Integrated rice-crayfish farming system does not mitigate the global warming potential during rice season

Comprehensive impacts of different integrated rice-animal co-culture systems on rice yield, nitrogen fertilizer partial factor productivity and nitrogen losses: A global meta-analysis

Integrated rice-animal co-culture (IRAC) is an ecological agricultural system combining rice cultivation with animal farming, which holds significant implications for food security and agriculture sustainable development. However, the comprehensive impacts of the co-culture on rice yield, nitrogen (N) losses, and N fertilizer partial factor productivity (NPFP) remain elusive and may vary under different environmental conditions and N management. Here, we conducted a meta-analysis of data from various IRAC systems on a global scale, including 371, 298, and 115 sets of data for rice yield, NPFP, and N losses, respectively. The results showed that IRAC could significantly increase rice yield (by 3.47 %) and NPFP (by 4.26 %), and reduce N2O emissions (by 16.69 %), NH3 volatilization (by 11.03 %), N runoff (by 17.72 %), and N leaching (by 19.10 %). Furthermore, there were significant differences in rice yield, NPFP, and N loss among different IRAC systems, which may be ascribed to variations in regional climate, soil variables, and N fertilizer management practices. The effect sizes of rice yield and NPFP were notably correlated with the rate and frequency of N application and the soil clay content. Moreover, a higher amount of precipitation corresponded to a larger effect size on rice NPFP. N2O emissions were closely associated with mean annual air temperature, annual precipitation, N application frequency, soil pH level, soil organic matter content, soil clay content, and soil bulk density. However, NH3 volatilization, N runoff, and N leaching exhibited no correlation with either the environmental conditions or the N management. Multivariate regression analysis further demonstrated that the soil clay content and N application rate are pivotal in predicting the effect sizes of rice yield, NPFP, and N2O emissions under IRAC. Specifically, IRAC with a low N application rate in soils with a high clay content could augment the effect size to increase rice NPFP and yield and reduce N2O emissions. In conclusion, IRAC offers a potent strategy to optimize rice yield and NPFP as well as mitigate N losses.

Effects of Hypoxia Stress on Survival, Antioxidant and Anaerobic Metabolic Enzymes, and Related Gene Expression of Red Swamp Crayfish Procambarus clarkii

The red swamp crayfish Procambarus clarkii is the most reared shrimp in China, but it is often affected by hypoxia stress in the process of seedling culture and adult crayfish culture. The oxygen consumption rate and asphyxiation point of juvenile crayfish (1.17 ± 0.03 g) and subadult crayfish (11.68 ± 0.11 g) at different temperatures (20, 22, 24, 26, and 28 °C) were studied. The survival, glycolysis, and expression of antioxidant genes were compared under 24 h acute hypoxia stress (1, 2, and 3 mg/L) and normal dissolved oxygen (7.5 mg/L). The results showed that the oxygen consumption rate and asphyxiation point of juvenile and subadult crayfish increased with increasing temperatures (20-28 °C). At the same temperature, the oxygen consumption rate and asphyxiation point of juvenile crayfish were significantly higher than those of subadult crayfish (p < 0.05). Within 24 h, the three hypoxia stress environments did not lead to the death of crayfish, indicating that P. clarkii has a strong ability to adapt to hypoxia. Hypoxia stress significantly affected the activities of antioxidant and anaerobic metabolic enzymes and gene expression in juvenile and subadult crayfish. The activities of the superoxide dismutase (SOD), catalase (CAT), and lactate dehydrogenase (LDH) and the content of lactic acid (LD) in the hepatopancreas of juvenile and subadult crayfish in the hypoxia stress groups increased significantly. The expression levels of SOD mRNA, CAT mRNA, Hsp70 mRNA, and crustin 4 mRNA in the hepatopancreas of juvenile and subadult crayfish in the hypoxia stress groups were significantly higher than those in the control group (p < 0.05), and the higher the degree of hypoxia stress, the higher the expression of each gene. The results showed that the antioxidant system of juvenile crayfish was more sensitive to hypoxia environments, and hypoxia stress resulted in increased stress levels in juvenile crayfish and subadult crayfish.

Effect of nitrogen application on greenhouse gas emissions and nitrogen uptake by plants in integrated rice-crayfish farming

Integrated rice-crayfish farming is an ecological rice farming mode. However, limited research has examined the comprehensive impacts of greenhouse gas (GHG) emissions, nitrogen (N) uptake, and N utilization in rice under this farming modality. Herein, a dual-factor experiment was performed from 2021 to 2022 to assess the comprehensive impacts of N application and rice farming mode on greenhouse gas (GHG) emissions, N uptake, N utilization, and rice yield in paddy fields. Under N application, the rice-crayfish co-culture exhibits a 2.3 % decrease in global warming potential (GWP) and a 17.3 % increase in greenhouse gas intensity relative to the rice monoculture. Moreover, the N uptake of rice within the rice-crayfish co-culture is 5.2 %-10.4 % higher than that in the rice monoculture. However, owing to low rice yield under the rice-crayfish co-culture, its N partial factor productivity decreases by 5.6 %-22.6 %, while N agronomic efficiency is reduced by 18.3 %-46.9 % compared with the rice monoculture. In addition, N application significantly inhibits CH4 emissions from paddy fields in the rice-crayfish co-culture mode. Compared with no N application, the CH4 emissions and GWP of N-applied treatment are decreased by 12.1 %-31.0 % and 6.0 %-15.8 %, respectively. Hence, N regulation might reduce GHG emissions in rice-aquatic animal co-culturing agriculture. Collectively, the results of this study suggest that switching from a rice monoculture to rice-crayfish co-culture can mitigate GHG emissions and promote rice N uptake; however, continuously improving the productivity of co-culturing agriculture is key to achieving high N utilization efficiency and low environmental impact.