Plant diversity and microbial activity as a function of soil carbon stocks in selected homegardens in the midland laterites of Kerala

Abstract

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 0.4ha), 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. 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.