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SEMINAR: Soil&Water Seminar, 11am Tues8th March:

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Soil&Water Seminar, 11am Tues8th March: : “The effect of tree belowground C allocation on the seasonal course of microbial N cycling in an European beech forest soil” Other events...
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“The effect of tree belowground C allocation on the seasonal course of microbial N cycling in an European beech forest soil”

ABSTRACT: Soil microbes in temperate forest ecosystems are able to cycle several hundreds of kg of nitrogen (N) ha-1 yr-1 and are therefore of paramount importance for N retention. Belowground C allocation by trees is an important driver of soil microbial decomposition processes and may thus directly affect N transformation processes over the course of the year. Our study aimed at unravelling plant controls on soil N cycling in a temperate beech forest in a seasonal context. This was approached by investigating the effects of tree girdling (an experimental manipulation that stops carbon (C) flow from the tree canopy to the roots) on microbial decomposition processes and microbial community composition at a high temporal resolution over a time period of two years.

In unmanipulated plots, we discovered (1) a summer N mineralization phase (between July – August) and (2) a winter N immobilisation phase (November - February) in both years of the experiment. The summer mineralization phase was characterised by a high N mineralization activity, low microbial N uptake and a subsequent high N availability in the soil. During the autumn/winter N immobilisation phase, gross N mineralization rates were low and microbial N uptake exceeded microbial N mineralization, which led to high levels of N in the microbial biomass and low N availability in the soil. The observed immobilisation phase during the winter may play a crucial role for ecosystem functioning, since it possibly protects dissolved N that is produced by autumn litter degradation from being lost from the ecosystem during the phase when plants are mostly inactive. The difference between microbial biomass N levels in winter and spring equals 38 kg N ha-1, and may thus account for almost one third of the annual plant N demand.

Cutting tree belowground carbon allocation by tree girdling strongly affected the seasonal course of N cycling: the winter N immobilisation phase disappeared in girdled plots (microbial N uptake and microbial biomass N were significantly reduced, while the amount of available N in the soil solution was enhanced). This was correlated to a reduced abundance of ectomycorrhizal fungi and a general shift in the microbial community in girdled plots. Our results suggest that plants may actively control the annual microbial N cycle by releasing recently fixed photosynthates to the soil. Tree belowground C allocation may promote N accumulation in microorganisms during the winter, which will ultimately feed back on plant N availability in the following growing season.
Speaker(s) Dr Christina Kaiser,Department of Chemical Ecology and Ecosystem Research at the University of Vienna, Austria
Location Agriculture Lecture Theatre (G.013), in the Agriculture NW wing (Map: http://www.uwa.edu.au/campus_map?id=1871)
Contact Ursula Salmon <[email protected]> : 6488 1508
Start Tue, 08 Mar 2011 11:00
End Tue, 08 Mar 2011 11:45
Submitted by Ursula Salmon <[email protected]>
Last Updated Wed, 25 Jan 2012 11:52
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