Photosynthetic compensation by the reproductive structures in the spring ephemeral Gagea lutea

Abstract

Growth and reproduction of spring ephemerals inhabiting deciduous forests progress simultaneously during a short period from snowmelt to canopy closure. To clarify the mechanism to mitigate the cost of reproduction, contributions of foliar and non-foliar photosynthetic products to seed production were examined in a spring ephemeral Gagea lutea. Leaf growth, foliar and non-foliar photosynthetic activities, and total assimilated products were compared among reproductive-intact, floral-bud removal and vegetative plants. Translocation of current photosynthetic products to individual organs was quantified by 13CO2-trace experiment. Bulb growth was compared between hand-pollination and floral-bud removal treatments. Finally, seed set was compared between intact, leaf-clipping and bract-clipping treatments. Fruit-forming plants retained leaves longer than vegetative and floral-bud removal plants, but the assimilative contribution of extended leaf longevity was negligible. Carbon supply by bract photosynthesis was large enough for fruit development, while carbon supply by fruit photosynthesis was offset by the high respiration loss. Foliar photosynthetic products were largely transported to bulbs, while translocation to reproductive functions was negligible. Because the floral-bud removal increased the bulb growth, lack of reproduction could lead to more storage. The leaf-clipping had no effect on seed production, while the bract-clipping significantly reduced the seed production. Therefore, current photosynthesis of leafy bracts might be a major carbon source for fruit development. This self-compensative mechanism of reproductive structure enables the continuous reproductive activity in this species

How do sink and source activities influence the reproduction and vegetative growth of spring ephemeral herbs under different light conditions?

“…Furthermore, the absence of significant difference in bulb size between the control and bract-removed plants indicates that bract photosynthesis basically contributes to seed production and there is no interference effect between seed production and bulb growth in this species as predicted by our previous study (Sunmonu et al 2013). Alternative respiratory pathways might be increased under enhanced light level and/or temperature.…”

“…These studies suggest that growing season length of spring ephemerals may be determined by temperature regime but not by light environment. The time of transfer, i.e., initiation of canopy closure coincided with the maximum leaf size period, and leaf size and photosynthetic activity tended to decrease after that due to the progress of partial leaf senescence (Sunmonu et al 2013). Therefore, delay of canopy closure may not contribute the carbon fixation of G. lutea as shown by other spring ephemerals (Gutjahr and Lapointe 2008;Gandin et al 2011).…”

“…Carbon fixation by leaf and bract was evaluated based on the census of leaf or bract growth, seasonal transition of photosynthetic activity, and ambient solar radiation (for details, refer Sunmonu et al 2013). …”

“…On the other hand, both leaf size and total carbon fixation were not influenced by the site and treatment as expected. This means that leaf carbon fixation simply depends on the sink intensity of bulb because most foliar photosynthetic products are transported to the bulb in this species (Sunmonu et al 2013). …”

“…Therefore, this species has two sources (leaf and bract) versus two sinks (fruit and bulb) in terms of carbon assimilation during a growth period. In the previous study (Sunmonu et al 2013), we reported the compensative ability of bracts when photosynthetic products by bracts were used for current seed production. On the other hand, photosynthetic products by leaves were used for bulb development and carbon translocation to reproductive function was negligible.…”