Biochar stability in soil: Decomposition during eight years and transformation as assessed by compound-specific ¹⁴C analysis

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• 作者：Yakov Kuzyakov ; Irina Bogomolova ; Bruno Glaser
• 关键词：Pyrogenic carbon ; Black carbon utilization ; Soil organic matter turnover ; Inert pools ; Microbial biomass ; Dissolved organic matter ; Lipid decomposition rates ; Benzenepolycarboxylic acids ; Polysaccharides ; Carbon sequestration
• 刊名：Soil Biology & Biochemistry
• 出版年：March, 2014
• 年：2014
• 卷：70
• 期：Complete
• 页码：229-236
• 全文大小：1348 K

文摘

Stability and transformation products of incomplete combustion of vegetation or fossil fuel, frequently called pyrogenic or black carbon and of biochar in soil, remains unknown mainly because of their high recalcitrance compared to other natural substances. Therefore, direct estimations of biochar decomposition and transformations are difficult because 1) changes are too small for any relevant experimental period and 2) due to methodological constraints (ambiguity of the origin of investigated compounds). We used ¹⁴C-labeled biochar to trace its decomposition to CO₂ during 8.5聽years and transformation of its chemical compounds: neutral lipids, glycolipids, phospholipids, polysaccharides and benzenepolycarboxylic acids (BPCA).

¹⁴C-labeled biochar was produced by charring ¹⁴C-labeled Lolium residues. We incubated the ¹⁴C-labeled biochar in a Haplic Luvisol and in loess for 8.5聽years under controlled conditions. In total only about 6% of initially added biochar were mineralized to CO₂ during the 8.5聽years. This is probably the slowest decomposition obtained experimentally for any natural organic compound. The biochar decomposition rates estimated by ¹⁴CO₂ efflux between the 5th and 8th years were of 7聽脳聽10^鈭? % per day. This corresponds to less than 0.3% per year under optimal conditions and is about 2.5聽times slower as reported from the previous shorter study (3.5 years).

After 3.5聽years of incubation, we analyzed ¹⁴C in dissolved organic matter, microbial biomass, and sequentially extracted neutral lipids, glycolipids, phospholipids, polysaccharides and BPCA. Biochar-derived C (¹⁴C) in microbial biomass ranged between 0.3 and 0.95% of the ¹⁴C input. Biochar-derived C in all lipid fractions was less than 1%. Over 3.5聽years, glycolipids and phospholipids were decomposed 1.6聽times faster (23% of their initial content per year) compared to neutral lipids (15%聽year^鈭?). Polysaccharides contributed ca. 17% of the ¹⁴C activity in biochar. The highest portion of ¹⁴C in the initial biochar (87%) was in BPCA decreasing only 7% over 3.5聽years. Condensed aromatic moieties were the most stable fraction compared to all other biochar compounds and the high portion of BPCA in biochar explains its very high stability and its contribution to long-term C sequestration in soil.

Our new approach for analysis of biochar stability combines ¹⁴C-labeled biochar with ¹⁴C determination in chemical fractions allowed tracing of transformation products not only in released CO₂ and in microbial biomass, but also evaluation of decomposition of various biochar compounds with different chemical properties.