我国典型茶园土壤硝化特征及其N₂O排放机制研究

【作者】 李勇；

【导师】 蔡祖聪； 程谊；

【作者基本信息】 南京师范大学 ， 自然地理学， 2023， 硕士

【摘要】 我国是传统的茶叶种植大国,种植历史悠久。与其他作物相比,茶树喜酸好铝、喜铵厌硝,且随着种植年限增加,茶树自身物质循环和根系代谢使得土壤pH值不断降低。茶树这些特点决定了其独特的土壤微生物群落结构及氮素循环特征。硝化作用是土壤氮素循环的关键过程之一,但对于茶树而言,不论是自养硝化还是异养硝化均不利于其对氮肥的吸收。此外,氮肥硝化产生的硝态氮不易被土壤吸附固定,而茶树生长的热带亚热带多雨环境势必会提高硝态氮向水体的迁移能力,不利于茶园土壤对氮素的保持。同时自养硝化产生的H⁺会进一步酸化土壤,抑制茶树生长。因此,有必要探明茶园土壤硝化特征及其控制因子,为降低茶园土壤硝化和酸化、提高氮肥利用率和减少氮素损失,提供理论依据和技术支持。本研究以我国典型茶园土壤为研究对象,采用¹⁵N示踪、乙炔抑制和实时荧光定量PCR技术相结合的方法,明确了我国典型茶园土壤自养和异养硝化作用的速率及其控制因子;阐明了茶园根际与非根际土壤的硝化特征以及N₂O排放途径;最终揭示了茶树凋落物返还对茶园土壤硝化速率及N₂O排放的影响机制。长期施肥刺激自养硝化作用,而自养硝化产生的H⁺加剧土壤酸化,土壤酸化反过来会抑制自养硝化,但土壤呈酸性且不断被酸化又为异养硝化的发生提供了条件。可见,茶园土壤的硝化作用途径及其控制因子较复杂。至今,我国典型茶园土壤初级自养和异养硝化速率及其各自的控制因子尚不清楚。因此,本研究选取我国茶叶主产区泰安、信阳、句容、郎溪、凤庆、英德、丽水和上饶的茶园土壤为研究对象,采用¹⁵N示踪结合乙炔抑制技术研究了我国典型茶园土壤初级自养硝化速率和异养硝化速率及其控制因子。结果表明,茶园土壤初级硝化速率为0.20～0.84 mg N kg^-1 d^-1,自养硝化速率为0.02～0.77 mg N kg^-1 d^-1以及异养硝化速率为0.06～0.24 mg N kg^-1 d^-1。加入硫酸铵能够显著提高初级硝化速率(0.24～1.52 mg N kg^-1 d^-1)和自养硝化速率(0.05～1.45 mg N kg^-1 d^-1),但对异养硝化速率没有影响。茶园土壤加硫酸铵与不加硫酸铵处理中自养硝化作用对总硝化的贡献率除上饶（23%、35%）和郎溪（12%、22%）较低外,其余均高于50%,自养硝化作用起主导作用,硫酸铵的加入能有效提高自养硝化对总硝化的贡献率。土壤pH是影响茶园土壤硝化速率的关键因素,其与初级硝化速率和自养硝化速率均呈显著正相关关系（P<0.05）,但与异养硝化速率呈显著负相关关系。土壤真菌丰度与异养硝化速率呈显著正相关关系,氨氧化古菌（AOA）丰度与自养硝化速率呈显著正相关关系。结构方程模型表明茶园土壤低pH值会通过降低AOA丰度来抑制自养硝化作用,而低pH又会提高真菌丰度进而促进异养硝化作用。综上所述,本研究揭示了我国典型茶园土壤硝化过程及其微生物驱动机制,为采取针对性措施实现茶园氮素增效减排提供理论依据。茶树根系发达,存在明显的根际效应,且根系在生长过程中会不断分泌有机酸致使根际酸化。因此,茶园根际与非根际土壤之间可能存在不同的硝化特征和N₂O排放途径。鉴于土壤pH是影响硝化作用的关键因子,本研究选取pH差异明显的泰安、句容、郎溪三地茶园根际与非根际土壤为研究对象,采用¹⁵N示踪技术研究茶园根际与非根际土壤硝化作用以及N₂O排放变化机制。结果表明,三地茶园的根际土壤初级硝化速率显著低于非根际土壤（P<0.05）。此外,三地茶园的根际土壤N₂O累积排放量亦显著低于非根际土壤。泰安根际与非根际土壤中,硝化对N₂O排放的贡献均约为80%,句容根际与非根际土壤中,硝化作用产生的N₂O占总排放量的比例为57～63%,而郎溪根际与非根际土壤中,硝化对N₂O排放的贡献仅为45～58%。可见,无论是根际土壤还是非根际土壤,N₂O排放主要来源于硝化过程。另外,三地茶园根际与非根际土壤的硝化作用产N₂O的占比不同,其中泰安根际与非根际土壤没有显著差异,郎溪根际土壤显著高于非根际土壤,句容根际土壤显著低于非根际土壤。相关性分析表明,根际土壤的AOA、氨氧化细菌（AOB）丰度与初级硝化速率和硝化产N₂O的贡献呈显著正相关关系,nos Z基因丰度与反硝化产N₂O的贡献呈显著正相关关系;非根际土壤中,只有AOB丰度与初级硝化速率呈显著正相关关系。无论根际土壤还是非根际土壤,pH与初级硝化速率和硝化过程产N₂O的贡献呈显著正相关关系,并且硝化速率与硝化产N₂O的贡献呈显著正相关关系,硝化作用越强硝化过程产生的N₂O越多。可见,与非根际土壤相比,根际土壤pH较低,硝化作用较弱,造成N₂O排放较慢。综上,本研究阐明了茶园根际与非根际土壤的硝化特征与N₂O排放变化机制,为茶园根际与非根际土壤氮素流失的研究提供了理论依据。在茶树-土壤系统中,每年有大量的茶树凋落物还田,提高了土壤碳的有效性,从而可能改变土壤初级硝化速率和N₂O排放。但是,茶树凋落物输入如何影响茶园土壤硝化速率以及N₂O排放至今仍不清楚。为此,本研究以泰安和郎溪两地茶园的根际与非根际土壤为研究对象,采用¹⁵N示踪技术研究茶树凋落物对土壤硝化作用和N₂O排放的影响。设置0.5%和1%两个水平的凋落物添加量。结果表明,凋落物添加对不同土壤的pH影响不同。加入凋落物后,泰安根际与非根际土壤pH显著降低（P<0.05）,而郎溪根际与非根际土壤pH显著升高,这说明添加凋落物虽然会加剧pH偏中性茶园土壤的酸化,但也可缓解强酸性茶园土壤的酸化。与对照处理相比,添加凋落物后,泰安根际与非根际土壤的初级硝化速率显著降低,而郎溪根际与非根际土壤的初级硝化速率在添加0.5%凋落物处理中显著加快,在添加1%凋落物处理中显著减慢。在两地根际与非根际土壤中,凋落物加入刺激土壤N₂O排放,增加反硝化过程对N₂O排放的贡献并降低硝化过程对N₂O排放的贡献。同时,凋落物加入显著增加土壤中细菌、真菌、硝化基因（AOA、AOB）和反硝化基因（nos Z、nir K、nir S）微生物丰度。相关性分析表明,土壤pH与初级硝化速率呈显著正相关关系,初级硝化速率与N₂O累积排放量呈显著负相关关系,而与硝化产N₂O的贡献呈显著正相关关系。土壤真菌、细菌、反硝化基因丰度与N₂O累积排放量呈显著正相关关系。综上所述,茶树凋落物加入能够抑制土壤硝化作用,并降低硝化作用对N₂O排放的贡献,增加土壤氮转化相关功能微生物丰度,刺激N₂O排放,进而提高反硝化对N₂O排放的贡献。更多还原

