Recent (<4 year old) leaf litter is not a major source of microbial carbon in a temperate forest mineral soil

Kramer, C., Trumbore, S., Froberg, M., Cisneros Dozal, L. M. , Zhang, D., Xu, X., Santos, G.M. and Hanson, P.J. (2010) Recent (<4 year old) leaf litter is not a major source of microbial carbon in a temperate forest mineral soil. Soil Biology and Biochemistry, 42(7), pp. 1028-1037. (doi: 10.1016/j.soilbio.2010.02.021)

Abstract

Microbial communities in soil A horizons derive their carbon from several potential sources: organic carbon (C) transported down from overlying litter and organic horizons, root-derived C, or soil organic matter. We took advantage of a multi-year experiment that manipulated the ¹⁴C isotope signature of surface leaf litter inputs in a temperate forest at the Oak Ridge Reservation, Tennessee, USA, to quantify the contribution of recent leaf litter C to microbial respiration and biomarkers in the underlying mineral soil. We observed no measurable difference (< 40‰ given our current analytical methods) in the radiocarbon signatures of microbial phospholipid fatty acids (PLFA) isolated from the top 10 cm of mineral soil in plots that experienced 3 years of litterfall that differed in each year by 750‰ between high-¹⁴C and low-¹⁴C treatments. Assuming any difference in ¹⁴C between the high- and low-¹⁴C plots would reflect C derived from these manipulated litter additions, we estimate that < 6% of the microbial C after 4 years was derived from the added 1–4-year-old surface litter. Large contributions of C from litter < 1 year (or >4 years) old (which fell after (or prior to) the manipulation and therefore did not differ between plots) are not supported because the ¹⁴C signatures of the PLFA compounds (averaging 200–220‰) is much higher that of the 2004–5 leaf litter (115‰) or pre-2000 litter. A mesocosm experiment further demonstrated that C leached from ¹⁴C-enriched surface litter or the O horizon was not a detectable C source in underlying mineral soil microbes during the first eight months after litter addition. Instead a decline in the ¹⁴C of PLFA over the mesocosm experiment likely reflected the loss of a pre-existing substrate not associated with added leaf litter. Measured PLFA Δ¹⁴C signatures were higher than those measured in bulk mineral soil organic matter in our experiments, but fell within the range of ¹⁴C values measured in mineral soil roots. Together, our experiments suggest that root-derived C is the major (>60%) source of C for microbes in these temperate deciduous forest soils.

• Item Type: Articles
• Keywords: Leaf litter, PLFA, compound specific, radiocarbon, microbial
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Cisneros, Dr Malu
• Authors: Kramer, C., Trumbore, S., Froberg, M., Cisneros Dozal, L. M., Zhang, D., Xu, X., Santos, G.M., and Hanson, P.J.
• Subjects: Q Science > Q Science (General)
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Soil Biology and Biochemistry
• ISSN: 0038-0717
• Published Online: 16 March 2010