Abstract
Although understanding the timing of the deposition of recent photosynthate into fine roots is critical for determining root lifespan and turnover using isotopic techniques, few studies have directly examined the deposition and subsequent age of root carbon. To gain a better understanding of the timing of the deposition of root carbon, we labeled four individual Sassafras albidum trees with 99% 13C CO2. We then tracked whether the label appeared in roots that were at least two weeks old and no longer elongating, at the time of labeling. We found that not only were the non-structural carbon pools (soluble sugars and starch) of existing first-order tree roots incorporating carbon from current photosynthate, but so were the structural components of the roots, even in roots that were more than one year old at the time of labeling.Our findings imply that carbon used in root structural and nonstructural pools is not derived solely from photosynthate at root initiation and have implications regarding the determination of root age and turnover using isotopic techniques.
Highlights
The timing of the deposition of photosynthetically derived carbon into roots is of considerable scientific importance because it has implications both for factors controlling root physiology and lifespan and for the determination of root age and turnover using isotopic techniques
In 2009, in addition to root structural carbon, both root soluble sugars and root starch were significantly enriched with 13C by labeling (P = 0.001 and P,0.0001) (Figure 5), with soluble sugars being most enriched followed by starch and structural carbon
The incorporation of current photosynthate into the structural carbon of roots which were at least two weeks old, and in some roots more than a year old, at the time of labeling has implications regarding the determination of root age and turnover using isotopic techniques
Summary
The timing of the deposition of photosynthetically derived carbon into roots is of considerable scientific importance because it has implications both for factors controlling root physiology and lifespan and for the determination of root age and turnover using isotopic techniques. After labeling the trees with 13C, preexisting roots of a known age were excised by cutting through the acetate window and individual first-order roots were analyzed for 13C in structural and nonstructural carbon pools.
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