Assessment of the Contributtion of soil Biota and litter Quality to carbon Sequestration of Different Physiognomy in Shasha Forest Reserve,Nigeria.
The study identified and compared plant species diversity, soil organism biodiversity and abundance, determined soil organic carbon (SOC) pool and litter biomass carbon together with other litter biochemical composition in six different physiognomies in Shasha Forest Reserve in Osun State. It also investigated the seasonal variation in soil carbon content and established relationship among the explanatory variables with a view to identifying the physiognomy most suitable for afforestation to mitigate climate change. Physiognomies used for the study were; secondary re-growth natural forest (SRNF),Terminalia superba plantation (TSP), Pinus caribaea plantation (PCP), Gmelina arborea plantation (GAP), Tectona grandis plantation (TGP) and Theobroma cacao plantation (TCP). Eight plots (25 m x 25 m) were randomly selected in each physiognomy for the study. Tree species were identified and analysed using Shannon-Weiner diversity indices. The below-ground biodiversity assessed were; soil seed bank, earthworm, enchytraeid, millipede, collembola, beetle, termite, nematode, bacteria and fungi using standard methods. Freshly senesced litters were collected using litter trap, dried, ground, sieved and analysed for carbon, nitrogen, lignin and phenolic acid content. Composites soil samples were collected in both dry and wet seasons from three quadrats of 5 m x 5 m, within each 25 m x 25 m plot. The soil samples were analysed for bulk density, organic carbon, total nitrogen, pH and humic substances using standard methods. Data were subjected to appropriate descriptive and inferential statistics. Floristic diversity indicated that both understory and overstory as well as tree saplings varied among the physiognomies with secondary re-growth natural forest, T. superba and P. caribaea plantations having the highest tree diversity. Tectona grandis (21) and Theobroma cacao (13) plantations had the least tree diversity. The belowground diversity showed that highest tree emergence occurred in TSP (33.3%), while the least occurred in TCP (6.6%), TGP (6.6%)and PCP (6.6%) respectively. The highest enchytraeids (237), termite (1338), earthworm (753) and mite (293) were observed in GAP, while SRNF, TSP and TGP had highest millipede, beetle and collembola abundance respectively. The bacterial feeding nematode was found to be highest in PCP (32), while TSP had the highest fungi feeding nematode (28.6%). The Total Heterotrophic Bacterial and Total Heterotrophic Fungi counts were not significantly different (p>0.05) across the different physiognomies. The concentration of humin and humic acid were highest under SRNF (0.55± 0.02) and TSP (0.31 ± 0.01) soils respectively, while the highest fulvic acid was recorded in soil under TGP (0.18 ± 0.06). Litter carbon content was higher in PCP (54.51± 0.02%) compared to other physiognomies. The highest content of lignin and phenolic acid were observed under PCP (36.51± 0.73%) and TGP (0.58± 0.01%) and TSP (34.05± 0.03%), while C/N and Lignin/N were highest in TGP. The soil pH in all the physiognomies was slightly acidic (5.83 ± 0.296-6.23 ± 0.067). Bulk density was significantly (p>0.05) higher in TGP (1.21± .015 gcm-3) relative to other physiognomies. There was seasonal variation in SOC accumulation, while highest value of SOC (22.65 MgC/ha) was recorded in TSP, the least was recorded in TGP (19.24 MgC/ha). The study concluded thatTerminalia superba (a native tree species) and Pinus caribaea plantation could be considered suitable for an afforestation project aiming to conserve biodiversity and enhance soil organic carbon (SOC) sequestration.