Effects of long-term planting on PhytOC storage and its distribution in soil physical fractions in Moso bamboo forests in subtropical China

Abstract

Phytoliths are siliceous substances that are abundant within intercellular spaces and inside cells of numerous types of plants. During the formation of phytoliths, between 0.2 and 5.8% of organic carbon (C) can be occluded within the phytoliths. Phytolith-occluded C (PhytOC) in terrestrial ecosystems is a stable C sink and can be distributed in organic matter that is not strongly associated with soil minerals (LFOM) or that is strongly associated with mineral particles (forming organo-mineral complexes) (HFOM). We (1) investigated the impact of plantation age and soil depth on the size of the PhytOC pool and its distribution in soil physical fractions in Moso bamboo (Phyllostachys pubescens) forests; and (2) explore the relationship among phytoliths and PhytOC (and their fractions) concentrations and the soil properties. We used a chronosequence approach by sampling 5-, 10-, 20-, 50-, and 100-year-old Moso bamboo stands to examine the effect of plantation age on PhytOC storage and its distribution between the LFOM and HFOM pools. Our results showed that PhytOC concentration and the concentration of PhytOC in LFOM and HFOM increased with increasing stand age in the topsoil (0–30 cm) but not in the subsoil (30–100 cm). Long-term planting of Moso bamboo forests increased the soil PhytOC pool size, as well as the LFOM- and HFOM-PhytOC fractions. The LFOM- and HFOM-PhytOC concentrations were positively correlated with soil organic C concentrations. The HFOM-PhytOC concentration was positively correlated with that of water-soluble silicon. We conclude that the increasing bamboo plantation age will promote PhytOC storage in the bulk soil and physical fractions in subtropical China. Management practices that increase PhytOC input and decrease PhytOC output should be developed in the future to increase PhytOC storage in bamboo plantations.