Patterns of carbon, nitrogen and phosphorus dynamics during decomposition of fern leaf and fine root in a subtropical forest

Abstract

Litter decomposition is a major driver of carbon and nutrient cycles and has major implications for carbon sequestration and plant nutrient availability in terrestrial ecosystems. The vast majority of litter decomposition studies have focused on the tree component in forest ecosystems, while little attention has been paid to understory components. Ferns, one ancient and diverse group of vascular plants, comprise a significant part of most forest understory layer. However, empirical study regarding decomposition rate and carbon, nitrogen and phosphorus release patterns of fern leaves and fine roots remains rare. Therefore, it is difficult to predict the ecological consequences of fern community changes resulting from forest management practices or other environmental changes. In this study, we examined the patterns of mass loss and carbon, nitrogen, and phosphorus gain, retention or loss during the decomposition of leaves and fine roots ( 2 mm) of 12 herbaceous fern species in a subtropical evergreen broad-leaved forest in Jinyun Mountain, Southwest China. We measured the initial carbon, nitrogen, and phosphorus concentrations of leaves and fine roots, and monitored the changes in carbon, nitrogen, and phosphorus after 113, 198, 386 and 586 day’ decomposition in the field. We hypothesized that: (H1) fern leaves would decompose faster than fine roots; (H2) nitrogen and phosphorus release patterns would be affected by the initial tissue nitrogen and phosphorus concentrations; and (H3) carbon, nitrogen and phosphorus release patterns of leaves and fine roots would coordinate across different fern species. The results showed that: (1) Initial carbon concentration of fern leaves were similar to fine roots, while initial nitrogen and phosphorus concentrations of leaves were significantly higher than those of fine roots. Litter mass, carbon, nitrogen and phosphorus remains of fern leaves were generally significantly lower than those of fine roots, supporting our first hypothesis (H1). (2) Carbon, nitrogen and phosphorus of fern leaves and roots exhibited different loss patterns. Leaf carbon, nitrogen and phosphorus generally directly lost during the entire decomposition process. By contrast, carbon, nitrogen and phosphorus of fine roots showed more complicated patterns such as direct loss, gain-loss, gain-loss-gain and always gain. In support of our second hypothesis (H2), we found that nitrogen or phosphorus release patterns were influenced by the initial tissue nitrogen or phosphorus concentrations, respectively. (3) Carbon remains between leaves and fine roots were significantly correlated after 113, 198 and 386 day’ decomposition in the field, but not after 586 d. Phosphorus remains between leaves and fine roots were significantly correlated after 198, 386 and 586 day’ decomposition in the field, but not after 113 d. By contrast, there was no significant relationship of the nitrogen remains between leaves and fine roots during the entire decomposition process. Thus, our third hypothesis (H3) was only partly supported. This result suggests that the above- and below-ground covariation patterns depend on specific element and the duration of decomposition. Our study improves our understanding of how fern species influence the carbon and nutrient cycling in subtropical forest.