Seasonal Patterns of Photosynthesis and Stomatal Conductance in Lowbush Blueberry Plants Managed in a Two-year Production Cycle

Abstract

Seasonal patterns of CO 2 assimilation (A CO2 ), leaf water potential (ψ 1 ) and stomatal conductance (g 1 ) were studied in three clones (`Augusta', `Brunswick', and `Chignecto') of lowbush blueberry ( Vaccinium angustifolium Ait.) over two growing seasons. Plants were managed in a 2-year cycle of fruiting (year 1) and burn-prune (year 2). In the fruiting year, A CO2 was lowest in mid-June and early September. Rates peaked between 10 and 31 July and declined after fruit removal in late August. Compared with the fruiting year, A CO2 in the prune year was between 50% and 130% higher in the early season, and between 80% and 300% higher in mid-September. In both years, however, mid-season maximum A CO2 for each clone was between 9 and 10 μmol·m –2 ·s –1 CO 2 . Assimilation of CO 2 increased with increasing photosynthetic photon flux (PPF) to between 500 and 600 μmol·s –1 ·m –2 in `Augusta' and `Brunswick', and to between 700 and 800 μmol·s –1 ·m –2 in `Chignecto'. Midday ψ 1 was generally lower in the prune year than in the fruiting year, reflecting year-to-year differences in soil water content. Stomatal conductance (g 1 ), however, was generally higher in the prune year than in the fruiting year over similar vapor pressure deficit (VPD) ranges, especially in June and September when prune year g 1 was often twice that observed in the fruiting year. In the fruiting year, g 1 declined through the day in response to increasing VPD in June, but was quite constant in mid-season. It tended to be higher in `Augusta' than in the other two clones. Stomatal closure imposes limitations on A CO2 in lowbush blueberries, but not all seasonal change in C-assimilative capacity can be explained by changes in g 1 .