洞庭湖水稻土有机氮组分及其与可矿化氮的关系特征

Organic nitrogen fractions and associated relationships with mineralizable nitrogen in paddy soils in Dongting Lake region of China

为深入理解土壤有机氮有效性,利用Bremner酸解法测定了洞庭湖区典型水稻土有机氮组分,采用淹水生物培养法测定了土壤可矿化氮,并分析了二者间的内在关系。结果表明,酸解氮是土壤有机氮素的主要存在形式,其占土壤全氮的比例为58.6%～83.8%,不同类型水稻土酸解氮含量总体上依潴育性水稻土、潜育性水稻土、淹育性水稻土的次序逐渐降低;酸解氮中,氨基酸氮、氨基糖氮、氨态氮与未知氮占土壤全氮的比例分别为25.6%～43.1%、2.6%～9.0%、11.9%～22.3%和8.0%～25.3%。土壤可矿化氮数量变化主要受有机碳、全氮及粘粒含量的影响。酸解氮各组分均与土壤可矿化氮显著正相关(R=0.427～0.858,P<0.05),但多元逐步回归和通径分析表明,氨基酸氮是对可矿化氮有直接重要贡献的组分,是可矿化氮的主要来源。氨基酸氮、氨基糖氮、氨态氮、未知氮与氮矿化势的通径分析决策系数分别为0.685、0.251、0.028、-0.050,表明提升有机氮中除未知氮外的其它酸解组分特别是氨基酸氮的分配比例有利于增加土壤可矿化氮供应容量。

Soil organic nitrogen(SON)consists of several N forms with complex chemical structure,which is the source of soil mineralizable N(SMN),it is therefore essential to elucidate the contributions of SON fractions to SMN in clearly understanding the SON availability.In this study,representative paddy soil samples were collected across the Dongting Lake region for identifying the intrinsically relations between SON fractions and SMN.The soil organic N composition and SMN were determined by Bremner s acid-hydrolysis method and waterlogged incubation procedure,respectively.The results showed that soil acid-hydrolyzable N(AHN)varied in the range of 545.7~2 276.9 mg/kg that accounted for 58.6%~83.8%of total soil N,and thus serves as the main component of SON.It also showed the content of AHN among different paddy soils subtypes generally decreased in the order of Fluvisols,Gleysols and Cambisols.As to proportions of varying AHN fractions in total soil N,the ratios for amino acid N(AAN),amino sugar N(ASN),ammonia N(AN)and unknown hydrolysable N(UHN)ranged from 25.6%~43.1%,2.6%~9.0%,11.9%~22.3%and 8.0%~25.3%,respectively.Some soil properties,i.e.,soil organic carbon,soil total N and clay content were all significantly(P<0.01)correlated to SMN(R=0.569~0.753),indicating that organic matter content and texture are important soil indices for affecting the amount variation of SMN.Pearson correlation analysis showed that all organic N components in AHN were all well correlated with SMN(R=0.427~0.858,P<0.05),however,multiple stepwise regression and path analyses showed that AAN is the only one organic N form that has important direct contribution to SMN and thus serves as the primary source of SMN.The values of decision coefficient in path analysis for AAN,ASN,AN and HUN were 0.685,0.251,0.028 and-0.050,respectively,which suggested that it is essentially beneficial to the increase of SMN supplying capacity with increasing the proportions of AAN,ASN and AN in SON.