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1. Radiocarbon and wood anatomy as complementary tools for generating tree-ring records in Bolivia

   https://doi.org/10.3389/fpls.2023.1135480  

   Pacheco-Solana, Arturo; Oelkers, Rose; D’Arrigo, Rosanne; Santos, Guaciara M.; Rodriguez-Caton, Milagros; Tejedor, Ernesto; Ferrero, Eugenia; Fuentes, Alfredo F.; Maldonado, Carla; Andreu-Hayles, Laia (February 2023, Frontiers in Plant Science)

   The science of tropical dendrochronology is now emerging in regions where tree-ring dating had previously not been considered possible. Here, we combine wood anatomical microsectioning techniques and radiocarbon analysis to produce the first tree-ring chronology with verified annual periodicity for a new dendrochronological species, Neltuma alba (commonly known as “algarrobo blanco”) in the tropical Andes of Bolivia. First, we generated a preliminary chronology composed of six trees using traditional dendrochronological methods (i.e., cross-dating). We then measured the 14 C content on nine selected tree rings from two samples and compared them with the Southern Hemisphere (SH) atmospheric 14 C curves, covering the period of the bomb 14 C peak. We find consistent offsets of 5 and 12 years, respectively, in the calendar dates initially assigned, indicating that several tree rings were missing in the sequence. In order to identify the tree-ring boundaries of the unidentified rings we investigated further by analyzing stem wood microsections to examine anatomical characteristics. These anatomical microsections revealed the presence of very narrow terminal parenchyma defining several tree-ring boundaries within the sapwood, which was not visible in sanded samples under a stereomicroscope. Such newly identified tree rings were consistent with the offsets shown by the radiocarbon analysis and allowed us to correct the calendar dates of the initial chronology. Additional radiocarbon measurements over a new batch of rings of the corrected dated samples resulted in a perfect match between the dendrochronological calendar years and the 14 C dating, which is based on good agreement between the tree-ring 14 C content and the SH 14 C curves. Correlations with prior season precipitation and temperature reveal a strong legacy effect of climate conditions prior to the current Neltuma alba growing season. Overall, our study highlights much potential to complement traditional dendrochronology in tree species with challenging tree-ring boundaries with wood anatomical methods and 14 C analyses. Taken together, these approaches confirm that Neltuma alba can be accurately dated and thereby used in climatic and ecological studies in tropical and subtropical South America. 

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2. Radiocarbon analysis confirms annual periodicity in Cedrela odorata tree rings from the equatorial Amazon

   https://doi.org/https://doi.org/10.1016/j.quageo.2020.101079  

   Santos, Guaciara M.; Granato-Souza, D.; Barbosa, A.C.; Oelkers, R.; Andreu-Hayles, L. (January 2020, Quaternary geochronology)

   A Cedrela odorata tree ring width chronology spanning from 1786 to 2016 was developed in the quasi-equatorial eastern Amazon Basin. Annual calendar dates were assigned using dendrochronological techniques at the Federal University of Lavras, Brazil. Due to its strategic location at the edge of the Equator (approximately 0°57′S), an independent confirmation of the annual periodicity of this century-long chronology would be of great value, allowing its future use for climate reconstruction and for filling gaps in upcoming atmospheric radiocarbon (14C) compilations. For reconstruction of atmospheric 14C, high reliability of the dendrochronological calendar dates is a requirement. Here, we used high-precision 14C bomb pulse dating (BPD) of selected C. odorata tree rings as a robust independent method to validate the dendrochronological dates. Eight calendar years from across the pre-to post-bomb period were tested through 14C analysis of α-cellulose extracts (19 targets in total were produced from those 8 calendar years). All dendrochronologically dated tree rings measured produced 14C values in perfect alignment with the Southern Hemisphere 14C bomb curve, further confirming the annual growth of this important record. Extraction of α-cellulose was attained by a recently implemented procedure at the Lamont-Doherty Earth Observatory (LDEO). The method was 14C assessed by high-precision measurements at the Keck Carbon Cycle Accelerator Mass Spectrometer (KCCAMS) at the University of California, Irvine (UCI) by measuring reference materials and unknown samples. High reproducibility of reference materials (within uncertainties) showed that the novel 150-funnel system and protocol developed at LDEO is reliable and can potentially expedite cellulose extractions for 14C analysis. 

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3. Growth Assessment of Native Tree Species from the Southwestern Brazilian Amazonia by Post-AD 1950 14C Analysis: Implications for Tropical Dendroclimatology Studies and Atmospheric 14C Reconstructions

   https://doi.org/10.3390/f12091177  

   Santos, Guaciara M.; Rodriguez, Daigard Ricardo; Barreto, Nathan de; Assis-Pereira, Gabriel; Barbosa, Ana Carolina; Roig, Fidel A.; Tomazello-Filho, Mário (September 2021, Forests)

