Biochar-Dual Oxidant Composite Particles Alleviate the Oxidative Stress of Phenolic Acid on Tomato Seed Germination.

Phenolic acid is a well-known allelochemical, but also a pollutant in soil and water impeding crop production. Biochar is a multifunctional material widely used to mitigate the phenolic acids allelopathic effect. However, phenolic acid absorbed by biochar can still be released. In order to improve the removal efficiency of phenolic acids by biochar, the biochar-dual oxidant (BDO) composite particles were synthesized in this study, and the underlying mechanism of the BDO particles in ameliorating p-coumaric acid (p-CA) oxidative damage to tomato seed germination was revealed. Upon p-CA treatment, the BDO composite particles application increased the radical length, radical surface area, and germination index by 95.0%, 52.8%, and 114.6%, respectively. Compared to using biochar or oxidants alone, the BDO particles addition resulted in a higher removal rate of p-CA and produced more O2•-, HO•, SO4•- and 1O2 radicals via autocatalytic action, suggesting that BDO particles removed phenolic acid by both adsorption and free radical oxidation. The addition of BDO particles maintained the levels of the antioxidant enzyme activity close to the control, and reduced the malondialdehyde and H2O2 by 49.7% and 49.5%, compared to the p-CA treatment. Integrative metabolomic and transcriptomic analyses revealed that 14 key metabolites and 62 genes were involved in phenylalanine and linoleic acid metabolism, which increased dramatically under p-CA stress but down-regulated with the addition of BDO particles. This study proved that the use of BDO composite particles could alleviate the oxidative stress of phenolic acid on tomato seeds. The findings will provide unprecedented insights into the application and mechanism of such composite particles as continuous cropping soil conditioners.

Water management increased rhizosphere redox potential and decreased Cd uptake in a low-Cd rice cultivar but decreased redox potential and increased Cd uptake in a high-Cd rice cultivar under intercropping.

Excessive Cd in crop grains is toxic to humans. We conducted a field experiment to investigate the effects of intercropping on rice yield and grain Cd content as well as a pot experiment to compare the rhizosphere redox potentials of low-Cd 'Zhuliangyou 189' and the neighboring high-Cd 'Changxianggu' that mediated Cd uptake in a flooded or a ridge-furrow system. In the field experiment, Cd removal from contaminated soil in intercropping was 1.44 times higher than that in monoculture of Zhuliangyou 189. In both Zhuliangyou 189 and Changxianggu, intercropping improved the grain yield and decreased grain Cd content. In the pot experiment, Fe plaque amount was strongly and positively correlated with bulk soil Fe(II) content, root H2O2 concentration, and Fe(II)-oxidizing ability of root bacteria but negatively correlated with Fe(II)-oxidizing ability of bulk soil bacteria and root Cd content. In Zhuliangyou 189, intercropping increased root H2O2 concentration, rhizosphere redox potential, iron plaque amount but decreased Cd bioavailability, Fe(II)-oxidizing ability of bulk soil bacteria, and organ Cd content. In the flooded system, Zhuliangyou 189 showed higher bulk soil Fe(II) content than Changxianggu. In the ridge-furrow system, ridges decreased the Fe(II)-oxidizing ability of root and bulk soil bacteria, thereby decreasing Fe plaque amount and increasing organ Cd content of rice. In both monoculture and intercropping systems, rice cultivars planted on ridges showed higher Cd bioavailability and lower bulk boil Fe(II) content than those planted in furrows.

How intercropping and mixed systems reduce cadmium concentration in rice grains and improve grain yields.

