Photosynthetic properties of spring geophytes assessed by chlorophyll fluorescence analysis.

Since spring ephemerals are credited to be all "sun" species with unusually elevate photosynthesis, in contrast to shade-tolerant trees and understory geophytes with a long aboveground cycle, we examined the photosynthetic efficiency of 6 woody species, 9 long-cycle geophytes, and 8 spring ephemeral geophytes using blue flashes of increasing energy with the Imaging PAM fluorometer. Several parameters were obtained: quantum yield of electron transport (ΦETR) or of PSII (ΦPSII), maximum measured photosynthesis rate (ETR), maximum extrapolated rate of photosynthesis (ETR), half-saturating photon flux density (K), and in some cases photochemical (qP) and non-photochemical quenching (NPQ). Results confirm the ecological consistency of the three plant groups, with internal differences. Woody species have low ETR and K values with good ΦETR; long-cycle herbs have low ETR and ΦETR and moderate K values; spring ephemerals have elevate ΦETR, ETR and K values. The mean ETR of ephemerals of 91 μmol m s exceeds that of long-cycle herbs 2.9-fold and woody species 4.8-fold, and corresponds to 19 μmol CO m s by assuming an ETR/ΦCO ratio of 4.7. Highest photosynthesis rates and K were exhibited by five ephemerals (Eranthis, Erythronium, Narcissus, Scilla, Tulipa) with peak ETR values equivalent to ∼40 μmol CO m s or ∼60 μmol CO (g Chl) s ("sun" species). According to a new, fluorescence based heliophily index, all trees and five long-cycle herbs were definitely "shade" species, while four long-cycle herbs and three ephemerals were intermediate shade-tolerant.