Effects of defoliation and shading on the physiological cost of reproduction in silky locoweed Oxytropis sericea.
BACKGROUND
The production of flowers, fruits and seeds demands considerable energy and nutrients, which can limit the allocation of these resources to other plant functions and, thereby, influence survival and future reproduction. The magnitude of the physiological costs of reproduction depends on both the factors limiting seed production (pollen, ovules or resources) and the capacity of plants to compensate for high resource demand.


METHODS
To assess the magnitude and consequences of reproductive costs, we used shading and defoliation to reduce photosynthate production by fully pollinated plants of a perennial legume, Oxytropis sericea (Fabaceae), and examined the resulting impact on photosynthate allocation, and nectar, fruit and seed production.


RESULTS
Although these leaf manipulations reduced photosynthesis and nectar production, they did not alter photosynthate allocation, as revealed by (13)C tracing, or fruit or seed production. That photosynthate allocation to reproductive organs increased >190 % and taproot mass declined by 29 % between flowering and fruiting indicates that reproduction was physiologically costly.


CONCLUSIONS
The insensitivity of fruit and seed production to leaf manipulation is consistent with either compensatory mobilization of stored resources or ovule limitation. Seed production differed considerably between the two years of the study in association with contrasting precipitation prior to flowering, perhaps reflecting contrasting limits on reproductive performance.
Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada. tida@ucalgary.ca
Takashi Y
TY
Ida
Lawrence D
LD
Harder
Gaku
G
Kudo
D000416:Alberta; D001692:Biological Transport; D035264:Flowers / Q000254:growth & development* / Q000378:metabolism; D005638:Fruit / Q000254:growth & development / Q000378:metabolism; D008027:Light; D033021:Oxytropis / Q000254:growth & development* / Q000378:metabolism; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism; D057048:Plant Nectar / Q000096:biosynthesis; D012639:Seeds / Q000254:growth & development / Q000378:metabolism
D057048:Plant Nectar