Seeds Use Temperature Cues to Ensure Germination under Nurse-plant Shade in Xeric Kalahari Savannah

Abstract

The data support the hypothesis that canopy species have developed mechanisms to prevent germination in open sun conditions. The results and data from the literature show that inhibition of germination at temperature regimes characteristic of open sun conditions can be found in fleshy-fruited species of widely divergent taxonomic groups. It is predicted that germination mechanisms to detect canopy shade based on temperature cues are widespread in species depending on nurse plants, especially bird-dispersed species.

Seed germination at different temperatures and seedling emergence at different depths of Rhamnus spp

“…In conclusion, suitable conditions including temperature and humidity are necessary for seed germination, emergence and seedling survival [47][48][49]. R. ludovici-salvatoris has shown a low ability for seed germination at 5-15ºC temperature regimes, as well as a low ability to emerge seedlings when compared with other temperature regimes and both populations of R.alaternus, even from shallow burials.…”

Subcanopy genetics —The relationship between canopy tree size and genetic variation of the savanna species <i>Pollichia campestris</i> Aiton (Illecebraceae)

“…Of all plant groups tested in the study of Kos and Poschlod [6] fleshy-fruited perennials showed the strongest ecological binding to subcanopy habitats since germination rates of their seeds were very low under matrix conditions. This is especially true for Pollichia campestris Aiton (Illecebraceae) where germination was completely inhibited under matrix conditions, making the species an ideal object for further researches.…”

“…While trees are forming the canopy vegetation, the matrix layer between the trees is dominated by herbaceous plants, especially grasses [2,3]. Due to several effects, including shading, nutrient accumulation and supply of nest sites and food, the trees provide a unique habitat for animals and specialised subcanopy plants [2,[4][5][6][7]. These plant species typically produce small edible fruits dispersed by frugivores, and their seeds predominantly germinate in the temperature regime found in the shade of nurse trees [6].…”

“…Due to several effects, including shading, nutrient accumulation and supply of nest sites and food, the trees provide a unique habitat for animals and specialised subcanopy plants [2,[4][5][6][7]. These plant species typically produce small edible fruits dispersed by frugivores, and their seeds predominantly germinate in the temperature regime found in the shade of nurse trees [6]. Some species may also occur in the matrix between the canopy trees, but especially those forming fleshy fruits show a marked concentration in the canopy environment.…”

“…Frugivorous animals therefore are important dispersal vectors for subcanopy plants by feeding and defecating at the resting and nest sites in and under the canopies (directed dispersal) [5,[8][9][10]. Small and fleshy fruits mainly are dispersed by birds [6,11,12], but also by small mammals [5]. Kos [10] found the Sociable Weaver (Philetarius socius) to be a legitimate dispersal agent of Lycium bosciifolium, and this bird species generally is considered to be an important dispersal agent for fleshyfruited plants [4,5,10].…”