SummaryLeaf dark respiration (R dark ) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of R dark and associated leaf traits. Data for 899 species were compiled from 100 sites (from the Arctic to the tropics). Several woody and nonwoody plant functional types (PFTs) were represented. Mixed-effects models were used to disentangle sources of variation in R dark .Area-based R dark at the prevailing average daily growth temperature (T) of each site increased only twofold from the Arctic to the tropics, despite a 20°C increase in growing T (8-28°C). By contrast, R dark at a standard T (25°C, R dark 25 ) was threefold higher in the Arctic than in the tropics, and twofold higher at arid than at mesic sites. Species and PFTs at cold sites exhibited higher R dark 25 at a given photosynthetic capacity (V cmax 25 ) or leaf nitrogen concentration ([N]) than species at warmer sites. R dark 25 values at any given V cmax 25 or [N] were higher in herbs than in woody plants.The results highlight variation in R dark among species and across global gradients in T and aridity. In addition to their ecological significance, the results provide a framework for improving representation of R dark in terrestrial biosphere models (TBMs) and associated land-surface components of Earth system models (ESMs).

Understanding of the extent of acclimation of light-saturated net photosynthesis (A ) to temperature (T), and associated underlying mechanisms, remains limited. This is a key knowledge gap given the importance of thermal acclimation for plant functioning, both under current and future higher temperatures, limiting the accuracy and realism of Earth system model (ESM) predictions. Given this, we analysed and modelled T-dependent changes in photosynthetic capacity in 10 wet-forest tree species: six from temperate forests and four from tropical forests. Temperate and tropical species were each acclimated to three daytime growth temperatures (T ): temperate - 15, 20 and 25 °C; tropical - 25, 30 and 35 °C. CO response curves of A were used to model maximal rates of RuBP (ribulose-1,5-bisphosphate) carboxylation (V ) and electron transport (J ) at each treatment's respective T and at a common measurement T (25 °C). SDS-PAGE gels were used to determine abundance of the CO -fixing enzyme, Rubisco. Leaf chlorophyll, nitrogen (N) and mass per unit leaf area (LMA) were also determined. For all species and T , A at current atmospheric CO partial pressure was Rubisco-limited. Across all species, LMA decreased with increasing T . Similarly, area-based rates of V at a measurement T of 25 °C (V ) linearly declined with increasing T , linked to a concomitant decline in total leaf protein per unit leaf area and Rubisco as a percentage of leaf N. The decline in Rubisco constrained V and A for leaves developed at higher T and resulted in poor predictions of photosynthesis by currently widely used models that do not account for T -mediated changes in Rubisco abundance that underpin the thermal acclimation response of photosynthesis in wet-forest tree species. A new model is proposed that accounts for the effect of T -mediated declines in V on A , complementing current photosynthetic thermal acclimation models that do not account for T sensitivity of V .

We explored the impact of canopy position on leaf respiration (R) and associated traits in tree and shrub species growing in a lowland tropical rainforest in Far North Queensland, Australia. The range of traits quantified included: leaf R in darkness (RD) and in the light (RL; estimated using the Kok method); the temperature (T)-sensitivity of RD; light-saturated photosynthesis (Asat); leaf dry mass per unit area (LMA); and concentrations of leaf nitrogen (N), phosphorus (P), soluble sugars and starch. We found that LMA, and area-based N, P, sugars and starch concentrations were all higher in sun-exposed/upper canopy leaves, compared with their shaded/lower canopy and deep-shade/understory counterparts; similarly, area-based rates of RD, RL and Asat (at 28 °C) were all higher in the upper canopy leaves, indicating higher metabolic capacity in the upper canopy. The extent to which light inhibited R did not differ significantly between upper and lower canopy leaves, with the overall average inhibition being 32% across both canopy levels. Log-log RD-Asat relationships differed between upper and lower canopy leaves, with upper canopy leaves exhibiting higher rates of RD for a given Asat (both on an area and mass basis), as well as higher mass-based rates of RD for a given [N] and [P]. Over the 25-45 °C range, the T-sensitivity of RD was similar in upper and lower canopy leaves, with both canopy positions exhibiting Q10 values near 2.0 (i.e., doubling for every 10 °C rise in T) and Tmax values near 60 °C (i.e., T where RD reached maximal values). Thus, while rates of RD at 28 °C decreased with increasing depth in the canopy, the T-dependence of RD remained constant; these findings have important implications for vegetation-climate models that seek to predict carbon fluxes between tropical lowland rainforests and the atmosphere.

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Summary 1.We investigated whether plants adapted to thermally contrasting environments (e.g. tropical-temperate habitats) exhibit inherent differences in leaf trait scaling relationships. 2. Thirteen tropical and 12 temperate species (all characteristic of wet forests) were grown in a glasshouse (25/20°C day/night). A range of leaf traits were quantified, including mass-based leaf nitrogen [N], mass per unit area (LMA), light-saturated photosynthesis (A) and respiration (R dark ). 3. Average area-and mass-based rates of net CO 2 exchange were higher in the temperate species, compared to their tropical counterparts. Average leaf [N] and LMA values were also higher in temperate species than in their tropical counterparts. 4. The higher LMA in the metabolically more active temperate species was the most striking contrast to the patterns and predictions of the GLOPNET leaf trait data base, and was associated with different elevations (i.e. y-axis intercepts) but not slopes of bivariate trait scaling relationships. As expected, mass-based rates of A and R dark scaled positively with increasing [N] and negatively with increasing LMA in both tropical and temperate species. No differences were found between temperate and tropical species groups in terms of log-log scaling relationships linking A and R dark to N. However, at any given LMA, mass-based values of [N], A and R dark were all higher in the temperate species than in their tropical counterparts. 5. Underpinning higher A in temperate species was a higher capacity for carboxylation (V cmax ) and RuBP regeneration (J max ), with J max :V cmax being greater in temperate species. 6. In conclusion, our results suggest that as a consequence of greater overall N investment as well as greater proportional N investment in metabolic capacity, cool-adapted temperate wet forest species exhibit higher photosynthetic and respiration rates than their warm-adapted tropical counterparts when compared in a common environment.

Aryl C-O and C-F can be transformed into C-Me via Ni-catalyzed coupling with MeMgBr under mild conditions.

An Fe(OTf)(3)/TfOH cocatalyzed sp-sp(3) C-C bond formation through the coupling of benzylic alcohols with terminal alkynes in the absence of base has been developed. H(2)O is the sole by-product.

Organocatalytic direct C3 alkenylation of indoles has been developed. Simple and readily available morpholine trifluoroacetic acid salt is employed as an efficient catalyst in this oxidative dehydrogenative reaction. Simplicity and practicality constitute the most attractive advantages of this reaction.