The Research On Photosynthesis And Moisture Physiology Characteristic Of Populus Euphratica In Ejina

This research made use of the open gas exchange system, LI-6400 Portable Photosynthesis System, the HR-33T Dew Point Microvokmeter and the Sap Flow System were carried on the research on natural Populus euphratica's photosynthetic and moisture physiology characteristic in Ejina. The results showed that: (1) The daily course curve of Populus euphratica photosynthetic rate (Pn) and transpiration rate (E) can be divided into two types, which are single-peak curve and two peaks curve, and they have typical lunch break phenomenon . Related coefficient of main influence factors and Pn from big to small in proper order is PAR, Tl, RH, Ci, Ta, Gs, related coefficient and E from big to small in proper order is Gs, PAR, Tl, RH, Ta, VPDL. (2) The photosynthetic rate of Populus euphratica and water use efficiency (WUE) seasonal changes both are July> May> September, the transpiration rate seasonal changes has no obvious rules. The photosynthetic rate is low because of the chlorophyll content of leaf is low in earlier stage; The photosynthetic rate descend gradually because of the decrepitude of the leaf. The water use efficiency is relevant to the photosynthetic rate and the transpiration rate. The luminous strength and atmosphere temperatures of July both accelerate photosynthesis highly ,the humidity of atmosphere is low and cause the pore close, the transpiration rate descend to cause the water use efficiency increase remarkably. (3) The Populus euphratica's water potential daily course presents the single peak curve, the water potential value is the tallest in dawn, the predawn water potential from big to small for sapling > robust tree> overgrown tree, which explains that the water uptake ability of overgrown tree is the strongest, the sapling's is the lowest. (4) On clearing sky day in growing period, flow velocity was mono-peak curve Populus euphratica in a day. And difference of flow velocity between Populus euphratica with different DBH was not obvious in May, while it was obvious of 15 cm>28 cm>60 cm (DBH) in August. The sap flow velocity of Populus euphratica with different DBH had different seasonal rules, for DBH is 60cm and 28cm, velocity was bigger in May then in August, while for 15cm, velocity in August was bigger; In the same depth flow velocity was different in different directions, and it was bigger in North-South, South, West direction, which showed sap flow in stem increased in line; Sapflow and sapwood area of Populus euphratica with 60cm (DBH) were higher than 15 cm and 28cm (DBH), and its velocity was lower. The sapwood which was close to radial section was an important factor affecting transpiration.