Abstract
Phytoremediation of cadmium (Cd)-polluted soil is an environmentally-friendly, cost-effective, and sustainable technology. Sweet sorghum is a promising candidate for phytoremediation, as it combines high Cd accumulation with the production of bioethanol. Nitrate plays a superior role in improving efficiency of Cd phytoremediation using sweet sorghum. Nevertheless, the specific effects of nitrate topdressing timing on Cd accumulation, bioethanol yield, and the associated rhizosphere microbiome in sweet sorghum remain unclear. This study demonstrated that applying nitrate at the seedling stage was significantly more effective than application at the jointing, flowering, or milk stages regarding phytoremediation of Cd-polluted soil. This early topdressing increased both fresh weight of internodes and total Cd accumulation in the shoots. Consequently, it also yielded the highest theoretical bioethanol production, reinforcing the benefit of early nitrate application for integrated phytoremediation and bioenergy. Further analysis revealed that soil nitrate content and shoot Cd accumulation were key factors in reshaping the rhizosphere microbial community and its functions. Nitrate topdressing at seedling stage depressed rhizosphere nitrogen fixation (indicated by downregulated nifK/H ) and denitrification (downregulated narG/H/I ), while enhancing ammonia cycle (upregulated nirA ). This shift ultimately increased soil nitrate content, which was positively correlated with higher shoot Cd accumulation. Additionally, metal resistance genes znuC s were also positively correlated with shoot Cd accumulation in sweet sorghum. Altogether, nitrate topdressing at seedling stage reshapes rhizosphere soil microbial functions, thereby improving sweet sorghum-assisted phytoremediation of Cd-polluted soil. • N topdressing at seedling stage promotes total internodes fresh weight of sweet sorghum grown in the Cd-polluted soil. • N topdressing at seedling stage remarkably increases shoot Cd accumulation as well as theoretical bioethanol yield. • Rhizosphere soil microbial divergence is driven by shoot Cd accumulation and soil nitrate content. • Soil N cycle genes nifK / H and narG / H / I are negatively correlated with shoot Cd accumulation. • znuC expression in rhizosphere soil is positively correlated with shoot Cd accumulation.
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Claims 12
Claim · model-written summary
Seedling-stage nitrate application was more effective for cadmium phytoremediation than application at later stages.
Verbatim
e0“applying nitrate at the seedling stage was significantly more effective than application at the jointing, flowering, or milk stages regarding phytoremediation of Cd-polluted soil”
t0“sweet sorghum”
Claim · model-written summary
Early nitrate topdressing increased internode fresh weight.
- Taxon
- sweet sorghumt0
- Organ / stage
- internodese0
- Treatment
- early topdressinge0
- Outcome
- fresh weight of internodese0
- Direction
- increasede0
Not reportedComparator
Verbatim
e0“This early topdressing increased both fresh weight of internodes and total Cd accumulation in the shoots”
t0“sweet sorghum”
Claim · model-written summary
Early nitrate topdressing increased shoot cadmium accumulation.
- Taxon
- sweet sorghumt0
- Organ / stage
- shootse0
- Treatment
- early topdressinge0
- Outcome
- total Cd accumulation in the shootse0
- Direction
- increasede0
Not reportedComparator
Verbatim
e0“This early topdressing increased both fresh weight of internodes and total Cd accumulation in the shoots”
t0“sweet sorghum”
Claim · model-written summary
Early topdressing gave the highest theoretical bioethanol production.
- Taxon
- sweet sorghumt0
- Treatment
- early topdressinge0
- Outcome
- theoretical bioethanol productione0
- Direction
- higheste0
Not reportedComparator
Verbatim
e0“This early topdressing increased both fresh weight of internodes and total Cd accumulation in the shoots. Consequently, it also yielded the highest theoretical bioethanol production”
t0“sweet sorghum”
Claim · model-written summary
Soil nitrate content and shoot cadmium accumulation were key drivers of rhizosphere microbial community and function.
- Taxon
- sweet sorghumt0
- Compound
- soil nitratee0
- Outcome
- rhizosphere microbial community and its functionse0
- Qualifier
- shoot Cd accumulatione0
Not reportedDirection
Verbatim
e0“soil nitrate content and shoot Cd accumulation were key factors in reshaping the rhizosphere microbial community and its functions”
t0“sweet sorghum”
Claim · model-written summary
Seedling-stage nitrate topdressing depressed rhizosphere nitrogen fixation.
- Taxon
- sweet sorghumt0
- Treatment
- Nitrate topdressing at seedling stagee0
- Gene
- nifK/He0
- Outcome
- rhizosphere nitrogen fixatione0
- Direction
- depressede0
Not reportedComparator
Verbatim
e0“Nitrate topdressing at seedling stage depressed rhizosphere nitrogen fixation (indicated by downregulated nifK/H )”
t0“sweet sorghum”
Claim · model-written summary
Seedling-stage nitrate topdressing depressed denitrification.
- Taxon
- sweet sorghumt0
- Treatment
- Nitrate topdressing at seedling stagee0
- Gene
- narG/H/Ie0
- Outcome
- denitrificatione0
- Direction
- depressede0
Not reportedComparator
Verbatim
e0“Nitrate topdressing at seedling stage depressed rhizosphere nitrogen fixation (indicated by downregulated nifK/H ) and denitrification (downregulated narG/H/I )”
t0“sweet sorghum”
Claim · model-written summary
Seedling-stage nitrate topdressing enhanced the ammonia cycle.
- Taxon
- sweet sorghumt0
- Treatment
- Nitrate topdressing at seedling stagee0
- Gene
- nirAe0
- Outcome
- ammonia cyclee0
- Direction
- enhancinge0
Not reportedComparator
Verbatim
e0“Nitrate topdressing at seedling stage depressed rhizosphere nitrogen fixation (indicated by downregulated nifK/H ) and denitrification (downregulated narG/H/I ), while enhancing ammonia cycle (upregulated nirA )”
t0“sweet sorghum”
Claim · model-written summary
The microbial functional shift increased soil nitrate content.
Verbatim
e0“This shift ultimately increased soil nitrate content”
t0“sweet sorghum”
Claim · model-written summary
Soil nitrate content was positively correlated with shoot cadmium accumulation.
Verbatim
e0“soil nitrate content, which was positively correlated with higher shoot Cd accumulation”
t0“sweet sorghum”
Claim · model-written summary
Rhizosphere metal resistance genes znuC s were positively correlated with shoot cadmium accumulation.
Verbatim
e0“metal resistance genes znuC s were also positively correlated with shoot Cd accumulation in sweet sorghum”
Claim · model-written summary
Rhizosphere nitrogen cycle genes nifK / H and narG / H / I were negatively correlated with shoot cadmium accumulation.
Verbatim
e0“Soil N cycle genes nifK / H and narG / H / I are negatively correlated with shoot Cd accumulation”
t0“sweet sorghum”
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