Cultivated alien plants with high invasion potential are more likely to be traded online in China.

Biological invasions have become a worldwide problem, and measures to efficiently prevent and control invasions are still in development. Like many other parts of the world, China is undergoing a dramatic increase in plant invasions. Most of the currently 933 established (i.e., naturalized) plant species, of which 214 are categorized as invasive, have been introduced into China for cultivation. It is likely that many of those species are still being traded, particularly online, by plant nurseries. However, studies assessing whether naturalized and invasive species are currently being traded more or less than nonnaturalized aliens are rare. We extracted online-trade information for 13,718 cultivated alien plant taxa on 1688.com, the largest website for domestic B2B in China. We analyzed how the presence in online-nursery catalogs, the number of online nurseries that offerred the species for sale, and the product type (i.e., seeds, live plants and vegetative organs) differed among nonnaturalized, naturalized noninvasive, and invasive species. Compared to nonnaturalized taxa, naturalized noninvasive and invasive taxa were 3.7-5.2 times more likely to be available for purchase. Naturalized noninvasive and invasive taxa were more frequently offered as seeds by online nurseries, whereas nonnaturalized taxa were more frequently offered as live plants. Based on these findings, we propose that, to reduce the further spread of invasive and potentially invasive plants, implementation of plant-trade regulations and a monitoring system of the online horticultural supply chain will be essential.

Does genotypic diversity of Hydrocotyle vulgaris affect CO2 and CH4 fluxes?

Biodiversity plays important roles in ecosystem functions and genetic diversity is a key component of biodiversity. While effects of genetic diversity on ecosystem functions have been extensively documented, no study has tested how genetic diversity of plants influences greenhouse gas fluxes from plant-soil systems. We assembled experimental populations consisting of 1, 4 or 8 genotypes of the clonal plant Hydrocotyle vulgaris in microcosms, and measured fluxes of CO2 and CH4 from the microcosms. The fluxes of CO2 and CO2 equivalent from the microcosms with the 1-genotype populations of H. vulgaris were significantly lower than those with the 4- and 8-genotype populations, and such an effect increased significantly with increasing the growth period. The cumulative CO2 flux was significantly negatively related to the growth of the H. vulgaris populations. However, genotypic diversity did not significantly affect the flux of CH4. We conclude that genotypic diversity of plant populations can influence CO2 flux from plant-soil systems. The findings highlight the importance of genetic diversity in regulating greenhouse gas fluxes.

Transgenerational Herbivory Effects on Performance of Clonal Offspring of the Invasive Plant Alternanthera philoxeroides.

Interactions between alien plants and local enemies in introduced ranges may determine plant invasion success. However, little is known about whether herbivory-induced responses are transmitted across vegetative generations of plants and whether epigenetic changes are involved during this process. In a greenhouse experiment, we examined the effects of herbivory by the generalist herbivore Spodoptera litura on the growth, physiology, biomass allocation and DNA methylation level of the invasive plant Alternanthera philoxeroides in the first- (G1), second- (G2) and third-generation (G3). We also tested the effects of root fragments with different branching orders (i.e., the primary- or secondary-root fragments of taproots) of G1 on offspring performance. Our results showed that G1 herbivory promoted the growth of the plants in G2 that sprouted from the secondary-root fragments of G1 but had a neutral or negative effect on the growth of the plants in G2 from the primary-root fragments. The growth of plants in G3 was significantly reduced by G3 herbivory but not affected by G1 herbivory. Plants in G1 exhibited a higher level of DNA methylation when they were damaged by herbivores than when they were not, while neither plants in G2 nor G3 showed herbivory-induced changes in DNA methylation. Overall, the herbivory-induced growth response within one vegetative generation may represent the rapid acclimatization of A. philoxeroides to the unpredictable generalist herbivores in the introduced ranges. Herbivory-induced trans-generational effects may be transient for clonal offspring of A. philoxeroides, which can be influenced by the branching order of taproots, but be less characterized by DNA methylation.

Soil heterogeneity in the horizontal distribution of microplastics influences productivity and species composition of plant communities.

