In situ 13C tracer experiments elucidate carbon translocation rates and allocation patterns in eelgrass Zostera marina

Abstract

Zostera marina L. carbon dynamics have been intensively studied, yet in situ translocation rate estimates remain elusive, particularly for north temperate seagrasses. To better understand carbohydrate synthesis, allocation and use in Z. marina, we conducted summer and winter in situ 13 C labeling experiments and measured the δ 13 C of bulk tissue and 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 belowground tissues (rhizome and roots) not directly exposed to the 13 C-dissolved inorganic carbon label, indicating that non-structural carbohydrate was translocated belowground. Rhizome δ 13 C increased for up to 2 wk after the 13 C label pulse. The isotopic enrichment of glucose, fructose and sucrose were similar and significantly greater than the enrichment of myo-inositol. Maximum enrichment occurred in the glucose pool, with leaf tissue at 258 ± 61 ‰ and rhizome tissue at 55.1 ± 28.8 ‰ during the July 2004 labeling period. Leaf excess 13 C loss rates (4 d average) were on the order of 11% 13 C d −1 , while the excess 13 C accumulation rate in the rhizome combined with roots was about 1.5% 13 C d −1 (4 d average). Whole plant excess 13 C loss rates as a result of respiration, detrital production and exudation ranged between about 8.8 and 10% 13 C d −1 (4 d average). The results provide important estimates of carbon uptake and translocation that can be used to better understand whole plant carbon budgets as well as the transfer of seagrass-derived carbon to other trophic communities.

Carbon stable isotope ratios of new leaves of Zostera marina in the mid-latitude region: Implications of seasonal variation in productivity

“…These results indicate that C movement is dominated by the translocation of newly-incorporated C, rather than by the resorption of C that was earlier incorporated into leaf structure, as demonstrated by 13 C tracer (Collier et al, 2010). Our results indicate that changes in seasonal temperature and solar irradiance likely alter the rates of carbon acquisition, but overall allocation patterns and translocation rates do not vary significantly in response to these environmental drivers (Kaldy et al, 2013).…”

Bivalve facilitation mediates seagrass recovery from physical disturbance in a temperate estuary

“…Propeller scars can create bare patches within seagrass beds by uprooting shoots and severing the rhizome connections (Zieman 1976, Byron and. Severing connections between clones in the rhizome could increase physiological stress and limit resource sharing among clones (Thayer et al 1984, Marbá et al 2006, Schwarzschild and Zieman 2008, Kaldy et al 2013. Seagrass has been shown to allocate more energy to the production of belowground biomass to increase resiliency after a disturbance (Peterson et al 2002, Connolly et al 2018.…”

Bioturbator‐stimulated loss of seagrass sediment carbon stocks

“…Plants were then removed from the solution, and thoroughly rinsed with distilled water to remove salts and excess label. This process and enrichment time likely concentrated enrichment in the labile compounds (e.g., soluble carbohydrates) within the seagrass leaves (Kaldy et al 2013), however, given the short time of this study (65 d), decomposition was most likely linked primarily to these compounds. Leaves were isolated from roots and rhizomes, and chopped into uniform pieces < 15 mm.…”