A greater foraging scale, not a higher foraging precision, may facilitate invasion by exotic plants in nutrient-heterogeneous conditions.

Background and Aims: Soil nutrient heterogeneity has been proposed to influence competitive outcomes among different plant species. Thus, it is crucial to understand the effects of environmental heterogeneity on competition between exotic invasive and native species. However, the effects of soil nutrient heterogeneity on the competition between invasive and native plants have rarely been linked to root foraging behaviour. Methods: In this study, a competition experiment was performed with two invasive-native species pairs (BP-VC, Bidens pilosa vs. Vernonia cinerea; MM-PS, Mikania micrantha vs. Paederia scandens) grown under homogeneous and heterogeneous conditions in a common greenhouse environment. Root activity was assessed by determining the amount of strontium (Sr) taken up by the shoot of each species. Key Results: The invasive species exhibited a greater foraging scale, whereas the native species exhibited a higher foraging precision. A trade-off between foraging scale and precision was observed within each pair of invasive-native species. Compared with soil homogeneity, soil heterogeneity significantly increased the biomass of the two invasive species, B. pilosa and M. micrantha, under competitive conditions. Within each pair, the invasive species exhibited greater relative competitive ability with respect to shoot mass, and considerably more Sr taken up by the invasive species compared with the native species. The Sr acquisition results indicate that nutrient-poor conditions may facilitate the competitive ability of the native species V. cinerea, whereas M. micrantha may possess a stronger competitive ability regardless of soil nutrient conditions. Conclusion: Soil nutrient heterogeneity has the potential to promote the invasion of these two exotic species due to their larger foraging scale, stronger competitive ability and greater root activity relative to their counterpart native species. The present work highlights the importance of soil heterogeneity in plant invasion, particularly with regards to root foraging traits and competition between invasive and native plants.

[Progress in the effects of warming on soil N2O and CH4 emission and the underlying micro-bial mechanisms]. / 增温对土壤N2O和CH4æŽ’æ”¾çš„å½±å“ä¸Žå¾®ç”Ÿç‰©æœºåˆ¶ç ”ç©¶è¿›å±•.

Global warming has received widespread concern. The increasing concentration of greenhouse gases (GHG) is one of the major factors contributing to global warming. Soil is a major source of GHG. Global warming could feed back on soil GHG emission. Warming influences the growth of plants, animals, microbes and their interactions, as well as the cycling of soil matters (especially nitrogen and carbon). Consequently, warming has the potential to affect soil GHG emission. We summarized the effects of warming on soil N2O, and CH4 emissions and the underlying mechanisms. In general, warming increased the emission of these two greenhouse gases, which are mainly related to the effects of temperature on the abundance and composition of ammonia oxidizing bacteria, denitrification functional genes, methane-producing bacteria and methane-oxidizing bacteria. Soil GHG emissions are affected by plant species characteristics, nutrient uptake and community composition, as well as soil nutrient element content, water content, pH and other physical and chemical properties. Further studies are needed to elucidate the microbial mechanisms of GHG emission. In addition, various warming patterns should be considered in the study of GHG emissions, and more attention should be paid on the interactive effects between warming and other environmental factors. It will provide solid theoretical basis for the prediction of global climate change and GHG emissions.

The effect of allometric partitioning on herbivory tolerance in four species in South China.

