Effects Of Growth Regulators On Florescence And Photosynthetic Characteristics Of Rhododendron Simsii Planch

Rhododendron simsii Planch.is an important ornamental flower.Previous studies have shown that the application of plant growth regulators is a feasible way to regulate florescence.In this study,Rhododendron simsii Planch.was sprayed with three indole acetic acid(IAA),gibberellin(GA3)and naphthalene acetic acid(NAA)at different concentrations and different times.The concentration gradients were 500,1000,1500,2000 and 2500 mg·L-1(fixed for 3 times spray),and the frequency gradients were 1,2 and 3 times(fixed for 1500 mg·L-1).Flowering period was observed after treatment.And LI-6400XT portable photosynthesizer was used to measure the diurnal variation of photosynthesis and light response curve of Rhododendron simsii Planch..The results showed that the effect of three growth regulators on the advance of flowering stage had peak concentration under different concentration treatments.IAA was 2000 mg·L-1,GA3 was 2000 mg·L-1,NAA was 1 500 mg·L-1,which could advance 4.4 days,7.8 days and 2.8 days,respectively.Among them,GA3 with 2000 mg·L-1 concentration had the best effect,and the flowering stages were earlier correspondingly,and the length of florescence and ornamental period was not changed.On the other hand,in the selected concentration range,IAA and GA3 did not show the characteristics of delaying the florescence of Rhododendron simsii Planch.,but the florescence was significantly delayed by 2500 mg·L-1 NAA treatment compared with the control group,which lasted for 4 days,and the flowering stages were shortened accordingly.Under different times of treatment,IAA spraying once,GA3 spraying three times and NAA spraying three times all showed obvious promoting effect.Among them,IAA spraying once had the best effect,the date of initial flowering stage is advanced by 3.8 days.All stages of flowering were advanced correspondingly,and the length of florescence and ornamental period did not change significantly.In comparison with the effects of spraying times on florescence,the treatment results of the three regulators showed no obvious trend.In the follow-up study,we can further explore from the three dimensions of improving spraying times,spraying time and spraying concentration.In terms of diurnal variation of photosynthesis,high concentration of IAA and GA3 significantly increased the net photosynthetic rate and transpiration rate of Rhododendron simsii Planch.,while NAA concentration of 2500 mg·L-1 inhibited it.The effects of three growth regulators on stomatal conductance and intercellular CO2 concentration of Rhododendron simsii Planch.were not significant.Among them,the high concentration of IAA and GA3 could make the stomatal conductance of Rhododendron simsii Planch.reach a higher value in the morning and keep a higher level of intercellular CO2 concentration in the evening.Growth regulators did not significantly change the light use efficiency and water use efficiency of Rhododendron simsii Planch..Similar to the diurnal variation of photosynthesis,high concentration of IAA and GA3 could enhance the ability of Rhododendron simsii Planch.to adapt to weak light,while 2500 mg·L-1 concentration of NAA could inhibit photosynthesis,while the effect of other concentration of NAA was not obvious.