Lilian Marchand

The interplay of stress and mowing disturbance for the intensity and importance of plant interactions in dry calcareous grasslands

BACKGROUND AND AIMS There is still debate regarding the direction and strength of plant interactions under intermediate to high levels of stress. Furthermore, little is known on how disturbance may interact with physical stress in unproductive environments, although recent theory and models have shown that this interplay may induce a collapse of plant interactions and diversity. The few studies assessing such questions have considered the intensity of biotic interactions but not their importance, although this latter concept has been shown to be very useful for understanding the role of interactions in plant communities. The objective of this study was to assess the interplay between stress and disturbance for plant interactions in dry calcareous grasslands. METHODS A field experiment was set up in the Dordogne, southern France, where the importance and intensity of biotic interactions undergone by four species were measured along a water stress gradient, and with and without mowing disturbance. KEY RESULTS The importance and intensity of interactions varied in a very similar way along treatments. Under undisturbed conditions, plant interactions switched from competition to neutral with increasing water stress for three of the four species, whereas the fourth species was not subject to any significant biotic interaction along the gradient. Responses to disturbance were more species-specific; for two species, competition disappeared with mowing in the wettest conditions, whereas for the two other species, competition switched to facilitation with mowing. Finally, there were no significant interactions for any species in the disturbed and driest conditions. CONCLUSIONS At very high levels of stress, plant performances become too weak to allow either competition or facilitation and disturbance may accelerate the collapse of interactions in dry conditions. The results suggest that the importance and direction of interactions are more likely to be positively related in stressful environments.

Phytotoxicity testing of lysimeter leachates from aided phytostabilized Cu-contaminated soils using duckweed (Lemna minor L.)

Aided phytostabilization of a Cu-contaminated soil was conducted at a wood preservation site located in southwest France using outdoor lysimeters to study leaching from the root zone and leachate ecotoxicity. The effects of Cu-tolerant plants (Agrostis gigantea L. and Populus trichocarpa x deltoides cv. Beaupré) and four amendments were investigated with seven treatments: untreated soil without plants (UNT) and with plants (PHYTO), and planted soils amended with compost (OM, 5% per air-dried soil weight), dolomitic limestone (DL, 0.2%), Linz-Donawitz slag (LDS, 1%), OM with DL (OMDL), and OM with 2% of zerovalent iron grit (OMZ). Total Cu concentrations (mgkg(-1)) in lysimeter topsoil and subsoil were 1110 and 111-153, respectively. Lysimeter leachates collected in year 3 were characterized for Al, B, Ca, Cu, Fe, Mg, Mn, P, K and Zn concentrations, free Cu ions, and pH. Total Cu concentration in leachates (mgL(-1)) ranged from 0.15±0.08 (LDS) to 1.95±0.47 (PHYTO). Plants grown without soil amendment did not reduce total Cu and free Cu ions in leachates. Lemna minor L. was used to assess the leachate phytotoxicity, and based on its growth, the DL, LDS, OM and OMDL leachates were less phytotoxic than the OMZ, PHYTO and UNT ones. The LDS leachates had the lowest Cu, Cu(2+), Fe, and Zn concentrations, but L. minor developed less in these leachates than in a mineral water and a river freshwater. Leachate Mg concentrations were in decreasing order OMDL>DL>PHYTO=OM=LDS>UNT=OMZ and influenced the duckweed growth.

Arundo donax L., a candidate for phytomanaging water and soils contaminated by trace elements and producing plant-based feedstock. A review.

Plants and associated microorganisms are used to remediate anthropogenic metal(loid) contamination of water, soils and sediments. This review focuses on the potential of Arundo donax L. (Giant reed) for alleviating risks due to soils, water, and sediments contaminated by trace elements (TE), with emphasis on its advantages and limits over macrophytes and perennial grasses used for bioenergy and plant-based feedstock. Arundo donax is relevant to phytomanage TE-contaminated matrices, notably in its native area, as it possesses characteristics of large biomass production even under nutrient and abiotic stresses, fast growth rate, TE tolerance and accumulation mainly in belowground plant parts. Cultivating A. donax on contaminated lands and in constructed wetlands can contribute to increase land availability and limit the food vs. plant-based feedstock controversy. To gain more tools for decision-taking and sustainable management, further researches on A. donax should focus on: interactions between roots, TE exposure, and rhizosphere and endophytic microorganisms; biomass response to (a)biotic factors; sustainable agricultural practices on marginal and contaminated land; integration into local, efficient, energy and biomass conversion chains with concern to biomass quality and production; Life-Cycle Assessment including contaminant behavior, as well as environmental, agricultural and socio-economic benefits and drawbacks.

