Imperata Grasslands:Carbon Source or Sink?

Imperata grasslands, among the oldest forms of managed village land use, provide rural people with subsistence and monitory benefits. Yet, little is known about their role in global carbon (C) budget under the scenario of changing climate. The present study was carried out in managed Imperata grassland in Cachar district, Assam, North East India. The study was designed to understand whether Imperata grasslands are C source or sink, because they are managed through annual fire practice. We studied (i) organic carbon accumulation rate in the soil, (ii) C input from aboveground biomass (CIAB), (iii) C input from belowground biomass (CIBB) and (iv) Soil CO₂ efflux/soil respiration (R_s) on monthly intervals from October 2013 to September 2014 following standard methods. Later monthly data were merged into four distinct seasons, viz. autumn, winter, summer and rainy season to have a clear vision of seasonal influence on C source/sink status. The study showed highest (2.52 g C m^-2 month^-1) soil organic carbon accumulation during summer season. Highest values for CIAB (14.31 g C m^-2 month^-1), CIBB (30.98 g C m^-2 month^-1) and R_s (31.85 g C m^-2 month^-1) were observed during rainy, autumn and summer seasons respectively. C budget analysis with respect to seasons showed Imperata grasslands act as C source during winter and summer, whereas they serve as sink during autumn and rainy seasons. However, annual C budget (across all the months) showed Imperata grasslands as a net sink of 38.45 g C m^-2 year^-1 (0.40 Mg C ha^-1 year^-1). Further research is needed to develop better management systems to enhance sink capacity of Imperata grasslands.