Spore number in Sphagnum and its dependence on spore and capsule size

Abstract

Spore number in eight species of Sphagnum, representing five taxonomic sections, was investigated in relation to capsule and spore size. Mean spore number ranged from 18,500 in S. tenellum to 243,000 in S. squarrosum. There was considerable intraspecific variation in spore number, which was mainly related to capsule size. The interspecific variation in spore number was determined by both capsule and spore size, with higher numbers of spores in species with large capsules and small spores. Capsule size among species seems to be positively correlated to the size of the capitulum. Spore size showed a strong, positive relationship to capsule size in three species studied, that was fitted by a quadratic regression. The smallest capsule analysed for each of the eight species always had the smallest spores, but in only two species did the largest capsule have the largest spores, further indicating a common curvilinear relationship between spore size and capsule size. The strong relationship (R²=O.98) obtained in a linear regression in which the capsule size to spore size ratio was used to predict spore number in different species, makes it possible to estimate the spore output of other species or populations of Sphagnum, from sizes of capsules and spores. The sizes of spores measured in this study agreed with results obtained in at least one previous study, but were generally smaller than those reported in several other studies. The discrepancy probably depends on the method of spore preparation. The present study identifies potential sources of errors in spore counts and measurements. Measures which help to avoid or correct for errors are evaluated to facilitate further studies.