Sandquist, D.R., and J.R. Ehleringer. 1998. Intraspecific variation of drought adaptation in brittlebush: leaf pubescence and timing of leaf loss vary with rainfall. Oecologia 113:162-169.

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Reflective pubescence on the leaves of the desert shrub Encelia farinosa (brittlebush) reduces leaf temperature and water loss and is considered adaptive in xeric environments. Yet little is known about intraspecific variation of this trait. Among three populations in the northern range of E. farinosa , which spans a very broad precipitation gradient, both leaf absorptance variation and differences in the timing of drought-induced leaf loss were broadly associated with climatic variability. Where mean annual rainfall is greatest, drought­induced leaf loss was earliest, but these plants also had higher overall leaf absorptance values. Higher absorptance increases the relative dependence on latent heat transfer (transpirational cooling), but it also provides greater instantaneous carbon assimilation. Plants at the driest site reached lower leaf absorptance values and maintained leaves longer into drought. Lower leaf absorptance reduces water consumption, and extended leaf longevity may buffer against the unpredictability of growing conditions experienced in the driest site. These observations are consistent with a trade-off scenario in which plants from wetter regions might trade off water conservation for higher instantaneous carbon gain, whereas plants from drier regions reduce water consumption and extend leaf longevity to maintain photosynthetic activity in the face of unpredictable growing conditions.