Influence of Water Limitation and Provenance on Reproductive Traits in a Common Garden of Frangula alnus Mill.

Abstract

Drought periods during the growing season will increase and intensify in Western Europe due to climate change. To better understand the consequences for woody perennials, we restricted watering of potted cuttings of Frangula alnus Mill. in a common garden setting in Belgium during the growing season of 2020. We focused on the responses of three provenances (Belgian, Italian and Swedish) for several reproductive traits in the year of the water limitation. F. alnus, as a shrub species, bears fruits fast. It can blossom on current season’s growth and can therefore produce ripened berries continuously during several months. The total berry count across the whole growing season was much lower in the water-limited plants, independent of the provenance. The local Belgian provenance produced more ripened berries in total than the Italian and Swedish provenances, both in the water-limited plants as in the control plants. Maximal berry production occurred in July. The control plants from the Belgian and Italian provenances displayed a second lower maximum in August. Mainly the Swedish provenance displayed a clear advancement of the maximum berry production among the water-limited plants in comparison to the control plants. Slight differences were detected in the average stone count per berry and in the average stone weight, with both traits displaying a single maximum through time. The Swedish provenance displayed the highest average stone count per berry and the Belgian provenance had the lightest average stone weight, both likely attributable to local adaptation. Remarkably, both stone traits were not affected by the water limitation. Results are discussed in the context of several drought response mechanisms including drought escape, drought avoidance, compensation growth, growth/reproduction trade-off and seed size/number trade-off.