Expected Effects of Climatic Change on Root and Tuber Crops

Despite their economic and global importance, little research has been done on the potential effects of climatic change on tuber and root crops with potato as a single exception. For the other crops, most of the limited studies have addressed specific questions and failed to provide broader significant information. In general, research focused on key questions that had to do with the response of different species/varieties to increasing air temperature and to rising [CO2] in the atmosphere. In particular, many studies have addressed the responses of various crops to [CO2], because changes in [CO2] have a significant impact on crop yields. Another reason is that the increase in [CO2] is, as well as ozone and SO2, a clearly detectable, measurable and unavoidable effect of anthropogenic activity on earth's atmosphere. There is clear evidence since the 1950s (Keeling et al., 1995) that atmospheric [CO2] is increasing, and plant physiologists have repeatedly demonstrated that such increases likely have already caused substantial increases in leaf photosynthesis of C3 species (Sage, 1994). Finally, projections based on reliable scenarios of industrial development, trading and transport are indicating that [CO2] as high as 550 mmol mol-1 will be unavoidably reached in the middle of the 21st century, (Houghton et al., 1992). This does not imply that those changes in temperature, precipitation, tropospheric ozone concentrations and nitrogen depositions have lower impacts, but explains why the 'CO2 effect' has been considered a major research topic. Scientists have repeatedly recognized that species with large below-ground sinks for carbon (Chu et al., 1992; Körner et al., 1995; Farrar, 1996) and with apoplastic mechanisms of phloem loading (Komor et al., 1996) are likely to be the best candidates for a large response to rising atmospheric [CO2]. There is also an increasing consensus among scientists that growth or storage sink limitations are possibly major factors constraining responses of plants to elevated [CO2]. This explains why the large CO2 response often observed in crop species with a large sink capacity (Kimball, 1983) could not be reproduced with natural vegetation or in nutrient-poor plant associations (Poorter, 1993; Körner and Miglietta, 1994). The potential effects of rising atmospheric [CO2] and temperature on physiological processes and the ecology of root and tuber crops will be analysed. The main part of the experimental results for potato was derived from a FACE (free air CO2 enrichment) experiment that was made in Italy in 1995 and from a series of experiments with open-top chambers (OTC) in the Netherlands. In the FACE experiment, a potato crop was grown in the field under natural conditions except for being exposed to elevated [CO2] by means of a sophisticated fumigation device (Miglietta et al., 1998), and plants were exposed to a gradient of [CO2] ranging from ambient to 660 |mmolmol-1. The OTC experiments allowed potato cultivars of different earliness to be compared in 700 mmol mol-1 CO2 (A.H.C.M. Schapendonk, personal communication, 1995). Further analysis of the potential effects of climatic change on potato production will use the results from simulation studies made at site and regional scales within the European Union-funded CLIVARA Project (Downing et al., 1999). Obviously, it is not always possible to extrapolate all the considerations and conclusions made for potato to the entire root and tuber crop category, but the information will guide the reader to a critical analysis of the issue and will help to identify the most important topics and where and why more research is needed.

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