We analyzed the linearity of relationships between soil test P (STP) and cumulative phosphorus (P) budget using data from six long-term fertilized grassland sites in four countries: France (Ercé and Gramond), Switzerland (Les Verrières), Canada (Lévis), and Finland (Maaninka and Siikajoki). STP was determined according to existing national guidelines. A linear-plateau model was used to determine the presence of deflection points in the relationships. Deflection points with (x, y) coordinates were observed everywhere but Maaninka. Above the deflection point, a significant linear relationship was obtained (0.33 < r ² < 0.72) at four sites, while below the deflection point, the relationship was not significant, with a negligible rate of STP decrease. The relationship was not linear over the range of STP encountered at most sites, suggesting a need for caution when using the P budget approach to predict STP changes in grasslands, particularly in situations of very low P fertilization. Our study provides insights and description of a tool to improve global P strategies aimed at maintaining STP at levels adequate for grassland production while reducing the risk of P pollution of water.

Salt stress induces cytotoxicity at the cellular level, influencing the vacuolization process, disrupting mitotic division, and thus inhibiting plant growth. The results for a range of species used in agriculture have shown that high soil salt levels affect germination, chlorophyl content and yield. In this study, an experiment was carried out in the laboratory using NaCl concentration treatments of 0, 100, 125 and 150 mM on sunflower seeds of the inbred line HA-89 obtained from the USDA gene bank. For the experiment, the seeds were germinated in a salt solution and analyzed cytologically by calculating the mitotic index, chromosomal aberration index, provacuolar index and vacuolization index. Following our cytological studies, we observed that the vacuolization phenomenon was caused by salt stress and progressively accentuated by the salt concentration levels and exposure times. The formation of vacuolized cells is due to the fusion of provacuoles, which contributes to a uniform or non-uniform distribution of genetic material around them. According to our results, the vacuolization index showed high values depending on the NaCl concentration and stress exposure time. Similarly, high salt concentrations significantly decreased the mitotic index and increased the chromosomal aberration index. The effect of salt stress causes cell vacuolization, a decrease in the mitotic index and an increase in the number of chromosomal aberrations in meristematic tissues, inhibiting growth and development and consequently leading to a reduction in productivity per unit area.