N2O emissions from oil palm on mineral soils: measurements and modelling challenges

In oil palm plantations, addition of nitrogen (N) via legume cover crops and fertilisers is a common practice to achieve the yield potential of the crop. It is associated with effects on climate change through emissions of N2O (Choo et al., 2011). As oil palm is the most rapidly expanding tropical perennial crop, and is expected to keep expanding in the next decades (Corley, 2009), this raises environmental concerns.We reviewed the available measurements for N2O and other N fluxes in oil palm plantations on mineral soils (Pardon et al., 2016). We saw that direct N2O emissions were the most uncertain N flux, ranging from 0.01 to 7.3 kg N ha-1 yr-1, with a tendency to be higher during the immature phase, to decrease with the age of palms and to be higher in poorly drained soils (Ishizuka et al., 2005; Banabas, 2007). However, only very few measurements were available on mineral soils, and data is still lacking to better understand the potential effects of spatial heterogeneity in plantations (soil properties, soil cover) and management practices (e.g. fertiliser application timing, splitting, placement). Indirect N2O emissions were related to emissions of NH3 and NO3- which were particularly high during the immature phase when the N inputs are high while the palms are still young. We compared 11 existing models and 25 sub-models to simulate oil palm N budget and losses, among which 8, 9 and 8 sub-models were specific to N2O emissions, NH3 volatilisation, and NO3- losses through leaching and runoff; respectively (Pardon et al., under review). We saw that direct N2O emissions estimates were some of the most variable across models, ranging from 0.3 to 7 kg N ha-1 yr-1 (Mosier et al., 1998; Bouwman et al., 2002b; IPCC 2006, from Eggleston et al., 2006; Crutzen et al., 2008; Meier et al., 2012; APSIM from Huth et al., 2014 ; Shcherbak et al., 2014). The main influential factors on direct N2O emissions were the rate of mineral fertiliser applied and the emission factors of the models. The models accounting for felled palms decomposition, empty fruit bunches applications, and biological N fixation also estimated a peak of N2O emissions during the immature phase. Therefore direct and indirect emissions of N2O in oil palm plantations seemed not to be negligible in terms of environmental effect, with ranges of 11 to 2,425 and 79 to 2,443 kg CO2e ha-1 yr-1 for measured and modelled values; respectively (assuming a global warming potential of 298 for N2O). However, in order to be able to adapt management practices to mitigate these emissions, knowledge is still lacking to better understand the potential effects of spatial heterogeneity and management practices on direct and indirect N2O emissions The main modelling challenges are to model the impact of management practices, taking into account the soil N dynamics and residues decomposition, and this over the whole cycle

As, Pb, Sb, and Zn transfer from soil to root of wild rosemary: do native symbionts matter?

International audienceThis is an in natura study aimed to determine the potential of Rosmarinus officinalis for phytostabilization of trace metal and metalloid (TMM)-contaminated soils in the Calanques National Park (Marseille, southeast of France). The link between rosemary tolerance/accumulation of As, Pb, Sb, and Zn and root symbioses with arbuscular mycorrhizal (AM) fungi and/or dark septate endophytes (DSE) was examined. Eight sites along a gradient of contamination were selected for soil and root collections. TMM concentrations were analyzed in all the samples and root symbioses were observed. Moreover, in the roots of various diameters collected in the most contaminated site, X-ray microfluorescence methods were used to determine TMM localization in tissues. Rosemary accumulated, in its roots, the most labile TMM fraction in the soil. The positive linear correlation between TMM concentrations in soil and endophyte root colonization rates suggests the involvement of AM fungi and DSE in rosemary tolerance to TMM. Moreover, a typical TMM localization in root peripheral tissues of thin roots containing endophytes forming AM and DSE development was observed using X-ray microfluorescence. Rosemary and its root symbioses appeared as a potential candidate for a phytostabilization process of metal-contaminated soils in Mediterranean area

Phytoremediation using native plants

The unprecedented growth in industrialization has significantly increased pollution in the environment causing public health concerns. The remediation of various contaminated environmental matrices presents a global challenge. Phytoremediation using native plants can serve a dual purpose of site remediation and ecological restoration. Native plants provide an ideal residence for microbial community in their rhizosphere with enzymatic ability to accumulate, stabilize, biodegrade or volatilize various inorganic and organic contaminants. A case study that compared a native plant, Chromolaena odorata, from crude oil-polluted land in Nigeria against a referenced plant, Medicago sativa, for polycyclic aromatic hydrocarbons (PAHs) remediation is presented in this chapter. It was observed that the native plant thrived, tolerated and degraded PAHs better than the reference plant but with no significant difference in PAH degradation. The use of plants is well suited to its natural contaminated area and solar-driven, prevents erosion and eliminates secondary airborne and waterborne waste but with some challenges. Phytoremediation using native species may be effective and efficient than its non-native counterparts, and it is ecologically safer, cheaper, aesthetically pleasing, socially acceptable and easier to cultivate. Native plants in phytoremediation can be further enhanced and improved using molecular techniques to optimize the harvest time, reduce growth duration and increase biomass production and root depth