Characterization of the complete chloroplast genome sequence of Pistia stratiotes (Araceae) and its phylogenetic implications.

Pistia stratiotes is an invasive aquatic weed in South China. In this study, the first complete chloroplast (cp) genome of P. stratiotes was reported and phylogenetic analysis was conducted with Araceae species based on the cp genome sequences. The genome is a circular molecule of 164,551 bp in length with 36.00% average GC content and includes a large single-copy region (90,705 bp), a small single-copy region (21,886 bp), and two inverted repeat regions (25,980 bp). It contains a total of 129 genes, including 84 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. The maximum likelihood tree indicated that P. stratiotes is related to the genus of Alocasia. The cp genome will provide useful molecular data for further phylogenetic and evolutionary analysis of P. stratiotes.

Invasive Chromolaena odorata species specifically affects growth of its co-occurring weeds.

Plant-plant interaction is essential to weed invasion success and is related to impacts on the environment. To understand interactions of the well-known invasive plant siamweed (Chromolaena odorata) and its neighbors (exotic Praxelis clematidea and native cadillo) in South China, and their competitive mechanisms above- and belowground, a multicultivation experiment was conducted. Competitive indices, plant morphological traits, soil nutrient contents, enzyme activities, and microbial biomass were measured. Competitive balance index and morphological traits revealed balanced competition between P. clematidea and siamweed, and suppressive effect of siamweed on cadillo. In coculture of siamweed and P. clematidea, the branch length of siamweed slightly lengthened, while the branch number of P. clematidea increased compared with their respective monocultures accordingly. Overall impacts of the two invaders on soil properties were near averages of their single impacts. In coculture of siamweed and cadillo, siamweed was more competitive in both light and nutrient capture; soil urease activity and acid phosphatase activity were magnified and mitigated compared with the averages of those in their respective monocultures, respectively. The species-specific results of siamweed competing with its co-occurring weeds would contribute to a better understanding of mechanism in synergistic effect of siamweed with the other invasive plants.

The complete chloroplast genome of Reevesia thyrsoidea (Malvaceae).

Reevesia thyrsoidea Lindl. is an important ornamental plant with horticultural, industrial, and timber usages. In this study, we reported a complete chloroplast genome of R. thyrsoidea, which was quadripartite and 161,786 bp in size, including two inverted repeats (25,466 bp for each) that separated one large single-copy (90,565 bp) and one small single-copy (20,289 bp) regions. The chloroplast genome contained 131 unique genes (86 protein-coding, 37 tRNA, and 8 rRNA), and 17 of them were double copies. Phylogenetic analysis using the chloroplast genome data indicated that R. thyrsoidea was sister to the species in the family Malvaceae.

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. clematidea in the 60 mg kg-1 Cd treatment was less than that in the control. Within the tested Cd concentration range, the C. odorata exhibited high bioaccumulation characteristics that meet the recommended standards to identify as a hyperaccumulator (shoot Cd concentration > 100 mg kg-1 with bioconcentration and transfer factors > 1). 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.

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.

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.

Effects of simulated acid rain on microbial characteristics in a lateritic red soil.

A laboratory experiment was performed to examine the impact of simulated acid rain (SAR) on nutrient leaching, microbial biomass, and microbial activities in a lateritic red soil in South China. The soil column leaching experiment was conducted over a 60-day period with the following six SAR pH treatments (levels): 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 and one control treatment (pH = 7). Compared with the control treatment, the concentrations of soil organic matter, total nitrogen, total phosphorus, total potassium, soil microbial biomass carbon (MBC), soil microbial biomass nitrogen (MBN), and average well color density (AWCD) in the Ecoplates were all significantly decreased by leaching with SAR at different pH levels. The decrease in MBC and MBN indicated that acid rain reduced the soil microbial population, while the decrease in AWCD revealed that acid rain had a negative effect on soil bacterial metabolic function. Soil basal respiration increased gradually from pH 4.0 to 7.0 but decreased dramatically from pH 2.5 to 3.0. The decrease in soil nutrient was the major reason for the change of soil microbial functions. A principal component analysis showed that the major carbon sources used by the bacteria were carbohydrates and carboxylic acids.

[Impact of Mikania micrantha invasion on soil meso- and micro-invertebrate community structure].

Mikania micrantha, a notorious exotic weed of Asteraceae family, has invaded successfully in southern China, and caused serious damages to native ecosystems. In this paper, a field survey was conducted in the Huolushan Forest Park of Guangzhou, China, aimed to understand the impact of M. micrantha invasion on the soil meso- and micro-invertebrate community. Three sampling sites were installed, including M. micrantha-invaded site, ecotone, and native vegetation site. Through four samplings in 2009, a total of 5206 soil meso- and micro-invertebrate individuals were collected, belonging to 4 phyla, 10 classes, and 19 orders, among which, Nematoda was the dominant group, and Acarina, Collembolan, and Rotifera were the common groups. M. micrantha invasion altered the characteristics of soil meso- and micro-invertebrate community structure. Compared with those at the other two sampling sites, the numbers of total individuals, Nematoda, and Acarina at M. micrantha-invaded site increased significantly, but the groups of soil meso- and micro-invertebrates had less change. At M. micrantha-invaded site, the density-group index (DG) of soil meso- and micro-invertebrates was significantly higher, Margalef richness index (D) and Simpson dominance index (C) tended to ascend, but Pielou evenness index (E) and Shannon index (H') tended to descend. The similarity coefficient of soil meso- and micro-invertebrate community between M. micrantha-invaded site and ecotone was higher than that between M. micrantha-invaded site and native vegetation site. The changes of local climate conditions, plant litters, root secretions, and soil physical-chemical properties caused by M. micrantha invasion could be the major contributing factors that altered the community structure of soil meso- and micro-invertebrates at M. micrantha-invaded site.

[Effects of rice-duck farming on paddy field water environment].

Field experiment was conducted to investigate the effects of rice-duck farming on the water environment in paddy field. The results showed that under rice-duck farming, the temperature and pH value of the surface water in paddy field decreased, and the electrical conductivity, oxidation-reduction potential, turbidity, and the contents of nitrogen (N), phosphorus (P) and potassium (K) increased. The total N, P, and K increased by 1.85-5.06 times, 2.01-8.70 times, and 42.79%-109.18%, respectively, as compared to those in conventional rice farming. All of these illustrated that rice-duck farming improved the paddy field water environment and nutrient supply, optimized the ecological environment of paddy field, and promoted the growth and development of rice.

[Effects of rice-duck farming system on physiological characters of rice].

A field experiment with four treatments of rice-duck farming was conducted in the Zengcheng Teaching and Research Base of South China Agricultural University to further understand the effects of this farming system on the physiological characters of rice. The results showed that rice-duck farming could decrease the plasma membrane permeability and the malondialdehyde and proline contents of rice leaves, but increase their soluble sugar content and superoxide dismutase, peroxidase and catalase activities, indicating that this farming system had positive effects to the improvement of rice plant resistance and the postponement of leaf aging, being of significance on the rice growth and development.