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Comparison of photosynthetic characteristics in cultivated and wild offspring of the invasive Callery pear (Pyrus calleryana Decne.)

Benjamin J. Merritt, Joshua B. Jones, Nicole A. Hardiman, Theresa M. Culley
Biological invasions 2014 v.16 no.2 pp. 393-400
Pyrus calleryana, cultivars, ecophysiology, genotype, hybridization, hybrids, photosynthesis, progeny, rootstocks, saplings, stomatal conductance, water use efficiency, Asia, United States
In most plant invasions, morphological and ecological characteristics are often examined to understand which might facilitate invasive spread, but ecophysiology may also be important to consider. This was examined in Callery pear (Pyrus calleryana Decne.), a popular ornamental tree from Asia that is sold throughout the United States and which has spread following hybridization among cultivar and rootstock genotypes. To determine the impact of ecophysiology on invasiveness in this species, we examined the photosynthetic rate, transpiration, stomatal conductance, and water use efficiency (WUE) in two generations of offspring grown under differing levels of stress over time. Individuals originating from seed of known cultivars (F₁ or ‘early generation hybrids’) or from wild individuals (F₂ or ‘advanced generation hybrids’) were measured in four sampling periods: 6-month-old saplings, 3-year-old Root-Bound saplings with no fertilization, the same saplings after transplantation into larger pots, and then after the saplings had experienced a period of water and nutrient stress. Ecophysiology differed significantly between the two generations, but the direction and magnitude of significance varied within the Root-Bound sampling period. Advanced generation hybrids exhibited greater photosynthetic and transpiration rates as well as stomatal conductance in the Root-Bound sampling period. In contrast, WUE was lower in the advanced generation hybrids in the Initial and Root-Bound sampling periods. Although P. calleryana exhibited moderate and comparable photosynthetic characteristics relative to other deciduous species, invasive spread in this species may be influenced by other traits, such as abundant seed production. Consequently, photosynthetic characteristics may not be the sole source of invasiveness in this species.