ISHS Acta Horticulturae 769: XXVII International Horticultural Congress - IHC2006: International Symposium on Asian Plants with Unique Horticultural Potential
STUDY ON DIURNAL VARIATION OF PHOTOSYNTHESIS IN MAGNOLIA GRANDIFLORA L. AND MAGNOLIA DENUDATE DESR. |
| Authors: | Mohua Yang, Zhihui Li, Youan Liu, Liqun Huang, Yan Yang, Fang Geng |
| Keywords: | Magnolia grandiflora, Magnolia denudate, net photosynthetic rate, diurnal variation, stepwise multi-regression |
| Abstract:
The diurnal variations of photosynthesis on Magnolia grandiflora and M. denudate have been studied under the same natural conditions using a Li-6400 portable photosynthesis system in China to provide foundational data on the physiological ecology in Magnolia plants for its introduction, cultivation and design. Samples of 3 leaves were taken from 6 trees each to determine their diurnal characteristics. All data was analyzed using SPSS. The results showed that the curves of diurnal variations of net photosynthetic rate (Pn) on the two plants were different. The diurnal variation of Pn on M. grandiflora was a midday depression pattern and had two peaks. The first peak, which occured in the morning, lasted longer than the second peak, which occured in the afternoon. The stomatal conductance (Cond) and the transpiration rate (Tr) were closely related to photosynthesis, which showed an obvious midday decline while the intercellar CO2 concentration (Ci) was slightly increased, so the mid-depress of Pn on M. grandiflora was mainly caused by non-stomatal limited elements, i.e., photo inhibition and photo respiration. The M. denudate diurnal variations on the Pn curves had a single peak that appeared in the morning with a slow decline lasting into the afternoon. The Tr was correlated to photosynthesis closely by the similar change trends they exhibited while the diurnal variations of Cond was different. The Cond also affected Ci and Tr to some degree. The vapor pressure deficit (Vpd) was attributes to PAR and air temperature. The water utilization efficiency (WUE) in M. grandiflora was higher than that of M. denudate. The analysis of stepwise multi-regression and partial correlation of Pn and other factors showed that the diurnal variation of Pn had closer relations with the elements as Cond, Tr, Vpd, the relative humidity of the air (RH) and PAR, which were the main limiting factors for M. grandiflora and M. denudate. This excludes PAR, which has no obvious relation with M. denudate. | |
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