Widespread agrochemicals differentially affect zooplankton biomass and community structure.

Anthropogenic environmental change is causing habitat deterioration at unprecedented rates in freshwater ecosystems. Despite increasing more rapidly than many other agents of global change, synthetic chemical pollution-including agrochemicals such as pesticides-has received relatively little attention in freshwater community and ecosystem ecology. Determining the combined effects of multiple agrochemicals on complex biological systems remains a major challenge, requiring a cross-field integration of ecology and ecotoxicology. Using a large-scale array of experimental ponds, we investigated the response of zooplankton community properties (biomass, composition, and diversity metrics) to the individual and joint presence of three globally widespread agrochemicals: the herbicide glyphosate, the neonicotinoid insecticide imidacloprid, and nutrient fertilizers. We tracked temporal variation in zooplankton biomass and community structure along single and combined pesticide gradients (each spanning eight levels), under low (mesotrophic) and high (eutrophic) nutrient-enriched conditions, and quantified (1) response threshold concentrations, (2) agrochemical interactions, and (3) community resistance and recovery. We found that the biomass of major zooplankton groups differed in their sensitivity to pesticides: ≥0.3 mg/L glyphosate elicited long-lasting declines in rotifer communities, both pesticides impaired copepods (≥3 µg/L imidacloprid and ≥5.5 mg/L glyphosate), whereas some cladocerans were highly tolerant to pesticide contamination. Strong interactive effects of pesticides were only recorded in ponds treated with the combination of the highest doses. Overall, glyphosate was the most influential driver of aggregate community properties of zooplankton, with biomass and community structure responding rapidly but recovering unequally over time. Total community biomass showed little resistance when first exposed to glyphosate, but rapidly recovered and even increased with glyphosate concentration over time; in contrast, taxon richness decreased in more contaminated ponds but failed to recover. Our results indicate that the biomass of tolerant taxa compensated for the loss of sensitive species after the first exposure, conferring greater community resistance upon a subsequent contamination event; a case of pollution-induced community tolerance in freshwater animals. These findings suggest that zooplankton biomass may be more resilient to agrochemical pollution than community structure; yet all community properties measured in this study were affected at glyphosate concentrations below common water quality guidelines in North America.

Coral bleaching resistance variation is linked to differential mortality and skeletal growth during recovery.

The prevalence of global coral bleaching has focused much attention on the possibility of interventions to increase heat resistance. However, if high heat resistance is linked to fitness tradeoffs that may disadvantage corals in other areas, then a more holistic view of heat resilience may be beneficial. In particular, overall resilience of a species to heat stress is likely to be the product of both resistance to heat and recovery from heat stress. Here, we investigate heat resistance and recovery among individual Acropora hyacinthus colonies in Palau. We divided corals into low, moderate, and high heat resistance categories based on the number of days (4-9) needed to reach significant pigmentation loss due to experimental heat stress. Afterward, we deployed corals back onto a reef in a common garden 6-month recovery experiment that monitored chlorophyll a, mortality, and skeletal growth. Heat resistance was negatively correlated with mortality during early recovery (0-1 month) but not late recovery (4-6 months), and chlorophyll a concentration recovered in heat-stressed corals by 1-month postbleaching. However, moderate-resistance corals had significantly greater skeletal growth than high-resistance corals by 4 months of recovery. High- and low-resistance corals on average did not exhibit skeletal growth within the observed recovery period. These data suggest complex tradeoffs may exist between coral heat resistance and recovery and highlight the importance of incorporating multiple aspects of resilience into future reef management programs.

Nitrogen and Sulfur Co-doped Carbon Dots Enhance Drought Resistance in Tomato and Mung Beans.

Drought stress is widespread worldwide, which severely restricts world food production. The antioxidant property of carbon dots (CDs) is promising for inflammation and disease treatment. However, little is known about the functions of CDs in the abiotic stress of plants, especially in drought-resistant fields. In this study, CDs were synthesized using cysteine and glucose by the hydrothermal method. The in vitro antioxidant capacity of CDs and the reactive oxygen species (ROS) scavenging capacity were evaluated. We speculate on the antioxidant mechanism of CDs by comparing size distribution, fluorescence spectra, elements, and surface functional groups of CDs before and after oxidation. Besides, we evaluated the effects of CDs on seed germination and seedling physiology under drought stress. Also, the responses of antioxidant CDs to long-term drought stress and subsequent recovery metabolism in tomato plants were evaluated. The results show that CDs accelerated the germination rate and the germination drought resistance index by promoting the water absorption of seeds. CDs enhanced the drought resistance of seedlings by improving the activity of peroxidase (POD) and superoxide dismutase (SOD). Moreover, CDs can activate the antioxidant metabolism activity and upregulate the expression of aquaporin (AQP) genes SlPIP2;7, SlPIP2;12, and SlPIP1;7. All of these results render tomato plants distinguished resilience once rewatering after drought stress. These results facilitate us to design and fabricate CDs to meet the challenge of abiotic stress in food production.