Abstract
The allocation of recently assimilated carbon (C) by plants depends on developmental stage and on environmental factors, but the underlying mechanisms are still a matter of debate. In the present study, we investigated the regulation of C uptake and allocation and their adjustments during plant growth. We induced different allocation strategies in the Mediterranean shrub Halimium halimifolium L. by a reduction of light (Low L treatment) and nutrient availability (Low N treatment) and analyzed allocation parameters as well as morphological and physiological traits for 15 months. Further, we conducted a 13CO2 pulse-labeling and followed the way of recently assimilated carbon to eight different tissue classes and respiration for 13 days. The plant responses were remarkably distinct in our study, with mainly morphological/physiological adaptions in case of light reduction and adjustment of C allocation in case of nutrient reduction. The transport of recently assimilated C to the root system was enhanced in amount (c. 200%) and velocity under nutrient limited conditions compared to control plants. Despite the 57% light reduction the total biomass production was not affected in the Low L treatment. The plants probably compensated light reduction by an improvement of their ability to fix C. Thus, our results support the concept that photosynthesis is, at least in a medium term perspective, influenced by the C demand of the plant and not exclusively by environmental factors. Finally, our results indicate that growing heterotrophic tissues strongly reduce the C reflux from storage and structural C pools and therefore enhance the fraction of recent assimilates allocated to respiration. We propose that this interruption of the C reflux from storage and structural C pools could be a regulation mechanism for C translocation in plants.
Highlights
The first step in understanding plant carbon (C) allocation is to investigate the translocation of recent photosynthates
Changes in Morphological and Physiological Traits and Biomass Allocation We found a high intraspecific variability of biomass allocation induced by 15 months of nutrient or light reduction (Figure 1)
Changed growing conditions are shown above the broken line: photosynthetic photon flux density (PPFD) measured at substrate surface and nitrogen (N) concentration in fertilizer solution
Summary
The first step in understanding plant carbon (C) allocation is to investigate the translocation of recent photosynthates. Photosynthetic C isotope discrimination can be used to trace the Intraspecific plasticity in C allocation fate of C from plant to ecosystem scale (see Dawson et al, 2002) but the natural C isotope signals are relatively small. Pulselabeling with stable or radioactive C isotopes provides a more efficient tool for a detailed analysis of C allocation in plants (for a recent review see Epron et al, 2012). It allows to investigate very fast translocation of C after photosynthetic fixation (Atkin, 2015). In a field study on grasses and shrubs, Carbone and Trumbore (2007) found that 48–61% of the recovered label was respired within 24 h across seasons and plant types
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