Basal area growth, carbon isotope discrimination, and intrinsic water use efficiency after fertilization of Douglas-fir in the Oregon Coast Range

Abstract

Many hectares of intensively managed Douglas-fir (Pseudotsuga menziesii Mirb. Franco) stands in western North America are fertilized with nitrogen (N) to increase growth rates, but only about ⅔ of all stands respond. Understanding the mechanisms of response facilitates prioritization of stands for treatment. The primary objective of this study was to test the hypothesis that the short-term basal area growth response to a single application of 224 kg N ha −1 as urea was associated with reduced stable carbon isotope discrimination (Δ 13 C) and increased intrinsic water use efficiency (iWUE) in a 20-yr-old plantation of Douglas-fir in the Oregon Coast Range, USA. Increment cores were measured to estimate earlywood, latewood, and total basal area increment over a time series from 1997 to 2015. Stable carbon isotope discrimination and iWUE were estimated using

Tree Growth and Water-Use Efficiency Do Not React in the Short Term to Artificially Increased Nitrogen Deposition

“…Among the studies that assessed the relationship between N, C and water cycles, Jennings et al [30] investigated the behavior of both iWUE and tree growth on a 60 years old black oak forest following long-term manipulative fertilizations, and showed that there was a positive effect on both. Similar findings were also obtained by Cornejo-Oviedo et al [37] on a 20 years old Douglas fir plantation. Here, N fertilization had a positive impact on iWUE, the increase of which promoted tree growth.…”

“…This result helps to explain the absence of physiological response to nitrogen treatments in terms of both WUE and growth rate that we observed in our study. Besides the above-mentioned research of Cornejo-Oviedo et al [37], other studies focusing on either below canopy fertilization or on both above and below addition normally applied greater quantities of N. For instance, Sheppard et al [44] applied N at two different rates (48 and 96 Kg N ha −1 yr −1 ); Jennings et al [30] applied 50 and 150 kg N ha −1 yr −1 and Zhang et al [22] 25 and 50 kg N ha −1 yr −1 . Only Gaige et al [24] applied a quantity similar to the one added in this study (18)(19)(20) kg N ha −1 yr −1 ), though for a longer period than in our experiment.…”

Water stress and CO2concentration interactions affect carbon isotope signatures of leaf and phloem organic matter

“…To date, numerous studies have confirmed the negative relationship between Δ Ca-leaf and water use efficiency at the leaf level (Medrano et al ., 2009; Cornejo-Oviedo et al ., 2017), as Δ Ca-leaf is highly correlated with C i /C a (Farquhar et al ., 1982; Table 3). We found that peak Δ Ca-leaf was reached at 60%–70% FC × C 400 , and the minimum value was found at 35–45% FC × C 800 (Fig.…”

Linking tree physiological constraints with predictions of carbon and water fluxes at an old‐growth coniferous forest

“…, Cornejo‐Oviedo et al. ) and that variability in observed water and carbon fluxes during the 18‐yr study period (1998–2015) was primarily driven by climate. Therefore, we did not simulate nitrogen limitation during this exercise.…”

“…ED2 groups plants not only into multiple PFTs, but also into numerous size classes, which enables vertical interactions and resource competitions among different sizes of trees. We assumed that photosynthesis at this mature site was primarily limited by light and water availability (Brooks and Coulombe 2009, Tarvainen et al 2016, Cornejo-Oviedo et al 2017 and that variability in observed water and carbon fluxes during the 18yr study period (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015) was primarily driven by climate. Therefore, we did not simulate nitrogen limitation during this exercise.…”