黄土旱塬24a不同秸秆还田土壤碳、氮、磷和胞外酶计量特征

Effects of 24 Years Different Straw Return on Soil Carbon,Nitrogen,Phosphorus,and Extracellular Enzymatic Stoichiometry in Dryland of the Loess Plateau,China

探索黄土旱塬区农田土壤碳、氮和磷生物地球化学循环特征,可为农作物高效生产和土地可持续利用提供科学依据和技术支撑.以山西寿阳24 a玉米旱作试验田为对象,研究长期秸秆覆盖还田、直接还田、过腹还田和不还田对土壤元素和胞外酶活性化学计量比的影响,并计算向量角度和长度用于指示微生物面临的资源限制情况,向量角大于45°和小于45°分别表示微生物受磷限制和氮限制,偏离45°越大表示限制程度越大,向量长度越长表示微生物受碳限制越严重.结果表明:(1)长期秸秆还田土壤C/N和C/P分布在9.81~14.28和14.58~21.92之间,均值分别为12.36和17.51,分别较试验初期降低了6.0%和4.2%;土壤N/P分布在1.27~1.57之间,均值为1.42,较初期提高了2.2%.土壤C/N和C/P均呈现出先降低后升高的变化趋势,土壤N/P基本呈现出持平趋势,且不同秸秆还田处理之间土壤元素计量比均无显著性差异.(2)相比24 a长期不还田处理,长期秸秆覆盖还田处理土壤β-1,4-葡萄糖苷酶(BG)和β-1,4-N-乙酰葡糖氨糖苷酶(NAG)活性显著提高了134.4%和107.5%(P<0.05),长期秸秆直接还田土壤BG和碱性磷酸酶(AP)活性显著降低了59.3%和59.5%(P<0.05),长期过腹还田下土壤NAG活性显著提高了102.8%(P<0.05).长期秸秆还田处理下土壤微生物整体面临碳限制和磷限制,长期秸秆覆盖还田加剧了微生物碳限制,秸秆过腹还田处理可以缓解碳限制程度.相比24 a长期不还田处理,过腹还田处理可以显著降低土壤酶计量碳氮比(EEA_(C/N),P<0.05),直接还田处理可以显著提高土壤酶计量碳磷比(EEA_(C/P),P<0.05),3种秸秆还田方式对土壤酶计量氮磷比(EEAN/P)均无显著影响.向量角度整体大于45°,向量长度较初期增加了3.8%~20.1%.(3)相关性分析表明,碳、氮投入与BG活性显著负相关;有效氮与NAG、AP活性和EEA_(C/N)存在显著相关;C/P与EEA_(C/N)显著正相关;N/P与NAG活性、AP活性、EEA_(C/N)和EEA_(C/P)之间存在显著相关性;EEAN/P与任何环境因子之间都不存在显著相关性.长期不同秸秆还田处理下土壤N、P元素的有效性、N/P对土壤胞外酶活性和其化学计量特征均产生了显著的影响,在以后的土壤高效培育和农业生产活动中,应更多关注农田土壤中有机碳的提升和氮、磷有效性的促进.

Exploring the biogeochemical cycle characteristics of soil carbon,nitrogen,and phosphorus in farmland in the dryland of the loess plateau can provide scientific basis and technical support for efficient crop production and sustainable land use.Here,based on a long-term(24 year)straw return field experiment in Shouyang,Shanxi province,the effects of different straw return regimes,i.e.,straw mulching(SM),direct straw return(DS),animal-digested straw return(AS),and non-straw return(CK),on the stoichiometric ratio of soil elements and extracellular enzyme activities were studied.The vector angle and length were calculated to indicate the resource constraints faced by microorganisms.The vector angle was greater than 45°and less than 45°,indicating that microorganisms were limited by phosphorus and nitrogen,respectively.The greater the deviation from 45°,the greater the degree of limitation,and the longer the vector length,the more severely limited by carbon.The results showed that①the soil C/N and C/P of long-term straw returning ranged from 9.81 to 14.28 and from 14.58 to 21.92,with the mean values of 12.36 and 17.51,respectively,which were 6.0%and 4.2%lower than that at the initial stage of the experiment.The soil N/P was distributed between 1.27 and 1.57,with an average of 1.42,which was 2.2%higher than that in the initial stage.The soil C/N and C/P ratios showed a trend of first decreasing and then increasing,the soil N/P ratio basically showed a flat trend,and there was no significant difference in soil element metering ratios between different straw returning treatments.②Compared with the 24-year long-term non-straw return treatment,the activities ofβ-1,4-glucosidase(BG)andβ-1,4-N-acetylglucosaminidase(NAG)in the soil of the long-term straw mulching treatment increased by 134.4%and 107.5%(P<0.05),the activities of BG and alkaline phosphatase(AP)in the soil of the long-term straw mulching treatment decreased by 59.3%and 59.5%(P<0.05),respectively,and the activities of NAG in the soil of the long-term straw mulching treatment increased by 102.8%(P<0.05).Under the long-term straw returning treatment,soil microorganisms were faced with carbon and phosphorus limitation as a whole.Long-term straw mulching aggravated microbial carbon limitation,and animal-digested straw return could alleviate the degree of carbon limitation.Compared with that in the 24-year long-term non-straw return treatment,soil EEA_(C/N)could be significantly reduced by the animal-digested straw return treatment,and soil EEA_(C/P) could be increased by the direct straw return treatment.The three straw returning methods had no significant indigenous effect on soil EEAN/P.The overall vector angle was greater than 45°,and the vector length increased by 3.8%-20.1%compared with that in the initial stage.③Correlation analysis showed that C and N inputs were significantly negatively correlated with BG activity;available nitrogen was significantly correlated with NAG activity,AP activity,and EEA_(C/N);C/P was significantly positively correlated with EEA_(C/N);there were significant correlations between N/P and NAG activity,AP activity,EEA_(C/N),and EEA_(C/P);and there was no significant correlation between EEAN/P and any environmental factors.In conclusion,the availability of soil nitrogen and phosphorus elements and N/P ratio had significant effects on soil extracellular enzyme activity and stoichiometric characteristics under different long-term straw returning treatments.In the future,more attention should be paid to the improvement of organic carbon and the promotion of nitrogen and phosphorus availability in farmland soil in soil-efficient cultivation and agricultural production activities.