Effect of soil moisture on microbial community and nutrient immobilization in ARD affected soils

Ryan Bartnick1, Nele Meyer1, Eva Lehndorff1
1 Soil Ecology, University of Bayreuth

P 3.12 in Research Poster Kaleidoscope

Apple replant disease (ARD) has affected the agricultural industry and apple plant production across the world for a long time without any clear distinction on sustainable ways to fight the disease. It is speculated that that ARD severity can be mitigated by maintaining a high soil moisture, although there is yet to be experimental evidence for it. This study utilized young, newly planted apple plants in pots with ARD-inoculated soil from a sandy loam with addition of 15N-labelled ammonium nitrate as a tracer to find out under which soil moistures ARD is most severe and how these moistures affect the microbial community and nutrient cycling within them. Overall, to answer which soil moisture is most promising for reducing nutrient immobilization by microbes and promote plants overcoming ARD. Soil moisture treatments were separated and maintained into three field capacities: 55%, 65%, and 75%. Microbes were quantified using a fumigation-extraction approach and isotopic determination of soil, plant, and microbes was analyzed. For the N-cycling to be spatially viewed, a soil gradient was taken from each pot in the following: bulk soil, near rhizosphere, rhizosphere, and rhizoplane. Increasing soil moistures in the rhizosphere increased microbial biomass carbon 49% and doubled the immobilization of the 15N tracer between 55% and 75% soil moistures. Higher soil moistures reduced nitrogen uptake and allocation to apple plant aboveground biomass, especially to the leaf content which had three times less 15N uptake in 75% compared to 55% soil moisture. Microbial biomass and 15N distribution in soil decreased with increasing distance to root. This study was not conclusive that plant biomass and growth is directly linked to N immobilization by microbes. It can be suggested that N cycling is affected by microbial growth and immobilization, but this is only a symptom of ARD and not a primary cause and effect of ARD severity.

Keywords: apple replant disease, soil moisture, nutrient immobilization, N cycling