Ole Pedersen

University of Copenhagen · Department of Biology

Background and aims The root barrier to radial O2 loss is a trait induced during soil flooding restricting oxygen loss from the roots to the anoxic soil. It can also restrict radial water loss, potentially providing tolerance towards drought during conditions of water deficit. Several root traits (aerenchyma and xylem vessels area) respond in a sim...

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 O 2 consumption. However, the mechanism underlying this process is still unknown. We treated pe...

Lobelia dortmanna is an iconic keystone species of northern softwater lakes in Europe as well as North America. It has suffered a dramatic decline in distribution in recent decades and the root causes are not well‐known, although elements such as eutrophication, acidification and brownification have been suggested as underlying reasons for the decl...

Adequate tissue O2 supply is crucial for plant function. We aimed to identify the environmental conditions and plant characteristics that affect plant tissue O2 status. We extracted data and performed meta-analysis on >1500 published tissue O2 measurements from 112 species. Tissue O2 status ranged from anoxic conditions in roots to >53kPa in submer...

Rice production worldwide represents a major anthropogenic source of greenhouse gas emissions. Nitrogen fertilization and irrigation practices have been fundamental to achieve optimal rice yields, but these agricultural practices together with by-products from plants and microorganisms, facilitate the production, accumulation and venting of vast am...

The huge variation in key root traits in the genus Oryza is also reflected in the flowers. Eight species of wild rice and three genotypes of cultivated rice showed contrasting differences in root traits including apparent permeance to oxygen of the outer part of the roots, radial water loss, tissue porosity, apoplastic barriers in the exodermis and...

As climate change intensifies, the development of resilient rice that can tolerate abiotic stresses is urgently needed. In nature, many wild plants have evolved a variety of mechanisms to protect themselves from environmental stresses. Wild relatives of rice may have abundant and virtually untapped genetic diversity and are an essential source of g...

The root barrier to radial O 2 loss (ROL) is a key root trait preventing O 2 loss from roots to anoxic soils, thereby enabling root growth into anoxic, flooded soils. We hypothesized that the ROL barrier can also prevent intrusion of hydrogen sulphide (H 2 S), a potent phytotoxin in flooded soils. Using H 2 S‐ and O 2 ‐sensitive microsensors, we me...

Excess water can induce flooding stress resulting in yield loss of crops, even in wetland plants such as rice. However, traits from species of wild Oryza have already been used to improve tolerance to abiotic stress in cultivated rice. This study aimed to establish root responses to sudden soil flooding among 8 wild relatives of rice with different...

A key trait conferring flood tolerance is the ability to grow adventitious roots as a response to submergence. The genetic traits of deepwater rice determining the development and characteristics of aquatic adventitious roots (AAR) had not been evaluated. We used near‐isogenic lines introgressed to test the hypothesis that the impressive shoot elon...

Hypersalinity is a major stressor to seagrasses, particularly in highly evaporative coastal estuaries and lagoons as well as those subjected to brine effluent from desalination systems, a condition likely to be heightened under a warming climate. While hypersalinity has been well established to cause physiological dysfunction, the effects on intern...

Aims Root tissue water can be lost to the dry topsoil via radial water loss (RWL) resulting in root shrinking and loss of contact with the rhizosphere. The root barrier to radial oxygen loss (ROL) has been shown to restrict RWL, therefore we hypothesized that the inducible barrier can be formed as a response to low soil water potential and play a r...

Flooding is constantly threatening the growth and yield of crops worldwide. When flooding kicks in, the soil becomes water-saturated and, therefore, the roots are the first organs to be exposed to excess water. Soon after flooding, the soil turns anoxic and the roots can no longer obtain molecular oxygen for respiration from the rhizosphere, render...

Throughout the freshwater continuum, Dissolved Organic Carbon (DOC) and the colored fraction, Chromophoric Dissolved Organic Material (CDOM), are continuously being added, removed, and transformed, resulting in changes in the chromophoricity and lability of organic matter over time. We examined, experimentally, the effect of increasing irradiation-...

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 al...

AIMS: Root tissue water can be lost to the dry topsoil via radial water loss (RWL) resulting in root shrinking and loss of contact with the rhizosphere. The root barrier to radial oxygen loss (ROL) has been shown to restrict RWL, therefore we hypothesized that the inducible barrier can be formed as a response to low soil water potential and play a...

Hypoxia and hydrogen sulfide (H2S) intrusion at night contribute to large-scale seagrass mortality events world-wide. Declining water quality has lowered irradiance and enhanced hypoxia in seagrass ecosystems, but linkages between low irradiance and seagrass internal pO2 in situ are not well understood. We examined low irradiance effects on leaf an...

Water column hypoxia, low partial pressure of oxygen (pO2), and hydrogen sulfide (H2S) intrusion, a phytotoxin, are factors linked to global seagrass decline. While many lab experiments have examined these relationships, field studies are needed to elucidate complex drivers of internal pO2 in situ. Herein, we examined plant pO2 and H2S dynamics usi...

Background and Aims While trait-based approaches have provided critical insights into general plant functioning, we lack a comprehensive quantitative view on plant strategies in flooded conditions. Plants adapted to flooded conditions have specific traits (e.g. root porosity, low root/shoot ratio and shoot elongation) to cope with the environmental...

In flooded soils, an efficient internal aeration system is essential for root growth and plant survival. Roots of many wetland species form barriers to restrict radial O2 loss (ROL) to the rhizosphere. The formation of such barriers greatly enhances longitudinal O2 diffusion from basal parts towards the root tip, and the barrier also impedes the en...

The root barrier to radial O2 loss (ROL) is a trait enabling waterlogging tolerance of plants. The ROL barrier restricts O2 diffusion to the anoxic soil so that O2 is retained inside root tissues. We hypothesised that the ROL barrier can also restrict radial diffusion of other gases (H2 and water vapour) in rice roots with a barrier to ROL. We use...

C4 perennial Urochloa spp. grasses are widely planted in extensive areas in the tropics. These areas are continuously facing waterlogging events, which limits plant growth and production. However, no commercial cultivar combining excellent waterlogging tolerance with superior biomass production and nutritional quality is available. The objective of...

Large-scale (>80 km²) seagrass mortality events have been reported worldwide. While the mechanisms triggering these sudden die-off events are not well understood, plant hypoxia and H2S intrusion, at times linked to hypersaline conditions, have been suggested to play a role. In the present study, we used microsensors (~100 μm) to measure pO2 light-d...

Drought and flooding are contrasting abiotic stressors for plants. Evidence is accumulating for root anatomical traits being essential for the adaptation to drought or flooding. However, an integrated approach to comprehensively understand root anatomical traits has not yet been established. Here we analysed the root anatomical traits of 18 wild Po...

Flooding is an environmental stress that leads to a shortage of O2 that can be detrimental for plants. When flooded, deepwater rice grow floating adventitious roots to replace the dysfunctional soil-borne root system but the features that ensure O2 supply and hence growth of aquatic roots have not been explored. We investigate the sources of O2 in...

Heavy rainfall causes flooding of natural ecosystems as well as farmland, negatively affecting plant performance. While the responses of the wild model organism Arabidopsis thaliana to such stress conditions is well understood, little is known about the responses of its relative, the important oil crop plant Brassica napus. For the first time, we a...

The leaf economics spectrum (LES) describes consistent correlations among a variety of leaf traits that reflect a gradient from conservative to acquisitive plant strategies. So far, whether the LES holds in wetland plants at a global scale has been unclear. Using data on 365 wetland species from 151 studies, we find that wetland plants in general s...

This Expert View provides an update on the recent development of new microsensors, and briefly summarizes some novel applications of existing microsensors, in plant biology research. Two major topics are covered, i) sensors for gaseous analytes (O2, CO2, H2S) and ii) those for measuring concentrations and fluxes of ions (macro- and micronutrients a...

Flooding causes oxygen deprivation in soils. Plants adapt to low soil oxygen availability by changes in root morphology, anatomy, and architecture to maintain root system functioning. Essential traits include aerenchyma formation, a barrier to radial oxygen loss, and outgrowth of adventitious roots into the soil or the floodwater. We highlight rece...

Plants have developed a suite of traits to survive the anaerobic and anoxic soil conditions in wetlands. Previous studies on wetland plant adaptive traits have focused mainly on physiological aspects under experimental conditions, or compared the trait expression of the local species pool. Thus, a comprehensive analysis of potential factors driving...

Plants typically respond to waterlogging by producing new adventitious roots with aerenchyma and many wetland plants form a root barrier to radial O 2 loss (ROL), but it was not known if this was also the case for lateral roots. We tested the hypothesis that lateral roots arising from adventitious roots can form a ROL barrier, using root‐sleeving e...

The molecular mechanisms controlling underwater elongation are based extensively on studies on internode elongation in the monocot rice ( Oryza sativa ) and petiole elongation in Rumex rosette species. Here, we characterize underwater growth in the dicot Nasturtium officinale (watercress), a wild species of the Brassicaceae family, in which submerg...

Roots in flooded soils experience hypoxia, with the least O 2 in the vascular cylinder. Gradients in CO 2 across roots had not previously been measured. The respiratory quotient (RQ; CO 2 produced : O 2 consumed) is expected to increase as O 2 availability declines. A new CO 2 microsensor and an O 2 microsensor were used to measure profiles across...

Change in plants as bicarbonate rises Freshwater plants can be broadly divided into two major categories according to their photosynthetic traits: Some use carbon dioxide as their carbon source, whereas others use bicarbonate. Iversen et al. found that the relative concentrations of these two inorganic carbon forms in water determine the functional...

Complex multicellular organisms evolved on Earth in an oxygen-rich atmosphere¹; their tissues, including stem-cell niches, require continuous oxygen provision for efficient energy metabolism². Notably, the maintenance of the pluripotent state of animal stem cells requires hypoxic conditions, whereas higher oxygen tension promotes cell differentiati...

Deepwater rice has a remarkable shoot elongation response to partial submergence. Shoot elongation to maintain air-contact enables 'snorkelling' of O2 to submerged organs. Previous research has focused on partial submergence of deepwater rice. We tested the hypothesis that leaf gas films enhance internode O2 status and stem elongation of deepwater...

Waterlogged soils contain monocarboxylic acids produced by anaerobic microorganisms. These ‘organic acids’ can accumulate to phytotoxic levels and promote development of a barrier to radial O2 loss (ROL) in roots of some wetland species. Environmental cues triggering root ROL barrier induction, a feature which together with tissue gas‐filled porosi...

Increasing terrestrial input of colored dissolved organic matter (CDOM) to temperate softwater lakes has reduced transparency, distribution of pristine rosette plants and overall biodiversity in recent decades. We examined microbial and UV-induced reduction of absorption by CDOM and dissolved organic carbon pools (DOC) in humic water from a groundw...

Life in seawater presents several challenges for seagrasses owing to low O2 and CO2 solubility and slow gas diffusion rates. Seagrasses have evolved numerous adaptations to these environmental conditions including porous tissue providing low-resistance internal gas channels (aerenchyma) and carbon concentration mechanisms involving the enzyme carbo...

Background and aims: Leaf tissue CO2 partial pressure (pCO2) shows contrasting dynamics over a diurnal cycle in C3 and Crassulacean Acid Metabolism (CAM) plants. However, simultaneous and continuous monitoring of pCO2 and pO2 in C3 and CAM plants under the same conditions was lacking. Our aim was to use a new CO2 microsensor and an existing O2 mic...

Responses of wheat (Triticum aestivum) to complete submergence are not well understood as research has focused on waterlogging (soil flooding). The aim of this study was to characterize the responses of two wheat cultivars differing vastly in submergence tolerance to test if submergence tolerance was linked to shoot carbohydrate consumption as seen...

The presence of oxygen in seagrass tissues, which plays a role in preventing seagrass die-off, is partly regulated by environmental conditions. Here, we examined the relationship between oxygen (O2) in the rhizomes of Posidonia sinuosa and key environmental variables at Garden Island, Western Australia. We made in situ measurements of internal oxyg...

Floods impede gas (O 2 and CO 2 ) exchange between plants and the environment. A mechanism to enhance plant gas exchange under water comprises gas films on hydrophobic leaves, but the genetic regulation of this mechanism is unknown. We used a rice mutant ( dripping wet leaf 7 , drp7 ) which does not retain gas films on leaves, and its wild‐type (Ki...

Groundwater-borne contaminants such as nutrients, dissolved organic carbon (DOC), coloured dissolved organic matter (CDOM) and pesticides can have an impact the biological quality of lakes. The sources of pollutants can, however, be difficult to identify due to high heterogeneity in groundwater flow patterns. This study presents a novel approach fo...

Background and aims: Soil waterlogging adversely impacts most plants. Melilotus siculus is a waterlogging-tolerant annual forage legume, but data were lacking for the effects of root-zone hypoxia on nodulated plants reliant on N2 fixation. The aim was to compare the waterlogging tolerance and physiology of M. siculus reliant on N2 fixation or with...

Groundwater borne contaminants such as e.g., nutrients, dissolved organic carbon (DOC), coloured dissolved organic matter (CDOM) and pesticides impact the biological quality of lakes. The sources of pollution can, however, be difficult to identify due to high heterogeneity in groundwater flow patterns. This study presents a novel approach for fast...

Lake Constance is the second largest lake in Europe. While naturally oligotrophic, the lake experienced a period of heavy eutrophication due to the input of domestic and industrial sewage and agricultural runoff in the 1960s and 1970s. This prompted concerted efforts from authorities to purify wastewaters and reduce agricultural nutrient input, ini...

Background and aims: Floating sweet-grass ( Glyceria fluitans ) can form aerial as well as floating leaves, and these both possess superhydrophobic cuticles, so that gas films are retained when submerged. However, only the adaxial side of the floating leaves is superhydrophobic, so the abaxial side is directly in contact with the water. The aim of...

Flooding of fields after sudden rainfall events can result in crops being completely submerged. Some terrestrial plants, including wheat (Triticum aestivum L.), possess superhydrophobic leaf surfaces that retain a thin gas film when submerged, and the gas films enhance gas exchange with the floodwater. However, the leaves lose their hydrophobicity...

Submergence invokes a range of stressors to plants with impeded gas exchange between tissues and floodwater being the greatest challenge. Many terrestrial plants including wheat (Triticum aestivum L.), possess superhydrophobic leaf cuticles that retain a thin gas film when submerged, and the gas films enhance gas exchange with the floodwater. Howev...

Terrestrial saltmarsh plants inhabiting flood-prone habitats undergo recurrent and prolonged flooding driven by tidal regimes. In this study, the role of internal plant aeration in contrasting hypoxic/anoxic conditions during submergence was investigated in the two halophytes Limonium narbonense Mill. and Sarcocornia fruticosa (L.) A.J. Scott. Moni...

The world is currently experiencing dramatic increases in flood events impacting on natural vegetation and crops. Flooding often results in low O2 status in root tissues during waterlogging, but sometimes also in shoot tissues when plants become completely submerged. Plants possess a suite of traits enabling tissue aeration and/or adjusted metaboli...

HIGHLIGHTS: Sedimentation of fine sediment particles onto seagrass leaves severely hampers the plants' performance in both light and darkness, due to inadequate internal plant aeration and intrusion of phytotoxic H2S. Anthropogenic activities leading to sediment re-suspension can have adverse effects on adjacent seagrass meadows, owing to reduced...

Lake Hampen, (Central Jutland, Denmark) is located high in the landscape near a seasonal moving groundwater divide. The lake is regarded as a flow-through lake during average to wet weather conditions with a large catchment making the lake groundwater-dominated. Monitoring of δ¹⁸O in mini-piezometers in the lake bed and wells at the lake shore and...

Apart from playing a key role in important biochemical reactions, molecular oxygen (O2) and its by-products also have crucial signaling roles in shaping plant developmental programs and environmental responses. Even under normal conditions, sharp O2 gradients can occur within the plant when cellular O2 demand exceeds supply, especially in dense org...

The submerged aquatic freshwater macrophyte Isoetes australis S. Williams grows in rock pools situated in south-western Australia, an environment where dissolved inorganic phosphorus (Pi) availability possibly limits growth. In contrast to the two coexisting aquatic species, Glossostigma drummundii and Crassula natans, I. australis did not form rel...

Floods and salinization of agricultural land adversely impact global rice production. We investigated whether gas films on leaves of submerged rice delay salt entry during saline submergence. Two-week-old plants with leaf gas films (+GF) or with gas films experimentally removed (−GF) were submerged in artificial floodwater with 0 or 50 mM NaCl for...

Seagrasses grow submerged in aerated seawater but often in low O 2 sediments. Elevated temperatures and low O 2 are stress factors. Internal aeration was measured in two tropical seagrasses, Thalassia hemprichii and Enhalus acoroides , growing with extreme tides and diel temperature amplitudes. Temperature effects on net photosynthesis ( P N ) and...

Traits for survival during flooding of terrestrial plants include stimulation or inhibition of shoot elongation, aerenchyma formation, and efficient gas exchange. Leaf gas films form on superhydrophobic cuticles during submergence and enhance underwater gas exchange. The main hypothesis tested was that the presence of leaf gas films influences the...

We review the detrimental effects of waterlogging on physiology, growth and yield of wheat. We highlight traits contributing to waterlogging tolerance and genetic diversity in wheat. Death of seminal roots and restriction of adventitious root length due to O2 deficiency result in low root:shoot ratio. Genotypes differ in seminal root anoxia toleran...

Photosynthesis of most seagrass species seems to be limited by present concentrations of dissolved inorganic carbon (DIC). Therefore, the ongoing increase in atmospheric CO2 could enhance seagrass photosynthesis and internal O2 supply, and potentially change species competition through differential responses to increasing CO2 availability among spe...

The general premise for successful archaeological in situ preservation in wetlands is that raising the water table will ‘seal the grave’ by preventing oxygen from reaching the deposit. The present review reveals that this may not be the entire picture, as a change in habitat may introduce new plant species that can damage site stratigraphy and arte...

The presence of epiphytic turf algae may modify the effects of ocean acidification on coralline algal calcification rates by altering seawater chemistry within the diffusive boundary layer (DBL) above coralline algal crusts. We used microelectrodes to measure the effects of turf algal epiphytes on seawater pH and the partial pressure of oxygen (pO2...

Oxygen deficiency associated with soil waterlogging adversely impacts root respiration and nutrient acquisition. We investigated the effects of O2 deficiency and salinity (100 mM NaCl) on radial O2 concentrations and cell-specific ion distributions in adventitious roots of barley (Hordeum vulgare). Microelectrode profiling measured O2 concentration...

Many stem-succulent halophytes experience regular or episodic flooding events, which may compromise gas exchange and reduce survival rates. This study assesses submergence tolerance, gas exchange and tissue oxygen (O2) status of two stem-succulent halophytes with different stem diameters and from different elevations of an inland marsh. Responses t...