Da. Klein et al., NITROGEN AVAILABILITY AND FUNGAL-BACTERIAL RESPONSES IN SUCCESSIONAL SEMIARID STEPPE SOILS, Arid soil research and rehabilitation, 10(4), 1996, pp. 321-332
Nitrogen availability plays a major role in influencing the microbial
community structure as plant-soil systems develop in succession. in th
is study, three successional sites, sampled 5, 13, and 39 years after
disturbance, were compared with an undisturbed native site, Microbial
responses were related to time since disturbance and soil nitrogen (N)
availability. Nitrogen was modified by mineral N and carbohydrate add
itions. Microscopic techniques were used to assess the biomass (total
and active) of bacteria and fungi at spring and summer samplings. In t
he undisturbed native plots, with decreased N availability, increases
occurred in microscopically assessed microbial biomass, primarily fung
al, in comparison with control plots. This fungal response did not occ
ur on the previously disturbed successional plots that were treated in
a similar manner. Ratio analyses of the various parameters provided a
dditional information related to these responses. For both samplings,
the ratio of total fungi/total bacteria increased from the 5-yr to the
native plot. Particularly in the spring sampling, where there was mor
e active plant growth, decreased N availability was associated with an
increase in this ratio on the late successional and native plots. In
contrast active/total fungal and active/total bacterial ratios were hi
ghest in the 5-yr plot, suggesting more available substrates for micro
bial use in comparison with the older plots, The active/total bacteria
l ratio did not show responses; however, an increased active bacteria
over active fungal ratio occurred on the earliest successional plot, w
hich was most distinct in the summer sampling. These results indicate
the long-term differential effects of disturbance and N availability o
n various active/total ratios of fungi versus bacteria, which suggest
that a shift from a more active bacterial community in early successio
nal plots to a system dominated by less active fungi occurs Inter in s
uccession.