Size-dependent associations of woody plant structural diversity with soil C:N:P stoichiometry in a subtropical forest

Abstract

Woody plant structural diversity and soil C:N:P stoichiometry have widely been examined for their spatial patterns and changes across environmental gradients, but the interactions and relationship of these biotic and abiotic variables have not been well understood. Here, we investigated the associations of woody plant structural diversity variables with soil total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), and their stoichiometry. We found only weak associations between soil C:N:P stoichiometry and species diversity variables, however, stronger significant associations were detected between C:N:P stoichiometry and species diversity variables for the adult trees and saplings when analyses were carried out with appropriate size stratification of woody plants. Most size diversity variables were significantly correlated with TOC, TN, TP, and their stoichiometric ratios, and the size diversity variables were greater in strength than species diversity in their associations with TOC, TN, TP, and C:N:P stoichiometric ratios. In most cases, C:N:P stoichiometric ratios were more sensitive than TOC, TN, or TP in predicting species diversity and size diversity. Our findings demonstrate that the associations of woody plant species diversity with TOC, TN, TP, C:N:P stoichiometry are size-dependent, and the size diversity is much more sensitive than species diversity in predicting the change of soil TOC, TN, TP, and C:N:P stoichiometric ratios. These findings also suggest that an appropriate size stratification will help demonstrate the linear relations between woody plant structural diversity and C:N:P stoichiometry and amplify the environmental signals from soil factors in predicting the biotic variables.

Woody Plant Structural Diversity Changes across an Inverse Elevation-Dependent Warming Gradient in a Subtropical Mountain Forest

“…where H ′ is the Shannon-Wiener diversity index, P i is the relative abundance of the i-th species in proportion to the total abundance of species in a quadrat; and E is the Pielou's evenness, S is the number of species in a quadrat. Size diversity was represented by variability in basal area (BA), size diversity index, and evenness [15]. We defined the size diversity as the variability in basal areas across quadrats.…”

“…We defined the size diversity as the variability in basal areas across quadrats. The size diversity index and evenness were calculated following Su, Jia, Zhang and Chen [15], which are based on the Shannon-Wiener index formula and Pielou's evenness, respectively.…”

“…In contrast, in a short-to-medium-range elevational gradient, changes in diversity patterns will be affected predominantly by temperature because of similar water availability from rainfalls. A small change in temperature due to the temperature lapse rate in mountain areas will exert an enormous influence on structural diversity [15,31,32].…”

“…Structural diversity is mainly composed of three components, i.e., spatial distribution, species diversity, and tree size diversity [15,33]. Changes in structural diversity are often affected by a variety of factors, including climate change [34,35], land use history [36], habitat heterogeneity [37], and inter-and intraspecific competitions [38,39].…”

“…The response of forest community to climate warming can be shown by examining the changes in community structure and species diversity across an inverse elevational gradient [5,10], because in a mountain landscape a warming trend exists with descending elevation according to an environmental temperature lapse rate of 0.65 • C per 100 m [8,9]. The subtropical mountain forest ecosystem is an ideal natural experimental environment for studying the variation of plant community structure and diversity along the elevational gradient, because the subtropical forest is rich in species resources [14,15], and the mountains with sloping topography can directly or indirectly affect the distribution of thermal radiation, the key factor controlling the richness, abundance, and dominance of plant species in a community [10,16]. Therefore, understanding the changes in composition, structure, and diversity of subtropical forest communities at different elevations can provide valuable information for the forestry sector and the scientific community to cope with climate change.…”