The interaction between biochar and soil changes nitrogen (N) dynamics in different ecosystems.Although multiple studies have reported influences of biochar on soil inorganic N (SIN) including ammonium (NH 4 + -N) and nitrate (NO 3 --N), the influences reported are contradictory. We undertook a meta-analysis to investigate how biochar properties and the interaction among biochar, soil and fertilisation affect SIN. This quantitative analysis used 56 studies with 1080 experimental cases from manuscripts published between 2010 and 2015. Overall, we found that biochar reduced SIN regardless of experimental conditions (approximately -11±2% of NH 4 + -N and -10±1.6% of NO 3 --N); however, 95% of cases were observed within one year after biochar application. SIN was best explained by residence time of biochar in soil, pyrolysis temperature, application rate, fertiliser type, and soil pH. The effects of biochar were complex due to the interaction of biochar with environmental factors. Most biochar trials used wood as a feedstock, but woody biochar did not decrease SIN as much as other plant-derived biochars. When biochar was used with NH 4 -based fertilisers, SIN decreased compared to biochar with no fertiliser. In contrast, adding organic fertiliser with biochar increased SIN compared to biochar alone. SIN was clearly reduced after one month of biochar application, suggesting that biochar should be applied at least one month prior to planting so plants are not affected by decreased N. Our results revealed that the interactions between biochar and environmental factors, pyrolysis temperature of biochar and biochar surface properties are the main driving factors affecting SIN. There were limited long term studies of greater than 1 year, thus the long term effects of biochar on SIN still remain unclear.

Biochar application to soils may increase carbon (C) sequestration due to the inputs of recalcitrant organic C. However, the effects of biochar application on the soil greenhouse gases (GHGs) fluxes appear variable among many case studies; therefore the efficacy of biochar as a carbon sequestration agent for climate change mitigation remains uncertain. We performed a meta-analysis of 91 published papers with 552 paired comparisons to obtain a central tendency of three main GHG fluxes (i.e., CO 2 , CH 4 , and N 2 O) in response to biochar application. Our results showed that biochar application significantly increased soil CO 2 fluxes by 22.14%, but decreased N 2 O fluxes by 30.92% and did not affect CH 4 fluxes. As a consequence, biochar application may significantly contribute to increased global warming potential (GWP) of total soil GHG fluxes due to the large stimulation of CO 2 fluxes. However, soil CO 2 fluxes were suppressed when biochar was added to fertilized soils, indicating that Accepted ArticleThis article is protected by copyright. All rights reserved. biochar application is unlikely to stimulate CO 2 fluxes in the agriculture sector, in which N fertilizer inputs are common. Responses of soil GHG fluxes mainly varied with biochar feedstock source and soil texture, and the pyrolysis temperature of biochar. Soil and biochar pH, biochar applied rate and latitude also influence soil GHG fluxes, but to a more limited extent.Our findings provide a scientific basis for developing more rational strategies towards widespread adoption of biochar as a soil amendment for climate change mitigation.

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The original domesticated carrots (Daucus carota) are thought to have been purple, accumulating large quantities of anthocyanins in their roots. A quantitative trait locus associated with anthocyanin pigmentation in purple carrot roots has been identified on chromosome 3 and includes two candidate genes, DcMYB6 and DcMYB7. Here, we characterized the functions of DcMYB6 and DcMYB7 in carrots. Overexpression of DcMYB7, but not DcMYB6, in the orange carrot 'Kurodagosun' led to anthocyanin accumulation in roots. Knockout of DcMYB7 in the solid purple (purple periderm, phloem, and xylem) carrot 'Deep Purple' using the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 system resulted in carrots with yellow roots. DcMYB7 could activate the expression of its DcbHLH3 partner, a homolog of the anthocyanin-related apple (Malus 3 domestica) bHLH3, and structural genes in the anthocyanin biosynthetic pathway. We determined that the promoter sequence of DcMYB7 in nonpurple carrots was interrupted either by DcMYB8, a nonfunctional tandem duplication of DcMYB7, or by two transposons, leading to the transcriptional inactivation of DcMYB7 in nonpurple carrot roots. As a result, nonpurple carrots fail to accumulate anthocyanins in their roots. Our study supports the hypothesis that another genetic factor suppresses DcMYB7 expression in the phloem and xylem of purple peridermal carrot root tissues. DcMYB7 also regulated the glycosylation and acylation of anthocyanins by directly activating DcUCGXT1 and DcSAT1. We reveal the genetic factors conditioning anthocyanin pigmentation in purple versus nonpurple carrot roots. Our results also provide insights into the mechanisms underlying anthocyanin glycosylation and acylation. Carrot (Daucus carota ssp. sativus; 2n 5 2x 5 18) provides rich health-promoting nutrients to humans. Carrots are classified into two groups according to exact botanical determination: the carotene group (variety sativus) and the anthocyanin group (variety atrorubens; Kammerer et al., 2004). Carotene group members, also known as nonpurple carrots, accumulate massive amounts of carotenoids in their roots (Clotault et al., 2008; Arscott and Tanumihardjo, 2010); anthocyanin group members, also known as purple carrots, accumulate high