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Soil Biology & Biochemistry

Dynamics of Microbial Communities during Decomposition of Carbon-13 Labeled Ryegrass Fractions in Soil

^a Dep. of Crop and Soil Science, Oregon State Univ., Agric. Life Sci. Bldg. 3017, Corvallis, OR 97331-7306
^b Dep. of Microbiology, 220 Nash Hall, Oregon State Univ., Corvallis, OR 97331-3804
^c Biological Sciences, Ecology, Evolution & Marine Biology, Univ. of California, Santa Barbara, CA 93106
^d Dep. of Crop and Soil Sciences, Univ. of Georgia, 3121 Miller Plant Sciences Bldg., Athens, GA 30602

^* Corresponding author (david.myrold{at}oregonstate.edu)

The soluble fraction of ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot.] straw comprises a major component of residue C and its presence or absence should influence the succession of decomposer communities. Changes in phospholipid fatty acid (PLFA) profiles are indicative of shifts in microbial community structure. We used ¹³C-labeled ryegrass to track substrate-derived C into microbial lipids during decomposition in a microcosm-based study. Treatments were unleached straw, leached straw, and leachate, plus an unamended control. Destructive sampling took place after 0.6, 1.6, 15, 18, 50, and 80 d of incubation. Phospholipid fatty acids were extracted from bulk soil and isolated straw (detritusphere), and analyzed by gas chromatography combustion isotope ratio mass spectroscopy (GC-C-IRMS). Distinct temporal shifts occurred in PLFAs in bulk soil samples; cy19:0 was an indicator for late succession communities in unleached straw and leachate treatments, and 18:26,9 characterized late samples in the leached straw treatment. The temporal shift was affected by the presence of the soluble fraction of straw. Microscale spatial effects were clear. Bulk soil and detritusphere communities were different and more ¹³C was detected in the 16:0 and 18:26,9 PLFAs of the detritusphere than bulk soil. Carbon-13 was slowest to appear in PLFAs of leached straw samples, illustrating the importance of the soluble fraction in promoting growth of the biomass in bulk soil and in detritusphere. The 18:26,9 PLFA, a fungal biomarker, was the most highly labeled in all treatments. Carbon-13 PLFA analysis provides greater insight into microbial community structure and functioning, facilitating more concrete conclusions regarding the role of functional groups of organisms.

Abbreviations: FAME, fatty acid methyl ester • GC-C-IRMS, gas chromatography-combustion-isotope ratio mass spectrometry • IRMS, isotope ratio mass spectrometer • ISA, indicator species analysis • MRPP, multi-response permutation procedure • PCA, principal components analysis • PLFA, phospholipid fatty acid

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