The process of organic materials increasing soil pH has not yet been fully understood. This study examined the role of cations and organic anions in regulating soil pH using organic compounds. Calcareous soil, acid soil, and paddy soil were incubated with different simple organic compounds, pH was determined periodically and CO2 emission was also measured. Mixing organic acids with the soil caused an instant decrease of soil pH. The magnitude of pH decrease depended on the initial soil acidity and dissociation degree of the acids. Decomposition of organic acids could only recover the soil pH to about its original level. Mixing organic salts with soil caused an instant increase of soil pH. Decomposition of organic salts of sodium resulted in a steady increase of soil pH, with final soil pH being about 2.7-3.2 pH units over the control. Organic salts with the same anions （citrate） but different cations led to different magnitudes of pH increase, while those having the same cations but different anions led to very similar pH increases. Organic salts of sodium and sodium carbonate caused very similar pH increases of soil when they were added to the acid soil at equimolar concentrations of Na^＋. The results suggested that cations played a central role in regulating soil pH. Decarboxylation might only consume a limited number of protons. Conversion of organic salts into inorganic salts （carbonate） was possibly responsible for pH increase during their decomposition, suggesting that only those plant residues containing high excess base cations could actually increase soil pH.
LI Zhi-An ZOU Bi XIA Han-Ping DING Yong-Zhen TAN Wan-Neng FU Sheng-Lei
籽粒苋是一种生物量大、易栽培的镉(Cd)富集植物,具有作为Cd污染土壤修复植物的潜力.比较了两个基因型籽粒苋(K112和R104)的耐Cd性特征,土壤Cd污染浓度范围是0～50mgkg-1,生长60d收获.结果表明,籽粒苋K112(Amaranthus hypochondriacus L. Cv.‘K112’)与R104(A. hypochondriacus L. Cv.‘R104’)生物量随土壤中Cd浓度的增加而逐步下降,在土壤中Cd浓度<16mgkg-1时,其生物量积累没有受到明显的影响.在本试验最高Cd浓度条件(50mgkg-1)下仍可生长,但生物量显著下降.两种籽粒苋叶中Cd含量随土壤中Cd浓度增加而快速上升,在土壤Cd浓度为16mgkg-1时,叶内Cd浓度分别达120.63和109.96mgkg-1(DW),达到超富集植物的临界标准.Cd在植物体内的分布特征为叶>根>茎.籽粒苋两个品种相比,K112吸收Cd的能力大于R104,尤其是在高Cd浓度时,两种籽粒苋对Cd的绝对提取量相似,并随土壤Cd浓度的上升而快速增加.籽粒苋K112和R104对土壤中的Cd具有很强的耐性和积累的能力,可作为Cd污染土壤的修复植物.
