DNA-content and chromosome number in populations of Poa alpina in the Alps reflect land use history

Poa alpina, a widespread alpine grass in the temperate and subarctic zone, is a polyploid complex including many cytotypes with a broad range of chromosome numbers. To assess the occurrence and frequency of cytotypes, and to test for effects of past and current land use on their distribution, we measured DNA content using flow cytometry in 543 individuals of Poa alpina from agriculturally used grassland parcels and from natural sites in 12 local communities from three cultural traditions in the Swiss Alps. We tested whether geography (local community), affiliation to three cultural traditions, current land use, fertilization, and elevation affected DNA-content of populations. DNA content among individuals was highly variable (2C values ranging 100–600 pg) indicating chromosome numbers between 14 and 69. Cultural tradition, geography (local community), and current land use significantly affected mean DNA-content of Poa alpina in populations from agriculturally used parcels. The range of DNA-content and cytotypes was larger in pastures than in meadows, and the distribution of cytotypes differed among cultural traditions. Plants with more chromosomes grew larger in a common garden suggesting higher vigour. Among reproducing plants, an almost equal share was either reproducing by seeds or by bulbils. Seed-producing individuals had a higher DNA-content. Results presented here suggest that human land use is reflected directly in the distribution of cytotypes of different ploidy level and chromosome number. The effect of different cultural traditions is an indication that the current distribution of cytotypes does not only reflect geographic variability and current land use, but also differences in land use in the past that are persisting to the present.