Warming effects on fine root biomass, morphology, and decomposition in a mountainous forest soil

Steve kwatcho kengdo1, Jacob Heinzle2, Ye Tian3, Carolina Urbina Malo3, Shi Chupei3, Andreas Schindlbacher2, Wolfgang Wanek3, Werner Borken1
1 Department of Soil Ecology, Bayreuth Center of Ecology and Environmental Research (BAYCEER), University of Bayreuth, Germany
2 Federal Research and Training Centre for Forests, Natural Hazards and Landscape, Vienna, Austria
3 Department of Microbiology and Ecosystem Science, Center of Microbiology and Environmental Systems Science, University of Vienna, Austria

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Tree fine roots (<2 mm) take up nutrients and water and represent a significant carbon pool in forest soils. Understanding how fine roots will respond to increasing temperature is a pre-requirement for predicting the functioning of forests in a warmer climate.  Here, biomass, morphology and mass loss of fine roots (in litter bags) were studied in a 140-year-old mountainous forest dominated by Norway spruce (Picea abies) and European beech (Fagus sylvatica) in the Austrian Alps. We hypothesized that 14 years of soil warming (+4°C) would alter fine root morphology, increase fine root biomass and mass loss of fine root litter. Soil warming increased fine root biomass (461 ± 67 and 538 ± 94 g m-2 for control and warming treatment respectively; n =6), but this increase was not significant. Fine root mass loss was similar under control (17.6%) and warming conditions (18.3%) after one year. Moreover, fine root surface area, specific root length and average root diameter increased (though not significantly) under warming, and this increase was more pronounced at the 0 – 10 cm than at 10 – 20 cm soil depth. Fine root biomass showed the same trend as the results obtained during a sampling campaign in October 2012 at the same site (513 ± 66 and 582 ± 95 g m-2 for control and warming respectively; n =3). Our results show that the similar response of fine root biomass, morphology and mass loss under control and warming conditions suggest fast acclimation of fine roots to soil warming. Data from 2012 showed an increase of fine root turnover measured by 14C signatures and thus increased carbon input to soils under warming conditions. Whether the increase in fine root turnover is consistent is subject of further investigations.

Keywords: soil warming; fine roots biomass; fine roots morphology; carbon turnover; acclimation.