Morphogenetic and structural responses to tree-shading in three temperate perennial grasses: implications for growth, persistence and defoliation practices

Abstract

In humid-temperate silvopastoral systems (SPS), light limitations can affect the growth and persistence of temperate forage species in the understory. Our objectives were to describe the morphogenic and structural changes expressed under tree-shading (UNDER) and under non-limiting light conditions (OPEN), and how these factors could impact growth, persistence and defoliation management practices of perennial C3 grasses of different tolerance to shade: Dactylis glomerata (tolerant), Festuca arundinacea (moderately tolerant) and Phalaris aquatica (heliophilous). The experiment was carried out in thirty-six pots. Half of them in the OPEN and the other, UNDER an experimental stand of Populus deltoides planted at a 4 m × 4 m arrangement (n = 6). There were three general shade response mechanisms determined by tree-shading: a high proportion of growing leaves per tiller, a low number of living leaves and a low leaf lifespan. The increase of the proportion of growing leaves determined the increase in the total green laminae per tiller, leading to a short term increase in light resource acquisition and growth rate. However this common response was driven by different morhogenetic mechanisms in the three species, based on increase of phyllochron, reduction of leaf lifespan or both simultaneously. However, under shading all species had similar low values of leaf lifespan and would have similar optimal defoliation frequencies. An among species trade-off between green lamina length per tiller versus density of tillers per plant was found-i.e. growing versus persisting-but was not associated with differential species shade tolerance. These results contribute to understanding the shade tolerance mechanisms behind the known suitability of the three species under deciduous trees.