Golden apple snail (GAS) is one of the 100 worst invasive alien species. With the application of molluscicides to kill and control the spreading of these snails, a large amount of dead GAS shells are remained in many farms. This study ascertained the characteristics and removal of cadmium (Cd) by the GAS shell (GASS) powders and the associate mechanisms. Results showed that when the concentration of shell powder increased from 0.05 to 10.00 g/L, pH from 1.5 to 5.5, contact time from 2 to 100 min, and temperature from 10 to 50°C, the Cd removal efficiency from the solution increased gradually and reached an equilibrium condition. The Cd removal efficiency decreased as the initial Cd concentration increased from 5 to 500 mg/L. The changes in the amount of Cd removal conformed to the Langmuir model with a capacity of 81.301 mg/g. A thermodynamic analysis indicated that the Cd removal by the GASS powder was an endothermic and spontaneous process. Our study also revealed that the solution pH was affected greatly by the amount of GASS powder. The powder X-ray diffractometer (XRD) and scanning electron microscopy indicated that the CdCO₃ precipitated on the surface of GAS shells. The Cd removal was related to the ion exchange and the micro-precipitation with a depletion of aragonite and calcite. This study suggests that shells of GAS could be used as an effective biomaterial for Cd removal from contaminated water.

Worldwide, rice blast (Pyricularia oryzae) causes more rice crop loss than other diseases. Acid rain has reduced crop yields globally for nearly a century. However, the effects of acid rain on rice-Pyricularia oryzae systems are still far from fully understood. In this study, we conducted a lab cultivation experiment of P. oryzae under a series of acidity conditions as well as a glasshouse cultivation experiment of rice that was inoculated with P. oryzae either before (P. + SAR) or after (SAR + P.) simulated acid rain (SAR) at pH 5.0, 4.0, 3.0 and 2.0. Our results showed that the growth and pathogenicity of P. oryzae was significantly inhibited with decreasing pH treatments in vitro culture. The SAR + P. treatment with a pH of 4.0 was associated with the highest inhibition of P. oryzae expansion. However, regardless of the inoculation time, higher-acidity rain treatments showed a decreased inhibition of P. oryzae via disease-resistance related enzymes and metabolites in rice leaves, thus increasing disease index. The combined effects of high acidity and fungal inoculation were more serious than that of either alone. This study provides novel insights into the effects of acid rain on the plant–pathogen interaction and may also serve as a guide for evaluating disease control and crop health in the context of acid rain.

Invasive species have had substantial impacts on global mangrove forests. Apple snails (Pomacea canaliculata) have invaded mangrove forests in China. To clarify the potential detritivorous diet of P. canaliculata, the growth and feeding indicators of invasive juvenile snails collected from mangroves in Guangzhou, China, were studied using decaying leaf litter from five mangrove species, including Acanthus ilicifolius, Acrostichum aureum, Kandelia candel, Aegiceras corniculatum, and Sonneratia apetala. The growth indicators of the survival ratio and specific growth rate were calculated by measuring the live weight of the snails and the number of dead snails after 30 days. The feeding indicator of the weight-specific daily feeding rate (WDR) was calculated by measuring the snail weight and the amount of leaf litter ingested after 120 h. A multiple-choice experiment was performed on the snails by providing the decaying leaf species together, while a no-choice experiment was performed using a single species of decaying leaf litter. The survival and specific growth ratio of P. canaliculata feeding on decaying leaf litter of A. ilicifolius were higher than those for A. aureum. The WDR values of P. canaliculata feeding on the decaying leaf litter of A. ilicifolius and S. apetala were both significantly higher than those for A. corniculatum, A. aureum, and K. candel. The lowest WDR value of P. canaliculata feeding on decaying leaf litter was observed for A. aureum in the no-choice experiment. P. canaliculata mainly fed on decaying leaf litter of A. ilicifolius and S. apetala. The phosphorous contents and ash of the decaying leaf litter positively affected the WDR values of P. canaliculata obtained in the multiple-choice and no-choice experiments. The contents of lignin, tannin, and flavonoid negatively affected the WDR values of P. canaliculata. The potential diet of invasive P. canaliculata in mangroves was closely tied to the chemical characteristics of the decaying leaf litter. P. canaliculata can invade A. ilicifolius and/or S. apetala mangroves by utilizing the debris on the mangrove ground. Understanding the potential detritivorous diet of P. canaliculata in invaded mangroves can help us to assess this species’ dispersal risk and provide support for mangrove management.

