Relationship between photosynthetic CO2 uptake rate and electron transport rate in two C4 perennial grasses under different nitrogen fertilization, light and temperature conditions

Abstract

We examined the feasibility of using chlorophyll fluorescence to estimate CO2 exchange (A) of C4 perennial grasses under different environmental as well as physiologic conditions using Pennisetum purpureum and Miscanthus floridulus, capable of year-round growth, to determine the association of electron transport rate (ETR) and A. The grasses were fertilized with three levels of nitrogen, and measurement involved the top two fully expanded leaves, with chlorophyll content 0.18–0.55 g m−2. Chlorophyll fluorescence, CO2 and H2O exchange were measured simultaneously at four seasonal temperatures (30–15 °C, September–January), six levels of photosynthetic photon flux density (PPFD) (0–2,000 μmol m−2 s−1) and two levels of relative humidity [60 % (15–30 °C) and 40 % (30 °C alone)]. Variables were recorded when A was stable. Most leaves with high chlorophyll content showed high A at the same PPFD and seasonal temperature. Despite a broad range of A obtained because of both stomatal and non-stomatal factors, ETR was still highly correlated linearly with net photosynthetic rates, when combining data for the same species for analysis. Thus, ETR could be used to assess the dynamic A of C4 perennial species through different seasons, even under varied light intensity, seasonal temperature, humidity, nitrogen fertilization and phenological stage.