Bearing fruit: flower removal reveals the trade-offs associated with high reproductive effort for lowbush blueberry

Abstract

Past studies have shown that taxa from disparate groups often respond similarly to reduced reproductive effort. These common responses imply that high reproductive effort trades off with a consistent set of other life functions for most angiosperms, albeit modulated by their growth form and life history. However, many questions remain about reproductive trade-offs in plants, including just how many other life functions they involve, how diverse these functions may be, and how the severity of these trade-offs may vary through time. To address these questions in a long-lived, iteroparous shrub, we performed flower removal on plots of lowbush blueberry, Vaccinium angustifolium (Ericaceae), over 3 years. We found significant physiological differences between removal and control plots for ten diverse traits. Vegetative phenology was shifted earlier by about 20% in removal plots, and removal plots had about 15% more vegetative biomass by mid-season as well. Removal plots produced about 10% more ripe fruit per reproductive node by harvest than control plots, and reproductive nodes in removal plots produced at least one fruit by harvest about 6% more often. While fruit water content and titratable acidity were increased by removal, other fruit traits, such as sugar content and fresh mass, were not. The strength of the removal effect varied significantly by year for seven traits; for many, such as vegetative mass/stem and ripe fruit production/node, the effect was stronger in years with more stressful abiotic conditions. Our results demonstrate that there are tangible but variable costs to high reproductive effort for flowering plants.

Flower power: Floral and resource manipulations reveal how and why reproductive trade‐offs occur for lowbush blueberry (Vaccinium angustifolium)

“…We used flower removal of multiple types coupled with nitrogen fertilization and midseason defoliation to test hypotheses for why reproductive trade‐offs occur for lowbush blueberry. In keeping with our past results (Bajcz & Drummond, ), flower removal, alone or in combination with other treatments, led to increases in five of six traits under study. The sixth trait, ripe fruit production per node, did not increase in response to standard flower removal in this study but did increase in response to biased flower removal (Table ).…”

“…We see two ways to interpret these results. Titratable acidity often declines during ripening in Vaccinium fruits (Ismail & Kender, ), so high fruit acidity may reflect slowed ripening, and we have shown previously that high reproductive effort may slow ripening in lowbush blueberry (Bajcz & Drummond, in press). In that light, node success rate, ripe fruit production, and fruit ripening rate (with titratable acidity as a proxy) may all be lowbush blueberry traits limited by high reproductive effort because higher reproductive effort entails production of a greater number of more basal nodes, which may tend to have lower average quality.…”

“…Over 2 years (2014–15), clones (genets) of V. angustifolium were selected for study at the University of Maine's Blueberry Hill Farm (Bajcz & Drummond, in press). Because commercial lowbush blueberry fields are managed on a 2‐year cycle in which all aboveground biomass is destroyed after each harvest (Bell, Rowland, Smagula, & Drummond, ), it was not possible to use the same clones across years.…”

“…We determined ripe fruit dry:fresh mass ratio by dividing the fresh mass (g) of four ripe fruit from each plot into their mass after being dried at 70°C for 72 hr. Lastly, in 2015 only, we estimated ripe fruit titratable acidity in percent citric acid equivalents by volume for each plot via titration of 1 ml fruit juice samples with a 0.005N sodium hydroxide solution to a pH endpoint of 8.2 (Bajcz & Drummond, in press).…”

“…Here, we continued our flower removal research on lowbush blueberry ( Vaccinium angustifolium ; Bajcz & Drummond, in press) to answer the questions posed above. We focused on six traits we have already shown to trade off with reproductive effort for this taxon: vegetative mass per stem, surface area per leaf, ripe fruit produced per reproductive node (hereafter simply “node”), the proportion of successful nodes (i.e ., those that produced >1 fruit by harvest), ripe fruit dry:fresh mass ratio, and fruit titratable acidity.…”