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Continuous cover forestry (CCF) has gained interest as an alternative to even-aged management particularly on drained peatland forests. However, relatively little is known about the physiological response of suppressed trees when larger trees are removed as a part of CCF practices. Consequently, studies concentrating on process-level modeling of the response of trees to selection harvesting are also rare. Here, we compared, modeled and measured harvest response of previously suppressed Norway spruce (Picea abies) trees to a selection harvest. We quantified the harvest response by collecting Norway spruce tree-ring samples in a drained peatland forest site and measuring the change in stable carbon and oxygen isotopic ratios of wood formed during 2010–20, including five post-harvest years. The measured isotopic ratios were compared with ecosystem-level process model predictions for |${\kern0em }^{13}$| C discrimination and |${\kern0em }^{18}$| O leaf water enrichment. We found that the model predicted similar but lower harvest response than the measurements. Furthermore, accounting for mesophyll conductance was important for capturing the variation in |${\kern0em }^{13}$| C discrimination. In addition, we performed sensitivity analysis on the model, which suggests that the modeled |${\kern0em }^{13}$| C discrimination is sensitive to parameters related to CO2 transport through stomata to the mesophyll. [ABSTRACT FROM AUTHOR]

Carbon isotope composition of tree‐ring (δ13CRing) is a commonly used proxy for environmental change and ecophysiology. δ13CRing reconstructions are based on a solid knowledge of isotope fractionations during formation of primary photosynthates (δ13CP), such as sucrose. However, δ13CRing is not merely a record of δ13CP. Isotope fractionation processes, which are not yet fully understood, modify δ13CP during sucrose transport. We traced, how the environmental intra‐seasonal δ13CP signal changes from leaves to phloem, tree‐ring and roots, for 7 year old Pinus sylvestris, using δ13C analysis of individual carbohydrates, δ13CRing laser ablation, leaf gas exchange and enzyme activity measurements. The intra‐seasonal δ13CP dynamics was clearly reflected by δ13CRing, suggesting negligible impact of reserve use on δ13CRing. However, δ13CP became increasingly 13C‐enriched during down‐stem transport, probably due to post‐photosynthetic fractionations such as sink organ catabolism. In contrast, δ13C of water‐soluble carbohydrates, analysed for the same extracts, did not reflect the same isotope dynamics and fractionations as δ13CP, but recorded intra‐seasonal δ13CP variability. The impact of environmental signals on δ13CRing, and the 0.5 and 1.7‰ depletion in photosynthates compared ring organic matter and tree‐ring cellulose, respectively, are useful pieces of information for studies exploiting δ13CRing. Summary statement: Intra‐annual tree‐ring δ13C signal of Scots pine recorded faithfully the environmental signal in leaf sucrose δ13C, with no clear signs of reserve use. The 13C‐enrichment of studied sink organs relative to leaves was dominated by post‐photosynthetic fractionations, such as sink organ respiration. [ABSTRACT FROM AUTHOR]

Stable isotope ratio analysis of tree rings has been widely and successfully applied in recent decades for climatic and environmental reconstructions. These studies were mostly conducted at an annual resolution, considering one measurement per tree ring, often focusing on latewood. However, much more information could be retrieved with high-resolution intra-annual isotope studies, based on the fact that the wood cells and the corresponding organic matter are continuously laid down during the growing season. Such studies are still relatively rare, but have a unique potential for reconstructing seasonal climate variations or short-term changes in physiological plant properties, like water-use efficiency. The reason for this research gap is mostly technical, as on the one hand sub-annual, manual splitting of rings is very tedious, while on the other hand automated laser ablation for high-resolution analyses is not yet well established and available. Here, we give an update on the current status of laser ablation research for analysis of the carbon isotope ratio (δ13C) of wood, describe an easy-to-use laser ablation system, its operation and discuss practical issues related to tree core preparation, including cellulose extraction. The results show that routine analysis with up to 100 laser shot-derived δ13C-values daily and good precision and accuracy (ca. 0.1‰) comparable to conventional combustion in an elemental analyzer are possible. Measurements on resin-extracted wood is recommended as most efficient, but laser ablation is also possible on cellulose extracted wood pieces. Considering the straightforward sample preparation, the technique is therefore ripe for wide-spread application. With this work, we hope to stimulate future progress in the promising field of high-resolution environmental reconstruction using laser ablation. [ABSTRACT FROM AUTHOR]

