Relating photosynthetic performance to leaf greenness in litchi: A comparison among genotypes

Abstract

In this study, leaf greenness (determined with a SPAD meter), photosynthesis, and chlorophyll fluorescence were analyzed on mature sun leaves in different litchi (Litchi chinensis Sonn.) cultivars to obtain an understanding of the relationship between leaf greenness and photosynthetic characteristics. Leaf greenness differed significantly among the 21 cultivars tested and was poorly correlated with N concentration, suggesting variations in leaf greenness among genotypes were unlikely a result of N differences. Four cultivars with different greenness, ‘Heiye’ (HY, SPAD 54–58), ‘Feizixiao’ (FZ, SPAD 49–52), ‘Nuomici’ (NM, SPAD 43–47) and ‘Baili’ (BL, SPAD 35–38) were selected for relating leaf greenness to photosynthesis. SPAD values were highly correlated with chlorophyll concentrations. Cultivars with darker leaves tended to have lower chlorophyll a/chlorophyll b ratios (Ca/Cb) than those with lighter leaves. Chloroplasts in dark green HY and FZ had more appressed lamellae, and denser grana and stroma than light green NM and BL. HY had also a higher maximum photosynthetic rate (Pmax) than the other cultivars tested. Pmax, light saturation point (LSP) and light compensation point (LCP) displayed significant linear correlations with SPAD values. Apparent quantum efficiency (AQE) seemed not related with leaf greenness, while dark respiration rate (Rd) displayed a strong negative correlation with it. Maximal and minimal yields of fluorescence (Fm and Fo) showed good positive correlations with SPAD values, whereas maximal photochemical efficiency of PSII (Fv/Fm) was not significantly different among cultivars and was poorly correlated with SPAD values. Effective quantum yield of photosystem II (ФPSII), photochemical quenching coefficient (qP), and non-photochemical quenching coefficient (qN) were poorly correlated with SPAD values. ФPSII decreased with the increase of light exposure, indicating an increased proportion of closed PSII reaction centers under higher light. The slope of this decrease was the lowest in NM and highest in BL and seemed not to be related to SPAD values. Hence, AQE, Fv/Fm, qP, qN and responsiveness of closure of the PSII reaction center under high light are independent of leaf greenness. Yet, darker green leaves contribute to better light energy capture and conversion, CO2 fixation, and ability to utilize both strong and weak light.