Minghua Song

Invasive alien plants in China: role of clonality and geographical origin

Biological invasions have become a significant threat to the global environment. Unfortunately, to date there is no consensus on invasion mechanisms and predictive models. Controversies range from whether we can reliably predict which species may become invasive to which species characteristics (e.g., life history, taxonomic groups, or geographic origin) contribute to the invasion processes. We examined 126 invasive alien plant species in China to understand the role of clonality and geographical origin in their invasion success. These species were categorized into three groups (I, II, III) based on their invasiveness in terms of current spatial occupation and the degree of damage to invaded habitats. Clonal plants consisted of almost half (44%) of the 126 invasive species studied, and consisted of 66% of 32 the most invasive alien plant species (Group I). There was a significant positive relationship between clonality and species invasiveness. A 68% of the 126 species studied originated in the continent of America (North and/or South America). These preliminary findings support that America is the primary geographical origin of invasive alien plant species in China and that clonality of the invasive plant species contributed significantly to the their invasiveness. The results suggest an urgent need at the global scale to investigate the mechanisms whereby plant clonal growth influences plant invasions, and the need for a focus at regional scale to examine factors affecting the exchange of invasive plant species between America and China.

Distributions of Dominant Tree Species on the Tibetan Plateau under Current and Future Climate Scenarios

Abstract A bioclimatic model was used to simulate distributions of the dominant tree species on the Tibetan Plateau. The model is based on physiological constraints to alpine plant growth. The bioclimatic variables used in this model are: minimum temperature in the coldest month, maximum temperature in the warmest month, accumulated growing-season warmth, and minimum value of soil moisture availability in the growing season. A comparison was made between simulated current distributions of tree species and their actual natural distributions on the Tibetan Plateau. It was shown that there is good agreement between simulated current and actual natural distributions. The simulated current distribution areas of tree species such as Abies spectabilis, Picea likiangensis var. linzhiensis, Pinus densata, Larix griffithiana were a little larger than their actual distributions. For Quercus aquifolioides and the relict species Betula platyphylla, simulated areas were a little smaller than their actual distributions. Future distributions of dominant tree species were predicted under a climate scenario with a CO2 concentration of 500 ppmv in the year 2100. The distribution areas of Abies spectabilis, Picea likiangensis var. linzhiensis, Pinus densata, Larix griffithiana and Quercus aquifolioides would shift and extend towards the north and west under the future climate scenario. For Betula utilis, the distribution areas would shift towards the north but they would shrink.

Importance of clonal plants and plant species diversity in the Northeast China Transect

In plant communities, the internal (genet-level) control mechanisms on a spatio-temporal scale of clonal plants impose strong constraints on spatial pattern as well as on competitive relations and, thus, species coexistence. Therefore, the presence of clonal species within a plant community affects spatio-temporal dynamics and plant species diversity. We examined the distribution of plants with different clonal growth forms in the Northeast China Transect (NECT) and correlated plant species diversity with the importance of clonal plants, and the importance of phalanx and guerilla clonal plants. Phalanx clonal plants were more abundant in western communities where the altitude was higher and both the soil nitrogen contents and precipitation were relatively low. Whereas guerilla clonal plants were more abundant in the middle of the NECT where the precipitation, mean annual temperature and photosynthetically active radiation were relatively high. In the relatively productive temperate typical steppe, plant species diversity was negatively correlated with the importance of phalanx clonal plants and positively correlated with the importance of guerilla clonal plants. In relatively unproductive temperate desert steppe, plant species diversity was positively correlated with the importance of both phalanx and guerilla clonal plants.

Simulated distribution of vegetation types in response to climate change on the Tibetan Plateau

Abstract Questions: What is the relationship between alpine vegetation patterns and climate? And how do alpine vegetation patterns respond to climate changes? Location: Tibetan Plateau, southwestern China. The total area is 2 500 000 km2 with an average altitude over 4000 m. Methods: The geographic distribution of vegetation types on the Tibetan Plateau was simulated based on climatology using a small set of plant functional types (PFTs) embedded in the biogeochemistry-biography model BIOME4. The paleoclimate for the early Holocene was used to explore the possibility of simulating past vegetation patterns. Changes in vegetation patterns were simulated assuming continuous exponential increase in atmospheric CO2 concentration, based on a transient ocean-atmosphere simulation including sulfate aerosol effects during the 21st century. Results: Forest, shrub steppe, alpine steppe and alpine meadow extended while no desert vegetation developed under the warmer and humid climate of the early Holocene. In the fut...Abstract Questions: What is the relationship between alpine vegetation patterns and climate? And how do alpine vegetation patterns respond to climate changes? Location: Tibetan Plateau, southwestern China. The total area is 2 500 000 km2 with an average altitude over 4000 m. Methods: The geographic distribution of vegetation types on the Tibetan Plateau was simulated based on climatology using a small set of plant functional types (PFTs) embedded in the biogeochemistry-biography model BIOME4. The paleoclimate for the early Holocene was used to explore the possibility of simulating past vegetation patterns. Changes in vegetation patterns were simulated assuming continuous exponential increase in atmospheric CO2 concentration, based on a transient ocean-atmosphere simulation including sulfate aerosol effects during the 21st century. Results: Forest, shrub steppe, alpine steppe and alpine meadow extended while no desert vegetation developed under the warmer and humid climate of the early Holocene. In the future climate scenario, the simulated tree line is farther north in most sectors than at present. There are also major northward shifts of alpine meadows and a reduction in shrub-dominated montane steppe. The boundary between montane desert and alpine desert will be farther to the south than today. The area of alpine desert would decrease, that of montane desert would increase. Conclusions: The outline of changes in vegetation distribution was captured with the simulation. Increased CO2 concentration would potentially lead to big changes in alpine ecosystems.

