MEASUREMENT AND SCALING OF CARBON DIOXIDE (CO2) EXCHANGE IN WHEAT USING FLUX-TOWER AND REMOTE SENSING

The present study investigates the characteristics of CO2 exchange (photosynthesis and respiration) over agricultural site dominated by wheat crop and their relationship with ecosystem parameters from MODIS. Eddy covariance measurements of CO2 and H2O exchanges was carried out at 10Hz interval and fluxes of CO2 were computed at half-hourly time steps. The net ecosystem exchange (NEE) was partitioned into gross primary productivity (GPP) and ecosystem respiration (Re) and integrated daily to derive seasonal course of CO2 exchange over wheat. Diurnal pattern in Net ecosystem exchange (NEE) reveals negative NEE during day-time representing CO2 uptake and positive during night as release of CO2. The amplitude of the diurnal variation in NEE increased with growth of wheat and reached its peak around the anthesis stage. The mid-day uptake during this stage was around 1.15 mg CO2 m-2 s-1 and night-time release was around 0.15 mg CO2 m-2 s-1. Large daily GPP above 30 g CO2 m-2 d-1 continued until mid of anthesis stage (15 march) and decline rapidly during maturity stage. Linear and non-linear least square regression procedures were employed to develop phenomenological models and empirical fits between flux tower based GPP and NEE with satellite derived variables and environmental parameters. Enhanced vegetation index was found significantly related to both GPP and NEE. However, NDVI showed little less significant relationship with both GPP and NEE. Furthemore, temperature-greenness model combining scaled EVI and LST was parameterized to estimate daily GPP over dominantly wheat crop site. (R2 = 0.77). Multi-variate analysis shows that inclusion of LST or air temperature with EVI improved variance explained in daily NEE and GPP