Factors Affecting Root Life-Span in Citrus

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9306872 Eissenstat In a range of ecosystems, there is greater annual biomass productionbelow ground than aboveground. In spite of the magnitude of root biomass production, there is extremely little information on factors influencing root death. Root carbon costs can be divided into that used for root construction and that used for root maintenance. Maintenance respiration can exceed the total cost of root construction in as little as two to three weeks, whereas roots of many species live an average of eight months or longer. Thus, plants experience a tradeoff between having long-lived roots and paying high lifetime maintenance costs vs. shorter lived roots that need to be constructed more often but with lower lifetime maintenance costs. We predict that species with small diameter roots of high specific root length (SRL; root length/mass) may have higher maintenance respiration costs than species of low SRL, which may in turn affect root- life span. Furthermore, when maintenance respiration increases, as caused by increases in soil temperature, root- life span may decrease. Root maintenance respiration and root life-span of individual roots and whole-root systems in pots will be examined to test these prediction in a combination of controlled laboratory under conditions where soil moisture, soil temperature and SRL are varied. This work has important implications for better understanding the effects of climate change on global CO2 sustainable agriculture and plant growth in general. ***