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Nutrient Dynamics in a Warmer World: Nitrogen Uptake by Trees

Castillo, Ana Cristina

Climate models project a reduced snowpack depth and delay of the onset of its seasonal formation in the northeastern United States over the next 100 years. Reduction of the snowpack leaves soils exposed to freezing air temperatures, which can induce soil frost and inhibit soil biotic activity. Increased soil frost may affect nutrient cycling by damaging fine roots and increasing root mortality. Repeated freezing damage and subsequent heightened production of fine roots in the following growing season may deplete nutrient and carbon reserves within trees. This may leave fine roots more susceptible to frost damage in the following winter, which could decrease nutrient uptake by trees in future years. In order to assess the effects of increased soil frost on nutrient uptake by trees in mixed temperate forests, I measured nitrogen uptake by excised fine roots from a snow removal experiment at Harvard Forest. There were no significant differences in soil freezing depth bet! ween reference and snow removal plots for the mild winter of 2011-2012. Fine roots from snow removal plots had higher mean rates of NH4+ (P = 0.0375) and NO3- uptake than fine roots from reference plots (P = 0.0645). Uptake of NH4+ was significantly greater than NO3- uptake in both reference (P = 0.011) and snow-removal (P = 0.003) plots. Differences in nutrient uptake by fine roots between the reference and snow-removal plots could be occurring for multiple reasons. Soil frost from the previous winter (2010/2011 winter) may have damaged fine roots, diminishing nutrient uptake capacity in the growing season of 2012. Furthermore, trees in the snow removal plots may be nutrient deficient from regenerating fine roots that died the previous winter (2010/2011 winter) when soil frost was greater. Increased fine root necromass and subsequent nutrient release through decomposition may increase nutrient availability in soils of the snow removal plots. However, increased soil ! nitrogen pools may lead to greater nutrient leaching from the ecosystem and change nutrient dynamics of northeastern forests.

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More About This Work

Academic Units
Ecology, Evolution, and Environmental Biology
Degree
B.A., Columbia University
Published Here
February 14, 2013
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