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Woody plants display some photosynthetic activity in stems, but the biological role of stem photosynthesis and the specific contributions of bark and wood to carbon uptake and oxygen evolution remain poorly understood. We aimed to elucidate the functional characteristics of chloroplasts in stems of different ages in Fraxinus ornus. Our investigation employed diverse experimental approaches, including microsensor technology to assess oxygen production rates in whole stem, bark, and wood separately. Additionally, we utilized fluorescence lifetime imaging microscopy (FLIM) to characterize the relative abundance of photosystems I and II (PSI : PSII chlorophyll ratio) in bark and wood. Our findings revealed light-induced increases in O2 production in whole stem, bark, and wood. We present the radial profile of O2 production in F. ornus stems, demonstrating the capability of stem chloroplasts to perform light-dependent electron transport. Younger stems exhibited higher light-induced O2 production and dark respiration rates than older ones. While bark emerged as the primary contributor to net O2 production under light conditions, our data underscored that wood chloroplasts are also photosynthetically active. The FLIM analysis unveiled a lower PSI abundance in wood than in bark, suggesting stem chloroplasts are not only active but also acclimate to the spectral composition of light reaching inner compartments., Woody plants display some photosynthetic activity in stems, but the biological role of stem photosynthesis and the specific contributions of bark and wood to carbon uptake and oxygen evolution remain poorly understood. We aimed to elucidate the functional characteristics of chloroplasts in stems of different ages in Fraxinus ornus. Our investigation employed diverse experimental approaches, including microsensor technology to assess oxygen production rates in whole stem, bark, and wood separately. Additionally, we utilized fluorescence lifetime imaging microscopy (FLIM) to characterize the relative abundance of photosystems I and II (PSI : PSII chlorophyll ratio) in bark and wood. Our findings revealed light-induced increases in O2 production in whole stem, bark, and wood. We present the radial profile of O2 production in F. ornus stems, demonstrating the capability of stem chloroplasts to perform light-dependent electron transport. Younger stems exhibited higher light-induced O2 production and dark respiration rates than older ones. While bark emerged as the primary contributor to net O2 production under light conditions, our data underscored that wood chloroplasts are also photosynthetically active. The FLIM analysis unveiled a lower PSI abundance in wood than in bark, suggesting stem chloroplasts are not only active but also acclimate to the spectral composition of light reaching inner compartments.

Plant roots are exposed to hypoxia in waterlogged soils, and they are further challenged by specific phytotoxins produced by microorganisms in such conditions. One such toxin is hexanoic acid (HxA), which, at toxic levels, causes a strong decline in root O2 consumption. However, the mechanism underlying this process is still unknown. We treated pea (Pisum sativum L.) roots with 20 mM HxA at pH 5.0 and 6.0 for a short time (1 h) and measured leakage of key electrolytes such as metal cations, malate, citrate and nonstructural carbohydrates (NSC). After treatment, mitochondria were isolated to assess their functionality evaluated as electrical potential and O2 consumption rate. HxA treatment resulted in root tissue extrusion of K+, malate, citrate and NSC, but only the leakage of the organic acids and NSC increased at pH 5.0, concomitantly with the inhibition of O2 consumption. The activity of mitochondria isolated from treated roots was almost unaffected, showing just a slight decrease in oxygen consumption after treatment at pH 5.0. Similar results were obtained by treating the pea roots with another organic acid with a short carbon chain, that is, butyric acid. Based on these results, we propose a model in which HxA, in its undissociated form prevalent at acidic pH, stimulates the efflux of citrate, malate and NSC, which would, in turn, cause starvation of mitochondrial respiratory substrates of the Krebs cycle and a consequent decline in O2 consumption. Cation extrusion would be a compensatory mechanism in order to restore plasma membrane potential., Plant roots are exposed to hypoxia in waterlogged soils, and they are further challenged by specific phytotoxins produced by microorganisms in such conditions. One such toxin is hexanoic acid (HxA), which, at toxic levels, causes a strong decline in root O2 consumption. However, the mechanism underlying this process is still unknown. We treated pea (Pisum sativum L.) roots with 20 mM HxA at pH 5.0 and 6.0 for a short time (1 h) and measured leakage of key electrolytes such as metal cations, malate, citrate and nonstructural carbohydrates (NSC). After treatment, mitochondria were isolated to assess their functionality evaluated as electrical potential and O2 consumption rate. HxA treatment resulted in root tissue extrusion of K+, malate, citrate and NSC, but only the leakage of the organic acids and NSC increased at pH 5.0, concomitantly with the inhibition of O2 consumption. The activity of mitochondria isolated from treated roots was almost unaffected, showing just a slight decrease in oxygen consumption after treatment at pH 5.0. Similar results were obtained by treating the pea roots with another organic acid with a short carbon chain, that is, butyric acid. Based on these results, we propose a model in which HxA, in its undissociated form prevalent at acidic pH, stimulates the efflux of citrate, malate and NSC, which would, in turn, cause starvation of mitochondrial respiratory substrates of the Krebs cycle and a consequent decline in O2 consumption. Cation extrusion would be a compensatory mechanism in order to restore plasma membrane potential.

Hexanoic acid (HA) produced by microorganisms in waterlogged soils causes a decline in plant root O2 consumption, but it is unknown if lack of respiration is due to mitochondrial dysfunction or substrate starvation. We treated Pisum sativum L. roots with 20 mM HA acid at pH 5 and 6 for 1 h and measured leakage of electrolytes, malate, citrate and non-structural carbohydrates (NSC). Afterwards, mitochondria were isolated to assess their functionality, evaluated as electrical potential formation and O2 consumption. HA treatment resulted in root tissue extrusion of K+, malate, citrate and NSC, but the leakage of the organic acids and NSC was increased at pH 5 with the inhibition of O2 consumption and a slight alteration of mitochondrial activity. In conclusion, we propose that undissociated form of HA enters the root cells inducing the efflux of organic acids and NSC and the starvation of mitochondrial respiratory substrates of Krebs cycle with a subsequent decline in O2 consumption.

