| The effects of photoperiod and photon flux ratios of red?R?and blue?B?light?R:B ratios?on the growth of tomato and pepper seedlings were studied.The previous studies have shown that tomatoes,being a photoperiod-sensitive species,can not improve photosynthetic products by cultivating under continuous light?CL?,while pepper,being a non-photoperiod-sensitive species,can adapt to CL.In this research,tomato and pepper seedlings were grown with 58±1 ?mol·m-2·s-1 light intensity under a photoperiod?light/dark,L/D?of 14/10 h?P24?,7/5 h?P12?or 3.5/2.5 h?P6?,each combined with a different R:B ratio,i.e.,7RB or RB.With the same day light integral?DLI?,tomato and pepper seedlings responded to different L/D rhythm and the interaction between photoperiods and R:B ratios,which was observed and explored.The measurements included the plant morphology,chlorophyll content,photosynthesis and chlorophyll fluorescence.It can put forward to finding a new direction to efficiently cultivate vegetable seedlings by the artificial light environment.The results are as follows:1.The results showed that the short photoperiods?P6 and P12?had a significant effect on the chlorophyll synthesis of tomato seedlings.Tomato seedlings showed the total chlorophyll a+b contents of P24 was 192.2 % of P6 and it was also 160.7 % of P12.The growth and photosynthetic characteristics of P6 and P12 were significantly decreased due to prohibit chlorophyll synthesis.There was no significant difference between 7RB and RB.The growth of seedlings of P24-7RB and P24-RB was healthy and there was no significant difference in morphology and chlorophyll contents.However,the net photosynthetic rate?Pn?and stomatal conductance?Gs?of P24-RB were significantly higher than those of P24-7RB.Appropriate increase of the proportion of blue light is beneficial to the photosynthesis of tomato seedlings.2.The effects of different photoperiods and R:B ratios of older tomato seedlings showed that the adaptability of P6 and P12 was enhanced when the tomato plants entered the mature stage.The photosynthetic system II quantum yield??PSII?and electron transfer rate?ETR?decreased firstly and then decreased under the condition of no significant change in the maximum photochemical efficiency?Fv / Fm?of photosynthetic system II in the first 15 days.On the contrary,non-photochemical quenching?NPQ?showed the opposite trends.It indicated that the tomato plants had undergone the adaptation process of special light environment.However,the photosynthetic characteristics and chlorophyll fluorescence parameters of P6 and P12 plants were significantly decreased after 15 days because of the low growth of tomato plants.At 25 d of the research,the dry mass of P24-RB was the highest,while the dry weight of P6-RB,P12-7RB and P12-RB was lower and there was no significant difference.P24 treatment of chlorophyll a + b contents and chlorophyll a / b were significantly higher than P6 and P12 treatment.Also,there was no significant difference between 7RB and RB.The net photosynthetic rates?Pn?of P24-RB and P12-RB were significantly higher than those of P24-7RB and P12-7RB,while P24-RB stomatal conductance?Gs?was significantly higher than that of P24-7RB.Fv / Fm,?PSII and ETR of P24 treatments were significantly higher than those of P6 and P12 treatments.NPQ of P24 was significantly lower than those of P6 and P12 treatment.3.The results showed that the pepper seedlings under P12-7RB had the highest dry mass?0.544 g?and the total leaf area?160.174 cm2?,which was 125.9 % of P24-7RB.The relative growth rate?RGR?of P6-RB was 0.0534 mg·g-1·d-1,the leaf area ratio?LAR?was 380.496 cm 2·g-1 and the leaf weight ratio?LWR?was 0.658 mg·g-1.RGR of P6-RB was 156.1 % of P24-RB and the specific leaf area?SLA?of P6-RB was 123.6 % of P24-RB.Although there was no significant difference in Pn,Gs and Tr between P6-RB and P24-RB,the growth of pepper seedlings of P6-RB was higher ?PSII(0.675 mol·m-2·s-1)and lower NPQ(0.166 ?mol·mol-1).In addition,seedlings treated with RB had significantly better photosynthetic performance compared with seedlings treated with 7RB.There was no significant difference in chlorophyll a + b contents between P6 and P12 and P24 being normal photoperiod.In summary,the research proved that the difference from the cycles of light period and dark period?P6 circulating 3 times within 24 h,P12 circulating twice within 24 h and P24 circulating once within 24 h?can affect the biosynthesis of chlorophyll in tomato seedlings with the same DLI.Growth of tomato seedling age will weaken the influence of changes of light and dark rhythm,whereas tomato plant of P6 and P12 had lower low light intensity tolerance compared with P24 treatment.On the other hand,P6 and P12 can improve the growth and development of pepper seedlings.P12-RB was beneficial to the accumulation of biomass,while P6-RB was favorable for chloroplast development and improved photosynthesis under low light intensity.The R:B ratios had a significant effect on the low light environment to cultivating seedlings.The growth of the seedlings was promoted by RB. |
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