ABSTRACT
BACKGROUND AND AIMS: Understanding how plant allometry, plant architecture and phenology contribute to fruit production can identify those plant traits that maximize fruit yield. In this study, we compared these variables and fruit yield for two shrub species, Vaccinium angustifolium and Vaccinium myrtilloides, to test the hypothesis that phenology is linked to the plants' allometric traits, which are predictors of fruit production. METHODS: We measured leaf and flower phenology and the above-ground biomass of both Vaccinium species in a commercial wild lowbush blueberry field (Quebec, Canada) over a 2-year crop cycle; 1 year of pruning followed by 1 year of harvest. Leaf and flower phenology were measured, and the allometric traits of shoots and buds were monitored over the crop cycle. We hand-collected the fruits of each plant to determine fruit attributes and biomass. KEY RESULTS: During the harvesting year, the leafing and flowering of V. angustifolium occurred earlier than that of V. myrtilloides. This difference was related to the allometric characteristics of the buds due to differences in carbon partitioning by the plants during the pruning year. Through structural equation modelling, we identified that the earlier leafing in V. angustifolium was related to a lower leaf bud number, while earlier flowering was linked to a lower number of flowers per bud. Despite differences in reproductive allometric traits, vegetative biomass still determined reproductive biomass in a log-log scale model. CONCLUSIONS: Growing buds are competing sinks for non-structural carbohydrates. Their differences in both number and characteristics (e.g. number of flowers per bud) influence levels of fruit production and explain some of the phenological differences observed between the two Vaccinium species. For similar above-ground biomass, both Vaccinium species had similar reproductive outputs in terms of fruit biomass, despite differences in reproductive traits such as fruit size and number.
Subject(s)
Blueberry Plants , Vaccinium , Flowers , Fruit , Plant Leaves , QuebecABSTRACT
Synchrony between host budburst and insect emergence greatly influences the time window for insect development and survival. A few alterations of bud phenology have been reported under defoliation without clear consensus regarding the direction of effects, i.e., advance or delay. Here, we compared budburst phenology between conifers in defoliation and control treatments, and measured carbon allocation as a potential mechanistic explanation of changes in phenology. In a 2-year greenhouse experiment, saplings of balsam fir, black spruce and white spruce of two different provenances (north and south) were subjected to either control (no larvae) or natural defoliation treatment (larvae added) by spruce budworm. Bud and instar phenology, primary and secondary growth, defoliation and non-structural carbohydrates were studied during the growing season. No differences were observed in bud phenology during the first year of defoliation. After 1 year of defoliation, bud phenology advanced by 6-7 days in black spruce and balsam fir and by 3.5 days in white spruce compared with the control. Because of this earlier bud break, apical and shoot growth exceeded 50% of its final length before mature instar defoliation occurred, which decreased the overall level of damage. A sugar-mediated response, via earlier starch breakdown, and higher sugar availability to buds explains the advanced budburst in defoliated saplings. The advanced phenological response to defoliation was consistent across the conifer species and provenances except for one species × provenance combination. Allocation of carbon to buds and shoots growth at the expense of wood growth in the stem and reserve accumulation represents a shift in the physiological resources priorities to ensure tree survival. This advancement in bud phenology could be considered as a physiological response to defoliation based on carbohydrate needs for primary growth, rather than a resistance trait to spruce budworm.
