低分子有机酸对东北黑土酶活性与养分关系的影响

Relationship between enzyme activities and nutrients of black soil subjected to low molecular organic acid

【目的】为深入分析应用土壤酶活性评价黑土肥力的可行性,建立土壤质量酶活性科学评价体系,研究土壤酶活性与养分的关系。【方法】以典型黑土区耕地土壤为研究对象,通过外源添加柠檬酸、酒石酸、草酸和乙酸4种常见的低分子有机酸,结合室内恒温处理的方法,研究了不同种类、浓度的有机酸体系及不同处理时间对黑土酶活性、养分含量及两者关系的影响。【结果】柠檬酸质量分数为1%时,可促进黑土脲酶活性,而草酸、乙酸对脲酶、蔗糖酶、磷酸酶、过氧化氢酶等土壤酶活性产生抑制作用,且以乙酸抑制作用最强。酒石酸只显著抑制磷酸酶活性,对脲酶、蔗糖酶和过氧化氢酶无影响。土壤添加柠檬酸可显著增加有机质含量,而添加酒石酸、乙酸主要提高速效磷含量,供试低分子有机酸对水解性氮含量均无显著影响。柠檬酸浓度对脲酶、蔗糖酶、过氧化氢酶活性的影响呈单峰波动,且存在浓度临界值,其值前后的酶活性与养分的相关关系相反。土壤添加柠檬酸处理1 d,4种酶活性都基本保持不变或略有下降,但在处理3~5 d时活性急剧增强,处理15 d后除蔗糖酶活性波动较大外,剩余酶活性基本维持在较高水平。对土壤添加柠檬酸处理过程中,4种酶活性与有机质和速效磷显著负相关,与水解性氮无明显关系。通径分析表明,有机质对蔗糖酶的正效应最大,但被速效磷的间接负效应抵消;速效磷主要通过直接负效应影响脲酶、磷酸酶活性;水解性氮对酶活性的影响很小。【结论】土壤酶活性与养分间的关系会因有机酸的存在及其种类、浓度、降解等条件的变化而变化。基于土壤酶活性与养分关系建立的土壤质量酶活性评价体系,在有机酸浓度变化范围较大的土壤体系中,需要重新界定。

【Objective】Responses of enzyme activities to nutrient availability could provide a theoretical basis for evaluating fertilization.However,these enzyme-based reactor systems may lose reliability when the environment conditions change（e.g.,soil types,organic acid microenvironment,etc.）.We aimed to understand the applicability of soil enzymes on the evaluation and maintenance of fertility of black soil.【Method】Soil enzyme activity and nutrient contents were determined,and their relationships were analyzed based on the organic micro-zone system with different types and concentrations of organic acids,and incubation durations.【Result】The results showed that the citric acid significantly improved urease activity,but oxalic acid and acetic acid inhibited urease,invertase,catalase,and phosphatase activities,and that acetic acid had the strongest inhibitory effects on soil enzymes activities.Tartaric acid only inhibited the phosphatase activities,but not that of the other enzymes.Soil organic matter increased when citric acid was added to the soil; however,tartaric acid and acetic acid mainly contributed to increasing available phosphorus concentration.Unimodal fluctuations were observed for urease,invertase,and catalase under different concentrations of citric acid; consequently,the inverse relationships between soil enzyme activities and nutrients were found.During the incubation period,activities of four enzymes remained stable or decreased slightly after the first day of incubation,but significantly increased after the third day of incubation.When incubated for 15 days,all the soil enzyme activities detected at a high level except the invertase,which showed high fluctuations during the whole incubation period.In addition,during the whole incubation period,soil enzyme activity was negatively correlated with organic matter and available phosphorus content,but not with the content of available nitrogen.Path analysis revealed that organic matter had a direct association with invertase,but this association was mediated by available phosphorus,which had direct negative effects on urease and phosphatase activities.【Conclusion 】Our results indicate that the relationships between soil enzymes activities and nutrients will change under different types,concentration,decomposing rates of organic acid.Therefore,the enzyme-based evaluation system for soil quality may lose reliability.In order to excavate the applicability of soil enzymes in soil assessment,more studies should be conducted on the relationships between soil enzymes and nutrients under different environmental conditions.