Giuliano Maselli Locosselli

Dendrobiochemistry, a missing link to further understand carbon allocation during growth and decline of trees

Key messageThe combination of dendrochronology with biochemical features such as nonstructural and structural carbohydrate dynamics may lead to more reliable views of how tree growth correlates with changes in natural environments.AbstractCarbon is fixed in forests worldwide, where large pools are stored in the woody tissues of trees. After assimilation via photosynthesis, its products are transported through the phloem to support metabolism, storage, and the construction of new tissues. The metabolic dynamics of the assimilated carbon of trees have been studied by plant biochemistry and physiology approaches, mostly in young trees. On the other hand, dendrochronology rarely employs these approaches. It has been used mostly for growth quantification related to mature trees. Therefore, both fields of tree science could be merged to bring new inferences about how the internal plant metabolic processes correlate with tree growth in their inhabiting environments. Here we review the current knowledge about (1) nonstructural and structural carbohydrates of trees, as studied by plant biochemistry and physiology; and (2) tree-ring analysis as a proxy for tree growth studied by dendrochronology. We further discuss the current evidence available in the literature and the perspectives of merging these plant science fields here named dendrobiochemistry. We expect that this compilation can provide additional insights into some unresolved issues related to tree biochemistry, physiology, and dendrochronology and consequently improve current understanding of terrestrial carbon cycle.

A multi-proxy dendroecological analysis of two tropical species (Hymenaea spp., Leguminosae) growing in a vegetation mosaic

Tree species use a variety of strategies to obtain resources. As a result, semi-deciduous forest species and cerrado species can grow in close proximity and in the same climate, while occupying very different vegetation types. The aim of this study was to understand the dynamic responses of Hymenaea courbaril, a forest species, and Hymenaea stigonocarpa, a cerrado species, to annual climatic variation and increasing atmospheric CO2 concentrations under the same macroclimatic conditions. To that goal, we constructed chronologies of tree-ring width, vessel area, and intrinsic water-use efficiency (calculated from tree-ring δ13C content) for Hymenaea trees growing in a mosaic of the two vegetation types. Our analyses revealed that both species responded to climatic variation in similar ways, but with different intensities and at different times of year. Climate models showed that precipitation had a stronger effect on tree-ring width and earlywood vessel area of H. courbaril and temperature was slightly more determinant for H. stigonocarpa. In addition, both species showed increasing intrinsic water-use efficiency over the last five decades, but only individuals with reduced growth rate presented this trend, suggesting that those specimens in favorable growth conditions do not respond to the atmospheric CO2 enrichment. Despite the trend in water-use efficiency found in some individuals, it did not reflect in a higher growth rate. The differences between the two species documented by us may be due to divergent sources of hydrological stress in the two vegetation types.

Edge Effects on the Phenology of the Guamirim, Myrcia Guianensis (Myrtaceae), a Cerrado Tree, Brazil

The Brazilian cerrado, a hotspot of biodiversity, has suffered intense fragmentation in the last decades with an associated increase in areas subjected to edge effects. Plant phenology may be influenced by abiotic changes induced by edge effects, such as increases in temperature and light. We studied the phenology of the guamirim (Myrcia guianensis, Myrtaceae) and its relation to local abiotic factors in a Brazilian cerrado area between 2005 and 2011, aiming to answer: (i) whether M. guianensis phenology differs between the edge and the interior and/or between cardinal orientations at the study site, given that environments facing east are lighter and warmer than environments facing south; and (ii) how microenvironmental factors influence the observed phenological patterns. We sampled 92 individuals in 36 transects (25m × 2m), distributed along the edge and in the interior (100m from the edge) of the east and south faces. Myrcia guianensis presented seasonal patterns of leafing and reproduction, but only reproduction was influenced by microenvironmental conditions. Individuals on the east edge — the warmest and driest environment with the most light — presented with the highest synchrony and intensity of reproductive phenophases, followed by the east interior, south interior and south edge. Flowering and fruiting onset and peak dates occurred around 20 days earlier on the east edge than the south face. Edge conditions, primarily cardinal orientation, and associated higher temperatures and light incidence influenced the reproductive phenology of M. guianensis and the onset of flowering and fruiting. We suggest that edges could be used to evaluate plant responses to the temperature increases predicted for future climate change scenarios.

Plasticity of stomatal distribution pattern and stem tracheid dimensions in Podocarpus lambertii: an ecological study.

