The efficiency of organic C sequestration in deep soils is enhanced by drier climates

Accurate assessment of organic C sequestration in deep soils is crucial to C management and understand the role of deep-rooted vegetation in the C cycle. Trees in drylands usually develop roots to access deep water resources. Deep soils typically contain large stores of sequestrated C because the microbial activities that decompose C are limited and C turnover time is long. However, we know little about whether root water uptake can benefit organic C sequestration in deep soils and the effect of precipitation on organic C sequestration. To address this, we selected five sites along a precipitation gradient from 422 mm to 606 mm on China's Loess Plateau, and collected soil samples down to 1000 cm to measure soil organic C (SOC) content and soil water content (SWC) in both apple orchards and arable lands. We found that SOC storage (SOCS) and soil water storage (SWS) of two vegetation types in 0-800 cm soil layers increased significantly with increasing mean annual precipitation (MAP). Apple orchards showed greater SOC sequestration, particularly in deep soils (200-1000 cm), across each precipitation gradient relative to the corresponding arable lands. The & UDelta;SOCS (difference in SOCS between apple orchards and the corresponding arable lands) in deep soils gradually decreased as MAP increased, and & UDelta;SOCS for MAP = 422 mm was almost twice as great as that for MAP = 606 mm. Moreover, the ratio of & UDelta;SOCS/& UDelta;SWS in deep soils significantly increased as MAP decreased in the interval 400-610 mm. This indicates that the efficiency of SOC sequestration in deep soils is enhanced in a drier climate. The findings here indicate that deep soils may contribute greatly to organic C sequestration, and may provide insights into the water-C relationships in deep soils.

Automated summary

The study found that increasing precipitation promotes organic C sequestration in deep soils, and apple orchards have a greater capacity for SOC sequestration compared to arable lands. The SOC sequestration in deep soils for MAP = 422 mm was almost twice as great as that for MAP = 606 mm. Additionally, lower precipitation leads to higher efficiency of SOC sequestration in deep soils.