Search

This study determines the functional role of the plant ultraviolet-B radiation (UV-B) photoreceptor, UV RESISTANCE LOCUS 8 (UVR8) under natural conditions using a large-scale 'synchronized-genetic-perturbation-field-experiment'. Laboratory experiments have demonstrated a role for UVR8 in UV-B responses but do not reflect the complexity of outdoor conditions where 'genotype × environment' interactions can mask laboratory-observed responses. Arabidopsis thaliana knockout mutant, uvr8-7, and the corresponding Wassilewskija wild type, were sown outdoors on the same date at 21 locations across Europe, ranging from 39°N to 67°N latitude. Growth and climatic data were monitored until bolting. At the onset of bolting, rosette size, dry weight, and phenolics and glucosinolates were quantified. The uvr8-7 mutant developed a larger rosette and contained less kaempferol glycosides, quercetin glycosides and hydroxycinnamic acid derivatives than the wild type across all locations, demonstrating a role for UVR8 under field conditions. UV effects on rosette size and kaempferol glycoside content were UVR8 dependent, but independent of latitude. In contrast, differences between wild type and uvr8-7 in total quercetin glycosides, and the quercetin-to-kaempferol ratio decreased with increasing latitude, that is, a more variable UV response. Thus, the large-scale synchronized approach applied demonstrates a location-dependent functional role of UVR8 under natural conditions., (© 2024 The Author(s). Plant, Cell & Environment published by John Wiley & Sons Ltd.)

Plants exhibit an array of drought responses and adaptations, where the trade-off between water loss and CO 2 uptake for growth is mediated by regulation of stomatal aperture in response to soil water content (SWC), among other factors. For crop yield stability, the question is how drought timing and response patterns relate to post-drought growth resilience and vigor. We earlier identified, in a few reference varieties of barley that differed by the SWC at which transpiration was curtailed, two divergent water use strategies: water-saving ("isohydric") and water-spending ("anisohydric"). We proposed that an isohydric strategy may reduce risk from spring droughts in climates where the probability of precipitation increases during the growing season, whereas the anisohydric is consistent with environments having terminal droughts, or with those where dry periods are short and not seasonally progressive. Here, we have examined drought response physiology in an 81-line barley ( Hordeum vulgare L.) diversity set that spans 20 th century European breeding and identified several lines with a third, dynamic strategy. We found a strong positive correlation between vigor and transpiration, the dynamic group being highest for both. However, these lines curtailed daily transpiration at a higher SWC than the isohydric group. While the dynamic lines, particularly cv Hydrogen and Baronesse, were not the most resilient in terms of restoring initial growth rates, their strong initial vigor and high return to initial transpiration rates meant that their growth nevertheless surpassed more resilient lines during recovery from drought. The results will be of use for defining barley physiological ideotypes suited to future climate scenarios., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Paul, Dalal, Jääskeläinen, Moshelion and Schulman.)

Shoot-level emissions of aerobically produced methane (CH 4 ) may be an overlooked source of tree-derived CH 4 , but insufficient understanding of the interactions between their environmental and physiological drivers still prevents the reliable upscaling of canopy CH 4 fluxes. We utilised a novel automated chamber system to continuously measure CH 4 fluxes from the shoots of Pinus sylvestris (Scots pine) saplings under drought to investigate how canopy CH 4 fluxes respond to the drought-induced alterations in their physiological processes and to isolate the shoot-level production of CH 4 from soil-derived transport and photosynthesis. We found that aerobic CH 4 emissions are not affected by the drought-induced stress, changes in physiological processes, or decrease in photosynthesis. Instead, these emissions vary on short temporal scales with environmental drivers such as temperature, suggesting that they result from abiotic degradation of plant compounds. Our study shows that aerobic CH 4 emissions from foliage are distinct from photosynthesis-related processes. Thus, instead of photosynthesis rates, it is more reliable to construct regional and global estimates for the aerobic CH 4 emission based on regional differences in foliage biomass and climate, also accounting for short-term variations of weather variables such as air temperature and solar radiation., (© 2024 The Authors New Phytologist © 2024 New Phytologist Foundation.)