【Abstract】 China is one of the leading producers of tea,which has been widely cultivated here since ancient times.Tea is unique compared to other crops in that it is adapted to acidic and aluminum(Al)-rich soils and prefers ammonium(NH4+)over nitrate(NO3-)for nitrogen(N)absorption.The long-term cultivation of tea trees lowers the soil pH due to the circulation of tea garden materials and the metabolism of tea tree roots.Depending on the growth characteristics of the tea tree,the soil microbial community structure and N-cycle in tea gardens are likely to be different from those in other environments.Nitrification includes autotrophic nitrification and heterotrophic nitrification,which is a key process in N-cycle.Autotrophic nitrification and heterotrophic nitrification are not conducive to the uptake of N fertilizer in tea plants.Besides,NO3-produced by nitrification of N fertilizer is not easily adsorbed and fixed by soil,on that account,the rainy tropical and subtropical environment where tea plants grow will definitely increase the transferability of NO3-to water,which is unconducive to the maintenance of N in tea garden soils.Moreover,H+produced by autotrophic nitrification will further acidify soil,hence inhibiting the growth of tea plants.Therefore,it is necessary to explore the nitrification characteristics and control factors of tea garden soil,so as to provide theoretical basis and technical support for taking targeted measures to control nitrification and acidification of tea garden soil,improve N utilization rate and reduce N loss,and finally realize the sustainable development and utilization of tea garden soils.The project used a combination of 15N tracing technique,acetylene(C2H2)inhibition methods,and real-time quantitative PCR technology to clarify the main factors controlling autotrophic nitrification and heterotrophic nitrification in typical Chinese tea garden soils,We elucidated nitrification characteristics and oxide(N2O)emission pathways in rhizosphere and non-rhizosphere soils of tea plantation and revealed the effects of tea tree litter input on soil nitrification rate and N2O emission.Long-term fertilization stimulates autotrophic nitrification,which releases H+and aggravates soil acidification.Soil acidification suppresses autotrophic nitrification,but the soil is acidic and continues to acidify,providing the conditions for heterotrophic nitrification to occur.Thus,the nitrification pathway and its controlling factors are more complex in tea garden soils.the gross autotrophic nitrification rates and heterotrophic nitrification rates and their controlling factors in tea garden soils remain unclear.Therefore,the gross autotrophic and heterotrophic nitrification rates and their control factors were studied using 15N tracers in combination with C2H2 inhibition techniques for Taian,Xinyang,Jurong,Langxi,Fengqing,Yingde,Lishui and Shangrao of tea garden soils in major tea producing regions.The results showed that the gross nitrification rates in tea plantations were 0.20～0.84 mg N kg-1 d-1,heterotrophic nitrification rates were 0.06～0.24 mg N kg-1 d-1,and autotrophic nitrification rates were 0.02～0.77 mg N kg-1 d-1.Addition of(NH4)2SO4 significantly increased gross nitrification rates(0.24～1.52 mg N kg-1 d-1)and autotrophic nitrification rates(0.05～1.45 mg N kg-1 d-1),but had no effect on heterotrophic nitrification rates.The contribution rates of soil autotrophic nitrification to nitrification in tea garden soils were higher than 50%,which played a dominant role,except Shangrao(23%,35%)and Langxi(12%,22%).The addition of(NH4)2SO4 can effectively improve the contribution rate of autotrophic