Effect of desiccation on phosphorus and potassium acquisition by a desiccation-tolerant moss and lichen

The hypothesis that desiccation-tolerant mosses and lichens may be more res ponsive to nutrient inputs accompanying intermittent desiccation than mesop hytic forest species was investigated employing species from semi-arid gras sland in Hungary. Shoot apices of the moss Syntrichia ruralis and marginal lobes of the lichen Cladonia convoluta were maintained for 7 weeks under co ntrolled conditions. They were cultivated with or without a weekly applicat ion of the major inorganic macronutrients, and either under constant hydrat ion or with one or two 24 h periods of desiccation each week. Growth of S. ruralis was stimulated by nutrient additions, but lower weight increments w ere achieved with increasing frequency of desiccation. All samples of the l ichen showed positive growth, and no significant treatment effects were det ected. A large net uptake of P occurred in nutrient-treated material of bot h species that was unaffected by the imposition of desiccation treatments. A smaller net uptake of K into the intracellular fraction was also observed when nutrients were applied, but in the moss this was against a baseline o f decreasing K content. In contrast, more of the original K content was ret ained in C. convoluta. In neither species was any clear evidence found for inhibition of nutrient uptake by the desiccation episodes. It is suggested that the lack of growth response in the lichen arises from an inability to bring together the additional nutrients, presumably mainly absorbed by the mycobiont, with photosynthate produced by the photobiont. (C) 2000 Annals o f Botany Company.