Carbon economy in walnut seedlings during the acquisition of autotrophy studied by long‐term labelling with ¹³CO₂

Abstract

A closed growth chamber was designed to study the acquisition of autotrophy by seedlings of walnut (Juglans regia L. cv. Lara) in controlled conditions (22°C, 12‐h photoperiod) during the first two months of growth. The chamber consisted of two airtight compartments, in which continuous gas exchange was measured on the aerial and subterranean parts of several batches of tree seedlings. Long‐term labelling with 13CO2 was used in the chamber to study the import, distribution, and respiratory losses of photoassimilates (autotrophic carbon) in relation to the partitioning and use of reserves of the maternal seed (heterotrophic carbon). The carbon economy of walnut seedlings was estimated by measurements of gas exchange, carbon content, and 13C/12C isotopic ratio in dry matter and respiratory CO2. The seedlings were entirely heterotrophic for energy and structural growth during the first 21 days after sowing. From day 22, photosynthesis appeared. At day 29, autotrophic carbon accounted for 25% and 30% of respiration in the root and shoot respectively; these proportions increased to 45% and 65% at day 54. The autotrophic carbon was incorporated into the dry matter of the shoot from day 32 but only after day 40 into the dry matter of the taproot. From day 32, the total contribution of heterotrophic carbon decreased regularly, and until day 43, it was essentially used for root growth. Thereafter, the contribution of heterotrophic carbon was negligible, and at day 54 the walnut seedlings were entirely autotrophic.

Stable carbon and nitrogen isotope compositions change with leaf age in two mangrove ferns

“…The differentiation of three developmental stages has been shown earlier by 13 CO 2 tracer studies (Améziane et al, 1997;Deléens et al, 1994;Maillard et al, 1994aMaillard et al, , 1994b. The first stage is predominantly heterotrophic, i.e.…”

Effects of Acetate on Facultative Autotrophy inChlamydomonas reinhardtii Assessed by Photosynthetic Measurements and Stable Isotope Analyses

“…Estep andHoering (1980, 1981) determined the fraction of reduced biomass resulting from photosynthesis during mixotrophic growth of Chlorella sorokiniana on Glc or acetate medium in the presence of 1% CO 2 using stable hydrogen isotope analysis. Differences in ␦ 13 C have also been used to determine the time of onset of autotrophy in developing seedlings (Deléens et al, 1984;Maillard et al, 1994aMaillard et al, , 1994b. Dual isotope methods have been applied to assess carbon and nitrogen allocation during maize stem elongation (Cliquet et al, 1990) and biomass derived from translocated Suc and photosynthesis in the partially photosynthetic hypsophylls (husks) of maize (Yakir et al, 1991) and in vitro-grown potato plantlets (Wolf et al, 1998).…”

Walnut (Juglans spp.) ecophysiology in response to environmental stresses and potential acclimation to climate change

“…3a). As the taproot develops from the seed in the first month of growth, N is allocated primarily to below-ground parts of seedlings, but rapidly developing aerial parts receive the majority of N during the second month of growth (Maillard et al 1994a; Fig. 3b).…”

“…1a). Photosynthesis begins thereafter but is negligible until the second month of growth (Maillard et al 1994a). In plantlets provided with a growing medium, autotrophy can be attained 8 days after transfer to a growth chamber (Chenevard et al 1997), but seedlings need at least 40-50 days before they no longer depend on the maternal seed (Maillard et al 1994a, b).…”

“…Like oaks and other large-seeded species, walnut uses carbohydrates stored in the maternal seed to develop its taproot (Maillard et al 1994a). For the first 3 weeks after sowing, the seedling is entirely heterotrophic, i.e., its growth depends exclusively on the seed's C reserves (Maillard et al 1994a;Fig. 1a).…”