Fencing reshapes spatial patterns of nutrient pools during peak-growing-season in the Tibetan grasslands: Spatial heterogeneity of C and N pools and elevational homogeneity of P pools

Abstract

Fencing can play an important role in the protection of carbon (C), nitrogen (N) and phosphorus (P) pools in grassland ecosystems. However, these effects on a wide range of climatic and geographic scales remain unclear. This study investigated 37 pairs of fencing and grazing sample sites in alpine grasslands across an 1800-km transect on the Tibetan Plateau to evaluate the effects of fencing on C, N, and P pools of aboveground plants, roots, soil and the entire ecosystem. Fencing increased the space average values of C, N and P pools of aboveground plants and roots by 11.07 %–38.33 % and the soil C pools by 11.05 % at 0–10 cm. Compared with 0–10 and 20–30 cm, the spatial average values of belowground roots C, N, and P pools at 10–20 cm were more sensitive to fencing. The effects of fencing on C, N and P pools of aboveground plants in alpine deserts were higher than those in alpine meadows and alpine steppes. Fencing heterogenized the spatial patterns of C and N pools of the ecosystem while homogenized the elevational pattern of the P pool. With increasing longitude, the responses of C, N, and P pools of the ecosystem to fencing were enhanced. Conversely, with increasing latitude and elevation, the effects of fencing on C, N, and P pools decreased. Therefore, the effects of fencing on the C, N, and P pools of the alpine grasslands were related to soil depth and grassland type. The sensitivities of nutrient pools of aboveground plants, roots and soil to fencing were different. Ecosystem P pool homogenization caused by fencing potentially disrupted phosphorus flow and ecological processes, and thus weakened ecosystem functionality. The effects of fencing on ecosystem nutrient pools were not always positive, which suggested that fencing should not be everywhere, at least for the restoration of C, N, and P pools.