Ecological theories can be applied to improve agricultural sustainability. In our study, a core hypothesis behind this claim is that "selfish behaviour" of rice cultivars results in "aversion" to a toxic substance in a multi-cropping system. We studied Changliangyou 772, a low-cadmium rice cultivar, cultivated with 11 different rice cultivars in intercropping and mixed systems. Rice cultivars with medium grain yield, ranging from 25 to 45 g plant-1, had distinctly higher yields in mixtures. Rice varieties with lower grain cadmium concentrations in monocultures had greater reductions in grain cadmium in the mixtures. In the intercropping systems, the yields of Changliangyou 772 were positively correlated with those of the neighbouring rice cultivars, while the grain cadmium showed a negative correlation with the grain cadmium of intercrops in the monocultures. The neighbouring cultivars with low grain cadmium concentrations in the intercropping showed higher cadmium concentrations in the monocultures. The intercropping and mixtures reduced the grain cadmium in two ways: 1) they increased the soil pH, resulting in lower cadmium bioavailability; and 2) they enhanced the iron plaque (Ip). However, a high Ip or cadmium concentration that was too high in the Ip weakened the Ip to block cadmium uptake by the roots.

Effects of glyphosate-based herbicides on survival, development and growth of invasive snail (Pomacea canaliculata).

This study tests the hypotheses that whether environmental relevance of glyphosate would help control spread of the invasive snail Pomacea canaliculata, or benefit its population growth worldwide. Our results showed that glyphosate induced acute toxicity to the snail only at high concentrations (96h LC50 at 175mg/L) unlikely to occur in the environment. Long-term exposures to glyphosate at sublethal levels (20 and 120mg/L) caused inhibition of food intake, limitation of growth performance and alterations in metabolic profiles of the snail. It is worth noting that glyphosate at 2mg/L benefited growth performance in P. canaliculata. Chronic exposures of glyphosate significantly enhanced overall metabolic rate and altered catabolism from protein to carbohydrate/lipid mode. Cellular responses in enzyme activities showed that the exposed snails could increase tolerance by their defense system against glyphosate-induced oxidative stress, and adjustment of metabolism to mitigate energy crisis. Our study displayed that sublethal concentrations of glyphosate might be helpful in control of the invasive species by food intake, growth performance and metabolic interruption; whether environmental relevance of glyphosate (≤2mg/L) benefits population growth of P. canaliculata is still inconclusive, which requires further field study.

Seasonal patterns of water quality and phytoplankton dynamics in surface waters in Guangzhou and Foshan, China.

During 2015, we studied the temporal patterns of nutrient concentrations and turbidity in water bodies with different degrees of agricultural and urban pressures across Guangzhou and Foshan (China). Data and observations were made by trained citizen scientists and professional researchers. Our study shows that all monitored water bodies, with the exception of Qiandeng Lake and Fengjiang River, had elevated NO3--N concentrations, which ranged from 0.10 to 6.83mg/L and peaked in late winter and early spring and reached a minimum in summer and mid-autumn. PO43-P concentrations ranged from 0.01 to 0.25mg/L and peaked during the winter, late-summer and late autumn. Turbidity values were highest at sites with agricultural activities, with maximums in the late winter and autumn, and the highest frequency (16% and 25%) of algae presence occurred in the spring and autumn. To better understand the characteristics and drivers of the algae occurrences, measurements of phytoplankton composition and physicochemical characteristics were conducted in three key seasons in the agricultural process, fallow, sowing and rainy season in 2016. Our focused study found that the occurrence of Bacillariophyta, Euglenophyta, Xanthophyta, Cryptophyta, Chrysophyta were positively correlated with dissolved oxygen and phosphorus concentrations, while Chlorophyta and Cyanophyta had positive correlations with turbidity, oxygen demand and nitrogen concentrations. Bacillariophyceae counted for the highest proportion of phytoplankton during the fallow season, comprising up to 60+% of the phytoplankton among the sites. During the rainy season, Chlorophyceae species were the majority, comprising up to 90+% of phytoplankton among the sampled sites. Our results pointed to the complexity of nutrient and phytoplankton dynamics in water bodies under multiple pressures, and to the value of using citizen scientists to determine contextual information to benefit more focused studies.