Study On The Photosynthetic Characteristics Of Dahurian Larch (Larix Gmelinii) In Natural Young Growth Stands

With the international advance LI-6400 portable photosynthesis, the author studied the photosynthetic characteristics of Dahurian Larch in natural young growth stands in Great Xinganling Mountains of Inner Mongolia. After four months of observation of the growth season, the author reveals in the thesis the day- and month-dynamic characteristics of the net photosynthetic rate of Dahurian Larches, which are of different ages, densities and stand classes. The author also compared the net photosynthetic rates of the leaves on different-age braches and with the crowns of different layers and directions. In addition, the author analyzed the effects of some ecological factors on net photosynthetic rate as well. The research indicates that the diurnal changes of net photosynthetic rate show not only a double-peak curve but a single-peak curve too. Larches of different ages have different net photosynthetic rate: the photosynthetic capacity of the young ones are bigger than that of the old ones; the stand density do not affect the net photosynthetic rate obviously; as far as the different stand classes are concerned, the diurnal changes of net photosynthetic rate is closely related to the photosynthetic active radiation. For the different layers of the crowns, there are greater ecological factors (illumination intensity, temperature, humidity etc.) on the upper layers than on the lower layers: the CO2 concentration of the lower layers is greater than that of the upper layers, which is indeed an exception; the net photosynthetic rate on the upper layers of the crown is generally greater than that of the lower layers. It showed that the CO2 concentration is not a main factor in the natural changing range of the CO2 concentration. Different directions of the crown have different photosynthetic active radiation, which is generally like exposed to the sun﹥North﹥in the shade of crown. However, the changes of net photosynthetic rate are not quite the same, which is North﹥exposed to the sun﹥in the shade of crown. All of the changes mentioned above are different in the different stages of the growth season. The diurnal changes of net photosynthetic rate show double-peak curve in the early stages while they show double-peak or single-peak curve in the late stages. The net photosynthetic rate of Duhurian Larch will increase with the growing strength of the illumination, but when the temperature is ﹤12℃ or ﹥39℃, the illumination strength will not affect photosynthetic rate. Given the condition of the other ecological factors, the net photosynthetic rate will increase with the increment of CO2 concentration and the light compensation point is in the range from 50 to 90μmolmol-1; during the 6am to 4pm of a day, the light saturation point is about 770 to 1900μmolmol-1. The CO2 concentration in the air dose not have much influence on the net photosynthetic rate when it is between 300~600μmolCO2mol-1.