Growth performance and element concentrations reveal the calcicole-calcifuge behavior of three Adiantum species

The calcicole or calcifuge behavior of wild plants has been related to element deficiency or toxicity. For fern species, however, knowledge about their adaptive differences and responses to soil environmental changes is virtually absent. In the karst regions of southern China, most Adiantum species favor calcareous soils, but A. flabellulatum prefers acidic soils. Such contrasting preferences for soil types in the same genus are interesting and risky because their preferred soils may "pollute" each other due to extreme precipitation events. We mixed calcareous and acidic soils at 1:1 (v/v) to simulate the "polluted" soils and grew three Adiantum species (the calcicole A. capillus-veneris f. dissectum and A. malesianum and the calcifuge A. flabellulatum) on the calcareous, acidic and mixed soils for 120 d and assessed their growth performance and element concentrations.

The calcareous soil showed the highest pH, Ca, Mg and P concentrations but the lowest K concentration, followed by the mixed soil, and the acidic soil. After 120 d of growth, the calcifuge A. flabellulatum on the calcareous and mixed soils exhibited lower SPAD and relative growth rate (RGR) than those on the acidic soil, and its leaf and root Ca, Mg and Fe concentrations were higher and K was lower on the calcareous soil than on the acidic soil. The calcicole A. capillus-veneris f. dissectum on the calcareous soil had similar leaf element concentrations and RGR with those on the mixed soil, but their leaf Ca, Fe and Al were lower and leaf P and K concentrations, SPAD and RGR were higher than those on the acidic soil. For the calcicole A. malesianum, leaf Ca, Fe and Al were lowest and leaf P and RGR were highest when grown on the mixed soil, intermediated on the calcareous soil, and on the acidic soil. Compared with A. malesianum, A. capillus-veneris f. dissectum had lower leaf Ca, Fe and Al but higher leaf Mg concentration when grown on the same calcareous or mixed soils.

A. capillus-veneris f. dissectum is a low leaf Ca calcicole species while A. malesianum is an Al accumulating calcicole species. They can effectively take up P and K to leaves and hence can thrive on calcareous soils. In contrast, the calcifuge A. flabellulatum grown on calcareous soils is stunted. Such growth performance may be attributed to the increased leaf Ca and decreased leaf K concentration. If their preferred soils are "polluted", A. flabellulatum can grow worse, A. capillus-veneris f. dissectum can remain almost unaffected while A. malesianum will perform better.