Shrub encroachment leads to accumulation of C, N, and P in grassland soils and alters C:N:P stoichiometry: A meta-analysis.

ABSTRACT

Soil stoichiometry of carbon (C), nitrogen (N), and phosphorus (P) are indicators for nutrient balance. Shrub encroachment into grasslands could change nutrient concentrations and stoichiometry in soils, but the general patterns remain unclear. With a meta-analysis of a global dataset covering 344 observations from 68 studies, we examined the responses of grassland soil CNP stoichiometry to shrub encroachment under various environmental conditions. Our results show that 1) Shrub encroachment significantly increased the concentrations of soil C (+29 %), N (+25 %), P (+20 %), CN (+5 %), CP (+12 %), and NP (+6 %). The magnitude of such effects varied with climate, soil texture, and soil layer. 2) Increases in SOC and TN concentrations mainly occurred in Mediterranean and very humid climate zones. Soil CP and NP decreased in semi-humid climate zone after shrub encroachment. 3) The increases in SOC and TN concentrations and in the CN, CP, and NP ratios after shrub encroachment were greater in the topsoil than in deeper soil layers. 4) Both finest-textured soil (clay) and coarsest-textured soil (sand) are beneficial for increase of soil nutrient concentrations following shrub encroachment. 5) The magnitude of the change in soil CN was negatively correlated with the duration of shrub encroachment, due to greater increases in soil TN than in SOC concentrations with longer durations of encroachment. Our results indicate that soil stoichiometric shifts in shrub-encroached grasslands are relatively sensitive to environmental factors, including soil texture, soil pH, and climate. These findings help us to better understand the effects of shrub encroachment on biogeochemical cycling, functioning, and services in grasslands across a broad range of spatio-temporal scales.