Dark and disturbed: a new image of early angiosperm ecology

Paleobiology, Winter 2004 by Feild, Taylor S, Arens, Nan Crystal, Doyle, James A, Dawson, Todd E, Donoghue, Michael J

In this study we take a fresh look at the problem of early angiosperm ecology by combining an improved knowledge of phylogeny with ecophysiological observations on Amborella, Austrobaileyales, Chloranthaceae, and Nymphaeales, aimed at recognition of common ecophysiological patterns in these groups. We focus on traits related to growth under varying light and disturbance regimes, including comparative leaf anatomy leaf photosynthetic performance, growth habit, seed size, and seedling establishment. The result is a new image of how the first flowering plants may have functioned and the environment they first occupied. Finally, we consider how these results relate to the Early Cretaceous fossil record.

Methods

Study Species and Field Sites

Seventy-two species of extant basal angiosperms were studied, representing Amborella, all water lily genera (Barclaya, Brasenia, Cabomba, Euryale, Nuphar, Nymphea, Ondinea, and Victoria), all genera in Austrobaileyales (Austrobaileya, Illicium, Kadsura, Schisandra, Trimenia), and Chloranthaceae (Ascarina, Chloranthus, Hedyosmum, Sarcandra). We examined individuals in natural populations (field sites in Australia, China, Costa Rica, Fiji, French Polynesia, New Caledonia, New Zealand, Papua New Guinea, and U.S.A.; Appendix 1), a common garden, and botanical gardens. Where taxonomic sampling could not be exhaustive, species were selected to encompass the habitat range of each lineage. Fieldwork was conducted from August 1999 to October 2002.

Plants grown in the common garden (Auburn, Alabama, 32�N,85�W) were obtained from local nurseries or raised from cuttings taken from natural populations. Plants were grown for 18 months under three light environments-100%, 30%, and 5% full sunlight-before measurements were taken.

Comparative Data

Six ecological and physiological characters were obtained from the field, herbarium vouchers, and published sources. Data sources for species character-state values are given in Appendix 2. The complete character matrix for the species sampled is provided in Appendix 3.

Photosynthetic Performance: Maximum Leaf Photosynthetic Rate and Light-Saturation Point.-Chlorophyll (Chl) fluorescence emission was used to quantify leaf photosyrithetic performance by determining maximum photosynthetic rate and the light intensity at which the photosynthetic system saturates (Bilger et al. 1995; Brodribb and Hill 1997; Rascher et al. 2000). We took Chl measurements of living plants in natural or garden settings with a portable pulse-amplitude modulated fluorometer (Mini-PAM, H. Walz, Effeltrich, Germany) operated using currently accepted protocols (Bilger et al. 1995; Brodribb and Hill 1997; Rascher et al. 2000). From lightresponse curves of Chl fluorescence emission, we calculated maximum ETR (ETR^sub max^) and the light intensity (PPFD^sub sat^) at which this flux occurred, and we used these calculations for interspecific comparisons of leaf photosynthetic performance (Appendix 4). Appendix 4 also provides a comprehensive discussion of procedures and a verification of sampling methods.