Summary: Intrinsic water‐use efficiency (iWUE), a key index for carbon and water balance, has been widely estimated from tree‐ring δ13C at annual resolution, but rarely at high‐resolution intraseasonal scale.We estimated high‐resolution iWUE from laser‐ablation δ13C analysis of tree‐rings (iWUEiso) and compared it with iWUE derived from gas exchange (iWUEgas) and eddy covariance (iWUEEC) data for two Pinus sylvestris forests from 2002 to 2019.By carefully timing iWUEiso via modeled tree‐ring growth, iWUEiso aligned well with iWUEgas and iWUEEC at intraseasonal scale. However, year‐to‐year patterns of iWUEgas, iWUEiso, and iWUEEC were different, possibly due to distinct environmental drivers on iWUE across leaf, tree, and ecosystem scales. We quantified the modification of iWUEiso by postphotosynthetic δ13C enrichment from leaf sucrose to tree rings and by nonexplicit inclusion of mesophyll and photorespiration terms in photosynthetic discrimination model, which resulted in overestimation of iWUEiso by up to 11% and 14%, respectively.We thus extended the application of tree‐ring δ13C for iWUE estimates to high‐resolution intraseasonal scale. The comparison of iWUEgas, iWUEiso, and iWUEEC provides important insights into physiological acclimation of trees across leaf, tree, and ecosystem scales under climate change and improves the upscaling of ecological models. [ABSTRACT FROM AUTHOR]

Sucrose has a unique role in recording environmental and physiological signals during photosynthesis in its carbon isotope composition (δ13C) and transport of the signal to tree rings. Yet, instead of sucrose, total organic matter (TOM) or water-soluble carbohydrates (WSC) are typically analysed in studies that follow δ13C signals within trees. To study how the choice of organic material may bias the interpretation of δ13C records, we used mature field-grown Scots pine (Pinus sylvestris) to compare for the first time δ13C of different leaf carbon pools with δ13C of assimilates estimated by a chamber-Picarro system (δ13CA_Picarro), and a photosynthetic discrimination model (δ13CA_model). Compared with sucrose, the other tested carbon pools, such as TOM and WSC, poorly recorded the seasonal trends or absolute values of δ13CA_Picarro and δ13CA_model. Consequently, in comparison with the other carbon pools, sucrose δ13C was superior for reconstructing changes in intrinsic water use efficiency (iWUE), agreeing in both absolute values and intra-seasonal variations with iWUE estimated from gas exchange. Thus, deriving iWUE and environmental signals from δ13C of bulk organic matter can lead to misinterpretation. Our findings underscore the advantage of using sucrose δ13C to understand plant physiological responses in depth. [ABSTRACT FROM AUTHOR]

Summary: We explore needle sugar isotopic compositions (δ18O and δ13C) in boreal Scots pine (Pinus sylvestris) over two growing seasons.A leaf‐level dynamic model driven by environmental conditions and based on current understanding of isotope fractionation processes was built to predict δ18O and δ13C of two hierarchical needle carbohydrate pools, accounting for the needle sugar pool size and the presence of an invariant pinitol pool.Model results agreed well with observed needle water δ18O, δ18O and δ13C of needle water‐soluble carbohydrates (sugars + pinitol), and needle sugar δ13C (R2 = 0.95, 0.84, 0.60, 0.73, respectively). Relative humidity (RH) and intercellular to ambient CO2 concentration ratio (Ci/Ca) were the dominant drivers of δ18O and δ13C variability, respectively. However, the variability of needle sugar δ18O and δ13C was reduced on diel and intra‐seasonal timescales, compared to predictions based on instantaneous RH and Ci/Ca, due to the large needle sugar pool, which caused the signal formation period to vary seasonally from 2 d to more than 5 d. Furthermore, accounting for a temperature‐sensitive biochemical 18O‐fractionation factor and mesophyll resistance in 13C‐discrimination were critical.Interpreting leaf‐level isotopic signals requires understanding on time integration caused by mixing in the needle sugar pool. See also the Commentary on this article by Ubierna et al., 236: 2003–2008. [ABSTRACT FROM AUTHOR]

