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Thermoregulation of leaf temperature (Tleaf ) may foster metabolic homeostasis in plants, but the degree to which Tleaf is moderated, and under what environmental contexts, is a topic of debate. Isotopic studies inferred the temperature of photosynthetic carbon assimilation to be a constant value of c. 20°C; by contrast, leaf biophysical theory suggests a strong dependence of Tleaf on environmental drivers. Can this apparent disparity be reconciled? We continuously measured Tleaf and whole-crown net CO2 uptake for Eucalyptus parramattensis trees growing in field conditions in whole-tree chambers under ambient and +3°C warming conditions, and calculated assimilation-weighted leaf temperature (TL-AW ) across 265 d, varying in air temperature (Tair ) from -1 to 45°C. We compared these data to TL-AW derived from wood cellulose δ18 O. Tleaf exhibited substantial variation driven by Tair , light intensity, and vapor pressure deficit, and Tleaf was strongly linearly correlated with Tair with a slope of c. 1.0. TL-AW values calculated from cellulose δ18 O vs crown fluxes were remarkably consistent; both varied seasonally and in response to the warming treatment, tracking variation in Tair . The leaves studied here were nearly poikilothermic, with no evidence of thermoregulation of Tleaf towards a homeostatic value. Importantly, this work supports the use of cellulose δ18 O to infer TL-AW , but does not support the concept of strong homeothermic regulation of Tleaf.

Understanding how tree growth is affected by rising temperature is a key to predicting the fate of forests in future warmer climates. Increasing temperature has direct effects on plant physiology, but there are also indirect effects of increased water limitation because evaporative demand increases with temperature in many systems. In this study, we experimentally resolved the direct and indirect effects of temperature on the response of growth and photosynthesis of the widely distributed species Eucalyptus tereticornis. We grew E. tereticornis in an array of six growth temperatures from 18 to 35.5°C, spanning the climatic distribution of the species, with two watering treatments: (a) water inputs increasing with temperature to match plant demand at all temperatures (Wincr ), isolating the direct effect of temperature; and (b) water inputs constant for all temperatures, matching demand for coolest grown plants (Wconst ), such that water limitation increased with growth temperature. We found that constant water inputs resulted in a reduction of temperature optima for both photosynthesis and growth by ~3°C compared to increasing water inputs. Water limitation particularly reduced the total amount of leaf area displayed at Topt and intermediate growth temperatures. The reduction in photosynthesis could be attributed to lower leaf water potential and consequent stomatal closure. The reduction in growth was a result of decreased photosynthesis, reduced total leaf area display and a reduction in specific leaf area. Water availability had no effect on the response of stem and root respiration to warming, but we observed lower leaf respiration rates under constant water inputs compared to increasing water inputs at higher growth temperatures. Overall, this study demonstrates that the indirect effect of increasing water limitation strongly modifies the potential response of tree growth to rising global temperatures.

The triose phosphate utilization (TPU) rate has been identified as one of the processes that can limit terrestrial plant photosynthesis. However, we lack a robust quantitative assessment of TPU limitation of photosynthesis at the global scale. As a result, TPU, and its potential limitation of photosynthesis, is poorly represented in terrestrial biosphere models (TBMs). In this study, we utilized a global data set of photosynthetic CO2 response curves representing 141 species from tropical rainforests to Arctic tundra. We quantified TPU by fitting the standard biochemical model of C3 photosynthesis to measured photosynthetic CO2 response curves and characterized its instantaneous temperature response. Our results demonstrate that TPU does not limit leaf photosynthesis at the current ambient atmospheric CO2 concentration. Furthermore, our results showed that the light-saturated photosynthetic rates of plants growing in cold environments are not more often limited by TPU than those of plants growing in warmer environments. In addition, our study showed that the instantaneous temperature response of TPU is distinct from temperature response of the maximum rate of Rubisco carboxylation. The new formulations of the temperature response of TPU derived in this study may prove useful in quantifying the biochemical limits to terrestrial plant photosynthesis and improve the representation of plant photosynthesis in TBMs.

