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.     

Dispersal and population genetic structure of Telmatherina antoniae,an endemic freshwater Sailfin silverside from Sulawesi,Indonesia

Population genetic structure in the presence of substantial dispersal provides a unique perspective on the evolution of reproductive isolation. We sampled Telmatherina antoniae, an endemic fish species, at 10 sites in Lake Matano, Indonesia. Significant genetic structure (F_ST = 0.03) was found, despite a migration rate of 10.2% and a mean dispersal distance of 13.6 km, estimated by genotype assignment. Neither dispersal distance nor direction differed from random expectations, indicative of no dispersal barrier in Lake Matano. However, Bayesian genotype cluster assignment identified a population structure consisting of four to six clusters that did not coincide with sample site distribution, but explained two to three times more genetic variance than sample site. The mechanism for continued isolation of those genetic clusters is unknown, but assortative mating and temporal isolation are obvious candidates. Our results resolve the apparent paradox of population genetic structure coupled with frequent dispersal, and highlight the importance of considering cryptic genetic structure.     

Applying the light : nutrient hypothesis to stream periphyton

1. The light : nutrient hypothesis (LNH) states that algal nutrient content is determined by the balance of light and dissolved nutrients available to algae during growth. Light and phosphorus gradients in both laboratory and natural streams were used to examine the relevance of the LNH to stream periphyton. Controlled gradients of light (12–426 μmol photons m^?2 s^?1) and dissolved reactive phosphorus (DRP, 3–344 μg L^?1) were applied experimentally to large flow‐through laboratory streams, and natural variability in canopy cover and discharge from a wastewater treatment facility created gradients of light (0.4–35 mol photons m^?2 day^?1) and DRP (10–1766 μg L^?1) in a natural stream. 2. Periphyton phosphorus content was strongly influenced by the light and DRP gradients, ranging from 1.8 to 10.7 μg mg AFDM^?1 in the laboratory streams and from 2.3 to 36.9 μg mg AFDM^?1 in the natural stream. Phosphorus content decreased with increasing light and increased with increasing water column phosphorus. The simultaneous effects of light and phosphorus were consistent with the LNH that the balance between light and nutrients determines algal nutrient content. 3. In experiments in the laboratory streams, periphyton phosphorus increased hyperbolically with increasing DRP. Uptake then began levelling off around 50 μg L^?1. 4. The relationship between periphyton phosphorus and the light : phosphorus ratio was highly nonlinear in both the laboratory and natural streams, with phosphorus content declining sharply with initial increases in the light : phosphorus ratio, then leveling off at higher values of the ratio. 5. Although light and DRP both affected periphyton phosphorus content, the effects of DRP were much stronger than those of light in both the laboratory and natural streams. DRP explained substantially more of the overall variability in periphyton phosphorus than did light, and light effects were evident only at lower phosphorus concentrations (≤25 μg L^?1) in the laboratory streams. These results suggest that light has a significant negative effect on the food quality of grazers in streams only under a limited set of conditions.     

A spatial analysis of the ecology and morphology of cicadas in the Pauropsalta annulata species complex (Hemiptera: Cicadidae)

The cicada Pauropsalta annulata Goding & Froggatt, 1904 comprises several distinct song types across its known distribution in eastern Australia, with these songs being statistically distinguishable from one another. Here we use spatial analysis of adult morphology and plant species associations to test further the hypothesis that P. annulata song types represent a complex of cryptic species. To structure this investigation we contrast different approaches and expectations given under the framework of ecological speciation with those of the recognition concept of species. Plotting the geographical distributions of these cicadas revealed that each of the P. annulata song types have independent geographical distributions, with relatively small areas of overlap. ‘Predicted distribution’ modelling revealed that the distribution of each song type forms a unique climatic envelope, which suggests that abiotic factors (rather than interactions among the cicadas themselves) influence the geographical representation of the different song types. One song type has consistent differences in male genitalia, and female ovipositor length differs significantly among three of the other song types. Each song type is strongly associated with a small number of tree species, and these associations are maintained in areas of sympatry. The spatial comparisons made in this study suggest that the P. annulata song types investigated actually represent three species. One of these species is represented by two of the song types originally recognized, and these appear to intergrade in sympatry, and thus represent subspecies. The spatial consistency of the plant associations and morphology exhibited by these (sub)species is significant because it represents an ecological measure of species stability. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 553–565.     

