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Abstract:
In this study, we investigated how co-occurrence patters of ammonia and nitrite oxidizers, which drive autotrophic
nitrification, are influenced by tree species composition
as well as soil pH in different forest soils. We expected that a
decline of ammonia oxidizers in coniferous forests, as a result
of excreted nitrification inhibitors and at acidic sites with low
availability of ammonia, would reduce the abundance of
nitrite-oxidizing bacteria (NOB). To detect shifts in cooccurrence
patterns, the abundance of key players was measured
at 50 forest plots with coniferous respectively deciduous
vegetation and different soil pH levels in the region
Schwäbische Alb (Germany). We found ammonia-oxidizing
archaea (AOA) and Nitrospira-like NOB (NS) to be dominating
in numbers over their counterparts across all forest types.
AOA co-occurred mostly with NS, while bacterial ammonia
oxidizers (AOB) were correlated with Nitrobacter-like NOB
(NB). Co-occurrence patterns changed from tight significant
relationships of all ammonia and nitrite oxidizers in deciduous
forests to a significant relationship of AOB and NB in
coniferous forests, where AOA abundance was reduced.
Surprisingly, no co-occurrence structures between ammonia
and nitrite oxidizers could be determined at acidic sites, although
abundances were correlated to the respective nitrogen
pools. This raises the question whether interactions with heterotrophic
nitrifiers may occur, which needs to be addressed in future studies.
