Reproductive effort in invasive and non-invasive Rubus
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We quantified the physiological costs and the total amount of resources allocated to reproduction in two closely related species of Rubus, one of which is invasive. These two species share several morphological and life-history characteristics and grow together in the Pacific Northwestern United States. Reproductive effort was manipulated in canes of both species by removing flower buds. The non-invasive species, R. ursinus, exhibited significantly greater water stress in the reproductive canes, as indicated by lower leaf water potential (Ψ) and reduced stomatal conductance (gs). This species also showed a reduction in leaf nitrogen concentration ([N]) associated with reproduction. Combined, these factors led to reduced photosynthesis (A) on a diurnal basis, lower water-use efficiency as inferred from δ13C, and reduced photosynthetic capacity. All of these effects were more pronounced during the fruiting stage than in the flowering stage. The invasive species, R. discolor, showed no changes in water stress, [N], δ13C, or A associated with reproduction. A model was used to estimate total gross photosynthesis (Agross) for reproductive and non-reproductive canes of both species over cane lifetime. Reproduction was associated with a greater decline in Agross for the non-invasive R. ursinus than for the invasive R. discolor. Although R. discolor allocated more resources directly to flowers and fruit than R. ursinus, the invasive species had significantly lower reproductive effort, or total amount of resources diverted from vegetative activity to reproduction, than the non-invasive species. By minimizing the reduction of photosynthesis associated with reproduction, this invasive species may be able to minimize the trade-offs commonly associated with reproduction.
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