Plant nitrogen (N), phosphorus (P), and potassium (K) concentrations and ratios serve as critical indicators of nutrient constraints in coastal ecosystems. However, the response of leaf–soil N-P-K stoichiometry in tropical coastal shelterbelt forests to seasonal rainfall variations remains poorly understood. This study measured total N, P, and K contents in leaves and soils of three typical tropical coastal shelterbelt forests in Wenchang, China—Casuarina equisetifolia L., Cocos nucifera L., and Pinus elliottii × caribaea—during August 2022 (wet season) and February 2023 (dry season). Key findings are as follows: (1) All three forests exhibited low N-P-K contents in both leaves and soils, with significant stand-specific variations. Soil N:P ratios were consistently below 14, indicating chronic N limitation for plant growth. (2) Wet seasons significantly altered leaf–soil N-P-K contents and stoichiometric ratios. (3) Leaf and soil stoichiometric traits exhibited strong correlations, but these relationships diverged under seasonal transitions. (4) Shifts from wet to dry seasons increased the sensitivity of N-P-K stoichiometric homeostasis, reflecting weakened nutrient buffering capacity. This study reveals stand-specific nutrient cycling patterns in tropical coastal shelterbelts, with seasonal rainfall modulating soil–leaf nutrient coupling and stoichiometric stability. These findings provide a theoretical basis for optimizing nutrient management and species configuration in tropical coastal ecosystems under climate variability.

Typhoon disturbances significantly influence forest carbon cycling by altering both physical structures and biogeochemical processes. Typhoon-induced fluctuations in soil respiration can substantially affect the carbon balance in forest ecosystems. In this study, we conducted a comparative investigation of soil respiration in plantations of Casuarina equisetifolia L. that were either affected or unaffected by the severe Typhoon Yagi, which ravaged Hainan Island, China, in 2024. The soil respiration and its components in Casuarina equisetifolia L. plantations in the coastal areas of Hainan, China, as well as their responses to environmental factors before and after typhoon disturbance, were investigated based on total soil respiration rate (R_s), heterotrophic respiration rate (R_h), 5 cm soil temperature (T₅), and 10 cm soil moisture (W₁₀) to support the carbon emission estimation in coastal sandy land plantations. The mean R_s and R_h in the typhoon-disturbed plots were (1.82 ± 0.16) and (1.19 ± 0.26) μmol·m⁻²·s⁻¹, respectively, while those in the control plots were (2.62 ± 1.08) and (1.41 ± 0.23) μmol·m⁻²·s⁻¹, respectively, with statistically significant differences (p < 0.05). In both plots, R_s exhibited a significant positive correlation with T₅ (p < 0.01). The T₅ correlation and Q₁₀ values for soil respiration were significantly higher in the typhoon-disturbed plots than in the control plots (p < 0.05). W₁₀ of the soil exhibited significant negative correlations with R_s and R_h in typhoon disturbance plots (p < 0.05). Consequently, typhoon disturbance markedly inhibited soil respiration and its components in the Casuarina equisetifolia L. plantations, indicating substantial impacts of typhoons on soil respiration processes and carbon cycling within the forest ecosystem. This study provides key parameters and empirical evidence to improve the accuracy of soil carbon emission estimates in Casuarina equisetifolia L. plantations on coastal sandy soils affected by typhoon events.

Ecological stoichiometric ratios of soil provide insights into the interactions and limitations among elements. This study examined the nutrient characteristics K, N, and P stoichiometric ratios in the soils collected from three distinct shelter forests (Casuarina equisetifolia, secondary forest, and Cocos nucifera) in a tropical coastal region of Hainan Province, China. Significant differences were observed among forest types in terms of stoichiometric ratios and nutrient levels in soil (p < 0.05). This may be related to the high species diversity in secondary forests and the complex composition of litter. soil nutrient levels in the secondary forest were higher than those in C. equisetifolia and C. nucifera. The effects of soil nutrient factors on soil ecological stoichiometric ratios differed across shelterbelt types. Soil organic matter, total potassium, available potassium, and ammonium nitrogen content substantially influenced the N:P, K:P, and N:K ratios (Q² > 0.5). Soil TN content was highly significantly positively correlated with N:P, N:K, in C. equisetifolia and C. nucifera (p < 0.01), whereas in the secondary forest, it was highly significantly positively correlated with SOM and NH₄⁺-N (p < 0.01). These results reflecting the complexity of nutrient cycling as well as the interdependence and mutual regulation between vegetation and soil in coastal shelter forest ecosystems.