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COPYRIGHT 2003 Natural History Magazine, Inc.
On several forays into the Salinas Grandes--one of Argentina's great salt deserts--we had dug up mysterious burrows, but we had never discovered what kind of animal made them. Our team of biologists was looking for a rare mammal, a salt-pan specialist with a store of unique genetic information. Our failure was like a weight I carried with me every day. The bad news, I told my three co-workers, was that we would go back one more time. There were groans; it was a long, hard field trip. The good news, I said, was that we wouldn't dig anymore. Moving tons of earth had already proved to be no way to find our quarry, presumed to be a rodent.
The year before, I had brought some Conibear traps to Argentina, spring-loaded traps (named for their inventor, Frank Conibear) that can seize and kill animals without the need for bait. The problem had been figuring out where to place the traps so that animals would step into them. I had never been able to catch anything in Conibear traps before, but now I pinned my hopes on them. "There must be some reason I carted them down here," I told myself.
Back we went, to the Gran Chaco area of Central Argentina, the road by now familiar, and made camp. That first day I spread out my two dozen Conibear traps, while the others set our standard array of baited traps. There was nothing to do now but wait. In the frigid winter night, I dreamed that a new, rare, salt-desert rodent got caught in one of my traps. In my dream, though, the animal was dragged away by a predator before I could get to it. The thought jolted me wide-awake. It was 3:00 A.M., and the Sun wouldn't be up for hours. The cold stillness hardly beckoned me out of my sleeping bag. I rationalized: How could I find the trap in the dark, anyway? I decided to wait for dawn.
Salt deserts or salt pans--"salinas" in Latin America--are among the most extreme habitats on Earth. In some cases they formed where ancient seas once intruded on the land, then retreated and evaporated, leaving crystalline salts--mainly sodium chloride--behind. In other areas, where arid mountains surrounded enclosed basins, salts weathered from the uplands by seasonal precipitation were carried with the runoff into the valley below; again, when the water evaporated, the salts remained. But in whatever way the salts accumulated, eventually they covered the soil with a blindingly white patina. Few species, plant or animal, can survive in the forbidding habitat.
Among the exceptions are certain halophytic, or salt-tolerant, plant species in the goosefoot family (the Chenopodiaceae, or chenopods), which thrive in hot salt deserts throughout the world. The salt concentrations in the stems and leaves of these plants are many times what they are in seawater; the salts keep precious fluids in the plants' cells from being drawn by osmotic pressure into the salty soil. At the same time, as the water in their cells evaporates, the plants must prevent their internal salt concentrations from...
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