Abstract
White clover (Trifolium repens L.) plants were grown from seed in perlite, inoculated with effective rhizobia and exposed to the same ‘concentration x days’ of 15N-labelled nitrate in four contrasting patterns of doses. Acetylene reduction was measured at intervals using an open, continuous-flow sytem. Mean dry weight per nodule and rates of acetylene reduction fell rapidly (2–3 d) during periods of exposure to high nitrate concentrations (> 7 mM N) and rose again, equally rapidly, when nitrate was withdrawn or substantially reduced. The fall in mean dry weight per nodule (50–66 per cent) was almost certainly too large to be accounted for by loss of soluble or storage carbohydrate only. No new nodules were formed during periods of high nitrate availability. When nitrate was supplied continuously at a moderate concentration (5.7 mM N) nodule numbers stabilised although existing nodules increased in dry weight by almost four-fold over the 30 d measurement period. Treatment had no effect on the percentage nitrogen in plant tissues although there were large differences in the proportions derived from nitrate and N2-fixation. Plants exposed continuously or frequently to small doses of nitrate took up more nitrate, and hence relied less heavily on N2-fixation, than those exposed to larger doses less often. Increased reliance on nitrate brought with it increased total dry weight and shoot: root ratios. Possible mechanisms involved in bringing about these differences in nitrogen nutrition and growth are discussed.
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Claims 10
Claim · model-written summary
High nitrate concentrations decreased nodule dry weight and acetylene reduction rates in white clover, which recovered when nitrate was withdrawn.
- Taxon
- Trifolium repens L.
Trifolium repense0 - Organ / stage
- nodulee1
- Treatment
- high nitrate concentrationse1
- Interactor
- effective rhizobiae0symbiont
- Outcome
- Mean dry weight per nodule and rates of acetylene reductione1
- Direction
- felle1
- Qualifier
- rose againe1
- Comparator
- nitrate was withdrawn or substantially reducede1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“White clover (Trifolium repens L.) plants were grown from seed in perlite, inoculated with effective rhizobia”
e1“Mean dry weight per nodule and rates of acetylene reduction fell rapidly (2–3 d) during periods of exposure to high nitrate concentrations (> 7 mM N) and rose again, equally rapidly, when nitrate was withdrawn or substantially reduced”
Claim · model-written summary
Nodule dry weight fell by 50–66% under high nitrate, too much to be explained by loss of carbohydrate alone.
- Taxon
- Trifolium repens L.Trifolium repense0
- Organ / stage
- nodulee2
- Treatment
- high nitrate concentrationse1
- Outcome
- mean dry weight per nodulee2
- Direction
- falle2
- Value
- 50–66 per cente2
- Qualifier
- too large to be accounted for by loss of soluble or storage carbohydrate onlye2
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“White clover (Trifolium repens L.) plants were grown from seed in perlite, inoculated with effective rhizobia”
e1“Mean dry weight per nodule and rates of acetylene reduction fell rapidly (2–3 d) during periods of exposure to high nitrate concentrations (> 7 mM N) and rose again, equally rapidly, when nitrate was withdrawn or substantially reduced”
e2“The fall in mean dry weight per nodule (50–66 per cent) was almost certainly too large to be accounted for by loss of soluble or storage carbohydrate only”
Claim · model-written summary
No new nodules were formed under high nitrate availability.
- Taxon
- Trifolium repens L.Trifolium repense0
- Treatment
- high nitrate availabilitye3
- Interactor
- effective rhizobiae0symbiont
- Outcome
- new nodules were formede3
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“White clover (Trifolium repens L.) plants were grown from seed in perlite, inoculated with effective rhizobia”
e3“No new nodules were formed during periods of high nitrate availability”
Claim · model-written summary
Continuous moderate nitrate supply (5.7 mM N) stabilised nodule numbers in white clover.
