Effect of climatic gradients on the photosynthetic responses of four Phragmites australis populations

Four populations of Phragmites australis collected from geographically distinct areas in Europe were propagated in outdoor experimental plots at four sites with dissimilar climate (Denmark, The Netherlands, Spain and Czech Republic). During the second growing season the photosynthetic characteristics of Phragmites leaves were evaluated under controlled conditions for each site, each population, and their interaction, and related to tissue nutrient and pigment content. The light-saturated rate of photosynthesis (P-max), dark respiration rate (R-d), light compensation point (I-c), and apparent quantum efficiency (phi (i)) were significantly affected by growth site, whereas differences between populations were less pronounced. Plants grown in the more northerly climates appeared to be more photosynthetically limited through lower P-max values and lower phi (i) levels, reflecting phenotypic acclimation to the lower summer temperatures and irradiance levels at the northern growth sites. The higher P-max levels in the southern climate were correlated with higher nutrient levels in the tissue of leaves. The study shows that the four genetically distinct populations of P. australis exhibited high phenotypic plasticity in photosynthetic response to climatic change. The degree of photosynthetic plasticity within P. australis genotypes is large, and generally larger than the genetically determined differences between European populations. The results are discussed in relation to the prospected global climate change. [KEYWORDS: reed; wetland; photosynthesis; P-max; respiration; light compensation point; quantum efficiency; genotypes; clone; plasticity; acclimation; climate Clone specific differences; salt tolerance; growth; plants; co2; respiration; diversity; dynamics; time; reed