Effect of soil fertility and transpiration rate on young wheat plants (Triticum aestivum) Cd/Zn uptake and yield

Using treated wastewater for crop irrigation can provide more adequate supply of high quality water for human consumption, but their heavy metal applications and synergetic effect must be regulated to ensure no physiological problems for both the plant and its consumer. The objective of the present project was to measure the influence of transpiration rate and soil fertility on Cd and Zn uptake by young wheat plants (Triticum aestivum) grown in triplicate sand pots, using two types of sands with a low and high fertility, monitored from days 7 to 30 (day 0 was emergence) with solutions containing various levels of Cd/Zn (0/0, 0.01/0, 0.10/0, 0.50/0, 0/25, 0.01/25, 0.10/25, 0.50/25 and 0.50/50 mg/L). Two growth chambers each with a different vapor pressure deficit (VPD) induced different transpiration rates, monitored from days 7 to 30. On days 15 and 30, three plants were removed from each pot, to measure their dry mass and Cd and Zn content. For the plants grown using soil 2, the roots were also collected and analyzed on day 30. Heavy metal treatments had no effect on transpiration rates per plant dry matter weight. VPD had no effect on plant transpiration rate and dry mass for soil 1, while it did from days 15 to 30 for soil 2, richer in P and K. The synergetic effect between Cd and Zn was quite variable, depending on the soil nutrient level, irrigation period and VPD or transpiration rate. In general, faster or higher plant dry mass accumulation tended to enhance the synergetic effect between Cd and Zn. In general, higher Cd levels generally decreased Zn uptake and higher Zn generally increased Cd uptake. For both soils, Zn decreased Cd uptake when applied under 5.6 mg/kg of soil, while it increased Cd uptake at higher applications. Soil nutrients were found to compete against heavy metals for plant uptake. Poorer soils also lead to a more efficient use of irrigation water per dry mass yield but to higher plant Cd and Zn content with risks of exceeding toxic levels. The level of Cd and Zn found in the shoot depended on the irrigation water Cd and Zn levels and the transpiration rate while the ratio of Cd to Zn found in the shoot depended more on the soil adsorption capability and the adsorption synergy between Cd and Zn.