Abstract
Fine root decomposition represents a large carbon (C) cost to plants, and serves as a potential soil C source, as well as a substantial proportion of net primary productivity. Coarse roots differ markedly from fine roots in morphology, nutrient concentrations, functions, and decomposition mechanisms. Still poorly understood is whether a consistent global pattern exists between the decomposition of fine (<2 mm root diameter) and coarse (≥2 mm) roots. A comprehensive terrestrial root decomposition dataset, including 530 observations from 71 sampling sites, was thus used to compare global patterns of decomposition of fine and coarse roots. Fine roots decomposed significantly faster than coarse roots in middle latitude areas, but their decomposition in low latitude regions was not significantly different from that of coarse roots. Coarse root decomposition showed more dependence on climate, especially mean annual temperature (MAT), than did fine roots. Initial litter lignin content was the most important predictor of fine root decomposition, while lignin to nitrogen ratios, MAT, and mean annual precipitation were the most important predictors of coarse root decomposition. Our study emphasizes the necessity of separating fine roots and coarse roots when predicting the response of belowground C release to future climate changes.
Highlights
That fine and coarse roots differ markedly in their morphology, nutrient concentrations, functions, and decomposition mechanisms[31,32,33,34], the global pattern between the decomposition of fine and coarse root is still largely unknown
Because temperature sensitivity of litter decomposition is inversely proportional to substrate quality[39,40,41], coarse root decomposition may have a higher dependence on temperature than that of fine roots
Several criteria were established for developing the database: (1) Root decay constants (k-values) should have been measured in situ so as to remove any potential effects from home-field advantage[45]; (2) the experimental data in the original paper should not have been designed for special purposes; (3) k-values should have been estimated by the litterbag technique—the best available method, not without limitations[46], for generating large decomposition datasets[4,47]; (4) only k-values reported using a single exponential model in the original paper or that could be calculated from figures or tables were considered; (5) clear ancillary site information or study site latitude and longitude should be determinable from the site description using Global Gazetteer Version 2.1
Summary
That fine and coarse roots differ markedly in their morphology, nutrient concentrations, functions, and decomposition mechanisms[31,32,33,34], the global pattern between the decomposition of fine and coarse root is still largely unknown Both climate and initial litter quality have been previously recognized as major decomposition-controlling factors at large spatial scales[2,4,35]. The dataset comprised 530 observations from 71 sampling sites, and contained information on initial root chemistry, including N, P, lignin, Ca, C to N, and lignin to N ratios as well as climate variables (MAT and mean annual precipitation [MAP]) This dataset enabled investigation of two questions, namely determination of whether a common global pattern of decomposition rates exists between fine and coarse roots, and identification of the main controlling factor(s) for fine and coarse root decomposition. Coarse root decomposition was found to have a higher dependence on MAT than that of fine roots, and coarse root and fine root decompositions were revealed to differ in their responses to litter quality
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