Nectar production and pollination in Alstroemeria aurea: Responses to level and pattern of flowering shoot defoliation

Alstroemeria aurea is a clonal perennial which occurs in the understory of the southern Andean forests. Plants consist of a series of 3-5 vegetative shoots and usually one flowering shoot sprouting each growing season from an underground rhizome. Inflorescences are terminal and synchronously protandrous. We compared the effects of defoliation of the flowering shoot on flower size, nectar production, pollen removal and deposition, and pollen grain size. Treatments were designed to test for the effects of level and position of leaf removal. They were: (1) 100% defoliation; (2) all leaves from the upper half of the shoot removed (=50% UH); (3) all leaves from the lower half removed (=50% LH), and (4) control (i.e. no defoliation). Defoliation was performed in four flowering patches 4-7 d before anthesis. Flower size (estimated by inner tepal length) was slightly, but significantly reduced by the removal of the lower leaves (100% defoliation and 50% LH treatments). Sugar production/6 h tended to be higher in control shoots than in defoliated ones, but the response was heterogeneous among: the four study flowering patches. Laboratory experiments suggest a great degree of autonomy of isolated flowers in terms of sugar nectar secretion, perhaps because of carbohydrates being stored in the nectaries prior to anthesis. No effect of defoliation was observed on the number of pollen grains removed from the anthers or deposited on the stigmas. Pollen grain size was significantly reduced by defoliation following the expected gradient ''Control > 50% LH > 50% UH > 100% defoliation''. To the extent that size reflects amount of reserves in pollen grains, defoliation might be affecting the post-pollination competitive ability of a donor plant.