Chemical stoichiometry characteristics of various organs of trees in high-density Populus tomentosa pulp forests under water-nitrogen coupling

Objective The stoichiometric ratio of plant ecology can represent the survival strategies of plants and reflect the response of plants to external changes in the ecosystem. Therefore, understanding the stoichiometric characteristics of Populus tomentosa trees can clarify the nutrient utilization strategy and nutrient distribution of P. tomentosa, which aims to provide theoretical support for efficient water and nitrogen cultivation of P. tomentosa.

Method This experiment took triploid P. tomentosa S86 pulp forest on the Yellow River Alluvial Plain of North China as the research object. A two-factor furrow irrigation water and fertilizer coupling experiment was set up. In the rainy season, destructive sampling was treated with W₂₀N_H, W₂₀N₀, W₄₅N_H and CK, and carbon, nitrogen and phosphorus contents of different leaves, branches, roots, trunks organs of 5-year-old P. tomentosa were measured.

Result (1) The organic carbon content of each organ of P. tomentosa ranged from 440.31 to 454.44 g/kg during the growing season; the nitrogen content of each organ ranged from 6.87 to 25.48 g/kg, the phosphorus content of each organ ranged from 0.70 to 1.71 g/kg. The ranges of C∶N, C∶P and N∶P ratio of each organ were 18.62−84.60, 292.05−1128.79, 6.82−18.05, respectively. (2)The total nitrogen content of branches and leaves in the aboveground part showed a decreasing trend with decreasing canopy height, while the carbon, nitrogen and phosphorus contents of fine roots in the belowground part did not differ significantly under each treatment. (3) The ranges of C∶N, C∶P, and N∶P ratio for different canopy leaves under each treatment were 14.20−22.45, 236.83−489.91, 15.24−23.65, respectively.

Conclusion In general, for the 5-year-old high-density P. tomentosa pulp forest trees, lack of irrigation and high fertilization (W₄₅N_H) have limited effect on nutrient accumulation in all organs, but full irrigation (W₂₀N₀) and full irrigation and high fertilization (W₂₀N_H) are sufficient to reduce N∶P in poplar leaves and alleviate N and P limitation in poplar cultivation in the yellow panhandle region, but full irrigation with or without fertilization do not have a significant effect on the reduction of N∶P ratio. Therefore, after long-term water management, the high-density pulp wood of P. tomentosa should consider reducing nitrogen fertilizer application to reduce environmental pollution and maintain high growth potential while meeting sufficient irrigation conditions.