Abstract:

Nutrient resorption is crucial for plant nutrient budgets and ecosystem nutrient cycling. To enhance our understanding of the adaptability of plants and nutrient cycling in terrestrial ecosystems of tropical coral island, it is essential to study the nutrient resorption patterns of dominant woody plants. In this study, we investigated leaf traits, nitrogen (N), and phosphorus (P) resorption efficiencies (RE) of two monodominant woody species (i.e., Pisonia grandis and Guettarda speciose) on a tropical coral island belonging to the Paracel Islands, South China Sea. The results showed that the specific leaf area (288.59 cm²∙g^-1 vs 150.42 cm²∙g^-1) and N:P ratio (11.39 vs 2.97) of P. grandis were higher, while concentrations of carbon (C), lignin, cellulose, and C:N ratio and lignin: N ratio of P. grandis were lower than those of G. speciose. Thus, P. grandis and G. speciose tended to exhibit resource acquisition strategies and resource protection strategies, respectively. The growth of the two species could be N-limited, as N:P ratios of mature leaves were below 14. Both P. grandis and G. speciose showed relatively high NRE (60.28% and 52.64%, respectively) and relatively low PRE (49.75% and 30.73%, respectively), indicating that these two species tended to adopt conservative N-use strategies. The two species resorbed P insufficiently with relatively high values of P resorption proficiencies (1.63 mg∙g^-1 and 3.76 mg∙g^-1, respectively). They tended to acquire P directly from the soil in the P-rich coral island ecosystem. In conclusion, P. grandis and G. speciose would adapt to the special habitat of tropical coral islands by coordinating leaf resource allocation, increasing leaf N resorption efficiency, and decreasing leaf P resorption efficiency.

Key words: Paracel Islands, Pisonia grandis, Guettarda speciose, dominant species, nutrient use strategy, nutrient resorption, leaf traits, soil nutrients

摘要：

养分再吸收对植物养分收支和生态系统养分循环至关重要,研究热带珊瑚岛特殊生境下优势植物的养分再吸收特征对于深入理解海岛植物适应性和海岛陆域生态系统养分循环具有重要意义。针对中国西沙群岛的热带珊瑚岛生境,以抗风桐（Pisonia grandis）和海岸桐（Guettarda speciose）两种代表性单优乔木为研究对象,比较了其叶片性状和养分再吸收特征,并分析了可能影响养分再吸收过程的因素。结果表明,抗风桐的比叶面积（288.59 cm²∙g^-1 vs 150.42 cm²∙g^-1）和叶片氮磷比（11.39 vs 2.97）显著高于海岸桐,但叶碳含量、木质素含量、纤维素含量、碳氮比和木质素氮比均显著低于海岸桐,说明抗风桐的适应策略偏向于资源获取,海岸桐则偏向于资源保护。抗风桐和海岸桐的成熟叶片氮磷比均小于14,表明其生长主要受氮限制。抗风桐和海岸桐均具有相对较高的氮再吸收效率（60.28%和52.64%）和较低的磷再吸收效率（49.75%和30.73%）,表明二者均趋于采取较保守的氮利用策略。抗风桐和海岸桐叶片磷再吸收程度分别为1.63 mg∙g^-1和3.76 mg∙g^-1,对磷再吸收不充分（>0.5 mg∙g^-1）,在富磷的珊瑚岛生态系统中更倾向于从土壤中直接获取磷以满足生长的需求。总之,抗风桐和海岸桐通过协调叶片资源分配、提高叶片氮再吸收效率和降低叶片磷再吸收效率以适应热带珊瑚岛的特殊生境。

关键词: 西沙群岛, 抗风桐, 海岸桐, 优势种, 养分利用策略, 养分再吸收, 叶片性状, 土壤养分