Dynamics in Stoichiometric Traits and Carbon, Nitrogen, and Phosphorus Pools across Three Different-Aged Picea asperata Mast. Plantations on the Eastern Tibet Plateau

Abstract

Understanding the variations in soil and plants with stand aging is important for improving management measures to promote the sustainable development of plantations. However, few studies have been conducted on the dynamics of stoichiometric traits and carbon (C), nitrogen (N), and phosphorus (P) pools across Picea asperata Mast plantations of different ages in subalpine regions. In the present study, we examined the stoichiometric traits and C, N, and P stocks in different components of three different aged (22-, 32-, and 42-year-old) P. asperata plantations by plot-level inventories. We hypothesized that the stoichiometric traits in mineral soil could shape the corresponding stoichiometric traits in soil microbes, tree roots and foliage, and the C, N, and P stocks of the total P. asperata plantation ecosystem would increase with increasing stand age. Our results show that the N:P ratio in mineral soil was significantly correlated with that in tree foliage and herbs. Additionally, the C:N ratio and C:P ratio in mineral soil only correlated with the corresponding stoichiometric traits in soil microbes and forest floor, respectively. Both the fractions of microbial biomass C in soil organic C and microbial biomass N in soil total N decreased with increasing stand age. The C, N, and P stocks of the total ecosystem did not continuously increase across stand development. In particular, the P stock of the total ecosystem exhibited a trend of increasing first and then decreasing. The aboveground tree biomass C accounted for more than 55% of the total ecosystem C stock regardless of stand age. In contrast, mineral soil and forest floor were the major contributors to the total ecosystem N and P stocks in all stands. This study suggested that all three different stands were N limited, and the stoichiometric homeostasis in the roots of P. asperata was more stable than that in the foliage. In addition, the soil microbial community assembly may change with increasing stand age for P. asperata plantations in the subalpine region.