Jiaen Zhang

Predicting the potential distribution of Lantana camara L. under RCP scenarios using ISI-MIP models

Projections of anthropogenically-induced global climate change and its impacts on potential distributions of invasive species are crucial for implementing effective conservation and management strategies. Lantana camara L., a popular ornamental plant native to tropical America, has become naturalized in some 50 countries and is considered one of the world’s worst weeds. To increase our understanding of its potential extent of spread and examine the responses of global geographic distribution, predictive models incorporating global distribution data of L. camara were generated. These models were used to identify areas of environmental suitability and project the effects of future climate change based on an ensemble of the four global climate models (GCMs) within the Inter-Sectoral Impact Model Intercomparis on Project (ISI-MIP). Each model was run under the four emission scenarios (Representative Concentration Pathways, RCPs) using the Maximum entropy (Maxent) approach. Future model predictions through 2050 indicated an overall expansion of L. camara, despite future suitability varying considerably among continents. Under the four RCP scenarios, the range of L. camara expanded further inland in many regions (e.g. Africa, Australia), especially under the RCP85 emission scenario. The global distribution of L. camara, though restricted within geographical regions of similar latitude as at present (35°Nu2009~u200935°S), was projected to expand equator-ward in response to future climate conditions. Considerable discrepancy in predicted environmental suitability for L. camara among GCMs highlights the complexities of the likely effects of climate change on its potential distribution and the need to improve the reliability of predictions in novel climates.

Predicting invasions of Wedelia trilobata (L.) Hitchc. with Maxent and GARP models

Wedelia trilobata (L.) Hitchc., an ornamental groundcover plant introduced to areas around the world from Central America, has become invasive in many regions. To increase understanding of its geographic distribution and potential extent of spread, two presence-only niche-based modeling approaches (Maxent and GARP) were employed to create models based on occurrence records from its: (1) native range only and (2) full range (native and invasive). Models were then projected globally to identify areas vulnerable to W. trilobata invasion. W. trilobata prefers hot and humid environments and can occur in areas with different environmental conditions than experienced in its native range. Based on native and full occurrence points, GARP and Maxent models produced consistent distributional maps of W. trilobata, although Maxent model results were more conservative. When used to estimate the global invasive distribution of the species, both modeling approaches projected the species to occur in Africa. The GARP full model succeeded in predicting the known occurrences in Australia, while the other models failed to identify favorable habitats in this region. Given the rapid spread of W. trilobata and the serious risk of this species poses to local ecosystems, practical strategies to prevent the establishment and expansion of this species should be sought.

Effects of Praxelis clematidea invasion on soil nitrogen fractions and transformation rates in a tropical savanna

Plant invasion has been reported to affect a mass of soil ecological processes and functions, although invasion effects are often context-, species- and ecosystem- specific. This study was conducted to explore potential impacts of Praxelis clematidea invasion on contents of total and available soil nitrogen (N) and microbial N transformations in a tropical savanna. Soil samples were collected from the surface and sub-surface layers in plots with non-, slight, or severe P. clematidea invasion in Hainan Province of southern China, which remains less studied, and analyzed for contents of the total and available N fractions and microbial N transformations. Results showed that total N content significantly increased in the surface soil but trended to decrease in the sub-surface soil in the invaded plots relative to the non-invaded control. Slight invasion significantly increased soil alkali-hydrolysable N content in the two soil layers. Soil net N mineralization rate was not significantly changed in both the soil layers, although soil microbial biomass N was significantly higher in plots with severe invasion than the control. There was no significant difference in content of soil N fractions between plots with slight and severe invasion. Our results suggest that invasion of P. clematidea promotes soil N accumulation in the surface soil layer, which is associated with increased microbial biomass N. However, the invasion-induced ecological impacts did not increase with further invasion. Significantly higher microbial biomass N was maintained in plots with severe invasion, implying that severe P. clematidea invasion may accelerate nutrient cycling in invaded ecosystems.

Mechanical stimulation of duck on rice phyto-morphology in rice-duck farming system: Mechanical stimulation of duck on rice phyto-morphology in rice-duck farming system

Integrated rice-duck farming system,developed from raising ducks in paddy fields,as one of Chinas traditional agri-culture was encouraged for safe production of rice in China,Japan and other countries in Southeast Asia.To study the effects of ducks on the growth characteristics of rice,a mechanical stimulation experiment was conducted under greenhouse conditions.Based on the analysis,mechanical stimulation showed some impacts of raising ducks on agronomic characteristics of rice.Different intensi-ties of mechanical stimulation restrained and decreased total rice height by 8~10 cm at harvest stage.The lengths of different sections of rice stem,especially the length of the above-ground second section,reduced under duck-rice farming.The thickness of rice stem increased under enhanced mechanical stimulation,with the highest increment of 0.17 cm after treatment for 40 days.While me-chanical stimulation for a certain period improved effective tillering capacity of rice,it obviously decreased shoot biomass by about 19.6% after treatment for 40 days.This led to an increase in root/shoot ratio of rice.Moreover,mechanical stimulation changed some characteristics of rice yield formation.Under enhanced stimulation intensity,average length of rice-ear increased by 8.88%.Also empty grain number per rice ear decreased by about 36.12%.Rice seed setting rate was higher by 3.79% under increased mechanical stimulation than the control.The findings of this study further verified the effects of mechanical stimulation on plant growth.It pro-vided the basic scientific references for the improvement and reasonable utilization of duck-rice integrated farming system.

