Stable isotopes in tree rings.

The temperature dependence of C 3 photosynthesis is known to vary with growth environment and with species In an attempt to quantify this variability, a commonly used biochemically based photosynthesis model was parameterized from 19 gas exchange studies on tree and crop species The parameter values obtained described the shape and amplitude of the temperature responses of the maximum rate of Rubisco activity ( V cmax ) and the potential rate of electron transport ( J max ) Original data sets were used for this review, as it is shown that derived values of V cmax and its temperature response depend strongly on assumptions made in derivation Values of J max and V cmax at 25 ° C varied considerably among species but were strongly correlated, with an average J max : V cmax ratio of 1·67 Two species grown in cold climates, however, had lower ratios In all studies, the J max : V cmax ratio declined strongly with measurement temperature The relative temperature responses of J max and V cmax were relatively constant among tree species Activation energies averaged 50 kJ mol − 1 for J max and 65 kJ mol − − − 1 for V cmax , and for most species temperature optima averaged 33 ° ° ° C for J max and 40 ° C for V cmax  However, the cold climate tree species had low temperature optima for both J max ( 19 ° C) and V cmax (29 ° ° ° C), suggesting acclimation of both processes to growth temperature Crop species had somewhat different temperature responses, with higher activation energies for both J max and V cmax , implying narrower peaks in the temperature response for these species The results thus suggest that both growth environment and

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Temperature response of parameters of a biochemically based model of photosynthesis. II. A review of experimental data

Photosynthetic capacity and its relationship to leaf nitrogen content are two of the most sensitive parameters of terrestrial biosphere models (TBM) whose representation in global-scale simulations has been severely hampered by a lack of systematic analyses using a sufficiently broad database. Here, we use data of qualitative traits, climate and soil to subdivide the terrestrial vegetation into functional types (PFT), and then assimilate observations of carboxylation capacity, V max (723 data points), and maximum photosynthesis rates, A max (776 data points), into the C 3 photosynthesis model proposed by Farquhar et al. to constrain the relationship of V 25 max (V max normalised to 25 °C) to leaf nitrogen content per unit leaf area for each PFT. In a second step, the resulting functions are used to predict V 25 max per PFT from easily measurable values of leaf nitrogen content in natural vegetation (1966 data points). Mean values of V 25 max thus obtained are implemented into a TBM (BETHY within the coupled climate-vegetation model ECHAM5/JSBACH) and modelled gross primary production (GPP) is compared with independent observations on stand scale. Apart from providing parameter ranges per PFT constrained from much more comprehensive data, the results of this analysis enable several major improvements on previous parameterisations. (1) The range of mean V 25 max between PFTs is dominated by differences of photosynthetic nitrogen use efficiency (NUE, defined as V 25 max divided by leaf nitrogen content), while within each PFT, the scatter of V 25 max values is dominated by the high variability of leaf nitrogen content. (2) We find a systematic depression of NUE on certain tropical soils that are known to be deficient in phosphorous. (3) V 25 max of tropical trees derived by this study is substantially lower than earlier estimates currently used in TBMs, with an obvious effect on modelled GPP and surface temperature. (4) The root-mean-squared difference between modelled and observed GPP is substantially reduced.

Quantifying photosynthetic capacity and its relationship to leaf nitrogen content for global-scale terrestrial biosphere models

With the development of rapid measurement techniques, stable oxygen isotope analysis of plant tissue is poised to become an important tool in plant physiological, ecological, paleoclimatic and forensic studies. Recent advances in mechanistic understanding have led to the improvement of process-based models that accurately predict variability in the oxygen isotope composition of plant organic material (δ18Op). δ18Op has been shown to reflect the isotope composition of soil water, evaporative enrichment in transpiring leaves, and isotopic exchange between oxygen atoms in organic molecules and local water in the cells in which organic molecules are formed. This review presents current theoretical models describing the influences on δ18Op, using recently published experimental work to outline strengths and weaknesses in the models. The potential and realised applications of the technique are described.

Stable oxygen isotope composition of plant tissue: a review

Virtually all current estimates of the maximum carboxylation rate ( V cmax ) of ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) and the maximum electron transport rate ( J max ) for C 3 species implicitly assume an infinite CO 2 transfer conductance ( g i ). And yet, most measurements in perennial plant species or in ageing or stressed leaves show that g i imposes a significant limitation on photosynthesis. Herein, we demonstrate that many current parameterizations of the photosynthesis model of Farquhar, von Caemmerer & Berry ( Planta 149, 78‐90, 1980) based on the leaf intercellular CO 2 concentration ( C i ) are incorrect for leaves where g i limits photosynthesis. We show how conventional A‐C i curve (net CO 2 assimilation rate of a leaf ‐ A n ‐ as a function of C i ) fitting methods which rely on a rectangular hyperbola model under the assumption of infinite g i can significantly underestimate V cmax for such leaves. Alternative parameterizations of the conventional method based on a single, apparent Michaelis‐Menten constant for CO 2 evaluated at C i [ K m (CO 2 ) i ] used for all C 3 plants are also not acceptable since the relationship between V cmax and g i is not conserved among species. We present an alternative A‐C i curve fitting method that accounts for g i through a non-rectangular hyperbola version of the model of Farquhar et al . (1980). Simulated and real examples are used to demonstrate how this new approach eliminates the errors of the conventional A‐C i curve fitting method and provides V cmax estimates that are virtually insensitive to g i . Finally, we show how the new A‐C i curve fitting method can be used to estimate the value of the kinetic constants of Rubisco in vivo is presented

