How fresh is maple syrup? Sugar maple trees mobilize carbon stored several years previously during early springtime sap‐ascent

Abstract

SummaryWhile trees store substantial amounts of nonstructural carbon (NSC) for later use, storage regulation and mobilization of stored NSC in long-lived organisms like trees are still not well understood.At two different sites with sugar maple (Acer saccharum), we investigated ascending sap (sugar concentration, d13 C, D 14 C) as the mobilized component of stored stem NSC during early springtime. Using the bomb-spike radiocarbon approach we were able to estimate the average time elapsed since the mobilized carbon (C) was originally fixed from the atmosphere and to infer the turnover time of stem storage. Sites differed in concentration dynamics and overall d 13 C, indicating different growing conditions. The absence of temporal trends for d 13 C and D 14 C indicated sugar mobilization from a well-mixed pool with average D 14 C consistent with a mean turnover time (TT) of three to five years for this pool, with only minor differences between the sites. Sugar maple trees hence appear well buffered against single or even several years of negative plant C balance from environmental stress such as drought or repeated defoliation by insects. Manipulative investigations (e.g. starvation via girdling) combined with D 14

Radiocarbon dating of seized ivory confirms rapid decline in African elephant populations and provides insight into illegal trade

“…S1C shows that the cleanair sites used to determine F 14 C of NH and SH are far from the African continent. (ii) Remobilization of nonstructural carbon during plant growth: Muhr et al (26) have shown that nonstructural carbon in perennial tissues (e.g., branches, stems, and roots) can be mobilized and used for growth several years after fixation and thus F 14 C of dietary foodstuff may lag the F 14 C of the atmosphere; because elephants have a high component of perennial plants in their diets, this effect could be important in understanding any offset between atmospheric F 14 C and newly formed tissue F 14 C in herbivores. Ehleringer et al (27) showed a significant range in F 14 C for plants collected at a single time from a single region.…”

Responses of the structure and function of the understory plant communities to precipitation reduction across forest ecosystems in Germany

“…Note: In the leaf bulk material is a mixture of structural carbon as well as of storage compounds and freshly assimilated carbon (Adams and Grierson 2001;Werner et al 2012). Stored carbon is used for early leaf growth in plants (Gaudinski et al 2009;Muhr et al 2016). Thus, we did not analyzed the leaf samples for Δ 13 C in spring 2012.…”

“…Δ 13 C in the leaf organic matter is a signal integrating C i /C a over the leaf life time, and the leaf bulk material is a mixture of structural carbon as well as of storage compounds and freshly assimilated carbon (Adams and Grierson 2001;Werner et al 2012). Stored carbon is used for early leaf growth in plants with significant carbon storage capacities such as trees, shrubs and perennial herbs (Gaudinski et al 2009;Muhr et al 2016), which could explain the missing environmental signal in early summer also in the 2nd year, as it is assumed that remobilized storage reserves can be older than 1 year at least in woody species (Gessler and Treydte 2016). However, the response to reduced precipitation in total leaf organic matter should become visible later in the growing season, when new assimilates and their integration in fresh structural organic matter contribute significantly to the leaf carbon pool.…”

Are Northeastern U.S. forests vulnerable to extreme drought?

“…One reason why drought-induced mortality events are rather rare in the Northeastern U.S. may be associated with the high buffering capacity of carbon stores in temperate deciduous trees (Hoch et al 2003;Muhr et al 2016). Non-structural carbohydrates are not only important for sustaining growth and respiration, they also play a key role in embolism repair (Zwieniecki and Holbrook 2009;Nardini et al 2011) and in osmotic adjustments (Wang and Stutte 1992;Guicherd et al 1997;Hartmann and Trumbore 2016) necessary for sustaining turgor pressure under drought conditions.…”

“…In fact, Hoch et al (2003) showed that temperate deciduous trees contained sufficient NSCs to replace canopy leaves four times. Similarly, Muhr et al (2016) concluded that A. saccharum likely contains sufficient carbon reserves to buffer against periods of low carbon supply such as defoliation or drought. Thus, carbon-limitation under short-term drought may not be an issue for drought-sensitive species that actively regulate stem and leaf water potential at the expense of reductions in carbon reserves through stomatal closure and leaf abscission.…”