MSc

In woody ecosystems, understanding the relationship between plant diversity,
microbial activity, and carbon sequestration is crucial, particularly in the context of
addressing climate change and promoting sustainable land management. Homegardens
are traditional land use systems that evolved through the generation of crop
intensification. Apart from the livelihood security and economic advantages, the
homegardens play a vital role in delivering many ecosystem services. In this context,
addressing the role of homegardens in terms of plant diversity, microbial activity, and
carbon sequestration is essential for ascertaining their potential contributions to
sustainable and environmentally friendly practices. With this background, the study
was carried out to investigate the carbon flux in the soil aggregates and their functional
relation with plant diversity and microbial activity in selected home gardens in the
midland laterites at the College of Forestry during the period 2022-23. The research
was conducted under five land use systems which include Small Homegarden (SHG
<0.2ha), a Medium Homegarden (MHG 0.2-0.4ha), a Large Homegarden (LHG
>0.4ha), a Forest area (Fo) and Treeless open area (TrO) of the Agro Ecological Unit
(North central laterite) of Kerala.
The plant diversity of the various homegardens revealed that the Simpson index
was high in the forest (0.90) and SHG (0.87) followed by MHG and relatively less in
LHG (0.63). The result of the physico-chemical properties of the soil revealed that the
bulk density was lower in the surface soil and increased with depth. The Mean Weight
Diameter (MWD) indicated the structural stability of soil which depicted that the forest
had MWD of 0.74 mm followed MHG (0.68mm) and SHG (0.63 mm) compared to an
open area (0.57 mm). The available nutrient distribution in the land use systems showed
a variable trend with available nitrogen and potassium higher in the forest followed by
SHG due to high plant diversity and associated litter and root dynamics. The available
phosphorus was higher in LHG and MHG compared to forest and SHG.
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Soil organic carbon per cent in the five depths under the landuse systems ranged
from 3.78 to 0.09 per cent and depicted a significant difference between all the land
use systems, greatly in the 0-20 cm depth, where forest reported high SOC followed by
SHG. The SOC stock (Mg C ha-1) under different land use systems followed a trend of
forest (202.21) > SHG (157.62) > MHG (135.79) > LHG (119.60) >TrO (24.29).
Macroaggregates in the different land use systems were reported to have high carbon
storage especially forest and SHGs compared to microaggregates or clay and slit
fractions. The microbial studies of various land use systems indicated considerable
variability. The bacterial populations were higher than actinomycetes and fungi in the
different land use systems. Among the land use systems, forest had the highest
microbial count and the bacterial and fungal population was on par with SHG. The
seasonal variation of enzyme activities revealed higher dehydrogenase activity in forest
followed by SHG. The microbial biomass Carbon (MBC) in the three homegardens
was relatively good and on par with the forest.
A random forest regression model was developed to understand the most
important variable affecting soil carbon stocks and the result revealed that C: N ratio,
followed by the Simpson index, clay and silt carbon influence the carbon stock. The
hierarchical cluster analysis grouped the land uses into four clusters based on the
Euclidian distance and average linkage method. The MHG and LHG were grouped into
one cluster because of their similarity and all other land use remained as independent
clusters. The SHG mimics forest, by the resemblance in numerous aspects, such as
microbial activity, soil carbon stock, MBC, and enzyme activity. Thus, we can conclude
that although SHG offer specific advantages due to the diverse plant species, efficient
resource utilization and space optimisation, the overall sustainability and carbon
sequestration potential of other homegardens classes can be improved with effective
management practices. Homegardens can play a crucial role as a nature-based solution
to mitigate climate change through various mechanisms that contribute to carbon
sequestration, biodiversity conservation, and sustainable land management.