Factors Affecting Soil Microbial Community Structure in Tomato Cropping Systems

Authors: Buyer, Jeffrey; Teasdale, John; Roberts, Daniel; Zasada, Inga; Maul, Jude

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2010
Publication Date: 2/17/2010
Citation: Buyer, J.S., Teasdale, J.R., Roberts, D.P., Zasada, I.A., Maul, J.E. 2010. Factors Affecting Soil Microbial Community Structure in Tomato Cropping Systems. Soil Biology and Biochemistry. 42:831-841.

Interpretive Summary: Soil microbes provide vital ecosystem services including nitrogen fixation and cycling, plant residue decomposition and carbon sequestration, and suppression of pathogens. Soil microbial communities in agroecosystems are affected by soil, climate, plant species, and management, but we do not yet know how all of these factors interact to control soil microbial populations. We identified some of the most important factors controlling microbial biomass and community structure in a tomato production system. We compared vetch cover crops, rye cover crops, black plastic mulch, white plastic mulch, and bare soil. None of the treatments had very much effect on tomato yield. Microbial biomass was increased by all cover crop treatments, including root only and shoot only. Cover cropping increased the absolute amount of all microbial groups, but Gram-positive bacteria decreased in proportion under cover crops. We attribute this decrease to increased readily available carbon under cover-cropped treatments, which favored other groups over Gram-positive bacteria. Vetch shoots increased the amount and proportion of Gram-negative bacteria, fungi, and mycorrhizal fungi in the rhizosphere of tomato plants. Soil temperature, soil moisture, and soil texture had much less effect than cover cropping on biomass and community structure. Management was found to be most important in determining soil microbial community composition, which suggests that in short time frames microbial community structure can be influenced by management decisions. These findings confirm that the soil microbial community is dynamic and responsive to annual land use management decisions and should not be treated as a black box in theory or process based models.

Technical Abstract: Soil and rhizosphere microbial communities in agroecosystems may be affected by soil, climate, plant species, and management. We identified some of the most important factors controlling microbial biomass and community structure in an agroecosystem utilizing tomato plants with the following nine treatments: bare soil, black polyethylene mulch, white polyethylene mulch, vetch cover crop, vetch roots only, vetch shoots only, rye cover crop, rye roots only, and rye shoots only. The following hypotheses were tested: (1) Temperature and moisture differences between polyethylene covered and cover cropped treatments are partly responsible for treatment effects on soil microbial community composition, and (2) Different species of cover crops have unique root and shoot effects on soil microbial community composition. Microbial biomass and community composition were measured by phospholipid fatty acid analysis. Microbial biomass was increased by all cover crop treatments, including root only and shoot only. Cover cropping increased the absolute amount of all microbial groups, but Gram-positive bacteria decreased in proportion under cover crops. We attribute this decrease to increased readily available carbon under cover-cropped treatments, which favored other groups over Gram-positive bacteria. Vetch shoots increased the amount and proportion of Gram-negative bacteria, fungi, and mycorrhizal fungi in the rhizosphere of tomato plants. Soil temperature, soil moisture, and soil texture had much less effect than cover cropping on biomass and community structure.