How phenology influences physiology in deciduous forest spring ephemerals

Abstract

Spring ephemerals of deciduous forest are adapted to take advantage of the high-light period available in early spring. They appear shortly after snow melt and complete their aboveground growth, including fruit production, within 2 months. After they produce new buds, they senesce and enter dormancy. Dormancy is not very deep in spring ephemerals and during summer differentiation occurs in the bud of the apparently resting organ. Low soil temperatures release dormancy, and the shoots and roots then grow slowly over autumn and winter. The goal of this paper is to show how this characteristic phenology influences many aspects of spring ephemerals' physiology, and the influences these different physiological parameters have on each other. Spring ephemerals have high photosynthetic rates that allow them to rapidly accumulate carbohydrates and complete their aboveground growth in a few weeks. To sustain high photosynthetic rates in early spring, the plants must be able to absorb water efficiently at low soil temperatures and to allocate large amounts of nutrients to the shoot to compensate for lower enzymatic activity at low temperatures. Nutrients are mainly absorbed in spring, although the root system is established in autumn. This means that a large amount of both carbohydrates and nutrients is translocated from the perennial organ to the developing shoot starting in autumn through early spring. Spring ephemerals have low nutrient absorption rates, but high resorption efficiency during leaf senescence. Nevertheless, their high nutrient needs restrict them to rich forest soils. The annual growth rate of spring ephemerals is very slow and this is more likely related to the inherent slow growth rate of the perennial organ than to their short leaf life. As soon as carbohydrate reserves are replenished in spring, sink limitation apparently builds up and induces leaf senescence. A better understanding of the factors controlling the growth rate of spring ephemerals is needed before we can predict these plants' response to climatic changes.

The importance of nitrogen and carbohydrate storage for plant growth of the alpine herb Veratrum album

“…The carbon assimilation of a leaf is linearly related to the N content of that leaf (Hirose & Werger, 1987;Evans, 1989). For spring ephemerals it has been suggested that the observed high photosynthetic rate early in the season allows them to complete their above-ground growth cycle in the short time span before the forest canopy closes (Lapointe, 2001). Similarly, the early season high nutrient concentrations may allow V. album to refill the carbohydrate stores used up during autumn, winter and early spring growth in a short period of time.…”

Can plantations develop understory biological and physical attributes of naturally regenerated forests?

“…These differences may have constrained the establishment of forest herbs associated with deciduous stands. For example, the acidic and nutrient-limited needle litter layer (Hunter, 1990;Augusto et al, 2002), together with cool and dark spring conditions found under conifer canopy compared to those of a deciduous canopy, may have inhibited the establishment of many spring-flowering herbs, which are known to be nutrient-and light-demanding during their short spring time, above ground vegetative cycle (Lapointe, 2001;Whigham, 2004). At the species level, we did not find in this stand type any high conservation value species, such as orchids, associated with acidic litter.…”

How do sink and source activities influence the reproduction and vegetative growth of spring ephemeral herbs under different light conditions?

“…They are mostly clonal and perennial (Whigham 2004) with yearly renewal of the underground parts. After shoot emergence, spring ephemerals assimilate carbon under high irradiance prior to canopy closure in the forest (Lapointe 2001;Rothstein and Zak 2001). This assimilated carbon may be directed towards vegetative growth and reproduction simultaneously.…”