In natural conditions, plants growth and development depends on environmental conditions, including the availability of micro- and macroelements in the soil. Nutrient status should thus be examined not by establishing the effects of single nutrient deficiencies on the physiological state of the plant but by combinations of them. Differences in the nutrient content significantly affect the photochemical process of photosynthesis therefore playing a crucial role in plants growth and development. In this work, an attempt was made to find a connection between element content in (i) different soils, (ii) plant leaves, grown on these soils and (iii) changes in selected chlorophyll a fluorescence parameters, in order to find a method for early detection of plant stress resulting from the combination of nutrient status in natural conditions. To achieve this goal, a mathematical procedure was used which combines principal component analysis (a tool for the reduction of data complexity), hierarchical k-means (a classification method) and a machine-learning method—super-organising maps. Differences in the mineral content of soil and plant leaves resulted in functional changes in the photosynthetic machinery that can be measured by chlorophyll a fluorescent signals. Five groups of patterns in the chlorophyll fluorescent parameters were established: the ‘no deficiency’, Fe-specific deficiency, slight, moderate and strong deficiency. Unfavourable development in groups with nutrient deficiency of any kind was reflected by a strong increase in F o and ΔV/Δt 0 and decline in φ Po, φ Eo δ Ro and φ Ro. The strong deficiency group showed the suboptimal development of the photosynthetic machinery, which affects both PSII and PSI. The nutrient-deficient groups also differed in antenna complex organisation. Thus, our work suggests that the chlorophyll fluorescent method combined with machine-learning methods can be highly informative and in some cases, it can replace much more expensive and time-consuming procedures such as chemometric analyses.Electronic supplementary materialThe online version of this article (10.1007/s11120-017-0467-7) contains supplementary material, which is available to authorized users.
Aims Ultramafic/serpentine soils constitute a stressful environment with many plant growth constrains such as a lack of macronutrients and high levels of potentially toxic metals. We considered the adaptive strategy of Lotus corniculatus L.-rhizobia symbiosis to Ni, Co and Cr stress conditions. Methods L. corniculatus nodulating rhizobia from ultramafic soil were isolated, identified and tested for nitrogen fixation, metal tolerance and plant growth promoting abilities. The structural and immunocytochemical analyses of root nodules were also performed. Results The isolates effective in nitrogen fixation were identified as Rhizobium and Mesorhizobium tolerant to Ni, Co, and Cr. Some strains directly promoted root growth of L. corniculatus and non-legume Arabidopsis thaliana under metal stress. The metal treated nodules showed structural alternations, i.e. enhanced accumulation of phenols and wall thickening with higher cellulose, hemicellulose, pectins, glycoproteins and callose content. Conclusions Our results revealed that metal tolerant, growth promoting rhizobacteria inhabiting L. corniculatus root nodules may improve plant growth in the ultramafic environment. Accumulation of phenols and reorganization of nodule apoplast can counteract harmful effects of Ni, Co and Cr on the symbiosis. These findings imply that L. corniculatus-rhizobia symbiosis is an important element of plant adaptation to metal stress occurring on the ultramafic soils.
Copper ore mining and processing release hazardous post-flotation wastes that are difficult for remediation. The studied tailings were extremely rich in Cu (1800 mg kg−1) and contaminated with Co and Mn, and contained very little available forms of P, Fe, and Zn. The plants growing in tailings were distinctly enriched in Cu, Cd, Co, Ni, and Pb, and the concentration of copper achived the critical toxicity level in shoots of Cerastium arvense and Polygonum aviculare. The redundancy analysis demonstrated significant relationship between the concentration of available forms of studied elements in substrate and the chemical composition of plant shoots. Results of the principal component analysis enabled to distinguish groups of plants which significantly differed in the pattern of element accumulation. The grass species Agrostis stolonifera and Calamagrostis epigejos growing in the tailings accumulated significantly lower amounts of Cu, but they also had the lowest levels of P, Fe, and Zn in comparison to dicotyledonous. A. stolonifera occurred to be the most suitable species for phytostabilization of the tailings with regard to its low shoot Cu content and more efficient acquisition of limiting nutrients in relation to C. epigejos. The amendments improving texture, phosphorus fertilization, and the introduction of native leguminous species were recommended for application in the phytoremediation process of the tailings.
This study examined the effects of waterlogging and forest litter introduced to soil on chemical properties of soil pore water and ecotoxicity of soils highly enriched in As. These effects were examined in a 21-day incubation experiment. Tested soil samples were collected from Złoty Stok, a historical centre of arsenic and gold mining: from a forested part of the Orchid Dump (19,600 mg/kg As) and from a less contaminated site situated in a neighboring forest (2020 mg/kg As). An unpolluted soil was used as control. The concentrations of As, Fe and Mn in soil pore water were measured together with a redox potential Eh. A battery of ecotoxicological tests, including a bioassay with luminescence bacteria Vibrio fischeri (Microtox) and several tests on crustaceans (Rapidtox, Thamnotox and Ostracodtox tests), was used to assess soil ecotoxicity. The bioassays with crustaceans (T. platyurus, H. incongruens) were more sensitive than the bacterial test Microtox. The study confirmed that the input of forest litter into the soil may significantly increase the effects of toxicity. Waterlogged conditions facilitated a release of As into pore water, and the addition of forest litter accelerated this effect thus causing increased toxicity.
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