Photosynthesis and aboveground carbon allocation of two co-occurring poplar species in an urban brownfield

Beyond Cleansing: Ecosystem Services Related to Phytoremediation

Phytotechnologies used for cleaning up urban and suburban polluted soils (i.e., brownfields) have shown some weakness in the excessive extent of the timeframe required for them to be effectively operating. This bottleneck is due to technical constraints, mainly related to both the nature of the pollutant itself (e.g., low bio-availability, high recalcitrance, etc.) and the plant (e.g., low pollution tolerance, low pollutant uptake rates, etc.). Despite the great efforts made in the last few decades to overcome these limitations, the technology is in many cases barely competitive compared with conventional remediation techniques. Here, we propose a new outlook on phytoremediation, where the main goal of decontaminating should be re-evaluated, considering additional ecosystem services (ESs) related to the establishment of a new vegetation cover on the site. The aim of this review is to raise awareness and stress the knowledge gap on the importance of ES associated with this technique, which can make phytoremediation a valuable tool to boost an actual green transition process in planning urban green spaces, thereby offering improved resilience to global climate change and a higher quality of life in cities. This review highlights that the reclamation of urban brownfields through phytoremediation may provide several regulating (i.e., urban hydrology, heat mitigation, noise reduction, biodiversity, and CO₂ sequestration), provisional (i.e., bioenergy and added-value chemicals), and cultural (i.e., aesthetic, social cohesion, and health) ESs. Although future research should specifically be addressed to better support these findings, acknowledging ES is crucial for an exhaustive evaluation of phytoremediation as a sustainable and resilient technology.

Free amino acids, carbon and nitrogen isotopic compositions responses to cadmium stress in two castor (Ricinus communis L.) species

Cadmium (Cd) toxicity induce various disturbances in metabolic processes and impair plant establishment. The composition of carbon and nitrogen stable isotopes (δ¹³C and δ¹⁵N) and free amino acids (FAAs) can reflect the response of plants to environmental stress. In the present study, a solution culture experiment was carried out, and the secretion characteristics of FAAs as well as δ¹³C and δ¹⁵N were evaluated as indicative of the functional performance of two castor species (Zibo-3 and Zibo-9) under various Cd concentrations stress (0, 1, 2, and 5 mg L^-1). The results indicated that: 1) The treatment of the plants with 5 mg L^-1 of a Cd solution resulted in a significant decline of biomasses by 22.4% and 11.6% in Zibo-3 and Zibo-9, respectively, relative to controls; additionally, the accumulation levels for Cd in Zibo-9 were higher than those in Zibo-3, thus Zibo-9 showed higher tolerance and enrichment ability to Cd. 2) The exposure of castor to Cd treatments results in significant modifications in individual FAAs, suggesting a differential sensitivity of each biosynthetic pathway to this stress; however, a positive correlation was found between the accumulation of total FAAs and Cd treatment dosages; higher proportion of asparagine and glutamate in total amino acids for Zibo-9, and abundant secretion of arginine in Cd treated Zibo-9 may be associated with the higher Cd-tolerance and Cd-accumulation in Zibo-9. 3) Cd stress increased leaf δ¹³C and δ¹⁵N values regardless of the castor species; δ¹³C and δ¹⁵N could be used as monitoring tools for heavy metal stress in plants.

Ecosystem Services, Physiology, and Biofuels Recalcitrance of Poplars Grown for Landfill Phytoremediation

