Ecophysiologcal Responses to Soil Drought in Two Contrasting Alternanthera philoxeroides Ecotypes

A potted experiment was conducted to compare ecophysiological responses to soil drought in two contrasting Alter-nanthera philoxeroides (Mart.)Griseb ecotypes (i.e xeric ecotype and aquatic ecotype).Drought significantly reduced plant height, internode length, leaf length, leaf width, total leaf area, specific leaf area, total biomass and relative growth rate, but had little effect on stem diameter in both ecotypes.Plant height, internonde length, stem diameter, leaf length, leaf width and total leaf area in aquatic ecotype were significantly higher than those in xeric ecotype across soil water content.However, the interaction of drought×ecotype indicated that drought decreased much more total leaf area, biomass and rela-tive growth rate in aquatic ecotype than those in xeric ecotype.Under drought condition, two kinds of ecotype could distributed more biomass to root and stem, less to leaf compared with well water treatment.Although drought decreased leaf relative water content and leaf pigments especially in aquatic ecotype, these two physiological parameters could be sustained a relative high level even under sever drought in the two kinds of ecotypes.Based on these results, authors suggested that both aquatic ecotype and xeric ecotype of A.philoxeroides could survive sever drought by increasing leaf thickness, reducing leaf size, changing biomass allocation as well as sustaining high leaf reality water content and leaf pigments.Furthermore , the xeric ecotype had higher drought resistance than aquatic ecotype.