Diel growth in eelgrass Zostera marina

Growth of eelgrass Zostera marina leaves was determined by sequential measurements of leaf length at time intervals of 4 to 12 h. Leaf growth rates at night were consistently lower (30 to 40 %) compared to daytime rates, and night-time rates were highly correlated with growth during the previous day. Diel patterns of O2 metabolism (measured at 2 to 4 h intervals) and leaf growth (at 4 h intervals) generally followed the daily irradiance cycle, with maximum growth and 0 2 production rates both occurring near midday. Rapid (hours to days) responses to changes in environmental conditions such as light and sediment fertility were detected using this leaf growth method. Quantitative comparison of diel integrals of growth (increases in leaf, root, and rhizome biomass) and net O2 production indicated that the 2 processes were in relative balance. Although eelgrass leaf growth was determined readily here on short time-scales, measurement of total plant growth required a longer study period approaching the plastochrone interval (leaf formation time). It was demonstrated, however, that separate cahbration studies relating root-rhizome growth to leaf growth can be conducted (over 1 to 2 wk) to allow estimates of short-term (4 to 12 h) responses of total plant growth to changes in environmental conditions.