Direct uptake of organically derived carbon by grass roots and allocation in leaves and phytoliths: <sup>13</sup>C labeling evidence
In the rhizosphere, the uptake of low-molecular-weight carbon (C) and nitrogen (N) by plant roots has been well documented. While organic N uptake relative to total uptake is important, organic C uptake is supposed to be low relative to the plant's C budget. Recently, radiocarbon analyses demon...
| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-03-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/1693/2016/bg-13-1693-2016.pdf |
| Summary: | In the rhizosphere, the uptake of low-molecular-weight carbon (C) and
nitrogen (N) by plant roots has been well documented. While organic N uptake
relative to total uptake is important, organic C uptake is supposed to be low
relative to the plant's C budget. Recently, radiocarbon analyses demonstrated
that a fraction of C from the soil was occluded in amorphous silica
micrometric particles that precipitate in plant cells (phytoliths). Here, we
investigated whether and to what extent organically derived C absorbed by
grass roots can feed the C occluded in phytoliths. For this purpose we added
<sup>13</sup>C- and <sup>15</sup>N-labeled amino acids (AAs) to the silicon-rich
hydroponic solution of the grass <i>Festuca arundinacea</i>. The experiment
was designed to prevent C leakage from the labeled nutritive solution to the
chamber atmosphere. After 14 days of growth, the <sup>13</sup>C and <sup>15</sup>N
enrichments (<sup>13</sup>C excess and <sup>15</sup>N excess) in the roots, stems and
leaves as well as phytoliths were measured relative to a control experiment
in which no labeled AAs were added. Additionally, the <sup>13</sup>C excess was
measured at the molecular level, in AAs extracted from roots and stems and
leaves. The net uptake of labeled AA-derived <sup>13</sup>C reached 4.5 % of the total AA
<sup>13</sup>C supply. The amount of AA-derived <sup>13</sup>C fixed in the plant was
minor but not nil (0.28 and 0.10 % of total C in roots and stems/leaves,
respectively). Phenylalanine and methionine that were supplied in high
amounts to the nutritive solution were more <sup>13</sup>C-enriched than other AAs
in the plant. This strongly suggested that part of AA-derived <sup>13</sup>C was
absorbed and translocated into the plant in its original AA form. In
phytoliths, AA-derived <sup>13</sup>C was detected. Its concentration was on the
same order of magnitude as in bulk stems and leaves (0.15 % of the
phytolith C). This finding strengthens the body of evidences showing that
part of organic compounds occluded in phytoliths can be fed by C entering the
plant through the roots. Although this experiment was done in nutrient
solution and its relevance for soil C uptake assessment is therefore limited,
we discuss plausible forms of AA-derived <sup>13</sup>C absorbed and translocated
in the plant and eventually fixed in phytoliths, and implications of our
results for our understanding of the C cycle at the soil–plant–atmosphere
interface |
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| ISSN: | 1726-4170 1726-4189 |