Influence of biochars, compost and iron grit, alone and in combination, on copper solubility and phytotoxicity in a Cu-contaminated soil from a wood preservation site

Two biochars, a green waste compost and iron grit were used, alone and in combination, as amendment to improve soil properties and in situ stabilize Cu in a contaminated soil (964mgCukg(-1)) from a wood preservation site. The pot experiment consisted in 9 soil treatments (% w/w): untreated Cu-contaminated soil (Unt); Unt soil amended respectively with compost (5%, C), iron grit (1%, Z), pine bark-derived biochar (1%, PB), poultry-manure-derived biochar (1%, AB), PB or AB+C (5%, PBC and ABC), and PB or AB+Z (1%, PBZ and ABZ). After a 3-month reaction period, the soil pore water (SPW) was sampled in potted soils and dwarf beans were grown for a 2-week period. In the SPW, all amendments decreased the Cu(2+) concentration, but total Cu concentration increased in all AB-amended soils due to high dissolved organic matter (DOM) concentration. No treatment improved root and shoot DW yields, which even decreased in the ABC and ABZ treatments. The PBZ treatment decreased total Cu concentration in the SPW while reducing the gap with common values for root and shoot yields of dwarf bean plants. A field trial is underway before any recommendation for the PB-based treatments.

Potential of Ranunculus acris L. for biomonitoring trace element contamination of riverbank soils: photosystem II activity and phenotypic responses for two soil series

Foliar ionome, photosystem II activity, and leaf growth parameters of Ranunculus acris L., a potential biomonitor of trace element (TE) contamination and phytoavailability, were assessed using two riverbank soil series. R. acris was cultivated on two potted soil series obtained by mixing a TE (Cd, Cu, Pb, and Zn)-contaminated technosol with either an uncontaminated sandy riverbank soil (A) or a silty clay one slightly contaminated by TE (B). Trace elements concentrations in the soil-pore water and the leaves, leaf dry weight (DW) yield, total leaf area (TLA), specific leaf area (SLA), and photosystem II activity were measured for both soil series after a 50-day growth period. As soil contamination increased, changes in soluble TE concentrations depended on soil texture. Increase in total soil TE did not affect the leaf DW yield, the TLA, the SLA, and the photosystem II activity of R. acris over the 50-day exposure. The foliar ionome did not reflect the total and soluble TE concentrations in both soil series. Foliar ionome of R. acris was only effective to biomonitor total and soluble soil Na concentrations in both soil series and total and soluble soil Mo concentrations in the soil series B.

Complementarity of three distinctive phytoremediation crops for multiple-trace element contaminated soil

Trace element (TE) contaminated land represents an important risk to the environment and to human health worldwide. These soils usually contain a variety of TEs which can be a challenge for plant-based remediation options. As individual plant species often possess a limited range of TE remediation abilities, functional complementarity principles could be of value for remediation of soil contaminated by multiple TEs using assemblages of species. Monocultures and polycultures of Festuca arundinacea, Medicago sativa and Salix miyabeana were grown for 4months in aged-polluted soil contaminated by Ag, As, Cd, Cr, Cu, Pb, Se and Zn. Above and belowground biomass yields, root surface area (RSA) and TE tissue concentrations were recorded. In monoculture, the greatest aboveground biomass was produced by S. miyabeana (S), the greatest belowground biomass was from M. sativa (M) and F. arundinacea (F) produced the highest RSA. The polycultures of F+M, F+S and F+M+S produced among the highest values across all three traits. F. arundinacea monoculture and its combination with S. miyabeana (F+S) accumulated the highest amounts of total TEs in belowground tissues, whereas the most effective combination (or monoculture) for aboveground extraction yields varied depending on the TE considered. The crops demonstrated complementarity in their biomass allocation patterns as well as facilitative interactions. When considering contamination with a particular TE, the best phytomanagement approach could include a specific monoculture option; however, when above and belowground biomass allocation patterns, TE-remediation abilities as well as nitrogen accessibility are considered, co-cropping all three species (F+M+S) was the most robust scenario for remediation of multiple-TE contaminated land. By more effectively addressing a diversity of TE, species assemblage approaches could represent an important advancement towards enabling the use of plants to address contaminated-land issues worldwide.

