Seasonal variations drive short‐term dynamics and partitioning of recently assimilated carbon in the foliage of adult beech and pine

Abstract

Summary13 CO 2 pulse-labelling experiments were performed in situ on adult beeches (Fagus sylvatica) and pines (Pinus pinaster) at different phenological stages to study seasonal and interspecific short-term dynamics and partitioning of recently assimilated carbon (C) in leaves.Polar fraction (PF, including soluble sugars, amino acids and organic acids) and starch were purified from foliage sampled during a 10-d chase period. C contents, isotopic compositions and 13 C dynamics parameters were determined in bulk foliage, PF and starch. Decrease in 13 C amount in bulk foliage followed a two-pool exponential model highlighting 13 C partitioning between 'mobile' and 'stable' pools, the relative proportion of the latter being maximal in beech leaves in May. Early in the growing season, new foliage acted as a strong C sink in both species, but although young leaves and needles were already photosynthesizing, the latter were still supplied with previous-year needle photosynthates 2 months after budburst. Mean 13 C residence times (MRT) were minimal in summer, indicating fast photosynthate export to supply perennial organ growth in both species. In late summer, MRT differed between senescing beech leaves and overwintering pine needles. Seasonal variations of 13 C partitioning and dynamics in field-grown tree foliage are closely linked to phenological differences between deciduous and evergreen trees.

The 18O‐signal transfer from water vapour to leaf water and assimilates varies among plant species and growth forms

“…We therefore compared our results with those of 13 CO 2 experiments (Epron et al, ). MRT WSC values derived from decay constant values after a 13 CO 2 pulse‐labelling ranged between 5 to 25 hr for beech and pine saplings across the season (Desalme et al, ) and 57.6 hr for nondrought stressed beech saplings (Ruehr et al, ) and were thus lower or similar to those of the present study. MRT Sugars values of broadleaf and conifer saplings ranged between 14 and 22 hr (Blessing, Werner, Siegwolf, & Buchmann, ; Galiano Pérez et al, ) and were lower compared with MRT Sugars values of 28 and 40 hr for broadleaf and conifer plants in the present study, respectively.…”

Functional differences in the microbial processing of recent assimilates under two contrasting perennial bioenergy plantations

“…These findings suggest that in miscanthus, a greater proportion of labelled assimilates were preferentially allocated toward the synthesis of new photosynthetic biomass and supporting structures. These results may reflect differences in the phenological stage of the two crops rather than differences in their physiology as Desalme et al (2017) also showed C partitioning to new photosynthetic biomass in C3 trees early in their growing seasons. This appeared to be confirmed by 2,4,7,14,21,28,42,76,104 and 194 days.…”

“…In addition to differences in metabolic pathways between taxa, the efficiency with which plants assimilate C is also dependent upon both environmental conditions and the phenological stage (Desalme et al, 2017;Gowik and Westhoff, 2011;Raines, 2011).…”

Drought impacts on tree phloem: from cell-level responses to ecological significance

“…The need for osmotic adjustment and synthesis of secondary metabolites could explain all or part of the observed increase in 13 CO2 or 14 CO2 label residence times in leaves under drought (Ruehr et al 2009;Blessing et al 2015;Dannoura et al 2019) (See also Table 1). While there is a clear need to better address how water stress of different intensities and different durations alters carbon partitioning within the leaf between growth, export, osmoregulation and defence (Desalme et al 2017), existing knowledge strongly suggests that the decrease in assimilation, increase in respiration over photosynthesis ratio, and upregulation of metabolic pathways that result in the formation of volatile compounds, osmotic solutes, and secondary metabolites decreases the fraction of assimilates available to be loaded in the phloem (Figure 2).…”