Experimental tests for determining the causes of the altitudinal distribution of Meum athamanticum Jacq. in the Harz Mountains

Abstract

Summary The objective of this study is to identify possible causes for the altitudinal limitation of a plant species with montane distribution, i.e. Meum athamanticum. The response of its growth to altitude was measured along an elevational gradient from 170 m to 1130 m a.s.l. in the Harz Mountains, Germany. Naturally occurring Meum plants and different age classes that had been transplanted to 7 sites along this gradient were monitored for several growth parameters. The growth rates differed only slightly among altitudes, a sign of a low phenotypical plasticity. The germination requirements were analyzed in growth chambers using different pre-treatments and temperatures. The seeds had a secondary dormancy that was effectively broken by a pre-treatment of alternating temperatures; whereas the temperature at germination time exerted almost no effect on germination rates. No specific requirements related to montane climate were detected. The plant’s frost tolerance directly after sprouting in spring was examined in freeze chamber experiments. Since significant frost damage detected by electrolyte leakage was observed only at − 9° C or below, frost sensitivity was excluded as a cause for the altitudinal distribution limit. The acclimation of net photosynthesis was measured by comparing the temperature optimum of autochthonous individuals and transplants. The optima differed only by 0.5 K between plants grown at 170 m or 600 m a.s.l. which indicates a low adaptive capability. The reduction of starch concentration as the main storage carbohydrate in Meum roots was monitored in natural populations and in transplants. The loss of starch during the winter was substantial at all sites but was highest at the lowest elevation. The general conclusion from our study is that Meum athamanticum is restricted to montane sites because its low phenotypical plasticity does not allow the exploitation of more favourable climatic conditions in the lowlands. In addition, the ability of Meum plants to thrive at higher temperatures is probably reduced by the carbon loss in winter.