Fine root turnover and longevity and their responses to nitrogen fertilization of nitrogen-fixing and non-nitrogen-fixing tree species

Abstract

Abstract Background and aims Fine root longevity and turnover respond to changes in soil nitrogen (N) determine plants’ performance at elevated N-level under global N-deposition. This study was conducted to understand the fine root dynamics of N-fixing and non-N-fixing tree species at elevated N-level by N fertilization. Methods To determine fine root dynamics (biomass, length density, longevity, and turnover rate) under N-fertilization, a three-year fertilization experiment at 150 g CO(NH2)2. m− 2 year− 1 was conducted for two N-fixing species and two non-N-fixing tree species. Results Fine root biomass of the two N-fixing tree species was lower than that of non-N-fixing tree species. N-fertilization decreased root length density, root surface area, and root volume of all tree species. The fine root turnover rate of N-fixing trees was higher but root longevity was lower than that of non-N-fixing species. For all four species, N fertilization decreased fine root turnover rate but increased fine root longevity. Moreover, both the root turnover rate and root longevity of the two N-fixing tree species were more sensitive than the two non-N-fixing tree species to N fertilization. The proportion of long-lived roots of non-N-fixing tree species was higher than that of N-fixing tree species. Conclusion Fine roots of N-fixing tree species have shorter longevity and faster turnover rate than that of non-N-fixing tree species. The fine root longevity and turnover of N-fixing tree species were more sensitive to elevated N-level than that of non-N-fixing species at elevated N-level, they have different response strategies to the increase of soil N.