Aspen shoots are carbon autonomous during bud break

Abstract

Current thinking holds that carbon autonomy of branches in trees is unlikely, particularly during bud break, when the new developing shoots require significant influx of carbon resources from more distant sources. Results from recent studies indicate that the impact of bud break on overall tree reserves might be small. In two studies the independence of flushing shoots from stored carbon reserves and the photosynthesis in developing new leaves and shoots of Populus tremuloides were explored. New developing shoots quickly became a positive carbon source and only a few days into flush, the photosynthetic system of the newly developing shoots was efficient enough to achieve positive carbon gain even at low light levels. Only 14% of the stored shoot reserves, without any mobilization from more distant reserves, were used during bud break and early shoot expansion. Without any underlying stress, shoots of deciduous trees appear to be carbon autonomous during bud break when demand on stored carbon should be the highest. The development of an efficient photosynthetic system in new shoots is critical in the recovery of carbon reserves in aspen. It minimizes the cost of bud break to the overall stored carbon reserves by optimizing the assimilation of carbon in the newly developed leaves, while eliminating the cost for mobilizing carbon reserves from more distant sources. This carbon autonomy of shoots has important implications for the whole tree carbon balance particularly to the non-photosynthetic tissues which functions solely depending on carbon export from the newly developing leaves and shoots.

Defoliation increases risk of carbon starvation in root systems of mature aspen

“…As a result, the reflushing of leaves after a defoliation event might not be as costly as one would expect. In abscised aspen shoots, stored reserves were lowered only by 14% during budflush and with shoot reserves being rebuilt after only 7 days after the flush of new leaves (Landhäusser 2011). It appears that in seedlings and small trees, the bole is small and will behave more like a branch on a mature tree where sinks are smaller and C reserves can accumulate even during periods of stress (Ludovici et al 2002;Sanz-Pérez et al 2009).…”

Are stored carbohydrates necessary for seed production in temperate deciduous trees?

“…). Recent studies have shown that deciduous temperate tree species use current photosynthates mostly for leaf formation, because developing leaves become C‐autonomous very soon after bud break (Keel & Schädel ; Landhäusser ). We can therefore use current leaves of deciduous tree species as an indicator of Δ 14 C of atmospheric CO 2 at the study site.…”

Partitioning of carbon allocation to reserves or growth determines future performance of aspen seedlings

“…Upon outplanting, root TNC reserves are important for seedlings to survive the stressful environmental conditions, such as high water stress encountered immediately after planting (Grossnickle, 2005). New root growth in the closely related European aspen (Populus tremula) was dependent on current photosynthates (Eliasson, 1968) so adequate root TNC reserves could allow for early root growth in seedlings while stem reserves are adequate to support the flush of the new foliage in the spring (Landhäusser, 2011).…”

“…These variables are currently being used for aspen and appear to be poor predictors for the quality of aspen planting stock. Stored carbohydrates reserves are important for the establishment and growth of seedlings, particularly in deciduous species that need to rely on the stored reserves to initiate leaf area and new root growth without current photosynthesis (Loescher et al, 1990;Turgeon, 1989;Chapin et al, 1990;Kozlowski, 1992;Kozlowski and Pallardy, 2002;Sprugel, 2002;Landhäusser, 2011).…”