【目的】土地利用变化引起土壤对环境胁迫的潜力发生改变,以土壤碱性磷酸酶(ALP)为例,研究土壤酶的Hormesis效应,揭示其与土地利用变化的关系。【方法】采集洪泽湖河湖交汇区湿地光滩、芦苇、柳树和杨树人工林,以及农田5种土地利用类型下的土壤,研究自然演替和人为土地利用改变下Cd诱导ALP的Hormesis效应及其差异,解析土地利用改变的影响。【结果】光滩和芦苇两种自然覆被下,Cd诱导ALP 的Hormesis效应最大刺激率(y_max)分别为8.81%和5.84%,诱导ALP表达Hormesis效应的Cd剂量范围(D₁-D₂)分别是0.39~3.02和0.22~3.77 mg/kg,剂量区间(Q_i)为7.74和17.14,ALP应对Cd胁迫的潜能(R)为11.34和7.85。相比较而言,农田人为土地利用改变下 y_max为5.22%,D₁-D₂为0.09~1.03 mg/kg,Q_i为11.44,R为3.02。【结论】芦苇围垦为农田使得y_max、Q_i和R均明显下降,这可能导致土壤对Cd胁迫伤害的补偿潜力下降。进一步分析表明,洪泽湖河湖交汇区不同土地利用下土壤质地、全氮以及溶解性有机碳含量对ALP的Hormesis效应表达产生了重要影响。

【Objective】 Hormesis is characterized as low doses stimulation and high doses inhibition with a typical biphasic dose-response curves under stressors. The phenomenon has been widely reported in different species and individuals (plant, animal, bacteria, protozoa, virus, and so on) within various endpoint types (such as growth, metabolic, reproduction, survival, immune response, and so on). Hormesis is considered to be evolutionarily based with broad potential implications for toxicology, risk assessment, and numerous other areas. In the field of environment science and technology, the Hormesis concept possibly upset the basis for environmental regulations. The government and the public are beginning to rethink the answer to this question “How clean is clean?”. However, in the previous studies almost all experimental models involved in the realm of Hormesis are organisms, hardly linking the findings to the community- or ecosystem-levels of organization. The fundamental problem “How clean is clean” did not find the expected solution from Hormesis yet. Recently, soil hormesis, stress-induced hormetic responses occurred in soils in absence of plants, is increasingly attracting researchers' interest. The soil itself is assumed to be an experimental model, focusing on revealing the population expression of potential hormetic responses of all active subjects in the soil. Soil enzyme, one of the crucial soil components, involves in catalyzing reactions necessary for organic matter decomposition, nutrient cycling and energy transfer in soil ecosystem, which was considered a typical biological indicator for assessing soil quality and reflect the microbiological activity in soils. Soil enzyme was found to be the best experimental models known for revealing soil hormesis. Land use change has profound effects on soil properties, including soil enzymes. Assuming conversion of land use types to be a special disturbance to soil ecosystems, we attempt to link the compensation potentials of soil ecosystems for the disturbance to soil enzymes’ Hormesis. 【Method】Based on the integrality of mutual feedback net among soil enzymes, soil alkaline phosphatase (ALP), a key enzyme that hydrolyzes organic phosphate to inorganic form thereby increasing soil available phosphorus supply, was selected as a representative to investigate the potential soil hormetic responses with Cd as an inducer under five land use types emerged chronologically, including mudflat (Mud), Phragmites australis (Phr), Salix babylonica (Sal), Populus alba L. (Pop) and farmland (wheat-rice rotation, WRR) in the confluence area of the Hung-tse Lake and Huaihe River, China. 【Result】 Under the natural cover of Mud and Phr, the maximum stimulation rates (y_max) of ALP induced by Cd were 8.81% and 5.84% with dose range (D₁-D₂) of 0.39-3.02 mg/kg and 0.22-3.77 mg/kg, and dose interval (Q_i) of 7.74 and 17.14, respectively. The potential for coping Cd stress (R) was 11.34 and 7.85, respectively. In contrast, parameters for WRR were 5.22 % (y_max), 0.09-1.03 mg/kg (D₁-D₂), 11.44 (Q_i), and 3.02 (R), respectively. This showed that conversion of Phr into WRR resulted in a significant decrease in y_max, Q_i, and R, implying that conversion from natural land use to farmland may lead to a decrease in the compensation potential of the soil to Cd stress. In addition, redundancy analysis showed Q_i was mainly affected by the contents of soil DOC and 0.1-2.0 μm particles, and the main factors affecting R parameters were pH and $SO_{4}^{2-}$ content. 【Conclusion】 Man-made reclamation of wetlands would substantially reduce the capacity of the soil to cope with stress. Soil enzymes’ Hormesis may provide new insight for identifying and eliminating the damage factors induced by land-use change.