BACKGROUND AND AIMS Leaf and wood plasticity are key elements in the survival of widely distributed plant species. Little is known, however, about variation in stomatal distribution in the leaf epidermis and its correlation with the dimensions of conducting cells in wood. This study aimed at testing the hypothesis that Podocarpus lambertii, a conifer tree, possesses a well-defined pattern of stomatal distribution, and that this pattern can vary together with the dimensions of stem tracheids as a possible strategy to survive in climatically different sites. METHODS Leaves and wood were sampled from trees growing in a cold, wet site in south-eastern Brazil and in a warm, dry site in north-eastern Brazil. Stomata were thoroughly mapped in leaves from each study site to determine a spatial sampling strategy. Stomatal density, stomatal index and guard cell length were then sampled in three regions of the leaf: near the midrib, near the leaf margin and in between the two. This sampling strategy was used to test for a pattern and its possible variation between study sites. Wood and stomata data were analysed together via principal component analysis. KEY RESULTS The following distribution pattern was found in the south-eastern leaves: the stomatal index was up to 25 % higher in the central leaf region, between the midrib and the leaf margin, than in the adjacent regions. The inverse pattern was found in the north-eastern leaves, in which the stomatal index was 10 % higher near the midrib and the leaf margin. This change in pattern was accompanied by smaller tracheid lumen diameter and length. CONCLUSIONS Podocarpus lambertii individuals in sites with higher temperature and lower water availability jointly regulate stomatal distribution in leaves and tracheid dimensions in wood. The observed stomatal distribution pattern and variation appear to be closely related to the placement of conducting tissue in the mesophyll.

The use of tree barks to monitor traffic related air pollution: a case study in São Paulo - Brazil

The analysis of chemical elements in the barks of trees is an alternative procedure to access spatial heterogeneity of traffic related air pollution. However, the role of tree species in the characterization of the variability of airborne pollution is poorly known. We present an observational study conducted in Sao Paulo, Brazil, based on the analysis of 498 trees from three common species: Tipuana tipu, Poincianella pluviosa and Ligustrum sp.. We considered ANCOVA models to compare the concentrations of Al, Fe, Zn, Cu, Mn, Ba and S in the bark of trees located close to streets with different levels of traffic intensity controlling for the extension of nearby green areas. The expected trend of increasing elemental concentration in the bark of trees located near streets with greater traffic intensity or close to smaller green areas was only fully evidenced by T. tipu. For instance, the concentrations of Zn, Fe, Al and Ba increase by 200%, 350%, 230% and 280% respectively, for trees of this species located near arterial streets when compared to those observed near local streets. On the other hand, the concentrations of Zn, Fe, Al and Ba are reduced by 41%, 45% 50%, 30%, respectively, for trees located near green areas. For P. pluviosa, the capacity to suggest an association between the tree bark concentration of chemical elements with increasing levels of air pollution and presence of green areas was only fully observed for Zn and Cu. For Ligustrum sp., weaker and sometimes non-expected associations between bark concentrations of the chemical elements and either street classification or green area extension were observed. Our results indicate that the choice of species is a key element in the use of tree barks as a biomonitoring tool in urban landscapes. Species like T. tipu, with rough and highly porous bark, are the most appropriate for such purpose.

The Influence of tree size and Microenvironmental changes on the wood Anatomy of Roupala Rhombifolia

We analysed how variation in microenvironmental conditions and stem size affects the wood anatomy of Roupala rhombifolia in three contrasting habitats in the same study area: open field, hilltop forest and riparian forest. The wood anatomy features analysed were: vessel area and density, vessel element length, fibre length, and ray width and height. Vegetation cover and soil attributes were also quantified and integrated into the analyses. Separate analyses were performed on i) raw anatomical data and ii) residuals from linear fits between wood anatomical features and plant height and stem diameter. Raw data showed a clear difference between specimens from riparian forest and open fields, which represented the most mesic and xeric anatomical features respectively. After residual extraction to correct size-related variation, only fibre length and vessel area differed between habitats. Vessel areas in riparian forest differed from those in hilltop forest, but were similar to those in open fields. This result can be explained when vegetation cover and soil are considered together. While open field and hilltop forest have similar soils and lower moisture availability when compared to riparian forest, water demand in open fields is lower, presumably resulting in higher water availability.

