原位酶谱技术分析旱地长期覆盖下根际酶活性空间分布

Spatial distribution of enzyme activities in rhizosphere soil under long-term mulching of dryland with in-situ zymography

根与土壤微生物产生的酶是土壤有机质分解的主要生物驱动因素,对土壤养分循环具有重要意义。该研究利用原位酶谱技术在不破坏作物根系的同时,研究了渭北旱塬长期覆盖春玉米根际土壤酶活性空间分布。田间试验于2020年6月在中国科学院长武黄土高原农业生态试验站进行。以春玉米“先玉335”为供试材料,采用完全随机区组设计,设置秸秆覆盖(SM)、地膜覆盖(FM)和无覆盖(CK)三个处理,于春玉米吐丝期获取根系剖面酶谱图,分析了β-葡萄糖苷酶和亮氨酸氨基肽酶在春玉米根际的分布。结果表明:β-葡萄糖苷酶在秸秆覆盖下根际活性分布(热点)面积最大,是地膜覆盖的1.9倍、无覆盖的8.1倍;同时其在秸秆覆盖下延根分布距离最长为2.5 mm;与之对应,动力学拟合结果也表明秸秆覆盖下的酶动力学参数酶活最大反应速率和米氏常值最大,其土壤底物周转时间最快。亮氨酸氨基肽酶在地膜覆盖下活性分布总面积最大,是秸秆覆盖的1.8倍、无覆盖的6.4倍;其在地膜覆盖下酶活性延根分布距离最长为4.5 mm,秸秆覆盖下的酶动力学参数也为最大,底物周转时间最快。研究揭示了地表覆盖通过调节作物根际土壤酶活性空间分布促进养分吸收,实现旱地玉米高产高效的酶动力学机制。

Enzymes produced by roots and soil microorganisms have been the biological driving factors of organic matter decomposition to nutrient cycling in soil.However,the enzyme investigation remains a technical question,due to the heterogeneity of spatial distribution around the roots in the rhizosphere.Soil in-situ zymogram can directly display the distribution enzyme activity by fluorescence mapping.This study aims to investigate the spatial distribution of soil enzyme activities in the rhizosphere of spring maize with different soil surface mulching in Weibei dryland.Taking the spring maize“Xianyu 335”as the research object,a field experiment was carried out without damaging the crop roots by soil in-situ zymogram in June 2020 at the Loess Plateau agroecological experimental station of the Chinese Academy of Sciences.A complete randomized block design was employed with three treatments of Straw Mulching(SM),Plastic Film Mulching(FM),and no-mulching(CK).The in-situ zymography of the root profile was obtained at the silking stage of spring maize.The reaction parameters were calculated with the Michaelis-Menten equation after the enzyme kinetic experiment and simulation.Besides,the correlations between the concentration of enzyme and the soil chemical/physical properties variables were determined for the driving factors of enzyme spatial distribution with the different mulching treatments.The results show that there was the maximum distribution area ofβ-Glucosidase Activity(BG)in the rhizosphere of SM treatment,which was 1.9 times that of plastic film mulching,and 8.1 times that of CK treatment.The longest distance(2.5 mm)along the roots ofβ-glucosidase distribution was found with the SM treatment,which was 0.7 mm further than that with the FM,and 1.5mm further than that with CK.Correspondingly,the kinetic fitting showed that there were the maximum enzyme kinetic parameters V_(max) and k_(m) of SM treatment,which was the fastest turnover time of soil substrate.The total distribution area of Leucine Aminopeptidase Activity(LAP)with the FM was the largest,which was 1.8 times that of SM,and 6.4 times that of CK.The longest distribution distance of enzyme activity with FM treatment was 4.5 mm,1.7 and 2.1 mm further than those with the SM,and CK treatment,respectively.There were the maximum enzyme kinetic parameters with the FM treatment,all the same as the turnover of the substrate.The CK treatment presented the smallest hot spot area and kinetic parameters and the longest substrate turnover time,compared with the rest.The SM treatment increased the distribution area and extent of BG activity,indicating the fastest turnover rate of soil substrate,using the input of C,water storage,and soil N contents improvement.The FM treatment increased the distribution area and extent of LAP activity,with the fastest turnover rate of soil substrate using the soil temperature and water improvement.The CK treatment presented the smallest distribution area and extent of BG and LAP activities,where there was no change in the C input and soil temperature.As such,an enzyme kinetic mechanism was achieved to regulate the spatial distribution of enzyme activity in the crop rhizosphere soil for more nutrient uptake,particularly for the high yield and high nutrients utilization efficiency of dryland maize.