growth of all four species increased with increasing temperatures. The two Artemisia species had the highest leaf biomass increment, followed by C. korshinskii, and then H. laeve. Shoot biomass increment was higher for A. ordosica and C. korshinskii, intermediate for A. sphaerocephala and lowest for H. laeve. C. korshinskii had the highest root biomass increment. The final soil water content at death for all four species varied from 1% to 2%. C. korshinskii, A. sphaerocephala, H. laeve and A. ordosica survived for 25–43, 24–41, 26–41, and 24–37 days without watering, respectively. C. korshinskii, A. sphaerocephala, H. Laeve, and A. ordosica seedlings survived longer at the lowest temperatures (12.5/22.5°C) than at the highest temperatures (20/30°C) by 18, 17, 15 and 13 days, respectively. Increased climatic temperatures induce the death of seedlings in years with long intervals between rainfall events. The adaptation of seedlings to droughts should be emphasized in revegetation efforts in the Ordos Plateau, Inner Mongolia.

Modeling soil salinity in an arid salt-affected ecosystem is a difficult task when using remote sensing data because of the complicated soil context (vegetation cover, moisture, surface roughness, and organic matter) and the weak spectral features of salinized soil. Therefore, an index such as the salinity index (SI) that only uses soil spectra may not detect soil salinity effectively and quantitatively. The use of vegetation reflectance as an indirect indicator can avoid limitations associated with the direct use of soil reflectance. The normalized difference vegetation index (NDVI), as the most common vegetation index, was found to be responsive to salinity but may not be available for retrieving sparse vegetation due to its sensitivity to background soil in arid areas. Therefore, the arid fraction integrated index (AFII) was created as supported by the spectral mixture analysis (SMA), which is more appropriate for analyzing variations in vegetation cover (particularly halophytes) than NDVI in the study area. Using soil and vegetation separately for detecting salinity perhaps is not feasible. Then, we developed a new and opera-tional model, the soil salinity detecting model (SDM) that combines AFII and SI to quantitatively estimate the salt content in the surface soil. SDMs, including SDM1 and SDM2, were constructed through analyzing the spatial characteristics of soils with different salinization degree by integrating AFII and SI using a scatterplot. The SDMs were then compared to the combined spectral response index (COSRI) from field measurements with respect to the soil salt content. The results indicate that the SDM values are highly correlated with soil salinity, in contrast to the performance of COSRI. Strong exponential relationships were observed between soil salinity and SDMs (R²>0.86, RMSE<6.86) compared to COSRI (R²=0.71, RMSE=16.21). These results suggest that the feature space  related to biophysical properties combined with AFII and SI can effectively provide information on soil salinity.

Mountainous ecosystems are considered highly sensitive and vulnerable to natural disasters and climatic changes. Therefore, quantifying the effects of elevation on grassland productivity to understand ecosystem-climate interactions is vital for mountainous ecosystems. Water-use efficiency (WUE) provides a useful index for understanding the metabolism of terrestrial ecosystems as well as for evaluating the degradation of grasslands. This paper explored net primary productivity (NPP) and WUE in grasslands along an elevational gradient ranging from 400 to 3,400 m asl in the northern Tianshan Mountains–southern Junggar Basin (TMJB), Xinjiang of China, using the Biome-BGC model. The results showed that: 1) the NPP increased by 0.05 g C/(m²×a) with every increase of 1-m elevation, reached the maximum at the mid-high elevation (1,600 m asl), and then decreased by 0.06 g C/(m²×a) per 1-m increase in elevation; 2) the grassland NPP was positively correlated with temperature in alpine meadow (AM, 2,700–3,500 m asl), mid-mountain forest meadow (MMFM, 1,650–2,700 m asl) and low-mountain dry grassland (LMDG, 650–1,650 m asl), while positive correlations were found between NPP and annual precipitation in plain desert grassland (PDG, lower than 650 m asl); 3) an increase (from 0.08 to 1.09 g C/(m²×a)) in mean NPP for the grassland in TMJB under a real climate change scenario was observed from 1959 to 2009; and 4) remarkable differences in WUE were found among different elevations. In general, WUE increased with decreasing elevation, because water availability is lower at lower elevations; however, at elevations lower than 540 m asl, we did observe a decreasing trend of WUE with decreasing elevation, which may be due to the sharp changes in canopy cover over this gradient. Our research suggests that the NPP simulated by Biome-BGC is consistent with field data, and the modeling provides an opportunity to further evaluate interactions between environmental factors and ecosystem productivity.