Trees allocate C from sources to sinks by way of a series of processes involving carbohydrate transport and utilization. Yet these dynamics are not well characterized in trees, and it is unclear how these dynamics will respond to a warmer world. Here, we conducted a warming and pulse-chase experiment on Eucalyptus parramattensis growing in a whole-tree chamber system to test whether warming impacts carbon allocation by increasing the speed of carbohydrate dynamics. We pulse-labelled large (6-m tall) trees with 13 C-CO2 to follow recently fixed C through different organs by using compound-specific isotope analysis of sugars. We then compared concentrations and mean residence times of individual sugars between ambient and warmed (+3°C) treatments. Trees dynamically allocated 13 C-labelled sugars throughout the aboveground-belowground continuum. We did not, however, find a significant treatment effect on C dynamics, as sugar concentrations and mean residence times were not altered by warming. From the canopy to the root system, 13 C enrichment of sugars decreased, and mean residence times increased, reflecting dilution and mixing of recent photoassimilates with older reserves along the transport pathway. Our results suggest that a locally endemic eucalypt was seemingly able to adjust its physiology to warming representative of future temperature predictions for Australia.

Autotrophic respiration is a major driver of the global C cycle and may contribute a positive climate warming feedback through increased atmospheric concentrations of CO2 . The extent of this feedback depends on plants' ability to acclimate respiration to maintain a constant carbon use efficiency (CUE). We quantified respiratory partitioning of gross primary production (GPP) and CUE of field-grown trees in a long-term warming experiment (+3°C). We delivered a 13 C-CO2 pulse to whole tree crowns and chased that pulse in the respiration of leaves, whole crowns, roots, and soil. We also measured the isotopic composition of soil microbial biomass and the respiration rates of leaves and whole crowns. We documented homeostatic respiratory acclimation of foliar and whole-crown respiration rates; the trees adjusted to experimental warming such that leaf-level respiration rates were not increased. Experimental warming had no detectable impact on respiratory partitioning or mean residence times. Of the 13 C label acquired by the trees, aboveground respiration consumed 10%, belowground respiration consumed 40%, and the remaining 50% was retained. Experimental warming of +3°C did not alter respiratory partitioning at the scale of entire trees, suggesting that complete acclimation of respiration to warming is likely to dampen a positive climate warming feedback.

The allocation of carbon (C) is an important component of tree physiology that influences growth and ecosystem C storage. Allocation is challenging to measure, and its sensitivity to environmental changes such as warming and altered water availability is uncertain. We exposed young Eucalyptus tereticornis trees to +3°C warming and elimination of summer precipitation in the field using whole-tree chambers. We calculated C allocation terms using detailed measurements of growth and continuous whole-crown CO2 and water exchange measurements. Trees grew from small saplings to nearly 9 m height during this 15-month experiment. Warming accelerated growth and leaf area development, and it increased the partitioning of gross primary production (GPP) to aboveground respiration and growth while decreasing partitioning below ground. Eliminating summer precipitation reduced C gain and growth but did not impact GPP partitioning. Trees utilized deep soil water and avoided strongly negative water potentials. Warming increased growth respiration, but maintenance respiration acclimated homeostatically. The increasing growth in the warmed treatment resulted in higher rates of respiration, even with complete acclimation of maintenance respiration. Warming-induced stimulations of tree growth likely involve increased C allocation above ground, particularly to leaf area development, whereas reduced water availability may not stimulate allocation to roots.

Climate is an important factor limiting tree distributions and adaptation to different thermal environments may influence how tree populations respond to climate warming. Given the current rate of warming, it has been hypothesized that tree populations in warmer, more thermally stable climates may have limited capacity to respond physiologically to warming compared to populations from cooler, more seasonal climates. We determined in a controlled environment how several provenances of widely distributed Eucalyptus tereticornis and E. grandis adjusted their photosynthetic capacity to +3.5°C warming along their native distribution range (~16-38°S) and whether climate of seed origin of the provenances influenced their response to different growth temperatures. We also tested how temperature optima (Topt ) of photosynthesis and Jmax responded to higher growth temperatures. Our results showed increased photosynthesis rates at a standardized temperature with warming in temperate provenances, while rates in tropical provenances were reduced by about 40% compared to their temperate counterparts. Temperature optima of photosynthesis increased as provenances were exposed to warmer growth temperatures. Both species had ~30% reduced photosynthetic capacity in tropical and subtropical provenances related to reduced leaf nitrogen and leaf Rubisco content compared to temperate provenances. Tropical provenances operated closer to their thermal optimum and came within 3% of the Topt of Jmax during the daily temperature maxima. Hence, further warming may negatively affect C uptake and tree growth in warmer climates, whereas eucalypts in cooler climates may benefit from moderate warming.

