连栽杉木人工林土壤氮循环功能基因丰度变化

Changes in the relative abundance of functional genes related to nitrogen cycling in continuously cultivated Chinese fir(Cunninghamia lanceolate) plantations

研究不同连栽代数杉木人工林土壤氮循环功能基因丰度的变化特征及其调控因子,可为亚热带人工林定向调控土壤氮素转化过程,提高氮素利用效率并减少其负面效应提供科学依据.以中亚热带不同连栽代数(一代FRP、二代SRP、三代TRP)杉木人工林和格氏栲天然林(NF)为研究对象,采用荧光定量PCR技术测定冬季和夏季土壤细菌16S rRNA、真菌18S rRNA和参与氮循环功能基因AOA、AOB、nifH、nirK、nirS、nosZ丰度,并分析其与土壤理化因子的相关关系.结果显示,天然林转变为杉木人工林后,整体上各氮循环功能基因丰度在天然林与一代林之间无显著差异.不同连栽代数杉木林土壤AOA和AOB基因丰度在两季变化规律一致,AOA基因丰度随连栽代数增加呈显著递减趋势(P<0.05),AOB基因丰度无显著差异.连栽杉木林土壤16S rRNA、18S rRNA、nifH、nirK、nirS和nosZ基因丰度变化特征因季节而异,冬季土壤nifH(7.05-8.15 copies/g)、nirS(6.78-8.08 copies/g)和nos Z(7.39-8.08 copies/g)基因丰度随连栽代数增加而下降,夏季土壤nirK(8.26-9.26 copies/g)基因丰度随连栽代数增加则为先增加后下降;杉木林土壤细菌16S(10.36-11.03 copies/g)基因丰度高于真菌18S(7.34-8.20 copies/g)基因丰度,且二者均为夏季略高于冬季.土壤含水量、可溶性有机氮和硝态氮可以较大程度地解释土壤功能基因丰度的变化.本研究表明亚热带杉木人工林中土壤AOA相比于AOB在数量上更占据优势地位,且其丰度随着连栽代数增加呈下降趋势,说明硝化作用可能随连栽代数增加而减弱,这也许是土壤系统在氮素匮乏条件下所采取的一种保氮策略.(图2表4参44)

This study investigated the abundance of functional genes involved in soil nitrogen(N)cycling and their driving factors,in different generations of Chinese fir plantations.We aimed to artificially regulate the N transformation process,enhance N use efficiency,and decrease its negative effect.Continuously cultivated Chinese fir plantations,first(FRP),second(SRP),and third generations(TRP),and Castanopsis kawakamiinatural forest(NF)in the mid-subtropics were selected for the study.The gene copy numbers of 16S rRNA,18S rRNA,AOA,AOB,nifH,nirK,nirS,and nosZ were measured using Q-PCR.The correlation between functional gene abundance and physicochemical parameters of the soil was analyzed.We observed that after conversion from natural forest to Chinese fir plantations,there was no significant difference in the abundance of N-cycling functional genes between NF and FRP.AOA and AOB gene abundance in the soil exhibited similar trends across generations in both seasons:AOA abundance in the soil during winter and summer decreased sharply(P<0.05)with the increase in generations,whereas AOB abundance remained largely unchanged.Variations in the abundance of 16S rRNA,18S rRNA,nifH,nirK,nirS,and nosZ genes among different generations were season-specific.In winter,gene abundance of nif H(7.05-8.15 copies/g dry soil),nir S(6.78-8.08copies/g dry soil),and nos Z(7.39-8.08 copies/g dry soil)decreased with increasing planting generations.In summer,nir K(8.26-9.26 copies/g dry soil)showed an initial increase and then decreased in cumulative planting generations.The 16S rRNA(10.36-11.03 copies/g dry soil)gene copy number was higher than that of 18S rRNA(7.34-8.20 copies/g dry soil)in all stands,and both genes were slightly higher expressed in summer than in winter.Soil moisture content,soluble organic nitrogen,and nitrate nitrogen are responsible,to a large extent,for changes in soil functional genes.In subtropical Chinese fir plantations,the abundance of AOA was significantly higher than that of AOB,and significantly decreased in increasing plantation generations,suggesting a weakening in nitrification with increased plantation generation.This may be a nitrogen-preserving strategy for adapting to nitrogen-deficient conditions.