Response of multi-ecological component stoichiometry and tree nutrient resorption to medium-term whole-tree harvesting in secondary forests in the Qinling Mountains, China

Abstract

Carbon (C):nitrogen (N):phosphorous (P) stoichiometry and nutrient resorption are important indicators of biogeochemical cycles and functioning in ecosystems. However, the response of multi-ecological component (plant, litter and soil) stoichiometry and tree nutrient resorption of multi-plant functional species to medium-term whole-tree harvesting (WTH) in secondary forests remains unclear. To reveal how WTH affects C:N:P stoichiometry and tree nutrient resorption, multi-plant organs, senesced leaves, litter and soil samples were collected from one secondary forest after 5 years of five different WTH treatments (CK: 0% (control), T1: 15%, T2: 30%, T3: 45%, T4: 60% of the stand volume removed) in the Qinling Mountains, China. Excluding shrub leaf C contents, WTH did not influence the C, N and P contents or stoichiometric ratios of multi-plant organs and litter (including senesced leaves) at the plot level. Soil C, N and P contents and C:P and N:P ratios significantly decreased following thinning measures, while the C:N ratio had no significant change. The tree N resorption efficiency (NRE) and P resorption efficiency (PRE) showed no significant differences at the plot level among the different thinning measures. Plant nutrient contents and stoichiometric ratios were tightly linkages with soil and stand attributes, while NRE was positively correlated with shrub Shannon-Wiener index. Redundancy and Pearson analyses indicated that the decreased soil nutrients resulted from decreased stand density, volume, litter biomass and available nutrients and increased understory diversity and biomass and soil pH. The N:P ratios of green leaves (trees and understory plants), senesced leaves and litters, as well as the NRE:PRE ratios, suggested that plant growth was limited by N in the study region. Overall, the undifferentiated plant and litter nutrient characteristics and tree nutrient resorption and declining soil nutrients demonstrate that although WTH significantly reduced soil fertility, the plants maintained nutrient homeostasis at the plot level. Furthermore, adaptive fertilization management strategies should be considered to shift the N-limitation status following WTH.