Herbivory tolerance can offset the negative effects of herbivory on plants and plays an important role in both immigration and population establishment. Biomass reallocation is an important potential mechanism of herbivory tolerance. To understand how biomass allocation affects plant herbivory tolerance, it is necessary to distinguish the biomass allocations resulting from environmental gradients or plant growth. There is generally a tight balance between the amounts of biomass invested in different organs, which must be analyzed by means of an allometric model. The allometric exponent is not affected by individual growth and can reflect the changes in biomass allocation patterns of different parts. Therefore, the allometric exponent was chosen to study the relationship between biomass allocation pattern and herbivory tolerance. We selected four species (Wedelia chinensis, Wedelia trilobata, Merremia hederacea, and Mikania micrantha), two of which are invasive species and two of which are accompanying native species, and established three herbivory levels (0%, 25% and 50%) to compare differences in allometry. The biomass allocation in stems was negatively correlated with herbivory tolerance, while that in leaves was positively correlated with herbivory tolerance. Furthermore, the stability of the allometric exponent was related to tolerance, indicating that plants with the ability to maintain their biomass allocation patterns are more tolerant than those without this ability, and the tendency to allocate biomass to leaves rather than to stems or roots helps increase this tolerance. The allometric exponent was used to remove the effects of individual development on allocation pattern, allowing the relationship between biomass allocation and herbivory tolerance to be more accurately explored. This research used an allometric model to fit the nonlinear process of biomass partitioning during the growth and development of plants and provides a new understanding of the relationship between biomass allocation and herbivory tolerance.

Differential responses of invasive and native plants to warming with simulated changes in diurnal temperature ranges.

Although many studies have documented the effects of global warming on invasive plants, little is known about whether the effects of warming on plant invasion differ depending on the imposed change in different diurnal temperature ranges (DTR). We tested the impact of warming with DTR change on seed germination and seedling growth of eight species in the family Asteraceae. Four of these are invasive (Eupatorium catarium, Mikania micrantha, Biodens pilosa var. radiate, Ageratum conyzoides) in China, and four are native (Sonchus arvensis, Senecios candens, Pterocypsela indica, Eupatorium fortunei). Four temperature treatments were set in growth chambers (three warming by 3 °C with different DTRs and control), and experiments were run to mimic wintertime and summertime conditions. The control treatment (Tc ) was set to the mean temperature for the corresponding time of year, and the three warming treatments were symmetric (i.e. equal night-and-day) (DTRsym), asymmetric warming with increased (DTRinc) and decreased (DTRdec) DTR. The warming treatments did not affect seed germination of invasive species under any of the conditions, but DTRsym and DTRinc increased seed germination of natives relative to the control, suggesting that warming may not increase success of these invasive plant species via effects on seed germination of invasive plants relative to native plants. The invasive plants had higher biomass and greater stem allocation than the native ones under all of the warming treatments. Wintertime warming increased the biomass of the invasive and wintertime DTRsym and DTRinc increased that of the native plants, whereas summertime asymmetric warming decreased the biomass of the invasives but not the natives. Therefore, warming may not facilitate invasion of these invasive species due to the suppressive effects of summertime warming (particularly the asymmetric warming) on growth. Compared with DTRsym, DTRdec decreased the biomass of both the invasive and native plants, while the asymmetric summer warming treatments (DTRinc and DTRdec) decreased the biomass of the invasive but not the native plants. In addition, wintertime DTRinc did not enhance the biomass of all the plants relative to DTRsym. Our results were obtained in an unrealistic setting; the growth conditions in chambers (e.g. low light, low herbivory, no competition) are quite different from natural conditions (high light, normal herbivory and competition), which may influence the effects of warming on the seedling establishment and growth of both invasive and native plants. Nonetheless, our work highlights the importance of asymmetric warming, particularly in regards to the comparison with the effects of symmetric warming on both invasive and native plants. Conclusions regarding the effects of future warming should be made cautiously because warming with different DTRs may suggest different implications for invasion, and effects of warming may be different in different seasons.

Effects of climate change on plant population growth rate and community composition change.

The impacts of climate change on forest community composition are still not well known. Although directional trends in climate change and community composition change were reported in recent years, further quantitative analyses are urgently needed. Previous studies focused on measuring population growth rates in a single time period, neglecting the development of the populations. Here we aimed to compose a method for calculating the community composition change, and to testify the impacts of climate change on community composition change within a relatively short period (several decades) based on long-term monitoring data from two plots-Dinghushan Biosphere Reserve, China (DBR) and Barro Colorado Island, Panama (BCI)-that are located in tropical and subtropical regions. We proposed a relatively more concise index, Slnλ, which refers to an overall population growth rate based on the dominant species in a community. The results indicated that the population growth rate of a majority of populations has decreased over the past few decades. This decrease was mainly caused by population development. The increasing temperature had a positive effect on population growth rates and community change rates. Our results promote understanding and explaining variations in population growth rates and community composition rates, and are helpful to predict population dynamics and population responses to climate change.

