Root growth and nitrogen cycling in temperate deciduous forests in an elevated carbon dioxide world

In this thesis, I present a series of studies aimed at examining how (A) fine root growth 1 dynamics and (B) root architecture, mycorrhizae, and nitrogen cycling in temperate forests may be affected by elevated CO{dollar}sb2.{dollar}; Elevated CO{dollar}sb2{dollar} leads to significant increases in the gross production and loss (turnover rates) of fine roots in Betula papyrifera but not Acer rubrum. For both species, gross root loss scales as a simple exponential function of gross root production and this scaling relationship was not affected by elevated CO{dollar}sb2.{dollar} The seasonal time course of the effect of CO{dollar}sb2{dollar} varies for gross root production and loss. Early in the growing season, elevated CO{dollar}sb2{dollar} enhances root production, and late in the growing season elevated CO{dollar}sb2{dollar} enhances root loss. This temporal separation in CO{dollar}sb2{dollar} effects led to transitory CO{dollar}sb2{dollar} enhancements in net root production in the middle of the growing season.; Using monoliths of forest soil, I found that elevated CO{dollar}sb2{dollar} leads to reductions in mineralization and consumption rates of NH{dollar}sb4sp+,{dollar} the primary form of available inorganic nitrogen. Consumption rates by both plants and soil microbes were reduced when consumption rates were calculated using {dollar}sp{lcub}15{rcub}{dollar}N pool dilution estimates. However, due to increased rapid immobilization of the added {dollar}sp{lcub}15{rcub}{dollar}N tracer, {dollar}sp{lcub}15{rcub}{dollar}N pool dilution studies in elevated CO{dollar}sb2{dollar} should employ a detailed budget of the fate of applied {dollar}sp{lcub}15{rcub}{dollar}N to make accurate determinations of N-cycling rates. In contrast to the reductions in NH{dollar}sb4sp+{dollar} cycling rates, below ground plant mycorrhizal, allocational, and architectural responses to elevated CO{dollar}sb2{dollar} suggested increased capacity for uptake of soil nutrients. Of these parameters, ectomycorrhizal colonization (% and total number of colonized root tips) was increased the most-increasing between 50 and 65%. These responses were consistant for two studies--one with monocultures of Betula alleghaniensis and another with naturally regenerating communities from intact monoliths of soil. In the naturally regenerating stands, the two birch species Betula papyvifera and Betula alleghaniensis were the most dominant species present. Elevated CO{dollar}sb2{dollar} led to a significant shift in the relative composition between these species, with B. alleghaniensis increasing in dominance relative to B. papyrifera.