The stress gradient hypothesis (SGH) states that plant-plant interactions shift from competition to facilitation in increasing stress conditions. In salt marshes, edaphic properties can weaken the application of the SGH by amplifying the intensity of flooding and controlling plant zonation. We identified facilitative and competitive interactions along flooding gradients and tested the role of edaphic properties in exacerbating stress and shaping plant-plant interactions. Morphological traits of two target halophytes (Limonium narbonense and Sarcocornia fruticosa), flooding intensity, soil texture and soil organic C were recorded. The relative plant fitness index was assessed for the two species based on the relative growth in plurispecific rather than monospecific plant communities. Plant fitness increased with increasing stress supporting the SGH. L. narbonense showed larger fitness in plurispecific stands whereas S. fruticosa performed better in conspecific stands. Significant intra- or interspecific interactions were observed along the stress gradient defined by the combination of flooding and clay content in soil. When considering the limited soil organic C as stressor, soil properties were more important than flooding in defining plant-plant interactions. We highlight the need for future improvements of the SGH approach by including edaphic stressors in the model and their possible interactions with the main abiotic drivers of zonation.

Sand shore ecosystems are extremely vulnerable to alien plant invasions. While most of the abiotic drivers of alien success have been identified, less is known on the role of biological processes driving the invasion. Studying the interactions between alien and native plant communities across different habitats and along the ecological succession (i.e. community maturity) can elucidate the dynamics of alien invasions in dune systems. In this study, we sampled alien and native plant communities in 100 patches across 10 natural coastal landscapes in NE Italy. The patches represented three main habitat types (foredune, backdune and salt marsh, which differ in terms of sea storm-related disturbance and soil salinity) distributed along a gradient of community maturity (i.e. number of years since the plant community was completely eroded by a sea storm). We analysed the effects of alien/native status, habitat type and maturity on species richness and colonization potential of plant species pools. Colonization potential was estimated by applying for the first time on plant data a species-habitat network approach, which allowed us to assess in detail the effect of each plant community on the others. In backdune habitats, alien plant species richness was negatively related with community maturity, which in turn had a positive effect on native species richness. Colonization potential was positively influenced by age for native communities and negatively for alien communities in salt marshes. Among habitat types, backdune patches were also particularly prone to alien invasions and very efficient donors of alien plants to other patches. Salt marshes were in general very resistant to invasion but potentially acting as secondary reservoirs for some backdune alien species. This study identified backdune habitats as key nodes for alien plant introduction and spread in coastal ecosystems, underlining the importance of maintaining mature undisturbed patches as a barrier to alien i

Aims Among terrestrial ecosystems, coastal sandy dunes are particularly prone to alien plant invasion. Many studies related the invasion of dune habitats to anthropic causes, but less is known about the role of soil properties and plant traits in plant invasion. In this study, we tested the relationships between soil features and alien plant invasion in dune systems, focusing on the interplay between soil nutrients, soil salinity and plant functional traits. Methods Study sites were sandy barrier islands of the Marano and Grado lagoon (northern Adriatic Sea). One hundred plots (4 m × 4 m) were selected within 10 areas according to the main habitats occurring along the ecological gradient of dune system (foredune, backdune and saltmarsh). In each plot, we recorded all plant species occurrence and abundance and we collected a soil core. For each soil sample, soil texture, conductivity (as proxy of soil salinity), organic carbon and nitrogen content were analyzed and related to the species number and cover of native and alien plants. Variation of main reproductive and vegetative functional traits among habitats was also analyzed for both alien and native species. Important Findings Soil properties were strongly related to overall plant diversity, by differently affecting alien and native species pools. In backdune, the most invaded habitat, a high soil conductivity limited the number of alien species, whereas the content of soil organic carbon increased along with alien plant abundance, suggesting also the occurrence of potential feedback processes between plant invasion and soil. We found a significant convergence between native and alien plant functional trait spectra only in backdune habitat, where environmental conditions ameliorate and plant competition increases. Our findings suggest that in harsh conditions only native specialized plants can thrive while at intermediate conditions, soil properties gradient acts in synergy with plant

Organic acids are known phytotoxins in some anaerobic waterlogged soils. In this work, we tested the influence of hexanoic acid (HxA) on pea roots. HxA had an inhibitory effect on root tissue O2 consumption but only at pH 5.0, not at pH 6.0. Intact root tissues exposed to 20 mM HxA for 1 h showed solute leakage. Mitochondria were isolated from pea roots after 1 h incubation in the presence or absence of HxA, at either pH 5.0 or 6.0. The maximum effect of HxA on  was detected at pH 5.0 in the presence of succinic acid and without BSA in the assay buffer. A smaller effect was induced by HxA at pH 5.0 with malic plus glutamic acids, while at pH pH 6.0 no effect was observed. Mitochondrial respiration was affected by HxA after root incubation at pH 5.0. The decrease of respiration was induced by HxA with both succinic acid and malic plus glutamic acids but BSA in the assay buffer enhanced the effect of HxA, at least with succinic acid. These findings strongly suggest that the toxicity of HxA is caused by its un-dissociated form, affecting plasmalemma permeability and mitochondrial activities.