Abstract
Herbaspirillum seropedicae, as an endophyte and prolific root colonizer of numerous cereal crops, occupies an important ecological niche in agriculture because of its ability to promote plant growth and potentially improve crop yield. More importantly, there exists the untapped potential to harness its ability, as a diazotroph, to fix atmospheric N2 as an alternative nitrogen resource to synthetic fertilizers. While mechanisms for plant growth promotion remain controversial, especially in cereal crops, one irrefutable fact is these microorganisms rely heavily on plant-borne carbon as their main energy source in support of their own growth and biological functions. Biological nitrogen fixation (BNF), a microbial function that is reliant on nitrogenase enzyme activity, is extremely sensitive to the localized nitrogen environment of the microorganism. However, whether internal root colonization can serve to shield the microorganisms and de-sensitize nitrogenase activity to changes in the soil nitrogen status remains unanswered. We used RAM10, a GFP-reporting strain of H. seropedicae, and administered radioactive 11CO2 tracer to intact 3-week-old maize leaves and followed 11C-photosynthates to sites within intact roots where actively fluorescing microbial colonies assimilated the tracer. We examined the influence of administering either 1 mM or 10 mM nitrate during plant growth on microbial demands for plant-borne 11C. Nitrogenase activity was also examined under the same growth conditions using the acetylene reduction assay. We found that plant growth under low nitrate resulted in higher nitrogenase activity as well as higher microbial demands for plant-borne carbon than plant growth under high nitrate. However, carbon availability was significantly diminished under low nitrate growth due to reduced host CO2 fixation and reduced allocation of carbon resources to the roots. This response of the host caused significant inhibition of microbial growth. In summary, internal root colonization did little to shield these endophytic microorganisms from the nitrogen environment.
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Claims 7
Claim · model-written summary
Low nitrate increased endophyte nitrogenase activity relative to high nitrate.
- Treatment
- low nitratee0
- Interactor
- Herbaspirillum seropedicaeHerbaspirillum seropedicaet0symbiont
- Outcome
- nitrogenase activitye0
- Direction
- highere0
- Comparator
- high nitratee0
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We found that plant growth under low nitrate resulted in higher nitrogenase activity as well as higher microbial demands for plant-borne carbon than plant growth under high nitrate.”
t0“Herbaspirillum seropedicae in Maize Seedlings”
Claim · model-written summary
Low nitrate increased microbial demand for plant-borne carbon relative to high nitrate.
- Treatment
- low nitratee0
- Interactor
- Herbaspirillum seropedicaeHerbaspirillum seropedicaet0symbiont
- Outcome
- microbial demands for plant-borne carbone0
- Direction
- highere0
- Comparator
- high nitratee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We found that plant growth under low nitrate resulted in higher nitrogenase activity as well as higher microbial demands for plant-borne carbon than plant growth under high nitrate.”
t0“Herbaspirillum seropedicae in Maize Seedlings”
Claim · model-written summary
Low nitrate significantly diminished carbon availability.
- Treatment
- low nitratee0
- Interactor
- Herbaspirillum seropedicaeHerbaspirillum seropedicaet0symbiont
- Outcome
- carbon availabilitye0
- Direction
- diminishede0
- Comparator
- high nitratee1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“However, carbon availability was significantly diminished under low nitrate growth due to reduced host CO2 fixation and reduced allocation of carbon resources to the roots.”
t0“Herbaspirillum seropedicae in Maize Seedlings”
e1“We found that plant growth under low nitrate resulted in higher nitrogenase activity as well as higher microbial demands for plant-borne carbon than plant growth under high nitrate.”
Claim · model-written summary
Low nitrate reduced host CO2 fixation.
- Treatment
- low nitratee0
- Interactor
- Herbaspirillum seropedicaeHerbaspirillum seropedicaet0symbiont
- Outcome
- host CO2 fixatione0
- Direction
- reducede0
- Comparator
- high nitratee1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“However, carbon availability was significantly diminished under low nitrate growth due to reduced host CO2 fixation and reduced allocation of carbon resources to the roots.”
t0“Herbaspirillum seropedicae in Maize Seedlings”
e1“We found that plant growth under low nitrate resulted in higher nitrogenase activity as well as higher microbial demands for plant-borne carbon than plant growth under high nitrate.”
Claim · model-written summary
Low nitrate reduced carbon allocation to roots.
- Treatment
- low nitratee0
- Interactor
- Herbaspirillum seropedicaeHerbaspirillum seropedicaet0symbiont
- Outcome
- allocation of carbon resources to the rootse0
- Direction
- reducede0
- Comparator
- high nitratee1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“However, carbon availability was significantly diminished under low nitrate growth due to reduced host CO2 fixation and reduced allocation of carbon resources to the roots.”
t0“Herbaspirillum seropedicae in Maize Seedlings”
e1“We found that plant growth under low nitrate resulted in higher nitrogenase activity as well as higher microbial demands for plant-borne carbon than plant growth under high nitrate.”
Claim · model-written summary
The host response significantly inhibited microbial growth.
- Interactor
- Herbaspirillum seropedicaeHerbaspirillum seropedicaet0symbiont
- Outcome
- microbial growthe0
- Direction
- inhibitione0
- Qualifier
- This response of the hoste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This response of the host caused significant inhibition of microbial growth.”
t0“Herbaspirillum seropedicae in Maize Seedlings”
Claim · model-written summary
Internal root colonization offered little shielding from the nitrogen environment.
- Organ / stage
- roote0
- Interactor
- Herbaspirillum seropedicaeHerbaspirillum seropedicaet0symbiont
- Outcome
- did little to shield these endophytic microorganisms from the nitrogen environmente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In summary, internal root colonization did little to shield these endophytic microorganisms from the nitrogen environment.”
t0“Herbaspirillum seropedicae in Maize Seedlings”
The same questions in other papers
nitrogen · Herbaspirillum seropedicae · Zea mays (maize)Results agree
2 papers in the same direction as this paper
- positive
- positive
Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.