长期不同施肥下褐土养分及酶活性的生态化学计量特征

Ecological stoichiometric characteristics of soil nutrients and eco-enzymatic activities under different long-term fertilizations in a cinnamon soil

【目的】研究长期不同施肥条件下褐土养分含量和与土壤有机质水解、碳氮磷有效性相关的酶活性及其化学计量变化特征,以深刻认识农田土壤元素循环的生物地球化学特征。【方法】依托1992年开始的山西寿阳旱地农田生态系统野外长期定位试验,选取其中不施肥对照(CK),4个单施无机肥处理(N_(1)P_(1)、N_(2)P_(2)、N_(3)P_(3)、N_(4)P_(4)),3个无机肥和有机肥配施处理(N_(2)P_(1)M_(1)、N_(3)P_(2)M_(3)、N_(4)P_(2)M_(2))和1个单施有机肥处理(M_(6))进行研究。于1992、2001、2006和2016年,分析了表层土壤(0—20 cm)中有机碳(C)、全氮(TN)、全磷(TP)、有效氮(AN)和有效磷(AP)含量及与碳氮磷循环相关的β-1,4-葡萄糖苷酶(β-1,4-glucosidase,BG)、β-1,4-N-乙酰氨基葡萄糖苷酶(β-1,4-N-acetylglucosidase,NAG)和碱性磷酸酶(alkaline phosphatase,ALP)活性。计算土壤养分之间和酶之间的化学计量比(C∶TN、C∶TP、TN∶TP和lnBG/lnNAG、lnBG/lnALP、lnNAG/lnALP)。计算酶向量角度(vector angle)和向量长度(vector length)。以向量角>45°或者<45°的多少来评价微生物受磷、氮限制的程度,向量角>45°越多表示微生物受磷限制越强,向量角<45°越多表示微生物受氮限制越强。以向量长度评价微生物受碳限制的程度,向量长度越长表示微生物受碳限制越强。【结果】1)除N4P4处理土壤C:TN显著高于M_(6)处理外,其他化肥和有机肥处理之间C:TN和C:TP不存在显著差异,而土壤TN:TP在各施肥处理下显著低于M_(6)处理(P<0.05)。与CK相比,M_(6)处理C∶TN显著降低了30.2%,TN∶TP显著升高了41.0%;N_(4)P_(4)处理C∶TP显著降低了23.3%,TN∶TP降低了17.6%(P>0.05)。土壤C∶AN平均为2.11~2.29,处理之间无显著差异;土壤C∶AP和AN∶AP随化肥和有机肥投入量增加而降低,4个有机肥处理的土壤C∶AP和AN∶AP降幅大于4个化肥处理。2)长期N_(2)P_(2)、N_(3)P_(3)和N_(4)P_(4)处理下,土壤lnBG/lnNAG、酶向量角度和酶向量长度略高于各有机肥处理(P>0.05),而lnNAG/lnALP略低于各有机肥处理(P>0.05);与1992年(试验开始年)相比,施肥处理后土壤lnBG/lnNAG均升高,lnNAG/lnALP均降低,向量角整体>45°,向量长度增加了11.1%~52.4%。3)相关性分析表明,AN与BG、NAG、ALP活性、lnBG/lnNAG及lnNAG/lnALP之间存在显著相关性;土壤C∶TN、C∶AN与酶活性lnBG/lnNAG、土壤TN∶TP与lnNAG/lnALP之间存在显著正相关,lnBG/lnALP与任何环境因子间都不存显著相关性。【结论】长期单施化肥易增加作物对有机碳的消耗和土壤稳定态磷素固持,微生物面临的碳、磷限制加剧;有机肥带入土壤的有机氮,加速了有机质分解,显著提高了土壤有效磷含量,有效缓解资源限制,促进褐土元素周转。综上,长期施肥显著改变了褐土元素化学计量特征,引起酶化学计量非稳态变化,土壤酶活性表现出强烈的资源依赖性。

【Objectives】We studied soil element content,the enzyme activity related to C,N and P availability and their stoichiometric changes to understand the effects of long-term fertilization on the biogeochemical characteristics and nutrients cycling of farmland.【Methods】The long-term field experiment was conducted in Shouyang County of Shanxi Province,and started in 1992.The study had nine fertilization treatments:no fertilizer control(CK),four chemical fertilizer treatments(N_(1)P_(1)、N_(2)P_(2)、N_(3)P_(3)、N_(4)P_(4)),three chemical fertilizer combined with manure treatments(N_(2)P_(1)M_(1)、N_(3)P_(2)M_(3)、N_(4)P_(2)M_(2)),and one manure treatment(M_(6)).Among these fertilization treatments,N_(1),N_(2),N_(3) and N_(4) represent urea N input rates of 60,120,180 and 240 kg/hm^(2);P_(1),P_(2),P_(3) and P_(4)represent super calciumphosphate input rates of 37.5,75.0,112.5 and 150.0 kg/hm^(2);M_(1),M_(2),M_(3) and M_(6) represent manure application rates of 22500,45000,67500 and 135000 kg/hm^(2),respectively.In 1992,2001,2006 and2016,soil samples were collected within 0–20 cm layer in all the nine treatments for the determination of soil organic carbon(C),total N(TN),total P(TP),available N(AN),available P(AP) content,and the activity of C-acquiring enzyme(β-1,4-glucosidase,BG),N-acquiring enzyme(β-1,4-N-acetylglucosidase,NAG) and Pacquiring enzyme(alkaline phosphatase,ALP).The soil elements stoichiometric ratios(C∶TN,C∶TP,TN∶TP) and enzyme C∶N(lnBG/lnNAG),enzyme C∶P(lnBG/lnALP) and enzyme N∶P(lnNAG/lnALP)ratios were analyzed.The enzyme vector angles > 45° and 0.05) and lnNAG/lnALP ratios were slightly lower(P>0.05) than the manure treatments under long-term N_(2)P_(2),N_(3)P_(3) and N_(4)P_(4) treatments.The lnBG/lnNAG was all higher but the lnNAG/lnALP was lower than their initials in 1992.The calculated vector angle was higher than45° for all fertilization treatments,and the vector length was 11.1%–52.4% higher than those in 1992.3)Significant correlations were found between AN and the activities of BG,NAG,ALP and the eco-enzymatic stoichiometries of lnBG/lnNAG and lnNAG/lnALP.There was no significant correlation between the contents of C,TP,AP and eco-enzymatic activities and stoichiometric ratios.Besides,soil C∶TN and C∶AN were positively correlated with lnBG/lnNAG(P<0.01),and TN∶TP positively correlated with lnNAG/lnALP(P<0.05).However,there was no significant correlation between lnBG/lnALP and all environmental factors.【Conclusions】Long-term application of chemical fertilizers promoted soil organic carbon consumption and phosphorus fixation,and aggravated the carbon and phosphorus limitation of microbial metabolism.The application of organic fertilizer increased soil organic nitrogen,accelerated organic matter decomposition,but significantly increased available phosphorus.Thus,application of organic fertilizer alleviated resource constraints faced by microorganism,and effectively promoted elements turnover in cinnamon soil.In summary,changes in soil element stoichiometry under long-term fertilization treatments would cause non-steady changes in ecoenzymatic stoichiometry,as the expression of enzyme activities is strongly dependent on resources.