Departmental Seminar at CES on 18 July 2023 at 11:00 am titled "Undertanding Soil Carbon Pools and Fluxes for the Trans-Himalayan Rangelands of Spiti" by Jose Mathew from IISc, Bangalore
Soil contains 2500 Petagrams of Carbon, which is two to three times as much as the Carbon in the atmosphere, or in land vegetation. The soil carbon pool receives organic matter from the land vegetation pool in the form of leaf litter, dead organisms and animal excreta. In turn, it loses carbon dioxide to the atmosphere through microbial respiration. Since the Industrial Revolution, atmospheric carbon dioxide levels have risen by 50% (from 280 to 421 parts per million), and global temperature has risen by about 1.1 degrees. Further, there is concern that rising temperatures may increase soil microbial respiration and hasten the release of carbon to the atmosphere, creating a positive feedback loop. We therefore need to study the rate at which carbon is lost from soil, and how human activities - such as land use patterns and agricultural practices - may alter it. In this thesis, I propose to study how much carbon is present, and how much is respired, from soil in the Spiti valley region of Himachal Pradesh, which is a part of the carbon-rich Trans-Himalayan rangelands. I will also look at how land use, fertilisation and warming affect soil respiration. The first chapter of this thesis will look at what climatic, ecological and anthropogenic factors influence soil respiration. Since soil respiration in different environments depends also on the substrates available, I will review published literature on catabolic response profiling, which measures soil respiration against various metabolic substrates. The second chapter will focus on understanding the spatial and chemical structure of soil pools and fluxes in Spiti. Current soil Carbon models, constructed based on principles of reaction kinetics, do not account for spatial heterogeneity. We plan to measure the amount of Carbon in various soil pools, and to perform lab incubations at different temperatures to understand the sensitivity of their fluxes to temperature. We will also distinguish between the two main soil carbon pools - mineral-associated and particulate organic matter. These pools have different flux rates and spatial distributions, and so would respond differently to changes in land use or temperature. The final chapter will look at how land use affects these various carbon pools. Land grazed by native wildlife in Spiti has been converted to livestock pasture and agricultural fields, and the global fertilisation experiment NutNet maintains plots with various types of fertiliser application. Differences in the magnitude and flux of each carbon pool will be measured for each treatment. This thesis is expected to improve our current understanding of the soil carbon loss by respiration, and to predict how land use change and fertilisation will influence the rate of this loss. This information will be useful in modelling climate change and soil quality, as well as in the making of policies related to land conversion and agricultural practices.