Microtensiometers Accurately Measure Stem Water Potential in Woody Perennials

Stem water potential (Ψstem) is considered to be the standard measure of plant water status. However, it is measured with the pressure chamber (PC), an equipment that can neither provide continuous information nor be automated, limiting its use. Recent developments of microtensiometers (MT; FloraPulse sensors), which can continuously measure water tension in woody tissue of the trunk of the tree, can potentially highlight the dynamic nature of plant water relations. Thus, this study aimed to validate and assess the usefulness of the MT by comparing the Ψstem provided by MT with those same measurements from the PC. Here, two irrigation treatments (a control and a deficit treatment) were applied in a pear (Pyrus communis L.) orchard in Washington State (USA) to capture the full range of water potentials in this environment. Discrete measurements of leaf gas exchange, canopy temperature and Ψstem measured with PC and MT were made every two hours for four days from dawn to sunset. There were strong linear relationships between the Ψstem-MT and Ψstem-PC (R2 > 0.8) and with vapor pressure deficit (R2 > 0.7). However, Ψstem-MT was more variable and lower than Ψstem-PC when Ψstem-MT was below −1.5 MPa, especially during the evening. Minimum Ψstem-MT occurred later in the afternoon compared to Ψstem-PC. Ψstem showed similar sensitivity and coefficients of variation for both PC and MT acquired data. Overall, the promising results achieved indicated the potential for MT to be used to continuously assess tree water status.

Composition of Organic Carbon-Based Compounds in the Stem Wood of Quercus mongolica Seedlings Grown Under Elevated CO2 and/or O3 Concentrations

In this study, we examined the composition of organic constituents of stem woody tissue together with tree growth in Quercus mongolica var. grosseserrata Blume seedlings raised under controlled CO2 and/or O3 concentrations in a Free-Air Concentration Enrichment system. After exposure to ambient air (control), elevated CO2 concentration (550 μmol mol–1 CO2), elevated O3 concentration (double that of the control), and a combination of elevated CO2 and O3 concentrations during a growing season, we measured the diameter and length of stem, and biomass of sampled seedlings and quantified the lignin, extractive, and holocellulose contents of the woody tissue of current-year stems. We confirmed that the growth of seedlings was enhanced under an elevated CO2 concentration condition. In line with this, the extractive content was lower in woody tissue formed under an elevated CO2 concentration than that formed under ambient air, whereas holocellulose content showed an inverse pattern. Elevated O3 concentration itself did not change the organic constituents of the woody tissue, but it reduced the influence of an elevated CO2 concentration. We thus assume that Q. mongolica formed woody tissue with a low extractive content under the high CO2 concentration condition, although this response was possibly mitigated by an elevated O3 concentration. Extractives contains antimicrobial components such as tannins, flavonoids, quinones, and terpenoids. The decrease in extractives within the widely distributed Q. mongolica in East Asia may have a non-negligible impact on C cycling in the future earth with high atmospheric CO2 concentration.

Hotter droughts alter resource allocation to chemical defenses in piñon pine

Heat and drought affect plant chemical defenses and thereby plant susceptibility to pests and pathogens. Monoterpenes are of particular importance for conifers as they play critical roles in defense against bark beetles. To date, work seeking to understand the impacts of heat and drought on monoterpenes has primarily focused on young potted seedlings, leaving it unclear how older age classes that are more vulnerable to bark beetles might respond to stress. Furthermore, we lack a clear picture of what carbon resources might be prioritized to support monoterpene synthesis under drought stress. To address this, we measured needle and woody tissue monoterpene concentrations and physiological variables simultaneously from mature piñon pines (Pinus edulis) from a unique temperature and drought manipulation field experiment. While heat had no effect on total monoterpene concentrations, trees under combined heat and drought stress exhibited ~ 85% and 35% increases in needle and woody tissue, respectively, over multiple years. Plant physiological variables like maximum photosynthesis each explained less than 10% of the variation in total monoterpenes for both tissue types while starch and glucose + fructose measured 1-month prior explained ~ 45% and 60% of the variation in woody tissue total monoterpene concentrations. Although total monoterpenes increased under combined stress, some key monoterpenes with known roles in bark beetle ecology decreased. These shifts may make trees more favorable for bark beetle attack rather than well defended, which one might conclude if only considering total monoterpene concentrations. Our results point to cumulative and synergistic effects of heat and drought that may reprioritize carbon allocation of specific non-structural carbohydrates toward defense.

