Chin J Plan Ecolo ›› 2003, Vol. 27 ›› Issue (1): 34-40.DOI: 10.17521/cjpe.2003.0005

• Research Articles • Previous Articles     Next Articles

Photosynthetic Character and Water Use Efficiency of Different Leaf Shapes of Populus Euphratica and Their Response to Co2 Enrichment

SU Pei-Xi, ZHANG Li-Xin, DU Ming-Wu, BI Yu-Rong, ZHAO Ai-Fen, LIU Xin-Min   

  • Published:2003-01-10
  • Contact: SU Pei-Xi

Abstract:

Populus euphratica Oliv. is an important tree species of desert riparian forest. Leaf shape of P. euphratica is variable but can be roughly classified into two types, namely poplar leaf and willow leaf. Representative leaves of these types were ovate and lanceolate respectively. In this study some standard adult plants with both ovate leaves and lanceolate leaves were selected from the Nature Reserve of Populus euphratica in Ejin Qi, Inner Mongolia (41°58′ N, 101°05′ E, 930 m a.s.l.). In this measurement, the branches were put at the same height, then live leaves were measured and their photosynthesis, transpiration and water use efficiency were compared using the LI-6400 Portable Photosynthesis System of LI-cor; the response to CO2 enrichment was also ompared. The purpose of the study was to explore the cause responsible for the changes of leaf shape of P. euphratica, so as to provide a scientific basis for the protection of P. euphratica forest. In addition, the response of the different leaf shapes to increased CO2 concentration was analyzed and the possible effects of climatic changes on the growth of P. euphratica were predicted. The results showed that under present atmospheric CO2 concentration (350 μmol·mol-1) and 1 000 μmol·m-2·s-1 of light intensity, the net photosynthetic rates (Pn) of ovate leaves (leaf blades of adult tree) (A) and lanceolate leaves (lower coppica shoot leaves of adult tree) (B) are 16.40 μmol CO2·m-2·s-1 and 9.38 μmol CO2·m-2·s-1 respectively; transpiration rates (E) are 10.8 mmol H2O·m-2·s-1 and 7.98 mmol H2O·m-2·s-1 respectively; water use efficiency (WUE) is 1.52 mmol CO2·mol-1H2O and 1.18 mmol CO2·mol-1H2O respectively. Under these conditions, the light saturation and compensation points of A are 1 600 μmol·m-2·s-1 and 79 μmol·m-2·s-1 respectively, while the corresponding values of B are 1 500 μmol·m-2·s-1 and 168 μmol·m-2·s-1. When CO2 concentration reaches 450 μmol·mol-1 and 1 000 μmol·m-2·s-1 of light intensity, the photosynthetic characteristics of A and B exhibited quite different responses. The Pn of A increased by 25.6%, to 20.60 μmol CO2·m-2·s-1, whereas the Pn of B decreased by 10.0%, to 8.44 μmol CO2·m-2·s-1. The E of both A and B decreased; values were 9.11 mmol H2O·m-2·s-1 and 6.26 mmol H2O· m-2·s-1 respectively. The WUE of A and B was 2.26 mmol CO2·mol-1H2O and 1.35 mmol CO2·mol-1H2O respectively, i.e. WUE of A increased by 48.7% and WUE of B increased by 14.4%. The light saturation of A rises by 150 μmol·m-2·s-1 but light compensation point falls by 36 μmol·m-2·s-1, while the light saturation point of B falls by 272 μmol·m-2·s-1 and light compensation point rises by 32 μmol·m-2·s-1. The two types of leaf blade exhibit completely contrary responses to CO2 concentration elevation; the poplar leaves are more adapted to atmospheric CO2 concentration elevation. This study shows that the willow leaves have a lower photosynthetic efficiency and so are likely mainly used to maintain normal growth. With the growth of the tree the willow leaves can no longer support normal growth and hence poplar leaves occur. Poplar leaves have higher resistance to atmospheric drought and higher photosynthetic efficiency. They can accumulate photosynthetic products to maintain the growth of P. euphratica in extremely adverse environments and reach a higher increment. This seems to be the real cause responsible for leaf shape changes of P. euphratica from seedlings to adult trees. With the increase in CO2 concentration the photosynthetic time of willow leaves shortens and light use efficiency decreases, but poplar leaves show the opposite tendency in these two respects. When the ground water level decreases and near-surface air becomes dry, or with climate warming due to increasing atmospheric CO2 concentration, the numberof willow leaves are predicted to decrease, even disappear.