Clonal plants and plant species diversity in wetland ecosystems in China

Abstract Clonal plants play important roles in maintaining wetland ecosystems in China. By analysing 108 wetland quadrats distributed throughout China, we evaluated (1) the importance of clonal growth forms in different Chinese wetlands, (2) how the abundance of clonal plants is related to climatic and geographical conditions, and (3) how plant species diversity is related to the abundance of clonal plants. Significant differences in clonal plant importance values were found between different regions of China. Clonal plants were more important in wetland ecosystems located towards the West and North and at higher elevations and, accordingly, experiencing a colder and drier climate. Plant species diversity showed a significant inverse correlation with the importance value of ‘guerilla’-type plants in most of the wetland regions. However, we found no significant correlation between plant species diversity and importance values of ‘phalanx’-type plants. In most Chinese wetlands, plant species diversity decreased with increasing importance of guerilla plants and also with an increase of the entire guild of clonal plants. In wetlands with low species richness, however, plant species diversity increased with increasing importance of guerilla plants and of all clonal plants together, suggesting that in these disturbed habitats clonal growth may facilitate the establishment of other, non-clonal wetland plants. Nomenclature: Anon. (1974); Anon. (1979–1999); Lang (1999).

Differential responses of arbuscular mycorrhizal fungi to nitrogen addition in a near pristine Tibetan alpine meadow

Elucidating the responses of soil microbial abundance and community composition to nitrogen (N) addition is important for predicting ecosystem function under increased atmospheric N deposition. We examined the arbuscular mycorrhizal (AM) fungal community under three N forms (NH4(+)-N, NO3(-)-N, and NH4NO3-N) and two N rates (1.5 and 7.5 g N m(-2) year(-1)) in an alpine meadow of the Qinghai-Tibetan Plateau. AM fungal extraradical hyphal density was significantly decreased by NH4(+)-N in May, but was not affected by N form nor N rate in August. N rate, but not N form, significantly affected AM fungal spore density; high N rate decreased spore density. No direct N addition effect was observed on AM fungal community; however, soil available phosphorus, pH, and NO3(-)-N were considered as important factors that influenced AM fungal community composition. Structural equation model results showed that N rate, not N form, strongly affected soil characteristics, which directly influenced community compositions of plants and AM fungi, as well as spore density. Therefore, AM fungal community was influenced by N addition, primarily because of altered soil characteristics, and partially by a modified plant community, but not or just slightly by direct N addition effects in this alpine meadow ecosystem.

Responses of ecosystem CO 2 fluxes to short-term experimental warming and nitrogen enrichment in an Alpine meadow, northern Tibet Plateau.

Over the past decades, the Tibetan Plateau has experienced pronounced warming, yet the extent to which warming will affect alpine ecosystems depends on how warming interacts with other influential global change factors, such as nitrogen (N) deposition. A long-term warming and N manipulation experiment was established to investigate the interactive effects of warming and N deposition on alpine meadow. Open-top chambers were used to simulate warming. N addition, warming, N addition × warming, and a control were set up. In OTCs, daytime air and soil temperature were warmed by 2.0°C and 1.6°C above ambient conditions, but soil moisture was decreased by 4.95 m3 m−3. N addition enhanced ecosystem respiration (Reco); nevertheless, warming significantly decreased Reco. The decline of Reco resulting from warming was cancelled out by N addition in late growing season. Our results suggested that N addition enhanced Reco by increasing soil N availability and plant production, whereas warming decreased Reco through lowering soil moisture, soil N supply potential, and suppression of plant activity. Furthermore, season-specific responses of Reco indicated that warming and N deposition caused by future global change may have complicated influence on carbon cycles in alpine ecosystems.

