Gluconacetobacter diazotrophicus inoculation of two lettuce cultivars affects leaf and root growth under hydroponic conditions

Authors: SEBRING, RYAN - Pennsylvania State University; DUIKER, SJOERD - Pennsylvania State University; BERGHAGE, ROBERT - Pennsylvania State University; REGAN, JOHN - Pennsylvania State University; LAMBERT, JOSHUA - Pennsylvania State University; Bryant, Ray

Submitted to: Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2021
Publication Date: 2/1/2022
Citation: Sebring, R.L., Duiker, S.W., Berghage, R.D., Regan, J.M., Lambert, J.D., Bryant, R.B. 2022. Gluconacetobacter diazotrophicus inoculation of two lettuce cultivars affects leaf and root growth under hydroponic conditions. Horticulturae. 12(3):1585. https://doi.org/10.3390/app12031585.
DOI: https://doi.org/10.3390/app12031585

Interpretive Summary: The bacteria, Gluconacetobacter diazotrophicus, is a naturally occurring microorganism that has been found living within sugarcane where it fixes nitrogen (N) and can provide up to 35% of the plant’s N requirement. We investigated the effects of inoculating leaf lettuce (Lactuca sativa L.) with this bacterium. Two cultivars, “Black Seeded Simpson” and “Bibb/Limestone,” were grown hydroponically in a growth chamber-controlled environment with or without inoculant and with seven levels of N fertilization ranging from deficient to excessive. After 30 days, we harvested the plants and measured leaf, root, and total biomass accumulation, nitrogen density, and carbon/nitrogen (C/N) ratios. Black Seeded Simpson demonstrated a shifting of production towards leaf tissues, with significantly greater leaf production and reduced root production. The observed increase in leaf biomass was greatest at the slightly deficient N rate of 105 mg L-1 N where inoculated plants produced 14.8% more leaf biomass than uninoculated. Lower N density and higher C/N ratios in inoculated leaf tissue indicated greater N use efficiency. Bibb/Limestone responded to inoculation with an average increase of 10.9% in leaf production and with greater root biomass. Bibb/Limestone also exhibited lower N density in inoculated shoot tissues with a corresponding increase in C/N ratio. For growers looking to maximize lettuce yields, G. diaz inoculation may benefit production by increasing leaf yields while not increasing N fertilizer requirements.

Technical Abstract: Growth-promoting effects of Gluconacetobacter diazotrophicus inoculation on leaf lettuce (Lactuca sativa L.) cultivars “Black Seeded Simpson” and “Bibb/Limestone” were investigated. Plants of each cultivar were grown hydroponically in Kratky jars in a growth chamber-controlled environment in a completely randomized factorial design with 3 or 4 replications. Each experiment was repeated once. Factors were (1) with or without inoculant and (2) seven levels of nitrogen (N) fertilization ranging from deficient (37.5 mg L-1 N) to excessive (172.5 mg L-1 N). Shoot, root, and total biomass accumulation, nitrogen density, and carbon/nitrogen (C/N) ratios were measured for each variety. Black Seeded Simpson demonstrated a shifting of production towards aerial tissues, with significantly greater shoot production and reduced root production. The observed increase in shoot biomass was greatest at the slightly deficient N rate of 105 mg L-1 N where inoculated plants produced 14.8% more than uninoculated. Lower N density and higher C/N ratios in inoculated shoot tissue indicate greater N use efficiency. Bibb/Limestone responded to inoculation with an average increase of 10.9% in shoot production and with greater root biomass. Bibb/Limestone also exhibited lower N density in inoculated shoot tissues with a corresponding increase in C/N ratio. For growers looking to maximize lettuce yields, G. diaz inoculation may present a beneficial additive to the growing system, increasing leaf yields while not increasing N fertilizer requirements.