生物炭對茶園土壤溫室氣體釋放及微生物活性之影響

Abstract

土壤中施加生物炭，有增加碳儲存及降低土壤溫室氣體釋放的潛力。本研究探討生物炭影響土壤微生物及溫室氣體釋放的機制。試驗生物炭為經700℃焙燒之柳杉，現地施作試驗位於行政院農委會茶業改良場的有機及慣行耕作區茶園，並採集土壤進行土壤分層箱(soil layering box)試驗。現地試驗之生物炭以0%、1%及2%之量施加，於施肥後定時收集兩個月間之氣體及土壤，進行分析。土壤分層培養箱置有一層生物炭於多層茶園土壤中間，經培養與分層採樣後，進行分析。土壤分層箱試驗結果顯示，有機田土壤的微生物數量分布不受生物炭處理影響。而在慣行田土壤分層箱中，生物炭層間的微生物數量高於上下兩層土及對照組的同層間土，並持續至試驗期第十二週。皮爾森相關係數顯示在有機田土壤分層箱中，微生物數量分布和非生物炭的有機質含量呈正相關，而在慣行田土壤分層箱中，則和水分及硝酸態氮含量呈正相關。有機田土壤分層箱中，生物炭層間的微生物生理活性低於土壤層間，而在慣行田土壤分層箱中則不受生物炭影響。族群生理圖譜之主成分分析結果顯示，在有機田土壤分層箱中，微生物族群結構有變化，並顯示生物炭層間的微生物活性較低，是因生物炭對養分的吸附力降低養分有效性及微生物吸收。而在慣行田土壤分層箱中，微生物活性、族群生理圖譜及溫室氣體釋放皆不受生物炭影響。現地施作試驗結果顯示，有機茶園經兩次施肥之後，生物炭處理組的土壤氧化亞氮釋放、微生物數量及活性皆較低。然而，第三次施肥之後，生物炭處理組及對照組的氧化亞氮釋放及微生物生長並無差異，可能因生物炭表面氧化所導致。而在慣行茶園中，生物炭雖然會增加土壤微生物生長，但不會顯著影響氧化亞氮釋放。生物炭增加二氧化碳釋放，皆可能發生於兩種茶園施肥之後，但並不會影響二氧化碳釋放總量。甲烷釋放於兩種茶園皆不受生物炭影響。

Applying biochar into soils has potential to increase carbon sequestration and reduce soil greenhouse gas (GHG) emission. This study was dedicated to investigate the mechanism through which biochar affects soil microorganism and GHG emissions. Biochar used in the experiment was generated from pyrolysis of Cryptomeria japonica (Linn. f.) D. Don. at 700˚C. The field experiment was located in the organic-farming tea garden (OTG) and conventional-farming tea garden (CTG) at Tea Research and Extension Station. Soils in the two gardens were obtained to conduct the soil layering box (SLB) experiment. In the field experiment, biochar was applied in the rates of 0% (control), 1% and 2% (w/w) in the OTG and CTG. Gas and soil were sampled within two months since each fertilizer application, and were subjected to the analysis. An SLB consisted of a biochar layer between soil layers. The soil and biochar were analyzed after incubation and sampling by layer. Results in the SLB experiment showed that there was no difference in microbial population among the (+BC) and (-BC) treatments of the O-SLBs, indicating that biochar had a limited impact on the distribution of microbial population. In the C-SLB, the (+BC) layers had larger microbial population compared with (+BC) upper layers, (-BC) smaller layers and the (-BC) layers in (-BC)-SLBs did, and such impact endured for at least 12 weeks. Pearson’s coefficient correlation revealed that in the O-SLBs, distribution of microbial numbers was related to non-biochar organic matter, while in the C-SLBs it was related to water and nitrate contents. Microbial activity in O-SLBs was smaller in biochar while was not different between biochar and soil in the C-SLBs. Principle component analysis for community-level physiological profiles (CLPP) revealed that in O-SLBs, the shift of microbial community might be present, and the smaller microbial activity in biochar might be due to great biochar nutrient-sorbing force which reduced nutrient availability for microbial utilization. In C-SLBs, microbial activity, CLPP and GHG fluxes were not different between (+BC)- and (-BC)-SLBs. In the field experiment, soil N2O effluxes, microbial population and activity in biochar-amended plots would decrease after the first two fertilizer applications in the OTG. However, after the third fertilizer application, no difference in N2O fluxes and microbial growth was present possibly due to biochar surface oxidation. In the CTG, although biochar increased microbial growth in the soil, it did not affect N2O emissions significantly. Biochar-induced CO2 emissions were likely present in the two gardens, but it did not lead to the change of cumulative CO2 fluxes. Methane fluxes were not affected by biochar in the two gardens.