Climate and atmospheric deposition effects on forest water-use efficiency and nitrogen availability across Britain

Abstract

Rising atmospheric CO 2 (c a) has been shown to increase forest carbon uptake. Yet, whether the c afertilization effect on forests is modulated by changes in sulphur (S dep) and nitrogen (N dep) deposition and how n dep affects ecosystem N availability remains unclear. We explored spatial and temporal (over 30-years) changes in tree-ring δ 13 C-derived intrinsic water-use efficiency (iWUE), δ 18 O and δ 15 N for four species in twelve forests across climate and atmospheric deposition gradients in Britain. The increase in iWUE was not uniform across sites and species-specific underlying physiological mechanisms reflected the interactions between climate and atmospheric drivers (oak and Scots pine), but also an age effect (Sitka spruce). Most species showed no significant trends for tree-ring δ 15 N, suggesting no changes in N availability. Increase in iWUE was mostly associated with increase in temperature and decrease in moisture conditions across the South-North gradient and over 30-years. However, when excluding Sitka spruce (to account for age or stand development effects), variations in iWUE were significantly associated with changes in c a and S dep. Our data suggest that overall climate had the prevailing effect on changes in iWUE across the investigated sites. Whereas, detection of N dep , S dep and c a signals was partially confounded by structural changes during stand development. The ability of forests to mitigate climate change depends on how well they cope and adapt to the rapid forecasted changes in atmospheric conditions, including pollutant emissions from anthropogenic activities, namely CO 2 , sulphur (S) and reactive nitrogen (N). While sulphur emissions have been successfully regulated in Europe and North America 1 , N compounds, particularly ammonia and nitrous oxide, continue at relatively high levels compared to the pre-industrial period 2-4. These changes in N and S atmospheric concentrations have occurred together with increasing atmospheric CO 2 concentration (c a), which recently exceeded 410 ppm 5 , with a relative change of 46% compared to pre-industrial levels. Atmospheric N and S compounds are deposited from the atmosphere onto terrestrial ecosystems and together with the increasing c a can have an effect on some of the processes underpinning forest carbon, water and nutrient cycling. Increases in c a affect leaf gas exchange by increasing photosynthesis (A) and reducing stomatal conductance (g s) 6 , thus raising intrinsic water use efficiency of trees (iWUE = A/g s). Higher iWUE has been commonly reported for conifer compared to broadleaf species 7. Moreover, the increase in iWUE derived from carbon isotope composition (δ 13 C) in tree rings 8 has generally been associated with an active response of trees to increasing c a , whereby intercellular CO 2 (c i) increased in a proportional way to c a , resulting in a constant c i /c a ratio, due to proportional regulation of A and g s 9. However, changes in N (N dep) and S (S dep) deposition can also influence carbon-water relations. Hig...

Growth plasticity of Gymnosperm trees did not avoid declining resilience to soil and atmospheric droughts during the 20th century

“…Other drivers, such as nitrogen deposition and increased atmospheric [CO2] may lead however to significant water savings for plant leaves and canopies [9][10][11] . Because of the interacting nature of many environmental drivers and plant physiological processes, it is difficult to predict whether long-term chronic effects of repeated severe droughts become amplified during subsequent events 12 .…”

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

“…The use of stable carbon isotopes in ecological research has consistently increased since the late 1980s (Figure 1), driven by a combination of developments in carbon isotope physiological theory (Badeck et al, 2005; Cernusak & Ubierna, 2022; Farquhar et al, 1989; Frank et al, 2015; Lavergne et al, 2022; McCarroll & Loader, 2004; Ubierna & Farquhar, 2014) and advancements in instrumentation for detection and measurement (Günther et al, 2000; Snyder et al, 2016; Wieser & Schwieters, 2005). In particular, a large focus of research leveraging stable carbon isotopes, which has grown considerably since 2008, has been to reconstruct and understand the long‐term environmental drivers controlling leaf intrinsic water use efficiency (iWUE = the ratio of net leaf photosynthesis [ A net ] to stomatal conductance to H 2 O [ g s ]) of plants (Figure 1) (Belmecheri et al, 2021; Frank et al, 2015; Guerrieri et al, 2019, 2020; Mathias & Thomas, 2021; Peñuelas et al, 2011). Moreover, iWUE is increasingly being used as a diagnostic of disturbance (e.g.…”

Foliar stable isotope ratios of carbon and nitrogen in boreal forest plants exposed to long-term pollution from the nickel-copper smelter at Monchegorsk, Russia

“…group of plants with similar physiological characteristics such as trees, shrubs and forbs, either evergreen or deciduous (Brooks et al 1997 ; Flanagan et al 1997a ; Lavergne et al 2020 ). The foliar and tree-ring δ 13 C values also vary with environmental factors, and particularly water availability including vapour pressure deficit that affects stomatal functions and photosynthesis (O’Leary 1981 ; Dawson et al 2002 ; Klein et al 2005 ; Guerrieri et al 2020 ). In other words, reduced water availability usually reduces stomatal conductance leading to increased δ 13 C values (Guerrieri et al 2020 ; Lavergne et al 2020 ; Marchand et al 2020 ).…”

“…Recent studies on tree-ring δ 13 C-derived intrinsic water use efficiency, which is an estimate of the leaf-level ratio between assimilation and stomatal conductance integrated across the whole canopy and the entire growing season (Medrano et al 2015 ) suggest, however, that especially the responses of boreal conifers to elevated CO 2 have been strongly overestimated in previous studies. This is because developmental changes (tree size, stand age), climate and differences in site conditions including atmospheric S and N pollution have not been accounted for (Guerrieri et al 2020 ; Marchand et al 2020 ; Savard et al 2020 ).…”