Contamination of soils by microplastics can have profound ecological impacts on terrestrial ecosystems and has received increasing attention. However, few studies have considered the impacts of soil microplastics on plant communities and none has tested the impacts of spatial heterogeneity in the horizontal distribution of microplastics in the soil on plant communities. We grew experimental plant communities in soils with either a homogeneous or a heterogeneous distribution of each of six common microplastics, i.e., polystyrene foam (EPS), polyethylene fiber (PET), polyethylene bead (HDPE), polypropylene fiber (PP), polylactic bead (PLA) and polyamide bead (PA6). The heterogeneous treatment consisted of two soil patches without microplastics and two with a higher (0.2%) concentration of microplastics, and the homogeneous treatment consisted of four patches all with a lower (0.1%) concentration of microplastics. Thus, the total amounts of microplastics in the soils were exactly the same in the two treatments. Total and root biomass of the plant communities were significantly higher in the homogeneous than in the heterogeneous treatment when the microplastic was PET and PP, smaller when it was PLA, but not different when it was EPS, HDPE or PA6. In the heterogeneous treatment, total and root biomass were significantly smaller in the patches with than without microplastics when the microplastic was EPS, but greater when the microplastic was PET or PP. Additionally, in the heterogeneous treatment, root biomass was significantly smaller in the patches with than without microplastics when the microplastic was HDPE, and shoot biomass was also significantly smaller when the microplastic was EPS or PET. The heterogeneous distribution of EPS in the soil significantly decreased community evenness, but the heterogeneous distribution of PET increased it. We conclude that soil heterogeneity in the horizontal distribution of microplastics can influence productivity and species composition of plant communities, but such an effect varies depending on microplastic chemical composition (types) and morphology (shapes).

Biochar-compost addition benefits Phragmites australis growth and soil property in coastal wetlands.

Salinity stress is common for plants growing in coastal wetlands. The addition of biochar in the soil may alleviate the negative effect of salinity through its unique physicochemical properties. To test this, we conducted a greenhouse experiment where the cosmopolitan wetland plant Phragmites australis was subjected to four salinity treatments (0, 5, 10 and 15‰) and three biochar treatments (no biochar addition, with biochar addition and with biochar-compost addition, both biochar and compost were made from P. australis) in a factorial design. Both biochar addition and biochar-compost addition to the substrate enhanced belowground mass of P. australis, application of biochar-compost significantly increased total mass by 35.5% and net photosynthesis rate of P. australis by 51.4%. Both biochar addition and biochar-compost addition significantly increased soil organic carbon content by 62.9% and 31.7%, respectively, but decreased soil ammonium nitrogen content. In the saline soil, application of the mixture of biochar-compost had a strong, and positive effect on the growth of P. australis, compared to biochar alone. Therefore, incorporation of biochar and compost might be an appropriate approach to improve the productivity of P. australis growing in coastal wetlands, where soil salinity is a common environmental stress.

Biochar addition affects root morphology and nitrogen uptake capacity in common reed (Phragmites australis).

Nitrogen (N) is a key factor that limits plant growth in most terrestrial ecosystems, and biochar reportedly improves soil characteristics and grain yields. However, the effects of biochar on plant N uptake in wetland ecosystems and the underlying mechanisms of these effects remain unclear. Therefore, our study sought to characterise the effects of biochar addition on Phragmites australis N absorption rates at two different N deposition conditions [30 and 60 kg N hm-2 yr-1; i.e., "low" and "high" N treatments, respectively]. Our results demonstrated that biochar significantly promoted root biomass growth in P. australis in the high N treatment group. In contrast, the low N treatment group exhibited an increased proportion of fine roots and a decrease in the average P. australis root diameter. The N absorption rate of P. australis in the low N treatment group significantly increased with biochar addition and ammonium N became the preferred N source. The absorption rates of both ammonium and nitrate N were negatively correlated with the average P. australis root diameter. Therefore, our findings indicate that biochar may affect the N uptake strategy of P. australis by altering root morphogenesis, thereby providing new insights into potential restoration strategies for wetland vegetation.

Biochar rhizosphere addition promoted Phragmites australis growth and changed soil properties in the Yellow River Delta.

