Abstract: Plant functional traits reflect key strategies of resource acquisition, use and conservation, and play an important role in shaping plant responses to environmental change. Soil phosphorus (P) is a major limiting factor for plant growth in tropical forest ecosystems. It’s changes may affect the resource utilization strategies of plants at different growth stages. This study aimed to examine the responses of functional traits and their relationships to P addition in seedlings and saplings in a tropical montane cloud forest. Taking the seedlings and saplings of the tropical cloud forest in the Bawangling area of National Park of Hainan Tropical Rainforest as the research objects, low, medium and high concentration phosphorus addition treatments were set up. The leaf thickness (LT), leaf dry matter content (LDMC), specific leaf area (SLA), leaf nitrogen and phosphorus contents (LN, LP) and branch density (BD) of the plants were measured. The functional traits responses and correlation changes of the seedlings and saplings under P addition conditions were analyzed. The results show that: (1) The growth stage of plants and P concentration significantly affect the functional traits of plants. Under the CK treatment, compared with saplings, seedlings exhibit a resource acquisition strategy; as the P concentration increases, the leaves of seedlings show high SLA, LP and low LT, LDMC, while the trait changes of saplings are not significant; the two ends of the PC1 axis respectively represent the resource acquisition and conservative strategies of plants, and seedlings show a resource acquisition strategy compared to saplings. (2) BD-LDMC, SLA-LN, SLA-LP, and LN-LP of seedlings and saplings were significantly positively correlated, and BD-SLA, LDMC-SLA, LDMC-LN, LDMC-LP, and SLA-LT were significantly negatively correlated, indicating that there were generally synergies and trade-offs among plant functional traits. Under the control treatment, the slopes of BD-LDMC, BD-SLA, LDMC-LN and SLA-LN were not significantly different between seedlings and saplings, while the slopes of LDMC-LP, SLA-LP and LN-LP were significantly different between seedlings and saplings, which was opposite under P addition treatment. This indicated that P addition changed the nutrient allocation strategy between seedlings and saplings. In the low and medium P concentration conditions, the seedlings tended to invest in resource acquisition-related structures, presenting an acquisitive strategy; while in the low P condition, the young trees showed a limited resource acquisitive strategy adjustment, and their response to P addition was relatively conservative. In conclusion, the responses of tropical cloud forest plants to P addition concentrations vary at different growth stages, which is helpful for understanding the resource utilization of plants and forest regeneration under the background of atmospheric P deposition.

Key words: phosphorus addition, growth stage, functional traits, trait-trait relationships, tropical cloud forest