Allocation dynamics of recently fixed carbon in beech saplings in response to increased temperatures and drought

Abstract

The response of carbon allocation to drought has often been studied in terms of short-term transport velocity of recently fixed carbon from leaves to roots and root respiration. However, its dynamic response to other environmental conditions, e.g., to changes in temperature, is less clear. Here, we investigated the effects of drought, increased temperatures and their combination on transport velocity as well as on distribution of recent photoassimilates for different compounds, such as sugars, starch, organic acids and amino acids. We used a (13)CO(2) pulse-labelling approach and studied the recovery of (13)C in different plant tissues and compounds of beech saplings (Fagus sylvatica L.) during a 9-day chase period. Neither total dry biomass nor dry weights of leaves or roots were affected by drought or increased temperatures. Generally, the fast transfer of recently fixed assimilates from leaves to roots took about 1 day, while (13)C enrichment in soil CO(2) efflux peaked only 2 days after labelling. Increased temperatures prolonged mean transfer times of recent photoassimilates from the leaves to the roots, probably caused by enhanced intermediate storage alongside basipetal transfer, clearly impacting short-term carbon allocation. This temperature effect was seen in the delayed peak in (13)C excess of root sugars, decoupling the roots from the leaves in the short term. On average, ∼40% of the (13)C label initially present in the plant was recovered in the roots (over all treatment combinations), providing strong evidence for preferred carbon allocation into the roots at the end of the growing season. Root starch was the principal compound for long-term storage of carbon, whereas leaf (transitory) starch was remobilized again after some days, exhibiting the longest mean residence times under dry and warm conditions. These observation clearly point to different functionalities of the same compound (i.e., starch) in different plant tissues and the crucial role of roots for long-term carbon storage.

Impact of interspecific competition and drought on the allocation of new assimilates in trees

“…Moreover, the 13 C excess in leaf WSOM, as a measure of the total uptake and conversion of 13 CO 2 to soluble sugars, was also not affected by the drought treatment. This is in agreement to the findings of Blessing et al (2015), but contradicts the observations of Ruehr et al (2009) for beech. The latter authors found clearly higher maximum d 13 C and 13 C excess in leaf WSOM in controls compared to drought-treated plants directly after labelling.…”

“…Moreover, it is necessary to consider the fate of newly assimilated carbohydrates in different plant tissues as well as the long-distance transport via the phloem (Paterson et al 2009;Ruehr et al 2009;Offermann et al 2011) to understand the biomass allocation dynamics as well as root functioning in plants under changing environmental conditions (Blessing et al 2015).…”

“…The biosphere mediates the C flow from the atmosphere to the soil system also on short time scales (Barthel et al 2011;Blessing et al 2015), and in future the frequency of extreme events such as drought will most likely increase. It is thus important to understand the mechanisms that drive C allocation, C transfer times and above-to-belowground coupling strength as affected by environmental drivers.…”

Impacts of leaf age and heat stress duration on photosynthetic gas exchange and foliar nonstructural carbohydrates in Coffea arabica

“…The decline in starch with no significant shifts in sucrose and glucose + fructose at day 2 may indicate the allocation of NSC to metabolic maintenance and repair in response to the 45‐min treatment (Bita & Gerats, 2013). This may also be due to increased respiration (Way & Yamori, 2014), as well as the remobilization of starch from source leaves to roots (Blessing, Werner, Siegwolf, & Buchmann, 2015), although we did not measure NSC in roots. By days 15 and 25, total NSC, starch, and sucrose of the 45‐min group had significantly accumulated compared to controls, coinciding with the full recovery of photosynthesis and F V / F M .…”

“…Also, soluble sugars such as sucrose are among the primary metabolites and osmolytes known to accumulate in response to heat stress (Wahid et al., 2007) and are necessary for protection from elevated temperature and maintaining water balance and membrane stability (Bita & Gerats, 2013; Farooq et al., 2008). Sucrose is translocated from source leaves to sink organs through the phloem, and its transient increase in plants subjected to 90 min of heat stress may also be associated with a disruption or inhibition of phloem transport (Blessing et al., 2015; Sala et al., 2012; Woodruff, 2014). The subsequent decline in sucrose after day 2 suggests that the demand for sucrose for repair, renewed growth, and ongoing metabolism was greater than the supply from photosynthesis, which was still inhibited on day 50.…”