Mixed heavy metal stress on photosynthesis, transpiration rate, and chlorophyll content in poplar hybrids

Abstract

The present work aimed to study the physiological effects of mixed heavy metals, cadmium (Cd), copper (Cu), chromium (Cr), and zinc (Zn) in four poplar hybrids. Poplar hybrids were treated once with six different concentrations (0, 5, 50, 100, 200, and 500 ppm) of mixed heavy metals for a period of 3 months. The photosynthetic and transpiration rates were measured before and during treatment using an LCiÀSD portable photosynthesis system whereas the photosynthetic pigments were analytically determined. According to the results obtained, poplar hybrids exhibited a decrease in chlorophyll content and carotenoids except for hybrid 1 (Eco 28) which showed an increase at 200 and 500 ppm heavy metal concentrations. The photosynthetic rate decreased with increasing heavy metal concentrations; however, an increase was observed at the highest concentration of 500 ppm at 14.54 mmol m ¡2 s ¡1 . Transpiration rates were significantly affected by increased heavy metals. Hybrid 1 (Eco 28) was deduced as the hybrid that has the ability to tolerate high levels of mixed heavy metals. Among the four poplar hybrids tested, hybrid 1 (Eco 28) was the best candidate for phytoremediative experiments under greenhouse conditions. These results are valuable in understanding how various tree hybrids respond to mixed heavy metal stress, especially when using them as bio indicators for phytoremediation experiments.

Gas exchange responses of two poplar clones (Populus euramericana (Dode) Guinier 561/41 and Populus nigra Linnaeus 63/135) to lead toxicity

“…Similarly, Pajević et al (2009) showed that A and E were significantly decreased in most of the Populus and Salix clones exposed to Pb, Cd, Ni. In addition, the reduction of A, E, g s in different poplar clones under heavy metal stress has been reported by Gu et al (2007), Pietrini et al (2010), and Chandra and Kang (2015). The inhibition of plant photosynthetic parameters under heavy metal stress results in damage to photosynthetic enzymes and chloroplast membranes, decrease in chlorophyll synthesis, replacement of heavy metals in the chlorophyll molecule, accumulation of heavy metals in the photosynthetic organs of plants (leaves) and interference of metal ions with the uptake of essential elements of the photosynthetic process (Chandra, Kang 2015).…”

“…In addition, Pajević et al (2009) demonstrated that photosynthesis and transpiration in most of the studied Populus Linnaeus and Salix Linnaeus clones exposed to Pb, Cd and Ni decreased significantly. Also, the decline in gas exchange parameters of different poplar clones in response to heavy metal stress has been shown by Gu et al (2007), Pietrini et al (2010), and Chandra and Kang (2015). On the other hand, He et al (2013) showed that while Cd exposure caused a decline in the photosynthesis of four poplar species (Populus alba Linnaeus × Populus glandulosa Ueki, Populus euramericana (Dode) Guinier, Populus cathayana Rehder, and Populus deltoides Bartram ex Marshall), no change was observed on Populus nigra Linnaeus and Populus popularis.…”

“…As regards, some physiological characteristics can be used as indicators of tolerance to contamination, while the analysis of gas exchange could show plant responses to heavy metal stress (Pietrini et al 2003). Likewise, in literature it has been reported that tree species belonging to the family Salicaceae are attended as ideal candidates for phytoremediation of soils contaminated with heavy metals, due to the extensive root system, fast growth, large biomass production, metal tolerance and metal accumulation potential (Bittsánszky et al 2009;Chandra, Kang 2015;Hosseini et al 2015). In general, Salicaceae species exhibit good tolerance to heavy metals, but interspecific and intraspecific differences do exist (Mrnka et al 2012).…”

“…On the other hand, trees have the capability to effectively stabilize the soil with their root system, prevent erosion, and reduce the spread of contaminants. Also, trees can be easily harvested and removed from the area with minimal risk, effectively taking with them a high quantity of the contaminants that were present in the soil (Paz-Alberto, Sigua 2013;Chandra, Kang 2015).…”

Response surface methodology based optimization of cadmium and lead remediation from aqueous solution by water hyacinth (Eichhornia crassipes [Mart.] Solms) and its anatomical study

“…However, excess of any kind of metal adversely affects plant metabolism and growth rate (Hall, 2002;Chandra and Kang, 2016). Stomata aperture is strongly regulated by divergent exogenous stimuli, such as light, drought stress, pathogens, temperature and others (Acharya and Assmann, 2009).…”