Application of super(13)C-labeled litter and root materials for in situ decomposition studies using phospholipid fatty acids

• Published in: Soil biology & biochemistry 2008-10, Vol.40 (10), p.2485-2493
• Main Authors: Moore-Kucera, Jennifer, Dick, Richard P
• Format: Article
• Language: English
• Subjects: Pseudotsuga menziesii
• ISSN: 0038-0717
• DOI: 10.1016/j.soilbio.2008.06.002

Microorganisms play a central role in litter decomposition and partitioning C between CO sub(2) evolution and sequestration of C into semi- permanent pools in soils. At the ecosystem level, forest stand age influences rates of litter accumulation and quality, and micro-climatology which could affect the microbial community structure and C sequestration processes. Although numerous laboratory experiments have studied the decomposition of model super(13)C-labeled compounds, few studies have verified these findings under field conditions. The objective of this study was to track decomposition of super(13)C-labeled Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) materials into the soil microbial community using super(13)C- phospholipids fatty acid (PLFA) analysis in three different aged forest stands. A field experiment was conducted that had three forest stand age treatments: old-growth (>500 yrs); 8-year-old clear-cut (CC8); and 25-year- old clear-cut (CC25) (landscape reps of n = 2). Each stand age had in situ microcosms that were amended with either super(13)C-labeled surface litter or root material. Microcosms were destructively sampled seven times over a 22-month period and the soil was analyzed for the relative amounts of super(13)C incorporated ( super(13)C% sub(INCORP)) into PLFAs and the proportional distribution of super(13)C incorporated into PLFAs. The super(13)C% sub(INCORP) was affected by stand age and super(13)C source with greater super(13)C% sub(INCORP) in samples from CC8 than OG or CC25. Also, the level of super(13)C% sub(INCORP) was greater for labeled litter than root material in five out of the seven sample dates. In general, 18:1[Omega]9 and 18:2[Omega]6,9 (common fungal biomarkers) had the greatest amount of super(13)C incorporation throughout the study period in both clear-cut and old-growth sites, especially in plots with super(13)C- labeled litter. Our data showed a low fungal super(13)C-PLFA: bacterial super(13)C- PLFA ratio (0.45) 1 month after incubation was initiated compared to 5, 7 and 9 months after incubation (two of these dates were >1.0). This suggests that initially bacteria played a greater role in the decomposition of the added needles with fungi playing a more important role in subsequent sample dates. Our results illustrate that the use of super(13)C-labeled materials in field studies coupled with super(13)C-PLFA profiling is a powerful tool for determining microbial dynamics during decomposition - enabling statis