Phytostabilisation can benefit from phytostimulatory rhizobacteria. Forty-three bacterial strains were isolated from the roots of the metallicolous legume Anthyllis vulneraria ssp. carpatica grown in a highly contaminated mine tailing (total Cd, Pb and Zn were up to 1200; 34,000; and 170,000 mg kg(-1), respectively). We aimed at evaluating their phytostimulatory effects on the development of leguminous metallophytes. Strains were screened for fluorescent siderophores and auxin synthesis, inorganic P solubilisation and 1-amino-cyclopropane-1-carboxylate deaminase (ACCd) activity to define a subset of 11 strains that were inoculated on the leguminous metallophytes A. vulneraria and Lotus corniculatus grown in diluted mine spoil (Zn 34,653; Pb 6842; and Cd 242, all in mg kg-1). All strains were affiliated to Pseudomonas spp. (except two), synthetised auxins and siderophores and solubilised P (except three), and seven of them were ACCd positive. The inoculation effects (shoot-root-nodule biomass, chlorophyll content) depended on legume species and bacterial strain genotype. Phytostimulation scores were unrelated to siderophore/auxin synthesis and P solubilisation rates. Inoculations of the strain nos. 17-43 triggered a 1.2-fold significant increase in the chlorophyll content of A. vulneraria. Chlorophyll content and root biomass of L. corniculatus were significantly increased following the inoculations of the strain nos. 17-22 (1.5-1.4-fold, respectively). The strongest positive effects were related to increases in the nodule biomass of L. corniculatus in the presence of three ACCd-positive strains (1.8-fold), one of which was the highest auxin producer. These data suggest to focus on interactions between ACCd activity and auxin synthesis to enhance nodulation of metallicolous legumes.

Phytostabilisation can benefit from phytostimulatory rhizobacteria. Forty-three bacterial strains were isolated from the roots of the metallicolous legume Anthyllis vulneraria ssp. carpatica grown in a highly contaminated mine tailing (total Cd, Pb and Zn were up to 1200; 34,000; and 170,000 mg kg(-1), respectively). We aimed at evaluating their phytostimulatory effects on the development of leguminous metallophytes. Strains were screened for fluorescent siderophores and auxin synthesis, inorganic P solubilisation and 1-amino-cyclopropane-1-carboxylate deaminase (ACCd) activity to define a subset of 11 strains that were inoculated on the leguminous metallophytes A. vulneraria and Lotus corniculatus grown in diluted mine spoil (Zn 34,653; Pb 6842; and Cd 242, all in mg kg-1). All strains were affiliated to Pseudomonas spp. (except two), synthetised auxins and siderophores and solubilised P (except three), and seven of them were ACCd positive. The inoculation effects (shoot-root-nodule biomass, chlorophyll content) depended on legume species and bacterial strain genotype. Phytostimulation scores were unrelated to siderophore/auxin synthesis and P solubilisation rates. Inoculations of the strain nos. 17-43 triggered a 1.2-fold significant increase in the chlorophyll content of A. vulneraria. Chlorophyll content and root biomass of L. corniculatus were significantly increased following the inoculations of the strain nos. 17-22 (1.5-1.4-fold, respectively). The strongest positive effects were related to increases in the nodule biomass of L. corniculatus in the presence of three ACCd-positive strains (1.8-fold), one of which was the highest auxin producer. These data suggest to focus on interactions between ACCd activity and auxin synthesis to enhance nodulation of metallicolous legumes.

The growth, development and functioning of legumes are often significantly affected by exposure to tropospheric ozone (O3) pollution. However, surprisingly little is known about how leguminous Nitrogen (N) fixation responds to ozone, with a scarcity of studies addressing this question in detail. In the last decade, ozone impacts on N-fixation in soybean, cowpea, mung bean, peanut and clover have been shown for concentrations which are now commonly recorded in ambient air or are likely to occur in the near future. We provide a synthesis of the existing literature addressing this issue, and also explore the effects that may occur on an agroecosystem scale by predicting reductions in Trifolium (clovers) root nodule biomass in United Kingdom (UK) pasture based on ozone concentration data for a “high” (2006) and “average” ozone year (2008). Median 8% and 5% reductions in clover root nodule biomass in pasture across the UK were predicted for 2006 and 2008 respectively. Seasonal exposure to elevated ozone, or short-term acute concentrations >100 ppb, are sufficient to reduce N-fixation and/or impact nodulation, in a range of globally-important legumes. However, an increasing global burden of CO2, the use of artificial fertiliser, and reactive N-pollution may partially mitigate impacts of ozone on N-fixation.