The cambium activity in a changing world

cambium activation, activity, and dormancy on temperate trees, where temperature stands out as the main factor finely tuning cell division, expansion, and differentiation. The total carbon fixed during cambium activity depends on the number of cells produced, type of cells and cell-wall characteristics (Fig. 1). For instance, a higher number of cells requires more carbon allocation for cell-wall construction. Likewise, fibers and tracheids have considerably thicker walls than the parenchyma requiring more carbon. Even the same types of cells like the tracheids receive additional deposition of cell walls in the latewood, increasing wood density (Begum et al. 2017) and the amount of carbon fixed there. Begum et al. point out that earlier initiation of cambium activity along with the delayed cambium dormancy have the potential to enhance the role of trees as carbon sinks and pools. These processes are induced by increasing the number of days above a certain threshold of temperature and keeping this temperature for a longer time. This is exactly what is expected during global warming. Naturally, a higher carbon allocation does not only require a longer period of cambium activity that results in a greater number of cells, but also depends on the qualities of these cells. The experiments reviewed by Begum et al. show a clear increase in the active period of the cambium, as well as changes in cell composition and cellular properties. Increasing the number of cells is not enough to increase the capacity of carbon sink of trees. If trees produce more cells with thinner walls, the overall result is a decrease in wood density, probably leveling off the carbon sink capacity of trees or even reducing it. Indeed, a lower wood density has been reported for different species with higher growth rates (Chave et al. 2009). This reduction in wood density is a result of changes in the proportional composition of cells in the wood, as well as the presence of thinner walls. One side effect of increasing the growth of trees is that they may Forests worldwide are key players in the terrestrial carbon cycle, where trees assimilate atmospheric carbon and allocate it during growth. By doing so, not only trees act as important terrestrial carbon sinks, but they are also large carbon pools mostly represented by the wood tissues from branches, stems, and roots (Mahli et al. 2011). These organs are a result of the secondary growth undertaken by the cambium activity. This meristem formed by delicate and thin-walled cells produces, through cell division, expansion and differentiation, a denser tissue mostly composed of cell walls. Between 42 and 61% of the dry mass of this tissue is pure carbon (Thomas and Martin 2012). Therefore, cell walls are the main carbon pools of trees (Locosselli and Buckeridge 2017), which in woody tissues have a long residence time proportional to the longevity of tree species (Galbraith et al. 2013). Such large carbon sinks are essential to control the rising concentrations of atmospheric CO2, which in turn mitigates the effects of climate change. To keep global warming under 1.5 °C by 2100, we will need to adopt negative emission procedures like afforestation, among others (Fuss 2017). This is only possible because forests assimilate and allocate large amounts of carbon in different organs, including the wood tissues through cambium activity (Fig. 1). It is important to note that climate itself is the main driver of cambium activity and, consequently, of carbon allocation in wood parts of trees. How climate modulates cambium activity, and its cellular products are scrutinized by Begum et al. in this issue. In their review, the authors carefully go through the steps of

Tree rings reveal the reduction of Cd, Cu, Ni and Pb pollution in the central region of São Paulo, Brazil

The concern about environmental pollution has risen in the last decades because of its effects on humans health. However, evaluation of the exposure to certain pollutants is currently hampered by the availability of past environmental data. Tree rings are an alternative to reconstruct environmental variability of pre-instrumental periods. Nevertheless, this approach has some reported limitations including migration of chemical elements in the tree rings. The aim of this study was to evaluate the distribution of Cd, Cu, Hg, Na, Ni, Pb, Zn in the tree rings of Tipuana tipu (Fabaceae) to aid the reconstruction of past environmental pollution. We sampled trees in the central region of the city of São Paulo, Brazil, and scanned their tree rings using LA-ICP-MS. We used these data to evaluate the temporal trends of chemical elements under investigation. Results show a non-random distribution of these chemical elements within the tree rings, with higher content in the cell-walls of vessels and lower content in the fibers. Sodium was the only element intimately related to the axial parenchyma cells. Due to differences in elemental composition of xylem cells, temporal trends where evaluated using distinct quartiles of data distribution in each tree ring. The first quartile represents the lower content found in fibers and parenchyma, while the third quartile corresponds to the higher content found in vessels. Data from vessels better represent the decreasing trend of Cd, Cu, Pb, and Ni in the last three decades. This reduction is less significant for Na and Zn. Our results highlight the potential to improve the records of environmental pollution using data from different cells. Pronounced reduction in Pb may be attributed to the lead phase-out in gasoline, while the decreasing trend of Cd, Cu, Ni pollution is probably related to increasing efficiency of vehicles and the deindustrialization of São Paulo. Chemical elements are non-randomly distributed in tree rings. Chemical content of vessels cell-walls is a reliable record of metal pollution, which is decreasing in São Paulo.