Spatial and temporal dynamics of mycorrhizas in Jaumea carnosa, a tidal saltmarsh halophyte

1 Jaumea carnosa (Less.) Gray was studied in three environmentally distinct regions of the Walker Creek marsh, California. This species was mycorrhizal at an upland site removed from tidal influences except when extreme tides coincided with winter precipitation, a tidal channel site, and a waterlogged marine site (pioneer zone). The percentage of root length colonized by arbuscular mycorrhizal fungi (%AM) was significantly lower (P < 0.001) in the upland site (approximate to 7%), compared to either the channel (approximate to 28%) or marine sites (approximate to 17%). 2 The vertical distribution of AM in the 40-cm rooting profile of Jaumea was, in most cases, positively associated (P < 0.05 to P < 0.01) with gravimetric soil moisture. Surprisingly, redox potential did not have a negative effect on AM. AM colonization levels were often > 20% in regions of the soil profile where redox potentials were less than 100 mV and soil moisture levels exceeded 120%. 3 Cross-sections of host plant roots revealed the localization of arbuscules in the radial files of aerenchymatous tissue which may facilitate the survival of AM fungi in reduced soils. Glomus intraradices Schenk & Smith was the dominant sporulating species from the marine site soils, while several undescribed species of Glomus dominated the channel and upland site soils. Species composition was similar in soil samples collected during dry (September) and wet (January) months. 4 In the upland site, %AM may be suppressed by the osmotic stresses associated with seasonal extremes of salinity. For the upland and channel sites, %AM and arbuscule frequencies were greatest during the winter months of December and early March, when plants were relatively dormant. In these sites, vesicles and hyphae were most abundant during the summer months. In the waterlogged and reduced soils of the marine site, AM levels did not change seasonally despite high levels of available phosphorus. 5 In the channel site, the tidal deposition of nitrogen-rich (and possibly spore-bearing) sediments, the presence of faunal activity in channel walls, and improved soil aeration associated with tidal inundation and retreat are among the proposed explanations for mycorrhizal abundance in this location of the Walker Creek marsh.