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Title: Seasonal photosynthesis and partitioning of nonstructural carbohydrates in leafy spurge (Euphorbia esula)

item Gesch, Russell - Russ
item Palmquist, Debra
item Anderson, James

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2007
Publication Date: 7/1/2007
Citation: Gesch, R.W., Palmquist, D.E., Anderson, J.V. 2007. Seasonal Photosynthesis and Partitioning of Nonstructural Carbohydrates in Leafy Spurge (Euphorbia esula). Weed Science. 55:346-351.

Interpretive Summary: Leafy spurge (spurge) is a problem weed that is found throughout the North American Great Plains. It is a perennial weed that grows from one year to the next because of buds found on its roots that can survive winter and then sprout new plants in the spring. Therefore, it is hard to kill. We know from past greenhouse experiments that as a spurge plant grows, there is some organic chemical or chemicals sent from either the stems or leaves to the root buds that prevents the buds from sprouting new plants until the following spring. We think the organic chemical is a sugar that is being sent by the plant’s leaves rather than coming directly from its roots, but no one has done an experiment to show whether this is really the case. A two-year experiment was done outdoors to test this theory. Our results showed that a large amount of sugar appears to be sent by leaves to root buds during mid-summer and then again in the fall. This sugar is likely what is causing the buds to stay dormant until the following year, rather than sprouting into new plants during late summer and fall, which would be killed during the winter. We think this information can help plant scientists find ways to disrupt the flow of sugars from spurge leaves to their root buds. By doing this scientists might be able to trick the root buds into sprouting again before winter and then letting the cold winter temperatures kill the plants. This way the plants won’t spread the next spring.

Technical Abstract: Previous evidence indicates that changes in well-defined phases of dormancy in underground adventitious buds of leafy spurge in late summer and autumn are regulated by complex sensing/signaling pathways involving aboveground sugar signals. However, little information exists concerning seasonal photosynthesis and carbohydrate partitioning of leafy spurge, although such information would help to elucidate the involvement of sugar in controlling bud dormancy. An outdoor study was conducted over two growing seasons to determine and model seasonal patterns of photosynthesis and carbohydrate partitioning and their relationship to underground adventitious bud development and dormancy status. Photosynthesis and total nonstructural carbohydrate (TNC) content of aboveground tissues was greatest during vegetative growth. While photosynthesis gradually declined over the growing season, TNC decreased sharply during reproductive phase followed by a gradual decline between midsummer and autumn. Leaf starch increased dramatically to midsummer before declining sharply throughout late summer and early autumn; sucrose content responded inversely indicating a mobilization of starch reserves and export of sugars to root buds. Because newly formed underground adventitious buds showed a continuous increase in TNC from midsummer through autumn, export of sugars from aboveground tissues likely contributed to the increase in TNC. These results may facilitate strategies for biological control of leafy spurge. For instance, diverting photosynthetic assimilate away from early-season starch storage in leaves might disrupt the normal seasonal flow of sugars to underground vegetative buds in late summer/early autumn, thereby weakening bud dormancy and development and potentially disrupting the subsequent year’s growth.