Abstract
Altitude is a determining factor of ecosystem properties and processes in mountains. This study investigated the changes in the concentrations of carbon (C), nitrogen (N), and phosphorus (P) and their ratios in four key ecosystem components (forest floor litter, fine roots, soil, and soil microorganisms) along an altitudinal gradient (from 50 m to 950 m a.s.l.) in subtropical China. The results showed that soil organic C and microbial biomass C concentrations increased linearly with increasing altitude. Similar trends were observed for concentrations of total soil N and microbial biomass N. In contrast, the N concentration of litter and fine roots decreased linearly with altitude. With increasing altitude, litter, fine roots, and soil C:N ratios increased linearly, while the C:N ratio of soil microbial biomass did not change significantly. Phosphorus concentration and C:P and N:P ratios of all ecosystem components generally had nonlinear relationships with altitude. Our results indicate that the altitudinal pattern of plant and soil nutrient status differs among ecosystem components and that the relative importance of P vs. N limitation for ecosystem functions and processes shifts along altitudinal gradients.
Highlights
The nature of nutrient limitation on plant growth[16,18] and that the litter N:P ratio may indicate the nature of nutrient limitation on the decomposition of leaf litter[19]
Just as ecosystem processes can differ in their responses to the changes in environmental conditions with changes in altitude[11,24], nutrient status may differ among ecosystem components and nutrients along altitudinal gradients[11,21]
We hypothesized that (1) mineral soil C concentration would increase while plant C concentration would be constant along the altitudinal gradient; (2) the N and P concentrations in litter and fine roots would decrease with increasing altitude; and (3) the N:P ratios in litter and fine roots would decrease with altitude
Summary
The nature of nutrient limitation on plant growth[16,18] and that the litter N:P ratio may indicate the nature of nutrient limitation on the decomposition of leaf litter[19]. Some other studies have demonstrated that altitudinal changes in nutrient ratios may differ among ecosystem components (leaves vs mineral soil, trees vs shrubs, etc.)[11,21]. Dissimilar changes in nutrient ratios along altitudinal gradients between ecosystem components indicate the differing sensitivities of ecosystem components to environmental changes along the gradient[11,20,21] Such dissimilar changes have important implications for the nature of nutrient limitation on different ecosystem functions (e.g., primary productivity) and processes (e.g., litter decomposition)[3,20,22]. Just as ecosystem processes can differ in their responses to the changes in environmental conditions with changes in altitude[11,24], nutrient status may differ among ecosystem components and nutrients along altitudinal gradients[11,21]. We hypothesized that (1) mineral soil C concentration would increase while plant C concentration would be constant along the altitudinal gradient; (2) the N and P concentrations in litter and fine roots would decrease with increasing altitude; and (3) the N:P ratios in litter and fine roots would decrease with altitude
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