Abstract
The combined effects of carbon dioxide (CO 2 ) enrichment and water deficits on nodulation and N 2 fixation were analysed in soybean [ Glycine max (L.) Merr.]. Two short‐term experiments were conducted in greenhouses with plants subjected to soil drying, while exposed to CO 2 atmospheres of either 360 or 700 μ mol CO 2 mol –1 . Under drought‐stressed conditions, elevated [CO 2 ] resulted in a delay in the decrease in N 2 fixation rates associated with drying of the soil used in these experiments. The elevated [CO 2 ] also allowed the plants under drought to sustain significant increases in nodule number and mass relative to those under ambient [CO 2 ]. The total non‐structural carbohydrate (TNC) concentration was lower in the shoots of the plants exposed to drought; however, plants under elevated CO 2 had much higher TNC levels than those under ambient CO 2 . For both [CO 2 ] treatments, drought stress induced a substantial accumulation of TNC in the nodules that paralleled N 2 fixation decline, which indicates that nodule activity under drought may not be carbon limited. Under drought stress, ureide concentration increased in all plant tissues. However, exposure to elevated [CO 2 ] resulted in substantially less drought‐induced ureide accumulation in leaf and petiole tissues. A strong negative correlation was found between ureide accumulation and TNC levels in the leaves. This relationship, together with the large effect of elevated [CO 2 ] on the decrease of ureide accumulation in the leaves, indicated the importance of ureide breakdown in the response of N 2 fixation to drought and of feedback inhibition by ureides on nodule activity. It is concluded that an important effect of CO 2 enrichment on soybean under drought conditions is an enhancement of photoassimilation, an increased partitioning of carbon to nodules and a decrease of leaf ureide levels, which is associated with sustained nodule growth and N 2 rates under soil water deficits. We suggest that future [CO 2 ] increases are likely to benefit soybean production by increasing the drought tolerance of N 2 fixation.
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Claims 11
Claim · model-written summary
Under drought, elevated CO2 delayed the decrease in N2 fixation rates associated with soil drying in soybean.
- Taxon
- soybean
Glycine maxt0 - Treatment
- elevated [CO 2 ]e0
- Outcome
- N 2 fixation ratese0
- Direction
- delay in the decreasee0
- Qualifier
- Under drought‐stressed conditionse1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“elevated [CO 2 ] resulted in a delay in the decrease in N 2 fixation rates”
e1“Under drought‐stressed conditions”
t0“Soybean”
Claim · model-written summary
Elevated CO2 allowed droughted soybean plants to sustain significant increases in nodule number and mass relative to ambient CO2.
- Taxon
- soybeanGlycine maxt0
- Treatment
- elevated [CO 2 ]e0
- Outcome
- nodule number and masse0
- Direction
- increasese0
- Qualifier
- plants under droughte0
- Comparator
- ambient [CO 2 ]e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“elevated [CO 2 ] also allowed the plants under drought to sustain significant increases in nodule number and mass relative to those under ambient [CO 2 ]”
t0“Soybean”
Claim · model-written summary
Total non-structural carbohydrate concentration was lower in the shoots of drought-exposed soybean plants.
- Taxon
- soybeanGlycine maxt0
- Organ / stage
- shootse0
- Treatment
- droughte0
- Outcome
- total non‐structural carbohydrate (TNC) concentratione0
- Direction
- lowere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The total non‐structural carbohydrate (TNC) concentration was lower in the shoots of the plants exposed to drought”
t0“Soybean”
Claim · model-written summary
Soybean plants under elevated CO2 had much higher TNC levels than those under ambient CO2.
- Taxon
- soybeanGlycine maxt0
- Treatment
- elevated CO 2e0
- Outcome
- TNC levelse0
- Direction
- much highere0
- Comparator
- ambient CO 2e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“plants under elevated CO 2 had much higher TNC levels than those under ambient CO 2”
t0“Soybean”
Claim · model-written summary
Drought stress induced a substantial accumulation of TNC in the nodules, paralleling the decline in N2 fixation, under both CO2 treatments.
- Taxon
- soybeanGlycine maxt0
- Organ / stage
- nodulese0
- Treatment
- drought stresse0
- Outcome
- accumulation of TNCe0
- Direction
- substantial accumulatione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“drought stress induced a substantial accumulation of TNC in the nodules that paralleled N 2 fixation decline”
t0“Soybean”
Claim · model-written summary
Under drought stress, ureide concentration increased in all plant tissues.
- Taxon
- soybeanGlycine maxt0
- Organ / stage
- all plant tissuese0
- Treatment
- drought stresse0
- Outcome
- ureide concentratione0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Under drought stress, ureide concentration increased in all plant tissues”
t0“Soybean”
Claim · model-written summary
Elevated CO2 resulted in substantially less drought-induced ureide accumulation in leaf and petiole tissues.
- Taxon
- soybeanGlycine maxt0
- Organ / stage
- leaf and petiole tissuese0
- Treatment
- elevated [CO 2 ]e0
- Outcome
- drought‐induced ureide accumulatione0
- Direction
- substantially lesse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“exposure to elevated [CO 2 ] resulted in substantially less drought‐induced ureide accumulation in leaf and petiole tissues”
t0“Soybean”
Claim · model-written summary
A strong negative correlation was found between ureide accumulation and TNC levels in the leaves.
- Taxon
- soybeanGlycine maxt0
- Organ / stage
- leavese0
- Outcome
- ureide accumulatione0
- Direction
- negativee0
- Qualifier
- TNC levelse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A strong negative correlation was found between ureide accumulation and TNC levels in the leaves”
t0“Soybean”
Claim · model-written summary
The authors indicate that ureide breakdown and feedback inhibition by ureides on nodule activity are important in the response of N2 fixation to drought.
- Taxon
- soybeanGlycine maxt0
- Compound
- ureidee0
- Outcome
- response of N 2 fixation to droughte0
- Qualifier
- feedback inhibition by ureides on nodule activitye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“indicated the importance of ureide breakdown in the response of N 2 fixation to drought and of feedback inhibition by ureides on nodule activity”
t0“Soybean”
Claim · model-written summary
The authors conclude that CO2 enrichment under drought enhances photoassimilation, increases carbon partitioning to nodules and decreases leaf ureide levels.
- Taxon
- soybeanGlycine maxe0
- Treatment
- CO 2 enrichmente0
- Outcome
- enhancement of photoassimilation, an increased partitioning of carbon to nodules and a decrease of leaf ureide levelse0
- Direction
- enhancemente0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“an important effect of CO 2 enrichment on soybean under drought conditions is an enhancement of photoassimilation, an increased partitioning of carbon to nodules and a decrease of leaf ureide levels”
Claim · model-written summary
The authors suggest that future CO2 increases are likely to benefit soybean production by increasing the drought tolerance of N2 fixation.
- Taxon
- soybeanGlycine maxe0
- Treatment
- future [CO 2 ] increasese0
- Outcome
- soybean productione0
- Direction
- benefite0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“future [CO 2 ] increases are likely to benefit soybean production by increasing the drought tolerance of N 2 fixation”
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