Carbon allocation to the root system of tropical tree Ceiba pentandra using 13C pulse labelling in an aeroponic facility

Abstract

Despite the important role of tropical forest ecosystems in the uptake and storage of atmospheric carbon dioxide (CO2), the carbon (C) dynamics of tropical tree species remains poorly understood, especially regarding belowground roots. This study assessed the allocation of newly assimilated C in the fast-growing pioneer tropical tree species Ceiba pentandra (L.), with a special focus on different root categories. During a 5-day pulse-labelling experiment, 9-month-old (~3.5-m-tall) saplings were labelled with 13CO2 in a large-scale aeroponic facility, which allowed tracing the label in bulk biomass and in non-structural carbohydrates (sugars and starch) as well as respiratory CO2 from the canopy to the root system, including both woody and non-woody roots. A combined logistic and exponential model was used to evaluate 13C mean transfer time and mean residence time (MRT) to the root systems. We found 13C in the root phloem as early as 2 h after the labelling, indicating a mean C transfer velocity of 2.4 ± 0.1 m h−1. Five days after pulse labelling, 27% of the tracers taken up by the trees were found in the leaves and 13% were recovered in the woody tissue of the trunk, 6% in the bark and 2% in the root systems, while 52% were lost, most likely by respiration and exudation. Larger amounts of 13C were found in root sugars than in starch, the former also demonstrating shorter MRT than starch. Of all investigated root categories, non-woody white roots (NRW) showed the largest 13C enrichment and peaked in the deepest NRW (2–3.5 m) as early as 24 ± 2 h after labelling. In contrast to coarse woody brown roots, the sink strength of NRW increased with root depth. The findings of this study improve the understanding of C allocation in young tropical trees and provide unique insights into the changing contributions of woody and non-woody roots to C sink strengths with depth.

Patterns of total root and shoot carbon dioxide fluxes and their impact on daily tree carbon budget in large tropical tree saplings

“…The functions of fine-and coarse-roots dictate different allocation (Mannerheim et al 2020), metabolic and respiration rates (Pregitzer et al 1998, Chen et al 2010, so that the thinner a root is, the higher is its respiration rate. Our findings confirm this trend in all the measurements of respiration of different root diameter classes, regardless of tree size and year.…”

“…Carbon assimilated during photosynthesis is either utilised by the leaves or is loaded to the phloem, and is then translocated to the different sink organs along the phloem pathway from the shoot to the roots (Mannerheim et al 2020). When sugars are un-loaded from the phloem in the roots, the C that they contain is incorporated into new structural biomass, into C reserves, mostly in coarse-roots, or is emitted out of the tree as CO2 after being consumed by respiration to maintain the root metabolism and functioning (Hartmann et al 2018).…”

Validation of Aeroponic Cultivation of Jalapeño Pepper (Capsicum annuum L.) through Thermal and Morphometric Characterization of Roots and Leaves

“…Aeroponics is a soilless cultivation technique [14][15][16][17][18][19][20][21][22][23][24][25], it is considered a potential method for cultivation of herbal plants due to the high growth rate and improvement in quantity and quality of production [26,27]. In aeroponic crops, to achieve maximum efficiency, it is important to analyze the environments with which the plants interact.…”

Sustainable Production of Insecticidal Compounds from Persea indica

“…[ 16 ], ginsenosides from Panax ginseng [ 17 ], β-sitosterol from Cannabis sativa roots [ 18 ], caffeic acid and methyl rosmarinate from Melissa officinalis [ 19 ] among others, including the sustainable production of medicinal endangered species [ 20 , 21 ]. Aeroponic cultivation of trees has been demonstrated to be a useful tool for eco-physiological studies such as drought pre-conditioning in temperate species [ 22 ] or above–below ground carbon fluxes and uptake in tropical species [ 23 , 24 ] and in forestry for vegetative reproduction of rare species [ 25 ] and reforestation [ 26 ]. However, the aeroponic cultivation of trees for the production of bioactive metabolites is uncommon.…”