Chin J Plant Ecol ›› 2012, Vol. 36 ›› Issue (3): 177-186.DOI: 10.3724/SP.J.1258.2012.00177

• Research Articles •     Next Articles

Effects of groundwater decline on photosynthetic characteristics and stress tolerance of Ulmus pumila in Hunshandake Sandy Land, China

SU Hua1,2, LI Yong-Geng2, SU Ben-Ying3, SUN Jian-Xin1,*()   

  1. 1Key Laboratory for Silviculture and Conservation of Ministry of Education, College of Forest Science, Beijing Forestry University, Beijing 100083, China
    2State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
    3College of Agriculture, Sichuan Agricultural University, Chengdu 611130, China
  • Received:2012-01-10 Accepted:2012-02-15 Online:2012-01-10 Published:2012-02-28
  • Contact: SUN Jian-Xin


Aims Ulmus pumila, a widespread tree in the semiarid ecosystems of northern China, forms sparse woodlands in Hunshandake Sandy Land. However, the population of U. pumila has been declining in recent years because of a lowered water table, mainly caused by increased human water consumption. Our objective was to clarify the relationships between tree ecophysiological activity and the water table in order to provide information for protection of the species.
Methods Saplings of U. pumila were planted in pots with simulated water tables at 1, 2, 3 and 4 m depth (U1, U2, U3 and U4, respectively). The impacts of water tables on the photosynthetic characteristics and stress tole- rence of U. pumila were determined by analyzing photosynthetic light and CO2 curves, pigments, predawn water potential, soluble sugar and proline.
Important findings Both the utilization efficiency of strong and weak light by U. pumila and the maximum photosynthetic rate decreased with lowered water table. Compared to U1, the light saturation point, apparent quantum yield and dark respiration rate of U2, U3 and U4 were significantly decreased successively (p < 0.05). The maximum net photosynthetic rate of U4 ((8.98 ± 0.08) μmol·m-2·s-1) was reduced by 16.9% compared to U1 ((10.81 ± 0.28) μmol·m -2·s-1). Light energy conversion efficiency of U. pumila also declined with lowered water table. Compared to U1, the photorespiratory rate, maximum RuBP saturated rate of carboxylation, maximum rate of electron transport and rate of triose-phosphate utilization decreased (p < 0.05) and CO2 compensation point increased in the order of U2 < U3 < U4 (p < 0.05). The soluble sugar and proline contents significantly increased (p < 0.05) with lowered water table, i.e. U1 < U2 < U3 < U4, indicating that the lowered water table induced the greater stress. Therefore, groundwater decline resulted in drought stress and down-graded photosynthetic ability. This implies that the decrease in U. pumila population might be caused by the lowered water table and that maintaining proper underground water table in Hunshandake Sandy Land is helpful to the sustainability of the sparse woodland ecosystem.

Key words: arid, CO2 response curve, osmotic adjustment substance, photosynthetic-light response curve, water table