MicroRNAs (miRNAs) have emerged as a class of regulators of gene expression through posttranscriptional degradation or translational repression in living cells. Increasing evidence points to the important relationship between miRNAs and environmental stress responses, but the regulatory mechanisms in plants are poorly understood. Here, we found that Arabidopsis thaliana intronic miR400 was cotranscribed with its host gene (At1g32583) and downregulated by heat treatment. Intriguingly, an alternative splicing (AS) event that occurred in the intron (306 bp) where MIR400 was located was specifically induced by heat stress. A 100 bp fragment was excised, and the remaining 206 bp intron containing MIR400 transcripts was retained in the host gene. The stress-induced AS event thus resulted in greater accumulation of miR400 primary transcripts and a low level of mature miR400. Together, these results provide the direct evidence that AS acts as a regulatory mechanism linking miRNAs and environmental stress in plants.

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The specially designed soil columns experiment was conducted to determine effects of waterlogging for 6 d at the third leaf stage (V3), the sixth leaf stage (V6), and the 10th day after the tasseling stage (10VT) on root growth and development of summer maize (Zea mays L.). Results showed that waterlogging significantly decreased root length, root length density, and number of root tips compared to the control (CK). Waterlogging significantly reduced the total absorption area and active absorption area with the most significant reduction in treatment at V3. The active absorption area of roots at V6, tasseling (VT), milking (R3), and physiological maturity (R6) stages decreased by 68, 67, 57, and 67%, respectively, due to waterlogging at V3. In addition, waterlogged plants generally had much lower root bleeding rates, which were significantly decreased by 46, 28, and 13% from the control by the treatment at V3, V6, and 10VT stages, respectively. The negative effects of waterlogging on root growth and development led to abnormal development of the aboveground biomass, resulting in significant reductions in dry matter, leaf area, net photosynthetic rate, and yield. Compared with grain yield of CK, yields under the treatments at V3, V6, and 10VT stages were reduced by 26, 21, and 13%, respectively. Responses of summer maize root growth and grain yield to waterlogging depended on the growth stage. Summer maize was most susceptible to waterlogging damage at V3 stage, followed by V6 and 10VT stages.Core Ideas We investigated summer maize root growth in response to waterlogging at different stages. We realized summer maize root was most susceptible to damage when waterlogging occurred at V3, followed by V6 and 10VT. Waterlogging reduced grain yield of summer maize, for the delay of root growth.

Thirty-six biochars produced from distinct feedstocks at different temperatures were evaluated for their potential to remove mercury (Hg) from aqueous solution at environmentally relevant concentrations. Concentrations of total Hg (THg) decreased by >90% in batch systems containing biochars produced at 600 and 700 °C and by 40-90% for biochars produced at 300 °C. Elevated concentrations of SO4(2-) (up to 1000 mg L(-1)) were observed in solutions mixed with manure-based biochars. Sulfur X-ray absorption near edge structure (XANES) analyses indicate the presence of both reduced and oxidized S species in both unwashed and washed biochars. Sulfur XANES spectra obtained from biochars with adsorbed Hg were similar to those of washed biochars. Micro-X-ray fluorescence mapping results indicate that Hg was heterogeneously distributed across biochar particles. Extended X-ray absorption fine structure modeling indicates Hg was bound to S in biochars with high S content and to O and Cl in biochars with low S content. The predominant mechanisms of Hg removal are likely the formation of chemical bonds between Hg and various functional groups on the biochar. This investigation provides information on the effectiveness and mechanisms of Hg removal that is critical for evaluating biochar applications for stabilization of Hg in surface water, groundwater, soils, and sediments.

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