The influence of mycorrhizal colonization on the vegetative growth and sexual reproductive potential of Lythrum salicaria L.

Lythrum salicaria L., purple loosestrife, is a heterostylous, perennial plant with prolific and at times invasive vegetative growth and sexual reproduction. Sexual reproduction occurs following pollination and fertilization between two different floral morphs. We investigated the influence of the arbuscular mycorrhizal fungus, Glomus aggregatum Schenck and Smith emend. Koske, on the vegetative growth and sexual reproductive potential of L. salicaria. Mycorrhiza decreased plant biomass both aboveground and belowground. Flower production, number of days to anthesis, numbers of flowers per inflorescence, and inflorescence lengths were not significantly different between mycorrhizal and non-mycorrhizal treatments. However, pollen production per anther and per flower increased with mycorrhizal colonization. Though ovule production was not affected, some aspects of purple loosestrife morphology did change. Plants with mycorrhizae produced inflorescence (in lateral positions) further up the stem. In addition, flower distribution within an inflorescence differed according to morph (short, mid, and long style) such that in the mid and long morphs flower number increased with inflorescence length and was unevenly distributed, while in the short morph this distribution appeared even. The relative biomass of stems, leaves, lateral branches, and reproductive structures were not significantly different in mycorrhizal plants, whereas in the absence of mycorrhizal colonization, stem biomass was higher relative to other structures. This study suggests some vegetative and reproductive characteristics in purple loosestrife change with an association with arbuscular mycorrhizal fungi.