Cadmium induced changes in Solidago chilensis Meyen (Asteraceae) grown on organically fertilized soil with reference to mycorrhizae, metabolism, anatomy and ultrastructure

Effects of biochar and crop straws on the bioavailability of cadmium in contaminated soil

Numerous studies have been investigated the potential of biochar (BC) derived from various materials and crop straw (CS) to decrease the bioavailability of heavy metals in soil contaminated with cadmium (Cd), and thereby reduce their potential risk to human health and the ecological environment. However, little attention has been given to the comparison of heavy metal remediation efficiency using BC and CS such as peanut vine (PV) and rice straw (RS), especially in soil contaminated with Cd. Here, we explore if Cd bioavailability is affected in contaminated soil by BC and CS. Peanuts were grown in plastic pots, which contained BC or CS at 5% (dry weight, w/w) in controlled environment mesocosms. The bioavailability of Cd in contaminated soil was measured by Cd concentration in the plant and the concentrations of various forms of Cd in the soil. At the same plant age, growth with BC (compared with PV and RS) led to 13.56% and 8.28% lower rates of Cd content in the aboveground parts, 40.65% and 35.67% lower rates of Cd content in the seeds, yet 9.08% and 7.09% lower rates of Cd content in the roots, yet 35.80% and 28.48% lower rates of exchangeable Cd content in the soil. Moreover, BC amendment enhanced the biomass of peanut and physiological quality. Thus, BC had a greater impact on immobilizing Cd in the soil. The results imply that BC was more significantly (P < 0.05) remarkable in decreasing the Cd bioavailability and improving the biomass of peanut. BC has greater potential for enhancing soil quality and promoting peanut growth. In conclusion, this research demonstrates an understanding of employing BC as a promising inexpensive and eco-friendly amendment to remediate soil contaminated with Cd.

Subcellular distribution and tolerance of cadmium in Canna indica L

Canna indica L. is a promising species for heavy metal phytoremediation due to its fast growth rate and large biomass. However, few studies have investigated cadmium (Cd) tolerance mechanisms. In the present study, Canna plants were cultivated under hydroponic conditions with increasing Cd concentrations (0, 5, 10, 15 mg/L). We found that the plants performed well under 5 mg/L Cd²⁺ stress, but damage was observed under higher Cd exposure, such as leaf chlorosis, growth inhibition, a decreased chlorophyll content, and destruction of the ultrastructure of leaf cells. Additionally, Canna alleviated Cd toxicity to a certain extent. After Canna was exposed to 5, 10 and 15 mg/L Cd²⁺ for 45 d, the highest Cd concentration was exhibited in roots, which was almost 17-47 times the Cd concentration in leaves and 8-20 times that in stems. At the subcellular level, cellular debris and heat-stable proteins (HSPs) were the main binding sites for Cd, and the proportion of Cd in the two subcellular fractions accounted for 71.4-94.2% of the total Cd. Furthermore, we found that granules could participate in the detoxification process when Cd stress was enhanced. Our results indicated that Canna indica L. can tolerate Cd toxicity by sequestering heavy metals in root tissues, fencing out by cell wall, and binding with biologically detoxified fractions (granules and HSPs).

Evaluation of connected clonal growth of Solidago chilensis as an avoidance mechanism in copper-polluted soils

Plant resistance to metals can be achieved by two strategies, tolerance and avoidance. Although metal tolerance has been broadly studied in terrestrial plants, avoidance has been less considered as a strategy to cope with soil metal pollution. Avoidance may be an effective alternative in herbaceous plants with connected clonal growth in environments having high heterogeneity in soil micro-spatial distribution of available metals and other soil conditions (i.e. organic matter). In this study, we performed a laboratory experiment on clonal growth of Solidago chilensis when exposed to copper-spiked soils (800 mg kg^-1) at different depths (0, 2, 5 and 8 cm depth), with (20%) and without addition of organic matter to mimic contrasting microhabitats found at smelter hinterlands (i.e. open bare ground and microhabitats below shrubs). Results showed that plants grown in the 2 cm-depth Cu-spiked soils were able to growth and produce ramets and rhizomes. However, increased Cu uptake of plants determined phytotoxic effects and a reduction in clonal spread in the 5 cm- and 8 cm-depth Cu-spiked soils. Addition of organic matter to the Cu-spiked soil layers allowed clonal spread. Considering that ramet and rhizome production is decreased but not inhibited when copper pollution is restricted to the uppermost soil layer (2 cm depth) and that organic matter eliminated soil copper toxicity allowing normal clonal spread, connected clonal growth may be an effective avoidance mechanism of Solidago chilensis, particularly in environments with high heterogeneity in micro-spatial distribution of metals and organic matter in the soil profile and between microhabitats.