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1. Does plant ecosystem thermoregulation occur? An extratropical assessment at different spatial and temporal scales

   https://doi.org/10.1111/nph.18632  

   Guo, Zhengfei; Still, Christopher J.; Lee, Calvin K. F.; Ryu, Youngryel; Blonder, Benjamin; Wang, Jing; Bonebrake, Timothy C.; Hughes, Alice; Li, Yan; Yeung, Henry C. H.; et al (December 2022, New Phytologist)

   Summary To what degree plant ecosystems thermoregulate their canopy temperature (T_c) is critical to assess ecosystems' metabolisms and resilience with climate change, but remains controversial, with opinions from no to moderate thermoregulation capability.With global datasets ofT_c, air temperature (T_a), and other environmental and biotic variables from FLUXNET and satellites, we tested the ‘limited homeothermy’ hypothesis (indicated byT_c&T_aregression slope < 1 orT_c < T_aaround midday) across global extratropics, including temporal and spatial dimensions.Across daily to weekly and monthly timescales, over 80% of sites/ecosystems have slopes ≥1 orT_c > T_aaround midday, rejecting the above hypothesis. For those sites unsupporting the hypothesis, theirT_c–T_adifference (ΔT) exhibits considerable seasonality that shows negative, partial correlations with leaf area index, implying a certain degree of thermoregulation capability. Spatially, site‐mean ΔTexhibits larger variations than the slope indicator, suggesting ΔTis a more sensitive indicator for detecting thermoregulatory differences across biomes. Furthermore, this large spatial‐wide ΔTvariation (0–6°C) is primarily explained by environmental variables (38%) and secondarily by biotic factors (15%).These results demonstrate diverse thermoregulation patterns across global extratropics, with most ecosystems negating the ‘limited homeothermy’ hypothesis, but their thermoregulation still occurs, implying that slope < 1 orT_c < T_aare not necessary conditions for plant thermoregulation. 

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2. High Heterogeneity in Canopy Temperature Among Co‐occurring Tree Species in a Temperate Forest

   https://doi.org/10.1029/2020JG005892  

   Yi, Koong; Smith, Jake W.; Jablonski, Andrew D.; Tatham, Elizabeth A.; Scanlon, Todd M.; Lerdau, Manuel T.; Novick, Kimberly A.; Yang, Xi (December 2020, Journal of Geophysical Research: Biogeosciences)

   Abstract Trees regulate canopy temperature (T_c) via transpiration to maintain an optimal temperature range. In diverse forests such as those of the eastern United States, the sensitivity ofT_cto changing environmental conditions may differ across species, reflecting wide variability in hydraulic traits. However, these links are not well understood in mature forests, whereT_cdata have historically been difficult to obtain. Recent advancement of thermal imaging cameras (TICs) enablesT_cmeasurement of previously inaccessible tall trees. By leveraging TIC and sap flux measurements, we investigated how co‐occurring trees (Quercus alba,Q. falcata, andPinus virginiana) change theirT_cand vapor pressure deficit near the canopy surface (VPD_c) in response to changing air temperature (T_a) and atmospheric VPD (VPD_a). We found a weaker cooling effect for the species that most strongly regulates stomatal function during dry conditions (isohydric;P. virginiana). Specifically, the pine had higherT_c(up to 1.3°C) and VPD_c(up to 0.3 kPa) in the afternoon and smaller sensitivity of both∆T(=T_c − T_a) and∆VPD (=VPD_c − VPD_a) to changing conditions. Furthermore, significant differences inT_cand VPD_cbetween sunlit and shaded portions of a canopy implied a non‐evaporative effect onT_cregulation. Specifically,T_cwas more homogeneous within the pine canopy, reflecting differences in leaf morphology that allow higher canopy transmittance of solar radiation. The variability ofT_camong species (up to 1.3°C) was comparable to the previously reported differences in surface temperature across land cover types (1°C to 2°C), implying the potential for significant impact of species composition change on local/regional surface temperature. 

