Effect of Tillage Treatment on the Diversity of Soil Arbuscular Mycorrhizal Fungal and Soil Aggregate-Associated Carbon Content

Abstract

No-tillage agriculture can sustain productivity and protect the environment. A comprehensive understanding of soil arbuscular mycorrhizal (AM) fungal diversity and soil carbon distribution within aggregate fractions is essential to the evaluation of no-tillage agriculture. The long-term field experiment included two tillage treatments (1) no tillage with straw returned to the soil (NTS), and (2) conventional mouldboard-plowing tillage without straw (CT), and was conducted on the Loess Plateau, north-western China, from October 2009. The soil samples were collected from the surface layer (0-20 cm depth) at the maturation stage of the summer maize (Zea mays L.) for analyzing aggregates separated by the dry-sieving method. The organic carbon content in the bulk soil and different particle size aggregates were measured using the dichromate oxidization method. The species compositions of soil AM fungi were compared by applying high-throughput sequencing of 18S rRNA. The results showed that the NTS had 9.1-12.2% higher percentage of soil macro-aggregates, resulting in 9.8% increase in mean weight diameter and 10.0% increase in bulk soil organic carbon content as compared with CT treatment. In addition, the NTS treatment had significantly higher percentages of Septoglomus and Glomus than the CT treatment. We also found some significant differences in the fungal communities of the soils of the two treatments. There was a strong positive relationship between bulk soil organic carbon and the percentages of Septoglomus and Glomus. Our results suggested that the NTS treatment had a protective effect on AM fungal community structures, which might play a key role in the development of agricultural sustainability in the Loess Plateau of China.

Keywords: AM fungi; Loess Plateau; maize field; no-tillage; soil carbon.

FIGURE 1

Effect of tillage treatments on soil aggregates size distributions. ^∗p < 0.05.

FIGURE 2

The MWD (mean weight diameter) under no tillage with crop straw returning (NTS) and conventional tillage without the crop straw (CT) treatments. Different letters above the standard error bars indicate significant differences between treatments at the p < 0.05 level.

FIGURE 3

The SOC (soil organic carbon content) in bulk soil and its aggregations under no tillage with crop straw returning (NTS) and conventional tillage without the crop straw (CT) treatments. ^∗p < 0.05 and ^∗∗p < 0.01.

FIGURE 4

Rarefaction curves of Chao 1 (A), and Shannon index (B) for no tillage with crop straw returning (NTS) and conventional tillage without the crop straw (CT) treatments.

FIGURE 5

The OTU number (A) and venn diagram (B) of soil Arbuscular mycorrhizal (AM) fungi under no tillage with crop straw return (NTS) and conventional tillage without the crop straw (CT) treatments. ^∗p < 0.05.

FIGURE 6

The differences in the LDA (Linear Discriminant Analysis) distribution histogram (A) and evolutionary branch diagram (B) of special microorganisms under two tillage treatments: no-tillage with crop straw return (NTS) and conventional tillage without crop straw (CT).

FIGURE 7

The proportion of sequences in Glomeromycotina under no tillage with crop straw return (NTS) and conventional tillage without the crop straw (CT) treatments.

FIGURE 8

Biplot of principal components PC1 and PC2 from all soil samples and variables: percentage of soil large macro-aggregates (B1); percentage of small macro-aggregates (B2); percentage of micro-aggregates (B3); percentage of the silt and clay fraction (B4); SOC in large macro-aggregates (C1); SOC in small macro-aggregates (C2); SOC in micro-aggregates (C3); SOC in the silt and clay parts (C4); mean weight diameter (MWD); percentage of Septoglomus (Septoglm); percentage of Glomus (Glomus); percentage of Glomerales unclassified (Glomeral) sequences for the following cases: no-tillage with crop straw (NTS) and conventional tillage without crop straw (CT), based on correlations of the 12 variables specified in Table 1.