Beneath the Bark: Assessing Woody Stem Water and Carbon Fluxes and Its Prevalence Across Climates and the Woody Plant Phylogeny

While woody stems are known to influence carbon and water dynamics, direct exchange with the atmosphere is seldom quantified, limiting our understanding of how these processes influence the exchange of mass and energy. The presence of woody stem chlorophyll in a diversity of climates and across a range of species suggests an evolutionary advantage to sustaining carbon assimilation and water relations through permeable stem tissue. However, no formal evaluation of this hypothesis has been performed. In this mini-review, we explore the interactions between woody stems and the atmosphere by examining woody stem photosynthesis and bark-atmosphere water exchange. Specifically, we address the following questions: (1) How do water and carbon move between the atmosphere and woody stems? (2) In what climate space is woody stem photosynthesis and bark water uptake advantageous? (3) How ubiquitous across plant families is woody stem photosynthesis and bark-atmosphere water exchange? In the literature, only seven species have been identified as exhibiting bark water uptake while over 300 species are thought to conduct woody stem photosynthesis. The carbon dioxide and water gained from these processes can offset respiration costs and improve plant water balance. These species span diverse biomes suggesting a broad prevalence of bark-atmosphere permeability. Finally, our results demonstrate that there may be an evolutionary component as demonstrated by a high Pagel’s lambda for the presence of stem photosynthesis. We end with recommendations for future research that explores how bark water and carbon interactions may impact plant function and mass flow in a changing climate.

Desempenho morfofisiológico de cultivares de soja de ciclo médio em condições de alagamento do solo

<p>O aumento no cultivo de soja no Brasil têm atingido áreas antes utilizadas para outros fins, como em regiões de solos de várzea, estando assim, sujeita a eventuais alagamentos do solo. Este trabalho objetivou avaliar alterações morfofisiológicas em cultivares de soja de ciclo médio, em condições de alagamento do solo, nos estádios fenológicos vegetativo e reprodutivo para recomendação de cultivares. Os experimentos foram conduzidos na Estação Experimental de Terras Baixas, da Embrapa Clima Temperado em Capão do Leão, RS. Foram aplicados três sistemas de manejo da água: condição normal de cultivo (sem alagamento), alagamento no período vegetativo (V3/V4) e alagamento no período reprodutivo (R2/R3). As avaliações realizadas durante o ciclo da cultura foram: altura de plantas, diâmetro da haste principal, índice do teor de clorofila, fenologia e número de nós nas hastes por planta. O alagamento do solo reduz o número de nós na haste principal, reduzindo a estatura das plantas, sendo os efeitos mais acentuados quando o alagamento ocorre no estádio vegetativo. Além disso, o alagamento do solo no período reprodutivo promove aumento do diâmetro da haste principal. O alagamento do solo causa retardamento de ocorrência dos estádios fenológicos, bem como do ciclo total das cultivares de soja.</p><p align="center"><strong><em>Morphophysiological performance of medium cycle soybean cultivars under flooding</em></strong><strong><em></em></strong></p><pre><strong>Abstract: </strong>The increase in soybean cultivation in Brazil has reached areas previously used for other purposes, such as in regions of lowland soils, thus being subject to possible soil flooding. This study aimed to evaluate morphophysiological changes in medium cycle soybean cultivars, under soil flooding conditions, in the vegetative and reproductive stages to recommend cultivars.<strong> </strong>The experiments were conducted at the Estação Experimental de Terras Baixas, EMBRAPA Clima Temperado in the Capão do Leão city, RS. Three water management systems were applied: normal cultivation condition (without flooding), flooding in the vegetative stage (V3 / V4) and flooding during the reproductive stage (R2 / R3). During the crop cycle, plant height, diameter of the main stem, chlorophyll content index, phenology and number of nodes in the stem per plant were collected. On the basis of the results this study, it can be concluded that he flooding reduces the number of nodes on the main stem, reducing plant height, with the most pronounced effects when flooding occurs in the vegetative stage. Furthermore, flooding the reproductive stage promotes increased diameter of the main stem. Flooding causes delay of occurrence of phenological stages and the total cycle of soybean cultivars.</pre>

Bark and woody tissue photosynthesis: a means to avoid hypoxia or anoxia in developing stem tissues

In woody plants, oxygen transport and delivery via the xylem sap are well described, but the contribution of bark and woody tissue photosynthesis to oxygen delivery in stems is poorly understood. Here, we combined stem chlorophyll fluorescence measurements with microsensor quantifications of bark O2 levels and oxygen gas exchange measurements of isolated current-year stem tissues of beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) to investigate how bark and woody tissue photosynthesis impairs the oxygen status of stems. Measurements were made before bud break, when the axial path of oxygen supply via the xylem sap is impeded. At that time, bark O2 levels showed O2 concentrations below the atmospheric concentration, indicating hypoxic conditions or O2 deficiency within the inner bark, but the values were always far away from anoxic. Under illumination bark and woody tissue photosynthesis rapidly increased internal oxygen concentrations compared with plants in the dark, and thereby counteracted against localised hypoxia. The highest photosynthetic activity and oxygen release rates were found in the outermost cortex tissues. By contrast, rates of woody tissue photosynthesis were considerably lower, due to the high light attenuation of the bark and cortex tissues, as well as resistances in radial oxygen diffusion. Therefore, our results confirm that bark and woody tissue photosynthesis not only play a role in plant carbon economy, but may also be important for preventing low oxygen-limitations of respiration in these dense and metabolically active tissues.