The Research On The Photosynthetic Characteristics Of Different Stand Ages Of Alnus Cremastogyme

With the international advance LI-6400 portable photosynthesis,the author studied the photosynthetic characteristics of two different stand age of Alnus cremastogyme in northern Hunan. Exploring the photosynthetic characteristics of Alnus cremastogyme Burk would not only make for understanding its photosynthetic ability and its response to changing environmental factors,also provide decision-making reference for different stand age breeding,introduction,cultivation and commerical appliance. The major results are shown as follow:The diurnal variation of net photosynthetic rate (Pn) between the upper and lower crown of three years old Alnus cremastogyme Burk showed as single peak curve in April,and the peak were appeared at 12:00 p.m.; Then showed double-peak curve in June and September,the supreme peak appeared at 8:00 a.m.,and the secondry peak at 14:00 p.m.There was two differ curves in October,the upper leaves showed double-peak curve type,and the lower leaves showed single peak at 12:00 p.m.The diurnal variation of net photosynthetic rate (Pn) between the upper and lower crown of eight years old Alnus cremastogyme Burk showed as double-peak curve in April and October, the supreme peak appeared at 8:00 a.m.to 10:00a.m.,and the secondry peak at 16:00 p.m.; Then showed single peak curve in June and September,and the peak appeared at 8:00 a.m.to 10:00a.m.and 12:00p.m..The seasonal variation of the mean monthly Pn values of two stand age plant in the upper and lower crown,respectively,revealed a single peak curve.And the peak were all appeared at June,the data of upper leaves were at 9.71μmol·m-2·s-1 and 10.01μmol·m-2·s-1; and and lower one was at 8.69μmol·m-2·s-1 and 8.29μmol·m-2·s-1.There was the lowest Pn in October of two stand age, especially in the lower side,has the negative value—0.07μmol·m-2·s-1.Highly significant difference of Pn was observed between the upper and lower crown or different monthly,or different stand age (p<0.017),respectively. The mean difference of stand age and month was significance at the 5% level. Likewise, Highly significant difference of Pn was observed between the two stand age (p=0.018),the middle one(6.0225) is obvious higher than the younger plants(4.6501) of Pn,showed it was have a higher photosynthetic ability, especially at June.The order of the mean monthly Pn values from high to low to be:June (9.1852)> April(7.1236)> September (3.4590)> October (1.6103); The difference between the upper and lower crown of two different stand age was not obvious(p>0.159).