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3. Isolation of an Elusive Phosphametallacyclobutadiene and Its Role in Reversible Carbon−Carbon Bond Cleavage

   https://doi.org/10.1002/anie.202203073  

   Jakhar, Vineet K.; Esper, Alec M.; Ghiviriga, Ion; Abboud, Khalil A.; Ehm, Christian; Veige, Adam S. (June 2022, Angewandte Chemie International Edition)

   Abstract The reactivity of phosphaalkynes, the isolobal and isoelectronic congeners to alkynes, with metal alkylidyne complexes is explored in this work. Treating the tungsten alkylidyne [^tBuOCO]W≡C^tBu(THF)₂(1) with phosphaalkyne (10) results in the formation of [O₂C(^tBuC=)W{η²‐(P,C)−P≡C−Ad}(THF)] (13‐^tBu_THF) and [O₂C(AdC=)W{η²‐(P,C)−P≡C−^tBu}(THF)] (13‐Ad_THF); derived from the formal reductive migratory insertion of the alkylidyne moiety into a W−C_arenebond. Analogous to alkyne metathesis, a stable phosphametallacyclobutadiene complex [^tBuOCO]W[κ²‐C(^tBu)PC(Ad)] (14) forms upon loss of THF from the coordination sphere of either13‐^tBu_THFor13‐Ad_THF. Remarkably, the C−C bonds reversibly form/cleave with the addition or removal of THF from the coordination sphere of the formal tungsten(VI) metal center, permitting unprecedented control over the transformation of a tetraanionic pincer to a trianionic pincer and back. Computational analysis offers thermodynamic and electronic reasoning for the reversible equilibrium between13‐^tBu/Ad_THFand14. 

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4. Mechanochemically accessing a challenging-to-synthesize depolymerizable polymer

   https://doi.org/10.1038/s41467-023-35925-2  

   Hsu, Tze-Gang; Liu, Shiqi; Guan, Xin; Yoon, Seiyoung; Zhou, Junfeng; Chen, Wei-Yuan; Gaire, Sanjay; Seylar, Joshua; Chen, Hanlin; Wang, Zeyu; et al (January 2023, Nature Communications)

   Abstract Polymers with low ceiling temperatures (T_c) are highly desirable as they can depolymerize under mild conditions, but they typically suffer from demanding synthetic conditions and poor stability. We envision that this challenge can be addressed by developing high-T_cpolymers that can be converted into low-T_cpolymers on demand. Here, we demonstrate the mechanochemical generation of a low-T_cpolymer, poly(2,5-dihydrofuran) (PDHF), from an unsaturated polyether that contains cyclobutane-fused THF in each repeat unit. Upon mechanically induced cycloreversion of cyclobutane, each repeat unit generates three repeat units of PDHF. The resulting PDHF completely depolymerizes into 2,5-dihydrofuran in the presence of a ruthenium catalyst. The mechanochemical generation of the otherwise difficult-to-synthesize PDHF highlights the power of polymer mechanochemistry in accessing elusive structures. The concept of mechanochemically regulating theT_cof polymers can be applied to develop next-generation sustainable plastics. 

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5. Challenge and Solution of Characterizing Glass Transition Temperature for Conjugated Polymers by Differential Scanning Calorimetry

   https://doi.org/10.1002/polb.24889  

   Qian, Zhiyuan; Galuska, Luke; McNutt, William W.; Ocheje, Michael U.; He, Youjun; Cao, Zhiqiang; Zhang, Song; Xu, Jie; Hong, Kunlun; Goodman, Renée B.; et al (November 2019, Journal of Polymer Science Part B: Polymer Physics)

   ABSTRACT Thermomechanical properties of polymers highly depend on their glass transition temperature (T_g). Differential scanning calorimetry (DSC) is commonly used to measureT_gof polymers. However, many conjugated polymers (CPs), especially donor–acceptor CPs (D–A CPs), do not show a clear glass transition when measured by conventional DSC using simple heat and cool scan. In this work, we discuss the origin of the difficulty for measuringT_gin such type of polymers. The changes in specific heat capacity (Δc_p) atT_gwere accurately probed for a series of CPs by DSC. The results showed a significant decrease in Δc_pfrom flexible polymer (0.28 J g⁻¹K⁻¹for polystyrene) to rigid CPs (10⁻³J g⁻¹K⁻¹for a naphthalene diimide‐based D–A CP). When a conjugation breaker unit (flexible unit) is added to the D–A CPs, we observed restoration of the Δc_patT_gby a factor of 10, confirming that backbone rigidity reduces the Δc_p. Additionally, an increase in the crystalline fraction of the CPs further reduces Δc_p. We conclude that the difficulties of determiningT_gfor CPs using DSC are mainly due to rigid backbone and semicrystalline nature. We also demonstrate that physical aging can be used on DSC to help locate and confirm the glass transition for D‐A CPs with weak transition signals. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2019, 57, 1635–1644 

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