Effect of Acid Deposition on the Chemical Properties of Soil Organic matter

13种酸性土壤（A_<0+1>，0- 15 cm）取自日本火山区（pH（H_2O）=2.81-3.93），9种参比土壤取自未受火山酸影响的地区（pH=4.10-4.74）。用0.1M NaOH溶液从土壤中提取胡敏酸，用盐酸酸化沉淀胡敏酸。在溶解和沉淀过程重复5次后，用2%HF处理腐殖酸以降低灰分含量。然后用CHCl_3洗涤以除去任何元素S。将所得腐殖酸冷冻干燥并进行S分析。在腐殖酸中测定的硫形态为总硫、酯硫酸盐硫、磺酸盐硫、巯基硫、无机硫和C键硫。C键S包括C-S-C。C-S-S-C和非离子含S基团。结果表明：1）酸性土壤硫含量（0.22 <plus-minus>± 0.10%）明显高于对照土壤（0.11 ± <plus-minus>0.03%），且从约100 ℃开始迅速增加; 0.15%左右。土壤pH值从3.5降低到2.8时，土壤pH值下降到2.8时，土壤pH值下降到0.40%。2)酸性土壤中胡敏酸（AHA）的全S（0.56 <plus-minus>± 0.21%）、总有机S（0.53 <plus-minus>± 0.19%）和磺酸盐S（740 ± <plus-minus>610 ppm）含量均高于对照土壤中的RUA（全S：0.34 <plus-minus>± 0.04%、总有机S：0.33 <plus-minus>± 0.04%、磺酸盐S：530 <plus-minus>± 320 ppm）。3)虽然巯基硫和无机硫的相对浓度较低（小于总硫的10%），但这两种组分也富含AHA（巯基硫：AHA为270 <plus-minus>~ 110 ppm，RHA为90 <plus-minus>~ 70 ppm;无机硫：AHA为370 <plus-minus>~ 190 ppm，RRA为110 <plus-minus>~ 30 ppm）。4)硫酸酯-S在两个样品中的浓度基本恒定（阿坝：1500 <plus-minus>~ 360 ppm，RHA：1560 <plus-minus>~ 320 ppm），与土壤的pH和S含量无关。

Thirteen acid soils(A_<0+1>, 0-15cm)were collected from volcanic regions of Japan(pH(H_2O)=2.81-3.93), and 9 reference soils from the regions unaffected by volcanic acids(pH=4.10-4.74). Hunic acids were extracted from those soils with 0.1M NAOH and precipitated by acidification(pH=2, HCl). After the dissolution and precipitationprocedure had been repeated 5 times, the humic acids were treated with 2% HF to reduce the ash content. and then washed with CHCl_3 to eliminate any elemental S. The resulting humic acids were freezedried and subjected to the S-analyses. The sulfur species determined in the humic acids were total S, ester sulfate-S, sulfonate-S, sulfhydryl-S, inorganic S, and C-bonded S. The C-bonded S included C-S-C. C-S-S-C, and non-ionic S-containing groups. The results obtained in this research are summarized as follows : 1)The S contents of of acid soils(0.22<plus-minus>0.10%)were clearly higher than those of reference soils(0.11<plus-minus>0.03%), and increased rapidly from ca. 0.15% to ca. 0.40% with decreasing soil PH(from 3.5 to 2.8). 2)The humic acids(AHA)from acid soils showed higher concentrations of total S(0.56<plus-minus>0.21%), total organic S(0.53<plus-minus>0.19%), and sulfonate-S(740<plus-minus>610ppm)compared with those(RUA)from reference soils(total S : 0.34<plus-minus>0.04%, total organic S : 0.33<plus-minus>0.04%, sulfonate-S : 530<plus-minus>320ppm). 3)Although the relative concentrations of sulfhydryl-S and inorganic S were low(less than 10% of total S), both components were also rich in AHA(sulfhydryl-S : 270<plus-minus> 110ppm for AHA and 90<plus-minus>70ppm for RHA, inorganic S : 370<plus-minus>190ppm for AHA and 110<plus-minus>30ppm for RRA). 4)Ester sulfate-S showed approximately constant concentrations in both samples(ABA : 1500<plus-minus> 360ppm, RHA : 1560<plus-minus>320ppm)regardless of the pH and S content of t