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Collaborative Research: Dynamic Roots as the Biophysical Link Between Deep Moisture and the Atmosphere

合作研究：动态根作为深层水分与大气之间的生物物理联系

基本信息

批准号：
1852707
负责人：
Ying Fan Reinfelder
金额：
$ 23.34万
依托单位：
Rutgers University New Brunswick
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-07-01 至 2025-06-30
项目状态：
未结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1852707&HistoricalAwards=false
关键词：
Collaborative Research Dynamic Roots Biophysical

项目摘要

Plants play an important role in moving water across the land surface between the atmosphere above and the soil below. Some plants can extend their roots substantially below the surface to take advantage of ground water, giving them a moisture reservoir that persists through dry seasons and droughts. When plants tap into this reservoir they transpire moisture through their leaves, providing a source of moisture to the atmosphere at a time when the air may be at its driest. The extent to which this transpired groundwater influences meteorological conditions such as precipitation, cloudiness, and atmospheric stability is not known, nor is its dependence on region, season, and other factors.The transpiration of groundwater involves a complex set of biological and physical processes which are difficult to observe and simulate. But the PIs have developed a scheme in which the bulk effect of these processes can be approximated using two observationally-motivated assumptions. First, the extent to which plants extend their roots to tap groundwater depends on their position relative to the local topography. In dry or seasonally dry climates plants on a hilltop are typically too high above the water table to effectively access groundwater, so we can assume that they rely exclusively on near-surface soil moisture. At the valley floor the water table can be so close to the surface that plant roots have to be shallow to avoid excessive salinity and waterlogging, so they also rely exclusively on near-surface moisture. Thus maximum groundwater uptake occurs at mid-hillslope locations, and groundwater usage depends on the Height Above Nearest Drainage (HAND). The PIs have developed a "giant hillslope" method to quantify this dependence in terms of a five-bin representation of small-scale HAND topography.Second, roots respond dynamically to the vertical profile of soil water. The PIs argue that root dynamics can be simply represented by assuming that roots actively extend to reach available groundwater, taking up water from whatever level offers the greatest moisture access for the least effort. This assumption is formalized using a scheme in which the transport of moisture through roots is analogous to the movement of electric current in a circuit: the roots act as "wires", through which a "current" of moisture flows from a specific soil layer to the plant leaves, driven by the "voltage" difference (i.e. water potential difference) between plant leaves and the soil layer tapped by the roots. The flow of moisture from a soil layer to the surface is then given by the ratio of the layer-to-leaves voltage drop to the resistance of the wire, in exact analogy to Ohm's law (electric current equals voltage divided by resistance).The PIs implement their root-groundwater scheme in the Noah land-surface model, which is coupled to the Weather Research and Forecasting (WRF) model to form a coupled land-atmosphere model. The model is then used to test the impact of groundwater transpiration on the continental-scale hydrological cycle. Among the scientific questions to be addressed is the extent to which groundwater transpiration promotes precipitation, both by making a substantial contribution to the moisture available for precipitation, and by reducing atmospheric stability.The research has societal value due to the importance of the hydrological cycle for water resources. The work is of particular value for building bridges between the research communities concerned with the separate but closely connected fields of land surface hydrology, continental-scale hydroclimate, and plant ecology. The implementation of the new scheme in the WRF model will make it available for operational use, as WRF is widely used for weather forecasting. The PIs also conduct educational and outreach activities in K-12 schools, and the project supports two graduate students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

植物在上面的大气和下面的土壤之间通过陆地表面输送水分方面起着重要的作用。一些植物可以将根伸展到地表以下，以利用地下水，使它们成为一个湿润的蓄水池，在旱季和干旱期间持续存在。当植物进入这个水库时，它们通过叶子散发水分，在空气最干燥的时候为大气提供水分来源。地下水蒸腾对降水、云量和大气稳定性等气象条件的影响程度尚不清楚，对地区、季节和其他因素的依赖性也是未知的。地下水的蒸腾涉及一系列复杂的生物和物理过程，难以观测和模拟。但PI已经开发出一种方案，在该方案中，这些过程的整体效应可以使用两个观测激励的假设来近似。首先，植物伸展根部以利用地下水的程度取决于它们相对于当地地形的位置。在干燥或季节性干燥的气候中，山顶上的植物通常高于地下水位太高，无法有效地获取地下水，因此我们可以假设它们完全依赖于近地表土壤水分。在谷底，地下水位可能离地表太近，以至于植物的根必须很浅，以避免过度的盐分和内涝，因此它们也完全依赖于近地表的水分。因此，最大的地下水吸收出现在中间山坡位置，而地下水的使用取决于最近排水系统(HAND)上方的高度。PIS开发了一种“巨型山坡”方法来量化这种依赖关系，方法是用五个面元表示小尺度手部地形。第二，根系对土壤水分的垂直剖面做出动态响应。PI认为，根的动态可以简单地表示为假设根积极地伸展到可用的地下水，从任何水平吸收水分，以最少的努力获得最大的水分。这一假设是通过一个方案形成的，在该方案中，水分通过根的传输类似于电流在电路中的运动：根起“电线”的作用，通过它，水分的“电流”从特定的土层流向植物叶片，受植物叶片和根部挖掘的土层之间的“电压”差(即水势差)的驱动。根据欧姆定律(电流等于电压除以电阻)，土壤水分从土壤层到地表的流量由层到叶的电压降与导线的电阻之比给出。PI在诺亚陆面模型中实施他们的根-地下水方案，该模型与天气研究和预报(WRF)模型耦合形成陆地-大气耦合模型。然后，该模型被用来测试地下水蒸腾对大陆尺度水文循环的影响。需要解决的科学问题之一是地下水蒸腾作用在多大程度上促进了降水，这既是通过大量贡献可用于降水的水分，也是通过降低大气稳定性。由于水文循环对水资源的重要性，这项研究具有社会价值。这项工作对于在陆地表面水文学、大陆尺度水文气候和植物生态学等独立但紧密联系的领域的研究界之间架起桥梁具有特别的价值。新方案在世界天气预报模式中的实施将使其可用于业务用途，因为世界天气预报模式被广泛用于天气预报。PIs还在K-12学校开展教育和外展活动，该项目支持两名研究生。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。