Germination and Establishment of Juncus Effusus L.: II. The Interaction Effects of Moisture and Competition

Abstract

In order to study the effects of available moisture on germination and early development of Juncus effusus, and of competition under these conditions, Juncus seeds were sown at different water tables alone and with two mixtures of grass and clover. There were wide differences in the numbers of Juncus plants establishing under different conditions of available moisture. 540 seedlings were removed from pots whose water table was up to the soil surface, 151 from all the mixtures where the water table was 2" (5.1 cm) below the surface, 12 where the table was 4" (10.2 cm) from the surface, while no seedlings at all established under the very dry conditions produced by a water table 8" (20 cm) below the soil surface. Sown species had less influence on initial establishment of the Juncus seedlings than had available moisture, though there were considerable differences in the effects of companion species on subsequent development of the seedlings. Mean weights of seedlings removed from the pots of J. effusus sown alone, J. effusus + Lolium perenne + Trifolium repens, and Juncus effusus + Agrostis tenuis + Trifolium repens - all with a water table up to the soil surface -were 96.9, 13.3, and 12.6 g respectively, while the mean numbers of seedlings removed were 37.0, 28.2 and 24.2. Counts of plant numbers and air-dry weights were taken of the species sown with Juncus effusus, and a comparison was made of the relative germination and subsequent germination of these species in relation to J. effusus under different conditions of available moisture. The discussion includes a short account of the practical implications of the data particularly in relation to results presented in an earlier paper.