- Taxon
- Trifolium repens L.Trifolium repense0
- Treatment
- nitrate was supplied continuously at a moderate concentration (5.7 mM N)e4
- Outcome
- nodule numberse4
- Direction
- stabilisede4
- Qualifier
- over the 30 d measurement periode4
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“White clover (Trifolium repens L.) plants were grown from seed in perlite, inoculated with effective rhizobia”
e4“When nitrate was supplied continuously at a moderate concentration (5.7 mM N) nodule numbers stabilised although existing nodules increased in dry weight by almost four-fold over the 30 d measurement period”
Claim · model-written summary
Under continuous moderate nitrate supply, existing nodules increased almost four-fold in dry weight over 30 days.
- Taxon
- Trifolium repens L.Trifolium repense0
- Organ / stage
- existing nodulese4
- Treatment
- nitrate was supplied continuously at a moderate concentration (5.7 mM N)e4
- Outcome
- dry weighte4
- Direction
- increasede4
- Value
- almost four-folde4
- Qualifier
- over the 30 d measurement periode4
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“White clover (Trifolium repens L.) plants were grown from seed in perlite, inoculated with effective rhizobia”
e4“When nitrate was supplied continuously at a moderate concentration (5.7 mM N) nodule numbers stabilised although existing nodules increased in dry weight by almost four-fold over the 30 d measurement period”
Claim · model-written summary
Nitrate treatment had no effect on the percentage nitrogen in white clover tissues.
- Taxon
- Trifolium repens L.Trifolium repense0
- Treatment
- Treatmente5
- Outcome
- percentage nitrogen in plant tissuese5
- Direction
- no_changeinferrede5
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“White clover (Trifolium repens L.) plants were grown from seed in perlite, inoculated with effective rhizobia”
e5“Treatment had no effect on the percentage nitrogen in plant tissues although there were large differences in the proportions derived from nitrate and N2-fixation”
Claim · model-written summary
The proportions of N derived from nitrate and from N2-fixation differed largely between treatments in white clover.
- Taxon
- Trifolium repens L.Trifolium repense0
- Interactor
- effective rhizobiae0symbiont
- Outcome
- proportions derived from nitrate and N2-fixatione5
- Qualifier
- large differencese5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“White clover (Trifolium repens L.) plants were grown from seed in perlite, inoculated with effective rhizobia”
e5“Treatment had no effect on the percentage nitrogen in plant tissues although there were large differences in the proportions derived from nitrate and N2-fixation”
Claim · model-written summary
Plants exposed continuously or frequently to small doses of nitrate took up more nitrate than those given larger doses less often.
- Taxon
- Trifolium repens L.Trifolium repense0
- Treatment
- small doses of nitratee6
- Outcome
- nitratee6
- Direction
- took up moree6
- Comparator
- larger doses less oftene6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“White clover (Trifolium repens L.) plants were grown from seed in perlite, inoculated with effective rhizobia”
e6“Plants exposed continuously or frequently to small doses of nitrate took up more nitrate, and hence relied less heavily on N2-fixation, than those exposed to larger doses less often”
Claim · model-written summary
Plants given small doses of nitrate frequently relied less heavily on N2-fixation than those given larger doses less often.
- Taxon
- Trifolium repens L.Trifolium repense0
- Treatment
- small doses of nitratee6
- Interactor
- effective rhizobiae0symbiont
- Outcome
- N2-fixatione6
- Direction
- relied less heavilye6
- Comparator
- larger doses less oftene6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“White clover (Trifolium repens L.) plants were grown from seed in perlite, inoculated with effective rhizobia”
e6“Plants exposed continuously or frequently to small doses of nitrate took up more nitrate, and hence relied less heavily on N2-fixation, than those exposed to larger doses less often”
Claim · model-written summary
Increased reliance on nitrate was associated with increased total dry weight and shoot:root ratio in white clover.
- Taxon
- Trifolium repens L.Trifolium repense0
- Treatment
- Increased reliance on nitratee7
- Outcome
- total dry weight and shoot: root ratiose7
- Direction
- increasede7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“White clover (Trifolium repens L.) plants were grown from seed in perlite, inoculated with effective rhizobia”
e7“Increased reliance on nitrate brought with it increased total dry weight and shoot: root ratios”
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