Biochar addition can enhance plant growth and change soil physicochemical properties in saline soil. However, it is unclear whether the positioning of biochar additions (e.g., rhizosphere addition and surface addition) alters such impacts and whether such positioning effects interact with salinity levels. In the Yellow River Delta, China, we carried out a field experiment in which biochar was not added (control) or was added to the soil surface (surface addition) or to the soil at the rhizosphere position (rhizosphere addition) of Phragmites australis in three sites with different salt levels (1‰ - low, 5‰ - medium and 10‰ - high). Rhizosphere addition of biochar significantly improved the growth of P. australis, especially its fine root mass. Both rhizosphere addition and surface addition of biochar significantly decreased nitrate nitrogen content and electrical conductivity, and the inhibitory effects were more effective at the sites with medium and high salt levels in 2018. Structural equation modeling showed that biochar addition could directly increase the fine root mass of P. australis by decreasing the soil electrical conductivity, further improving the total mass of P. australis. Overall, rhizosphere addition of biochar is a better choice for improving the productivity of P. australis in saline soil and is beneficial to P. australis wetland restoration in the Yellow River Delta. Long-term field research is needed to better understand the effect and mechanism of biochar application.

Clonal integration in Phagmites australis mitigates effects of oil pollution on greenhouse gas emissions in a coastal wetland.

Clonal integration, i.e., resource sharing within clones, enables clonal plants to maintain biomass production when ramets (asexual individuals) under stress are connected to those not under stress. Oil pollution can strongly reduce biomass production, and connected ramets within clones may experience different levels of oil pollution. Therefore, clonal integration may help plants maintain biomass production despite oil pollution. Because biomass production is often negatively correlated with greenhouse gas emissions, we hypothesized that oil pollution would increase greenhouse gas emissions and that clonal integration would reduce such an effect. We tested these hypotheses in a coastal wetland dominated by the rhizomatous grass Phragmites australis near a major site of oil production in the Yellow River Delta in China. We applied 0, 5, or 10 mm crude oil per year for two years in plots within stands of P. australis and tested effects of severing rhizomes connecting ramets inside and outside a plot (i.e. preventing clonal integration) on biomass production, soil chemistry and greenhouse gas emissions. When severed, ramets inside plots with no added oil produced about 220 g aboveground biomass m--2 over the second growing season, and plots absorbed about 500 g total CO2 equivalents m-2. Adding 10 mm oil per year reduced aboveground biomass by about 30%, and caused plots to emit about 800 g CO2 equivalents m-2. Leaving ramets connected to those outside plots eliminated the negative effects of oil pollution on biomass production, and caused plots given 10 mm oil per year to emit about 50% fewer total CO2 equivalents. We conclude that oil pollution can increase greenhouse gas emissions and clonal integration can reduce the effect of oil pollution on biomass production and greenhouse gas emissions. Our study provides the first experimental evidence that clonal integration in plants can reduce greenhouse gas emissions.

Soil resource heterogeneity competitively favors an invasive clonal plant over a native one.

Soil resource heterogeneity can affect plant growth and competitive ability. However, little is known about how soil resource heterogeneity affects competitive interactions between invasive and native plants. We conducted an experiment with an invasive clonal plant Alternanthera philoxeroides and a coexisting native one Alternanthera sessilis. The experiment was a randomized design with three factors, i.e. two species (A. philoxeroides and A. sessilis), two interspecific competition treatments (with and without) and five soil treatments (three homogeneous treatments and two small-scale heterogeneous treatments consisting of two patches of 10 cm × 15 cm and with different initial planting positions). Irrespective of competition, increasing soil resource availability increased the growth of A. philoxeroides. Increasing soil resource availability also increased the growth of A. sessilis without competition, but had no impact with competition. Irrespective of competition, soil resource heterogeneity increased biomass and ramet production of A. philoxeroides, and such effects were independent of initial planting position. For A. sessilis, however, soil resource heterogeneity only increased ramet production when the initial plant was grown in the low-resource patch without competition. Our results suggest that both high soil resource availability and small-scale soil resource heterogeneity can increase the relative competitive ability of the invasive plant A. philoxeroides when grown with its native congener A. sessilis. These findings may partly explain the invasion success of this clonal species in area with high soil resource availability and heterogeneity caused by e.g. nitrogen deposition, fertilization and disturbance.