Globally 40–70 Pg of carbon (C) are stored in coarse woody debris on the forest floor. Climate change may reduce the function of this stock as a C sink in the future due to increasing temperature. However, current knowledge on the drivers of wood decomposition is inadequate for detailed predictions. To define the factors that control wood respiration rate of Norway spruce and to produce a model that adequately describes the decomposition process of this species as a function of time, we used an unprecedentedly diverse analytical approach, which included measurements of respiration, fungal community sequencing, N2 fixation rate, nifH copy number, 14C‐dating as well as N%, δ13C and C% values of wood. Our results suggest that climate change will accelerate C flux from deadwood in boreal conditions, due to the observed strong temperature dependency of deadwood respiration. At the research site, the annual C flux from deadwood would increase by 27% from the current 117 g C/kg wood with the projected climate warming (RCP4.5). The second most important control on respiration rate was the stage of wood decomposition; at early stages of decomposition low nitrogen content and low wood moisture limited fungal activity while reduced wood resource quality decreased the respiration rate at the final stages of decomposition. Wood decomposition process was best described by a Sigmoidal model, where after 116 years of wood decomposition mass loss of 95% was reached. Our results on deadwood decomposition are important for C budget calculations in ecosystem and climate change models. We observed for the first time that the temperature dependency of N2 fixation, which has a major role at providing N for wood‐inhabiting fungi, was not constant but varied between wood density classes due to source supply and wood quality. This has significant consequences on projecting N2 fixation rates for deadwood in changing climate. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of δ13C and δ18O in modern resin is crucial for interpreting (sub)fossilized resin records and resin production dynamics. We measured the δ13C and δ18O offsets between resin acids and their precursor molecules in the top‐canopy twigs and breast‐height stems of mature Pinus sylvestris trees. We also investigated the physiological and environmental signals imprinted in resin δ13C and δ18O at an intra‐seasonal scale. Resin δ13C was c. 2‰ lower than sucrose δ13C, in both twigs and stems, likely due to the loss of 13C‐enriched C‐1 atoms of pyruvate during isoprene formation and kinetic isotope effects during diterpene synthesis. Resin δ18O was c. 20‰ higher than xylem water δ18O and c. 20‰ lower than δ18O of water‐soluble carbohydrates, possibly caused by discrimination against 18O during O2‐based diterpene oxidation and 35%–50% oxygen atom exchange with water. Resin δ13C and δ18O recorded a strong signal of soil water potential; however, their overall capacity to infer intraseasonal environmental changes was limited by their temporal, within‐tree and among‐tree variations. Future studies should validate the potential isotope fractionation mechanisms associated with resin synthesis and explore the use of resin δ13C and δ18O as a long‐term proxy for physiological and environmental changes. [ABSTRACT FROM AUTHOR]

Carbon isotope composition of tree-ring (δ 13 C Ring ) is a commonly used proxy for environmental change and ecophysiology. δ 13 C Ring reconstructions are based on a solid knowledge of isotope fractionations during formation of primary photosynthates (δ 13 C P ), such as sucrose. However, δ 13 C Ring is not merely a record of δ 13 C P . Isotope fractionation processes, which are not yet fully understood, modify δ 13 C P during sucrose transport. We traced, how the environmental intra-seasonal δ 13 C P signal changes from leaves to phloem, tree-ring and roots, for 7 year old Pinus sylvestris, using δ 13 C analysis of individual carbohydrates, δ 13 C Ring laser ablation, leaf gas exchange and enzyme activity measurements. The intra-seasonal δ 13 C P dynamics was clearly reflected by δ 13 C Ring , suggesting negligible impact of reserve use on δ 13 C Ring . However, δ 13 C P became increasingly 13 C-enriched during down-stem transport, probably due to post-photosynthetic fractionations such as sink organ catabolism. In contrast, δ 13 C of water-soluble carbohydrates, analysed for the same extracts, did not reflect the same isotope dynamics and fractionations as δ 13 C P , but recorded intra-seasonal δ 13 C P variability. The impact of environmental signals on δ 13 C Ring , and the 0.5 and 1.7‰ depletion in photosynthates compared ring organic matter and tree-ring cellulose, respectively, are useful pieces of information for studies exploiting δ 13 C Ring ., (© 2023 The Authors. Plant, Cell & Environment published by John Wiley & Sons Ltd.)

Intrinsic water-use efficiency (iWUE), a key index for carbon and water balance, has been widely estimated from tree-ring δ 13 C at annual resolution, but rarely at high-resolution intraseasonal scale. We estimated high-resolution iWUE from laser-ablation δ 13 C analysis of tree-rings (iWUE iso ) and compared it with iWUE derived from gas exchange (iWUE gas ) and eddy covariance (iWUE EC ) data for two Pinus sylvestris forests from 2002 to 2019. By carefully timing iWUE iso via modeled tree-ring growth, iWUE iso aligned well with iWUE gas and iWUE EC at intraseasonal scale. However, year-to-year patterns of iWUE gas , iWUE iso , and iWUE EC were different, possibly due to distinct environmental drivers on iWUE across leaf, tree, and ecosystem scales. We quantified the modification of iWUE iso by postphotosynthetic δ 13 C enrichment from leaf sucrose to tree rings and by nonexplicit inclusion of mesophyll and photorespiration terms in photosynthetic discrimination model, which resulted in overestimation of iWUE iso by up to 11% and 14%, respectively. We thus extended the application of tree-ring δ 13 C for iWUE estimates to high-resolution intraseasonal scale. The comparison of iWUE gas , iWUE iso , and iWUE EC provides important insights into physiological acclimation of trees across leaf, tree, and ecosystem scales under climate change and improves the upscaling of ecological models., (© 2022 The Authors New Phytologist © 2022 New Phytologist Foundation.)