Anthropogenic drivers of soil microbial communities and impacts on soil biological functions in agroecosystems

Soil carbon sequestration, greenhouse gas emissions, and water pollution under different tillage practices

Long-term no-tillage application increases soil organic carbon, nitrous oxide emissions and faba bean (Vicia faba L.) yields under rain-fed Mediterranean conditions.

Soil microbial transformations of nitrogen (N) can be affected by soil health management practices. Here, we report in situ seasonal dynamics of the population size (gene copy abundances) and functional activity (transcript copy abundances) of five bacterial genes involved in soil N cycling (ammonia-oxidizing bacteria [AOB] amoA, nifH, nirK, nirS, and nosZ) in a long-term continuous cotton production system under different management practices (cover crops, tillage, and inorganic N fertilization). Hairy vetch (Vicia villosa Roth), a leguminous cover crop, most effectively promoted the expression of N cycle genes, which persisted after cover crop termination throughout the growing season. Moreover, we observed similarly high or even higher N cycle gene transcript abundances under vetch with no fertilizer as no cover crop with N fertilization throughout the cover crop peak and cotton growing seasons (April, May, and October). Further, both the gene and transcript abundances of amoA and nosZ were positively correlated to soil nitrous oxide (N2O) emissions. We also found that the abundances of amoA genes and transcripts both positively correlated to field and incubated net nitrification rates. Together, our results revealed relationships between microbial functional capacity and activity and in situ soil N transformations under different agricultural seasons and soil management practices.IMPORTANCE Conservation agriculture practices that promote soil health have distinct and lasting effects on microbial populations involved with soil nitrogen (N) cycling. In particular, using a leguminous winter cover crop (hairy vetch) promoted the expression of key functional genes involved in soil N cycling, equaling or exceeding the effects of inorganic N fertilizer. Hairy vetch also left a legacy on soil nutrient capacity by promoting the continued activity of N cycling microbes after cover crop termination and into the main growing season. By examining both genes and transcripts involved in soil N cycling, we showed different responses of functional capacity (i.e., gene abundances) and functional activity (i.e., transcript abundances) to agricultural seasons and management practices, adding to our understanding of the effects of soil health management practices on microbial ecology.

Soil Health Management Enhances Microbial Nitrogen Cycling Capacity and Activity

The standard cultivation system in the North China Plain is double cropping of winter wheat and summer maize. The main effects of this cultivation system on root development and yield are decreases in soil nutrient content and depth of the plow layer under either long-term no-tillage or rotary tillage before winter wheat sowing and no tillage before summer maize sowing. In this study, we investigated the combined effects of tillage practices before winter wheat and summer maize sowing on soil properties and root growth and distribution in summer maize. Zhengdan 958 (ZD958) was used as experimental material, with three tillage treatments: rotary tillage before winter wheat sowing and no tillage before summer maize sowing (RTW + NTM), moldboard plowing before winter wheat sowing and no tillage before summer maize sowing (MPW + NTM), and moldboard plowing before winter wheat sowing and rotary tillage before summer maize sowing (MPW + RTM). Tillage practice showed a significant (P   MPW + NTM > MPW + RTM. Soil bulk densities were 3.3% and 515% lower in MPW + NTM and MPW + RTM, respectively, than that in RTW + NTM, and soil penetration resistances were respectively 17.8% and 20.4% lower, across growth stages and soil depths. Root dry matter and root length density were highest under MPW + RTM, with the resulting increased root activity leading to a yield increase of summer maize. Thus the marked effects of moldboard plowing before winter-wheat sowing on root length density, soil penetration resistance, and soil bulk density may contribute to higher yield.

Soil physical properties and maize root growth under different tillage systems in the North China Plain

The dynamics of N mineralization and nitrification may be altered by tillage, which ultimately affects crop growth and yield. This study investigated effects of tillage on soil nitrogen dynamics in a subtropical rice (Oryza sativa L.) soil (Hydragric Anthrosols, WRB classification) under combination ridge with no-tillage (RNT) and conventional tillage (CT) for 22 years in Chongqing, China. Soil mineralization, nitrification and changes in abundance of ammonia-oxidizing bacteria (AOB) and archaea (AOA) were investigated to test the hypothesis that RNT decreases nitrification in the rice-based ecosystem. Soil mineralization and nitrification rates decreased after 22 years of RNT compared with CT. Soil pH decreased about 0.5 units after 22 years of RNT, and this difference may be responsible for the decrease of N mineralization and nitrification rates observed under RNT. The nitrification process was best fitted by a first-order kinetic model for both CT and RNT. While the nitrification rate was significantly lower for RNT (2.96 mg N kg−1 day−1) than CT (3.40 mg N kg−1 day−1), AOB and AOA amoA gene copies were significantly higher for RNT than CT. This suggested that the functional expression (i.e., nitrification) may not be closely related to numbers of microorganisms that have the ability to nitrify. The AOA dominated in abundance over the AOB for both CT and RNT paddy soils, with AOA to AOB ratios ranging from 13 to 52, and the AOA abundance showed similar changes with AOB, suggesting that AOA may also play an important role in soil nitrification. Results implied that RNT may increase soil N retention by keeping N longer in the NH4+ state, thus decreasing the potential for N loss from leaching.

Tillage effects on soil nitrification and the dynamic changes in nitrifying microorganisms in a subtropical rice-based ecosystem: A long-term field study

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Tillage effects on soil nitrification and the dynamic changes in nitrifying microorganisms in a subtropical rice-based ecosystem: A long-term field study