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Soil alkalization severely affects crop growth and agricultural productivity. Alkali salts impose ionic, osmotic, and high pH stresses on plants. The alkali tolerance molecular mechanism in roots from halophyte Puccinellia tenuiflora is still unclear. Here, the changes associated with Na2CO3 tolerance in P. tenuiflora roots were assessed using physiological and iTRAQ-based quantitative proteomic analyses. We set up the first protein dataset in P. tenuiflora roots containing 2,671 non-redundant proteins. Our results showed that Na2CO3 slightly inhibited root growth, caused ROS accumulation, cell membrane damage, and ion imbalance, as well as reduction of transport and protein synthesis/turnover. The Na2CO3-responsive patterns of 72 proteins highlighted specific signaling and metabolic pathways in roots. Ca2+ signaling was activated to transmit alkali stress signals as inferred by the accumulation of calcium-binding proteins. Additionally, the activities of peroxidase and glutathione peroxidase, and the peroxiredoxin abundance were increased for ROS scavenging. Furthermore, ion toxicity was relieved through Na+ influx restriction and compartmentalization, and osmotic homeostasis reestablishment due to glycine betaine accumulation. Importantly, two transcription factors were increased for regulating specific alkali-responsive gene expression. Carbohydrate metabolism-related enzymes were increased for providing energy and carbon skeletons for cellular metabolism. All these provide new insights into alkali-tolerant mechanisms in roots.

Although critical for global climate and the carbon cycle, the nature of past ocean circulation changes remains elusive. Based on deep-water carbonate ion ([CO3 2-]) reconstructions for wide locations, we discover a low-[CO3 2-] water mass in the South Atlantic at ~3-4 km (extending northward up to ~20°S) during the Last Glacial Maximum. Multiple proxies suggest that this low-[CO3 2-] signal likely reflects an extensive expansion of carbon-rich Pacific deep waters, revealing an ocean circulation scheme different from the long-held view for the glacial deep Atlantic. Comparison of high-resolution [CO3 2-] records from different water depths in the South Atlantic indicates that this expansion occurred between ~38 and ~28 thousand years ago. We infer that the associated carbon sequestration might have contributed critically to the contemporary ~20 ppm atmospheric CO2 decline and thereby helped pushing the global climate to the glacial maximum. Ocean circulation and the carbon cycle are intricately linked, and ocean circulation reconstructions can therefore provide important insights into mechanisms for past atmospheric CO2 changes. Ocean circulation in the deep Atlantic Ocean (>~2.5 km) during the Last Glacial Maximum (LGM; 18-22 ka) is traditionally viewed to follow a mixing model between northernand southern-sourced deep waters produced in the polar Atlantic, without much need to involve waters from other oceans 1-4. Using this long-held ocean circulation model, however, it is difficult to explain the observed older radiocarbon ages (14 C ages) and more radiogenic neodymium isotopic (Nd) signatures at ~3.8 km than at ~5 km in the LGM South Atlantic 5,6 (Fig. 1). Burke et al. 7 showed that sluggish recirculation of southern-sourced waters combined with reduced mixing with 14 C-rich northern-sourced waters can contribute to the old 14 C ages at ~3.

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Lacustrine sediments on the eastern Tibetan Plateau (TP) contain a wealth of information on local and regional tectonic activity. High-resolution grain-size and magnetic susceptibility measurements were conducted on the 23.4-m-thick Lixian lacustrine sedimentary sequence spanning from 19.3 to 6.0 ka, revealing 70 prehistoric seismic events on the eastern TP. The seismic events caused intermittent increases in source materials that endowed the samples of an individual event layer with a gradual fining trend along the C = M line on a C (one percentile)-M (median diameter) plot. Grain-size distribution and end-member modeling imply that dust particles of <20 μm in size were transported primarily by long-term suspension, while medium to coarse silt and sand were transported primarily by short-term suspension, such as aeolian transport constrained by local topography. Provenance analysis based on U-Pb zircon ages indicates that dust particles generated by earthquakes at Lixian had no effect on dust deposition at Xinmocun and Diaolin, and vice versa. These prehistoric seismic events, revealed by variations in grain size and magnetic susceptibility, thus provide invaluable information on the long-term behavior of local seismic activity.

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