nitrification to nitrification.Soil pH was the key factor affecting the nitrification rate of tea garden soils,and was significantly positively correlated with the gross nitrification rate and autotrophic nitrification rate(P<0.05),but had a significant negative correlation with the heterotrophic nitrification rate.Fungal abundance was positively correlated with heterotrophic nitrification rates,and ammonia-oxidizing archaea(AOA)abundance was positively correlated with autotrophic nitrification rates.Structural equation modeling showed that low soil pH suppresses autotrophic nitrification by reducing the abundance of AOA,while low pH promotes heterotrophic nitrification by decreasing the abundance of fungi.In conclusion,this study revealed the nitrification process and microbial driving mechanism of tea garden soils,which provided a theoretical basis for taking targeted measures to increase N efficiency and reduce N emission in tea garden soils.Tea plants have developed a root system,which has an obvious rhizosphere effect.In addition,the root system will continuously secrete organic acid during growth,resulting in rhizosphere acidification.Therefore,there may be different nitrification properties and N2O emission pathways between rhizosphere and non-rhizosphere of tea garden soils.Considering that soil pH is a key factor in nitrification,In this study,rhizosphere and non-rhizosphere of tea garden soils in Taian,Jurong and Langxi with obvious pH differences were selected as research objects.The 15N tracer technique was used to study the nitrification of rhizosphere and non-rhizosphere soils and the mechanism of change in N2O emission in tea garden soils.The results showed that the gross nitrification rate of rhizosphere soil was significantly lower than that of nonrhizosphere soil(P<0.05).The cumulative N2O emission from the rhizosphere soil is significantly lower than that from the non-rhizosphere soil in the three tea plantations.Nitrification contributes about 80%to N2O emission in rhizosphere and nonrhizosphere soils in Taian,57～63%in Jurong,and 45～58%in Langxi.In conclusion,N2O emission was mainly derived from nitrification in both rhizosphere and nonrhizosphere soils.In addition,the contribution of rhizosphere and non-rhizosphere soil to nitrification differed among the three tea plantations.There was no significant difference between the two rhizosphere soils in Taian,but rhizosphere soil in Langxi was significantly higher than that in non-rhizosphere soil,while that in Jurong was significantly lower.Correlation analysis showed that AOA and AOB in rhizosphere soil were positively correlated with gross nitrification rate and N2O production,while abundance of nosZ was positively correlated with N2O production by denitrification.In non-rhizosphere soil,only ammonia-oxidizing bacteria(AOB)was positively correlated with gross nitrification rate.Both rhizosphere and non-rhizosphere soil pH were significantly positively correlated with gross nitrification rate and N2O production emission in the nitrification process,and there was a significant positive correlation between nitrification rate and N2O production emission in the nitrification process.The stronger the