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In botany, drought tolerance is the ability by which a plant maintains its biomass production during arid or drought conditions. [ 1 ] [ 2 ] [ 3 ] Some plants are naturally adapted to dry conditions , surviving with protection mechanisms such as desiccation tolerance , detoxification , or repair of xylem embolism. [ 3 ]
Resistance to drought is a quantitative trait, with a complex phenotype, often confounded by plant phenology. Breeding for drought resistance is further complicated since several types of abiotic stress, such as high temperatures, high irradiance, and nutrient toxicities or deficiencies can challenge crop plants simultaneously.
Drought is a complex phenomenon − relating to the absence of water − which is difficult to monitor and define. [18] By the early 1980s, over 150 definitions of "drought" had already been published. [19] The range of definitions reflects differences in regions, needs, and disciplinary approaches.
In 2012, the head of AP Grading, Trevor Packer, stated that the reason for the low percentages of 5s is that "AP World History is a college-level course, & many sophomores aren't yet writing at that level." 10.44 percent of all seniors who took the exam in 2012 received a 5, while just 6.62 percent of sophomores received a 5. [23]
Global distribution of the 4.2 kiloyear event. The hatched areas were affected by wet conditions or flooding, and the dotted areas by drought or dust storms. [1] The 4.2-kiloyear (thousand years) BP aridification event (long-term drought), also known as the 4.2 ka event, [2] was one of the most severe climatic events of the Holocene epoch. [3]
Identifying the genes responsible for drought tolerance in barley plants and applying them to other plant species or other barley varieties via transgenics has also shown promising results. One study expressed the hva1 gene from barley in creeping bentgrass , and found that it improved drought tolerance by lessening the effects of water-deficit ...
[10] [11] One scholar has calculated the size of chinampas using Codex Vergara as a source, finding that they usually measured roughly 30 m × 2.5 m (100 ft × 10 ft). [12] In Tenochtitlan , the chinampas ranged from 90 m × 5 m (300 ft × 20 ft) [ 12 ] to 90 m × 10 m (300 ft × 30 ft) [ 12 ] [ 13 ] They were created by staking out the shallow ...
Animation of US drought map 2006-2008. The 2006–08 Southeastern United States drought was a crippling drought that struck the southeast of the U.S. Several reasons, including an unusually strong Bermuda high pressure and La Niña in the eastern Pacific Ocean (which causes dry conditions across the southern U.S.) were responsible for the drought. 2007 was particularly dry across the region ...