Leaf anatomy of Deschampsia antarctica (Poaceae) from the Maritime Antarctic and its plastic response to changes in the growth conditions

The leaf blade anatomical features of Deschampsia antarctica Desv. growing in Robert Island, South Shetland Islands, Maritime Antarctic (62 degrees 22 'S 59 degrees 43'W) and in clones cultivated in the laboratory for two year s, at 2 +/- 1.5 and 13 +/- 1.5 degrees C and 180 mu mol m(-2) s(-1) of irra diance were studied by light and scanning electron microcospy. Since D. ant arctica is growing under the harsh environmental conditions of the Maritime Antarctic for at least five millennia, it is postulated, that their leaf a natomy may show genotypic adaptations to this environment, which should be maintained when clones of this plant are cultivated under different conditi ons. In this Antarctic habitat, mean air temperature of January was ca. 2.8 degrees C (<8 to -2.5 degrees C) and the maximal irradiance was ca. 2000 m mol m(-2) s(-1). A strong variation was found in the anatomical characteris tics of the leaf surface and in the leaf cross section, between plants grow ing in the field and their clones growing at the highest temperature in the laboratory (13 degrees C). The leaf surface of the Antarctic samples showe d more xerophytic characteristics (smaller leaf surface and epidermal cells , higher leaf thickness, higher stomata density and number of cells per are a) than the leaves of plants cultivated at 13 degrees C. Additionally, Anta rctic samples presented stomata in both surfaces and epidermal cells with t urgid papillae. Therefore, the taxonomic value of epidermal characteristics for identification of Poaceae could be questioned.. In the leaf transverse section the vascular bundles of the Antarctic samples appeared surrounded with two bundle sheaths: an outer, with parenchymatous cells without chloro plasts, and an inner or mestome with thick walls. The outer bundle sheath w as absent in leafs of plants growing at 13 degrees C. Xylem of leaf Antarct ic samples did not present lacuna and their vessel lumens were smaller than at 13 degrees C. Leaf anatomical characteristics of plants growing at 2 de grees C correspond to an intermediate state between the two mentioned condi tions. The results suggest that the leaf anatomical features of D. antarcti ca do not correspond to a genotypic adaptation to the harsh environmental A ntarctic conditions, but rather to a plastic response of the phenotype to a meliorated growth conditions in the laboratory.