Effects of environmental stress and nutlet morph on proportion and within-flower number-combination of morphs produced by the fruit-dimorphic species Lappula duplicicarpa (Boraginaceae)

Phenotypic plasticity in species with heteromorphic diaspores is considered to be a plastic bet-hedging strategy in environmentally fluctuating habitats. The primary aim of this study was to determine the influence of level of abiotic (soil moisture and nutrient availability) and biotic (pure and mixed density) factors on the long-glochid (LN; high dispersal, low dormancy)/short-glochid (SN; low dispersal, high dormancy) nutlet ratio and on nutlet combination of the fruit-dimorphic cold desert winter annual/spring ephemeral Lappula duplicicarpa derived from different nutlet morphs. We hypothesized that stress would decrease the LN: SN ratio. All levels of the four treatments resulted in significant variation in the LN: SN ratio and in the proportion of each nutlet combination. Reproductive biomass varied less than plant mass in plants from both morphs. In favorable environments, the LN: SN ratio and number of SN-3LN and 4LN combinations were relatively high, while in unfavorable environments they were relatively low, thus supporting our hypothesis. Relative allocation to reproductive biomass was significantly negatively correlated with allocation to vegetative biomass. The downward shift that occurred in the LN: SN diaspore ratio in response to stressful growth conditions in Lappula duplicicarpa is assumed to be a bet-hedging strategy.