Publications

Ecosystem reliance on groundwater, defined here as water stored in the saturated zone deeper than one meter beneath the surface, has been documented in many semi-arid, arid, and seasonally-dry regions around the world. In California, groundwater sustains ecosystems and mitigates mortality during drought. However, the effect of groundwater on carbon cycling still remains largely unresolved. Here we use 20 years of eddy covariance, groundwater, and tree growth measurements to isolate the impact of groundwater on carbon cycling in a semi-arid Mediterranean system in California during the summer dry season. We show that daily ecosystem groundwater use increases under positive groundwater anomalies and is associated with increased carbon assimilation and evapotranspiration rates. Negative groundwater anomalies result in significantly reduced ecosystem groundwater uptake, gross primary productivity, and evapotranspiration, with a simultaneous increase in water use efficiency. Three machine learning algorithms better predict gross primary productivity and tree growth anomalies when trained using groundwater data. These models suggest that groundwater has a unique effect on carbon assimilation and allocation to woody growth. After controlling for the effect of soil moisture, which is often decoupled from groundwater dynamics at the site, wet groundwater anomalies increase canopy carbon assimilation by 179.4 ± 25.7 g C m<sup>-2</sup> (17 % of annual gross primary productivity) over the course of the summer season relative to dry groundwater anomalies. Similarly, annual tree growth increases by 0.175 ± 0.035 mm (17.7 % of annual growth) between dry and wet groundwater anomalies, independent of soil moisture dynamics. Our results demonstrate the importance of deep subsurface water resources to carbon assimilation and woody growth in dryland systems, as well as the benefits of collocated, long-term eddy covariance and ancillary datasets to improve understanding of complex ecosystem dynamics.

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A high-power P2-Na2/3(Mn1/2Fe1/4Co1/4)O2 (P2-MFC) cathode material is synthesized and investigated for Na-ion batteries. P2 type stacking is observed for a wide range of Na content (0.34 < x < 0.95). Even at 30 C rate a discharge capacity of 130 mAh g−1 is maintained, which is currently the highest rate performance among Na ion intercalation compounds. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

ABSTRACT We have developed a novel method to clone terpene synthase genes. This method relies on the inherent toxicity of the prenyl diphosphate precursors to terpenes, which resulted in a reduced-growth phenotype. When these precursors were consumed by a terpene synthase, normal growth was restored. We have demonstrated that this method is capable of enriching a population of engineered Escherichia coli for those clones that express the sesquiterpene-producing amorphadiene synthase. In addition, we enriched a library of genomic DNA from the isoprene-producing bacterium Bacillus subtilis strain 6051 in E. coli engineered to produce elevated levels of isopentenyl diphosphate and dimethylallyl diphosphate. The selection resulted in the discovery of two genes ( yhfR and nudF ) whose protein products acted directly on the prenyl diphosphate precursors and produced isopentenol. Expression of nudF in E. coli engineered with the mevalonate-based isopentenyl pyrophosphate biosynthetic pathway resulted in the production of isopentenol.

A low-temperature grafting approach using two CuI molecular precursors ([CuOSi(OtBu)3]4 and [CuOtBu]4) and a high-temperature exchange reaction using CuCl were utilized with a mesoporous silica support (SBA-15) to investigate the effects of catalyst preparation on the nature of copper−support interactions and site speciation. Detailed X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine-structure studies (EXAFS) studies were performed to characterize the nature of the Cu sites and the Cu−support interactions. The freshly prepared materials from the nonaqueous grafting of [CuOSi(OtBu)3]4 (CuOSi/SBA (x.x), where x.x refers to the Cu weight %) exhibit CuI site isolation (by EXAFS and XANES). In contrast, EXAFS and XANES studies of the freshly prepared materials from the nonaqueous grafting of [CuOtBu]4 (CuOtBu/SBA (x.x)) suggest that the Cu−O−Cu linkages of the molecular precursor remain intact upon interacting with the support. Isolated CuI sites are observed as the major species in the freshly prepared material from the high-temperature exchange reaction using CuCl (CuCl/SBA (3.0)) (by XANES and EXAFS). Treatment of the materials under He at 573 K leads to loss of the organic species from the grafted materials (by 1H NMR spectroscopy, thermogravimetric analysis, EA, and IR spectroscopy). EXAFS and XANES studies revealed that CuCl/SBA (3.0) and the CuOSi/SBA (x.x) materials still exhibit up to 95% isolated CuI sites, whereas the CuOtBu/SBA (x.x) materials only exhibit Cu as Cu0 nanoparticles of ca. 7 Å in diameter. After calcination under O2 at 573 K, residual chloride from the high-temperature preparation of CuCl/SBA (3.0) leads to formation of crystalline CuO particles, whereas the CuOSi/SBA (x.x) and CuOtBu/SBA (x.x) materials exhibit more amorphous CuO character after an identical oxidative treatment.

Halide perovskite is a unique dynamical system, whose structural and chemical processes happening across different timescales have significant impact on its physical properties and device-level performance. However, due to its intrinsic instability, real-time investigation of the structure dynamics of halide perovskite is challenging, which hinders the systematic understanding of the chemical processes in the synthesis, phase transition, and degradation of halide perovskite. Here, we show that atomically thin carbon materials can stabilize ultrathin halide perovskite nanostructures against otherwise detrimental conditions. Moreover, the protective carbon shells enable atomic-level visualization of the vibrational, rotational, and translational movement of halide perovskite unit cells. Albeit atomically thin, protected halide perovskite nanostructures can maintain their structural integrity up to an electron dose rate of 10,000 e^-/Ų·s while exhibiting unusual dynamical behaviors pertaining to the lattice anharmonicity and nanoscale confinement. Our work demonstrates an effective method to protect beam-sensitive materials during <i>in situ</i> observation, unlocking new solutions to study new modes of structure dynamics of nanomaterials.

Abstract Solid‐state packing plays a defining role in the properties of a molecular organic material, but it is difficult to elucidate in the absence of single crystals that are suitable for X‐ray diffraction. Herein, we demonstrate the coupling of divergent synthesis with microcrystal electron diffraction (MicroED) for rapid assessment of solid‐state packing motifs, using a class of chiral nanocarbons—expanded helicenes—as a proof of concept. Two highly selective oxidative dearomatizations of a readily accessible helicene provided a divergent route to four electron‐deficient analogues containing quinone or quinoxaline units. Crystallization efforts consistently yielded microcrystals that were unsuitable for single‐crystal X‐ray diffraction, but ideal for MicroED. This technique facilitated the elucidation of solid‐state structures of all five compounds with &lt;1.1 Å resolution. The otherwise‐inaccessible data revealed a range of notable packing behaviors, including four different space groups, homochirality in a crystal for a helicene with an extremely low enantiomerization barrier, and nanometer scale cavities.