Non-invasive determination of plant biomass with microwave resonators

Non-invasive and rapid determination of plant biomass would be beneficial for a number of research aims. Here, we present a novel device to non-invasively determine plant water content as a proxy for plant biomass. It is based on changes of dielectric properties inside a microwave cavity resonator induced by inserted plant material. The water content of inserted shoots leads to a discrete shift in the centre frequency of the resonator. Calibration measurements with pure water showed good spatial homogeneity in the detection volume of the microwave resonators and clear correlations between water content and centre frequency shift. For cut tomato and tobacco shoots, linear correlations between fresh weight and centre frequency shift were established. These correlations were used to continuously monitor diel growth patterns of intact plants and to determine biomass increase over several days. Interferences from soil and root water were excluded by shielding pots with copper. The presented proof of principle shows that microwave resonators are promising tools to quantitatively detect the water content of plants and to determine plant biomass. As the method is non-invasive, integrative and fast, it provides the opportunity for detailed, dynamic analyses of plant growth, water status and phenotype.     

Killickia (Lamiaceae): a new genus from KwaZulu-Natal, South Africa

The genus Killickia is described to accommodate the South African endemic species formerly placed in Micromeria sect. Hesperothymus . Morphological data, as well as results from unpublished phylogenetic studies support its separation from the genera Micromeria and Clinopodium . A new species Killickia lutea Bräuchler is described and three new combinations are made. Killickia is characterised as comprising solitary- or few-flowered cymes, a campanulate to subcampanulate (obconical) calyx with similar teeth, a corolla tube with two pubescent ridges and nutlets with scattered minute hairs. A thickened marginal vein in the leaves as typical for Micromeria is absent. As currently understood all species are restricted to the Drakensberg mountains and KwaZulu-Natal Midlands in eastern South Africa. A key to the species, brief notes on anatomy and ecology are provided.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 575–586.     

Effects of Low Temperature on Potential Net Photosynthesis in Two Field-grown Winter Cereals

Winter wheat and winter barley were tested for their photochemicaland osmotic potentials during the course of one growth cyclein the field. Prolonged winter conditions induced an absolutehigh in potential net photosynthesis (P_N) of winter wheat. Barleyexhibited relatively low P_N rates, which may explain the inferiorfrost hardiness of this species. Osmotic potentials () in bothspecies were quite similar, followed rather uniform trends andwere never extreme. There are doubts, however, whether the assessments truly reflected the osmotic stress on cell membranesin frost-hardened leaves. Increased deposition of cryoprotective assimilates in wheatas the cause of continued frost hardiness is discussed. Triticum aestivum, Hordeum sativum, wheat, barley, potential photosynthesis, winter hardiness