The effects of transient increases in UVB radiation on plants are not well known; whether cumulative damage dominates or, alternately, an increase in photoprotection and recovery periods ameliorates any negative effects. We investigated photosynthetic capacity and metabolite accumulation of grapevines (Vitis vinifera Cabernet Sauvignon) in response to UVB fluctuations under four treatments: fluctuating UVB (FUV) and steady UVB radiation (SUV) at similar total biologically effective UVB dose (2.12 and 2.23 kJ m -2  day -1 ), and their two respective no UVB controls. We found a greater decrease in stomatal conductance under SUV than FUV. There was no decrease in maximum yield of photosystem II (F v /F m ) or its operational efficiency (ɸ PSII ) under the two UVB treatments, and F v /F m was higher under SUV than FUV. Photosynthetic capacity was enhanced under FUV in the light-limited region of rapid light-response curves but enhanced by SUV in the light-saturated region. Flavonol content was similarly increased by both UVB treatments. We conclude that, while both FUV and SUV effectively stimulate acclimation to UVB radiation at realistic doses, FUV confers weaker acclimation than SUV. This implies that recovery periods between transient increases in UVB radiation reduce UVB acclimation, compared to an equivalent dose of UVB provided continuously. Thus, caution is needed in interpreting the findings of experiments using steady UVB radiation treatments to infer effects in natural environments, as the stimulatory effect of steady UVB is greater than that of the equivalent fluctuating UVB., (© 2024 The Author(s). Physiologia Plantarum published by John Wiley & Sons Ltd on behalf of Scandinavian Plant Physiology Society.)

Solar radiation is scattered by cloud cover, aerosols and other particles in the atmosphere, all of which are affected by global changes. Furthermore, the diffuse fraction of solar radiation is increased by more frequent forest fires and likewise would be if climate interventions such as stratospheric aerosol injection were adopted. Forest ecosystem studies predict that an increase in diffuse radiation would result in higher productivity, but ecophysiological data are required to identify the processes responsible within the forest canopy. In our study, the response of a boreal forest to direct, diffuse and heterogeneous solar radiation conditions was examined during the daytime in the growing season to determine how carbon uptake is affected by radiation conditions at different scales. A 10-year data set of ecosystem, shoot and forest floor vegetation carbon and water-flux data was examined. Ecosystem-level carbon assimilation was higher under diffuse radiation conditions in comparison with direct radiation conditions at equivalent total photosynthetically active radiation (PAR). This was driven by both an increase in shoot and forest floor vegetation photosynthetic rate. Most notably, ecosystem-scale productivity was strongly related to the absolute amount of diffuse PAR, since it integrates both changes in total PAR and diffuse fraction. This finding provides a gateway to explore the processes by which absolute diffuse PAR enhances productivity, and the long-term persistence of this effect under scenarios of higher global diffuse radiation., (© 2024 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Plant-mediated CH 4 transport (PMT) is the dominant pathway through which soil-produced CH 4 can escape into the atmosphere and thus plays an important role in controlling ecosystem CH 4 emission. PMT is affected by abiotic and biotic factors simultaneously, and the effects of biotic factors, such as the dominant plant species and their traits, can override the effects of abiotic factors. Increasing evidence shows that plant-mediated CH 4 fluxes include not only PMT, but also within-plant CH 4 production and oxidation due to the detection of methanogens and methanotrophs attached to the shoots. Despite the inter-species and seasonal differences, and the probable contribution of within-plant microbes to total plant-mediated CH 4 exchange (PME), current process-based ecosystem models only estimate PMT based on the bulk biomass or leaf area index of aerenchymatous plants. We highlight five knowledge gaps to which more research efforts should be devoted. First, large between-species variation, even within the same family, complicates general estimation of PMT, and calls for further work on the key dominant species in different types of wetlands. Second, the interface (rhizosphere-root, root-shoot, or leaf-atmosphere) and plant traits controlling PMT remain poorly documented, but would be required for generalizations from species to relevant functional groups. Third, the main environmental controls of PMT across species remain uncertain. Fourth, the role of within-plant CH 4 production and oxidation is poorly quantified. Fifth, the simplistic description of PMT in current process models results in uncertainty and potentially high errors in predictions of the ecosystem CH 4 flux. Our review suggest that flux measurements should be conducted over multiple growing seasons and be paired with trait assessment and microbial analysis, and that trait-based models should be developed. Only then we are capable to accurately estimate plant-mediated CH 4 emissions, and eventually ecosystem total CH 4 emissions at both regional and global scales., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest associated with this manuscript., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

The transport processes of methane (CH 4 ) in tree stems remain largely unknown, although they are critical in assessing the whole-forest CH4 dynamics. We used a physically based dynamic model to study the spatial and diurnal dynamics of stem CH 4 transport and fluxes. We parameterised the model using data from laboratory experiments with Pinus sylvestris and Betula pendula and compared the model to experimental data from a field study. Stem CH 4 flux in laboratory and field conditions were explained by the axial advective CH 4 transport from soil with xylem sap flow and the radial CH 4 diffusion through the stem conditions. Diffusion resistance caused by the bark permeability did not significantly affect gas transport or stem CH 4 flux in the laboratory experiments. The role of axial diffusion of CH 4 in trees was unresolved and requires further studies. Due to the transit time of CH 4 in the stem, the diurnal dynamics of stem CH 4 fluxes can deviate markedly from the diurnal dynamics of sap flow., (© 2023 The Authors. Plant, Cell & Environment published by John Wiley & Sons Ltd.)