Phytomanagement and Remediation of Cu-Contaminated Soils by High Yielding Crops at a Former Wood Preservation Site: Sunflower Biomass and Ionome

This long-term trial aimed at remediating the biomass production and other soil functions at a former wood preservation site. 28 field plots with total topsoil Cu in the 198 - 1169 mg kg-1 range were assessed. 24 plots (OMDL) were amended in 2008 with a compost (made of pine bark chips and poultry manure, OM, 5% w/w) and dolomitic limestone (DL, 0.2%), and thereafter annually phytomanaged with a sunflower – tobacco crop rotation; in 2013, one untreated plot (UNT) was amended with a green waste compost (GW, 5%) whereas 12 former OMDL plots received a second compost dressing using this green waste compost (OM2DL, 5%). In 2011, one plot was amended with the Carmeuse basic slag (CAR, 1%) and another plot with a P-spiked Linz-Donawitz basic slag (PLD, 1%). Thus six soil treatments, i.e. UNT, OMDL, OM2DL, GW, CAR and PLD, were cultivated in 2016 with sunflower (Helianthus annuus L. cv Ethic). Shoots were harvested, wet-digested and their ionome analysed. Soil texture and physico-chemical parameters were determined in all plots. All amendments improved the soil nutrient status and the soil pH, which was slightly acidic in the UNT soil. Total organic C and N and extractable P contents peaked in the OM2DL soils. Both OMDL and OM2DL treatments led to higher shoot DW yields and Cu removals than the GW, CAR and PLD treatments. Shoot DW yields decreased as total topsoil Cu rose in the OMDL plots, on the contrary to the OM2DL plots, demonstrating the benefits to repeat compost application after five years. Shoot Cu concentrations notably of OMDL and OM2DL plants fitted into their common range and can be used by biomass processing technologies and oilseeds as well. In overall, there is a net gain in soil physico-chemical parameters and underlying soil functions.

Using AFLP genome scanning to explore serpentine adaptation and nickel hyperaccumulation in Alyssum serpyllifolium

Background and aimsAlyssum section Odontarrhena is the largest single clade of Ni-hyperaccumulator plants, most of which are endemic to ultramafic (serpentine) soils. Alyssum serpyllifolium is a facultative hyperaccumulator able to grow both on limestone-derived and ultramafic soils. Analysis of different populations of this species with contrasting phenotypes could allow the identification of genes involved in Ni-hyperaccumulation and serpentine tolerance.MethodsA glasshouse pot experiment on compost-amended ultramafic soil was carried out with three ultramafic (U) and two non-ultramafic (NU) populations of A. serpyllifolium. The leaf ionome was determined by elemental analysis and used as a proxy for serpentine adaptation. A Ni-hyperaccumulating phenotype was estimated from leaf Ni concentrations. Cultured plants were genotyped using Amplified Fragment Length Polymorphism (AFLP) markers. Outlier analysis and regressions of leaf ionome over band distribution were applied to detect markers potentially involved in Ni-hyperaccumulation and serpentine tolerance.ResultsAs well as U populations, some plants from NU populations were found to be able to hyperaccumulate Ni in leaves to concentrations exceeding 0.1% (w/w). U populations had a higher Ca/Mg leaf ratio than NU populations, mainly due to Mg exclusion. 374 AFLP markers were amplified and a potential adaptive value was identified in 34 of those markers.ConclusionsPhenotype regression analyses were found to be more powerful than outlier analyses and indicated that regulation of foliar concentrations of Ni, Ca, Mg and P are the main factors involved in serpentine adaptation. More research is needed in order to resolve the ancestral or recently -evolved nature of Ni-hyperaccumulation.

Modulation of trace element bioavailability for two earthworm species after biochar amendment into a contaminated technosol

Biochars are used as amendments to improve soil quality, but their effects on edaphic organisms such as earthworms remain controversial. This study aimed to assess the effects of adding a poultry manure-derived biochar into a contaminated technosol on trace element (TE) (i.e. As, Cd, Cu, Pb, and Zn) bioavailability for two earthworm species, Aporrectodea icterica and Aporrectodea longa. Three components of the bioavailability concept were determined using a pot experiment: (1) total soil TE (potentially reactive) and TE concentrations in the soil pore water (environmental availability), (2) TE concentrations in depurated whole earthworm bodies (environmental bioavailability) and (3) ecophysiological and biochemical effects on earthworms (toxicological bioavailability). Biochar addition increased TE concentrations in the soil pore water respectively from 1.8, 2.7, 9.4, 0.7 and 959 to 6, 6.2, 19.3, 6.9, and 3003 µg L−1 for As, Cd, Cu, Pb and Zn. Biochar addition did not influence TE environmental bioavailability for earthworms, except a decreased As concentration (32.5 to 15.2 µg g−1) in A. icterica. This suggests an inter-specific variability in As homeostasis in the Aporrectodea genus. In line with this internal As decrease, the Glutathione-S-transferase (GST) activity decreased by 42% and protein and lipid contents slightly increased (14 and 25%, respectively) in A. icterica tissues. The body weight of both earthworm species decreased for the biochar-amended soil. Environmental TE availability depended on both the biochar addition and the earthworm activity in the contaminated soil, while environmental and toxicological bioavailabilities resulted from the earthworm species, the targeted TE and biochar supply to the soil.