Light-saturated photosynthetic rate in high-nitrogen rice (Oryza sativa L.) leaves is related to chloroplastic CO2 concentration

Abstract

To identify the effect of nitrogen (N) nutrition on photosynthetic efficiency and mesophyll conductance of rice seedlings (Oryza sativa L., cv. 'Shanyou 63' hybrid indica China), hydroponic experiments with different concentrations of N were conducted in a greenhouse. Although leaf N concentration on a dry mass basis increased with increasing supply of N, no significant differences in seedling biomass were observed. A higher light-saturated CO(2) assimilation rate (A) with a high concentration of supplied N was associated with a higher carboxylation efficiency (CE), but not a higher apparent quantum yield (alpha). Based on classic photosynthetic models, both the Rubisco content and the ribulose bisphosphate (RuBP) regeneration rate were sufficient for light-saturated photosynthesis in rice seedlings; the estimated chloroplastic CO(2) concentration (C(c)) and mesophyll conductance (g(m)) demonstrated that a low C(c) was the ultimate limiting factor to photosynthetic efficiency with a higher N supply. Due to a greater chloroplast size (i.e. a shorter distance to the plasma membrane) with a higher supply of N, the CO(2) transport resistance in the liquid phase (g(liq)) in high-N leaves was lower than that in low-N leaves, which resulted in higher g(m) and C(c) in high-N leaves. Although CE(A/Ci) was higher with a high supply of N, there were no differences in CE(A/Cc) between plants grown with different concentrations of N, indicating that the carboxylation capacity of Rubisco between plants grown at different N concentrations was constant. The enhanced photosynthetic rate with supply of a high N concentration was attributed to a higher CO(2) concentration in the chloroplasts, related to a higher mesophyll conductance due to an increased chloroplast size.

Water absorption is affected by the nitrogen supply to rice plants

“…Water absorption, photosynthetic rate and WUE are increased under high N supply Plant growth or crop productivity is always correlated with the N supply, and high N supply can improve photosynthesis and the shoot dry weight but inhibit root growth, resulting in a decreased root/shoot ratio (Linkohr et al 2002;Tian et al 2005;Li et al 2009). In the present study, we observed similar patterns in both rice cultivars, with an increased shoot weight and lower root/shoot ratio under high N supply ( Table 2).…”

“…After equilibration to a steady state, the gas exchange parameters, including light-saturated photosynthetic rate (A), stomatal conductance (g s ), intercellular CO 2 concentration (C i ) and transpiration rate (T r ), were recorded. More details about measurement can be found in our previous studies or other studies (Long et al 1996;Long and Bernacchi 2003;Li et al 2009). Water use efficiency (WUE) was calculated as the ratio of A to T r (A/T r ), and the stomata limitation (L s ) was calculated from the equation of L s = (A i -A)/A i (Farquhar and Sharkey 1982), where A i is the light-saturated photosynthetic rate when C i was 390 μmol·mol −1 .…”

Coordination of Leaf Photosynthesis, Transpiration, and Structural Traits in Rice and Wild Relatives (Genus Oryza)

“…The combined leaf gas-exchange and chlorophyll fluorescence data from the A-C i response curves were used to calculate g m (mol CO 2 m 22 s 21 bar 21 CO 2 ) using the variable J method (Di Marco et al, 1990;Harley et al, 1992), applied as in Li et al (2009). According to Genty et al (1989), the total electron transport rate (J T ; mmol e 2 m 22 s 21 ) was determined as…”

“…The default value taken for a leaf was 0.85 (Li et al, 2009) and that for b was 0.45, assuming that approximately 45% of the photons are absorbed by PSII (Laisk et al, 2006). f PSII was computed as…”

Partial nitrate nutrition amends photosynthetic characteristics in rice (Oryza sativa L. var. japonica) differing in nitrogen use efficiency

“…It is well known that the ambient CO 2 passing to a carboxylation site must pass through a series of gas (air) and liquid phases (mesophyll cells) (Evans and Caemmerer 1996;Aalto and Juurola 2002), and g m is mainly determined by its conductance in the liquid phase (Long and Bernacchi 2003). Therefore, g m is partly dependent on leaf anatomy, i.e., the distance between the intercellular space and the catalytic site, chloroplast volume, mesophyll cell size and leaf thickness (Evans and Caemmerer 1996;Li et al 2009). This suggests that a higher g m under PNN-than under NH 4…”