Plant-soil interactions and stand decline in alfalfa: mechanisms and mitigation strategies
Date
2022-03-22
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0003-2564-8869
Type
Thesis
Degree Level
Masters
Abstract
In agricultural systems, effects of plants on soil microbial communities have been demonstrated to feedback over time and impact plant growth and productivity through plant-soil feedback (PSF). When negative, PSF results in productivity decline, limiting alfalfa (Medicago sativa) production. Unlike negative PSF, positive PSF promotes plant growth and improves productivity. Despite this, we do not fully understand the mechanisms of PSF and are thus limited in our strategies to mitigate productivity decline. Using the plant-soil feedback framework, we collected vegetation and soil samples from alfalfa stands grown to mixture (alfalfa-grass) and monoculture at stand ages 1 to 6 years old, near Saskatoon, SK. These soils were used in a completely randomized experimental design to inoculate 4 alfalfa varieties, viz. 2010, Foothold, 3010, and Spyder, and 5 other forage species, viz. Onobrychis viciifolia, Trifolium pratense, Vicia americana, Elymus lanceolatus, and Agropyron cristatum, of which traits depicting root economic spectrum and symbiosis were sampled. Additionally, next-generation amplicon sequencing was used to identify amplicon sequence variants (ASVs) of soil bacteria, oomycetes, and arbuscular mycorrhizal and other fungi in the inoculum associated with PSF. Field conditions including plant diversity, soil phosphorus, soil texture, weed abundance, and fiber content of focal crop mediated how plants condition soil microbial communities. These conditioning effects altered the relative composition of soil mutualists, plant-growth promoting microbes, saprotrophs and pathogens, all of which affected PSF. These PSFs, however, differed depending on the variety and crop species identity due to differences in how these plant types interacted with the soil microbiome. This allowed me to identify more than 30 soil microbial taxa that promoted positive or negative PSF, although the important taxa were rarely consistent among varieties or species. Root trait expressions for high resource conservative strategies and symbioses with mutualists lead to more positive PSF while the opposite traits (more resource acquisitive strategies and reduced symbioses) lead to more negative PSF. These root traits, however, varied among the species and to a smaller extent among the varieties, indicating that some crop species and cultivars can resist soil biotic stress under certain field conditions, and thus alleviate stand decline. This plant-soil feedback approach will be useful in trait-based selection during pasture rejuvenation and cultivar development for resistance to soil biotic stress. The resources provided in this study will therefore enhance sustainable management of productivity decline in agroecosystems.
Description
Keywords
Agroecosystem, grasses, legumes, mixture, monoculture, native and non-native forages, plant-soil feedback, soil microbial communities
Citation
Degree
Master of Science (M.Sc.)
Department
Plant Sciences
Program
Plant Sciences