The long-term use of mineral fertilizers has decreased the soil fertility in papaya (Carica papaya L.) orchards in South China. In situ earthworm breeding is a new sustainable practice for improving soil fertility. A field experiment was conducted to compare the effects of four treatments consisting of the control (C), chemical fertilizer (F), compost (O), and in situ earthworm breeding (E) on soil physico-chemical properties and soil enzyme activity in a papaya orchard. The results showed that soil chemical properties, such as pH, soil organic matter (SOM), total nitrogen (TN), available nitrogen (AN), and total phosphorus (TP) were significantly improved with the E treatment but declined with the F treatment. On 31 October 2008, the SOM and TN with the O and E treatments were increased by 26.3% and 15.1%, respectively, and by 32.5% and 20.6% compared with the F treatment. Furthermore, the O and E treatments significantly increased the activity of soil urease and sucrase. Over the whole growing season, soil urease activity was 34.4%~40.4% and 51.1%~58.7% higher with the O and E treatments, respectively, than that with the C treatment. Additionally, the activity of soil sucrase with the E treatment was always the greatest of the four treatments, whereas the F treatment decreased soil catalase activity. On 11 June 2008 and 3 July 2008, the activity of soil catalase with the F treatment was decreased by 19.4% and 32.0% compared with C. Soil bulk density with the four treatments was in the order of O ≤ E < F < C. The O- and E-treated soil bulk density was significantly lower than that of the F-treated soil. Soil porosity was in the order of C < F < E < O. Soil porosity with the O and E treatments was 6.0% and 4.7% higher, respectively, than that with the F treatment. Meanwhile, the chemical fertilizer applications significantly influenced the mean weight diameter (MWD) of the aggregate and proportion of different size aggregate fractions. The E treatment significantly increased the MWD, but the F treatment decreased it. The MWD with the E treatment was 14.5% higher than that with the F treatment. The proportion of >2 mm size aggregates in the O and E treatments was vastly improved. In conclusion, in situ earthworm breeding in orchards performed better than traditional compost and chemical fertilizer in improving soil aggregation, chemical properties, and enzyme activity. This is a new, organic fertilizer application for improving soil structure, chemical properties, and soil enzymes due to the activities of the earthworms and the production of vermicomposting.

The successful establishment of invasive populations is closely linked to environmental factors. It is unclear whether coexisting species in the native area follow the same genetic pattern in the invaded continents under the local climate factors. Two coexisting morphologically similar snails (Pomacea canaliculata and P. maculata), native to tropical and sub-tropical South America, have become invasive species for agriculture production and wetland conservation across five continents over 40 years. We analyzed the correlation between the genetic diversity of the two snails and the climate factors or habitat changes. Based on the 962 sequences from the invaded continents and South America, the nucleotide diversity in the agricultural habitat was low for P. canaliculata, whereas it was high for P. maculata, compared with that in the non-agricultural habitat. The two snails showed a divided population structure among the five continents. The P. canaliculata population in the invaded continents has remained stable, whereas the P. maculata population expanded suddenly. Seven main haplotype networks and two ancestral haplotypes (Pc3, Pm1) were found in the P. canaliculata and P. maculata populations. The haplotypes of the two snails were related to local climate factors. The overall fixation index of P. canaliculata and P. maculata was 0.2657 and 0.3097 between the invaded continents and South America. The population expansion of the two snails fitted the isolation-by-distance model. We discovered nine new sequences from the sampling locations. Overall, the genetic diversity and genetic differentiation of the two invasive snails were closely related to geographic separation, agricultural habitat, and climate factors.