Soil microbial carbon utilization, enzyme activities and nutrient availability responses to Bidens pilosa and a non-invasive congener under different irradiances

Two Bidens species (Bidens pilosa and B. bipinnata) that originate from America have been introduced widely in pan-tropics, with the former regarded as a noxious invasive weed whereas the latter naturalized as a plant resource. Whether the two species exhibit different effects on the belowground system remains rarely studied. This study was conducted to investigate soil microbial carbon (C) utilization, enzyme activities and available nitrogen, phosphorus and potassium contents under the two species in a subtropical garden soil of southern China under different levels of light intensity. Results showed that the microbial C utilization and enzyme activities were not significantly different under the two species, implying that the strong invasiveness of B. pilosa could not be due to the plant-soil microbe interactions, at least plant-induced alterations of microbial community function to utilize C substrates. Alternatively, available soil nitrogen and potassium contents were significantly higher under B. pilosa than under B. bipinnata in full sun, indicating that the strong invasiveness of B. pilosa could result from rapid nutrient mobilizations by B. pilosa. However, the differences turned non-significant as light intensity decreased, suggesting that light availability could substantially alter the plant effects on soil nutrient mobilizations.

Cadmium bioaccumulation and antioxidant enzyme activity in hepatopancreas, kidney, and stomach of invasive apple snail Pomacea canaliculata

AbstractThe acute toxicity of Cd was tested, and metal bioaccumulation in tissue was determined for the alien invasive species Pomacea canaliculata and its native competitor Sinotaia quadrata under experimental conditions. The invasive species was more tolerant to Cd toxicity than native species, for which the LC50 values were 4.26, 2.24, and 1.98xa0mg/L at exposure times of 48, 72, and 96xa0h, respectively, approximately three times higher than those of the native snails. The viscera accumulated the highest Cd concentration, followed by the foot and shell in both species. Metal concentrations in the above three tissues of P. canaliculata were much higher than those of S. quadrata, irrespective of Cd dose and exposure time. For P. canaliculata, the highest concentration of metal was further observed in the hepatopancreas (0.64–3.98xa0mg/g) followed by the kidney (0.067–3.78xa0mg/g), with lowest levels in the stomach (0.062–1.53xa0mg/g). Among the five antioxidant enzymes, the most responsive enzymes were CAT, ALP, and GST in the hepatopancreas; CAT, POD, and GST in the kidney; and POD in the stomach of exposed animals. These results, demonstrating a high Cd tolerance, may partly explain the ability of P. canaliculata to displace S. quadrata in Cd-contaminated habitat. The Cd wasxa0accumulated mainly in the hepatopancreas and kidney of invasive species, which changed the activity of antioxidant enzymes allowing the animals to cope with the toxicity.n Graphical abstractCadmium bioaccumulation and antioxidant enzyme activity in the invasive Pomacea canaliculata.

Turn bane into a boon: Application of invasive plant species to remedy soil cadmium contamination

Cadmium (Cd) is one of the mostly hazardous soil pollutants and has threatened human health by accumulating in grains of crops. Phytoremediation is a promising technique to remedy soil Cd contamination, but reported Cd hyperaccumulators remain limited. In this study, we explored potential applicability of three invasive plant species (Chromolaena odorata, Bidens pilosa and Praxelis clematidea) to remove soil Cd using greenhouse experiment. Results showed that the three species grew well with Cd treatments compared to the controlled individuals, suggesting that the species had high Cd tolerance by physiological adjustments such as up-regulating the antioxidant enzyme activities. The only exception was that the height of P.xa0clematidea in the 60u202fmgu202fkg-1 Cd treatment was less than that in the control. Within the tested Cd concentration range, the C.xa0odorata exhibited high bioaccumulation characteristics that meet the recommended standards to identify as a hyperaccumulator (shoot Cd concentrationu202f>u202f100u202fmgu202fkg-1 with bioconcentration and transfer factorsu202f>u202f1). The other two species had also the shoot bioconcentration factor and transfer factor greater than one, while the shoot Cd concentration was relatively lower. Our results highlight a potential applicability of the invasive species used in this study for remediation of the soil Cd contamination, which turns bane into a boon.

Invasion of Praxelis clematidea increases the chemically non-labile rather than labile soil organic carbon in a tropical savanna

ABSTRACT Soil organic carbon (SOC) consists of various classes of organic substances that can be pooled as labile and non-labile fractions. Previous studies have suggested that plant invasion increases SOC content, but whether invasion consistently alters SOC fractions remains unclear. Consequently, the present study was conducted to observe the effects of Praxelis clematidea invasion on SOC fractions in a tropical savanna of southern China. Soil samples were collected in two surface soil layers (0–10 and 10–20 cm) from non-, slightly and severely invaded plots to analyse the total SOC, readily oxidizable SOC (ROC), and non-readily oxidizable SOC (NROC) content. The results showed that severe P. clematidea invasion significantly increased the SOC content by 47% in the surface soil (p < 0.001). The increase in SOC content largely originated from the accumulation of NROC (the non-labile fraction), rather than ROC which typically is regarded as the labile OC fraction. This change may be beneficial to long-term soil C stabilization because chemical recalcitrance is an important pathway to prevent SOC from decomposition. Although the mechanisms for NROC accumulation have not been thoroughly elucidated to date, our results suggest that P. clematidea invasion may facilitate soil C sequestration in this tropical savanna.