Clonal Integration and Population Structure in Perennials: Effects of Severing Rhizome Connections

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Abstract
Short rhizomes in perennial plants lead to compact genet architecture and populations consisting of monoclonal patches. Long rhizomes lead to spreading genets and polyclonal patches. To test if shoot integration within genets was higher in the first case than in the second, we compared shoots of connected genets to artificially disconnected shoots for three Aster species (spreading genets), Solidago canadensis (compact genets), and S. gigantea (intermediate) grown in high and low density, pure and mixed sands. Severing rhizome connections stimulated plant growth in S. canadensis but had only small effects on growth in Aster and S. gigantea. In low density, the production of new rhizome and shoot modules of S. canadensis, and to a lesser degree of S. gigantea, was restricted by integration. Aster performed better and S. canadensis worse in mixed than in pure stands. Intact connections did not increase the competitive ability of s. canadensis grown in mixture. Shoots of S. canadensis, but not of S. gigantea and Aster, were more variable if connected in pairs than if isolated (or connected in fours). The results confirm the prediction that integration increases with increasing genet compactness, i.e., Aster < S. gigantea < S. canadensis. They further indicated that destroying physical connections in integrated genets may decrease between—shoot competition rather than between—shoot cooperation. Ecological consequences of high vs. low clonal integration in perennial plants are discussed.