Effect of nitrogen addition on the decomposition and release of compounds from fine roots with different diameters: the importance of initial substrate chemistry

AimsInitial substrate chemical characteristics are the most important factor in the regulation of fine root decomposition. However, it remains unclear how nitrogen (N) deposition changes the decomposition process by affecting initial substrate chemical characteristics with different fine root diameter sizes.MethodsWe compared the root decomposition processes across three diameter sizes (very fine roots, < 0.5mm; intermediate fine roots, 0.5-1.0mm; largest fine roots, 1.0-2.0mm) of Pinus tabulaeformis treated with N addition (control, low, medium, high N are 0, 3, 6, and 9gNm(-2) y(-1) respectively) for two years.Results(1) The root decomposition rates, which were mainly determined by initial N, phosphorus (P), cellulose and lignin concentrations, and carbon (C)/N and lignin/N ratios, increased with the root diameters. (2) The effect of N addition on fine root decomposition rate was not significant (P>0.05), but low N addition enhanced the correlation coefficients between initial chemical indexes and decomposition rates. (3) Low N addition increased the release rates of C and cellulose in the very fine roots but not intermediate fine and largest fine roots, while the medium and high N addition decreased the release rates of N, P, cellulose and lignin in the very fine and intermediate fine roots by affecting the initial C, N, P, starch, cellulose and lignin concentrations. (4) Release of compounds from large diameter fine roots is less responsive to N addition than that from the small ones.ConclusionsThe initial substrate chemistry plays an important role during the N addition affecting fine root decomposition and release of chemical compounds. Our results suggest that N deposition may change the biogeochemical processes of forest ecosystems by affecting the release of compounds from fine roots.