Abstract
Effects of phosphate fertilization on symbiotic associations between white clover (Trifolium repens L.) and arbuscular mycorrhizal fungi (AMF) were investigated. In sown grassland fertilized at three phosphate levels (-P, P, 2P), we examined the percentages of root length colonization (%RLC) with three different AMF staining methods, i.e. colonized mycelium (TB%), active energy metabolism mycelium (SDH%) and active phosphate metabolism mycelium (ALP%); and analyzed AMF community structures using PCR-DGGE. The %RLCs generally decreased with increasing fertilization level. The peak of TB% was detected following peaks of SDH% and ALP% which were activated immediately after defoliation. Effects of phosphate fertilization were particularly significant at these peaks. ALP%/SDH% showed a negative correlation with phosphorus concentration of white clover. AMF community structure analysis sequenced ten prominent DGGE bands (DGGE_TR1-10). Most of the bands belonged to Glomus genus. DGGE_TR3 (Glomus-B group) band was dominant regardless of both phosphate fertilization levels and sampling dates, while DGGE_TR5 and DGGE_TR10 (Glomus-Ad group) bands were apparent in 2P treatment. Other species were unlikely to be significantly affected by phosphate fertilization. The results show that phosphate fertilization had a clear effect on ALP% at the initial stage of plant growth and right after defoliation, with no significant effects on AMF community structures.
