Soil organic carbon pool plays an important role in the global C cycle and climate change mitigation. Therefore, improving our understanding of some factors such as plant biodiversity that can affect forest soil C storage is fundamentally important for anticipating changes. This study was carried out in the mixed-beech forests of Glandrood located in Noor using a systematic network of points including 400 m2 plot for trees layer regularly distributed by a distance of 100 m from each other. Within each sampling plot, five different smaller sub-plots (1m2) corresponded to the herbal coverage on the four cardinals and the center of sampling plots in order to measure Shannon-winner index H΄, Pielou index J΄, Species richness SR, Dominance index D, Abundance index and Species Importance Value index SIV. After removing the litter and large plant materials, soil samples were collected at 0-10, 10-30 and 30-50 cm depths within each sub-plot, air dried and 2 mm sieved. The results of one-way ANOVA indicated that soil organic C pool was significantly different in the second depth compared to other soil layers. Based on the Pearson's correlation test across different soil layers, a positive strong correlation was detected between soil organic carbon storage at the first depth and abundance of tree layer. Furthermore, the aforementioned test showed that there was a strong correlation between Pielou index, dominance index of herbal coverage and soil C pool weight in the third depth as well as across the whole depths. Moreover, there was a inverse correlation between Dominance of herbal coverage and soil C pool weight in the third depth and the whole depth. In addition, there was a positive strong correlation between Shannon's index of herbal coverage and soil C pool weight in the third depth, total soil C pool weight. In contrast to the above conclusion, there was no significant correlation between species richness, SIV and soil C pool weight in different depths. This illustrated that soil organic C pool variation was independent of species richness and species importance value of both trees and herbal layers.

Keywords: Soil organic C pool, Plant diversity, Coverage of tree and herbs, Mixed-beech forest, Glandrood of Noor

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