Water sources of dominant species in three alpine ecosystems on the Tibetan Plateau, China

Plant water sources were estimated by two or three compartment linear mixing models using hydrogen and oxygen isotope (deltaD and delta18O) values of different components such as plant xylem water, precipitation and river water as well as soil water on the Tibetan Plateau in the summer of 2005. Four dominant species (Quercus aquifolioides, Pinus tabulaeformis, Salix rehderiana and Nitraria tangutorum) in three typical ecosystems (forest, shrub and desert) were investigated in this study. Stable isotope ratios of the summer precipitations and the soil water presented variations in spatial and temporal scales. delta18O values of N. tangutorum xylem water were constant in the whole growth season and very similar to those of deep soil water. Water sources for all of the plants came from both precipitations and soil water. Plants switched rapidly among different water sources when environmental water conditions changed. Rainwater had different contributions to the plants, which was influenced by amounts of precipitation. The percentage of plant xylem water derived from rainwater rose with an increase in precipitation. Water sources for broad-leaved and coniferous species were different although they grew in the same environmental conditions. For example, the broad-leaved species Q. aquifolioides used mainly the water from deep soil, while 92.5% of xylem water of the coniferous species P. tabulaeformis was derived from rainwater during the growth season. The study will be helpful for us to fully understand responses of species on the Tibetan Plateau to changes in precipitation patterns, and to assess accurately changes of vegetation distribution in the future.

Litter species traits, but not richness, contribute to carbon and nitrogen dynamics in an alpine meadow on the Tibetan Plateau

AimsLitter, as afterlife of plants, plays an important role in driving belowground decomposition processes. Here we tested effects of litter species identity and diversity on carbon (C) and nitrogen (N) dynamics during litter decomposition in N-limited alpine meadow soil from the Qinghai–Tibet Plateau.MethodsWe incubated litters of four meadow species, a sedge (“S”, Kobresia humilis), a grass (“G”, Elymus nutans), a herb (“H”, Saussurea superba), and a legume (“L”, Oxytropis falcata), in monoculture and in mixture with meadow soil. CO2 release was measured 21 times during the incubation, and soil available N and microbial biomass C and N were measured before and after the experiment.ResultsThe organic C decay rate did not differ much among soils amended with monocultures or mixtures of litter, except in the H, S, L, and S+H treatments, which had much higher decay rates. Potential decomposable C pools were lowest in the control, highest in the L treatment, and intermediate in the S treatment. Mineralized N was completely immobilized by soil microbes in all treatments except the control, S+L, and S+G+L treatments. Litter mixtures had both additive and non-additive effects on CO2-C emission (mainly antagonistic effects), net N mineralization (mainly synergistic), and microbial biomass C and N (both). Overall, these parameters were not significantly correlated with litter species richness. Similarly, microbial C or N was not significantly correlated with litter N content or C/N. However, cumulative CO2-C emission and net N mineralization were positively correlated with litter N content and negatively correlated with litter C/N.ConclusionsLitter N content and C/N rather than litter species richness drove the release of CO2-C and net available N in this ecosystem. The antagonistic effects of litter mixtures contributed to a modest release of CO2-C, but their synergistic effects enhanced net available N. We suggest that in alpine meadow communities, balancing species with high and low N contents will benefit soil carbon sequestration and plant competition for available N with soil microbes.

Clonality-Climate Relationships along Latitudinal Gradient across China: Adaptation of Clonality to Environments

Plant clonality, the ability of a plant species to reproduce itself vegetatively through ramets (shoot-root units), occurs in many plant species and is considered to be more frequent in cold or wet environments. However, a deeper understanding on the clonality-climate relationships along large geographic gradients is still scarce. In this study we revealed the clonality-climate relationships along latitudinal gradient of entire China spanning from tropics to temperate zones using clonality data for 4015 vascular plant species in 545 terrestrial communities. Structural equation modeling (SEM) showed that, in general, the preponderance of clonality increased along the latitudinal gradient towards cold, dry or very wet environments. However, the distribution of clonality in China was significantly but only weakly correlated with latitude and four climatic factors (mean annual temperature, temperature seasonality, mean annual precipitation, precipitation seasonality). Clonality of woody and herbaceous species had opposite responses to climatic variables. More precisely, woody clonality showed higher frequency in wet or climatically stable environments, while herbaceous clonality preferred cold, dry or climatically instable environments. Unexplained variation in clonality may be owed to the influences of other environmental conditions and to different clonal strategies and underlying traits adopted by different growth forms and phylogenetic lineages. Therefore, in-depth research in terms of more detailed clonal growth form, phylogeny and additional environmental variables are encouraged to further understand plant clonality response to climatic and/or edaphic conditions.