Fluctuations in the abundance of ammonia oxidizers and the contents of inorganic nitrogen in solarized soil

Solarization makes a great impact on the abundance of ammonia oxidizers and nitrifying activity in soil. To elucidate fluctuations in the abundance of ammonia oxidizers and nitrification in solarized soil, copy numbers of <i>amoA</i> gene of ammonia-oxidizing bacteria (AOB) and archaea (AOA), viable number of ammonia oxidizers and inorganic nitrogen contents were investigated in greenhouse experiments. The copy number of <i>amoA</i> gene and the viable number of ammonia oxidizers were determined by the quantitative polymerase chain reaction and most probable number methods, respectively. Abundance of AOB based on the estimation of <i>amoA</i> gene copy numbers and viable counts of ammonia oxidizers was decreased by the solarization treatment and increased during the tomato (<i>Solanum lycopersicum</i> L.) cultivation period following the solarization. Effect of solarization on the copy number of <i>amoA</i> gene of AOA was less evident than that on AOB. The proportion of nitrate in inorganic nitrogen contents was declined by the solarization and increased during the tomato cultivation period following the solarization. Positive correlations were found between the proportion of nitrate in inorganic nitrogen content and the copy number of bacterial or archaeal <i>amoA</i> gene or the viable number of ammonia oxidizers; the copy number of bacterial <i>amoA</i> gene showed a strong correlation with the viable number of ammonia oxidizers. The present study revealed influences of solarization on the fluctuation in the abundance of ammonia oxidizers and dynamics of inorganic nitrogen contents in soil and the results indicate that the determination of <i>amoA</i> gene of AOB is possibly a quick and useful diagnostic technique for evaluating suppression and restoration of nitrification following solarization.

土壤日光消毒（solarization）对土壤中氨氧化菌的丰度与硝化活性具有显著影响。为阐明经日光消毒处理的土壤中氨氧化菌丰度及硝化作用的动态变化，本研究通过温室盆栽试验，检测了氨氧化细菌（ammonia-oxidizing bacteria, AOB）与氨氧化古菌（ammonia-oxidizing archaea, AOA）的<i>amoA</i>基因拷贝数、氨氧化菌活菌数及无机氮含量。其中，<i>amoA</i>基因拷贝数采用定量聚合酶链式反应（quantitative polymerase chain reaction）法测定，氨氧化菌活菌数则通过最概然数（most probable number, MPN）法检测。基于<i>amoA</i>基因拷贝数与氨氧化菌活菌数估算得到的AOB丰度，经日光消毒处理后显著降低，并在后续番茄（<i>Solanum lycopersicum</i> L.）栽培期内逐渐升高。日光消毒对AOA的<i>amoA</i>基因拷贝数的影响则显著弱于对AOB的影响。无机氮组分中硝态氮的占比经日光消毒后显著下降，并在后续番茄栽培期内逐步升高。无机氮组分中硝态氮的占比，与细菌或古菌<i>amoA</i>基因拷贝数、氨氧化菌活菌数均呈显著正相关；其中细菌<i>amoA</i>基因拷贝数与氨氧化菌活菌数的相关性尤为显著。本研究阐明了日光消毒对土壤氨氧化菌丰度动态及无机氮组分变化的调控作用，结果表明，检测AOB的<i>amoA</i>基因可作为一种快速有效的诊断手段，用于评估日光消毒后土壤硝化作用的抑制与恢复效果。