Optimizing Crop Production with Bacterial Inputs: Insights into Chemical Dialogue between Sphingomonas sediminicola and Pisum sativum.

The use of biological inputs is an interesting approach to optimize crop production and reduce the use of chemical inputs. Understanding the chemical communication between bacteria and plants is critical to optimizing this approach. Recently, we have shown that Sphingomonas (S.) sediminicola can improve both nitrogen supply and yield in pea. Here, we used biochemical methods and untargeted metabolomics to investigate the chemical dialog between S. sediminicola and pea. We also evaluated the metabolic capacities of S. sediminicola by metabolic profiling. Our results showed that peas release a wide range of hexoses, organic acids, and amino acids during their development, which can generally recruit and select fast-growing organisms. In the presence of S. sediminicola, a more specific pattern of these molecules took place, gradually adapting to the metabolic capabilities of the bacterium, especially for pentoses and flavonoids. In turn, S. sediminicola is able to produce several compounds involved in cell differentiation, biofilm formation, and quorum sensing to shape its environment, as well as several molecules that stimulate pea growth and plant defense mechanisms.

A shift from phenol to silica-based leaf defences during long-term soil and ecosystem development.

The resource availability hypothesis predicts that plants adapted to infertile soils have high levels of anti-herbivore leaf defences. This hypothesis has been mostly explored for secondary metabolites such as phenolics, whereas it remains underexplored for silica-based defences. We determined leaf concentrations of total phenols and silicon (Si) in plants growing along the 2-million-year Jurien Bay chronosequence, exhibiting an extreme gradient of soil fertility. We found that nitrogen (N) limitation on young soils led to a greater expression of phenol-based defences, whereas old, phosphorus (P)-impoverished soils favoured silica-based defences. Both defence types were negatively correlated at the community and individual species level. Our results suggest a trade-off among these two leaf defence strategies based on the strength and type of nutrient limitation, thereby opening up new perspectives for the resource availability hypothesis and plant defence research. This study also highlights the importance of silica-based defences under low P supply.

Potential use of mealworm frass as a fertilizer: Impact on crop growth and soil properties.

Rearing insects is expected to dramatically increase during the next few years, and this will be associated with generating high quantities of frass (insect excreta). It is necessary to find solutions allowing the efficient valorization of these by-products before a major upscaling of the industry takes place. Therefore, this study aims at investigating the fertilizer potential of frass. A pot experiment was established and soil was amended either with mealworm (Tenebrio molitor L.) frass (10 Mg ha-1), with mineral fertilizer (NPK) at equivalent nutrient level to frass or with a mixture of 50% NPK and 50% frass. Changes of soil properties and growth and nutrient uptake by barley (Hordeum vulgare L.) were then analyzed. Due to its rapid mineralization and the presence of nutrient in a readily-available form, we found that frass is as efficient as mineral NPK fertilizer to improve biomass and N, P and K uptake by barley. Compared to mineral fertilizer, water soluble P concentration is five times lower in the presence of frass, which prevents P from loss and sorption onto soil constituents. More importantly, BIOLOG EcoPlate reveals that addition of frass stimulates soil microbial activity, especially when it is mixed with mineral fertilizer, suggesting a synergistic effect between both amendments. Taken together, our results indicate that frass has a great potential to be used as a partial or a complete substitute for mineral NPK fertilizer. This is especially relevant in the context of a reduced availability of mineral fertilizers while being consistent with circular economy's principles.

Plant Functional Traits: Soil and Ecosystem Services.

Decline of ecosystem services has triggered numerous studies aiming at developing more sustainable agricultural management practices. Some agricultural practices may improve soil properties by expanding plant biodiversity. However, sustainable management of agroecosystems should be performed from a functional plant trait perspective. Advances in functional ecology, especially plant functional trait effects on ecosystem processes and services, provide pivotal knowledge for ecological intensification of agriculture; this approach acknowledges that a crop field is an agroecosystem whose ecological processes influence soil properties. We highlight the links between plant functional traits and soil properties in relation to four major ecosystem processes involved in vital ecosystem services: food production, crop protection, climate change mitigation, and soil and water conservation, aiming towards ecological intensification of sustainable agricultural and soil management.

