Climate variability of the southern Amazon inferred by a multi-proxy tree-ring approach using Cedrela fissilis Vell.

The analysis of climate variability and development of reconstructions based on tree-ring records in tropical forests have been increasing in recent decades. In the Amazon region, ring width and stable isotope long-term chronologies have been used for climatic studies, however little is known about the potential of wood traits such as density and chemical concentrations. In this study, we used well-dated rings of Cedrela fissilis Vell. from the drought-prone southern Amazon basin to assess the potential of using inter-annual variations of annually-resolved ring width, wood density, stable oxygen isotope (δ18OTR) measured in tree-ring cellulose and concentration of Sulfur (STR) and Calcium (CaTR) in xylem cells to study climate variability. During wet years, Cedrela fissilis produced wider and denser rings with higher CaTR and lower STR, as well as depleted δ18OTR values. During dry years, a wider range of responses was observed in growth, density and STR, while lower CaTR and enriched δ18OTR values were found. The annual centennial chronologies spanning from 1835 to 2018 showed good calibration skills for reconstructing local precipitation, evapotranspiration (P-PET), Amazon-wide rainfall, as well as climate modes related to sea surface temperature (SST) anomalies such as El Niño South Oscillation (ENSO), Tropical Northern Atlantic (TNA), and the Western Hemisphere Warm Pool (WHWP) oscillations. CaTR explained 42 % of the variance of local precipitation (1975-2018), RW explained 30 % of the P-PET variance (1975-2018), while δ18OTR explained 60 % and 57 % of the variance of Amazon rainfall (1960-2018) and El Niño 3.4 (1920-2018), respectively. Our results show that a multi-proxy tropical tree-ring approach can be used for high-reliable reconstructions of climate variability over Amazon basin at inter-annual and multidecadal time scales.

Space-resolved determination of the mineral nutrient content in tree-rings by X-ray fluorescence.

X-ray fluorescence spectroscopy (XRF) offers rapid, multi-elemental, low cost and non-destructive elemental analysis. Different studies have used this technique to investigate distribution and concentration of essential and deleterious elements in vegetation. Special emphasis has been recently placed on the key aspects concerning sampling processes, laboratory protocols and calibration methods for quantitative analysis. The aim of the present study was to develop a quantitative methodology to determine the nutrient content in Pinus taeda tree-rings by XRF. Using a 1 mm X-ray excitation beam from a Rh X-ray tube at 30 kV and 600 µA, and dwell time of 20 s, we present calibration curves for P, S, K, Ca, Mn and Fe based on multi-elemental standard addition using wood matrix of 17-year-old Pinus taeda trees. Satisfactory recoveries of our XRF approach for Ca, P, Mn, S and K (<115%), and tolerable for Fe (123%) were obtained compared to inductively coupled plasma optical emission spectrometry results. The non-destructive and quantitative XRF method allows assessing annual element concentrations of P. taeda trees, in order to provide tools for monitoring the nutrient dynamic in an experimental plantation. Furthermore, a method for elemental quantification based on multi-elemental standard addition using wood matrix is described as a useful procedure for future applications.

Evidence to wood biodeterioration of tropical species revealed by non-destructive techniques.

The wood biodeterioration process is one of the symptoms produced by biotic agents that affect the biomechanics of urban trees and reduce their useful life and environmental services. This process is mainly studied through methods that are time-consuming or destructive and provide little information regarding the degradation process at the cellular scale. Based on a non-destructive study of five tropical urban trees: Poincianella pluviosa (sibipiruna), Pterocarpus rhorii (aldrago), Rhamnidium elaeocarpum (saguaraji), Trichilia clausenii (Catiguá) and Lafoensia glyptocarpa (mirindiba rosa); the wood decaying zone, by xylophagous fungi, was analized. The trunk-wood samples containing the decaying zone were extracted with metal probes. Their microscopic anatomical structures were characterized and their microdensity and chemical composition analyzed by X-ray densitometry and X-ray fluorescence, respectively. Degraded cell wall fiber and vessels obstructed by mycelial mass were observed in wood decay zones. The presence of wood compartmentalized by the formation of extractive deposits was also observed, as a possible resistance mechanism varying among species. Likewise, phosphorus (P), calcium (Ca), calcium/manganese molar ratio and wood density increase were observed in barrier zones, while iron (Fe) was related to the decay zone. Altogether, the present study show for detailed evaluation of the wood biodeterioration process at the microscopic scale. The potential of non-destructive techniques for application in the physiological analysis of trees was also demonstrated.