Warming experiments underpredict plant phenological responses to climate change.

Warming experiments are increasingly relied on to estimate plant responses to global climate change. For experiments to provide meaningful predictions of future responses, they should reflect the empirical record of responses to temperature variability and recent warming, including advances in the timing of flowering and leafing. We compared phenology (the timing of recurring life history events) in observational studies and warming experiments spanning four continents and 1,634 plant species using a common measure of temperature sensitivity (change in days per degree Celsius). We show that warming experiments underpredict advances in the timing of flowering and leafing by 8.5-fold and 4.0-fold, respectively, compared with long-term observations. For species that were common to both study types, the experimental results did not match the observational data in sign or magnitude. The observational data also showed that species that flower earliest in the spring have the highest temperature sensitivities, but this trend was not reflected in the experimental data. These significant mismatches seem to be unrelated to the study length or to the degree of manipulated warming in experiments. The discrepancy between experiments and observations, however, could arise from complex interactions among multiple drivers in the observational data, or it could arise from remediable artefacts in the experiments that result in lower irradiance and drier soils, thus dampening the phenological responses to manipulated warming. Our results introduce uncertainty into ecosystem models that are informed solely by experiments and suggest that responses to climate change that are predicted using such models should be re-evaluated.

Vertical migration by the marine dinoflagellate Prorocentrum triestinum maximises photosynthetic yield.

Although vertical migration has been widely documented in many dinoflagellate species, the adaptive advantages of the strategy remain unclear. To investigate relationships between diurnal vertical migration and depth-related variation in photosynthetic yield in a marine dinoflagellate, Prorocentrum triestinum (Schiller), two experimental approaches were adopted. First, vertical distribution patterns of P. triestinum in a shallow estuary were investigated with respect to depth-related variation in photosynthetic rate. Second, changes in vertical positioning of P. triestinum in response to manipulations in incident light flux were investigated in an artificial water column. During the field experiment, changes in dissolved oxygen concentration in bottle cultures of P. triestinum indicated maximum rates of photosynthesis at 0.5 m depth. Cell densities of P. triestinum in the water column were also highest at 0.5 m depth and varied in accordance with photosynthetic yield. Fluorescence measurements indicated photoinhibition at super-saturating photosynthetic photon flux densities (PPFDs). Similar patterns were evident in the artificial water column. Depth distribution of P. triestinum varied significantly according to incident PPFD; the band of maximum cell density shifted downward in response to an increase in PPFD and upward in response to a PPFD decrease. Distributions of cells with respect to PPFD were very similar to those observed in the field experiment. Overall, vertical positioning of P. triestinum during the day is consistent with an active migratory mechanism for maximising photosynthetic production.