Water Management and Plant Performance in a Changing Climate: Introduction to Colloquium

Climate change refers to any significant shift or variability in temperature, precipitation, humidity, light, or wind. These changes may be of relatively short duration or last for an extended period that could be decades or longer [Intergovernmental Panel on Climate Change (IPCC), 2007)]. Throughout history, earth’s climate has been changing naturally. However, the rapid warming we have been witnessing in the past several decades is not solely the result of natural processes. Some are attributed to an increase in anthropogenic activities such as burning fossil fuels for the production of personal and commercial transportation, deforestation, and various agricultural and industrial practices (U.S. Environmental Protection Agency, 2010). With the increase in the world population from 1.25 billion in 1850 to 6.5 billion in 2005, world energy consumption has increased 40 times (Lal, 2007). The earth’s atmospheric carbon dioxide (CO2) concentration was 280 mmol mol until the 1800s. It increased exponentially during the industrial era reaching 315 mmol mol in 1957 and 362 mmol mol in 1994 (Schimel et al., 1994). Human activities have increased atmospheric concentrations of greenhouse gases such as CO2, methane (CH4), and nitrous oxide (N2O), which occur naturally in the atmosphere (IPCC, 2007) resulting in a 0.74 C rise in the global average surface temperature to approximately over the past 100 years (Trenberth et al., 2007). As of 2010, the atmospheric CO2 concentration is 388 mmol mol and it is expected to increase to 450 mmol mol by 2030 and 700 mmol mol by 2050 (IPCC, 2001) as the world’s population approaches nine billion (United Nations, Department of Economic and Social Affairs Population Division, 2009). A number of studies have shown positive effects on plant growth and productivity from an increase in atmospheric CO2 concentration (Kimball et al., 2002). An increase in CO2 concentration (from 330 mmol mol to 660 mmol mol) increases yields of C3 crops [e.g., soybeans (Glycine max L.), cotton (Gossypium spp. L.), alfalfa (Medicago sativa L.), wheat (Triticum aestivum L.), rice (Oryza sativa L.), barley (Hordeum vulgare L.), and potatoes (Solanum tuberosum L.)] by 33% and yields of C4 crops {e.g., corn [Zea mays] and sorghum [Sorghum bicolor (L.) Moench.} by 10% (Kimball, 1983; Long et al., 2006; Pinter et al., 2000; U.S. Climate Change Science Program, 2008). In addition, studies showed that CO2 enrichment alone could boost water use efficiency and increase yield of waterlimited crops (e.g., grains) (Drake et al., 1997; Idso and Idso, 1994). For example, in addition to increases in yield, CO2 enrichment increases water use efficiency (WUE) in wheat (Hunsaker et al., 1996), soybean (Jones et al., 1985a, 1985b), and rice (Oryza sativa L.) (Baker et al., 1990). Similar observations reported by Conley et al. (2001) indicted that cumulative evapotranspiration of sorghum was reduced without a loss in yield. Other beneficial effects were documented by Wechsung et al. (1999) on the increase of root growth and biomass of wheat under dry conditions and that of cotton (Rogers et al., 1992) as a result of CO2 enrichment. Projected increases in CO2 and air temperature will continue to contribute to climate warming in the next century (Alcamo et al., 1996; IPCC, 2001). The northern high latitudes have warmed by 0.8 C since the early 1970s (Hansen et al., 1999). Warming is predicted to be greatest at high northern latitudes during fall and winter (IPCC, 2007) with reduced rainfall in the subtropics and increased precipitation in eastern America, northern Europe, and parts of Asia. Such changes appear to have a profound effect on plant periodicity as has been found in Europe (Menzel and Fabian, 1999), and plant phenology (IPCC, 2001), especially for plants that depend on accumulation of degree-days to reach flowering or fruiting (Peñuelas and Filella, 2001). The increase in temperature may extend the growing season (longer crop cycle), i.e., early planting and late harvest time will be anticipated (Porter, 2005). It has been documented that flowering had been 1 week earlier in the Mediterranean plant species for 1952–2000 (Peñuelas et al., 2002), in Hungary for 1851–1994 (Walkovszky, 1998), in Wisconsin for 1936–1998 (Bradley et al., 1999), and in Washington, DC, for 1970– 1999 (Abu-Asab et al., 2001). It is expected that the production of certain crops may shift across regions as a result of climate change. Increases in temperature will cause the optimum crop growth latitude to move northward. For example, yields of some agronomic crops such as soybean are expected to decrease in southern U.S. states (U.S. Climate Change Science Program, 2008) and increase in the Midwest (Boote et al., 1996, 1997). Similarly, warming temperatures will cause production of many cool-season vegetable crops [such as potato, lettuce (Lactuca sativa L.), broccoli (Brassica oleracea L.), and spinach (Spinacea oleracea L.)] to decline. In addition, it will negatively impact fruit trees such as apples [Malus ·sylvestris (L.) Mill. domestica (Borkh.) Mansf.] that require a certain amount of chilling (Hartfield et al., 2008). In northern temperate areas, heat-demanding warm-season crops [e.g., corn and sunflower (Helianthus annuus)] are projected to replace many of the present grain cereals and oilseed crops (Olesen and Bindi, 2002). Thus, the impact of climate change on agriculture will lead to intensified production in northern Europe and less in southern Europe exacerbated by a reduction in water use for irrigation resulting from increased water scarcity (Alcamo et al., 2007; Olesen and Bindi, 2002). The effect of high temperature may surpass the impact of water availability for plants. For example, under well-watered conditions, when increases in temperature exceed the temperature threshold for pollination, grains may not produce seed and the quality of vegetable crops (e.g., tomato, Lycopersicon esculentum Mill.) may decrease (Kunkel et al., 2008). The impact of night temperature on plant growth and yield is as important as that of day temperature. Warmer nights increase plant respiration rates, resulting in further depletion of carbohydrates and yield reduction of fruits and vegetables [e.g., snap beans (Phaseolus vulgaris L.)] (Arevalo, 2008). Bud, flower, and fruitlet abscission is commonly found in tomato plants grown under high night temperatures, especially because tomatoes require lower night than day temperatures (Peet et al., 1998; Sato et al., 2004). Increases in the average global air temperature will likely lead to changes in precipitation and atmospheric moisture and such changes may vary from region to region (IPCC, 2007). Although some regions (e.g., tropics) will experience more frequent and intense precipitation events, precipitation is expected to decrease in other regions (e.g., the Mediterranean, northern Africa, northern Sahara, Central America, the American Southwest, and southwestern Australia during winter). Water scarcity, as a result of changes in precipitation patterns and intensity and decreases in natural water storage capacity from glacier or snowmelt-fed river basins, will increase the competition between agricultural and urban users as population growth increases. Under climate change, water and its availability and quality will create bigger challenges than energy security (IPCC, 2008). Agriculture is the dominant user of fresh water (Gleick, 2003a,2003b), and demandforwater will continue to increase with increases in population and economic growth (Rosegrant et al., 2009). It is anticipated that the world’s population will approach nine billion by 2050 (United Nations, Department of Economic and Social Received for publication 8 Oct. 2010. Accepted for publication 10 Nov. 2010. I thank George Wulster and A.J. Both for reviewing this manuscript. This paper was part of the colloquium ‘‘Water Management and Plant Performance in a Changing Climate’’ held 4 Aug. 2010 at the ASHS Conference, Palm Desert, CA, and sponsored by the Water Utilization and Plant Performance in a Changing Climate (WUM) Working Group. e-mail [email protected].