Decline in Soil Microbial Abundance When Camelina Introduced Into a Monoculture Wheat System.

Jeremy C Hansen,William F Schillinger,Tarah S Sullivan,Timothy C Paulitz

doi:10.3389/fmicb.2020.571178

Jeremy C Hansen, William F Schillinger + Show 2 more

Open Access

https://doi.org/10.3389/fmicb.2020.571178

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Abstract

Camelina [Camelina sativa (L.) Crantz] of the Brassicaceae family is a potential alternative and oilseed biofuel crop for wheat (Triticum aestivum L.)-based cropping systems of the Inland Pacific Northwest (PNW) of the United States. We investigated the effect of this relatively new rotational crop on soil microbial communities. An 8-year cropping systems experiment was initiated in 2007 at Lind, WA, to compare a 3-year rotation of winter wheat (WW)-camelina (C)-fallow (F) to the typical 2-year WW-F rotation. All phases of both rotations (total = 20 plots) were present every year to allow valid statistical analysis and data interpretations. Monoculture WW-F is the dominant system practiced by the vast majority of farmers on 1.56 million ha of cropland in the PNW drylands that receive <300 mm average annual precipitation. Microbial abundance and community composition were determined using phospholipid fatty acid analysis (PLFA) from soil samples collected during 3 consecutive years beginning in 2010. The abundance of fungi, mycorrhizae, Gram positive and negative bacteria, and total microbial abundance all declined over the 3-year period in the WW-C-F rotation compared to the WW-F rotation. All microbial lipid biomarkers were significantly less in fallow compared to WW of the WW-C-F rotation. The 2-year WW-F rotation demonstrated few differences in microbial lipid abundance and community structure between the rotation phases. Microbial abundance declined and community structure shifted in the 3-year WW-C-F rotation likely due to the combination of a Brassica crop followed by a 13-month-long fallow. The results of this study suggest that camelina in combination with a fallow period may disrupt microbial communities that have become stable under historical WW-F monocropping. Such disturbances have the potential to affect soil processes that have been provided by wheat-adapted microbial communities. However, the disruption appears to be short-lived with the microbial abundance of WW in the WW-C-F rotation, returning to similar levels observed in the WW-F rotation.

Highlights

The productivity of semi-arid, cereal-based agroecosystems is most often limited by water and nutrients (Maaz et al, 2018)
Though we see an overall decline in microbial biomarkers in the winter wheat (WW)-C-F rotation, the microbial community demonstrates resilience through its ability to return to the levels observed in the WW and fallow (WW-F) rotation. This indicates that WW is able to recruit back a large microbial community from the previous community, whether there was a year of F before WW or back-to-back years of C plus F
Results presented here show a sequential decline in microbial biomarkers associated with the 3-year WW-C-F rotation

Summary

Introduction

The productivity of semi-arid, cereal-based agroecosystems is most often limited by water and nutrients (Maaz et al, 2018). Farmers use soil and residue management practices that capture precipitation during the wet periods, maintain moisture in the soil, and sow crops that efficiently use available water (Deng et al, 2005) Such practices are important in the low-precipitation zone of the Inland Pacific Northwest (PNW) of the United States, where the 2-year winter wheat-fallow (WW-F) rotation, which produces only one crop every other year, is dominant as it provides greater yield stability, less economic risk, and higher net economic returns compared to alternative spring-sown cereal and broadleaf crops such as wheat, barley (Hordeum vulgare L.), oat (Avena sativa L.), pea; Pisum sativum L.), canola (WC; Brassica napus L.), condiment mustard (Brassica spp.), chickpea (Cicer arietinum L.), lentil (Lens culinaris L.), safflower (Carthamus tinctorius L.), sunflower (Helianthus annuus L.), and flax (Linum usitatissimum L.) so far tested (Schillinger et al, 2006; Young et al, 2014). Such rotational benefits are often attributed to control of soil-borne diseases and weeds (Kirkegaard et al, 2000; Morra and Kirkegaard, 2002)

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