Estimating the impact of mountain landscape on hydrology or water balance is essential for the sustainable development strategies of water resources. Specifically, understanding how the change of each landscape influences hydrological components will greatly improve the predictability of hydrological responses to mountain landscape changes and thus can help the government make sounder decisions. In the paper, we used the VIC (Variable Infiltration Capacity) model to conduct hydrological modeling in the upper Heihe River watershed, along with a frozen-soil module and a glacier melting module to improve the simulation. The improved model performed satisfactorily. We concluded that there are differences in the runoff generation of mountain landscape both in space and time. About 50% of the total runoff at the catchment outlet were generated in mid-mountain zone (2,900–4,000 m asl), and water was mainly consumed in low mountain region (1,700–2,900 m asl) because of the higher re-quirements of trees and grasses. The runoff coefficient was 0.37 in the upper Heihe River watershed. Barren landscape produced the largest runoff yields (52.46% of the total runoff) in the upper Heihe River watershed, fol-lowed by grass¬land (34.15%), shrub (9.02%), glacier (3.57%), and forest (0.49%). In order to simulate the impact of landscape change on hydrological components, three landscape change scenarios were designed in the study. Scenario 1, 2 and 3 were to convert all shady slope landscapes at 2,000–3,300 m, 2,000–3,700 m, and 2,000–4,000 m asl respectively to forest lands, with forest coverage rate increased to 12.4%, 28.5% and 42.0%, respectively. The runoff at the catchment outlet correspondingly declined by 3.5%, 13.1% and 24.2% under the three scenarios. The forest landscape is very important in water conservation as it reduced the flood peak and in-creased the base flow. The mountains as “water towers” play important roles in water resources generation and the impact of mountain land¬scapes on hydrology is significant.

Water storage has important significance for understanding water cycles of global and local domains and for monitoring climate and environmental changes. As a key variable in hydrology, water storage change represents the sum of precipitation, evaporation, surface runoff, soil water and groundwater exchanges. Water storage change data during the period of 2003–2008 for the source region of the Yellow River were collected from Gravity Recovery and Climate Experiment (GRACE) satellite data. The monthly actual evaporation was estimated according to the water balance equation. The simulated actual evaporation was significantly consistent and correlative with not only the observed pan (20 cm) data, but also the simulated results of the version 2 of Simple Bio-sphere model. The average annual evaporation of the Tangnaihai Basin was 506.4 mm, where evaporation in spring, summer, autumn and winter was 130.9 mm, 275.2 mm, 74.3 mm and 26.1 mm, and accounted for 25.8%, 54.3%, 14.7% and 5.2% of the average annual evaporation, respectively. The precipitation increased slightly and the actual evaporation showed an obvious decrease. The water storage change of the source region of the Yellow River displayed an increase of 0.51 mm per month from 2003 to 2008, which indicated that the storage capacity has significantly increased, probably caused by the degradation of permafrost and the increase of the thickness of ac-tive layers. The decline of actual evaporation and the increase of water storage capacity resulted in the increase of river runoff.

 Tamarix spp. (Saltcedar) is a facultative phreatophyte that can tolerate drought when groundwater is not accessed. In addition to deep water uptake, hydraulic redistribution (HR) is another factor contributing to the drought tolerance of Tamarix spp. In this study, data on soil volumetric moisture content (θ), lateral root sap flow, and relevant climate variables were used to investigate the patterns, magnitude, and controlling factors of HR of soil water by roots of Tamarix ramosissima Ledeb. in an extremely arid land in Northwest China. Results showed evi-dent diurnal fluctuations in θ at the depths of 30 and 50 cm, indicating “hydraulic lift” (HL). θ increased remarkably at 10 and 140 cm but decreased at 30 and 50 cm and slightly changed at 80 cm after rainfall, suggesting a possible “hydraulic descent” (HD). However, no direct evidence was observed in the negative flow of lateral roots, supporting HR (including HL and HD) of T. ramosissima. The HR pathway unlikely occurred via lateral roots; instead, HR possibly occurred through adventitious roots with a diameter of 2–5 mm and a length of 60–100 cm. HR at depths of 20–60 cm ranged from 0.01–1.77 mm/d with an average of 0.43 mm/d, which accounted for an average of 22% of the estimated seasonal total water depletion at 0–160 cm during the growing season. The climate factors, particularly vapor pressure deficit and soil water potential gradient, accounted for at least 33% and 45% of HR variations with depths and years, respectively. In summary, T. ramosissima can be added to the wide list of existing species involved in HR. High levels of HR may represent a considerable fraction of daily soil water depletion and substantially improve plant water status. HR could vary tremendously in terms of years and depths, and this variation could be attributed to climate factors and soil water potential gradient.

This paper discussed the optimization of conditions for remediation of crude oil-polluted soil based on pot experiment by applying reed-specific degrading bacteria, and using response surfaces methodology. We took the initial crude oil concentration, the amount of inoculation, the ratio of nitrogen and phosphorus, and the use of surfactant (Tween-80) as independent variables (factors), and the degrading ratio of crude oil as the dependent variable (response) after a 90-day experiment. The experiment explored the impacts of each independent variable and their interactions on the bioremediation of crude oil-polluted soil using the Box-Behnken design. Working with a simulated forecasting model the study obtained optimization values for the treatment parameters of 200 g/kg of the reed+specific degrading bacteria, a nitrogen to phosphorus ratio of about 6.0, and 0.2% surfactant. Under experimental conditions, for crude oil concentrations of 10, 30 and 50 g/kg, the optimal effects of the treatments achieved 71.87%, 66.61% and 54.52% degradation of the crude oil, respectively. The results can provide a basis for the technical development of plant-microorganism combined bioremediation of crude oil-polluted soil.