Photosynthetic rate and trace element contents in Cordia dichotoma Forst. f. in summer and winter

XIAO Yu;YANG Hao;HAN Wei-dong;College of Agriculture,Guangdong Ocean University;

Cordia dichotoma Forst.f.;;photosynthetic rate;;diurnal variation;;correlation analysis;;trace elements

【Objective】In this paper,the diurnal variation tendency of the photosynthetic rate and related influencing factors of Cordia dichotoma Forst. f. in winter and summer were studied,and the contents of trace elements in the plant were determined. The results could provide a basis for the artificial cultivation and development of medicinal value of the plant.【Method】The diurnal variation of net photosynthetic rate(P_n)and its related influencing factors[photosynthetic active radiation(PAR)and andstomatal conductance(G_s)]were measured by LCi-SD portable photosynthetic instrument.The contents of Cu,Fe,Zn,Mn,Cr,Se and Co in annual branches,biennial branches and leaves of C. dichotoma were determined by inductively coupled plasma atomic emission spectrometry(ICP-MS).【Result】The diurnal peak value of P_n and transpiration rate(T_r)in winter were 8.62 μmol/(m~2·s)and 3.86 mmol/(m~2·s)at 10:00 am,respectively. In summer,the peak of P_n and Troccurred at 10:00 am,maximum P_nvalue was 8.60 μmol/(m~2·s),maximum T_rvalue was5.17 mmol/(m~2·s),midday depression phenomenon occurred at noon,and their sub-peak value were 5.31 μmol/(m~2·s)and3.68 mmol/(m~2·s)at 14:00 pm,respectively. PAR peak occurred at 10:00 am and 12:00 am respectively in winter and summer[1027 and 1685 μmol/(m~2·s)]. In both winter and summer,G_sin the morning was higher than that in the afternoon,showed a downward trend. The results of correlation analysis showed that the P_nof C. dichotomain winter and summer were extremely significant positively correlated with T_r(P<0.01,the same below),T_rsignificantly positively correlated with G_s and relative humidity(RH)(P<0.05,the same below). In winter,P_n was extremely positively correlated with PAR,and significantly positively correlated with G_s,and had no significant correlation with intercellular CO_2 concentration(C_i),RH and atmospheric CO_2 concentration(C_a)(P>0.05,the same below). T_r was significantly positively correlated with PAR,and G_swas significantly correlated with RH. RH was significant positive correlated with PAR. In summer,P_n was extremely positively correlated with G_s and RH,and there was no significant correlation between PAR and P_n,between C_i and P_n,between C_a and P_n,T_r was significantly correlated with G_s and RH,RH was significantly positively correlated with G_s. C. Dichotoma contained abundant Fe,Zn and Mn elements,the contents of Fe,Zn and Mn in the leaves were the highest(133.19,13.68 and 76.3 mg/kg respectively),which was significantly higher than that of Cr,Se and Co;and the contents of Cr,Se and Co were all lower than 0.40 mg/kg. The concentration of Fe,Zn,Mn,Cr,Se and Co elements in the C. dichotomas howed as:leaves>annual branches>biennial branches,while Cu accumulation trend showed as:annual branches>leaves>biennial branches.【Conclusion】The diurnal variations of P_n and T_r in C. dichotoma in winter represent a single-peak curve,and T_r,PAR and G_s are the main factors to affect the diurnal variations of P_n in winter. The diurnal variations of P_n and Trin C. dichotoma in summer represented a bimodal curve,and T_r,RH and G_s are the main factors to affect the diurnal variations of P_n in summer. The contents of trace elements such as Fe,Mn and Zn in C. dichotoma are high,which is consistent with the characteristics of high trace element content in traditional Chinese medicine commonly used in treating rheumatism.