nitrification,the more N2O is produced during the nitrification.Rhizosphere soils have lower pH and weaker nitrification than non-rhizosphere soils,which in turn results in lower N2O emissions.In conclusion,this study clarifies the nitrification properties and N2O emission change mechanisms of rhizosphere and nonrhizosphere soils in tea gardens,and provides a theoretical basis for the study of N loss in rhizosphere and non-rhizosphere of tea garden soils.In tea tree-soil systems,large amounts of tea tree litter enter the soil each year,increasing the soil carbon availability and potentially altering the gross nitrification rate and N2O emission from the soil.However,it is still unclear how tea tree litter input affects the nitrification rate and N2O emission of tea garden soil.Therefore,we examined the impact of litter return on nitrification and N2O emission in rhizosphere and non-rhizosphere soils of tea plantations in Taian and Langxi using 15N tracer techniques.Litter addition levels were set at 0.5%and 1%.The results showed that tea litter had different effects on pH of different soils.The pH values of the rhizosphere and non-rhizosphere soil in Taian were significantly decreased after litters were added(P<0.05),and the pH value increased significantly in the rhizosphere and non-rhizosphere soils of Langxi after the addition of litters,indicating that the addition of tea tree litters in the neutral soil of the tea garden could aggravate soil acidification,while the addition of tea tree litters in the strongly acidic soil of the tea garden could alleviate soil acidification.The addition of tea tree litters had a significant effect on the gross nitrification rates of rhizosphere and non-rhizosphere soils compared to the control treatment.The gross nitrification rates of the rhizosphere and non-rhizosphere soils in Taian significantly decreased,while the gross nitrification rates of the rhizosphere and non-rhizosphere soils in Langxi significantly accelerated in the addition of 0.5%litters and significantly slowed down in the addition of 1%litters In both rhizosphere and nonrhizosphere soils,the addition of tea tree litter stimulated soil N2O emission,increased the contribution of denitrification process to N2O emission and decreased the contribution of nitrification process to N2O emission.The addition of tea litter significantly increased the microbial abundance of bacteria,fungi,nitrification genes(AOA,AOB)and denitrification genes(nosZ,nirK,nirS)in soil.Correlation analysis showed that soil pH was significantly positively correlated with gross nitrification rate,soil nitrification rate was negatively correlated with cumulative N2O emission,but positively correlated with nitrification contribution to N2O.Abundance of fungi,bacteria and denitrification genes had a positive and significant relationship with cumulative N2O emissions.In conclusion,the addition of tea tree litter suppresses soil nitrification,reduces the contribution of nitrification to N2O emission,increases the abundance of functional microorganisms associated with soil nitrogen conversion,stimulates N2O emission,and subsequently increases the contribution of denitrification to N2O emission.更多还原