Plant distribution can be reflected by the different growth and morphological responses to water level and shade in two emergent macrophyte seedlings in the Sanjiang Plain

In the Sanjiang Plain (North East China), narrowleaf small reed (Deyeuxia angustifolia) usually distributes widely in typical meadow or marsh, while reed (Phragmites australis), the concomitant species, is distributed sparsely in the D. angustifolia communities or relative open sites. To date, the mechanisms responsible for their different distribution patterns are far from clear. Both water level and light are important factors determining plant distribution in wetland ecosystems and therefore, the aim of this paper was to identify the role of these two factors and their potential interaction on plant distribution in this plain. Growth responses and biomass allocation of the two macrophytes were investigated by growing them in three irradiances (300, 100, 20 mu mol m(-2) s(-1)) and two water levels (0 and 5 cm) under greenhouse conditions. Biomass accumulation, mean relative growth rate (RGR), height and mean relative elongation rate (RER) of both species significantly decreased with the reduction of light availability. Biomass accumulation, RGR, height and RER of P. australis were significantly inhibited by higher water level. However, water level had no effect on the growth of D. angustifolia. Stem mass fraction was higher at 0-cm water level in D. angustifolia, and was not affected by water level in P. australis. These data suggest that D. angustifolia has a higher adaptive ability to acclimate to flooding and shade stresses than does P. australis, which might be an important reason for their different distribution patterns.