Abstract
Drought and soil nitrogen (N) deficiency are the limiting factors for poplar plantation productivity improvement in semi-arid regions. N addition could alleviate the growth decline of trees caused by drought; however, the effectiveness under severe drought and the underlying ecophysiological understanding remains uncertain. To further clarify the mechanisms of N addition in regulating tree biomass accumulation under different drought levels, we investigated the effects of 6 g NH 4 NO 3 per plant addition on the carbon and N assimilation and biomass accumulation of potted poplar seedlings under moderate or severe drought (40 % or 20 % of field capacity) conditions, with a particular emphasis on carbon and N interactions. We found that under moderate drought, N addition markedly promoted the activities of antioxidases, nitrate reductase (39 %), and N concentration (56 %) in leaves, significantly alleviated the damages of the membranes and photosystem II, and increased both leaf area (69 %) and chlorophyll content per unit leaf area, along with net photosynthesis rate (34 %), thereby significantly alleviating growth restrictions. However, under severe drought, although N addition increased the accumulation of both soluble sugars and N of the whole plant, it did not ameliorate the damage to membranes and photosystem II, nor did it improve chlorophyll content, leaf area, or biomass accumulation. Therefore, N addition could increase leaf area, enhance antioxidants, and positively influence leaf carbon assimilation (0.60, p ˂ 0.001) in poplar seedlings under moderate drought. The restrictions on leaf area and carbon assimilation were exacerbated during severe drought, which mitigated the positive effects of N addition on carbon assimilation and biomass accumulation. The findings of this study suggest that the growth of hybrid poplar can be enhanced by applying N fertilizer under mild drought conditions. In contrast, N fertilization has no significant effect in severe drought conditions. • The role of N addition in mitigating biomass accumulation under drought was investigated. • N addition enhanced N and C assimilation, which improved biomass production (44 %) under moderate drought. • Under severe drought, N addition still enhanced N assimilation and total N accumulation (58 %). • N addition did not promote leaf C assimilation or biomass production under severe drought.
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Claims 12
Claim · model-written summary
Under drought, nitrogen addition changed activities of antioxidases.
PopulusNot reportedComparatorValue
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“under moderate drought, N addition markedly promoted the activities of antioxidases, nitrate reductase (39 %), and N concentration (56 %) in leaves”
t0“poplar seedlings”
Claim · model-written summary
Under drought, nitrogen addition changed nitrate reductase.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“under moderate drought, N addition markedly promoted the activities of antioxidases, nitrate reductase (39 %), and N concentration (56 %) in leaves”
t0“poplar seedlings”
Claim · model-written summary
Under drought, nitrogen addition changed N concentration.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“under moderate drought, N addition markedly promoted the activities of antioxidases, nitrate reductase (39 %), and N concentration (56 %) in leaves”
t0“poplar seedlings”
Claim · model-written summary
Under drought, nitrogen addition changed damages of the membranes and photosystem II.
Not reportedTreatmentComparatorValue
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“significantly alleviated the damages of the membranes and photosystem II”
t0“poplar seedlings”
Claim · model-written summary
Under drought, nitrogen addition changed leaf area.
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“increased both leaf area (69 %) and chlorophyll content per unit leaf area, along with net photosynthesis rate (34 %)”
t0“poplar seedlings”
Claim · model-written summary
Under drought, nitrogen addition changed chlorophyll content per unit leaf area.
Not reportedTreatmentComparatorValue
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“increased both leaf area (69 %) and chlorophyll content per unit leaf area, along with net photosynthesis rate (34 %)”
t0“poplar seedlings”
Claim · model-written summary
Under drought, nitrogen addition changed net photosynthesis rate.
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“increased both leaf area (69 %) and chlorophyll content per unit leaf area, along with net photosynthesis rate (34 %)”
t0“poplar seedlings”
Claim · model-written summary
Under drought, nitrogen addition changed soluble sugars and N of the whole plant.
Not reportedComparatorValue
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N addition increased the accumulation of both soluble sugars and N of the whole plant”
t0“poplar seedlings”
Claim · model-written summary
Under drought, nitrogen addition changed damage to membranes and photosystem II.
Not reportedTreatmentComparatorValue
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“it did not ameliorate the damage to membranes and photosystem II”
t0“poplar seedlings”
Claim · model-written summary
Under drought, nitrogen addition changed chlorophyll content, leaf area, or biomass accumulation.
Not reportedTreatmentComparatorValue
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“nor did it improve chlorophyll content, leaf area, or biomass accumulation”
t0“poplar seedlings”
Claim · model-written summary
Under drought, nitrogen addition changed biomass production.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N addition enhanced N and C assimilation, which improved biomass production (44 %) under moderate drought”
t0“poplar seedlings”
Claim · model-written summary
Under drought, nitrogen addition changed total N accumulation.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N addition still enhanced N assimilation and total N accumulation (58 %)”
t0“poplar seedlings”
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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.