The legacy of enhanced N and S deposition as revealed by the combined analysis of δ13C, δ18O and δ15N in tree rings

Abstract

This study aimed to evaluate the effects of long-term repeated aerial nitrogen (N) and sulphur (S) misting over tree\ud canopies of a Sitka spruce plantation in Scotland. We combined d13C and d18O in tree rings to evaluate the changes in\ud CO2 assimilation (A) and stomatal conductance (gs) and to assess their contribution to variations in the intrinsic wateruse\ud efficiency (WUEi, i.e., the A/gs ratio). Measurements of d15N enabled shifts in the ecosystem N cycling following\ud misting to be assessed. We found that: (i) N applications, with or without S, increased the ratio between A and gs in\ud favour of A, thus supporting a fertilizer effect of added N. (ii) After the treatments ceased, the trees quickly adjusted to\ud the reductions of N deposition, but not to the reduction in S deposition, which had a negative effect on WUEi by\ud reducing A. This indicates that the beneficial role of N deposition may be negated in forests that previously received a\ud high load of acid rain. (iii) d15N in tree rings reflected the N dynamics caused by canopy retention, with the fingerprint\ud also present in the litter, after the experiment stopped. (iv) Both our results (obtained using canopy applications) and a\ud collection of published data (obtained using soil applications) showed that generally WUEi increased in response to an\ud increase of N applications, with the magnitude of the changes related to soil conditions and the availability of other\ud nutrients. The shifts observed in d15N in tree rings also suggest that both the quantity of the applied N and its quality,\ud mediated by processes occurring during canopy N retention, are important determinants of the interactions between\ud N and C cycles. Stable isotopes are useful probes to understand these processes and to put the results of short-term experiments into context

The effects of prescribed burning on Pinus halepensis Mill. as revealed by dendrochronological and isotopic analyses

“…Further, Beghin et al (2012) recorded a higher N% in surviving Scots pine trees after a wildfire suggesting changes in the soil nitrogen supply. This increase in N availability, enables trees to enhance the efficiency by which they assimilate CO 2 , thus confirming the strong relationship between photosynthetic rate (A) and N supply (Warren and Adams, 2006;Guerrieri et al, 2011).…”

“…Recently, it has been demonstrated not only that P. halepensis is able to survive to wildfires (Fournier et al, 2013) but also that with its great plasticity it has developed various anatomical and ecophysiological adaptations to past fire events (De Micco et al, 2013;Battipaglia et al, 2014b Tree rings are considered a valuable archive of information concerning changes in tree growth in response to environmental stress factor, such as fire (Schweingruber, 1988). However, the combination of the three isotopes d 13 C, d 18 O and d 15 N in tree rings can provide more specific information on the underlying ecophysiological processes (Guerrieri et al, 2011;Leonelli et al, 2012Leonelli et al, , 2013. In particular, plant d 13 C is inversely and linearly correlated with the ratio of intercellular (ci) to atmospheric (ca) CO 2 concentrations in leaves (Farquhar et al, 1989).…”

Species-specific trajectories of nitrogen isotopes in Indiana hardwood forests, USA

“…Wood has very low N concentrations, and most of the N in wood is located in proteins complexed with cellulose in cell walls (Bao et al, 1992;Showalter, 1993). N isotopes in wood have recorded clearance events in Ontario (Bukata and Kyser, 2005) and New Hampshire (McLauchlan et al, 2007), regional pollution in eastern Canada (Bukata and Kyser, 2007;Savard et al, 2009) and Switzerland (Saurer et al, 2004), and short-term fertilization experiments in California (Hart and Classen, 2003), France (Elhani et al, 2005), and Scotland (Guerrieri et al, 2011). Ultimately, the analysis of natural abundance nitrogen isotopes in wood has the potential to elucidate whether forests are generally experiencing increased or decreased N availability.…”

Reconstructing terrestrial nutrient cycling using stable nitrogen isotopes in wood

“…When N additions are highly enriched (high δ 15 N), ring δ 15 N shows a dramatic increase at the onset of N addition and a slow decline over several years following the initial peak (Elhani et al 2003, Hart andClassen 2003). When N additions do not have uniquely high δ 15 N signatures, the increase in tree ring δ 15 N may be less dramatic (Balster et al 2009, Elhani et al 2005, Guerrieri et al 2011. In these cases, the increase in ring δ 15 N is not due to a direct manipulation of source δ 15 N, but to indirect transformation of the soil N pool under high N availability due to pool mixing and isotope fractionation effects.…”