Emerging effects of root hairs on plant scale soil water relations

虽然根毛在养分获取中的重要性已经被广泛接受，但它们在水分吸收中的作用仍然存在争议。在第一阶段，我们在实验室和田间证明，玉米根毛对沙质和壤质土壤中的土壤-植物水力都没有影响。这一结果与最近在大麦中报道的相反，这表明根毛的作用是特定于物种和土壤的。这项更新建议的总体目标是揭示根毛在水分吸收中的作用，从根际到田间的小范围相互作用。我们计划将实验和模型研究相结合，以量化不同物种的毛发是否在什么土壤和气候条件下以及通过什么机制影响植物-土壤系统的电导，并最终影响植物-土壤关系。我们假设：(I)毛发的长度、密度、沿根的分布、周转、收缩和恢复，因此根-土壤接触是特定于物种和土壤的；(Ii)无毛突变体发育不同的根水力结构，因此可能具有不同的根系水分吸收模式，以弥补根毛的缺乏。该项目分为四个工作包(WP)。在WP1a中，我们将使用同步辐射X射线CT来量化玉米和大麦根毛在壤土和沙地中的空间分布，并研究根毛功能的时间动态，包括土壤干/湿过程中的周转(老化)和收缩/恢复。在WP1b中，我们将测量在沙质和壤质土壤中生长的两个大麦基因型(WT和BRB)根毛对水分吸收的影响，并将结果与第一阶段用玉米获得的结果进行比较。将建立一个根毛模型，从功能上表示根毛对水分吸收的影响(WP1c)。在WP2中，我们计划利用中子照相术来表征这两个玉米和大麦突变体的根构型和根段水力传导性，并研究无毛突变体是否发展了不同的根系水力构型来弥补毛发的缺乏。在WP3中，我们将在一系列良好控制的条件下调查玉米根毛对长柱吸水的影响，这些条件扩大了田间小区可以考虑的条件范围(例如，养分和水分胁迫之间的相互作用)。后者不仅有助于SEC和SPE之间的升级，而且还提供了一个系统来研究根毛在受控良好的田间条件下的作用，从而解开根水力结构和根际效应(根毛)之间的权衡。在WP4中，我们将继续测量和模拟根毛和土壤质地对田间和整个种植周期的蒸腾和叶水势的影响。这个项目的结果是从机理上理解根毛对从微观到田间尺度的水分吸收的作用。

Although the importance of root hairs in nutrient acquisition is well accepted, their role in water uptake remains controversial. In the first phase, we demonstrated, both in the lab and in the field, that maize root hairs exhibited no effects on soil-plant hydraulics in both sandy and loamy soils. This result is opposite to what has been recently reported in barley, which suggests that the role of root hairs is species and soil specific. The overall objective of this renewal proposal is to reveal the role of root hairs in water uptake, from the small scale interactions in the rhizosphere up to the field. We plan to combine experimental and modelling studies to quantify whether, in what soil and climatic conditions, and by which mechanisms hairs of different species impact plant-soil system conductance, and ultimately plant-soil relations. We hypothesize that: (i) hairs length, density, distribution along the root, turnover, shrinkage and recovery and hence root-soil contact is species and soil specific; (ii) hairless mutants develop different root hydraulic architecture and thus might have a different root water uptake pattern to compensate for the lack of root hairs.The project is structured into four work packages (WP). In WP1a, we will use Synchrotron X-ray CT to quantify the spatial distribution of maize and barley root hairs in loam and sand and investigate the temporal dynamics of root hair functions, including turnover (aging) and shrinkage/recovery during soil drying/wetting. In WP1b, we will measure the impact of root hairs on water uptake of two barley genotypes (WT vs brb) grown in sandy and loamy soils and we will compare the results to those obtained with maize in the first phase. A root hair model will be built to functionally represent the impact of root hairs on water uptake (WP1c). In WP2, we plan to utilize neutron radiography to characterize the root architecture and root segment hydraulic conductances of the two maize and barley mutants and investigate whether the hairless mutant developed different root hydraulic architectures to compensate for the lack of hairs. In WP3, we will investigate the impact of maize root hairs on water uptake in long columns under a range of well-controlled conditions that expand the range of conditions that can be considered in the field plot (e.g. interactions between nutrient and water stress). The latter WP would not only facilitate the upscaling between the SEC and SPE, but also provide a system to study the role of root hairs in well-controlled, field-like conditions and hence disentangling the trade-off between root hydraulic architecture and rhizosphere effects (root hairs). In WP4, we will continue to measure and model the effect of root hairs and soil texture on transpiration and leaf water potential in the field and over an entire cropping cycle.The outcome of this project is a mechanistic understanding of the role of root hairs on water uptake from the micro to the field scales.