Biodiversity of Jinggangshan Mountain: the importance of topography and geographical location in supporting higher biodiversity.

Diversity is mainly determined by climate and environment. In addition, topography is a complex factor, and the relationship between topography and biodiversity is still poorly understood. To understand the role of topography, i.e., altitude and slope, in biodiversity, we selected Jinggangshan Mountain (JGM), an area with unique topography, as the study area. We surveyed plant and animal species richness of JGM and compared the biodiversity and the main geographic characteristics of JGM with the adjacent 4 mountains. Gleason's richness index was calculated to assess the diversity of species. In total, 2958 spermatophyte species, 418 bryophyte species, 355 pteridophyte species and 493 species of vertebrate animals were recorded in this survey. In general, the JGM biodiversity was higher than that of the adjacent mountains. Regarding topographic characteristics, 77% of JGM's area was in the mid-altitude region and approximately 40% of JGM's area was in the 10°-20° slope range, which may support more vegetation types in JGM area and make it a biodiversity hotspot. It should be noted that although the impact of topography on biodiversity was substantial, climate is still a more general factor driving the formation and maintenance of higher biodiversity. Topographic conditions can create microclimates, and both climatic and topographic conditions contribute to the formation of high biodiversity in JGM.

Effects of nanosized constriction on thermal transport properties of graphene.

Thermal transport properties of graphene with nanosized constrictions are investigated using nonequilibrium molecular dynamics simulations. The results show that the nanosized constrictions have a significant influence on the thermal transport properties of graphene. The thermal resistance of the nanosized constrictions is on the order of 10(7) to 10(9) K/W at 150 K, which reduces the thermal conductivity by 7.7% to 90.4%. It is also found that the constriction resistance is inversely proportional to the width of the constriction and independent of the heat current. Moreover, we developed an analytical model for the ballistic thermal resistance of the nanosized constrictions in two-dimensional nanosystems. The theoretical prediction agrees well with the simulation results in this paper, which suggests that the thermal transport across the nanosized constrictions in two-dimensional nanosystems is ballistic in nature. PACS: 65.80.CK; 61.48.Gh; 63.20.kp; 31.15.xv.

Non-Additive effects on decomposition from mixing litter of the invasive Mikania micrantha H.B.K. with native plants.

A common hypothesis to explain the effect of litter mixing is based on the difference in litter N content between mixed species. Although many studies have shown that litter of invasive non-native plants typically has higher N content than that of native plants in the communities they invade, there has been surprisingly little study of mixing effects during plant invasions. We address this question in south China where Mikania micrantha H.B.K., a non-native vine, with high litter N content, has invaded many forested ecosystems. We were specifically interested in whether this invader accelerated decomposition and how the strength of the litter mixing effect changes with the degree of invasion and over time during litter decomposition. Using litterbags, we evaluated the effect of mixing litter of M. micrantha with the litter of 7 native resident plants, at 3 ratios: M1 (1∶4, = exotic:native litter), M2 (1∶1) and M3 (4∶1, = exotic:native litter) over three incubation periods. We compared mixed litter with unmixed litter of the native species to identify if a non-additive effect of mixing litter existed. We found that there were positive significant non-additive effects of litter mixing on both mass loss and nutrient release. These effects changed with native species identity, mixture ratio and decay times. Overall the greatest accelerations of mixture decay and N release tended to be in the highest degree of invasion (mix ratio M3) and during the middle and final measured stages of decomposition. Contrary to expectations, the initial difference in litter N did not explain species differences in the effect of mixing but overall it appears that invasion by M. micrantha is accelerating the decomposition of native species litter. This effect on a fundamental ecosystem process could contribute to higher rates of nutrient turnover in invaded ecosystems.