Rainy season dynamics of carbon, nitrogen and phosphorus and their stoichiometric characteristics in Ochroma lagopus

Exploring the response of carbon (C), nitrogen (N), phosphorus (P) and their stoichiometric characteristics of annual Ochroma lagopus seedlings to the rainy season is important to reveal the nutrient partitioning pattern of annual Ochroma lagopus during the rainy season. The annual Ochroma lagopus plantation forest in Jinghong Farm, Xishuangbanna Prefecture, was used as the research object to determine the C, N and P contents and their stoichiometric characteristics in the leaves and roots of the annual Ochroma lagopus seedlings through periodic sampling, and to explore the dynamic change characteristics during the rainy season. The N and P contents of leaves of annual Ochroma lagopus seedlings showed a decreasing and then increasing trend over time, and both contents were highest in October (N:10.04 ± 0.85mg·g^-1, P:2.18 ± 0.21mg·g^-1) and lowest in August (N:8.81 ± 1.13mg·g^-1, P:1.80 ± 0.19mg·g^-1), while C contents showed a gradual increasing trend over time, with the highest in October (495.37 ± 25.81mg·g^-1);Root C, N, P contents and stoichiometric ratios over time were not significantly different (P > 0.05) except for C: N values in June and October, which were significantly different (P < 0.05);The results of the source of variation analysis showed that the sampling time, organ and their interaction had a significant effect (P < 0.05) on the variation of C content and N content of annual Ochroma lagopus seedlings; There was a highly significant positive correlation (P < 0.01) between leaf P content and N content in annual Ochroma lagopus seedlings, and also a significant positive correlation (P < 0.05) between leaf P content and root C content, and a significant negative correlation (P < 0.05) between leaf N: P values and root N content; There were both anisotropic and isotropic growth relationships among the C, N, and P contents of different organs in Ochroma lagopus seedlings, with C-N, C-P, and N-P all showing anisotropic growth relationships in roots(P _-1.0<0.01) and isotropic growth relationships in leaves༈P _-1.0>0.05༉. Annual Ochroma lagopus seedlings have strong carbon storage capacity in the rainy season, but they cannot effectively retain N and P elements during growth, and the N: P values of Ochroma lagopus leaves are lower than 14, indicating that their growth is more limited by N. Moreover, in the rainy season, Ochroma lagopus has a different nutrient allocation strategy, and the root system is able to obtain more nutrients compared with the leaves, and the root system has a higher nutrient utilization efficiency compared with the leaves, therefore, nitrogen fertilizer should be appropriately applied to the one-year-old young Ochroma lagopus forests when the rainy season arrives.