Copper and cobalt accumulation in plants: a critical assessment of the current state of knowledge.

This review synthesizes contemporary understanding of copper-cobalt (Cu-Co) tolerance and accumulation in plants. Accumulation of foliar Cu and Co to > 300 µg g-1 is exceptionally rare globally, and known principally from the Copperbelt of Central Africa. Cobalt accumulation is also observed in a limited number of nickel (Ni) hyperaccumulator plants occurring on ultramafic soils around the world. None of the putative Cu or Co hyperaccumulator plants appears to comply with the fundamental principle of hyperaccumulation, as foliar Cu-Co accumulation is strongly dose-dependent. Abnormally high plant tissue Cu concentrations occur only when plants are exposed to high soil Cu with a low root to shoot translocation factor. Most Cu-tolerant plants are Excluders sensu Baker and therefore setting nominal threshold values for Cu hyperaccumulation is not informative. Abnormal accumulation of Co occurs under similar circumstances in the Copperbelt of Central Africa as well as sporadically in Ni hyperaccumulator plants on ultramafic soils; however, Co-tolerant plants behave physiologically as Indicators sensu Baker. Practical application of Cu-Co accumulator plants in phytomining is limited due to their dose-dependent accumulation characteristics, although for Co field trials may be warranted on highly Co-contaminated mineral wastes because of its relatively high metal value.

Comparison of translocation methods to conserve metallophyte communities in the Southeastern D.R. Congo.

In southeastern Democratic Republic of Congo, unique metallophyte communities supporting numerous endemic species occurred on the highly mineralized copper cobalt (Cu-Co) hills throughout the province. These hills are economically valuable mineral reserves; mining activities represent therefore a threat to the long-term persistence of these communities. Ex situ conservation program was set up by a mining company to rescue and conserve the diversity of Cu-Co communities until restoration activities are initiated. Two kinds of Cu-Co communities: the steppe and the steppic savanna, were translocated using topsoil spreading and whole-turf translocation. In this study, we assessed the effectiveness of these two techniques in conserving Cu-Co communities and their potential use in future restoration programs. More than 2 years after the translocation, whole-turf translocation appeared to be the better technique for ex situ conservation of endemic Cu-Co species. Not only did whole-turf successfully translocate numerous target species that were not present in the topsoil areas, but it also resulted in fewer ruderal and non-target species compared to topsoil spreading. Topsoil spreading recorded low seedling emergence from seed bank due to large proportions of dormant seeds or the absence of a seed bank, especially for the steppic savanna. Restoration of the steppe is currently more successful than for steppic savanna where the lack of dominant and structuring species likely contributed to divergence in species composition compared to reference ecosystem. Our study stresses the fact that tropical old-growth grasslands, which require probably several centuries to assemble, are difficult to restore or translocate.

Potential of copper-tolerant grasses to implement phytostabilisation strategies on polluted soils in South D. R. Congo : Poaceae candidates for phytostabilisation.

Phytostabilisation (i.e. using plants to immobilise contaminants) represents a well-known technology to hamper heavy metal spread across landscapes. Southeastern D.R. Congo, Microchloa altera, a tolerant grass from the copper hills, was recently identified as a candidate species to stabilise copper in the soil. More than 50 grasses compose this flora, which may be studied to implement phytostabilisation strategies. However, little is known about their phenology, tolerance, reproductive strategy or demography. The present study aims to characterize the Poaceae that may be used in phytostabilisation purposes based on the following criteria: their ecological distribution, seed production at two times, abundance, soil coverage and the germination percentage of their seeds. We selected seven perennial Poaceae that occur on the copper hills. Their ecological distributions (i.e. species response curves) have been modelled along copper or cobalt gradients with generalised additive models using logic link based on 172 presence-absence samples on three sites. For other variables, a total of 69 quadrats (1 m(2)) were randomly placed across three sites and habitats. For each species, we compared the number of inflorescence-bearing stems (IBS) by plot, the percentage of cover, the number of seeds by IBS and the estimated number of seeds by plot between sites and habitat. Three species (Andropogon schirensis, Eragrostis racemosa and Loudetia simplex) were very interesting for phytostabilisation programs. They produced a large quantity of seeds and had the highest percentage of cover. However, A. schirensis and L. simplex presented significant variations in the number of seeds and the percentage of cover according to site.

