Vegetation restoration drives the dynamics and distribution of nitrogen and phosphorous pools in a temperate desert soil-plant system

Abstract

The role vegetation restoration and succession play in regulating Nitrogen (N) and Phosphorous (P) pools remains unexplored and poorly understood. To examine the effects of vegetation restoration and succession from a shifting sand dune to restored vegetation at different ages (23, 33, 50, and 58 years) on the dynamics and distribution of N and P pools in a soil-plant system, a comprehensive field investigation was conducted and N(P) concentrations and densities of soil, shrubs (including leaves, new branches, aging branches, and roots), and grass (including aboveground, roots, and litter) at each site were analyzed and quantified. We found that total N (TN) and total P (TP) density for the plant-soil system, in live shrub biomass as well as soil TN (STN) density in subsoil (10-100 cm), decreased between 23 and 50 years, and then increased from 50 to 58 years. STN and soil TP (STP) densities in topsoil (0-10 cm), and N and P densities of herbage and dead shrubs, continued to increase with restoration. N and P were primarily stored in soils and accounted for 89.83%-92.06% and 99.33%-99.48% of the TN and TP pools, respectively. In the first 23 years, live shrubs made up the second largest N and P pools, however, herbage made up the second largest N and P pools after 23 years. The ratios of N and P in herbage to TN and TP density increased from 3.71% to 6.31%, and 0.33%-0.43%, gradually approaching the native site (6.39% and 0.46%). The ratios of N and P in live shrubs to TN and TP density in the soil-plant system decreased from 4.55% to 1.08% and from 0.33% to 0.13%. Our results indicated that the restored ecosystem was a N(P) source from 0 to 50 (0-23) years, and a N(P) sink from 50 to 58 (23-58) years, with strong potential for accumulating more N (147.18 g m^-2) and P (102.67 g m^-2) to reach the natural site levels. These results suggest that vegetation restoration and succession may profoundly alter N and P geochemical cycles through N(P) redistribution in a temperate desert plant-soil system. Proper N and P addition at the initial stage of vegetation restoration may promote the recovery of desertified land.

Keywords: Distribution patterns; Nitrogen pool; Phosphorous pool; Restoration series; Vegetation restoration.