Organic matter storage in soil: A comparative study across ecosystems

Baidya, Disha (2023) Organic matter storage in soil: A comparative study across ecosystems. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Disha Baidya (18MS078)) Thesis_18MS078.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

Soil organic matter (SOM) formed after the transfer of organic debris derived from above and below-ground biomass is quantitatively estimated using the leaf wax compounds (n-alkanes) and compound specific carbon isotopic ratios (δ¹³C). However, site-specific and source-specific factors may influence the SOM estimates, which may show variation in organic matter (OM) abundance spatially. The factors controlling plant-to-soil biomass signaling is yet to be properly understood and hence sampling sites (1 m × 1 m) were chosen which comprise forest (C₃), grassland (C₄), and mixed (C₃/C₄) ecosystem from the lower-Ganga floodplain. The spatial heterogeneity in the SOM distribution in each ecosystem is well reflected in the total n-alkane concentration and different n-alkane molecular indices such as CPI, LMW/HMW, and ACL. CPI values increases from source vegetation to litter and LMW/HMW values shows a lot of variation in the soil samples of each ecosystem within those small experimental sites suggesting non-uniform assimilation of OM in soil. The mean bulk δ¹³C values of SOM are -27.0±0.7‰, -16.7±0.5‰, and -17.6±0.9‰ in the forest, grassland, and mixed ecosystem respectively. Although the bulk δ¹³C increases (4.7‰) and decreases (-2.6‰) from source to soil sink in the forest and grassland ecosystems respectively, the compound-specific (n-alkane) δ13C values decreases in both forest (-2.6‰) and grassland (-3.4‰) ecosystems from source to soil sink. The mixed ecosystem SOM, however, reflects a combination of the vegetation source type ((C₃/C₄) in both δ¹³C values of bulk and compound-specific n-alkane homologues. The non-uniform distribution of OM and modification in carbon isotopic ratios in soil from the source are mainly attributed in the forest ecosystem by the variable influx of OM from the litter assemblages (twigs, leaves, flowers, fruits, and small fragments). In the grassland ecosystem, organic carbon distribution could be possibly imparted by the earthworm activity, influx of occluded organic carbon from phytoliths and OM supply from below-ground biomass (grassroots). Varied OM distribution in the mixed ecosystem could be due to the restricted fresh organic carbon supply coupled with non-uniform intake of OM by microbes residing in the top surface soil layer. This study shows that intrinsic properties associated with an ecosystem play an essential role in the spatial variation of OM distribution and provides information about the possible pathways or processes involved in the modification of OM stored in soil.

Actions (login required)

View Item