单宁酸对不同pH茶园土壤中活性铝形态分布的影响

Effects of tannic acid on active aluminum forms distribution in tea garden soils with different pH

采集云南省普洱市和江西省南昌县两地典型的茶园土壤，通过添加HCl和Ca（OH）2调节土壤pH，研究不同pH（3．0、3．5、4．0、4．5）茶园土壤添加0．4mmol·kg-1、2．0mmol·kg、4．0mmol·kg、8．0mmol．kg-1、12．0mmol．kg-1单宁酸后，活性铝形态交换态铝（Al3＋）、单聚体羟基铝[AI（OH）2＋、AI（OH）；]、酸溶无机铝[AI（OH）3^0]和殖酸铝[Al-HA]的分布特征。结果表明：单宁酸添加量为0～0．4mmol·kg-1和0～2．0mmol·kg-1时，江西南昌和云南普洱茶园土壤中交换态铝随土壤pH的增加呈明显下降趋势，而羟基态铝、酸溶无机铝和腐殖酸铝呈逐渐上升趋势；当单宁酸浓度增至2．0mmol·kg-1以上时，随土壤pH的增加，单宁酸对活性铝释放的抑制作用增强，各形态活性铝含量都较低，且不同pH处理土壤间的差异不显著。0～20cm土层土壤与20～406m土层土壤变化规律大致相似，总体上看，下层土壤活性铝总量高于上层。云南普洱茶园土壤活性铝总量明显高于江西南昌的茶园土壤。相关分析表明，0～20Gm土层土壤中，pH与羟基态铝、腐殖酸铝、土壤酸碱缓冲容量（pHBc3呈正相关（r=O．796，P〈0．01；r=0．960，P〈0．01；r=0．852，P〈0．01）；pHBC与交换态铝、羟基态铝呈负相关（F一0．904，P〈0．01；r=-0．645，P〈0．05），而与腐殖酸铝呈正相关（r=0．795，P〈0．01）。同时，单宁酸加入浓度为0～0．4mmol-kg-1时，土壤pH明显上升，之后随着单宁酸加入浓度的增加土壤pH持续下降，土壤pH（YpH）与单宁浓度（clDN）在此阶段基本符合方程：YpH=-0．04CDN＋3．82俾。=0．95，P〈0．01）的线性变化趋势，在单宁酸浓度达到8．0～12．0mmol·kg-1时，土壤pH基本不再变化。

The effects of tannic acid on the distribution of active aluminum forms in typical tea garden soils with different pH in Pu＇er of Yunnan Province and Nanchang of Jiangxi Province were studied by field observations and laboratory analyses. The tested 4 active aluminum forms in tea garden soils are exchangeable aluminum [A13＋], unimer hydroxyl aluminum [AI（OH）2＋ and Al（OH）2＋], acid-soluble aluminum [Al（OH）3^0] and humic-acid aluminum [A1-HA]. Experimental results showed that at tannic acid addition level of 0-0.4 mmol-kg i in Nanchang tea garden and 0-2.0 mmol·kg-1 in Pu＇er tea garden, soil exchangeable aluminum content decreased whereas hydroxyl aluminum, acid-soluble aluminum and humic-acid aluminum increased significantly with increasing soil pH. When the concentration of tannic acid exceeded 2.0 mmol·kg-1, the inhibition effect of high concentration of tannic acid on active aluminum content strengthened with increasing soil pH. The variation trend in 20-40 cm soil layer was similar to that in 0-20 cm soil layer. Generally, active aluminum content in upper soil layer was less than that in subsoil layers and the total content of active aluminum in Pu＇er tea garden soil was higher than that in Nanchang tea garden soils. Correlation analysis showed that soil pH was positivelycorrelated with soil pH buffie capacity （pHBC）, hydroxyl aluminum, humic-acid aluminum （r = 0.852, 0.796, 0.960; P 〈 0.01, 0.01, 0.01） in 0--20 cm soil layer, pHBC showed a significant negative correlation with exchangeable aluminum （r = 0.904, P 〈 0.01） and hydroxyl aluminum （r = 0.645, P 〈 0.05） and a positive correlation with humic-acid aluminum （r = 0.795, P 〈 0.01）. At tannic acid concentration of 0-0.4 mmol·kg-1, soil pH significantly increased to a peak before steadily decreasing. The relationship between pH （YpH） and tannic acid concentration （CDN） was best described by the following equation -- Ypn = --0.04CDN ＋ 3.82 （R2 = 0.95, P 〈 0.01）. When the concentration of tannic acid increased to 8.0-12.0 mmol-kg-1, soil pH remained unchanged. It was thus clearly noted that the effects of tannic acid on active aluminum content were not the same in different regions of tea garden soils. Low concentration of tannic acid improved soil content of various forms of activie aluminum. With increasing amounts of tannic acid, however, contents of various forms of active aluminum were inhibited. With increasing soil pH, high concentrations of tannic acid inhibited the release of active aluminum. Both pH and tannic acid in garden soils had a mutual weakening effect on active aluminum.