International audience; The temperature response of photosynthesis is one of the key factors determining predicted responses to warming in global vegetation models (GVMs). The response may vary geographically, owing to genetic adaptation to climate, and temporally, as a result of acclimation to changes in ambient temperature. Our goal was to develop a robust quantitative global model representing acclimation and adaptation of photosynthetic temperature responses. We quantified and modelled key mechanisms responsible for photosynthetic temperature acclimation and adaptation using a global dataset of photosynthetic CO2 response curves, including data from 141 C3 species from tropical rainforest to Arctic tundra. We separated temperature acclimation and adaptation processes by considering seasonal and common‐garden datasets, respectively. The observed global variation in the temperature optimum of photosynthesis was primarily explained by biochemical limitations to photosynthesis, rather than stomatal conductance or respiration. We found acclimation to growth temperature to be a stronger driver of this variation than adaptation to temperature at climate of origin. We developed a summary model to represent photosynthetic temperature responses and showed that it predicted the observed global variation in optimal temperatures with high accuracy. This novel algorithm should enable improved prediction of the function of global ecosystems in a warming climate.

The temperature sensitivity of soil organic matter (SOM) decomposition has been a source of much debate, given the potential feedbacks with climate warming. Here, we evaluated possible seasonal variation in the temperature sensitivity of microbially mediated soil fluxes related to decomposition (net N mineralization, net nitrification, proteolysis, the maximum velocity (Vmax) of proteolysis, microbial respiration, and the Vmax of four soil exo-enzymes) across forests dominated by eastern hemlock (Tsuga canadensis), white ash (Fraxinus americana), and red oak (Quercus rubra) in central Massachusetts, USA. We asked two simple questions: (1) do temperature sensitivities vary across forest types or different steps of the decomposition process, and (2) do temperature sensitivities display plasticity on a seasonal time frame? We observed substantial variation in temperature sensitivities (Q10 and R10 values) across the different fluxes and forest types. The ash soils exhibited the strongest temperature sensitivities and the mineral-N fluxes exhibited higher temperature sensitivities relative to the proteolytic fluxes or microbial respiration. The Vmax of soil exo-enzymes varied considerably in an interactive manner across forests and time, and the response of some enzymes was consistent with the thermal plasticity. The enzymatic kinetic properties Vmax and Km (half-saturation constant) were strongly correlated with slopes that differed across enzymes, reflecting an enzyme-specific tradeoff between maximum catalytic rate and substrate-binding efficiency. Generally, Q10 values were largely constant, but R10 values varied in a manner consistent with distinct seasonal plasticity. There was a consistent seasonal shift in R10 values coincident with snowmelt, suggesting that the time following snowmelt is a particularly interesting and dynamic period of microbial activity in these temperate forests.

The earth’s future climate state is highly dependent upon changes in terrestrial C storage in response to rising concentrations of atmospheric CO2. Here we show that consistently enhanced rates of net primary production (NPP) are sustained by a C-cascade through the root-microbe-soil system; increases in the flux of C belowground under elevated CO2 stimulated microbial activity, accelerated the rate of soil organic matter decomposition and stimulated tree uptake of N bound to this SOM. This process set into motion a positive feedback maintaining greater C gain under elevated CO2 as a result of increases in canopy N content and higher photosynthetic N-use efficiency. The ecosystem-level consequence of the enhanced requirement for N and the exchange of plant C for N belowground is the dominance of C storage in tree biomass but the preclusion of a large C sink in the soil.

