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

Abstract

Spring ephemeral herbs inhabiting deciduous forests commonly complete reproduction and vegetative growth before canopy closure in early summer. Effects of shading by early canopy closure on reproductive output and vegetative growth, however, may vary depending on the seasonal allocation patterns of photosynthetic products between current reproduction and storage for future growth in each species. To clarify the effects of sink-source balance on seed production and bulb growth in a spring ephemeral herb, Gagea lutea, we performed a bract removal treatment (source reduction) and a floral-bud removal treatment (sink reduction) under canopy and open conditions. Leaf carbon fixations did not differ between the forest and open sites and among treatments. Bract carbon fixations were also similar between sites but tended to decrease when floral buds were removed. Seed production was higher under open condition but decreased by the bract-removal treatment under both light conditions. In contrast, bulb growth was independent of light conditions and the bract-removal treatment but increased greatly by the bud-removal treatment. Therefore, leaves and bracts acted as specialized source organs for vegetative and reproductive functions, respectively, but photosynthetic products by bracts were flexibly used for bulb growth when plants failed to set fruits. Extension of bright period was advantageous for seed production (i.e., source limited) but not for vegetative growth (i.e., sink limited) in this species.

Warm temperature conditions restrict the sexual reproduction and vegetative growth of the spring ephemeral Gagea lutea (Liliaceae)

“…4b). This trend was in contrast to the previous report on this species (Sunmonu and Kudo 2014), where the bulb size was maintained when plants were (Fig. 1c).…”

“…Because the width of leaves and bracts was smaller than the chamber size (2 × 3 cm), we corrected photosynthetic parameters by the replacement of chamber area by actual leaf area that was included in the chamber. This protocol of photosynthetic measurement was determined based on our previous studies in G. lutea (Sunmonu et al 2013;Sunmonu and Kudo 2014).…”

“…Short lifespan, rapid decrease in photosynthetic activity, high respiration rate even in the fruiting stage, and small size of bracts in the GH plot indicated low photosynthetic assimilation in warm conditions, as detected in the leaves. Because photosynthesis by bracts is completely responsible for seed production in this species (Sunmonu et al 2013;Sunmonu and Kudo 2014), reduced bract assimilation in the GH plot might be responsible for the lower fruit and seed production.…”

“…To predict the response of spring ephemerals to climate change, however, the responses of reproductive plants should be clarified because the timing and frequency of extreme temperature events could be important also for sexual reproductive phases and final reproductive output (Kudo et al 2004). In addition, sensitivity to thermal environment may vary between reproductive and non-reproductive plants, reflecting the specific carbon allocation strategy (Sunmonu and Kudo 2014).…”

Light acclimation strategies change from summer green to spring ephemeral as wild‐leek plants age

“…under lower light conditions. Growth in mature plants is most likely limited by bulb growth rate (sink-limitation), as reported in other spring ephemerals ( Badri et al, 2007 ;Gutjahr and Lapointe, 2008 ;Sunmonu and Kudo, 2014 ). Th is would explain why higher light conditions and the resulting higher photosynthetic rates ( Fig.…”