Relative importance of soil microbial diversity for soil respiration in semi-natural grassland soils

Ingo Schöning1, Emily Solly1, Heiko Nacke2, Tesfaye Wubet3, Sven Marhan4, Marion Schrumpf1
1 Department fo Biogeochemical Processes, Max-Planck-Institute for Biogeochemistry
2 Department of Genomic and Applied Microbiology, Georg-August-University of Göttingen
3 Department of Soil Ecology, Helmholtz Centre for Environmental Research
4 Soil Biology Unit, Hohenheim University

O 5.2 in Linking biodiversity and biogeochemistry

15.07.2014, 11:20-11:40, H19

Decomposition in soils is a key ecosystem function that controls the release of carbon dioxide from the soil to the atmosphere. Decomposition in grasslands is assumed to be negatively related to land-use intensity as a result of fertilization and a subsequent decrease of belowground species diversity. In grassland soils a large number of different microorganisms are involved in the decomposition. Although much functional redundancy was observed for microorganisms, there is some evidence for the importance of species identity for soil organic matter decomposition in experimental grasslands. From previous experimental studies, however, the relative importance of microbial diversity for the decomposition of soil organic matter in semi-natural grasslands remains unclear. Only recently new methods such as pyrosequencing have been developed for the analysis of microbial communities which led to the discovery of many new species, whereas in previous studies traditional methods for the characterization of soil microbial diversity such as phospholipid fatty acid analysis have been used. Here, we study the complex relation among grassland-management (including fertilization, grazing, mowing), abiotic soil properties, microbial biomass, microbial diversity and soil respiration to assess the relative importance of biotic and abiotic factors for soil organic matter decomposition in grasslands.

We collected mineral soil samples (0-10 cm) from 150 grassland plots in three different German regions (Schorfheide-Chorin, Hainich-Dün, Schwäbische Alb) and determined soil properties such as pH, soil texture, soil C and N contents and soil microbial biomass. An aliquot of each soil sample was incubated (20 ̊C, 60% WHC) for 14 days and the evolving CO2 was determined. Moreover the fungal and bacterial diversity (Shannon diversity) were determined using 454 pyrosequencing. We then applied structural equation modeling to assess the above- and belowground effects on soil organic matter decomposition in grasslands. We could show that grassland management had significant negative indirect effects on decomposition mediated by the C/N ratio of soils and the microbial biomass. We also found a significant positive effect (p<0.05) of grassland management on the bacterial diversity but surprisingly we could not detect any significant direct or indirect relation between bacterial diversity and soil respiration. In contrast, to the soil bacterial diversity, the soil fungal diversity was not explained by grassland management. However, the soil fungal diversity was indirectly related to the soil respiration via the microbial biomass (p<0.001). Our results show, that the soil fungal diversity is of higher importance for the soil respiration than the soil bacterial diversity. Our results further indicate a clear impact of grassland management on the soil respiration. However, contrary to our expectations, the impact of grassland management on soil respiration was mediated neither by soil bacterial nor by soil fungal diversity.

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Letzte Änderung 19.06.2014