Long-term poplar phytoremediation data are lacking, especially for ecosystem services throughout rotations. We tested for rotation-age differences in biomass productivity and carbon storage of clones Populus deltoides Bartr. ex Marsh × P. nigra L. ‘DN34′ and P. nigra × P. maximowiczii A. Henry ‘NM6′ grown for landfill phytoremediation in Rhinelander, WI, USA (45.6° N, 89.4° W). We evaluated tree height and diameter, carbon isotope discrimination (Δ), and phytoaccumulation and phytoextraction of carbon, nitrogen, and inorganic pollutants in leaves, boles, and branches. We measured specific gravity and fiber composition, and determined biofuels recalcitrance of the Rhinelander landfill trees versus these genotypes that were grown for biomass production on an agricultural site in Escanaba, MI, USA (45.8° N, 87.2° W). ‘NM6′ exhibited 3.4 times greater biomass productivity and carbon storage than ‘DN34′, yet both of the clones had similar Δ, which differed for tree age rather than genotype. Phytoaccumulation and phytoextraction were clone- and tissue-specific. ‘DN34′ generally had higher pollutant concentrations. Across contaminants, stand-level mean annual uptake was 28 to 657% greater for ‘NM6′, which indicated its phytoremediation superiority. Site-related factors (not genotypic effects) governed bioconversion potential. Rhinelander phytoremediation trees exhibited 15% greater lignin than Escanaba biomass trees, contributing to 46% lower glucose yield for Rhinelander trees.

Comparative analysis of the seed germination of pakchoi and its phytoremediation efficacy combined with chemical amendment in four polluted soils

The seed germination plant growth parameters and level of heavy metal accumulation were investigated in pakchoi cultured in four contaminated soils with different levels of heavy metals supplemented with citric acid (CA) or calcium phosphate (CP). Results showed that the seed germination energy, germination percentage and germination index parameters were similar, while the seed vigor (SV) significantly (p < 0.05) decreased as the soil pollution level increased. The lengths of the shoots and roots presented the same trend as SV. All the seedlings grew in heavily polluted soil without any amendments before harvesting; therefore, no plant material was available for subsequent analyses. The photosynthesis parameters of pakchoi cultured in lightly polluted soil without amendment (LPS), lightly polluted soil with CA (LPSA) and moderately polluted soil with CP (MPSP) were similar. The concentrations of Pb, Zn, Mn, Cu and Cd in the shoots, roots and whole plants were in the order of MPSP > LPSA > LPS. Pakchoi cultured in MPSP showed the most promising results in terms of plant height, biomass and heavy metal accumulation. Pakchoi presented the highest translocation and bioaccumulation factors for Cd and the lowest for Pb.HighlightsSoil pollution and the type of chemical amendment had no effect on the seed germination of pakchoi.Citric acid addition in lightly polluted soil improved pakchoi growth and heavy metal extraction.Pakchoi cultured in moderately polluted soil with calcium phosphate amendment presented the highest biomass and heavy metal concentration.

Nature based solutions for contaminated land remediation and brownfield redevelopment in cities: A review

Urban industrialization has caused severe land contamination at hundreds of thousands of sites in cities all around the world, posing a serious health risk to millions of people. Many contaminated brownfield sites are being left abandoned due to the high cost of remediation. Traditional physical and chemical remediation technologies also require high energy and resource input, and can result in loss of land functionality and cause secondary pollution. Nature-based solutions (NBS) including phytoremediation and conversion of brownfield sites to public greenspaces, holds much promise in maximizing a sustainable urban renaissance. NBS is an umbrella concept that can be used to capture nature based, cost effective and eco-friendly treatment technologies, as well as redevelopment strategies that are socially inclusive, economically viable, and with good public acceptance. The NBS concept is novel and in urgent need of new research to better understand the pros and cons, and to enhance its practicality. This review article summarizes NBS's main features, key technology choices, case studies, limitations, and future trends for urban contaminated land remediation and brownfield redevelopment.

