Costs of sporophyte production in the moss,Dicranum polysetum

We investigated the cost of sporophyte production in the moss Dicranum polysetum both by examining patterns of growth and reproduction in unmanipulated shoots and by experimentally manipulating sexual reproduction.The estimated proportion of total carbon investment allocated to sexual reproduction in sporophyte-producing shoots over the study period was 74.8%. Unmanipulated shoots that aborted all sporophytes had a significantly higher growth in the top shoots than shoots that produced sporophytes. In sporophyte-producing shoots, total apical growth decreased proportionately with the number of sporophytes.Experimental prevention of sporophyte development resulted in significantly higher total apical growth of the gametophytes. Shoots where current perichaetia were lacking when marked had a mass increase in the top shoots similar to manipulated sporophytic shoots whereas sporophytic control shoots grew significantly less than these two categories.The difference between control shoots and manipulated shoots in the mass of vegetative apical growth was mainly because of different length increments whereas mass per unit length was similar between groups. The probability to reproduce sexually in the year after the manipulation, and the biomass allocated to this reproduction, were not affected by the experimental treatment.