磷差异性调控水稻根际nirK/nirS型反硝化菌组成与丰度

磷作为一种重要的生命元素,对反硝化微生物的活性和功能有重要影响.反硝化功能基因nir K和nir S是编码亚硝酸还原酶的两种同工酶基因,但是,磷对具有同种功能的nir K和nir S型反硝化菌的调控是否存在差异尚不十分清楚.本文采集严重缺磷红壤性水稻土设置水稻盆栽试验,通过外源添加磷肥设置对照(CK,P:0 mg·kg-1),低磷(P1,P:15 mg·kg-1),高磷(P2,P:30 mg·kg-1)这3个磷添加水平,研究不同磷水平对水稻亚硝酸还原酶基因的组成与丰度的调控作用.结果表明,在长期缺磷土壤上施用磷肥对含亚硝酸还原酶基因nir K和nir S的细菌种群的调控作用有明显差异.不管是根际还是非根际土,含nir S的微生物种群均对施磷水平表现敏感,尤其是高磷(P2)水平,施磷可导致nir S丰度提高2～3倍,同时显著改变nir S型反硝化微生物的组成结构.相比之下,施磷后含nir K基因的微生物组成结构和丰度变异较小.与非根际土壤相比,高磷水平条件下根际土中nir S的基因拷贝数和群落结构均发生了显著变化,缺磷和低磷条件下水稻生长只引起根际土nir S种群组成结构发生显著变化,但其丰度与非根际无显著差异.但不同磷水平条件下nir K的基因丰度和组成结构在根际和非根际土之间几乎无显著变化.综上所述,在严重缺磷水稻土中加施磷肥会显著提高水稻根际和非根际土中nir K和nir S型反硝化菌数量,并改变其种群组成结构,且nir S比nir K型种群响应更敏感.不同磷水平条件下的水稻根系生长均显著改变了根际土壤中nir K和nir S种群组成结构,但除了在高磷水平条件下显著增加了nir S丰度外,对nir K和nir S丰度均影响较小.研究结果可为进一步深入探究施肥对土壤反硝化过程的影响提供理论依据.

Differential Responses of Rhizospheric nirK- and nirS-type Denitrifier Communities to Different Phosphorus Levels in Paddy Soil

Phosphorus is an essential life element, which can affect the activities and functions of denitrifiers. Both nirK and nirS genes can code nitrite reductase; however, it remains unclear whether nirK- and nirS-containing denitrifers respond differentially to changes in the availability of phosphorus in paddy soil. In this study, P-deficient paddy soil was used to grow rice plants. Three phosphorus levels established by applying P fertilizer at a rate of 0 mg·kg^-1 (CK), 15 mg·kg^-1 (P1), and 30 mg·kg^-1(P2), respectively. The abundance and community structure of nirK- and nirS- containing denitrifers were determined using quantitative PCR and high-throughput sequencing techniques. Results indicated that nirK- and nirS-containing communities responded differentially to changes in the P levels. The nirS-containing communities are more sensitive to the changes in P in both rhizosphere and bulk soil samples. In addition, the abundance of nirS genes was 2-3 times higher in the P2 treatment than in the CK treatment. Furthermore, the nirS community structure is also clearly differed from the CK treatment. However, P addition only induced partial modification of the community structure and abundance of nirK-containing denitrifiers. Moreover, compared to the bulk soil with each phosphorus level, the nirS community structure in the rhizosphere soil changed significantly; however, only the P2 treatment induced significant increases in the abundance of the nirS gene. In contrast, no significant differences in the abundance and composition of nirK-containing denitrifers were detected between rhizosphere and bulk soils under different phosphorus levels. Collectively, application of phosphate fertilizer in P-deficient paddy soil could significantly increase the abundance of nirK- and nirS-containing denitrifiers, changing their community structures, with nirS-type showing a greater sensitivity than nirK-type denitrifiers. In comparison, the denitrifying communities in the rhizosphere were more sensitive to variable P levels than that in the bulk soil. Compared to bulk soils, rice growth shifted the community structure of nirS- and nirK-containing denitrifiers in rhizosphere soils at each level of P, but failed to induce significant changes in their abundance (except for P2) that could cause a significant increase in nirS abundance. These results could provide a theoretical basis for exploring the effects of fertilization on soil denitrification.