New Phytologist

doi: 10.1111/nph.18251pmid: N/A

Cushman, K. C.; Albert, Loren P.; Norby, Richard J.; Saatchi, Sassan

doi: 10.1111/nph.19237pmid: 37915249

Spitzer, Clydecia M.; Blume‐Werry, Gesche

doi: 10.1111/nph.19286pmid: 37784258

Kottler, Ezra

doi: 10.1111/nph.19240pmid: 37697636

Kongsted, Thea E.; Glover, Beverley J.

doi: 10.1111/nph.19202pmid: 37578088

Wuyun, Tana; Niinemets, Ülo; Hõrak, Hanna

doi: 10.1111/nph.19215pmid: 37635267

doi: 10.1111/nph.19231pmid: 37915250

Liang, Jie; Krauss, Ken W.; Finnigan, John; Stuart‐Williams, Hilary; Farquhar, Graham D.; Ball, Marilyn C.

doi: 10.1111/nph.19308pmid: 37823336

Limitations and utility of three measures of water use characteristics were evaluated: water use efficiency (WUE), intrinsic WUE and marginal water cost of carbon gain (∂E/∂A) estimated, respectively, as ratios of assimilation (A) to transpiration (E), of A to stomatal conductance (gs) and of sensitivities of E and A with variation in gs. Only the measure ∂E/∂A estimates water use strategy in a way that integrates carbon gain relative to water use under varying environmental conditions across scales from leaves to communities. This insight provides updated and simplified ways of estimating ∂E/∂A and adds depth to understanding ways that plants balance water expenditure against carbon gain, uniquely providing a mechanistic means of predicting water use characteristics under changing environmental scenarios.

Martínez‐Sancho, Elisabet; Cernusak, Lucas A.; Fonti, Patrick; Gregori, Alessandro; Ullrich, Bastian; Pannatier, Elisabeth Graf; Gessler, Arthur; Lehmann, Marco M.; Saurer, Matthias; Treydte, Kerstin

doi: 10.1111/nph.19278pmid: 37753542

The oxygen isotope composition (δ18O) of tree‐ring cellulose is used to evaluate tree physiological responses to climate, but their interpretation is still limited due to the complexity of the isotope fractionation pathways. We assessed the relative contribution of seasonal needle and xylem water δ18O variations to the intra‐annual tree‐ring cellulose δ18O signature of larch trees at two sites with contrasting soil water availability in the Swiss Alps. We combined biweekly δ18O measurements of soil water, needle water, and twig xylem water with intra‐annual δ18O measurements of tree‐ring cellulose, xylogenesis analysis, and mechanistic and structural equation modeling. Intra‐annual cellulose δ18O values resembled source water δ18O mean levels better than needle water δ18O. Large parts of the rings were formed under high proportional exchange with unenriched xylem water (pex). Maximum pex values were achieved in August and imprinted on sections at 50–75% of the ring. High pex values were associated with periods of high atmospheric evaporative demand (VPD). While VPD governed needle water δ18O variability, we estimated a limited Péclet effect at both sites. Due to a variable pex, source water has a strong influence over large parts of the intra‐annual tree‐ring cellulose δ18O variations, potentially masking signals coming from needle‐level processes.

Holloway‐Phillips, Meisha; Cernusak, Lucas A.; Nelson, Daniel B.; Lehmann, Marco M.; Tcherkez, Guillaume; Kahmen, Ansgar

doi: 10.1111/nph.19248pmid: 37680025

Oxygen and hydrogen isotopes of cellulose in plant biology are commonly used to infer environmental conditions, often from time series measurements of tree rings. However, the covariation (or the lack thereof) between δ18O and δ2H in plant cellulose is still poorly understood. We compared plant water, and leaf and branch cellulose from dominant tree species across an aridity gradient in Northern Australia, to examine how δ18O and δ2H relate to each other and to mean annual precipitation (MAP). We identified a decline in covariation from xylem to leaf water, and onwards from leaf to branch wood cellulose. Covariation in leaf water isotopic enrichment (Δ) was partially preserved in leaf cellulose but not branch wood cellulose. Furthermore, whilst δ2H was well‐correlated between leaf and branch, there was an offset in δ18O between organs that increased with decreasing MAP. Our findings strongly suggest that postphotosynthetic isotope exchange with water is more apparent for oxygen isotopes, whereas variable kinetic and nonequilibrium isotope effects add complexity to interpreting metabolic‐induced δ2H patterns. Varying oxygen isotope exchange in wood and leaf cellulose must be accounted for when δ18O is used to reconstruct climatic scenarios. Conversely, comparing δ2H and δ18O patterns may reveal environmentally induced shifts in metabolism.