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The importance of biopores for the microbial diversity and nutrient turnover in the subsoil

Marie Uksa1, Doreen Fischer1, Timo Kautz2, Ulrich Köpke2, Michael Schloter1
1 Helmholtz Zentrum München, Research Unit Environmental Genomics, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany
2 University of Bonn, Institute of Organic Agriculture, Katzenburgweg 3, 53115 Bonn, Germany

O 5.6 in Linking biodiversity and biogeochemistry

15.07.2014, 15:30-15:50, H19

Soils below the plough layer provide a stock of nutrients and trace elements and a habitat for microbes, which received little attention in the past despite their importance for nutrient cycling and plant nutrition [1]. Previous studies performed so far suggest that the microbial biomass, diversity and activity rapidly decrease with depth in soil [2, 3]. However, the investigations have mostly focused on bulk soil neglecting the soil heterogeneity. In contrast to topsoils, which are regularly homogenized by the agricultural management, in subsoils spatial heterogeneity patterns are far more pronounced. Especially biopores, which are formed by tap roots and soil fauna and link the subsoil to the topsoil, might serve as important hotspots for microbes in the subsoil due to higher nutrient availability. To investigate the role of biopores for the microbial performance, microbial diversity and their functional potential for nutrient turnover in the subsoil of an arable field up to the depth of 1 m was assessed in different soil compartments including drilosphere, rhizosphere, and bulk soil, and compared to topsoil. Besides bacterial community structure, potential microbial activities related to carbon and nitrogen turnover were measured.

Interestingly, all measured parameters indicated that the differences between topsoil and subsoil in the drilosphere and rhizosphere were very low or absent: The microbial biomass, enzymatic activity and the absolute or relative abundance of functional gene markers for nitrification and denitrification did not decrease with increasing depth as it has been observed in bulk soil. Additionally, the bacterial community fingerprints of the drilosphere and rhizosphere were more restricted to the investigated compartment than to the depth, whereas for the bulk soil a significant difference between topsoil and subsoil community patterns was found. These results indicate the importance of biopores as hotspots for microbial activities mainly in deeper soil layers. The restriction to bulk soil measurements in subsoils leads to an underestimation of the subsoil diversity and its potential for nutrient turnover.

References

[1] Kautz, T., et al. (2013). "Nutrient acquisition from arable subsoils in temperate climates: A review." Soil Biology & Biochemistry 57: 1003-1022.
[2] Fischer, D., Uksa, M., Tischler, W., Kautz, T., Köpke, U., & M. Schloter (2013). "Abundance of ammonia oxidizing microbes and denitrifiers in different soil horizons of an agricultural soil in relation to the cultivated crops." Biology and Fertility of Soils 49(8): 1243-1246.
[3] Eilers, K.G., et al. (2012). "Digging deeper to find unique microbial communities: The strong effect of depth on the structure of bacterial and archaeal communities in soil." Soil Biology & Biochemistry 50: 58-65. 



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last modified 2014-06-19