Role of geomorphic surface on the above-ground biomass and soil organic carbon storage in a semi-arid region of Iranian loess plateau

Abstract

The so-called Iranian loess plateau is a unique landscape with a complex topography and steppe vegetation developed under semi-arid climate. We studied the relationships between geomorphic features, soils, biomass of above-ground vegetation (biomass) and soil organic carbon storage (SOCS) to further enhance our understanding of geomorphological processes, soil formation and evaluating SOCS in this strongly dissected landscape. Based on the previous knowledge, the effect of slope aspect on differentiation of soils is considerable in the studied area. Therefore, slope aspect was included as a phase of the geomorphic surface (PGS) in the geomorphic hierarchy to better analyze and understand the soil variation and development. A total of 220 soil samples were taken in different PGS from three depths 0–20, 20–40 and 40–60 cm. For additional details, biomass sampling was collected on 1 m2 quadrat in every location where the soil samples were taken. Results showed that the 0–20 cm layer with 2.13 kg m−2 had the maximum amount of SOC density (SOCD). Among studied units, moderately flat plain (VA111), loess tableland (TB111) and middle hill with north aspect (Hi211_2) had the highest SOCD compared to other units in the three studied depths. The results also indicated that PGS Hi211_2 had a significantly higher SOCD and biomass than PGS middle hill with south aspect (Hi211_1) in three soil layers. The highest values of SOCS were similarly found in the surface soil layer of PGS Hi211_2 accounting for 42816.55 Mg equal to 36.84% of total SOCS. In all PGSs, there were a positive significant correlations between biomass and SOCD (r2 = 0.62, p = 0.01, n = 80). Therefore, the present study revealed that the variation of SOCD is mainly controlled by the PGS in hillslope landscape. Findings of SOCS denoted the importance of protecting surface and subsurface soil layers in hillslope to store SOC. In general, an accurate understanding of geomorphic surface is needed to accurately estimate SOCS, biomass and to evaluate soil and ecosystem related effects on global warming of ecologically sensitive semi-arid areas.