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2004.01140.x

On the need to incorporate sensitivity to CO2 transfer conductance into the Farquhar–von Caemmerer–Berry leaf photosynthesis model

Responses of photosynthesis (A) to intercellular CO2 concentration (ci) in 2-year-old Pinus radiata D. Don seedlings were measured at a range of temperatures in order to parametrize a biophysical model of leaf photosynthesis. Increasing leaf temperature from 8 to 30°C caused a 4-fold increase in Vcmax, the maximum rate of carboxylation (10.7–43.3 μol m−2 s−1 and a 3-fold increase in Jmax, the maximum electron transport rate (20.5–60.2 μmol m −2 s−1). The temperature optimum for Jmax was lower than that for Vcmax, causing a decline in the ratio Jmax:Vcmax from 2.0 to 1.4 as leaf temperature increased from 8 to 30°C. To determine the response of photosynthesis to leaf nitrogen concentration, additional measurements were made on seedlings grown under four nitrogen treatments. Foliar N concentrations varied between 0.36 and 1.27 mol kg−1, and there were linear relationships between N concentration and both Vcmax and Jmax. Measurements made throughout the crown of a plantation forest tree, where foliar N concentrations varied from 0.83 mol kg−1 near the base to 1.54 mol kg−1 near the leader, yielded similar relationships. These results will be useful in scaling carbon assimilation models from leaves to canopies.

The response of photosynthetic model parameters to temperature and nitrogen concentration in Pinus radiata D. Don

Seasonal cycles in stable carbon isotope composition (δ13C) were measured within annual rings of Pinus radiata D. Don from trees in two plantation sites which differ markedly in annual water balance. The amplitudes of seasonal δ13C variation at the wet and dry sites were 1–2 and 4 respectively. Mean δ13C values from the wet site were 3 more 13C depleted than those from the dry site implying lower water-use efficiency (carbon assimilation per unit transpiration). A process-based, leaf-level model of stomatal conductance and CO2 assimilation was combined with a water balance model to estimate the average daily intercellular CO2 concentration (ci). Over two growing seasons at each site there was generally good agreement between mean canopy-level ci derived from the tree-ring δ13C data and modelled leaf-level ci levels. Further, the ratio of annual CO2 assimilation to transpiration estimated by the model for each site correlated with the differences in water-use efficiency between the sites. Carbon isotope discrimination of leaves in the canopy was thus reflected directly in the stem wood, and its dynamic variation within a site, as well as between sites, was driven principally by the interaction of seasonally changing micrometeorological variables and soil water availability.

Seasonal Changes in Stable Carbon Isotope Ratios within Annual Rings of Pinus radiata Reflect Environmental Regulation of Growth Processes

The three dimensional distribution of intercepted radiation, intercellular CO2 concentration (Ci) and late summer needle nitrogen (N) concentration were determined at the tips of all 54 branches in a 6·2-m-tall Pinus radiata D. Don tree growing in a New Zealand plantation. Measurements included above- and below-canopy irradiance, leaf stable carbon isotopic composition (δ13C) and tree canopy architecture. The radiation absorption component of the model, MAESTRO, was tested on site and then used to determine the branch tip distribution of intercepted radiation. We hypothesized that in branch tip needles: (i) the allocation of nitrogen and other nutrients would be closely associated with the distribution of intercepted radiation, reflecting carbon gain optimization theory, and (ii) Ci would predominantly reflect changes in photosynthetic rate (A) rather than stomatal conductance (gs), indicating that the increase in A for a given increase in N concentration was larger than the corresponding increase in gs. Needle nitrogen concentration was poorly related to intercepted radiation, regardless of the period over which the latter was calculated. At a given height, there was a large azimuthal variation in intercepted radiation but N concentration was remarkably uniform around the tree canopy. There was, however, a linear and positive correspondence between N concentration and δ13C and needle height above ground (r2 = 0·73 and 0·68, respectively). The very strong linear correspondence between N concentration and Ci (r2 = 0·71) was interpreted, using gas exchange measurements, as supporting our second hypothesis. Recognizing the strong apical control in P. radiata and possible effects of leaf nitrogen storage in an evergreen species, we propose that the tree leader must have constituted a very strong carbon sink throughout the growing season, and that the proximity of branch tip needles to the leader affected their photosynthetic capacity and nutrient concentration, independent of intercepted radiation. This implies an integrated internal determination of resource allocation within the tree and challenges the current convention that resources are optimally distributed according to the profile of intercepted radiation.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-3040.1998.00314.x

A. S. Walcroft

Papers

The response of photosynthetic model parameters to temperature and nitrogen concentration in Pinus radiata D. Don

Seasonal Changes in Stable Carbon Isotope Ratios within Annual Rings of Pinus radiata Reflect Environmental Regulation of Growth Processes

Nitrogen allocation and carbon isotope fractionation in relation to intercepted radiation and position in a young Pinus radiata D. don tree

The effects of long-term, partial shading on growth and photosynthesis in Pinus radiata D. Don trees