Abstract:

Objective: Forest fire is one of the important disturbance factors in forest ecosystem. Plants have ecological adaptability to different forest fire environments. Study on the adaptive changes of twig functional traits of Pinus tabuliformis under different fire severities would help to reveal the ecological trade-off strategies and adaptive mechanisms of P. tabulaeformis under different fire environments, and provide a theoretical basis for the ecological restoration of P. tabuliformis after fire. Method: P. tabuliformis in the burned area (unburned, light burned, moderate burned) of Qinyuan county, Shanxi Province was targeted. The differences and correlations among twig functional traits (twig tissue density, twig nitrogen content, twig phosphorus content, twig organic carbon content, twig nitrogen-phosphorus ratio, twig carbon-phosphorus ratio, twig carbon-nitrogen ratio) under different fire severities were studied by one-way analysis of variance and Pearson correlation analysis. The change trend of economic spectrum of P. tabuliformis twigs under different fire severities was explored by principal component analysis. Result: 1) Under three fire severities, the variation coefficient of twig carbon-phosphorus ratio was the largest, and that of twig organic carbon content was the smallest. With the increase of fire severity, twig tissue density first decreased and then increased. Twig tissue density in the control was significantly higher than that in the light burned by 11.8%, and significantly higher than that in the moderate burned by 5.6%. Twig phosphorus content increased with the increase of fire severity, which of the moderate burned was significantly higher than that of the control by 27.8%. Twig nitrogen-phosphorus ratio decreased with the increase of fire severity, which in the moderate burned was significantly lower than that of the control by 19.1%. There were no significant differences among other twig functional traits with the change of fire severity. 2) Under different fire severities, there were similar results in the correlation of twig functional traits: there was a highly significant negative correlation between twig nitrogen content and twig carbon-nitrogen ratio, and a highly significant negative correlation between twig phosphorus content, and twig nitrogen-phosphorus ratio, as well as twig carbon-phosphorus ratio, and a highly significant positive correlation between twig nitrogen-phosphorus ratio and twig carbon-phosphorus ratio. Therefore, the coupling relationship between the above traits was the most stable in the twig functional traits of P. tabuliformis. However, the increase of fire severity weakened the correlation between some traits. Compared with the control and the light burned, there were no significant correlations among twig nitrogen content, twig phosphorus content and twig carbon-phosphorus ratio, between twig phosphorus content and twig carbon-nitrogen ratio, and between twig carbon-phosphorus ratio and twig carbon-nitrogen ratio under the moderate burned. 3) There existed a twig economic spectrum of P. tabuliformis growing in the burned area. Along the fire severity of 'unburned-light burned-moderate burned', the resource trade-off strategy of twig moved to 'fast investment-benefit type', indicating that the growth rate of twigs would be accelerated. Conclusion: Fire severity has a significant effect on the functional traits of P. tabuliformis twigs, changes the allocation strategy of nutrient elements. The growth recovery of P. tabuliformis twig would be accelerated under light and moderate burned conditions. The research result can provide theoretical support for ecological restoration of burned P. tabuliformis.

Key words: Pinus tabuliformis, forest fire, fire severity, twig functional trait, twig economic spectrum