Simulating oxygen isotope ratios in tree ring cellulose using a dynamic global vegetation model

Abstract

Abstract. Records of stable oxygen isotope ratios in tree rings are valuable tools to reconstruct past climatic conditions and investigate the response of trees to those conditions. So far the use of stable oxygen isotope signatures of tree rings has not been systematically evaluated in dynamic global vegetation models (DGVMs). DGVMs integrate many hydrological and physiological processes and their application could improve proxy-model comparisons and the interpretation of oxygen isotope records. Here we present an approach to simulate leaf water and stem cellulose δ18O of trees using the LPX-Bern DGVM (LPX-Bern). Our results lie within a few per mil of measured tree ring δ18O of 31 different forest stands mainly located in Europe. Temporal means over the last 5 decades as well as interannual variations for a subset of sites in Switzerland are captured. A sensitivity analysis reveals that relative humidity, temperature, and the water isotope boundary conditions have the largest influence on simulated stem cellulose δ18O, followed by all climatic factors combined, whereas increasing atmospheric CO2 and nitrogen deposition exert no impact. We conclude that simulations with LPX-Bern are useful for investigating large-scale oxygen isotope patterns of tree ring cellulose to elucidate the importance of different environmental factors on isotope variations and therefore help to reduce uncertainties in the interpretation of δ18O of tree rings.

Comparisons of the Performance of δ13C and δ18O of Fagus sylvatica, Pinus sylvestris, and Quercus petraea in the Record of Past Climate Variations

“…However, these assumptions cannot be tested with our data. Finally, the fraction of oxygen exchange between carbohydrates and water at the site of cellulose synthesis may vary from a species to another (e.g., Sternberg & Ellsworth, ). A lower fraction induces a higher δ 18 O in cellulose, and relatively small changes in the exchange rate have a significant impact on the isotopic composition (e.g., 10% change induced 1.9‰ variation in the δ 18 O of some cellulose according to Keel et al, ). Song et al () and Li et al () both suggested that the 18 O enrichment of pine species compared to oak species ( Pinus rigida versus Quercus velutina and Quercus prinus and Pinus densiflora versus Quercus serrate and Quercus variabilis ) could reveal a lower fraction of oxygen exchange.…”

Persistence and Plasticity in Conifer Water‐Use Strategies

“…The mixing term ranges from 0 to 1 and describes the efficiency with which isotopic exchange between photosynthates and xylem water occurs during cellulose metabolism. This model and close variants have been used in numerous studies and we refer readers to Roden et al (); Barbour et al (); Evans (); Ogée et al (); Keel et al () and references therein for additional details.…”

“…To solve for in equation , the modeled estimates of transpiration, photosynthesis, leaf temperature, leaf VPD, and canopy conductances from SCOPE were passed through Supplementary equations 1‐10 (Barbour et al, ; Keel et al, ; Ogée et al, ; Roden et al, ). The cellulose model also required estimates of the path length of the leaf, which was set at a fixed value of 0.01 cm (Keel et al, ), and the exchange efficiency between xylem water and sugars during cellulose metabolism (i.e., pe ), which was set at 0.42 (Roden et al, ). The model produced 30‐minute estimates of the isotopic ratio of cellulose for all time‐steps when photosynthesis was greater than 0 and the air temperature was above the critical threshold for xylogenesis (Rossi et al, ).…”

Global Patterns in Net Primary Production Allocation Regulated by Environmental Conditions and Forest Stand Age: A Model‐Data Comparison

“…The LPX‐Bern 1.3 model (Keel et al, ; Keller et al, ; Spahni et al, ; Stocker et al, ) was developed from LPJ model. The LPX‐Bern model uses the same annual allocation scheme and allometric equations as LPJ model.…”