DOI: 10.5061/dryad.3ffbg79ff
title: Isotopic and morphologic proxies for reconstructing light environment from fossil leaves: a modern calibration in the Daintree Rainforest, Australia

description: Premise: Within closed canopy forests, vertical gradients of light and
 atmospheric CO 2 drive variations in leaf carbon isotope ratios, leaf mass
 per area (LMA), and the micromorphology of leaf epidermal cells.
 Variations in such traits observed in preserved or fossilized leaves could
 enable inferences of past forest canopy closure and the habitat of
 individual taxa. However, as yet no calibration study has examined how
 multiple traits in combination reflect position within a modern closed
 canopy forest or how these could be applied to the fossil record. Methods:
 Leaves were sampled from throughout the vertical profile of the tropical
 forest canopy using the 48.5 m crane at the Daintree Rainforest
 Observatory, Queensland, Australia. Carbon isotope ratios, LMA, petiole
 metric (i.e. petiole-width 2 / leaf-area) and leaf micromorphology (i.e.
 undulation index and cell area) were compared within species across a
 range of canopy positions, as quantified by leaf area index (LAI). Key
 Results: Individually, cell area, δ 13 C, and petiole metric all
 correlated with both LAI and LMA, but the use of a combined model provided
 significantly greater predictive power. Conclusions: Using the observed
 relationships with leaf carbon isotope ratio and morphology to estimate
 the range of LAI in fossil floras can provide a measure of canopy closure
 in ancient forests. Similarly, estimates LAI and LMA for individual taxa
 can provide comparative measures of light environment and growth strategy
 of fossil taxa from within a flora. Please be aware that if you ask to
 have your user record removed, we will retain your name in the records
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description: All leaf samples were
 obtained from the Daintree Rainforest Observatory (DRO), located in Cape
 Tribulation (-16.117 N, 145.45 E), 140 kilometres north of Cairns in Far
 North Queensland, Australia. The DRO, administered by James Cook
 University, includes two 1 ha permanent tree-census plots. One of these
 plots can be accessed by a 48.5 m high canopy-access crane (Leibherr Model
 91EC). Forest at the DRO is described as a complex mesophyll vine forest
 Type 1a (Tracey, 1982) with a tall but irregular canopy varying in height
 from 25 to 33 m with indistinct stratification of the subcanopy. Within
 the crane plot there are 85 different canopy tree species (comprising 60
 genera, and 35 families) representing a basal area of ~33
 m<sup>2</sup> ha<sup>-1</sup> (Tng et al., 2016).
  The Daintree Rainforest is considered one of the oldest
 continuously-vegetated tropical systems on earth and while not as speciose
 as some tropical closed forest systems, it represents a broad phylogenetic
 diversity, with many Gondwana ‘relic’ species (Costion et al.,
 2015). Initial
 leaf samples for canopy-understory comparisons (Data Sheet 1) were
 collected in 2014 from 89 species of plant found within the closed forest
 canopy of the DRO. This included both monocotyledonouos (7),
 dicotyledonous (81) and one cycad species <i>Bowenia
 spectabilis</i>. A range of growth forms have been sampled including
 trees and shrubs (collectively referred to here as trees) and lianas.
 Samples were collected from both the upper canopy crown (using the canopy
 access crane) and the understory ~ 0.4 to 1.5m, with an attempt made to
 collect the same species from both environments. During this initial
 sampling, in-situ leaf physiological measurements (e.g. light saturated
 photosynthesis (A<sub>sat</sub>), and responses to
 [CO<sub>2</sub>] (A-C<sub>i</sub>)<sub>
 </sub>, and irradiance (A-I) curves) were made on at least two
 leaves of 71 species collected. In all upper canopy samples, 12 leaves
 were harvested with nine analysed for basic leaf functional traits and
 three leaves frozen for later micro-morphological analysis. In the case of
 understory samples only the two leaves used for physiological measurements
 were harvested and analysed for leaf functional traits given typically
 limiting leaf material. In 2017, additional leaves were
 sampled across the light gradient continuum found in the forest canopy
 (Data Sheet 2).  Five species (<i>Argyrodendron peralatum, Myristica
 globosa ssp. muelleri, Endiandra microneura, Cleistanthus
 myrianthus</i> and <i>Rockinghamia angustifolia</i>)
 were harvested due to their prevalence at all forest strata of the study
 site. Leaves were sampled from the upper crown, interior crown (i.e.
 partial cover by surrounding vegetation), the understory as well as from
 within a significant tree fall gap. At each location six leaves have been
 harvested, with three analysed for basic leaf functional traits as above
 and the remainder archived for micromorphological analysis. At each
 sampling location, leaf area index (LAI) was determined using a LAI-2200C
 Plant Canopy Analyzer (Licor, Nebraska). In addition, and to examine the
 impact of environmental stress upon the fidelity of leaf traits, parallel
 upper and interior canopy samples were also collected from individuals
 impacted by a long-term (3-y) throughfall exclusion, or “drought”,
 experiment being conducted within the DRO crane plot (Tng et al., 2018).
 The throughfall exclusion plot (0.4 ha), wherein rainfall/thoughfall is
 intercepted and diverted off the plot has resulted in an area of elevated
 water stress within the crane accessible arc that includes replicated
 individuals of species found under natural conditions.
description: See associated paper for method details on trait determination.
 Note 2014 samples listed in Data sheet 2 are repeats of thoe listed in
 Data Sheet 1.