Ammonium (NH
4+) toxicity in yellow passionfruit (
Passiflora edulis Sims f.
flavicarpa
O. Deg.) may be mitigated by Si application. This study aimed to evaluate the interaction effect of Si and high level of NH
4+ on yellow passionfruit seedlings nutrition, physiology, growth, and DM production. Pots were filled with pinus bark and nutrition solution was applied. Treatments were arranged in a completely randomized design, with five replicates, in a 2 × 2 factorial scheme: two ratios of NH
4+ and nitrate, NO
3+ (40/60%, without high level of NH
4+; and 75/25%, with high level of NH
4
+) at N concentration of 13 mmol N L
-1, in the absence and presence of Si (2.0 mmol L
-1). Sixty days after seedling transplant it was evaluated: N, Si, K, Ca and Mg root and shoots accumulation, leaf green color index (GCI), electrolyte leakage index (ELI), intracellular CO
2 concentration (C
i), transpiration rate (T
r), stomatal conductance (g
s), net photosynthesis rate (Pn), stem diameter, leaf area, root length, N use efficiency (NUE) and root and shoot DM content. Plants cultivated with
Si had 19.1% and 16.3% lower T
r and g
s, respectively, regardless NH
4+ concentration. Moreover, C
i and P
n were 13.2% and 16.4%, respectively, higher in plants that received Si. Plants cultivated under high NH
4+ concentrations, with Si application had 17% bigger stem diameter and 15.4% bigger root length than plants without Si application. Si application in yellow passionfruit seedlings cultivated with high level of NH
4
+ increased accumulation and NUE, root length, root DM, and GCI. In addition, Si application reduced ELI, which resulted in higher stem diameter. These results prove that Si application mitigates NH
4+ toxicity in yellow passionfruit seedlings.
