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 understor y of the southern Andean forests. Plants consist of a series of 3-5 ve getative shoots and usually one flowering shoot sprouting each growing season from an underground rhizome. Inflorescences are terminal and s ynchronously protandrous. We compared the effects of defoliation of th e flowering shoot on flower size, nectar production, pollen removal an d 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 remo ved (=50% UH); (3) all leaves from the lower half removed (=50% LH), a nd (4) control (i.e. no defoliation). Defoliation was performed in fou r flowering patches 4-7 d before anthesis. Flower size (estimated by i nner tepal length) was slightly, but significantly reduced by the remo val of the lower leaves (100% defoliation and 50% LH treatments). Suga r production/6 h tended to be higher in control shoots than in defolia ted ones, but the response was heterogeneous among: the four study flo wering patches. Laboratory experiments suggest a great degree of auton omy of isolated flowers in terms of sugar nectar secretion, perhaps be cause 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 si ze was significantly reduced by defoliation following the expected gra dient ''Control > 50% LH > 50% UH > 100% defoliation''. To the extent that size reflects amount of reserves in pollen grains, defoliation mi ght be affecting the post-pollination competitive ability of a donor p lant.