A comparative study of photosynthetic characteristics between Pennisetum purpureum × P.americanum cv. Reyan No.4 and Miscanthus floridulus

Objective The purpose of this study was to obtain high quality raw materials for producing biofuels.

Method Diurnal variation of photosynthetic characteristics of Pennisetum purpureum×P. americanum cv. Reyan No.4 and Miscanthus floridulus was studied and the correlation between net photosynthetic rate and major impact factors was analyzed using the LI-6400 portable photosynthesis analyzer in the field.

Result and conclusion The results showed that diurnal variation of the net photosynthetic rate (Pn) of 'Reyan No.4' and M. floridulus showed a "single peak", with no "midday depression" phenomenon. Pn of 'Reyan No.4' (25.45 μmol·m^-2·s^-1) was slightly higher than that of M. floridulus (25.08 μmol·m^-2·s^-1). Transpiration rate (Tr), water use efficiency (WUE), light use efficiency (LUE) and stomatal conductance (Gs) were similar to Pn and reached the maximum at about 13:00. Tr, LUE and Gs of 'Reyan No.4' were slightly higher than those of M. floridulus. Diurnal variation of stomatal limitation value (Ls) for both grasses was bell-shaped, reaching the highest value (0.86 μmol·m^-2·s^-1) at about 11:00 and the lowest in the early morning and late afternoon, but diurnal variation of intercellular CO₂ mole fraction (x_i) was the opposite. Pn of two grasses was negatively correlated with atmospheric CO₂ mole fraction (x_a) (P < 0.05), and positively correlated with relative air humidity (RH) and Gs (P < 0.05), respectively. These results indicate 'Reyan No.4' has a stronger photosynthetic capacity than M. floridulus.