Sourcing the chemical components of trees in California
A redwood tree usually weighs around 50,000 pounds, which can yield as much of 250 cubic feet of usable lumber. That’s a lot of mass, and if you were considering a 50,000 pound animal, it would be hard to not take an interest in that creature’s dietary needs (if only to make sure you weren’t one of them.) We know what trees take in, but in some cases it’s not clear how trees might be satisfying their nutritional needs. Analysis from the Sierra Nevada mountains found that the giant sequoias living there aren’t always shopping local, taking in nutrients from as far away as the Gobi Desert in China.
The major question for giant trees like sequoias or redwoods is phosphorus. These giant trees grow mostly on soil made from granite bedrock, which shouldn’t have enough crucial nutrients like phosphorus to sustain such large plants. Rather than carve into living trees, researchers figured they could collect a sample of what soil was circulating in the mountains with pans designed to collect dust. The dust might not represent deeper layers of soil exactly, but it would give a fair representation of what elements were available to the trees living there.
The dust collected was then analysed, using the isotopes of each component to figure out its point of origin. At higher elevations, 45 percent of the dust originated in Asia, having been blown high into the atmosphere to cross the Pacific Ocean. At lower altitudes, Asian dust was less concentrated, and more dust was seen from California’s own Central Valley. While the Asian dust made the bigger journey, the Californian dust was actually more surprising. As the study progressed, more Central Valley dust was found at higher altitudes, which researchers suspect was due to drought conditions drying and distributing topsoil more than usual.
Of course, a sequoia or redwood tree isn’t 25 tons of phosphorus— most of that bulk is carbon, grabbed out of the air’s ample supplies of carbon dioxide. During photosynthesis, trees and other plants break down carbon dioxide, releasing oxygen and building glucose, starch and cellulose. That cellulose (C6H12O6) then locks up a lot of carbon in leaves and well, wood, which is very helpful in a world with an ever-growing surplus of carbon dioxide. On a macro-scale, forests in the United States alone are estimated to absorb around 827 million tons of carbon dioxide each year thanks to their normal growth processes. Since the CO2 is airborne, some of it might also be coming from Asia, but its abundant availability means that it isn’t the ingredient researchers are trying to track down.
Source: Gobi Desert Dust Helps Sustain California's Sierra Nevada by Robert S. Eshelman, Live Science