[audio:http://wamcradio.org/EarthWise/wp-content/uploads/2013/09/EW-09-09-13-Nutrient-Reabsorption.mp3|titles=EW 09-09-13 Nutrient Reabsorption]
As the long days of summer wane, and we feel a chill in the air, we know that autumn is on the way. In the past, we’ve discussed why the leaves of forest trees turn brilliant colors in the fall. Some pigments degrade, allowing us to see others that have been hidden behind the scenes.
But, there are other changes going on in leaves as well. Much of the biochemical machinery that leaves contain to conduct photosynthesis is dismantled in the fall, so that important plant nutrients, like nitrogen and phosphorus, can be reabsorbed for use next year. Nitrogen and phosphorus are drawn from aging leaves and sequestered in woody tissues for the winter.
Dropped leaves have only half the content of these nutrients, saving a lot of root activity that would be needed to take up these nutrients from the soil in the spring.
When leaves fall, they become part of the forest’s nutrient cycle. Fungi and bacteria in soils degrade them, releasing their remaining nutrients for plant uptake in the spring. This is particularly true for calcium and potassium. At a New Hampshire forest that Cary Institute scientists have studied for decades, some 85% of the calcium and potassium taken up by the forest is derived from the decomposition of leaves in the soil.
Nutrient cycling occurs naturally in forests, but we disrupt it in suburban settings. When we rake up and remove fallen leaves from our lawn, we break the nutrient cycle in the soil, requiring us to fertilize in the spring.
So save yourself some time and money: grind and mulch your lawn this fall.
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Photo, taken on November 12, 2008, courtesy of David Joyce via Flickr.
Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY.