Nuria Pedrol

Phenotypic plasticity and acclimation to water deficits in velvet-grass: a long-term greenhouse experiment. Changes in leaf morphology, photosynthesis and stress-induced metabolites.

Summary Wild velvet-grass ( Hocus lanatus ) collected from a natural population along a drought gradient, previously demonstrated as genetically homogeneous, was studied for phenotypic plasticity and acclimation mechanisms to water deficits. A three months greenhouse experiment was designed with plants submitted to nine levels of water availability, three months being the usual length of summer drought in field conditions. Aboveground biomass, total soluble proteins, free proline, free polyamines, leaf morphology, stomatal and hair characteristics, and net photosynthetic rates were analysed, and their significance discussed. Moderate drought did not damage the velvet-grass, and the plants grew better than without water limitation. Water stress-typical responses were shown as time and severity dependent in all the measured parameters. Lowest water availability treatments induced significative increase in free proline and soluble protein contents, as well as reductions in leaf size and aboveground biomass. Spermidine contents rose significatively in the most severe water stress. Furthermore, velvet-grass acclimated progressively to long-term water limitation.

Eucalyptus globulus Leaves Incorporated as Green Manure for Weed Control in Maize

Abstract The use of eucalyptus leaves for weed control in maize-based cropping systems is proposed. Aqueous extracts of eucalyptus are known to exert phytotoxicity on many weeds and crops, but there is also experimental evidence of the relative tolerance of maize. Based on in vitro dose-response bioassays of leaf aqueous extracts, we conducted greenhouse pot experiments testing incorporated eucalyptus leaves as green manure. The phytotoxic effects were tested on the germination, establishment and growth of maize and some representative accompanying weeds, in comparison to the PRE herbicide metolachlor. Eucalyptus fresh leaves incorporated into the soil as green manure at 1 and 2% w/w reduced the emergence of the dicot weed species redroot pigweed and black nightshade. After one month of incorporation, both doses reduced aerial biomass >94% two monocot weed species (barnyardgrass + large crabgrass) with respect to the eucalyptus-free pots, and around 80% for the small seeded dicots. Although the aerial biomass of maize was reduced by 33%, the final relative yield of maize biomass with respect to the untreated control increased by 37%. On the assessment of the temporal phytotoxic effects, the reduction of aerial biomass in maize could be overcome by adopting a relay-planting of maize after 12 to 15 days from eucalyptus incorporation. Our results constitute evidence that the incorporation of E. globulus residues to soil could be a feasible practice to reduce the reliance on synthetic herbicides in maize-based cropping systems. Nomenclature: S-metolachlor; barnyardgrass, Echinochloa crus-galli (L.) P. Beauv. ECHCG; black nightshade, Solanum nigrum L. SOLNI; eucalyptus, Eucalyptus globulus Labill. EUGL; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; redroot pigweed, Amaranthus retroflexus L. AMARE; maize, Zea mays L

Genomic Approaches to Understanding Allelochemical Effects on Plants

Little is known concerning the mode of action of allelochemicals or plant defense responses mounted against them. Theoretically, changes in the expression of genes encoding the primary target or other proteins in the same pathway should occur soon after phytotoxin exposure. Defense responses, such as the induction of genes involved in chemical detoxification, may occur later, depending on the nature of the chemosensors which presumably exist in plant cells. We first used yeast (Saccharomyces cerevisiae) to test the concept of transcriptome profiling of toxicant modes of action. Characteristic gene induction profiles related to specific molecular target sites were verified with several fungicides. A battery of xenobiotic defense-associated genes were found to be dramatically induced in Arabidopsis following exposure to an array of structurally unrelated xenobiotics, including a herbicide, an allelochemical, and herbicide safeners. These genes are unlikely to be strongly linked to the mode of action of a specific phytotoxin, but rather constitute a coordinately-controlled xenobiotic defense gene network. Transcriptional profiling experiments using microarrays are being conducted to examine the effects of various herbicides and natural phytotoxins on the Arabidopsis transcriptome.

Improving Soil Fertility to Support Grass–Legume Revegetation on Lignite Mine Spoils

The short-term sequential effects of different treatments on soil fertility and revegetation of mine spoils were examined in a lignite mine in northwestern Spain. Experimental plots were established both on old and recent spoils after tillage and treated with compost or nitrogen (N), phosphorus (P), potassium (K), + magnesium limestone before seeding with a grass–legume species mixture. Compost improved plant production and, contrary to NPK, maintained soil N levels and supplied enough P for the establishment and early growth of the vegetation. Severe magnesium (Mg), calcium (Ca), and K limitations in recent spoils were only alleviated by compost + magnesium limestone, allowing the rapid growth and coating of the soil surface. The amendment based on NPK + magnesium limestone improved plant production in the short term but caused proliferation of weeds. Results suggest that revegetation in combination with the appropriate amendments is a key issue for the reclamation of lignite mine spoils.

PHOTOSYNTHESIS OF NATURAL COCKSFOOT POPULATIONS UNDER WATER AND SALT STRESSES

Sampling of natural cocksfoot (Dactylis glomerata L.) populations was carried out on the O Morrazo peninsula in NW Spain, characterized by a strong moisture gradient. The plants were kept in greenhouse under standard conditions. Nevertheless, they differ in height of plants, length and width of flag leaves, panicle size, stomatal density and size as well as in flowering period. The effects of two levels of soil water deficit and two levels of salinity on photosynthetic rate were tested. One population was exceptionally well adapted to its original environment with great tolerance to water deficit and salinity

Ecophysiology of Perennial Grasses under Water Deficits and Competition

Galician peninsulas are characterised by the existence of strong bioclimatic gradients with regards to soil water availability, specially during summer drought, providing very different life conditions to plants from near places. Coastal populations of perennial gasses in the extreme of the gradient suffer the most severe water deficits, aggravated by salinity and the presence of sandy and thin soils. Some of these grasses occupy close ecological niches, competing closely for limited resources. Previous studies on grass species populations distributed along a summer drought gradient, in a maximum distance of 20 Km (O Morrazo peninsula and Cies Islands. Galicia, NW Spain) have not shown genetic distances or physiological and morphological differences leading to consider different genotypes or ecotypes; thus, acclimation mechanisms and plasticity of metabolism are expected. The main objective of this work is the ecophysiological characterisation of three wild grasses from this area: Holcus lanatus L., Koeleria glauca (Schrader) DC., Dactylis glomerata L., compared to a pair of commercial cultivars widely used in this area: D.glomerata cv. Micol, and Lolium perenne cv. Sun., with regards to their capacities of acclimation to water stress: salinity and drought, besides to their competitive abilities.

Unravelling the bioherbicide potential of Eucalyptus globulus Labill: Biochemistry and effects of its aqueous extract

In the worldwide search for new strategies in sustainable weed management, the use of plant species able to produce and release phytotoxic compounds into the environment could be an effective alternative to synthetic herbicides. Eucalyptus globulus Labill. is known to be a source of biologically active compounds responsible for its phytotoxic and allelopathic properties. Our previous results demonstrated the bioherbicide potential of eucalyptus leaves incorporated into the soil as a green manure, probably through the release of phytotoxins into the soil solution. Thus, the aims of this study were to understand the phytotoxicity of the eucalyptus leaves aqueous extract applied in pre- and post-emergence, and to identify and quantify its potentially phytotoxic water-soluble compounds. The effects were tested on the germination and early growth of the model target species Lactuca sativa and Agrostis stolonifera, and on physiological parameters of L. sativa adult plants after watering or spraying application. Dose-response curves and ED50 and ED80 values for eucalyptus aqueous extracts revealed pre-emergence inhibitory effects on both target species, effects being comparable to the herbicide metolachlor. While spraying treatment reduced the aerial and root biomass and increased the dry weight/fresh weight ratio of lettuce adult plants, watering application reduced protein contents and chlorophyll concentrations with respect to control, reflecting different modes of action depending on the site of phytotoxin entry. Via HPLC analyses, a total of 8 phenolic compounds (chlorogenic, two ρ-coumaric derivatives, ellagic, hyperoside, rutin, quercitrin, and kaempferol 3-O-glucoside) and other 5 low weight organic acids (citric, malic, shikimic, succinic and fumaric acids) were obtained from aqueous extract, the latter being identified for the first time in E. globulus. Despite some phytotoxic effects were found on lettuce adult plants, the use of eucalyptus aqueous extract would be discarded in post-emergence, whereas it was promising as a pre-emergence bioherbicide.

Volatile organic compounds of Acacia longifolia and their effects on germination and early growth of species from invaded habitats

ABSTRACT Acacia longifolia, a highly invasive species that invades coastal ecosystems in Mediterranean areas, produces significant impacts at different scales. Abundant foliage and thick canopies create a dense atmosphere that led us to hypothesise that the release of volatile organic compounds (VOCs) could play a role in the reduction of biodiversity observed in invaded areas. Therefore, we suggested that VOCs emitted by A. longifolia could exert inhibitory effects on physiological and biochemical parameters of native species. Using glass chamber bioassays, we evaluated the effect of aerial contact between VOCs from different plant parts of A. longifolia material and some native species. Volatile chemical composition was further analysed using GC-MS. Our results indicated that VOCs produced a notably reduction of seed germination. Furthermore, volatiles from leaves and flowers significantly decreased root length, shoot length and biomass for all species. Proline and malondialdehyde content did not significantly increase after contact with VOCs. Finally, chemical profile of VOCs from flowers, leaves and litter was significantly different, both qualitatively and quantitatively. As far as we know, our results constitute the first evidence of phytotoxicity induced by VOCs from A. longifolia, suggesting that flowers and leaves could influence its surrounding environment through VOCs release. GRAPHICAL ABSTRACT Abbreviations: NBT: nitroblue tetrazolium; EDTA: Ethylenediaminetetraacetic acid;

Measuring Photosynthesis and Respiration with Infrared Gas Analysers

Earth primary productivity reflects the balance between two important biological processes: photosynthesis and respiration (Atkin et al. 2015; Niinemets 2016). Photosynthesis (A) refers to the assimilation of the atmospheric CO2 and its conversion into sugars, the first basic organic compounds entering the metabolism. This process of CO2 fixation uses the sun radiation as the energy source, and water as the electron donor, which in turn releases oxygen in the atmosphere. Dark respiration (RD) or mitochondrial respiration (Atkin and Tjoelker 2003) employs the products of photosynthesis through the glycolysis (cytosol), the tricarboxylic acid cycle (TCA, matrix of mitochondria) and the electron transport rate chain (ETC, inner membrane mitochondria) to produce ATP and carbon skeletons needed for growth, cell maintenance, and other essential cellular processes. During the process of respiration, O2 is consumed, and CO2 is released to the atmosphere within the same order of magnitude than photosynthesis (Jansson et al. 2010), which highlights the importance of considering this process in the leaves, whole-plant and global models of carbon, water, and oxygen fluxes (Valentini et al. 2000; Canadell et al. 2007; Atkin et al. 2015). The velocity and extent of both processes can be assessed at the leaf level using infrared-based gas exchange analysers.

Optimal and synchronized germination of Robinia pseudoacacia, Acacia dealbata and other woody Fabaceae using a handheld rotary tool: concomitant reduction of physical and physiological seed dormancy

AbstractThe Fabaceae (legume family) is one of the largest families of plants with a worldwide distribution and a major role in agriculture and in agroforestry. A hard seed coat impermeable to water is a typical feature of several species. Physical dormancy delays and reduces germination so that mechanical, physical and chemical scarification methods have been classically used to break seed dormancy of many species. We evaluate the effectiveness of a methodology to scarify seeds of several woody Fabaceae of ecological and economical importance, including Robinia pseudoacacia and Acacia dealbata and the shrubs Cytisus scoparius, C. multiflorus and Ulex europaeus. We describe the optimized use of a handheld rotary tool (HRT), and compare its effectiveness with other scarification methods reported to break dormancy such as boiling or dry heating. Total germination and/or speed of germination were enhanced after the application of the HRT, with germination percentages significantly higher than those achieved by other methods of scarification. Based on a thorough literature review, a mode of action for the HRT is suggested which could operate by breaking the physical and physiological dormancy of treated seeds through the combined action of coat abrasion and moderate temperatures. Considering these results, we recommend the application of this rapid, effective, low-cost and highly reproducible HRT method to break seed dormancy and enhance germination of these species and others with similar dormancy constraints.