Root cooling strongly affects diel leaf growth dynamics,water and carbohydrate relations in Ricinus communis

In laboratory and greenhouse experiments with potted plants, shoots and roots are exposed to temperature regimes throughout a 24 h (diel) cycle that can differ strongly from the regime under which these plants have evolved. In the field, roots are often exposed to lower temperatures than shoots. When the root‐zone temperature in Ricinus communis was decreased below a threshold value, leaf growth occurred preferentially at night and was strongly inhibited during the day. Overall, leaf expansion, shoot biomass growth, root elongation and ramification decreased rapidly, carbon fluxes from shoot to root were diminished and carbohydrate contents of both root and shoot increased. Further, transpiration rate was not affected, yet hydrostatic tensions in shoot xylem increased. When root temperature was increased again, xylem tension reduced, leaf growth recovered rapidly, carbon fluxes from shoot to root increased, and carbohydrate pools were depleted. We hypothesize that the decreased uptake of water in cool roots diminishes the growth potential of the entire plant – especially diurnally, when the growing leaf loses water via transpiration. As a consequence, leaf growth and metabolite concentrations can vary enormously, depending on root‐zone temperature and its heterogeneity inside pots.     

Contrasting dynamics of water and mineral nutrients in stems shown by stable isotope tracers and cryo‐SIMS

Lateral exchange of water and nutrients between xylem and surrounding tissues helps to de‐couple uptake from utilization in all parts of a plant. We studied the dynamics of these exchanges, using stable isotope tracers for water (H₂¹⁸O), magnesium (²⁶Mg), potassium (⁴¹K) and calcium (⁴⁴Ca) delivered via a cut stem for various periods to the transpiration stream of bean shoots (Phaseolus vulgaris cv. Fardenlosa Shiny). Tracers were subsequently mapped in stem cross‐sections with cryo‐secondary ion mass spectrometry. The water tracer equilibrated within minutes across the entire cross‐section. In contrast, the nutrient tracers showed a very heterogeneous exchange between xylem vessels and the different stem tissues, even after 4 h. Dynamics of nutrients in the tissues revealed a fast and extensive exchange of nutrients in the xylem parenchyma, with, for example, calcium being completely replaced by tracer in less than 5 min. Dilution of potassium tracer during its 30 s transit in xylem sap through the stem showed that potassium concentration was up‐regulated over many hours, to the extent that some of it was probably supplied by phloem recirculation from the shoot.     

A Case Study on Human Upper Limb Modelling for Dynamic Simulation

Modelling consists of developing a representation of the properties of an object or a phenomenon with respect to the goals of its analysis. In this paper, the procedure presented is that followed in the CHARM project for human upper limb modelling with respect to the project constraints on the model implementation and simulation. The objective is to develop a Comprehensive Human Animation Resource Model allowing the simulation of human motion, including the finite element simulation of soft tissue deformation and muscular contraction. Generally, models are presented based on assumptions left for a fortiori validation. The a priori considerations which lead to these assumptions are rarely detailed. Here, the aim is to form a basis for the choices and assumptions which are to be made prior to the validation. The analysis is based on the general approach for the modelling of multi-body deformable systems as well as on previous studies on the human upper limb.     

Mature semiarid chaparral ecosystems can be a significant sink for atmospheric carbon dioxide

Carbon flux in arid and semiarid area shrublands, especially in old‐growth shrub ecosystems, has been rarely studied using eddy covariance techniques. In this study, eddy covariance measurements over a 100‐year old‐growth chamise‐dominated chaparral shrub ecosystem were conducted for 7 years from 1996 to 2003. A carbon sink, from −96 to −155 g C m⁻² yr⁻¹, was determined under normal weather conditions, while a weak sink of −18 g C m⁻² yr⁻¹ and a strong source of 207 g C m⁻² yr⁻¹ were observed as a consequence of a severe drought. The annual sink strength of carbon in the 7‐year measurement period was −52 g C m⁻² yr⁻¹. The results from our study indicate that, in contrast to previous thought, the old‐growth chaparral shrub ecosystem can be a significant sink of carbon under normal weather conditions and, therefore, be an important component of the global carbon budget.