Effect of nitrogen deposition on centennial forest water-use efficiency

Abstract

The uptake of carbon dioxide (CO2) from the atmosphere through photosynthesis is accompanied by an inevitable loss of water vapor through the stomata of leaves. The rate of leaf-level CO2 assimilation per unit stomatal conductance, i.e. intrinsic water-use efficiency (WUEi), is thus a key characteristic of terrestrial ecosystem functioning that is central to the global hydroclimate system. Empirical evidence and theory suggest a positive response of forest WUE to increased CO2 levels globally. Although evidence exists for a positive effect of ecosystem nitrogen (N) inputs on WUEi, it is not clear how trends in atmospheric N deposition have affected WUEi in the past. Here we combine twentieth-century climate and nitrogen deposition with stable isotope signature in tree rings and document a WUEi trend reversal at two sites in Switzerland, that matches the timing of a trend reversal in atmospheric N deposition. Using generalized additive models (GAMs), we fitted observed WUEi time series to multiple environmental covariates. This suggested N deposition to have a significant effect on long-term WUEi at the site that was exposed to higher N deposition levels. The ratio of the increase in WUEi in response to increase in CO2 (dWUEi/dCO2) declined by 96% after 1980 (from 0.53 to 0.02) in the beech forest and declined by 72% in the spruce forest (from 0.46 to 0.13) concurrent with a sharp decline in N deposition. Using the GAM model for two scenarios, we show that had N deposition levels not declined after 1980s, WUEi would have increased more strongly in response to increasing CO2. Although the increase in N deposition was limited to the 1950–1980 decades and the signals have declined with improvements in air quality across Europe, the role of atmospheric pollution must be reconsidered in interpretation of tree ring studies and for building environmental proxies that are pivotal to understanding future sink capacity of terrestrial ecosystems in response to climate change.

Chemical Regulation Effect of Water Use Efficiency of Maize Intercropping

“…It also provides e ective technical support for e cient water use and water conservation in farmland at the micro level. However, in comparison, the research results on the optimization of agricultural water use structure and water resources management are not very signi cant [17,18] northwest oasis irrigation areas of Gansu Province. When the irrigation quota of wheat and maize is 6750 m 3 /hm 2 , the yield can reach 15000 kg/hm 2 [19].…”

Differences in leaf gas exchange strategies explain Quercus rubra and Liriodendron tulipifera intrinsic water use efficiency responses to air pollution and climate change

“…However, we found several environmental factors interacted with iCO 2 to moderate the integrated response of iWUE in the two study species. For both Quru and Litu, we found increasing NO x stimulated iWUE, but to a greater extent at low [CO 2 ] (Figure S4), likely through increased N deposition resulting in higher plant available N stimulating A net (Gharun et al, 2021;Jennings et al, 2016;Leonardi et al, 2012). We additionally found iCO 2 stimulated Quru iWUE less when it was warm (Figure S4; Table S5), pointing to the interactive effects between atmospheric pollutants and climate on tree physiology (Zuidema et al, 2020), but also suggesting leaf respiration may increase proportionally more than photosynthesis.…”

“…Moreover, these acidic air pollutants remain a major issue in many forested areas of the world (Aas et al, 2019;Akimoto et al, 2022) and are important to interpreting tree-ring records in North America and Europe (Battipaglia et al, 2010;Gharun et al, 2021;Lanning et al, 2019;Leonelli et al, 2012;Rinne et al, 2010;Savard, 2010;Savard et al, 2020). Sulfur pollution negatively impacts leaf physiology by reducing rates of photosynthesis (Choi et al, 2014) and stomatal conductance (Borer et al, 2005) which is reflected in tree iWUE (Rinne et al, 2010;Thomas et al, 2013).…”

isocalcR: An R package to streamline and standardize stable isotope calculations in ecological research

“…Moreover, iWUE is increasingly being used as a diagnostic of disturbance (e.g. air pollution, drought, forest thinning, fire) impacts on tree physiology (Gharun et al, 2021; McDowell et al, 2010; Rinne et al, 2010; Savard, 2010; Tepley et al, 2020) and could augment studies primarily using physiological instruments, but that also report ∆ 13 C (Stenzel et al, 2021). The recent uptick in studies using stable carbon isotopes has spurred the collation and archival of recommended forcing data (atmospheric CO 2 concentration, C a ; atmospheric δ 13 CO 2 composition, δ 13 C atm ) necessary to perform complex calculations to derive physiological variables like iWUE (Belmecheri & Lavergne, 2020).…”

“…Moreover, iWUE is increasingly being used as a diagnostic of disturbance (e.g. air pollution, drought, forest thinning, fire) impacts on tree physiology (Gharun et al, 2021;McDowell et al, 2010;Rinne et al, 2010;Savard, 2010;Tepley et al, 2020) and could augment studies primarily using physiological instruments, but that also report ∆ 13 C (Stenzel et al, 2021).…”