Plant Nutrient Relations
Plant Nutrient Relations
Alpine soils do not generally exhibit high levels of inorganic fertility, which is the result of inadequate mineralization of organic litter, a consequence of the cool, short alpine growing season (Rehder and Schäfer 1978; Gokceoglu and Rehder 1977; Rehder 1976a, 1976b; Fisk and Schmidt 1995; chapters 11, 12). Slow mineralization rates, in turn, result in a soil that is high in organic humus, and more likely than the soil of other ecosystems, to sequester and bind inorganic nutrients, especially N and P. Accordingly, alpine plants are exposed to a difficult situation in their efforts to obtain the inorganic ions required to support growth and reproduction. In accommodating the relative infertility of alpine soils, plants rely on a number of different traits, some of which are ubiquitous and some of which are more restricted in their distribution. Biomass allocation patterns favor high root:shoot ratios, increasing the potential for nutrient absorption by the roots relative to nutrient utilization by the shoot. Nutrient-use efficiencies (biomass produced per mass of senescent nutrient) tend to be high in alpine plants due to efficient resorption prior to leaf senescence. In several alpine growth forms, strict internal controls over seasonal phenology and growth (e.g., preformed buds and strongly enforced dormancy patterns) bring growth demands for nutrients more into balance with the limited supply provided by the soil. Luxury uptake and long-term storage during pulses of high nutrient availability provide plants with a means of bridging the gap between incongruent periods of high nutrient supply and high nutrient demand. Association of fungi with the roots of some alpine plants has the potential to enhance N and P acquisition. Finally, some alpine species can overcome the limitations imposed by scarce inorganic nutrient supplies through high rates of organic nutrient assimilation. It is the aim of this chapter to further consider each of these traits, with particular emphasis on their relationship to N and P acquisition. Topics concerning soil processes and their role in controlling nutrient availability have been covered elsewhere (chapter 8) and will not be repeated. Rather, this review focuses on nutrient relations from the plant’s perspective.
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