Photosynthetic capacity, chlorophyll content and leaf and cell morphology were compared inGrimmia antarcticifrom wet and dry sites in the Bailey Peninsula SSSI, near Casey Station, East Antarctica. In wet sitesG. antarcticigrew as a turf with tall shoots of loosely packed long leaves: in very dry sites it formed small cushions with short shoots of small tightly packed leaves. Intermediate forms (large cushions) were also frequently observed in less extreme situations. Cell size and number were greater in drier sites. The chlorophyll content, chlorophyll a/b ratio and the light saturated photosynthetic and dark respiration rates at full turgor and under enhanced conditions of CO2were the same. This rules out a direct effect of water stress on the integrity of the photosynthetic apparatus and implies that the cushion form is a product of direct effects of water availability on cell division and differentiation and CO2assimilation under field conditions.
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