Net primary production (NPP) declines as forests age, but the causal role of decreased gross primary production (GPP), or increased autotrophic respiration (Ra) is still a matter of debate. This uncertainty complicates predicted responses to future climate, as higher atmospheric carbon dioxide (CO2) concentrations may amplify the carbon (C)sink in temperate forests if GPP controls the decline in NPP, but increased temperatures may decrease this C-sink if Ra controls the NPP decline. We quantified NPP in forests dominated by loblolly pine (Pinus taeda) in North Carolina, USA that varied from 14 to 115 years old. We used a sap-flow approach to quantify summer canopy photosynthesis by pines and later-successional hardwood trees, and measured wood CO2 efflux to investigate age-related changes in pine Ra. Despite increasing production by later-successional hardwoods, an 80% decline in pine NPP caused ecosystem NPP to decline with age by ! 40%. The decline in pine NPP was explained by reduced stomatal conductance and photosynthesis, supporting the hypothesis that increasing hydraulic limitation and declining GPP drove the age-related decline of NPP in this species. The difference between GPP and NPP indicated that pine Ra also declined with age; this was corroborated by measurements of reduced stem CO2 efflux with increasing age. These results indicate that C cycling in these successional temperate forests is controlled by C input from GPP, and elements of global change that increase GPP may increase the C-sink in aging warm-temperate pine forests.

Declining net primary production (NPP) with forest age is often attributed to a corresponding decline in gross primary production (GPP). We tested two hypotheses explaining the decline of GPP in ageing stands (14-115 years old) of Pinus taeda L.: (1) increasing N limitation limits photosynthetic capacity and thus decreases GPP with increasing age; and (2) hydraulic limitations increasingly induce stomatal closure, reducing GPP with increasing age. We tested these hypotheses using measurements of foliar nitrogen, photosynthesis, sap-flow and dendroclimatological techniques. Hypothesis (1) was not supported; foliar N retranslocation did not increase and declines were not observed in foliar N, leaf area per tree or photosynthetic capacity. Hypothesis (2) was supported; declines were observed in light-saturated photosynthesis, leaf- and canopy-level stomatal conductance, concentration of CO(2) inside leaf air-spaces (corroborated by an increase in wood δ(13) C) and specific leaf area (SLA), while stomatal limitation and the ratio of sapwood area (SA) to leaf area increased. The sensitivity of radial growth to inter-annual variation in temperature and drought decreased with age, suggesting that tree water use becomes increasingly conservative with age. We conclude that hydraulic limitation increasingly limits the photosynthetic rates of ageing loblolly pine trees, possibly explaining the observed reduction of NPP.

Carbon-use efficiency (CUE), the ratio of net primary production (NPP) to gross primary production (GPP), describes the capacity of forests to transfer carbon (C) from the atmosphere to terrestrial biomass. It is widely assumed in many landscape-scale carbon-cycling models that CUE for forests is a constant value of � 0.5. To achieve a constant CUE, tree respiration must be a constant fraction of canopy photosynthesis. We conducted a literature survey to test the hypothesis that CUE is constant and universal among forest ecosystems. Of the 60 data points obtained from 26 papers published since 1975, more than half reported values of GPP that were not estimated independently from NPP; values of CUE calculated from independent estimates of GPP were greater than those calculated from estimates of GPP derived from NPP. The slope of the relationship between NPP and GPP for all forests was 0.53, but values of CUE varied from 0.23 to 0.83 for different forest types. CUE decreased with increasing age, and a substantial portion of the variation among forest types was caused by differences in stand age. When corrected for age the mean value of CUE was greatest for temperate deciduous forests and lowest for boreal forests. CUE also increased as the ratio of leaf mass-to-total mass increased. Contrary to the assumption of constancy, substantial variation in CUE has been reported in the literature. It may be inappropriate to assume that respiration is a constant fraction of GPP as adhering to this assumption may contribute to incorrect estimates of C cycles. A 20% error in current estimates of CUE used in landscape models (i.e. ranging from 0.4 to 0.6) could misrepresent an amount of C equal to total anthropogenic emissions of CO2 when scaled to the terrestrial biosphere.

