The Effect Of Ringing On Senescence Of Citrus Plant And Its Mechanism

Ringing and girdling are common regulatory measures used to promote flowering and retain fruit in citrus production.The application of ringing and girdling in southern China is more common than that in other regions,causing leaf etiolation and senescence were more serious and the growing years of citrus was much shorter than that in other regions.It is necessary to study the mechanisms of damage and premature senescence induced by ringing and girdling treatments in citrus.The 3-year-old ?Anliu? orange grafted on Honglimeng and 8-year-old ?Anliu? orange grafted on Trifoliate orange were used as experimental materials at the first physiological drop period in 2015 and 2016,and the treatments were as follows :(1)ringing once;(2)ringing twice(ringing again after fifteen days);(3)spiral girdling(the width of girdling was 2.5 ㎜);(4)control.The effects of ringing and girdling on the growth of summer shoot and autumn shoot were investigated.The photosynthetic performance,mineral element content,antioxidant system,osmotic adjustment substance and phytohormone content of leaves after ringing and girdling treatments were determined.The main results were as follows:(1)The effect of ringing and girdling treatments on summer shoot and autumn shoot of ?Anliu? orange was investigated.The results showed that the effects of ringing and girdling on the growth of summer shoot were slight,and only the girdling treatment significantly reduced the length of summer shoot.The effect of girdling on the growth of autumn shoot was significant.Ringing once treatment reduced the length of autumn shoot by 29.9% compared with the control,while girdling treatment reduced the number and diameter of autumn shoot by 45.7% and 15.4%,respectively.(2)The results showed that ringing and girdling decreased the chlorophyll relative content(SPAD),net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs)and intercellular CO2 concentration(Ci)of the leaves with different degrees at 30 d after treatments.Girdling treatment had a long-term impact on SPAD and Pn with significantly decreased values compared with the control between 30 d and 210 d after treatment.The impact of ringing twice treatment on photosynthetic performance was significant before 90 d after treatment.Ringing once treatment had a little effect on photosynthetic performance of ?Anliu? orange.(3)The effects of ringing and girdling on N content in leaves were significant.Among all treatments,ringing twice treatment had the greatest effect on P content,which was reduced by 25.9% compared with the control at 30 d after treatment.Girdling significantly decreased leaf K and Mg content,with the Mg content decreased by 36.4% at 30 d after treatment and K content decreased by 28.9% at 120 d after treatment compared with the control.Both ringing and girdling treatments decreased the N,P,K and Mg contents in leaves of ?Anliu? orange with different degrees.But all treatments had no significant effect on the Ca content of the leaves.(4)The activities of antioxidant enzymes(SOD,POD and CAT)in the leaves of ?Anliu? orange were improved between 30 d and 150 d after ringing and girdling;The contents of antioxidant compounds(GSH and As A)in leaves were significantly decreased at 30 d after treatment,then began rising to a peak and returned to a normal state slowly at last.The MDA content was increased in all treatments,and ringing twice and girdling treatment significantly increased it compared with the control.The enzymatic and nonenzymatic oxidation reactions were enhanced by ringing and girdling treatment,moreover,the impacts of ringing twice and girdling treatment were stronger than ringing once treatment.Both pot and field experiments shared a similar trend.(5)The overall level of proline(Pro)content in the pot experiment was significantly higher than that in the field experiment.Ringing and girdling treatments significantly reduced pro content in the leaves of ?Anliu? orange between 30 d and 180 d after treatment.Girdling treatment,in which the pro content showed a great fluctuation,had the most significant effect,followed by ringing twice treatment and ringing once treatment.(6)The effects of ringing and girdling on ABA content in the leaves of ?Anliu? orange in pot experiment were more significant than that in field experiment.Girdling treatment significantly increased the ABA content in leaves compared with the control with 2-fold in pot experiment and 2.2-fold in field experiment at 60 d after treatment.However,the ABA content of ringing twice treatment was slightly lower than that of girdling treatment.