Coping with Heat Waves and Droughts in a Future Warmer World
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"To gain more insight into the effects of climate extremes on plants," in the words of Dreesen et al., they conducted two experiments (one in July and another in August) in an experimental field at the University of Antwerp (Belgium), in which plant mesocosms that consisted of three temperate annual or biannual herbaceous species were exposed to either a heat wave or serious drought, or both extreme stresses together, where ten-day heat waves were simulated with infrared lamps and drought (of either 20 or 17 days duration) was created by withholding water input and removing the water table, after which the plants experienced normal weather until the end of the growing season.
The four researchers report finding, "surprisingly," that total above- and below-ground end-of-season community biomass "was stimulated in response to drought extremes in both periods," and that "effects of heat extremes varied but never reduced biomass," as was also the case with respect to combined heat and drought. "This increase in total community biomass," as they continue, "originated exclusively from stimulated root growth." They indicate that "the exact mechanism for this unexpected result could not be ascertained," but they say that "greater whole-plant nitrogen stocks clearly indicated enhanced nutrient availability," which "may have arisen from increased net mineralization or from greater root exploration under the influence of 'mid-season drought'."
Dreesen et al. conclude that plant "community responses to climate extremes are not necessarily negative." In fact, the massive worldwide analysis of Niu et al. (2012) suggests that the norm is actually positive in the case of temperature.
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