14 research outputs found

    Reconstructing terrestrial nutrient cycling using stable nitrogen isotopes in wood

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    Although recent anthropogenic effects on the global nitrogen (N) cycle have been significant, the consequences of increased anthropogenic N on terrestrial ecosystems are unclear. Studies of the impact of increased reactive N on forest ecosystems—impacts on hydrologic and gaseous loss pathways, retention capacity, and even net primary productivity— have been particularly limited by a lack of long-term baseline biogeochemical data. Stable nitrogen isotope analysis (ratio of Âč⁔N to Âč⁎N, termed ÎŽÂč⁔N) of wood chronologies offers the potential to address changes in ecosystem N cycling on millennial timescales and across broad geographic regions. Currently, nearly 50 studies have been published utilizing wood ÎŽÂč⁔N records; however, there are significant differences in study design and data interpretation. Here, we identify four categories of wood ÎŽÂč⁔N studies, summarize the common themes and primary findings of each category, identify gaps in the spatial and temporal scope of current wood ÎŽÂč⁔N chronologies, and synthesize methodological frameworks for future research by presenting eight suggestions for common methodological approaches and enhanced integration across studies. Wood ÎŽÂč⁔N records have the potential to provide valuable information for interpreting modern biogeochemical cycling. This review serves to advance the utility of this technique for long-term biogeochemical reconstructions

    Water availability drives gas exchange and growth of trees in northeastern US, not elevated CO2 and reduced acid deposition

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    Dynamic global vegetation models (DGVM) exhibit high uncertainty about how climate change, elevated atmospheric CO(2) (atm. CO(2)) concentration, and atmospheric pollutants will impact carbon sequestration in forested ecosystems. Although the individual roles of these environmental factors on tree growth are understood, analyses examining their simultaneous effects are lacking. We used tree-ring isotopic data and structural equation modeling to examine the concurrent and interacting effects of water availability, atm. CO(2) concentration, and SO(4) and nitrogen deposition on two broadleaf tree species in a temperate mesic forest in the northeastern US. Water availability was the strongest driver of gas exchange and tree growth. Wetter conditions since the 1980s have enhanced stomatal conductance, photosynthetic assimilation rates and, to a lesser extent, tree radial growth. Increased water availability seemingly overrides responses to reduced acid deposition, CO(2) fertilization, and nitrogen deposition. Our results indicate that water availability as a driver of ecosystem productivity in mesic temperate forests is not adequately represented in DGVMs, while CO(2) fertilization is likely overrepresented. This study emphasizes the importance to simultaneously consider interacting climatic and biogeochemical drivers when assessing forest responses to global environmental changes
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