Experiments on the effects of water availability and exclusion of fungal hyphae on nutrient uptake and establishment of Pinus sylvestris seedlings in carpets of the moss Pleurozium schreberi

Abstract

The feathermoss Pleurozium schreberi has the capacity to suppress tree seedling regeneration in late successional northern boreal forests. We investigated, through a field experiment in a P. schreberi-dominated old-growth Norway spruce forest in northern Sweden, the effects of three precipitation regimes representing the range of natural July precipitation amounts (28, 112 and 256 mm), and extra influences of temporary exclusion of fungal hyphae in senescent shoots of P. schreberi, on seedling establishment, growth and nutrient acquisition of Pinus sylvestris. Seedling establishment of Pinus sylvestris was enhanced by increased amounts of artificial precipitation. Seedlings in plots with the lowest precipitation had a much lower mortality and significantly higher total nutrient content, higher specific absorption rate (SAR) and lower nutrient use efficiency (NUE) compared to seedlings grown in plots with the highest precipitation. Seedling nutrient (especially N and P) content was also significantly higher when fungal hyphae were excluded, and this was most evident in treatments with the intermediate precipitation level. Seedlings in plots without hyphal isolation but with intermediate precipitation levels had much lower total contents of N, P and Mg after one growing season than were initially present in the seeds, indicative of a net nutrient loss during the early establishment phase. Possible rhizosphere interactions, causing immobilisation of nutrients and seedling nutrient losses are discussed in relation to results from greenhouse experiments where no such nutrient losses were found in seedlings. We hypothesize that P. schreberi, in association with ericaceous plants and fungal hyphae, is a powerful controller of tree regeneration from seeds over wide precipitation gradients, due to its inhibition of seedling establishment and strong interference with nutrient acquisition of new seedling cohorts.