An exceptional role for flowering plant physiology in the expansion of tropical rainforests and biodiversity

Abstract

Movement of water from soil to atmosphere by plant transpiration can feed precipitation, but is limited by the hydraulic capacities of plants, which have not been uniform through time. The flowering plants that dominate modern vegetation possess transpiration capacities that are dramatically higher than any other plants, living or extinct. Transpiration operates at the level of the leaf, however, and how the impact of this physiological revolution scales up to the landscape and larger environment remains unclear. Here, climate modelling demonstrates that angiosperms help ensure aseasonally high levels of precipitation in the modern tropics. Most strikingly, replacement of angiosperm with non-angiosperm vegetation would result in a hotter, drier and more seasonal Amazon basin, decreasing the overall area of ever-wet rainforest by 80 per cent. Thus, flowering plant ecological dominance has strongly altered climate and the global hydrological cycle. Because tropical biodiversity is closely tied to precipitation and rainforest area, angiosperm climate modification may have promoted diversification of the angiosperms themselves, as well as radiations of diverse vertebrate and invertebrate animal lineages and of epiphytic plants. Their exceptional potential for environmental modification may have contributed to divergent responses to similar climates and global perturbations, like mass extinctions, before and after angiosperm evolution.

Leaf fossil record suggests limited influence of atmospheric CO 2 on terrestrial productivity prior to angiosperm evolution

“…Nonangiosperms average about 2.5 mm of vein length per square millimeter of leaf area and rarely reach higher than 5 mm mm −2 , but angiosperms average around 10 mm mm , with high vein densities appearing independently in at least three angiosperm lineages: the magnoliids, monocots, and eudicots (14,25,26). This abundance of vasculature was shown to correlate with much higher physiological activity, including a fourfold increase in transpiration capacity and more than a doubling of assimilation capacity, that resulted in important implications both for tropical climate and vegetation feedbacks and for the rise to ecological dominance of angiosperms over the Cretaceous and early Paleocene (14,(27)(28)(29). However, those correlations of leaf vein density with transpiration and assimilation capacities are based on empirical measurements of living plants grown under the low ambient CO 2 concentrations of the modern world (14,25,30).…”

Pennsylvanian ‘fossil forests' in growth position (T 0 assemblages): origin, taphonomic bias and palaeoecological insights

“…Gastaldo et al 20046;DiMichele et al 2009), based on the distribution of in situ stumps and the architectures of the trees known from prostrate specimens. This means that the potential for extensive recycling of water may have been limited compared with closed canopy angiosperm forests (Boyce & Lee 2010), although recent physiological analyses of the potential of these plants to move water via evapotranspiration is ambiguous, the leaves suggesting limited potential (Boyce 2009), but stem anatomy suggesting the potential for relatively high rates (Cichan 1986;Wilson & Knoll 2010). Alternatively, selective preservation may mask original diversity, with only the most resistant, anatomically suitable plants being preserved in place.…”

Tectonic-driven climate change and the diversification of angiosperms

“…Their radiation was characterized by high and rapid diversification (3,4), high rates of speciation throughout the Cretaceous (5), and unprecedented ecological dominance. Most hypotheses to explain angiosperm radiation invoke biotic (instrinsic) factors, such as pollinating insects (6), coevolution with herbivorous insects (7), morphological novelties (8), or ecophysiological innovations (9)(10)(11) as well as macroevolutionary patterns (1). However, recent studies have shown that extrinsic influences combined with biotic factors may drive species diversity at the multimillion-year time scale (6,12), reviving the potential role of global climate change (13,14) on angiosperm radiation.…”