Estimation of net photosynthetic rate based on in-situ hyperspectral data

Carbon absorption of plant is one of the essential parameters in assessing terrestrial ecosystem functions with respect to global warning. It is, however, not easy to estimate carbon absorption directly on the ground. In this study, an experiment method was designed to estimate the saturated Amax from hyperspectral data in the laboratory and in the field scale. Firstly, we measure the relationship between biochemical concentrations and parameters of "Blackman" photosynthetic rate model. Secondly we measure the relationship between biochemical concentration and hyperspectral characteristics. High-resolution reflectance over a range of 333 -2507nm with resolution of about 1.5-10 nm and net Amax - photon flux density (PFD) were measured respectively by the GER 2600 and Li-6400. Also, chlorophyll a, chlorophyll b, chlorophyll a+b and nitrogen concentration were quantitative analyzed from in situ measurement of cucumber's fresh leaves that were cultivated for different biochemical concentration in a greenhouse chamber. Correlation between saturated Amax and chlorophyll a and nitrogen concentration was r(2)=0.90, and 0.91, respectively. Chlorophyll b didn't show any correlation with saturated Amax Chlorophyll a and nitrogen concentrations were estimated by using the first derivative spectral reflectance (RF') of fresh leaf. RF' at 678.011nm correlated best with chlorophyll a concentration (r(2)=0.81). RF' at 732.122nm correlated best with nitrogen concentration (r(2)=0.86). Finally, net Amax at given PFD was estimated by the photosynthetic rate model. A correlation between the actual net Amax and the estimated net Amax was r(2)=0.74. In this study, both chlorophyll a and nitrogen concentrations show good correlation with saturated Amax.