Modular and Demographic Analysis of Plant Leaf Area in Sward and Woodland Populations of Dactylis Glomerata and Bromus Erectus

Abstract

SUMMARY (1) Dactylis glomerata and Bromus erectus, two perennial grasses, were studied in two contrasted habitats: an open sward where D. glomerata is more frequent, and an adjacent Quercus pubescens woodland where B. erectus is more frequent. (2) A modular demographic analysis of the growth of above-ground plant parts was used as a non-destructive method to follow the seasonal evolution of leaf photosynthetic area and its age structure. (3) The four populations had similar seasonal changes in total photosynthetic area per plant, with two production peaks occurring in autumn and spring. The increase in tiller and leaf numbers occurred before the peaks of total leaf area per plant which resulted from leaf elongation. As the mean temperature of the air decreased, the rate of leaf emergence decreased but the longevity of the leaves increased, resulting in an increased proportion of older age-classes of photosynthetic area in winter. A similar shift towards older age-classes occurred during the summer drought. (4) The tree canopy affected the water status of the plants, as measured by leaf water potential, leading to increased leaf longevity and leaf length during the summer in the woodland compared to the sward. Except during summer, plants of each species had a similar total photosynthetic area in both habitats, but with a different combination of shoot and leaf components: in the woodland, individuals had fewer tillers but a higher photosynthetic area per tiller than in the sward. (5) B. erectus had a larger leaf area per plant than D. glomerata in both habitats from a higher number of tillers per plant, an increased number of leaves per tiller and a larger leaf size. Leaf longevity was longer in B. erectus. The decrease in the rate of leaf emergence in winter was more pronounced for B. erectus than for D. glomerata. (6) The effect of the environment on the size and components of the leaf area was similar for D. glomerata and B. erectus despite the contrasted frequency of the species in open and shady habitats.