Organotin(IV) complexes of the type, R2Sn[S2P(OR)2]2 (where R = Me, n-Bu and R = o-, m-, p-C6H4Me) have been obtained by the reaction of Me2SnCl2 or n-Bu2SnCl2 with ammonium salts of the corresponding O,O-ditolyl dithiophosphates on stirring in benzene and have been characterized by elemental analysis and IR, 1H, 13C, 31P and 119Sn NMR spectroscopy. Trends in data are discussed. The crystal structures of Me2Sn[S2P(OC6H4Me-o)2]2 and n-Bu2Sn[S2P(OC6H4Me-o)2]2 are reported. The environment around the tin atom in both molecules may be described as having skew-trapezoid bipyramidal geometry.

BuSnCl2[(OPPh2)(SPPh2)N] (1) and BuSnCl[(OPPh2)(SPPh2)N](2) (2) were prepared by reacting BuSnCl3 and K[(OPPh2)(SPPh2)N], in 1: 1 and 1: 2 molar ratios. The compounds were investigated in solution by multinuclear (H-1, C-13, P-31, Sn-119) NMR spectroscopy. Variable-temperature P-31 NMR studies indicate dynamic behaviour in solution. The solid-state molecular structure was established by single-crystal X-ray diffraction revealing 5- and 6-coordinated metal atoms in 1 and 2, respectively, as a result of the monometallic biconnective behaviour of the monothioimidodiphosphinato moieties. Preliminary results on the in vitro biological activity are reported.

[2-(Me2NCH2)C6H4]Se-S(S)PR2 [R = Ph (1), (OPr)-Pr-i (2)] were prepared by reacting [2-(Me2NCH2)C6H4](2)Se-2 with the appropriate disulfanes, [R2P(S)S](2). The compounds were characterized by multinuclear magnetic resonance (H-1, C-13, P-31). The molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. Both compounds are monomeric and the nitrogen atom of the pendent CH2NMe2 arm is strongly coordinated to the selenium atom. The organophosphorus ligands are monodentate, thus resulting in a T-shaped coordination geometry around selenium.

The reaction of N-(2-chloroethyl)benzamide and N-[3-bromopropyl]phthalimide with ArTe- Na+ generated in situ by borohydride reduction of Ar2Te2, has resulted in N-[2-(4-methoxyphenyltelluro)ethyl] benzamide (L-1) and N-[2-(4-methoxyphenyl telluro)propyl] phthalimide (L-2) respectively, which are potentially (Te, N)-type ligands. Their NMR (H-1 and C-13) spectra are characteristic and single crystal structures are solved. The Te-C(alkyl) distance [2.140(8)/2.151(4) Angstrom] is longer than Te-C(aryl) distance [2.107(8)/2.128(5)A].

The review is focused on the (XPR 2 )(YPR′ 2 )NH acids (X, Y=O, S, Se; R, R′=alkyl, aryl, OR) and their main group metal derivatives. The methods of preparation, spectroscopic studies and molecular structures of known imidodiphosphorus acids and related derivatives as well as those of inorganic and organometallic main group metal complexes containing either protonated or deprotonated imidodiphosphorus ligand moieties are systematized and discussed.

The reactions of β‐lapachone (1) with 1,2‐diaminoethane (2) and 1,2‐diaminopropane (4) gave the tetracyclic pyrazine derivatives (3) and mixtures of (5) and (6), respectively, while reaction with o‐phenylene diamine (7) gave the quinoxaline derivative (8). The structure of pyrazine derivative (3) is confirmed by single‐crystal X‐ray diffraction study.

The reaction between 2-aminobenzenethiol and ethyl acetoacetate is studied under a variety of conditions, and a procedure for the exclusive synthesis of 1,4-benzothiazines by the neat reaction of substituted aminothiols with beta-ketoesters and beta-dicarbonyl compounds in 85-96% yield is described. With microwave heating, even when both the reactants are solid, yields are high, reaction times brief, and work-up easy. A facile reaction is also observed even in a solid-state reaction. The molecular structure of ethyl 7-chloro-3-methyl-4H-1,4-benzothiazine-2-carboxylate (4d) was determined by single-crystal X-ray diffraction.