Differential effects of nickel dosages on in vitro and in vivo seed germination and expression of a high affinity nickel-transport family protein (AT2G16800) in trembling aspen (Populus tremuloides)

It has been demonstrated that a number of metals including mercury (Hg), zinc (Zn), cadmium (Cd), cobalt (Co), lead (Pb), copper (Cu), and nickel (Ni) decrease seed germination rates and plant growth. The threshold levels of metal toxicity on seed germination, plant development, and gene regulation have not been studied in detail. The main objective of this study was to assess in vitro and in vivo the effects of different doses of nickel on Trembling aspen (Populus tremuloides) seed germination and regulation of the high affinity nickel transporter family protein (AT2G16800) gene. The in vitro assays showed that Nickel completely inhibited seed germination even at the lowest concentration of 0.401 mg Ni per mL (in media) tested. However, when the same concentration of nickel (150 mg Ni per 1 kg of dry soil) was added to soil samples, during the vivo assays, almost all of the seeds germinated. Significant inhibition of seed germination was observed when soil samples were treated with at least 400 mg/kg of Ni. No damages were observed on growing seedlings treated with 150, 400, and 800 mg/kg of Ni. Only the highest dose of 1, 600 mg/kg resulted in visible leaf and stem damages and reduced growth on 75% of seedlings. A significant repression of the AT2G16800 gene was observed for the 400, 800, and 1600 mg/kg of nickel treatments compared to the water control with the lowest level of expression observed in samples treated with 800 mg/kg of Ni. Results of this study suggest that P. tremuloides populations will likely be sustainable for long term in sites that are highly contaminated with Ni including mining regions since the bioavailable amount of this metal is usually below 400 mg/kg in Canada.

Urban Re-Greening: A Case Study in Multi-Trophic Biodiversity and Ecosystem Functioning in a Post-Industrial Landscape

The biodiversity of urban and post-industrial ecosystems is a highly relevant and growing new frontier in ecological research. Even so, the functionality of these ecosystems may not always be successfully predicted based on prior biodiversity and ecosystem functioning theory. Indeed, evidence suggests that the general biological impoverishment within the urban context envisioned thirty years ago was overstated. Many of the world’s urban centers support some degree of biodiversity that is indigenous, as well as a complex array of non-native species, resulting in highly functional, and often, novel communities. For over two decades, a multi-disciplinary team has examined the sub-lethal impact of soil metal contamination on the multi-trophic biodiversity and ecosystem functioning of a post-industrial brownfield in the New York City metropolitan area. We do this through examinations of photosynthesis, carbon allocation, and soil enzyme activity as well as multi-trophic metal translocation via the plant and rhizosphere. In this paper, we synthesize the findings of our research network and apply the results to a framework of functional diversity. Due to the unique constraints many post-industrial lands impose on communities, functional diversity may be more meaningful to ecosystem health than species richness.

Maintenance of photosynthesis by Betula populifolia in metal contaminated soils

Improving our understanding of plant responses to elevated trace metal concentrations under field conditions will enhance restoration and urban greening practices in settings with contaminated soils. This study examined the effects of trace metal pollution on the leaf gas exchange rates of mature, field-grown Betula populifolia Marsh. (gray birch) trees, additionally assessing whether elevated temperature and drought compounded the effects of trace metal contamination. The study compared B. populifolia growing in areas of comparatively high and low trace metal loads (HML and LML, respectively) within a former rail yard at Liberty State Park in Jersey City, New Jersey, USA. Gas exchange parameters were determined monthly from May through September in 2014 and 2015 using a portable photosynthesis system. The effects of drought and high temperature were assessed during a short heat wave in July 2015 and via a manipulative experiment, respectively. During a few of the measurement months, some parameters differed significantly between the LML and HML groups. However, when considered over the entire study period, no significant differences in biophysical parameters were observed between groups. The photosynthetic capacity of B. populifolia thus appears to be fairly robust across this site's steep gradient of trace metal contamination. Nonetheless, leaf mass per unit area was significantly lower in the HML group, indicating that metal loads affected resource allocation within trees. Also, immediately following the heat wave in 2015, intrinsic water use efficiency declined significantly in the HML group, suggesting that extreme climatic conditions can have a disproportionate effect on the physiological performance of plants growing in metal contaminated soils.