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N-nutrients in nitrogen fertilizers are a critical resource for modern agricultural production, with most economies relying on imports to secure adequate supplies. The N-nutrient trade system is vital for global food security and ecological safety. We analyzed the N-nutrient trade network from 1991 to 2020, using the perspective of the temporal rich club (TRC), to identify the core functional groups of global N-nutrient trade. Our analysis revealed that the Netherlands, US, France, China, UK, Belgium, Germany, and Spain form the stable cornerstone group from which other economies derive the complete trade network. We found that simply increasing the volume of import and export trade is insufficient to create an extensive and stable trade structure. Instead, the most effective way to enter the core of the trade network is to increase upstream and downstream trade partners and enhance its own importance and reputation. Our mathematical model suggests that the generation mechanism of the TRC phenomenon in the N-nutrient trade network is due to the coexistence of the attraction of reputation in supply and demand and the path-dependence mechanism. By understanding these mechanisms, we can provide a new perspective on the evolution of the trade network and the stability of the system.

Hormonal results may be compromised in field samples maintained without cold storage. This study determined that progestagen, testosterone and cortisol concentrations in blood with anticoagulant were stable at 37°C up to 62 h. Without anticoagulant, progestagens also were stable, but cortisol and testosterone in blood decreased over time., The value of biological samples collected in the field is compromised if storage conditions result in analyte degradation, especially in warmer climates like Thailand. We evaluated the effects of time and temperature on immunoactive steroid hormone stability in Asian elephant (Elephas maximus) blood stored with and without an anti-coagulant before centrifugation. For each elephant (5 male, 5 female), whole blood was aliquoted (n = 2 ml each) into 13 red top (without anticoagulant) or purple top (with anticoagulant) tubes. One tube from each treatment was centrifuged immediately and the serum or plasma frozen at −20°C (Time 0, T0). The remaining 12 aliquots were divided into stored temperature groups: 4°C, room temperature (RT, ~22°C), and 37°C, and centrifuged after 6, 24, 48 and 62 h of storage. Serum and plasma concentrations of progestagens in females, testosterone in males and cortisol in both sexes were quantified by validated enzyme immunoassays. Steroid concentration differences from T0 were determined by a randomized complete block ANOVA and Dunnett’s tests. The only evidence of hormone degradation was cortisol and testosterone concentrations in serum stored at 37°C. Testosterone concentrations declined by 34% at 48 h and 52% at 62 h, cortisol was decreased by 19% after 48 h and 27% after 62 h at 37°C, respectively. None of the other aliquots displayed significant changes over time at any temperature. In conclusion, steroids appear to be stable in blood for nearly 3 days at room or refrigeration temperatures before centrifugation; steroids in samples with ethylenediaminetetraacetic acid were particularly stable. However, warmer temperatures may negatively affect steroids stored without anti-coagulant, perhaps due to red blood cell metabolism. Thus, under field conditions with no access to cold or freezer temperatures, collection of plasma is a better choice for elephants up to at least 62 h before centrifugation.