Sex differences in nitrogen flux in fern gametophytes

Total net ammonium (NH 4 + ), nitrate (NO 3 − ), and proton (H + ) fluxes were investigated in fern gametophytes of the swordfern, Polystichum munitum (Kaulf.) C.Presl. Flux measurements were performed with a microelectrode ion flux measurement system. Overall, net influx of NH 4 + and H + was observed. By comparison, NO 3 − showed a net efflux. Male Polystichum munitum gametophytes displayed greater per-unit-area NH 4 + uptake than female/hermaphrodite gametophytes, though the latter showed greater NH 4 + uptake at the whole-organism level. This finding suggests that fern gametophytes may conform to the expectations of nutrient-based sex determination.