Lignin phenols in sediment cores and its indications of degradation and organic carbon sources of the Yantan Reservoir, China

Three sediment cores collected from the Yantan Reservoir, located in the Pearl River, southwest China, were analyzed for lignin phenols, elemental and stable carbon isotopic composition to investigate the variation patterns, vegetation sources, degradation stage, and relative proportions of terrestrial sedimentary organic carbon (OC). Significant temporal and spatial heterogeneity in terrestrial OC burial was indicated by the changes of lignin contents at different depths in different sampling sites: the inlet zone, the central reservoir zone in front of dam and the reservoir bay. The interception impact of upstream dam, the influence of artificial regulation, as well as the role of interzonal recharge made the terrestrial OC burial remains complex in the reservoir. The oxidized lignin signatures showed spatial heterogeneity suggesting active oxidative degradation and demethylation/demethoxy degradation of sedimentary lignin during deposition, especially in the inlet zone. An angiosperm herbaceous tissue and gymnosperm woody tissue contributed the sedimentary lignin. A soil-plankton-plant three-end-member mixing model revealed that soil-derived OC dominated before impoundment and at the early stage of reservoir operation, while the contribution of autochthonous OC began to dominate after gradually aging and eutrophicating of the reservoir. Our study of lignin evolution in reservoir highlights important temporal and spatial reservoir carbon components and their contribution to sedimentary carbon pools, providing new insights into the estimation of organic carbon burial in reservoirs.

Drought increases chlorophyll content in stems of Vitis interspecific hybrids

Plants respond to drought stress through different physiological mechanisms. To highlight a specific adaptation strategy related to stem photosynthetic activity, woody tissue pigmentation was studied. In this work, 25 Vitis hybrids were studied in two experimental vineyards: one of them with sufficient water availability and the other showing drought stress. 1500 reflectance spectra of woody tissues were collected. Beside the spectral elaboration and interpretation, indexes for the pigment quantification were calculated. The content and the proportion in chlorophylls (a and b) in stems were significantly modified in response to water stress. Genotypes were classified based on their plasticity/elasticity and adaptive/susceptible behavior. The cluster analysis produced 4 main groups based on their average spectra and on the spectral variations between watered and stress conditions. The most interesting genotypes concerning this trait were pointed out. Nevertheless, this adaptation mechanism could also be due to an increased detoxification necessity related to other physiological disfunctions caused by water stress. A multi-parameter approach is encouraged for phenotyping of abiotic stress tolerant plant selection. In the next future, this work will support the release of new drought tolerant rootstocks for viticulture.

New insights into large tropical tree mass and structure from direct harvest and terrestrial lidar

A large portion of the terrestrial vegetation carbon stock is stored in the above-ground biomass (AGB) of tropical forests, but the exact amount remains uncertain, partly owing to the lack of measurements. To date, accessible peer-reviewed data are available for just 10 large tropical trees in the Amazon that have been harvested and directly measured entirely via weighing. Here, we harvested four large tropical rainforest trees (stem diameter: 0.6–1.2 m, height: 30–46 m, AGB: 3960–18 584 kg) in intact old-growth forest in East Amazonia, and measured above-ground green mass, moisture content and woody tissue density. We first present rare ecological insights provided by these data, including unsystematic intra-tree variations in density, with both height and radius. We also found the majority of AGB was usually found in the crown, but varied from 42 to 62%. We then compare non-destructive approaches for estimating the AGB of these trees, using both classical allometry and new lidar-based methods. Terrestrial lidar point clouds were collected pre-harvest, on which we fitted cylinders to model woody structure, enabling retrieval of volume-derived AGB. Estimates from this approach were more accurate than allometric counterparts (mean tree-scale relative error: 3% versus 15%), and error decreased when up-scaling to the cumulative AGB of the four trees (1% versus 15%). Furthermore, while allometric error increased fourfold with tree size over the diameter range, lidar error remained constant. This suggests error in these lidar-derived estimates is random and additive. Were these results transferable across forest scenes, terrestrial lidar methods would reduce uncertainty in stand-scale AGB estimates, and therefore advance our understanding of the role of tropical forests in the global carbon cycle.

Reemergence of Cylindrocladium Crown Rot of Roses in Florida

On April 2017, four out of 10,000 Double Knock Out Red roses were observed presenting partially wilted and chlorotic foliage in a commercial nursery in Gadsden Co., Florida. Closer examination of the plant crown revealed brown discoloration of the woody tissue. Under high temperature (85°F) and humidity (70%), shoots progressively turned chlorotic and necrotic, leading to plant death in 4 months. A rapid-growing fungus presenting orange-brown mycelium and abundant cylindrical spores was isolated from infected woody crown tissue. BLAST analysis of the resulting sequence (GenBank no. MT019606) of this pathogen had 100% identity to Calonectria cylindrospora β-tubulin gene (GenBank no. FJ918509.1). Koch’s postulates were conducted on healthy Double Knock Out roses. Two weeks after inoculation, shoots of inoculated plants turned progressively chlorotic and then necrotic, leading to plant death in 2 months. The same pathogen was reisolated from infected plant parts, which sequence also had 100% identity to C. cylindrospora β-tubulin gene (GenBank no. FJ918509.1). This pathogen is the same as one of three isolated from crown rot of roses back in 1994 and identified as Cylindrocladium scoparium (teleomorph: C. cylindrospora [Ellis & Everh.]). In this new occurrence, all infected plants were removed from the nursery, and no further infections were detected. This finding is important for commercial growers to be aware of the potential presence of this pathogen in their nurseries. Knowing the symptoms will help them recognize the disease and take action to prevent spread of the disease.

