Controlling action of soil organic matter on soil moisture retention and its availability

Abstract

Aims Assessment of the ecological benefits of forest in soil water retention based on conventionally monitored factors and exploration of the relation between forest carbon-sink function and hydrological benefits has special meaning in Millennium Ecosystem Assessment.Our objectives were to 1) characterize the spatial and temporal variations of soil moisture in three subtropical forests and 2) determine the controlling action of soil organic matter on soil moisture retention during vegetation succession.Methods Standard plots were established in Pinus massonniana coniferous forest(PF),mixed Pinus massonniana-broad-leaved forest(PBF) and monsoon evergreen broad-leaved forest(MBF).We measured soil water content every 10 days from 2002 to 2008 using neutron probes and analyzed soil organic matter content in the laboratory by the potassium dichromate oxidation method.Important findings With natural succession from planted PF to climax MBF,soil water content(0–30 cm soil layer) increased significantly;soil water content was highest in MBF and lowest in PBF.The distribution patterns of soil moisture in the three forests were different: the soil moisture of MBF decreased with soil depth,was more homogeneous in the soil profile in PBF and was lower at the surface than in deeper layers in PF.The soil water characteristic curves showed that under the same matrix suction the magnitude of soil water content(0–40 cm soil layer) was: MBF PBF PF;the soil of MBF was the most retentive.Further analysis indicated that soil porosity had the greatest impact on soil moisture,followed by saturated soil water content and soil organic matter content,while soil bulk density had a minimal impact.In the process of natural succession,soil moisture was significantly correlated with the soil organic matter content(p = 0.014),as the soil organic matter could affect soil moisture holding(p = 0.030).Accordingly,we recommend soil organic matter as an effective and integrated index for appraising forest ecosystem services.