Storage of soil phytoliths and phytolith-occluded carbon along a precipitation gradient in grasslands of northern China

Abstract

Climatic factors including mean annual precipitation (MAP) significantly influence the carbon (C) cycle in terrestrial ecosystems and Earth overall. Phytolith-occluded carbon (PhytOC) is an important C sequestration mechanism and as such plays a vital role in global long-term C sequestration. Understanding the spatial variability in the storage of soil phytoliths and PhytOC and its relationship with climate is critical for evaluating the impact of global climate change on terrestrial ecosystem functions. However, little is known about the responses of soil phytoliths and PhytOC to MAP in grassland ecosystems. This study sampled soil from 24 natural, semi-arid steppe sites along a 2,500 km transect with a precipitation gradient of 243–481 mm yr−1 in northern China. We investigated the influence of precipitation on the spatial distributions of soil phytoliths and PhytOC storage. Storage of soil phytoliths in bulk soil (0–100 cm depth) ranged from 21.3 ± 0.4 to 88.4 ± 20.3 t ha−1 along the precipitation gradient. Amounts of soil phytoliths and PhytOC storage were significantly and positively correlated with MAP. Multiple regression analysis revealed that phytolith storage in bulk soil was best predicted by MAP (R = 0.5) and soil organic carbon (SOC, R = 0.4), with these two variables accounting for about 58% of the total variation observed. Considering the forecasted increase in MAP in the Inner Mongolian steppe due to climate change, and the strong influence of MAP on the annual net primary productivity (ANPP) and related soil PhytOC input from litter decomposition in this region, we expect that ecosystem primary productivity will increase from deserts to meadow steppe and thereby promote soil PhytOC storage. These findings have important implications for understanding the dynamics of soil phytoliths, and predicting the impacts of global climate change on ecosystem functions and management practices in the East Asian steppe ecosystems.