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This study investigated the effects of salinity (NaCl) and cadmium (Cd) on leaf growth and photosynthetic parameters of tomato plants (Solanum lycopersicum cv. Rio Grande). Cd and NaCl treatments considerably reduced leaf dry matter and leaf area of tomato plants. Stomatal conductance decreased significantly with increased NaCl and Cd in the growth medium, with the decrease occurring at an early stage under Cd treatments. For the fluorescence parameters, there was no significant difference in the maximum quantum efficiency of PSII (Fv/Fm) for either type of stress. However, the quantum yield of PSII photochemistry (ΦPSII), photochemical quenching (qp), and the intrinsic efficiency of PSII (Фexc) decreased significantly under both NaCl and Cd treatments. Decreases in ΦPSII, qp, and Фexc were coupled with a significant increase in non-photochemical quenching (NPQ), and the highest NPQ was obtained in NaCl-treated plants. The correlation between electron transport rate (ETR) and stomatal conductance showed that stomatal closure is associated with a down-regulation of ETR, which is compensated by an increase in non-photochemical quenching.
Field experiments were conducted to evaluate the use of a novel ¹⁵N isotope technique for comparing the dynamics of N derived from sewage sludge applied to sorghum to the dynamics of N derived from the commercial fertilizer, urea. The treatments included a control, sludge applied at three rates (3, 6 and 9 t/ha, or 113, 226 and 338 kg N/ha) and N-urea applied at three rates (150, 250 and 350 kg N/ha). Recovery of ¹⁵N-labelled sludge was similar for the different nitrogen rates applied, with a mean value of 27%. However, the recovery of ¹⁵N-urea decreased as the rate of N application increased (from 38% to 27%). Approximately 22% and 19% of the ¹⁵N from sludge and urea, respectively, remained in the 0-60 cm layer of soil, most of which was present in the 0-20 cm layer. Furthermore, losses of ¹⁵N-labelled fertilizer were not affected by the N fertilization source, and the greatest losses, which were measured in response to the highest N application rate, were 59%.
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