Abstract:
Eucalyptus is one of the most commonly established plantation forests in the world.
However, they emit α-pinene which is known to have allelopathic characteristics that
suppress the microbial activities. Therefore, organic matter decomposition rates could be
affected by α-pinene in plantation soil which may lead to higher carbon sequestration in
soil. Further emission of α-pinene could be affected by the stand age of the plantation. To
investigate these the present study of the relationship between soil α-pinene content,
microorganisms, and organic carbon (OC) content in 30,13 and 4 -year-old Eucalyptus
grandis plantations were studied. As the control plantation, an adjacent Patana grassland
(previous land-use before afforestation) was used. Three plots (20 × 20 m) were
established within each site and 12 soil samples from each site were collected from 30 cm
depth. Soil OC content was measured using the Walkley-Black method and microbial
counts were taken using the pour plate method. The α-pinene in soil samples were
analyzed using GC-MS. The highest OC content was observed in 30-year-old E.
grandis plantation (3327.09 Kg) and interestingly the lowest bacterial and fungal
populations (2.15 x 103 CFU mL-1
and 1.07 x 103 CFU mL-1
) and the highest α-pinene
content ((0.47% ± 0.09) were recorded in the same. There were significant positive
relationships between stand age and α- pinene and OC in soil (Pearson correlation value
0.982, 0.913; p < 0.05). The OC had shown a significant negative relationship with the
bacterial and fungal population (Person correlation 0.669,0.653, p < 0.05). The results
showed that with the stand age, α-pinene content in soil increases and affects negatively
on microbial populations which results in higher OC content in the soil. Therefore, we
can conclude that as Eucalyptus grandis plantations ages they support soil carbon
sequestration and the findings could be useful in promoting the minimizing of
atmospheric CO2 level.
Keywords: Eucalyptus grandis, Stand age, α-pinene, Organic carbon, Carbon
sequestration
