The ecophysiology of early angiosperms

Abstract

Angiosperms first appeared during the Early Cretaceous, and within 30 million years they reigned over many floras worldwide. Associated with this rise to prominence, angiosperms produced a spectrum of reproductive and vegetative innovations, which produced a cascade of ecological consequences that altered the ecology and biogeochemistry of the planet. The pace, pattern and phylogenetic systematics of the Cretaceous angiosperm diversification are broadly sketched out. However, the ecophysiology and environmental interactions that energized the early angiosperm radiation remain unresolved. This constrains our ability to diagnose the selective pressures and habitat contexts responsible for the evolution of fundamental angiosperm features, such as flowers, rapid growth, xylem vessels and net-veined leaves, which in association with environmental opportunities, drove waves of phylogenetic and ecological diversification. Here, we consider our current understanding of early angiosperm ecophysiology. We focus on comparative patterns of ecophysiological evolution, emphasizing carbon-and water-use traits, by merging recent molecular phylogenetic studies with physiological studies focused on extant basal angiosperms. In doing so, we discuss how early angiosperms established a roothold in preexisting Mesozoic plant communities, and how these events canalized subsequent bursts of angiosperm diversification during the Aptian-Albian.

Fossil evidence for low gas exchange capacities for Early Cretaceous angiosperm leaves

“…diagnose whether these fossil leaves came from plants adapted to wet (.2000 mm yr 21 rainfall) and forest understory habitats like those characterizing Amborella as well as most Austrobaileyales and Chloranthales (Feild et al 2004(Feild et al , 2009. Specifying the habitat context of austrobaileyoid/chloranthoids is critical for determining how functional trait diversity in extant basal lineages bears on how the first flowering plants functioned and the selective contexts responsible for diverse hypothesized key innovations of early angiosperm success (Hickey and Doyle 1977;Retallack and Dilcher 1981;Taylor and Hickey 1996;Feild and Arens 2007;Williams 2008;Feild et al 2009). Paleoenvironmental proxy records indicate high annual rainfalls (up to 4500 mm yr 21 ) and tropical to paratropical temperatures for all of the fossils sampled (Upchurch and Wolfe 1987;Upchurch and Dilcher 1990;Upchurch 1995;White et al 2001;Ufnar et al 2008).…”

“…Importantly, the regeneration niches of Austrobaileyales and Chloranthales provide living proof that microsites combining fluvial disturbance with low evaporative demand, low carbon, and sandy sedimentology exist (Feild et al 2004;Ito et al 2006;Feild 2009). Such dark and disturbed sites are often near higher flowenergy channels in tropical floodplain zones, semi-shaded stream margins (not necessarily with tall closed forest canopies) along upstream cutbanks of floodplains (Ito et al 2006;Feild and Arens 2007;Feild et al 2009). …”

Rise to dominance of angiosperm pioneers in European Cretaceous environments

“…2 A and B). One may question whether the earliest angiosperms were shade tolerant as proposed by the "damp, dark, and disturbed habitats" hypothesis (36,38). An ecophysiological study of hypothetical living relatives of the zone I Potomac (Aptian-Albian) group angiosperms indicates that, if the assumed living related angiosperms are a good model of the physiology of the earliest angiosperms, they may have been shade tolerant (40).…”

Fossil evidence for a herbaceous diversification of early eudicot angiosperms during the Early Cretaceous

“…Teeth of this type are sites of guttation; the loss of water at tooth apices prevents flooding of the leaf mesophyll under conditions of high soil moisture, high humidity and low evaporative demand [53][54][55]. Environments such as forest understory and riparian corridors in tropical and temperate climates typically host plants with hydathodal teeth [49,[56][57][58][59][60][61]; but hydathodal teeth also occur in some marginally or semi-aquatic ranunculalean herbs that grow under bright, subareal conditions [39].…”