   Tree-ring width chronologies of cedro (Cedrela fissilis Vell.) (1875 to 2018), jatobá (Hymenaea courbaril L.) (1840 to 2018) and roxinho Peltogyne paniculata Benth.) (1910 to 2018) were developed by dendrochronological techniques in the southern Amazon Basin. Acceptable statistics for the tree-ring chronologies were obtained, and annual calendar dates were assigned. Due to the lack of long-term chronologies for use in paleoclimate reconstructions in degraded forest areas, dendrochronological dating was validated by 14C analysis. Tree-rings selected for analysis corresponded to 1957, 1958, 1962, 1963, 1965, 1971, and 1972. Those are critical calendar years in which atmospheric 14C changes were the highest, and therefore their tree-ring cellulose extracts 14C signatures when in alignment with existing post-AD 1950 atmospheric 14C atmospheric curves would indicate annual periodicity. Throughout our correlated calendar years and post-AD 1950 14C signatures, we indicate that H. courbaril shows an erratic sequence of wood ages. The other two tree species, C. fissilis and P. paniculata, are annual in nature and can be used successfully as paleoclimate proxies. Moreover, due to the sampling site’s strategic location in relation to the Tropical Low-Pressure Belt over South America, these trees can be used to enhance the limited amount of observational data in Southern Hemisphere atmospheric 14C calibration curves. 

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4. Ammonia-salt solvent promotes cellulosic biomass deconstruction under ambient pretreatment conditions to enable rapid soluble sugar production at ultra-low enzyme loadings

   https://doi.org/10.1039/C9GC03524A  

   Chundawat, Shishir P.; Sousa, Leonardo da; Roy, Shyamal; Yang, Zhi; Gupta, Shashwat; Pal, Ramendra; Zhao, Chao; Liu, Shih-Hsien; Petridis, Loukas; O'Neill, Hugh; et al (January 2020, Green Chemistry)

   Here, we report a novel ammonia : ammonium salt solvent based pretreatment process that can rapidly dissolve crystalline cellulose into solution and eventually produce highly amorphous cellulose under near-ambient conditions. Pre-activating the cellulose I allomorph to its ammonia–cellulose swollen complex (or cellulose III allomorph) at ambient temperatures facilitated rapid dissolution of the pre-activated cellulose in the ammonia-salt solvent ( i.e. , ammonium thiocyanate salt dissolved in liquid ammonia) at ambient pressures. For the first time in reported literature, we used time-resolved in situ neutron scattering methods to characterize the cellulose polymorphs structural modification and understand the mechanism of crystalline cellulose dissolution into a ‘molecular’ solution in real-time using ammonia-salt solvents. We also used molecular dynamics simulations to provide insight into solvent interactions that non-covalently disrupted the cellulose hydrogen-bonding network and understand how such solvents are able to rapidly and fully dissolve pre-activated cellulose III. Importantly, the regenerated amorphous cellulose recovered after pretreatment was shown to require nearly ∼50-fold lesser cellulolytic enzyme usage compared to native crystalline cellulose I allomorph for achieving near-complete hydrolytic conversion into soluble sugars. Lastly, we provide proof-of-concept results to further showcase how such ammonia-salt solvents can pretreat and fractionate lignocellulosic biomass like corn stover under ambient processing conditions, while selectively co-extracting ∼80–85% of total lignin, to produce a highly digestible polysaccharide-enriched feedstock for biorefinery applications. Unlike conventional ammonia-based pretreatment processes ( e.g. , Ammonia Fiber Expansion or Extractive Ammonia pretreatments), the proposed ammonia-salt process can operate at near-ambient conditions to greatly reduce the pressure/temperature severity necessary for conducting effective ammonia-based pretreatments on lignocellulose. 

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5. Evaluating possible sources of error in tree-ring ¹⁴ C data using multiple trees across South America

   https://doi.org/10.1017/RDC.2024.105  

   Santos, Guaciara M; Nguyen, Lucas D; Griffin, June N; de_Oliveira_Barreto, Nathan; Ortega-Rodriguez, Daigard R; Barbosa, Ana Carolina; Assis-Pereira, Gabriel (December 2024, Radiocarbon)

   Abstract A limitation in fine-tuned tree-ring radiocarbon (¹⁴C) data is normally associated with overall data uncertainty. Tree-ring¹⁴C data variance as a result of sample heterogeneity can be reduced by adopting best practices at the time of sample collection and subsequent preparation and analysis. Variance-reduction of¹⁴C data was achieved by meticulous sample handling during increment core or cross-sectional cuttings, in-laboratory wood reductions, and cellulose fiber homogenization of whole rings. To demonstrate the performance of those procedures to final¹⁴C results, we took advantage of the replicated data from assigned calendar years of two Pantropical post-1950 AD tree-ring¹⁴C reconstructions. TwoCedrela fissilisVell. trees spaced 22.5 km apart, and two trees of this species together with onePeltogyne paniculataBenth tree spaced 0.2 to 5 km apart were sampled in a tropical dry and moist forest, respectively. Replicate¹⁴C data were then obtained from grouped tree-ring samples from each site. A total of 88% of the replicated¹⁴C results fell into a remarkably consistent precision/accuracy range of 0.3% or less, even though multiple tree species were used as pairs/sets. This finding illustrates how adopting a few simple strategies, in tandem with already established chemical extraction procedures and high-precision¹⁴C analysis, can improve¹⁴C data results of tropical trees. 

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