Globally, the legume–rhizobia symbiosis, contained within specialised organs called root nodules, is thought to add at least 30 Tg N annually to agricultural land. The growth and functioning of a modern white clover (Trifolium repens cv. Crusader) and red clover (T. pratense cv. Merviot) cultivar were investigated in current and future ozone scenarios in solardomes. Both cultivars developed leaf injury and had significant reductions in root biomass and root nodule number in response to ozone, with Crusader also displaying a reduced size and mass of nodules. In-situ measurements of N-fixation in Crusader by acetylene reduction assay revealed reduced N-fixation rates in a future scenario with an increased background and moderate peaks of ozone. The implications for the sustainability of temperate pasture are discussed.

Saplings of alder (Alnus glutinosa), birch (Betula pendula), hazel (Corylus avellana), beech (Fagus sylvatica), ash (Fraxinus excelsior) and oak (Quercus robur) were exposed to five episodic ozone regimes in solardomes, with treatment means between 16 and 72 ppb. All trees were kept fully watered for the first 5 weeks of exposure, after which half the trees continued to be well-watered, whereas the other half were subjected to a moderate drought by applying approximately 45 % of the amount of water. Species-specific reductions in growth in response to both ozone and drought were found, which could result in reduced potential carbon sequestration in future ozone climates. In well watered conditions, the ozone treatments resulted in total biomass reductions for oak (18 %), alder (16 %), beech (15 %), ash (14 %), birch (14 %) and hazel (7 %) in the 72 ppb compared with the 32 ppb treatment. For beech, there was a reduction in growth in response to ozone in the well-watered treatment, but an increase in growth in response to ozone in the drought treatment, in contrast to the decreased growth that would occur as a result of stomatal closure in response to either the ozone or drought treatment, and therefore assumed to result from changes in hormonal signalling which could result in stomatal opening in combined ozone and drought conditions. For alder, in addition to a decrease in root biomass, there was reduced biomass of root nodules with high compared with low ozone for both drought-treated and well-watered trees. There was also a large reduction in the biomass of nodules from drought trees compared with well-watered. It is therefore possible that changes in the nitrogen dynamics of alder could occur due to reduced nodulation in both drought and elevated ozone conditions.

Fast-growing metal-accumulating woody plants are considered potential candidates for phytoextraction of metals. Shuikoushan mining, one of the biggest Pb and Zn production bases in China, presents an important source of the pollution of environment during the last 100 years. Over 150 km²of fertile soil have been contaminated by the dust, slag, and tailings from this mining. The goal of the present work has been to determine the content of Pb, Zn, Cd, and Cu in wild woody plants (18 species) naturally growing in this area. Two hundred five plant and soil samples from 11 contaminated sites were collected and analyzed. In addition, to assess the ability of multi-metal accumulation of these trees, we proposed a predictive comprehensive bio-concentration index (CBCI) based on fuzzy synthetic assessment. Our data suggest some adult trees could also accumulate a large amount of metals. Pb concentrations in leaves of Paulownia fortunei (Seem.) Hemsl. (1,179 mg/kg) exceeded the hyperaccumulation threshold (1,000 mg/kg). Elevated Pb concentrations (973.38 mg/kg) were also found in the leaves of Broussonetia papyrifera (L.) Vent., with a Pb bio-concentration factor of up to 0.701. Endemic species, Zenia insignis Chun exhibited huge potential for Zn and Cd phytoextraction, with the highest concentrations of Zn (1,968 mg/kg) and Cd (44.40 mg/kg), characteristic root nodules, and fast growth rates in poor soils. As for multi-metal accumulation ability, native species B. papyrifera was calculated to have the most exceptional ability to accumulate various metals simultaneously (CBCI 2.93), followed by Amorpha fruticosa L. (CBCI 2.72) and Lagerstroemia indica L. (CBCI 2.53). A trend of increasing metal from trunks to leaves (trunks < branches < leaves) and towards fine roots has been shown by metal partitioning between tissues. The proposed CBCI would allow for the selection of suitable trees for phytoremediation in the future.