Response of growth dynamics of two spring geophytes to light regime in a lime-beech forest

Biomass accumulation, leaf longevity and growth rate of two spring forest geophytes, Scilla bifolia L. and Arum maculatum L. were estimated separately for three size groups within each population of these species. Despite the differences in leaf longevity, both species showed a similar pattern of biomass accumulation in relation to their phenologies and reproductive demands. Eco-physiological acclimation to changing light environment was assumed through photosynthetic parameters and dynamics of leaf area index in the predominant size group of each species. A light response curve was measured under natural light for each species through the continuum of its phenology to quantify the photosynthetic photon flux density at light saturation, light-saturated photosynthetic rate, light compensation point, and dark respiration. Light-saturated assimilation per leaf area basis, dark respiration rate and light compensation points were significantly higher in S. bifolia relative to A. maculatum. However, the acclimation of photosynthesis that would respond to light changes in environment was not found in S. bifolia. In contrast, in A. maculatum a marked shift in the light dependence of photosynthesis through the season was noticed, which resulted in a strong photosynthetic acclimation to the low-light conditions. Accompanied by significant leaf area index, this efficient low-light photosynthesis enabled greater leaf longevity, and consequently longer accumulative period to A. maculatum. From the different parameters that we determined (both photosynthetic acclimation and growth strategy) it would appear that these species belong to two distinct subgroups: S. bifolia to the early and A. maculatum to the late vernals.