WHY HAVE GREEN STEMS

Photosynthetic activity of the cortical tissues of Cytisus scoparius. Link stems were examined in regard to individual biomass production and allocation, structural attributes of stem tissue, chlorophyll content, photosynthetic rates and ability to recover from herbivory. Biomass production and allocation were assessed through growth analysis of plants given one of four treatments: all stems loosely wrapped with aluminium foil; plants defoliated once; plants defoliated repeatedly; and controls. Stem photosynthesis made a significant contribution to growth and biomass production of this mesic species. Cortical stem tissue is structurally very similar to leaf tissue. Chlorophyll content and biomass accumulation of stems, leaves, roots, and nodules changed significantly with simulated herbivory. Apparently, in Cytisus scoparius, stem photosynthesis helps meet different needs, depending on which factor or combination of factors are most critical in any given habitat. For an invasive, weedy perennial like Cytisus scoparius, this flexibility may itself be the most important benefit of having photosynthetic stems. Photosynthetic stems may play an important role in the success of leguminous shrubs in general and in the success of invasive leguminous shrubs in particular.