阿魏酸、对羟基苯甲酸及其混合液对土壤氮及相关微生物的影响

通过室内培养法,研究了不同浓度的阿魏酸、对羟基苯甲酸及其混合液对土壤氮素、与氮素转化相关的微生物和酶的影响。结果表明,10^-4mol/L阿魏酸和对羟基苯甲酸使土壤铵态氮降低了11.18%和10.87%,硝态氮降低了6.33%和3.95%;10^-3mol/L阿魏酸、对羟基苯甲酸及其混合液分别使可溶性有机氮降低了6.59%、10.16%和10.39%。阿魏酸、对羟基苯甲酸及其混合液抑制了氨化细菌、硝化细菌和反硝化细菌的生长,削弱了土壤脲酶与蛋白酶的活性。与对照相比,10^-4mol/L混合液降低了26.04%的氨化细菌、30.79%的硝化细菌和16.74%的反硝化细菌。10^-3mol/L阿魏酸减少了3.33%的土壤脲酶和20.87%的蛋白酶活性;10^-3mol/L对羟基苯甲酸降低了土壤脲酶6.63%,蛋白酶22.94%;10^-3mol/L混合液减少了土壤脲酶7.47%和蛋白酶23.79%。混合液对土壤氮素转化的抑制作用最强,表明阿魏酸和对羟基苯甲酸存在协同作用。阿魏酸和对羟基苯甲酸等酚酸类化合物通过抑制土壤氮素转化微生物及其酶活性,从而影响土壤氮素转化。

Effects of ferulic acid, p-hydroxybenzoic acid and their mixture on mineral nitrogen and relative microbial function groups in forest soils

Phenolic compounds is an important class of plant secondary metabolites, whose molecular structure contains at least one hydroxyl connected directly to the benzene ring on the aromatic compounds. Phenolic compounds in the soils from the decomposition of plant parts and their residues play an important role in soil nitrogen (N) transformations by altering soil microbial activity. Previous studies of effects of phenolic compounds on soil N transformations and relative microbial activities have focused on macromolecular phenolic compounds such as tannic acids. However, the effects of lower molecular weight phenolic compounds such as ferulic acid and p-hydroxybenzoic acid on soil N transformations are not well understood. In this paper, concentrations of 10^-4 mol/L and 10^-3 mol/L of ferulic acid, p-hydroxybenzoic acid and their mixture were respectively added to forest soils for investigating the effects of phenolic compounds on soil mineral N, microbes and enzyme activity within one month incubation under room temperature. The results showed that concentrations of NH⁺₄-N, NO^-₃-N and dissolved organic N (DON) were lower in the soils amended with different phenolic acids than those without any such amendment. NH⁺₄-N was respectively reduced by 11.2% and 10.9% in the soils with the addition of 10^-4 mol/L ferulic acid and p-hydroxybenzoic acid. The addition of these ferulic acid and p-hydroxybenzoic acid lowered the soil NO^-₃-N by 6.3% and 4.0%. The addition of 10^-3 mol/L ferulic acid, p-hydroxybenzoic and the mixture decreased DON by 6.6%, 10.2% and 10.4%, respectively. Ammonifiers, nitrifiers, denitrifiers and microbial enzymes in the soils were inhibited by the addition of these phenolic compounds. The quantities of ammonifiers, nitrifiers and denitrifiers were lowered by 26.0%, 30.8% and 16.7% respectively in the soils amended with the mixture addition in comparison with the control. These suggested that hydroxyl groups in phenolic compounds could be a major functional group inhibiting activities of ammonifiers, nitrifiers and denitrifiers in the soils. Ferulic acid, p-hydroxybenzoic acid and their mixture greatly decreased the activities of urease and protease. The activities of urease and protease were reduced by 3.3% and 20.9% respectively with the addition of 10^-3 mol/L ferulic acid, and reduced by 6.6% and 22.9% with the addition of 10^-3 mol/L p-hydroxybenzoic. The mixture of 10^-3 mol/L inhibited the activity of urease by 7.5% and that of protease by 23.8%. Phenolic compounds entering into the soils could lead to the imbalance between intracellular microbial enzymes and extracellular enzymes and change in conformation of these enzymes. The mixture of ferulic acid and p-hydroxybenzoic acid having the greatest inhibition indicated that there was a synergistic effect on soil N transformations between ferulic acid and p-hydroxybenzoic acid. This study suggests that phenolic acids such as ferulic acid and p-hydroxybenzoic acid released from the plant litters, could inhibit microbial functional groups (ammonifiers, nitrifiers and denitrifiers) and enzyme activity (urease and protease) related to the N transformations in the soils, and thereby lower the available N in the soils for plants growth, which could be one of the major detrimental factors for the continous cropping systems.