Ecological stoichiometric characteristics of sapling branches of dominant species in different forest types in southern Yunnan

Objective Exploring ecological stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) of different forest types of great importance to better understanding nutrient elements distribution patterns, limitation status, and nutrient absorption and utilization efficiency.

Method The dominant species of three forests in tropical seasonal rainforests, tropical montane rainforests and mid-montane moist evergreen broad-leaved forests were studied in southern Yunnan. The samples of sapling branches from different forest types and canopy layers were collected in the field to analyze the C, N, P contents and their stoichiometric characteristics.

Result The C content in sapling branches of dominant species in southern Yunnan ranged from 441.67 mg/g to 494.33 mg/g, N content ranged from 6.26 mg/g to 12.47 mg/g, and P content ranged from 0.34 mg/g to 1.06 mg/g. The C and N contents of sapling branches among three forests generally increased with the elevation gradient, and the P content was the highest in the mid-montane moist evergreen broad-leaved forests. The C∶N and C∶P ratios in tropical seasonal rainforests and tropical montane rainforests were relatively high. The N∶P ratio in three forests were between 10 and 20. The C and N contents of sapling branches in upper canopy were smaller than lower canopy, while the P content in upper canopy was greater than lower canopy. The N∶P ratio was similar to 10 in upper canopy, while it was was similar to 20 in lower canopy. In the tropical seasonal rainforest, there was a significant negative correlation between N and P content, C∶N and C∶P ratios, and C∶N and N∶P ratios. In the tropical montane rainforests, there was a significant positive correlation between N and P content, C∶N and C∶P ratios, and C∶N and N∶P ratios. In the mid-montane moist evergreen broad-leaved forests, there was a significant positive correlation between C and P content, N and P content, C∶N and C∶P ratios, and C∶N and N∶P ratios. There was no significant correlation between the C, N, P contents in the upper and lower canopy in southern Yunnan.

Conclusion The C, N, P contents in sapling branches of dominant species in southern Yunnan was relatively high, and the element distribution pattern was characterized by low C∶N and low C∶P. The growth of plants in southern Yunnan were may be co-limited by N and P. The nutrient absorption and utilization efficiency of the upper canopy was slightly higher than that of the lower canopy. The canopy layer have a great effect on nutrient contents and their stoichiometric characteristics, which was greater than that of elevation gradient of sapling branches in southern Yunnan, and the canopy layer is the main factor. This study provides a scientific basis for further revealing the coping mechanism of species adaptation to various ecological environments.