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Background and Scope Because of the crucial role coarse roots (>2 mm diameter) play in plant functions and terrestrial ecosystems, detecting and quantifying the size, architecture, and biomass of coarse roots are important. Traditional excavation methods are labor intensive and destructive, with limited quantification and repeatability of measurements over time. As a nondestructive geophysical tool for delineating buried features in shallow subsurface, ground penetrating radar (GPR) has been applied for coarse root detection since 1999. This article reviews the state-ofknowledge of coarse root detection and quantification using GPR, and discusses its potentials, constraints, possible solutions, and future outlooks. Some useful suggestions are provided that can guide future studies in this field. Conclusions The feasibility and accuracy of coarse root investigation by GPR have been tested in various site conditions (mostly in controlled conditions or within plantations) and for different plant species (mostly tree root systems). Thus far, single coarse root identification and coarse root system mapping have been conducted using GPR, including roots under pavements in urban environment. Coarse root diameter and biomass have been estimated from indexes extracted from root GPR radargrams. Coarse root development can be observed by repeated GPR scanning over time. Successful GPR-based coarse root investigation is site specific, and only under suitable conditions can reliable measurements be accomplished. The best quality of root detection by GPR is achieved in well-drained and electrically-resistive soils (such as sands) under dry conditions. Numerous factors such as local soil conditions, root electromagnetic properties, and GPR antenna frequency can impact the reliability and accuracy of GPR detection and quantification of coarse roots. As GPR design, data processing software, field data collection protocols, and root parameters estimation methods are continuously improved, this noninvasive technique could offer greater potential to study coarse roots.

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The Critical Zone (CZ) is the thin layer of the Earth's terrestrial surface and near-surface environment that ranges from the top of the vegetation canopy to the bottom of the weathering zone and plays fundamental roles in sustaining life and humanity. The past few years have seen a number of Critical Zone Observatories (CZOs) being developed following the first CZOs established in the United States in 2007. This update summarizes major research findings in CZ science achieved in the past 5 yr or so (2011)(2012)(2013)(2014)(2015)(2016), especially those obtained from recognized CZOs. A conceptual framework of "deep" science-deep time, deep depth, and deep coupling-is used to synthesize recent CZ studies across a broad range of spatial and temporal scales. This "deep" science concept emphasizes the integration of Earth surface processes that underlies the contributions of CZ science to terrestrial environmental research. We identify some main knowledge gaps and major opportunities to advance the frontiers of CZ science. We advocate that the CZ scientific community work toward a global network of CZOs to link sites, people, ideas, data, models, and tools. We hope that this update can stimulate continuous scientific advancement and practical applications of CZ science worldwide.Abbreviations: CZ, Critical Zone; CZO, Critical Zone Observatory; DOC, dissolved organic carbon; DOM, dissolved organic matter; EEMT, effective energy and mass transfer; ET, evapotranspiration; GPR, ground-penetrating radar; SOC, soil organic carbon; TDR, time-domain reflectometry; WTT, water transmit times.The Earth's Critical Zone (CZ) is defined as the thin layer of the Earth's surface and near-surface terrestrial environment from the top of the vegetation canopy (or atmosphere-vegetation interface) to the bottom of the weathering zone (or freshwater-bedrock interface) (National Research Council, 2001). This zone encompasses the near-surface biosphere, the entire pedosphere, the surface and near-surface portion of the hydrosphere and the atmosphere, and the shallow lithosphere (Lin, 2010). This concept of the CZ provides a unifying framework for integrating belowground-aboveground, abiotic-biotic, and time-space in mass and energy flows to holistically understand complex terrestrial ecosystems and offers a fertile ground for interdisciplinary research (Anderson et al., 2007;Lin et al., 2011). Thus, the integrated study of the CZ has been recognized as one of the most compelling research fields in Earth and environmental sciences in the 21st century (National Research Council, 2001.Environmental processes within the CZ, such as mass and energy exchange, soil formation, streamflow generation, and landscape evolution are crucial to sustaining biodiversity and humanity Field et al., 2015). The CZ supplies nearly every life-sustaining resource on which life originates, evolves, and thrives (National Research Council, 2001;Lin, 2014). This zone provides diverse services to human society and determines human livelihood (Lin, 2014;Field et al., 2...

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Subsurface lateral preferential flow (LPF) has been observed to contribute substantially to hillslope and catchment runoff. However, the complex nature of LPF and the lack of an appropriate investigation method have hindered direct LPF observation in the field. Thus, the initiation, persistence, and dynamics of LPF networks remain poorly understood. This study explored the application of time-lapse ground-penetrating radar (GPR) together with an artificial infiltration to shed light on the nature of LPF and its dynamics in a hillslope. Based on our enhanced field experimental setup and carefully refined GPR data postprocessing algorithms, we developed a new protocol to reconstruct LPF networks with centimeter resolution. This is the first time that a detailed LPF network and its dynamics have been revealed noninvasively along a hillslope. Real-time soil water monitoring and field soil investigation confirmed the locations of LPF mapped by time-lapse GPR surveys. Our results indicated the following: (1) Increased spatial variations of radar signals after infiltration suggested heterogeneous soil water changes within the studied soil, which reflected the generation and dynamics of LPF; (2) Two types of LPF networks were identified, the network at the location of soil permeability contrasts and that formed via a series of connected preferential flow paths; and (3) The formation and distribution of LPF networks were influenced by antecedent soil water condition. Overall, this study demonstrates clearly that carefully designed time-lapse GPR surveys with enhanced data postprocessing offer a practical and nondestructive way of mapping LPF networks in the field, thereby providing a potentially significant enhancement in our ability to study complex subsurface flow processes across the landscape.

BackgroundThe mosquito Aedes albopitus is a competent vector for the transmission of many blood-borne pathogens. An important factor that affects the mosquitoes’ development and spreading is climate, such as temperature, precipitation and photoperiod. Existing climate-driven mechanistic models overlook the seasonal pattern of diapause, referred to as the survival strategy of mosquito eggs being dormant and unable to hatch under extreme weather. With respect to diapause, several issues remain unaddressed, including identifying the time when diapause eggs are laid and hatched under different climatic conditions, demarcating the thresholds of diapause and non-diapause periods, and considering the mortality rate of diapause eggs.MethodsHere we propose a generic climate-driven mechanistic population model of Ae. albopitus applicable to most Ae. albopictus-colonized areas. The new model is an improvement over the previous work by incorporating the diapause behaviors with many modifications to the stage-specific mechanism of the mosquitoes’ life-cycle. monthly Container Index (CI) of Ae. albopitus collected in two Chinese cities, Guangzhou and Shanghai is used for model validation.ResultsThe simulation results by the proposed model is validated with entomological field data by the Pearson correlation coefficient r2 in Guangzhou (r2 = 0.84) and in Shanghai (r2 = 0.90). In addition, by consolidating the effect of diapause-related adjustments and temperature-related parameters in the model, the improvement is significant over the basic model.ConclusionsThe model highlights the importance of considering diapause in simulating Ae. albopitus population. It also corroborates that temperature and photoperiod are significant in affecting the population dynamics of the mosquito. By refining the relationship between Ae. albopitus population and climatic factors, the model serves to establish a mechanistic relation to the growth and decline of the species. Understanding this relationship in a better way will benefit studying the transmission and the spatiotemporal distribution of mosquito-borne epidemics and eventually facilitating the early warning and control of the diseases.