Leaf absorptance (0.4-3 nm), %

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1 Encelia farinosa is an amazing drought-deciduous shrub of the Mohave and Sonoran Deserts. It produces deciduous leaves with a thick layer of hairs that result in an increased leaf reflectance (decreased absorptance) of solar radiation. In field measurements last spring on two plants growing near each other, but in different microsites, I observed the following: Midday measurements under full sun Leaf Air temperature, C temperature C Leaf absorptance (0.4-3 nm), % 31% 23% Leaf conductance, mol m-2 s Leaf water potential, MPa How interesting. On leaves of a number of other green-leaved shrubs nearby (different species), I measured leaf temperatures ranging from 35 C to 40 C. I must now go back to my office to figure out how these patterns arise. Encelia farinosa, /photos/encelia-farinosa-f-web-n868.jpg, lia_farinosa-3.jpg, /0/0a/Encelia_farinosa_form.jpg

2 On a road trip from Galveston, Texas to Regina, Saskatchewan, I stopped off a four different locations as shown below. The scenery at each location was gorgeous (at least gorgeous to a botanist). I took very careful notes about the biomes and species present along this road trip. Several features absolutely stood out and reiterated what I had heard Professor Ehleringer lecture on years ago. Perhaps the most surprising observation I made along this gradient is that there were big changes in the species present at northern-most versus southern-most locations. As I had lots of time on my hands during this trip, I took time to do both leaf anatomy and root drawings of each of the common species along this transect. 26

3 Over the past summer, I examined the photosynthetic and transpiration rates of leaves on a large number of drought deciduous coastal shrubs growing along the southern California coast. Each of the plants I examined last summer had C3 photosynthesis. One of those measured species was Encelia californica, which is closely related to the desert shrub Encelia farinosa. All of my measurements were collected on plants growing in the field, but having received supplemental irrigation. For each of the measurements collected on different species, the leaves were exposed to an atmospheric environment of 390 ppm (= 390 µmol/mol). And the leaf temperatures were kept constant at 30 C. The light levels incident on leaves were allowed to vary, allowing me to measure the responses of leaves to variation in the amount of sunlight. Below are the data that I collected. Or at least, here are most of the data, and the missing values should be obvious since I remember that outstanding lecture from Professor Ehleringer this year. PFD A g CO2 g H2O ci ci/ca µmol m -2 s -1 µmol CO 2 m -2 s -1 mol CO 2 m -2 s -1 mol H 2 O m -2 s -1 µmol/mol When I plotted the data, the patterns were especially clear. What puzzled me was why the ci/ca ratio remained essentially constant over such a wide range of sunlight conditions. In tomorrow s experiment, I will repeat the same measurements of leaf responses to changing sunlight levels, only this time I will the atmospheric CO 2 levels to values not found today on Earth, but which were realistic in the past. Encelia californica, 27

4 Last summer, I had the best of vacations. I called it the 4-30 vacation, because I visited four different cities in North America and South America. Each of these cities was coastal and each was located at 30 from the equator. To the right is a map of the four cities I visited. Below ares four climate diagrams from each of the cities I visited on the 4-30 trip. 28

5 I love road trips and taking time to see plants and biomes along the way. Crossing back and forth across the United States is a real treat for me, especially when I collect data along the way. Over the past three summers, I have come across four pairs of cities in which each city shares the same name. Wow. What a coincidence, but the coincidence stopped there. My notes, shown on page 30, details these differences among paired-name cities. Below are the climate diagrams for these paired cities. Interestingly, while the cities shared a common name, that was not the case with the vegetation in the proximity of paired cities. 29