Optimal N management affects the fate of urea-15N and improves N uptake and utilization of wheat in different rotation systems.

Rice-wheat and maize-wheat rotations are major cropping systems in the middle and lower reaches of Yangtze River in China, where high nitrogen (N) inputs and low N efficiency often exacerbate resource waste and environmental pollution. Due to the changes in factors such as soil properties and moisture content, the N fate and the N utilization characteristics of wheat in different rotations are significantly different. Efficient N management strategies are thus urgently required for promoting maximum wheat yield in different rotation systems while reducing N loss. A 2-year field experiment using isotopic (15N) tracer technique was conducted to evaluate the fate of 15N-labeled urea in wheat fields and the distribution characteristics of N derived from different sources. The wheat yield and N use efficiency under various N rates (180 and 240 kg ha-1, abbreviated as N180 and N240) and preceding crops (rice and maize, abbreviated as R-wheat and M-wheat) were also investigated. The results showed that N240 increased N uptake and grain yield by only 8.77-14.97% and 2.51-4.49% compared with N 180, but decreased N agronomic efficiency (NAE) and N physiological efficiency (NPE) by 14.78-18.79% and 14.06-31.35%. N240 also decreased N recovery in plants by 2.8% on average compared with N180, and increased N residue in soil and N loss to the environment. Compared with that of basal N, the higher proportion of topdressing N was absorbed by wheat rather than lost to the environment. In addition, the accumulation of topdressing N in grain was much higher than that of basal N. Compared with that in R-wheat treatment, plants in M-wheat treatment trended to absorb more 15N and reduce unaccounted N loss, resulting in higher yield potential. Moreover, the M-wheat treatment increased N recovery in 0-20 cm soil but decreased 80-100 cm soil compared with R-wheat treatment, indicating a lower risk of N loss in deeper soil. Collectively, reducing N application rate and increasing the topdressing ratio is an effective way to balance sustainable crop yield for a secure food supply and environmental benefit, which is more urgent in rice-wheat rotation.

The Inhibiting Effects of High-Dose Biochar Application on Soil Microbial Metagenomics and Rice (Oryza sativa L.) Production.

Biochar is usually considered as an organic improver which can improve soil and increase crop yields. However, the unrestricted application of biochar to normal-fertility farmland will cause chemical stress on crops and affect agricultural production. At present, the effects and mechanisms of high-dose applications of biochar on rice (Oryza sativa L.) production and soil biological characteristics have not been fully studied. In this greenhouse pot experiment, combined with soil microbial metagenomics, three treatments in triplicates were conducted to explore the responses of rice production, soil chemical properties, and soil biological properties to high-dose applications of biochar (5%, w/w) prepared using peanut waste (peanut hulls and straw). The results show that peanut hulls, with a loose texture and pore structure, are a raw material with stronger effects for preparing biochar than peanut straw in terms of its physical structure. In a rice monoculture system, high-dose applications of biochar (5%, w/w) can slightly increase the grains per spike, while significantly inhibiting the spike number per pot and the percentage of setting. High-dose applications of biochar also have significant negative effects on the diversity and stability of soil bacterial and archaeal communities. Moreover, the microbial metabolism and nutrient cycling processes are also significantly affected by changing the soil carbon/nitrogen ratio. This study discusses the response mechanisms of rice production and soil biology to high-dose biochar applications, and complements the understanding of irrational biochar application on agricultural production and land sustainability.

4-Vinylanisole promotes conspecific interaction and acquisition of gregarious behavior in the migratory locust.

Chemical signals from conspecifics are essential in insect group formation and maintenance. Migratory locusts use the aggregation pheromone 4-vinylanisole (4VA), specifically released by gregarious locusts, to attract and recruit conspecific individuals, leading to the formation of large-scale swarms. However, how 4VA contributes to the transition from solitary phase to gregarious phase remains unclear. We investigated the occurrence of locust behavioral phase changes in the presence and absence of 4VA perception. The findings indicated that solitary locusts require crowding for 48 and 72 h to adopt partial and analogous gregarious behavior. However, exposure to increased concentrations of 4VA enabled solitary locusts to display behavioral changes within 24 h of crowding. Crowded solitary locusts with RNAi knockdown of Or35, the specific olfactory receptor for 4VA, failed to exhibit gregarious behaviors. Conversely, the knockdown of Or35 in gregarious locusts resulted in the appearance of solitary behavior. Additionally, a multi-individual behavioral assay system was developed to evaluate the interactions among locust individuals, and four behavioral parameters representing the inclination and conduct of social interactions were positively correlated with the process of crowding. Our data indicated that exposure to 4VA accelerated the behavioral transition from solitary phase to gregarious phase by enhancing the propensity toward proximity and body contact among conspecific individuals. These results highlight the crucial roles of 4VA in the behavioral phase transition of locusts. Furthermore, this study offers valuable insights into the mechanisms of behavioral plasticity that promote the formation of locust swarms and suggests the potential for 4VA application in locust control.

4-Vinylanisole is an aggregation pheromone in locusts.

Locust plagues threaten agricultural and environmental safety throughout the world1,2. Aggregation pheromones have a crucial role in the transition of locusts from a solitary form to the devastating gregarious form and the formation of large-scale swarms3,4. However, none of the candidate compounds reported5-7 meet all the criteria for a locust aggregation pheromone. Here, using behavioural assays, electrophysiological recording, olfactory receptor characterization and field experiments, we demonstrate that 4-vinylanisole (4VA) (also known as 4-methoxystyrene) is an aggregation pheromone of the migratory locust (Locusta migratoria). Both gregarious and solitary locusts are strongly attracted to 4VA, regardless of age and sex. Although it is emitted specifically by gregarious locusts, 4VA production can be triggered by aggregation of four to five solitary locusts. It elicits responses specifically from basiconic sensilla on locust antennae. We also identified OR35 as a specific olfactory receptor of 4VA. Knockout of OR35 using CRISPR-Cas9 markedly reduced the electrophysiological responses of the antennae and impaired 4VA behavioural attractiveness. Finally, field trapping experiments verified the attractiveness of 4VA to experimental and wild populations. These findings identify a locust aggregation pheromone and provide insights for the development of novel control strategies for locusts.