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To clarify the impacts of climate change on the potential distribution of six crane species in the Great Xing'an Mountains region, and promote the effective protection of these species, we selected key environmental variables such as climate, topography, and vegetation type based on Pearson correlation and Jackknife analysis, and modeled the potential distribution of six crane species in the Great Xing'an Mountains using MaxEnt with the current and the future climate change scenarios (RCP4.5 and RCP8.5). We identified the priority protection areas (PPAs) and the target PPAs by zonation and ArcGIS. The results showed that with the current climate condition, the sui-table habitats of these species were mainly distributed in the central and the northwest part of the Great Xing'an Mountains. With RCP4.5 and RCP8.5 scenarios, the suitable habitats of Grus monacha, Grus japonensis, Grus vipio, Grus grus and Anthropoides virgo would decrease, while that of Grus leucogeranus would expand by 5.4%-6.3%. With current and the future climate change scenarios, the PPAs of these species were mainly distributed in the northwest, southeast and west-central parts of the Great Xing'an Mountains. The protect rate could reach about 20.1%-23.8% of the target PPAs conserved by protected areas (PAs). The protection gaps were mainly distributed in the west of Mohe County, the north-central of Ergun, the central and east of Genhe, the northeast of Yakeshi, and the south of Oroqen Autonomous Banner. We proposed to expand PAs to provide a strong guarantee for the effective protection of cranes species.

Nutrient-induced shifts of dominant species reduce ecosystem stability via increases in species synchrony and population variability.

The mechanisms underlying nutrient-induced diversity-stability relationships have been examined extensively. However, the effects of nutrient-induced shifts of dominant species on ecosystem stability have rarely been evaluated. We compiled a dataset from a long-term nitrogen (N) and phosphorus (P) enrichment experiment conducted in an alpine grassland on the Tibetan Plateau to test the effects of nutrient-induced shifts of dominant species on stability. Our results show that N enrichment increased synchrony among the dominant species, which contributed to a significant increase in synchrony of the whole community. Meanwhile, N-induced shifts in dominant species composition significantly increased population variability. Increases in species synchrony and population variability resulted in a decline in ecosystem stability. Our study has important implications for progress in understanding the role of plant functional compensation in the stability of ecosystem functions, which is critical for better understanding the mechanisms driving both community assembly and ecosystem functions.

Effects of arbuscular mycorrhizal fungi and soil nutrient addition on the growth of Phragmites australis under different drying-rewetting cycles.

The frequency of soil drying-rewetting cycles is predicted to increase under future global climate change, and arbuscular mycorrhizal fungi (AMF) are symbiotic with most plants. However, it remains unknown how AMF affect plant growth under different frequencies of soil drying-rewetting cycles. We subjected a clonal wetland plant Phragmites australis to three frequencies of drying-rewetting cycles (1, 2, or 4 cycles), two nutrient treatments (with or without), and two AMF treatments (with or without) for 64 days. AMF promoted the growth of P. australis, especially in the 2 cycles of the drying-rewetting treatment. AMF had a significant positive effect on leaf mass and number of ramets in the 2 cycles of the drying-rewetting treatment with nutrient addition. In the 2 cycles of drying-rewetting treatment without nutrient addition, AMF increased leaf area and decreased belowground to aboveground biomass ratio. These results indicate that AMF may assist P. australis in coping with medium frequency of drying-rewetting cycles, and provide theoretical guidance for predicting how wetland plants respond to future global climate change.

Effects of waterlogging on carbon assimilate partitioning in the Zoigê alpine wetlands revealed by 13CO2 pulse labeling.

Waterlogging has been suggested to affect carbon (C) turnover in wetlands, but how it affects C allocation and stocks remains unclear in alpine wetlands. Using in situ (13)CO2 pulse labelling, we investigated C allocation in both waterlogged and non-waterlogged sites in the Zoigê wetlands on the Tibetan Plateau in August 2011. More than 50% of total (13)C fixed by photosynthesis was lost via shoot respiration. Shoots recovered about 19% of total (13)C fixed by photosynthesis at both sites. Only about 26% of total fixed (13)C was translocated into the belowground pools. Soil organic C pool accounted for 19% and roots recovered about 5-7% of total fixed (13)C at both sites. Waterlogging significantly reduced soil respiration and very little (13)C was lost via soil respiration in the alpine wetlands compared to that in grasslands. We conclude that waterlogging did not significantly alter C allocations among the C pools except the (13)CO2 efflux derived from soil respiration and that shoots made similar contributions to C sequestration as the belowground parts in the Zoigê alpine wetlands. Therefore, changes in waterlogging due to climate change will not affect C assimilate partitioning but soil C efflux.