Mycorrhizae in an experimental urban landscaped site in central Arizona-Phoenix

The primary objective of this project is to study Mycorrhizal relationships at an
experimental xeric urban landscaped site . One study quantified the local diversity
and spatial patterns of arbuscular mycorrhizal fungal (AMF) species. AMF species at
25 points in a 9.2 x 9.2 m regular grid pattern were identified using trap cultures.
A total of twelve species were detected, with seven species detected in one plot and
eleven in the other. Sampling effort curves and jackknife estimates indicate that a
limited number of species was still undetected. No single species was dominant at
either plot, and a rank-frequency plot for the site revealed a log-normal species
distribution. The number of AMF species was not correlated with proximity to plants.
Despite the patchiness of plants in the plots, the number of species detected per
point exhibited spatial structuring only at the smallest sampling scale in a single
plot, and only a single species in each plot was non-randomly distributed.The
results indicate that there is a diverse AMF propagule bank at the site and/or there
has been significant in-migration from the surrounding metacommunity. The second
study examined the effects of three shoot pruning techniques (shearing every 6
weeks, heading back every 6 months and renewal pruning every year) on root length
density, biomass, AMF colonization and soil respiration in two woody shrubs, Nerium
oleander (oleander) and Leucophyllum frutescens (Texas sage). Roots were sampled at
the base of plants by soil coring to depths of 0-20 cm and 20-40 cm in February,
after the shearing and heading back treatments had been imposed, but prior to the
first renewal pruning, and in May, after all treatments had been imposed. Shearing
stimulated root biomass in Nerium in February, but shearing and renewal pruning
reduced biomass compared to unpruned plants in both species in May. Nerium
colonization was stimulated by shearing and heading back in February and by shearing
and renewal pruning in May. Root biomass, length, and soil respiration associated
with Leucophyllum were reduced by all pruning treatments in May. The results
indicate that heading back may be the most appropriate pruning practice for these
shrubs in xeric landscaping.