Crop rotation associating a legume and the nickel hyperaccumulator Alyssum murale improves the structure and biofunctioning of an ultramafic soil

Abstract

Nickel (Ni) agromining aims to phytoextract heavy metals using hyperaccumulators whilst at the same time rehabilitating ultramafic soils. After removing the bioavailable metal, ultramafic soils are improved in terms of their agronomic properties with the aim of future agricultural uses. The low fertility of ultramafic soils can be compensated by integrating legumes already used in traditional agro‐systems because of their importance in soil nitrogen enrichment. However, few studies have evaluated the potential profits of legumes on Ni agromining and their potential benefits on soil biological fertility. Here, we characterized the effect of a crop rotation with two plants, a legume (Vicia sativa) and a hyperaccumulator (Alyssum murale), on the phytoextraction efficiency and on soil structure and biofunctioning. A pot experiment was set up in controlled conditions to grow A. murale and four treatments were tested: rotation with V. sativa (Ro), fertilized mono‐culture (FMo), non‐fertilized mono‐culture (NFMo) and bare soil without plants (BS). No significant difference was found between the Ro and NFMo treatments for the dry biomass yield. However, the Ro treatment showed the highest Ni concentrations ([Ni]) in A. murale shoots compared to FMo and NFMo treatments. The Ro treatment plants had more than twice as many leaves [Ni] compared to FMo. Soil physico‐chemical analyses showed that the Ro treatment was better structured and showed the highest presence of bacterial micro‐aggregates, as well as less non‐aggregated particles. Legumes integration in Ni‐agromining systems could be a pioneering strategy to reduce chemical inputs and to improve soil biofunctioning and thus fertility.

Soil Microstructures Examined Through Transmission Electron Microscopy Reveal Soil-Microorganisms Interactions

“…Micrometer characterization of these fractions is thus well suited to identify microhabitats in relation to soil use. Others studies highlighted using the same approach to examine impacts of biological activity (by roots and microorganisms) on the stability and composition of 0-20 µm aggregates in a maizecropped soil (see section Soil-Microorganism Interactions at Hotspots of Biological Activity), the relationship between soil stability and the nature of aggregated organic matter from plants and microorganisms (Watteau et al, 2012) and the impact of crop rotation on soil structure (Saad et al, 2017). The biochemistry and turnover of organic matter are closely related to the size of organic matter and its associations with mineral soil components, and thus influence aggregate stability (Oades, 1984;Tiessen and Stewart, 1988).…”

A global forum on ultramafic ecosystems: from ultramafic ecology to rehabilitation of degraded environments

“…Two papers report on original results from the effects of agromining on soil biology, microbiology and quality. Saad et al (2018) discuss the effects of a new agro-ecological nickel agromining system that uses co-cropping of hyperaccumulators with legumes. Kanso et al (2018) report on the effect of nitrogen fertilization on agromining of Ni with Alyssum murale and subsequent effects on microbial diversity and functionality.…”

Bacterial community diversity in the rhizosphere of nickel hyperaccumulator plant species from Borneo Island (Malaysia)

“…These results concur not only with studies that use cultivation‐based approaches (Abou‐Shanab et al ., ; Álvarez‐López et al ., ) but also with studies based on molecular techniques using high‐throughput sequencing techniques. These studies underline that these three phyla were predominant in different environments with contaminated and non‐contaminated soils (Roesch et al ., ; Buée et al ., ; Chu et al ., ; Zhao et al ., ; Bordez et al ., ; Saad et al ., ) but also in the rhizosphere of hyperaccumulators found in temperate climate such as Albania or Greece (Lopez et al ., , ). Many studies suggest that Proteobacteria and Actinobacteria are the most common phyla in the rhizosphere of many plant species (Green and Bohannan, ; Singh et al ., ; Kaiser et al ., ) and bacteria belonging to these two phyla have been defined as copiotrophic (Fierer et al ., ; Kopecky et al ., ; Lienhard et al ., ).…”