Objective Exploring ecological stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) of different forest types is of great importance to better understanding nutrient element 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 broadleaved forests were studied in southern Yunnan Province of southwestern China. 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 Province ranged from 441.67 to 494.33 mg/g, N content ranged from 6.26 to 12.47 mg/g, and P content ranged from 0.34 to 1.06 mg/g, respectively. 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 broadleaved forests.The average values of C and N contents of sapling branches among three forests generally increased with the elevation gradient, and the average P content was the highest in the mid-montane moist evergreen broadleaved forests. The average values of C∶N ratio was highest in tropical seasonal rainforests and lowest in tropical mountain rainforests; The average values of C∶P and N∶P ratios were highest in tropical mountain rainforests and lowest in mid-montane moist evergreen broadleaved forests. The average values of N∶P ratio in three forests was between 10 and 20. The average values of C and N contents of sapling branches in upper canopy were smaller than lower canopy, while the average P content in upper canopy was greater than lower canopy. The average N∶P ratio was close to 10 in upper canopy, while it was close to 20 in lower canopy. In the tropical seasonal rainforest, there was a significant negative correlation between C∶N and N∶P ratios (P < 0.05). In the tropical montane rainforests, there was a significant positive correlation between C∶N and C∶P ratios (P < 0.05). In the mid-montane moist evergreen broadleaved forests, there was a significant positive correlation between C∶N and C∶P ratios, as well as C∶N and N∶P ratios (P < 0.05). There was no significant correlation between C, N, P contents in the upper and lower canopy in southern Yunnan Province.
Conclusion C, N, P contents in sapling branches of dominant species in southern Yunnan Province were relatively high, and element distribution pattern was characterized by low C∶N and low C∶P. On the one hand, it reflects the relatively fast decomposition and release of carbon in forest vegetation in southern Yunnan, and the growth of plants may be colimited by N and P. On the other hand, the nutrient absorption and utilization efficiency of the upper canopy was slightly higher than that of lower canopy. The canopy layer has a great effect on nutrient contents and their stoichiometric characteristics, which was greater than that of elevation gradient of sapling branches in southern Yunnan Province.
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