Copper and cobalt mobility in soil and accumulation in a metallophyte as influenced by experimental manipulation of soil chemical factors.

The influence of Fe oxides, Mn oxides and organic matter (OM) on the Cu and Co mobility in soil and accumulation in the metallophyte Anisopappus chinensis (Ac), as compared with Helianthus annuus (Ha), was experimentally investigated. Growth and accumulation response when increasing the exchangeable Cu and Co concentrations in soil were also investigated. Plants were cultivated on soil where concentrations of Cu, Co, Fe oxides, Mn oxides and OM content were varied according to 36 treatments. The OM supply decreased the Cu mobility and increased the Co mobility, resulting in decreasing the foliar Cu of Ac and increasing the foliar Co of Ha. The Fe oxides supply could increase the Cu accumulation for Ac, but was not verified for Ha. Compared with Ha, Ac increasingly accumulated Cu and Co without negative effect on plant growth while increasing Cu and Co mobility to phytotoxic concentrations. The results revealed promising perspectives for the use of Ac in Cu-contaminated environment phytoremediation applications.

Phytostabilisation of copper-contaminated soil in Katanga: an experiment with three native grasses and two amendments.

This study evaluates the feasibility of using the grass species Rendlia altera, Monocymbium ceresiiforme, Cynodon dactylon, and amendments (compost and lime) for the phytostabilisation of soils contaminated by Cu in the province of Katanga (Democratic Republic of Congo). Species were grown on control and Cu-contaminated plots (artificially contaminated with 2,500 mg kg(-1) Cu) unamended (NA), amended with 4.5 kg compost m(-2) or 0.2 kg lime m(-2). R. altera was also grown on contaminated plots amended with 22.5 kg compost m(-2) or 1 kg lime m(-2). Plant survival, growth, and reproduction were monitored for two years. Cu-concentration in leaves of R. altera and M. ceresiiforme were analysed. pH and extractable Cu (0.01 M CaCl2) in soil were analysed in April 2007 and 2008. Results showed that R. altera seems to be the best candidate because of its highest survival on NA, followed by M. ceresiiforme, while liming was necessary to ensure survival of C. dactylon. Lime increased plant reproduction and reduced Cu accumulation in leaves compared to compost. However, higher survival and number of spikes of R. altera obtained in experiment 2 with 22.5 kg compost m(-2) suggest that lime x compost interactions should be investigated in further studies.

Genetic architecture of zinc hyperaccumulation in Arabidopsis halleri: the essential role of QTL x environment interactions.

SUMMARY: This study sought to determine the main genomic regions that control zinc (Zn) hyperaccumulation in Arabidopsis halleri and to examine genotype x environment effects on phenotypic variance. To do so, quantitative trait loci (QTLs) were mapped using an interspecific A. halleri x Arabidopsis lyrata petraea F(2) population. *The F(2) progeny as well as representatives of the parental populations were cultivated on soils at two different Zn concentrations. A linkage map was constructed using 70 markers. *In both low and high pollution treatments, zinc hyperaccumulation showed high broad-sense heritability (81.9 and 74.7%, respectively). Five significant QTLs were detected: two QTLs specific to the low pollution treatment (chromosomes 1 and 4), and three QTLs identified at both treatments (chromosomes 3, 6 and 7). These QTLs explained 50.1 and 36.5% of the phenotypic variance in low and high pollution treatments, respectively. Two QTLs identified at both treatments (chromosomes 3 and 6) showed significant QTL x environment interactions. *The QTL on chromosome 3 largely colocalized with a major QTL previously identified for Zn and cadmium (Cd) tolerance. This suggests that Zn tolerance and hyperaccumulation share, at least partially, a common genetic basis and may have simultaneously evolved on heavy metal-contaminated soils.