To better understand how forest management, phenology, vegetation type, and actual and simulated climatic change affect seasonal and inter-annual variations in soil respiration (R-s), we analyzed m ...

The high yield syntheses of Me2GeHX (X = F, Cl, Br, I) and Me2GeHPs (Ps = CN, N3, NCO, NCS, OAc) are reported. The dimethylgermane derivatives are identified and characterized by various physical m...

The synthesis of a series of methylseleno-derivatives of Group IV, Me4 –nM(SeMe)n(M = Si, Ge, or Sn, n= 1–4), is reported. The preparative routes include reactions of methaneselenol with Group IV amines; the dehydrohalogenation of methaneselenol and a Group IV halide; and the reactions of Group IV halides with ‘methylselenolithium’, methylselenomagnesium iodide, lithium tetramethylselenoaluminate, and methylseleno(trimethyl)silane. The n.m.r. and vibrational spectra are reported and discussed. The reactions of the series Me3MSeMe with some protic reagents were studied.

Die symm. substituierten Disilylchalkogenide (I) werden durch Umsetzung der entsprechenden Iodo- oder Bromosilane mit H2O, HgS, LiA1(SeH)4 bzw. LiZTe dargestellt.

Methyl- and phenylgermanes (I) react with the Na-salt (II) in CS2 at low temp. under exclusion of moisture to yield the compounds (III).

The silyl and germyl derivatives of selenophenol, SiH3(SePh), GeH3(SePh) and SiH2(SePh)2, and the methylated analogues MMenH3–n(SePh)(M = Si, n= 2 or 3; M = Ge, n= 1–3; M = Sn, n= 3) have been prepared and characterized. The comparative synthetic routes include reactions of halides with lithium benzeneselenolate, lithium tetra(phenylseleno) aluminate, and trimethyl(phenylseleno)silane, and also of selenophenol with bisgermylcarbodi-imides. The spectroscopic properties of these species are reported and discussed. The seleno-boranes, B(SePh)3 and B(SeMe)3, -phosphine, P(SePh)3, and -arsine, As(SePh)3, are formed by reactions of the corresponding chlorides with SiMe3(SePh) and SiMe3(SeMe). Reduction of B(SePh)3 by trimethylsilane is quantitative but a similar reaction with monosilane does not occur.

Organogermanium derivatives of dithiophosphoric acid of general formula R 4 − n Ge[SP(S)(OR′) 2 ] n , where n = 1–3, R, = Me, Ph and R′ = Me, Et, have been prepared and characterized by means of 1 H, 13 C NMR and vibrational spectroscopy and mass spectrometry. The spectroscopic results indicate that the dithiophosphate groups are monodenate and that an approximate tetrahedral geometry about the germanium atom is maintained. This is in part confirmed by a preliminary X-ray crystallographic determination of PhGe[SP(S)(OMe) 2 ] 3 , whose crystals are orthorhombic, space group Pn 2 2 1 a , a 13.674(4), b 14.566(3), c 13.154(3) A, V 26201(1) A 3 and Z = 4 from 1225 observed reflections [1 > 2σ I ].

The molecular structures of the title compounds in the gas phase have been determined by electron diffraction. The analyses were based on the rg interatomic distances. For Me2GeF2 principal parameters are: rg(Ge–C) 1.928 ± 0.003 A, rg(Ge–F) 1.739 ± 0.002A; F–Ge–F 105.4 ± 2.0°, F–Ge–C 107.3 ± 0.7°, and C–Ge–C 121.0 ± 3.5°. For MeGeF3 principal parameters are: rg(Ge–F) 1.714 ± 0.002, rg(Ge–C) 1.904 ± 0.009 A; F–Ge–F 105.5 ± 0.9°, and F–Ge–C 113.2 ± 0.6°(uncertainties estimated to include both systematic and random errors). Observed variations in r(Ge–F) and r(Ge–C) are correlated with estimated bond polarities.