How different soil moisture levels affect the microbial activity

ABSTRACT: The lowland soils are characterized by high susceptibility to water saturation. This anaerobic condition is usually reported in paddy fields and alters the decomposition process of soil organic compounds. The aim of this study was to evaluate the soil microbial and enzymatic activity of a lowland soil at different soil moisture contents. A poorly drained Albaqualf cultivated with irrigated rice was used to evaluate microbial and enzymatic activity in treatments with different levels of soil moisture, being: i) 60% of field capacity (FC) (60�); ii) 100% of FC (100�); iii) flooded soil with a 2 cm water layer above soil surface, and iv) soil kept at 60� with late flood after 29 days the incubation. The greater soil microbial activity was observed in the 100� treatment, being 41% greater than 60� treatment and only 2% higher than flooded treatment. The enzymatic activity data by fluorescein diacetate (FDA) hydrolysis corroborated the higher CO2 release in treatments with higher soil moisture content. Differently from the results reported, the main methodologies to evaluate microbial activity still recommend maintenance of the soil with a moisture content close to 60% of the FC. However, in lowland soil with history of frequent paddy fields, the maintenance of moisture close to 60% of the FC can limit the microbial activity. The soil respiration technique can be used to evaluate the microbial activity in flooded soil conditions. However, further studies should be conducted to understand the effect of the cultivation history on the microbial community of these environments.

摘要：低地土壤的典型特征为极易发生水分饱和。这类厌氧环境常见于稻田，会改变土壤有机化合物的分解过程。本研究旨在评估不同土壤含水率条件下低地土壤的微生物与酶活性。供试土壤为种植灌溉稻的排水不良型漂白淋溶土（Albaqualf），设置4组处理以探究不同土壤含水率对微生物及酶活性的影响：i) 田间持水量（field capacity, FC）的60%（60%FC）；ii) 100%FC；iii) 土壤表面覆有2 cm水层的淹水土壤；iv) 培养29天后再进行淹水处理的60%FC土壤。100%FC处理组的土壤微生物活性最高，较60%FC处理组提升41%，仅比淹水处理组高2%。通过荧光素二乙酸酯（fluorescein diacetate, FDA）水解法测得的酶活性数据，佐证了土壤含水率更高的处理组CO₂释放量更高的结论。与现有研究结论相悖的是，当前主流的土壤微生物活性评价方法仍建议将土壤含水率维持在田间持水量的60%左右。但对于具有长期稻田种植历史的低地土壤而言，将含水率维持在60%FC左右反而会抑制微生物活性。土壤呼吸法可用于评价淹水土壤条件下的微生物活性，但仍需开展进一步研究以明确种植历史对这类环境中微生物群落的影响。