The effects of sesame/peanut intercropping on photosynthetic fluorescence characteristics in functional leaf of sesame.

Abstract

To unravel functional leaf photosynthetic mechanisms underlying enhanced yield of sesame in sesame/peanut intercropping, a field experiment was carried out in 2017 and 2018 with four treatments including (1) three-row sesame intercropped with six-row peanut (IC 3:6), (2) two-row sesame intercropped with four-row peanut (IC 2:4), (3) sole cropped sesame (SS), and (4) sole cropped peanut (SP). We measured the parameters of gas exchange, characteristics of photosynthetic response curve to light and CO2, and characteristics of chlorophyll rapid fluorescence induction kinetic curves of the functional leaves of sesame. The results showed that the partial land equivalent ratio of intercropped sesame was greater than 1/3. The light saturation point (Isat), maxi-mum net photosynthetic rate (Pn max), maximum electron transport rate (Jmax), triose phosphate utilization rate (TPU), maximum carboxylation rate of Rubisco (Vc max) were increased significantly under intercropping. Further, absorption energy flux per CS (ABS/CSo), trapping energy flux per CS (TRo/CSo), number of active reaction centers per CS (RC/CSm), and electron transport flux per CS (ETo/CSo) in intercropped treatments were enhanced compared to that under sesame monoculture. However, the ratio between variable fluorescence Fk to amplitude Fj-Fo (Wk) and ratio between variable fluorescence Fj to amplitude Fp-Fo (Vj) in functional leaves of intercropped sesame were significantly decreased. The efficiency of converting light energy into electricity of PS2 reaction center (Ψo), electron transfer efficiency from PS2 to end acceptor of PS1 (ΨRo), electron transfer efficiency of the electron transport chain (δR), PS1 photochemical activity, and the coordination between PS2 and PS1 in functional leaves of intercropped sesame were increased. The net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), Pn max, Jmax, Vc max, TPU, Ψo, ΨRo and δR were significantly higher in IC 3:6 than those in IC 2:4. We conclude that intercropping improves net photosynthetic rate and yield of sesame by increasing light absorption, electronic transmission, activity of PS2 donator/receptor sides, and CO2 fixation, with stronger effects in IC 3:6 than IC 2:4.