Is leaf pubescence of Cape Proteaceae a xeromorphic or radiation-protective trait?
R. P. Skelton A D , J. J. Midgley A , J. M. Nyaga A , S. D. Johnson B and M. D. Cramer A C
+ Author Affiliations
- Author Affiliations
A Department of Botany, University of Cape Town, Private Bag XI, Rondebosch 7701, South Africa.
B School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg 3209, South Africa.
C School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, WA 6009, Australia.
D Corresponding author. Email: skelrob@gmail.com
Australian Journal of Botany 60(2) 104-113 https://doi.org/10.1071/BT11231
Submitted: 8 September 2011 Accepted: 13 January 2012 Published: 6 March 2012
Abstract
Although pubescence has traditionally been considered to be related to the water economy of plants, the results are ambivalent and vary between different species. We tested two contrasting hypotheses for the functional significance of leaf pubescence of Proteaceae species from the Cape Floristic Region. First, we hypothesised that pubescence is a xeromorphic trait that conserves water by increasing the boundary layer resistance to diffusion. Water loss was measured in two morphotypes of Leucospermum conocarpodendron (L.) Buek that differ in the degree of leaf pubescence, using both gas exchange and gravimetric techniques. Pubescence contributed less than 5% of total leaf resistance and pubescent leaves transpired at least as rapidly as glabrous leaves due to having larger numbers of small stomata per leaf area. Although pubescence was not associated with drier sites in L. conocarpodendron, there was a weak negative correlation between rainfall and pubescence across 18 other Proteaceae species. We also hypothesised that pubescence is a radiation-protective trait. We assessed the effect of pubescence on light reflectance, leaf temperature, fluorescence and gas exchange characteristics in situ. Pubescent leaves of L. conocarpodendron were 19.2 ± 0.08% more reflective than glabrous leaves and had significantly greater pre-dawn photochemical efficiency. There was a positive association between leaf pubescence and habitat temperature in Proteaceae. We conclude that although pubescence is unlikely to be a xeric adaptation, it could serve a role in reducing photoinhibition and heat loading in Proteaceae species.
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