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 (FETR) or of PSII (FPSII), maximum measured photosynthesis rate (ETRhv), maximum extrapolated rate of photosynthesis (ETRem), half-saturating photon flux density (KPAR), 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 ETRem and KPAR values with good FETR; long-cycle herbs have low ETRem and FETR and moderate KPAR values; spring ephemerals have elevate FETR, ETRem and KPAR values. The mean ETRem of ephemerals of 91 mmol m-2 s-1 exceeds that of long-cycle herbs 2.9-fold and woody species 4.8-fold, and corresponds to 19 mmol CO2 m-2 s-1 by assuming an ETR/FCO2 ratio of 4.7. Highest photosynthesis rates and KPAR were exhibited by five ephemerals (Eranthis, Erythronium, Narcissus, Scilla, Tulipa) with peak ETRem values equivalent to ~40 mmol CO2 m-2 s-1 or ~60 mmol CO2 (g Chl)-1 s-1 (“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 shadetolerant.