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In Situ Carbon Stable Isotope Tracer Experiments Elucidate Carbon Translocation Rates and Allocation Patterns in Zostera marina L. (eelgrass)
Citation:
Kaldy, Jim, C. Brown, AND C. Andersen. In Situ Carbon Stable Isotope Tracer Experiments Elucidate Carbon Translocation Rates and Allocation Patterns in Zostera marina L. (eelgrass). MARINE ECOLOGY PROGRESS SERIES. Inter-Research, Luhe, Germany, 487:27-39, (2013).
Impact/Purpose:
Seagrass carbon dynamics and photosynthetic physiology have received intense attention over the last 3 decades. Understanding seagrass carbon dynamics and balance is necessary to protect and restore this valuable ecosystem engineer. Although many studies have examined how much carbon is fixed and how large the storage reserves are, few studies have examined of how much carbon is moved around within a plant and which compounds are mobilized. Our goal was to examine the patterns of carbon allocation and to estimate translocation rates of fixed carbon in situ under winter and summer conditions. We conducted three isotope tracer enrichment experiments and measured the bulk tissue isotope ratio as well as the δ 13C of individual carbohydrate pools. Using these data, we were able to determine carbon translocation rates for a field population of Z. marina. The results provide important estimates of C uptake and translocation that can be used in modeling efforts designed to better understand natural and anthropogenic stresses affecting this species.
Description:
The intertidal seagrass Zostera marina is an important species that provides critical habitat for a number of estuarine species. Despite its widespread distribution, there is limited information on seasonal patterns of carbon dynamics of plants growing in situ, particularly estimates of translocation for plants growing in the northern reaches of its distribution. In order to better understand carbohydrate synthesis, allocation and use in Z. marina, we conducted in situ 13C labeling experiments and measured the bulk tissue isotope ratio as well as the δ 13C of individual carbohydrate compounds. Leaf tissue exhibited immediate isotope enrichment within hours of the tracer pulse. As the isotope ratio of the leaf tissue decreased over a period of days, enrichment became more evident in the below-ground tissues (rhizome and roots) not directly exposed to the 13C-DIC label, indicating that non-structural carbohydrate (NSC) was translocated below-ground. Transport of NSC, as indicated by changes in tissue δ 13C values, continued to be mobilized for at least 4 d. Rhizome δ 13C continued to increase for up to 2 weeks after the 13C label pulse. We detected 4 carbohydrate compounds in the plant tissues. The isotopic enrichment of glucose, fructose and sucrose were similar, and significantly greater than the enrichment of myo-inositol (Kruskal-Wallis ANOVA on ranks, p<0.05). Maximum enrichment occurred in the glucose pool with leaf tissue at +258 ± 61‰ and rhizome tissue at + 55.1 ± 28.8‰ during the July labeling period. Leaf 13C loss rates were on the order of 11% 13C d-1, while the 13C accumulation rate in the rhizome combined with roots was about 1.5% 13C d-1. Whole plant 13C loss rates, as a result of respiration, detrital production, and exudation, ranged between about 8.8 and 10 % 13C d-1. The results provide important estimates of C uptake and translocation that can be used in modeling efforts designed to better understand natural and anthropogenic stresses affecting this species.