The ancestors of Gossypium arboreum and Gossypium herbaceum provided the A subgenome for the modern cultivated allotetraploid cotton. Here, we upgraded the G. arboreum genome assembly by integrating different technologies. We resequenced 243 G. arboreum and G. herbaceum accessions to generate a map of genome variations and found that they are equally diverged from Gossypium raimondii. Independent analysis suggested that Chinese G. arboreum originated in South China and was subsequently introduced to the Yangtze and Yellow River regions. Most accessions with domestication-related traits experienced geographic isolation. Genome-wide association study (GWAS) identified 98 significant peak associations for 11 agronomically important traits in G. arboreum. A nonsynonymous substitution (cysteine-to-arginine substitution) of GaKASIII seems to confer substantial fatty acid composition (C16:0 and C16:1) changes in cotton seeds. Resistance to fusarium wilt disease is associated with activation of GaGSTF9 expression. Our work represents a major step toward understanding the evolution of the A genome of cotton.

Upland cotton is the most important natural-fiber crop. The genomic variation of diverse germplasms and alleles underpinning fiber quality and yield should be extensively explored. Here, we resequenced a core collection comprising 419 accessions with 6.55-fold coverage depth and identified approximately 3.66 million SNPs for evaluating the genomic variation. We performed phenotyping across 12 environments and conducted genome-wide association study of 13 fiber-related traits. 7,383 unique SNPs were significantly associated with these traits and were located within or near 4,820 genes; more associated loci were detected for fiber quality than fiber yield, and more fiber genes were detected in the D than the A subgenome. Several previously undescribed causal genes for days to flowering, fiber length, and fiber strength were identified. Phenotypic selection for these traits increased the frequency of elite alleles during domestication and breeding. These results provide targets for molecular selection and genetic manipulation in cotton improvement.

Upland cotton (Gossypium hirsutum) is the most important natural fiber crop in the world. The overall genetic diversity among cultivated species of cotton and the genetic changes that occurred during their improvement are poorly understood. Here we report a comprehensive genomic assessment of modern improved upland cotton based on the genome-wide resequencing of 318 landraces and modern improved cultivars or lines. We detected more associated loci for lint yield than for fiber quality, which suggests that lint yield has stronger selection signatures than other traits. We found that two ethylene-pathway-related genes were associated with increased lint yield in improved cultivars. We evaluated the population frequency of each elite allele in historically released cultivar groups and found that 54.8% of the elite genome-wide association study (GWAS) alleles detected were transferred from three founder landraces: Deltapine 15, Stoneville 2B and Uganda Mian. Our results provide a genomic basis for improving cotton cultivars and for further evolutionary analysis of polyploid crops.

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Phosphorus (P) recycling or reuse by pyrolyzing crop residue has recently elicited increased research interest. However, the effects of feedstock and pyrolysis conditions on P species have not been fully understood. Such knowledge is important in identifying the agronomic and environmental uses of biochar. Residues of three main Chinese agricultural crops and the biochars (produced at 300°C-600°C) derived from these crops were used to determine P transformations during pyrolysis. Hedley sequential fractionation and 31 P NMR analyses were used in the investigation. Our results showed that P transformation in biochar was significantly affected by pyrolysis temperature regardless of feedstock (Wheat straw, maize straw and peanut husk). Pyrolysis treatment transformed water soluble P into a labile (NaHCO 3 -P i ) or semi-labile pool (NaOH-P i ) and into a stable pool (Dil. HCl P and residual-P). At the same time, organic P was transformed into inorganic P fractions which was identified by the rapid decomposition of organic P detected with solution 31 P NMR. The P transformation during pyrolysis process suggested more stable P was formed at a higher pyrolysis temperature. This result was also evidenced by the presence of less soluble or stable P species, such as such as poly-P, crandallite (CaAl 3 Contents lists available at ScienceDirectScience of the Total Environment j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v P forms at higher pyrolysis temperature although their solubility or stability requires further investigation. Results suggested that a relatively lower pyrolysis temperature retains P availability regardless of feedstock during pyrolysis process.

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Biochar, a by‐product of biomass pyrolysis, has been suggested as a mean to combat climate change, and at the same time to achieve agricultural and environmental benefits. As one possible source of the components with high aromatic structure in soil humus, biochar is of great importance in increasing soil carbon storage and improving soil nutrient retention and nutrient availability, and in maintaining the balance of soil ecosystem. This paper briefly reviewed and synthesized recent findings and discussions regarding the production and characteristics of biochar, its effects on global climate change and particularly in relation to the environmental effects of biochar in soils. Agronomic benefits of biochar application are critically highlighted because researches show that biochar had varied effects on crop productivity thorough the different bio‐physical interactions between the biochar and the soils, which are deserved for further investigations. Potential pitfalls and knowledge gaps were briefly discussed on the environmental behavior and the effects of biochar in agricultural ecosystem.

• Lower pyrolysis temperature (b 400°C) biochar retained P availability and increased plant growth.• Negative (antagonistic) interaction occurred between biochar and P fertilization on the biomass production and plant P concentration • Very limited utility value of biochar application occurred in saline sodic soil. G R A P H I C A L A B S T R A C TThe growth of Suaeda salsa in biochar amended saline sodic soils with (P 1 ) or without (P 0 ) P fertilization.a b s t r a c t a r t i c l e i n f o Little is known about the interactive effects between biochar application and phosphorus (P) fertilization on plant growth and P uptake. For this purpose, five wheat straw biochars (produced at 25°C, 300°C, 400°C, 500°C and 600°C for 4 h) with equal P (36 mg kg −1 ) amount, with and without additional P fertilization (100 mg kg) were applied in a pot experiment to investigate the growth of Suaeda salsa and their uptake of P from biochar and P fertilization amended saline sodic soil. Soil P fractions, dry matter yield, and plant P concentrations were determined after harvesting 90 days. Our results confirmed that relatively lower pyrolysis temperature (b400°C) biochar retained P availability and increased plant growth. The plant P concentration was significantly correlated with NaHCO 3 -P i (P b 0.05), and NaOH-P i (P b 0.1) during early incubation time (4 days) for biochar amended soil. As revealed by statistical analysis, a significant (P b 0.05) negative (antagonistic) interaction occurred between biochar and P fertilization on the biomass production and plant P concentration. For plant biomass, the effects size of biochar (B), P, and their interaction followed the order of B × P (0.819) N B (0.569) ≈ P (0.568) based on the partial Eta squared values whereas the order changed as P (0.782) N B (0.562) N B × P (0.515) for plant P concentration. When biochar and P fertilization applied together, phosphate precipitation/sorption reaction occurred in saline sodic soil which explained the decreased plant P Contents lists available at ScienceDirectScience of the Total Environment j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v availability and plant yield in saline sodic soil. The negative interaction effects between biochar and P fertilization indicated limited utility value of biochar application in saline sodic soil.