New insights into large tropical tree mass and structure from direct harvest and terrestrial lidar

A large portion of the terrestrial vegetation carbon stock is stored in the above-ground biomass (AGB) of tropical forests, but the exact amount remains uncertain, partly due to the difficulty of making direct, whole-tree measurements. We harvested four large tropical rainforest trees (stem diameter: 0.6–1.2 m, height: 30–46 m, AGB: 3960–18 584 kg) in a natural closed forest stand in East Amazonia, and measured above-ground green mass, moisture content and woody tissue density. We found approximately 40 % of green mass was water, and the majority of AGB was most often found in the crown, but varied from 42–62 %. Woody tissue density varied substantially intra-tree, with both height and radius, but variations were not systematic inter-tree. Terrestrial lidar data were collected pre-harvest, from which volume-derived AGB estimates were retrieved. These estimates were more accurate than traditional allometric counterparts (mean tree-scale relative error: 3 % vs. 15 %). Error in lidar-derived estimates remained constant across tree size, whilst error in allometric-derived estimates increased up to 4 −fold over the diameter range. Further, unlike allometric estimates, the error in lidar estimates decreased when up-scaling to the cumulative AGB of the four trees. Terrestrial lidar methods therefore can help reduce uncertainty in tree- and stand-scale AGB estimates, which would substantially advance our understanding of the role of tropical forests in the global carbon cycle.

Assessment of the effect of thermotherapy on Candidatus Liberibacter asiaticus viability in woody tissue of citrus via graft-based assay and RNA-assay

By 2019, Florida’s citrus production declined over 70%, mostly due to Huanglongbing (HLB), caused by the bacterium Candidatus Liberibacter asiaticus (CLas). Thermotherapy on HLB-affected trees was proposed to maintain short-term field productivity. Thermotherapy could eliminate HLB from affected branches was hypothesized, therefore objectives were to show which time-temperature combinations eliminated CLas from woody tissues. Valencia twigs collected from HLB-affected field trees were steam chamber treated at different time-temperature combinations [50°C for 60 s, 55°C for 0 s, 30 s, 60 s, 90 s, 120s, 60°C for 30 s, and untreated control (UTC)]. Three independent repetitions of 13 branches/treatment were used, grafted onto rootstocks, and tested for CLas after 6, 9, and 12 months. For the RNA-based CLas viability assay, 3 branches/treatment were treated, and bark samples peeled for RNA extraction and subsequent gene expression analysis. From grafting study, at 12 months after grafting, four trees grafted with twigs treated at 55°C for 90 s or 55°C for 120 s had detectable CLas DNA. In those individuals, titers were significantly lower (P ≤ 0.0001) and could be degrading DNA remnants. Additionally, CLas 16S rRNA expression decreased significantly (P ≤ 0.0001) at 55°C for 90 s, 55°C for 120 s, and 60°C for 30 s (3.4-, 3.4- and 2.3-fold change, respectively) 5 days post-treatment. Heat injury, not total CLas kill, could explain limited transcriptional activity changes; however, failed recovery and eventual CLas death resulted in no CLas detection in most of the grafted trees treated with the highest temperatures or longest durations.

Shelling of Growth Rings at Softwood Surfaces Exposed to Natural Weathering

Shelling is the delamination of growth rings and the projection of woody tissue from wood surfaces. Shelling disrupts coatings and makes refinishing difficult, and a better understanding of the phenomenon is needed to help alleviate its unwanted effects. We tested whether confocal profilometry could quantify shelling in flat-faced and profiled-faced western larch deckboards exposed to natural weathering and examined the effects of growth-ring orientation and angle on shelling. Confocal profilometry was able to quantify shelling in both deckboard types. Shelling developed at the surface of flat-faced deckboards oriented pith-side-up, whereas it was absent from boards oriented bark-side-up. We found an inverse correlation between the height of shelled growth rings and the angle of growth rings to the surface of flat-faced boards. Shelling occurred in profiled-faced boards oriented pith-side-up due to the delamination of growth ring tips and projection of latewood from wood surfaces. A superficially similar although less pronounced phenomenon was seen in profiled-faced boards oriented bark-side-up. The shelling of profiled-faced boards oriented pith-side-up created lanceolate-shaped slivers of latewood that projected from the peaks of profiles. Some of these latewood tips were sharp and, for this reason, we suggest that profiled-faced western larch deckboards should always be oriented bark-side-up rather than pith-side-up.