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|Title:||Retranslocation and volatilization of shoot nitrogen during drought in perennial prairie grasses|
|Author(s):||Heckathorn, Scott Alan|
|Doctoral Committee Chair(s):||DeLucia, Evan H.|
|Department / Program:||Plant Biology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
Biology, Plant Physiology
|Abstract:||Decreases in shoot nitrogen (N) and increases in root or rhizome N often appear to coincide with drought in several perennial C$\sb4$ grasses native to tallgrass prairie. This suggests that remobilization of shoot N may occur in response to water stress in these species, which would likely have important consequences for growth and survival during and after drought. Little is known about retranslocation of N or other nutrients in response to drought or other environmental stresses in plants, although such retranslocation, if common, would have important implications for stress physiology and nutrient relations, ecosystem nutrient cycling, and crop, forest, and range management practices. The overall objectives of my dissertation research were (1) to determine the extent to which drought-induced retranslocation of shoot N to roots or rhizomes occurs in six perennial C$\sb4$ grasses of tallgrass prairie encompassing a wide range of drought tolerance; and (2) to investigate some of the photosynthetic costs and N-protection benefits that I hypothesized are associated with retranslocation.
Using a combination of methodologies, I demonstrated that C$\sb4$ prairie grasses do retranslocate N from the entire shoot (culms and blades) to belowground tissues specifically in response to drought. Additionally, the degree of retranslocation varies among species and is probably related to drought tolerance. Mesic grasses remobilize as much as 30% of shoot N to roots and rhizomes, while xeric species appear to retranslocate little N during drought. Foliar N volatilization also contributes to decreased shoot N content during drought in prairie grasses and also exhibits a mesic-to-xeric gradient in magnitude (total N losses range from 0.7-5.5% of whole-plant N, in mesic-to-xeric species, respectively). Retranslocation and volatilization, together with growth dilution, decrease shoot N concentration ca. 30-40% during drought in prairie grasses (decreases are somewhat smaller in recently expanded leaves). Retranslocation can account for up to 70% of this decrease, depending on species (mesic $>$ xeric), while volatilization is responsible for 2-10% (xeric $>$ mesic); drought-related growth dilution accounts for the remaining 26-89% (xeric $>$ mesic). Decreases in shoot N concentration account for one-third to one-half of the 69-78% decrease in photosynthetic capacity per unit leaf area during drought in these species (photoprotective downregulation, primarily, and damage, to a lesser extent, are responsible for the remainder). Post-drought recovery of photosynthetic capacity requires 8-12 days, and, decreases in foliar N concentration, which are largely due to retranslocation in mesic grasses, can account for ca. 50-70% of the 23-38% decrease in potential carbon assimilation integrated over the post-drought recovery period.
The carbon costs of N retranslocation may be offset by the potential protective benefits of remobilizing shoot N to belowground tissues during drought, limiting loss of plant N to fire, herbivory, and volatilization when drought curtails soil N uptake and photosynthesis. Results of an experiment in which plants were clipped prior to or following drought indicate that retranslocation can limit loss of shoot N, increasing post-drought plant N-status and growth. These results suggest that retranslocation may therefore represent a compromise between N protection and carbon acquisition.
|Rights Information:||Copyright 1995 Heckathorn, Scott Alan|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9543604|