Researchers have discovered a previously unknown mechanism that causes increased water use in forests, advancing our understanding of forest water cycles and highlighting threats to plants from water stress, as happens from acid rain. When fossil fuels are burned, sulfuric and nitric acid eventually fall back to earth in rain and snow, causing acidification of the soil. When that happens, a significant amount of calcium washes out of the soil, causing calcium deficiency and more water use in plants. Calcium plays a unique role in plant cells by regulating the minute pores, called stomata, in leaves or stems. Without enough calcium, plants can't close these pores, and their water use increases. The plants pump more water through transpiration, the process of water movement through a plant and its evaporation from leaves, to meet the calcium demand. Traditionally, forest water use was considered a function of meteorological factors, species composition and soil water availability. The impacts of soil biogeochemistry on large-scale forest water use had not been investigated.
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