Introducing terahertz technology into plant biology: A novel method to monitor changes in leaf water status

We present a novel, non-destructive method for determination of changes in leaf water content in the fi eld based on terahertz (THz) technology. In this method, terahertz waves, which are strongly absorbed by water, are generated and detected using a photomixer that converts the optical beat signal of two interfering diode lasers into THz radiation. This allows a coherent detection as basis for the determination of changes in leaf water contents. The reliability of this innovative method was verifi ed by monitoring changes in the leaf water content of young coffee plants in parallel using classical, destructive thermogravimetrical measurements as well as by THz spectroscopy. The broad applicability of this novel device was shown by long- and short-term measurements. The changes in leaf water content during drought stress induced dehydration as well as during the course of rapid re-hydration after re-watering vividly highlight the tremendous potential of this novel technique and its high reliability. The fi ndings presented here provide the basis for THz-based in vivo determination of changes in the leaf water content under fi eld conditions.

[1]  D. Sims,et al.  Estimation of vegetation water content and photosynthetic tissue area from spectral reflectance: a comparison of indices based on liquid water and chlorophyll absorption features , 2003 .

[2]  D. Roberts,et al.  Deriving Water Content of Chaparral Vegetation from AVIRIS Data , 2000 .

[3]  B. Rock,et al.  Detection of changes in leaf water content using Near- and Middle-Infrared reflectances , 1989 .

[4]  L. S. Karatzas,et al.  Measurements of leaf water content using terahertz radiation , 1999 .

[5]  B. Gao.  NDWI—A normalized difference water index for remote sensing of vegetation liquid water from space , 1996 .

[6]  M. Koch,et al.  Continuous wave terahertz spectrometer as a noncontact thickness measuring device. , 2008, Applied optics.

[7]  J. Eitel,et al.  Suitability of existing and novel spectral indices to remotely detect water stress in Populus spp. , 2006 .

[8]  C. Tucker.  Remote sensing of leaf water content in the near infrared , 1980 .

[9]  R. Fensholt,et al.  Derivation of a shortwave infrared water stress index from MODIS near- and shortwave infrared data in a semiarid environment , 2003 .

[10]  C. Joerdens,et al.  Evaluation of leaf water status by means of permittivity at terahertz frequencies , 2009, Journal of biological physics.

[11]  Fawwaz T. Ulaby,et al.  Microwave Dielectric Properties of Plant Materials , 1984, IEEE Transactions on Geoscience and Remote Sensing.

[12]  Anatoly A. Gitelson,et al.  Non‐destructive detection of water stress and estimation of relative water content in maize , 2009 .

[13]  W. DiNatale,et al.  Generation and detection of coherent terahertz waves using two photomixers , 1998 .

[14]  D. M. Klaus,et al.  The assessment of leaf water content using leaf reflectance ratios in the visible, near‐, and short‐wave‐infrared , 2008 .

[15]  John A. Gamon,et al.  Monitoring drought effects on vegetation water content and fluxes in chaparral with the 970 nm water band index , 2006 .

[16]  N. M. Kelly,et al.  Spectral absorption features as indicators of water status in coast live oak ( Quercus agrifolia ) leaves , 2003 .

[17]  B. Rock,et al.  Measurement of leaf relative water content by infrared reflectance , 1987 .

[18]  J. Peñuelas,et al.  Estimation of plant water concentration by the reflectance Water Index WI (R900/R970) , 1997 .