Although only needed in small quantities, mineral nutrients like calcium, magnesium, zinc, copper, iron and manganese are important for plants. However, plants absorb these nutrients only from soils, and their availability may be greatly affected by soil nitrogen (N) and phosphorus (P) availability. Here we used a forest fertilization experiment to find the patterns of plant leaf mineral nutrients under different soil N and P addition treatments (including no fertilization control plots, +N, +P and +NP plots).

We found that N fertilization did not change soil pH, but greatly reduced the soil availability of all these minerals except copper, and these reduction further affected their concentrations in plants, especially of calcium, magnesium and manganese. The results indicate that long-term (six to eight years) N addition reduced the concentrations of several mineral nutrients in leaves, and we did not observe any change of transpiration to take up mobile soil nutrients and maintain foliar nutrient concentrations at high N supply. We conclude that the responses of foliar mineral nutrients to N and P fertilization are more complicated than those of N and/or P themselves (generally P addition increased foliar P concentration, while N addition had no significant effects on foliar N concentration).

The specific decreases of mineral nutrient concentrations following long-term N deposition may influence key physiological process in the studied tropical understory species, and ultimately reduce their fitness and survival under high N deposition.

Fig. 1 Understory Plant Community in a tropical forest, South China.