西南地区pH影响紫色土硝化作用机制研究

Mechanisms research on how pH affects nitrification in purple soils of Southwest China

硝化作用是一个对pH高度敏感的典型过程,但pH影响土壤硝化作用的机制尚不完全明了。本研究以西南地区3种发育于同一母质的不同pH的紫色土(酸性紫色土pH=5.7,中性紫色土pH=7.3,石灰性紫色土pH=8.0)作为供试材料,研究pH对紫色土硝化强度及氨氧化微生物的长期效应;通过人为添加酸(H_2SO_4)或碱(NaOH)短期改变土壤pH的方法,研究pH对紫色土硝化作用强度、氨氧化微生物活性及丰度的短期效应。结果表明,pH的短期改变对酸性与石灰性紫色土的硝化作用无显著影响(P>0.05),但对中性紫色土的硝化速率影响显著(P<0.05);氨氧化古菌(AOA)的amo A基因在酸性土壤环境中的表达更高(3.04×10~8/g干土,AOA/AOB=31.8),而氨氧化细菌(AOB)则更适应于石灰性紫色土环境(2.35×10~8/g干土,AOA/AOB=0.07)。研究表明,紫色土的硝化作用强度受pH的影响显著,且在不同pH土壤中其作用机制各不相同。硝化微生物群落和活性主导了酸性和石灰性紫色土中的硝化作用,而中性紫色土中的硝化作用则是由底物浓度所主导。研究推测长期稳定的pH是影响硝化微生物群落和活性的关键因素,而pH的短期改变则主要影响硝化反应的底物有效性。

Nitrification processes are highly sensitive to soil pH but the mechanisms through which pH affects soil nitrification are not fully understood.In the present study,three types of purple soils with different pH values were identified from the same parent material in southwest China（acid purple soil pH=5.7,neutral purple soil pH=7.3,calcareous purple soil pH=8.0）.These soil types were used to investigate the long-term effects of soil pH on nitrification and ammonia oxidizers and the short-term effects of soil pH on nitrification and the activities and abundance of ammonia oxidizers.Tests were undertaken by artificially adding acid（H_2SO_4） or alkali（Na OH） to change soil pH.The results showed that short-term pH changes had no significant effect（P〉0.05） on nitrification in acidic and calcareous purple soils whereas they had a significant effect（P〈0.05） on nitrification in the neutral purple soil.The gene amo A of ammonia-oxidizing archaea（AOA） was expressed much more fully in the acid soil（3.04×10^8/g dry soil,AOA/AOB=31.8）,whereas ammonia-oxidizing bacteria（AOB） were more adapted to the calcareous purple soil environment（2.35×10^8/g dry soil,AOA/AOB=0.07）.These results indicate that soil pH can significantly affect nitrification in purple soils and that different pH levels have different mechanisms.The activities and community of nitrifying microorganisms were the dominant factors for nitrification in acidic and calcareous purple soils,while substrate concentration was the dominant factor in neutral purple soil.The key factor affecting the activity and community of nitrifying microorganisms is the long-term stable soil pH,while short-term pH changes mainly influence the substrate availability of nitrification.