保护性耕作碳氮磷生态化学计量特征及其耦合机制研究

Conservation tillage has been widely adopted in the crop grown regions in China. Conservation tillage, residue mulching and multi-cropping prevent soil and water erosion in order to maintain soil health. Ecological stoichiometry is a discipline that studies the balance between multiple chemical elements in ecological processes. The research on the C：N：P ecological stoichiometry and its coupling mechanism under conservation tillage is very important to know the balance between carbon, nitrogen and phosphorus cycles in agricultural ecosystem. The study area is a long-term experiment (from 2001) consisting of a series of conservation tillage practices in the Loess Plateau. The studied tillage measures included no-tillage without mulching (NT), conventional tillage with straw incorporation (TS), no-tillage with straw mulching (NTS), conventional tillage with plastic film mulching (TP) and no-tillage with plastic film mulching (NTP). Two sequences of wheat/peas and peas/wheat rotation systems were adopted under different conservation tillage systems. Through the determination of plant/soil carbon, soil nitrogen and phosphorus content, extracellular enzymes (BG, NAG, LAP, and AP) activity, greenhouse gas emissions, and by ecological stoichiometry theory and biostatistics, would be used to study the characteristics of the C：N：P ecological stoichiometry and its coupling mechanism under conservation tillage. Ecological characteristics of stoichiometric coupling relationship between plant and soil carbon nitrogen and phosphorus would be determined to understand the regulation factors and availability of farmland ecosystem nutrient under long-term conservation tillage. This would provide the theory and the basis of carbon cycle, nitrogen and phosphorus balance of farmland ecosystem.

保护性耕作由于其良好的固碳保水效应而被誉为深刻影响世界农业的一场革命，开展保护性耕作条件下碳氮磷生态化学计量特征及其耦合机制研究，对于揭示农田生态系统养分的可获得性及碳氮磷元素的循环和平衡机制具有重要意义。本项目以设置在黄土高原旱作农田的春小麦、豌豆双序列轮作长期保护性耕作试验（2001年设置，设传统耕作+不覆盖、免耕+不覆盖、传统耕作+秸秆还田、免耕+秸秆覆盖4个处理）为基础，通过测定植株/土壤碳氮磷含量、土壤胞外酶（BG、NAG、LAP、AP）活性、农田温室气体排放量等，以生态化学计量学及生物统计学为手段，研究长期保护性耕作条件下碳氮磷生态化学计量特征，探讨不同耕作措施对碳氮磷化学计量特征的影响，揭示植物-土壤碳氮磷生态化学计量特征的耦合关系，明确长期保护性耕作条件下农田生态系统养分调控因素及可获得性，为大尺度研究农田生态系统碳循环、氮磷元素平衡及制约关系、减缓温室效应提供理论依据。

本研究基于布设在黄土高原旱作农田的春小麦、豌豆双序列轮作长期保护性耕作试验（共设4个处理：传统耕作+不覆盖、免耕+不覆盖、传统耕作+秸秆还田、免耕+秸秆覆盖4个处理）研究了保护性耕作措施对农田作物、土壤生态化学计量学的影响及其植物-土壤生态化学计量特征耦合关系。主要结论如下：.1.不同处理下春小麦叶片或籽粒N:P均未达到显著差异，而小麦茎秆N:P达到显著差异；不同处理下豌豆相同器官（叶片、茎秆、籽粒）N:P均未达到显著差异，说明不同耕作措施下植物N:P不能体现植物养分限制性和土壤供给性，而不同耕作处理对春小麦叶片或茎秆的C:N、C:P的影响达到了显著水平，说明春小麦叶片和茎秆的C:N、C:P对土壤氮素、磷素的供给能力具有指示作用。.2.春小麦不同器官化学计量比均不具有内稳性，说明春小麦不具有保持其各器官化学计量比相对稳定的控制能力，随其对应的土壤化学计量比的变化呈部分比例变化。春小麦农田土壤微生物具有保持其自身化学计量比相对稳定的控制能力，但也受其对应的土壤化学计量比的影响。春小麦农田土壤生态酶活性化学计量比随其对应的土壤化学计量比变化呈部分比例变化。.3.豌豆具有保持其籽粒氮磷比相对稳定的控制能力，但也受土壤氮磷比的影响。除豌豆籽粒氮磷比外，豌豆不具备保持其籽粒碳氮比、碳磷比以及叶片、茎秆碳氮比、碳磷比、氮磷比相对稳定的控制能力，均随其对应的土壤化学计量比呈部分比例变化。豌豆农田土壤微生物具有保持其自身碳氮比、碳磷比相对稳定的控制能力，但也分别受土壤碳氮比、碳磷比的影响，而不具有保持其氮磷比相对稳定的控制能力，随土壤氮磷比的变化呈部分比例变化。豌豆农田土壤βG:(NAG+LAP) 保持在相对稳定变化范围，但也受土壤碳氮比的影响，而土壤βG:AP和(NAG+LAP):AP分别随土壤碳磷比和氮磷比的变化呈部分比例变化。