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

Abstract

Phytoremediation, a technique used to reclaim heavy metal-contaminated soils, requires an understanding of plant physiological responses to heavy metals. However, the majority of studies documenting heavy metal impact on plant functioning have been performed in laboratory or greenhouse settings. We predicted that increased soil heavy metal concentrations reduce photosynthesis and biomass production in trees growing in metal contaminated soil in a naturally re-vegetated urban brownfield. Leaf gas exchange, leaf carbon and nitrogen concentration, and tree biomass were recorded and compared for Populus deltoides and Populus tremuloides growing in an urban brownfield. The CO compensation point (CCP) differed significantly between soil metal concentrations and species, with P. deltoides displaying a greater CCP and P. tremuloides displaying a lower CCP as soil metal concentration increased, despite no changes in dark respiration for either species. In terms of biomass, only total branch weight (TBW) and leaf area (LA) differed significantly between soil metal concentrations, though the difference was largely attributable to variation in diameter at breast height (DBH). Furthermore, TBW and LA values for P. deltoides did not decrease with increasing soil metal concentration. Soil metal concentration, thus, had minimal effect on the relationship between tree age and DBH, and no effect on relationships of tree age and height or LA, respectively. Significant differences between soil metal concentrations and species were found for δN (isotopic nitrogen ratio) while leaf nitrogen content (% N) also differed significantly between species. Long-term water use efficiency derived from carbon isotope analysis (iWUE) differed significantly between trees grown on different soil metal concentrations and a significant species-metal concentration interaction was detected indicating that the two study species responded differentially to the soil metal concentrations. Specifically, P. tremuloides enhanced while P. deltoides reduced long-term iWUE as soil metal concentration increased, further emphasizing the importance of species and possible genotype selection for phytoremediation.

Carbon and nitrogen cycling in a lead polluted grassland evaluated using stable isotopes (δ13C and δ15N) and microbial, plant and soil parameters

“…A molecular approach, analyzing gene copies of different genes involved in N cycling, may reveal more details on which processes have been affected (Hallin et al 2009;Wallenstein and Vilgalys 2005). Previous studies on trees in heavy metal polluted mine tailing soil and an industrial urban soil also found a depletion in 15 N (Parraga-Aguado et al 2014;Radwanski et al 2017), which is in agreement with our finding in this study. On the contrary, in a forest soil surrounding a copper smelter, various tree and herbaceous species classified according to their mycorrhizal association showed an increase in 15 N, which was linked to increased rooting depth and/or a decrease in mycorrhizal formations (Chashchina et al 2018).…”

“…Furthermore, Pb is a metal which generally accumulates in roots, with very little translocation to shoots (Siedlecka 1995). Thus, despite detecting various negative effects of Pb on nutrient cycling, the slowly adapted ecosystem as a whole seems to be able to bear strong resistance to contamination, as previously reported (Radwanski et al 2017;Rantalainen et al 2006;Selonen and Setälä 2015).…”

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

“…However, specific leaf mass differences were. As in the former studies [47,63], both B. populifoloia and P. deltoids exhibited less mass per unit leaf area in areas of high soil metal loads. One plausible explanation is that there is a cost to production of phytochelatin enzymes, which are known to play a role in the detoxification of the metals once translocated [64].…”

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

“…Therefore, despite being beyond the scope of the current study, ∆-assisted, multi-trait selection of productive clones should be carefully considered in future efforts, focusing on both growth and high WUE [ 51 , 57 ]. Such efforts are important, as they take into account linkages between WUE and phytoremediation that are associated with potential stress impacts from landfill soil properties and contamination sources [ 10 , 31 , 32 , 33 , 34 , 35 ].…”

“…Thus, water use efficiency (WUE), which is strongly correlated with both δ 13 C stable carbon isotope ratios and carbon isotope discrimination (Δ) [ 29 , 30 ], is an important trait during genotype selection for phytoremediation. However, research using Δ in phytoremediation with trees is scarce [ 31 ], especially when considering potential stress impacts that are caused by landfill soil properties [ 32 , 33 ] and/or highly variable contamination sources [ 10 , 34 , 35 ] on plant water regimes during phytoremediation processes.…”