Quantification and depth distribution analysis of carbon, nitrogen, and microbiomes in soils of Miyawaki forests in Kerala

Abstract

A study entitled “Quantification and depth distribution analysis of carbon, nitrogen and microbiomes in soils of Miyawaki forests in Kerala” was undertaken with the objectives of quantifying the levels of carbon and nitrogen in Miyawaki forest soils in Kerala, analysing the effect of increasing carbon sinks in achieving carbon sequestration and to investigate abundance of microbiomes in these soils. A preliminary survey was conducted to identify the locations where Miyawaki forests were established and is existent in the entire Kerala state. Altogether 58 Miyawaki forests have been established till date in Kerala. Five well established and oldest Miyawaki forests out of these were selected for further study. A survey was conducted during December 2023 in the selected study area and 20 georeferenced soil samples were collected from surface and subsurface layers from five Miyawaki forest and nearby undisturbed plots. The selected sites were located at Puliyarakonam, Peyad, Kanakakkunnu, Vilappilsala and Chalai. The soil samples were characterized for selected physical, chemical and biological attributes, carbon pools and nitrogen fractions. Various carbon indices like carbon pool index (CPI), lability index (CLI) and management index (CMI) were worked out. The carbon sequestration potential of each Miyawaki forest was also calculated. A metagenomic analysis of one sample each from Miyawaki forest and undisturbed plot was also conducted. A minimum data set (MDS) of indicators to assess soil quality index (SQI) was set up using Principal component analysis (PCA). The spatial variation in temperature within the confines of the Miyawaki forest as well as outside were recorded for a period of three months from March 2024 to May 2024 at two locations, viz., Puliyarakonam and Vilappilsala. The soils under study belong to sandy clay loam. The bulk density was found to be the lowest in the Miyawaki forest (1.15 Mg m-3) than the control. Other physical properties like water holding capacity (60.28%), soil moisture content (34.83%) and water stable aggregates (88.48%) were found to be higher in the surface soils of Miyawaki forest than the control plots. The soil acidity (pH 5.40) and EC (0.059 dSm-1) were found to be more in the Miyawaki forest. Soil biological properties like soil enzyme dehydrogenase activity (80.20 mg TPF g-1 soil 24 h-1), bacterial density (7.573 log cfu g-1), fungal count (5.507 log cfu g-1) and actinobacterial count (4.909 log cfu g-1) were also found to be higher in Miyawaki forest and decreased with depth. A higher total organic carbon of 10.31% was recorded in Miyawaki forest, which was observed to decrease with depth. Other carbon fractions like water soluble carbon (21.21 mg kg-1), labile carbon (4.51 mg g-1), particulate organic carbon (1.03%) and microbial biomass carbon (152.69 mg kg-1) were also observed to be higher in the Miyawaki forest when compared to the control plots. Total nitrogen content (0.36%) and available nitrogen (264.26 kg ha-1) was highest in Miyawaki forest. A higher C:N ratio was observed in Miyawaki forest (28.77) and was observed to increase with depth. The soil organic carbon stock (38.08 Mg ha-1) and carbon sequestration rates 9.05 Mg ha-1yr-1 were also found higher in Miyawaki forest soils compared to the control plots. A temperature difference up to 3.93°C and 4.21°C was observed between the mean maximum temperature between the inside and outside of Miyawaki forest during the summer months in Puliyarakonam and Vilappilsala respectively. No significant difference was observed for CPI, CLI, CMI, and SQI. The study on Miyawaki forests in Kerala reveal their substantial contribution to soil carbon storage and nutrient enrichment. The findings indicate that these forests not only enhance soil quality through increased organic carbon and nitrogen levels but also support a diverse microbiome, which is vital for soil health. Miyawaki forests in Kerala exhibit lower bulk density and higher water holding capacity compared to control plots, indicating improved soil structure and moisture retention. Additionally, the significant temperature regulation observed within the forests highlights their role in moderating local microclimates. Overall, the results underscore the potential of Miyawaki forests as effective carbon sinks and valuable ecological assets, advocating for their expansion as a strategy for carbon sequestration and soil restoration in the region. Further research is recommended to explore the long-term ecological impacts and management practices that can optimize these benefits.