Analysis of spectroscopic measurements of leaf water content at terahertz frequencies using linear transforms

We provide a unified framework for a range of linear transforms that can be used for the analysis of terahertz spectroscopic data, with particular emphasis on their application to the measurement of leaf water content. The use of linear transforms for filtering, regression, and classification is discussed. For illustration, a classification problem involving leaves at three stages of drought and a prediction problem involving simulated spectra are presented. Issues resulting from scaling the data set are discussed. Using Lagrange multipliers, we arrive at the transform that yields the maximum separation between the spectra and show that this optimal transform is equivalent to computing the Euclidean distance between the samples. The optimal linear transform is compared with the average for all the spectra as well as with the Karhunen–Loève transform to discriminate a wet leaf from a dry leaf. We show that taking several principal components into account is equivalent to defining new axes in which data are to be analyzed. The procedure shows that the coefficients of the Karhunen–Loève transform are well suited to the process of classification of spectra. This is in line with expectations, as these coefficients are built from the statistical properties of the data set analyzed.

Measurements of leaf water content using terahertz radiation

A novel technique for the noninvasive continuous measurement of leaf water content is presented. The technique is based on transmission measurements of terahertz radiation with a null-balance quasi-optical transmissometer operating at 94 GHz. A model for the propagation of terahertz radiation through leaves is presented. This, in conjunction with leaf thickness information determined separately, may be used to quantitatively relate transmittance measurements to leaf water content. Measurements using a dispersive Fourier transform spectrometer in the range of 100 GHz-500 GHz using Phormium tenax and Fatsia japonica leaves are also reported.

QTLs for shelf life in lettuce co-locate with those for leaf biophysical properties but not with those for leaf developmental traits

Developmental and biophysical leaf characteristics that influence post-harvest shelf life in lettuce, an important leafy crop, have been examined. The traits were studied using 60 informative F-9 recombinant inbed lines (RILs) derived from a cross between cultivated lettuce (Lactuca sativa cv. Salinas) and wild lettuce (L. serriola acc. UC96US23). Quantitative trait loci (QTLs) for shelf life co-located most closely with those for leaf biophysical properties such as plasticity, elasticity, and breakstrength, suggesting that these are appropriate targets for molecular breeding for improved shelf life. Significant correlations were found between shelf life and leaf size, leaf weight, leaf chlorophyll content, leaf stomatal index, and epidermal cell number per leaf, indicating that these pre-harvest leaf development traits confer post-harvest properties. By studying the population in two contrasting environments in northern and southern Europe, the genotype by environment interaction effects of the QTLs relevant to leaf development and shelf life were assessed. In total, 107 QTLs, distributed on all nine linkage groups, were detected from the 29 traits. Only five QTLs were common in both environments. Several areas where many QTLs co-located (hotspots) on the genome were identified, with relatively little overlap between developmental hotspots and those relating to shelf life. However, QTLs for leaf biophysical properties (breakstrength, plasticity, and elasticity) and cell area correlated well with shelf life, confirming that the ideal ideotype lettuce should have small cells with strong cell walls. The identification of QTLs for leaf development, strength, and longevity will lead to a better understanding of processability at a genetic and cellular level, and allow the improvement of salad leaf quality through marker-assisted breeding.

Characterization of a highly biodiverse floodplain meadow using hyperspectral remote sensing within a plant functional trait framework

We assessed the potential for using optical functional types as effective markers to monitor changes in vegetation in floodplain meadows associated with changes in their local environment. Floodplain meadows are challenging ecosystems for monitoring and conservation because of their highly biodiverse nature. Our aim was to understand and explain spectral differences among key members of floodplain meadows and also characterize differences with respect to functional traits. The study was conducted on a typical floodplain meadow in UK (MG4-type, mesotrophic grassland type 4, according to British National Vegetation Classification). We compared two approaches to characterize floodplain communities using field spectroscopy. The first approach was sub-community based, in which we collected spectral signatures for species groupings indicating two distinct eco-hydrological conditions (dry and wet soil indicator species). The other approach was “species-specific”, in which we focused on the spectral reflectance of three key species found on the meadow. One herb species is a typical member of the MG4 floodplain meadow community, while the other two species, sedge and rush, represent wetland vegetation. We also monitored vegetation biophysical and functional properties as well as soil nutrients and ground water levels. We found that the vegetation classes representing meadow sub-communities could not be spectrally distinguished from each other, whereas the individual herb species was found to have a distinctly different spectral signature from the sedge and rush species. The spectral differences between these three species could be explained by their observed differences in plant biophysical parameters, as corroborated through radiative transfer model simulations. These parameters, such as leaf area index, leaf dry matter content, leaf water content, and specific leaf area, along with other functional parameters, such as maximum carboxylation capacity and leaf nitrogen content, also helped explain the species’ differences in functional dynamics. Groundwater level and soil nitrogen availability, which are important factors governing plant nutrient status, were also found to be significantly different for the herb/wetland species’ locations. The study concludes that spectrally distinguishable species, typical for a highly biodiverse site such as a floodplain meadow, could potentially be used as target species to monitor vegetation dynamics under changing environmental conditions.

Contrasting effects of necrotrophic and biotrophic plant pathogens on the aphid Aphis fabae

Phytophagous insects have to contend with a wide variation in food quality brought about by a variety of factors intrinsic and extrinsic to the plant. One of the most important factors is infection by plant pathogenic fungi. Necrotrophic and biotrophic plant pathogenic fungi may have contrasting effects on insect herbivores due to their different infection mechanisms and induction of different resistance pathways, although this has been little studied and there has been no study of their combined effect. We studied the effect of the biotrophic rust fungus Uromyces viciae-fabae (Pers.) Schroet (Basidiomycota: Uredinales: Pucciniaceae) and the necrotrophic fungus Botrytis cinerea Pers. (Ascomycota: Helotiales: Sclerotiniaceae) singly and together on the performance of the aphid Aphis fabae Scop. (Hemiptera: Aphididae) on Vicia faba (L.) (Fabaceae). Alone, botrytis had an inhibitory effect on individual A. fabae development, survival and fecundity, while rust infection consistently enhanced individual aphids’ performance. These effects varied in linear relation to lesion or pustule density. However, whole-plant infection by either pathogen resulted in a smaller aphid population of smaller aphids than on uninfected plants, indicating a lowering of aphid carrying capacity with infection. When both fungi were applied simultaneously to a leaf they generally cancelled the effect of each other out, resulting in most performance parameters being similar to the controls, although fecundity was reduced. However, sequential plant infection (pathogens applied five days apart) led to a 70% decrease in fecundity and 50% reduction in intrinsic rate of increase. The application of rust before botrytis had a greater inhibitory effect on aphids than applying botrytis before rust. Rust infection increased leaf total nitrogen concentration by 30% while infection by botrytis with or without rust led to a 38% decrease. The aphids’ responses to the two plant pathogens individually is consistent with the alteration in plant nutrient content by infection and also the induction of different plant defence pathways and the possible cross-talk between them. This is the first demonstration of the complex effects of the dual infection of a plant by contrasting pathogens on insect herbivores. Key words: Vicia faba, Botrytis cinerea, Uromyces viciae-fabae, tripartite interactions, induced resistance

The influence of commercial film-forming polymers on reducing salt spray injury in evergreen oak (Quercus ilex L.) and laurel (Prunus laurocerasus L.)

A field trial was undertaken to determine the influence of four commercially available film-forming polymers (Bond [alkyl phenyl hydroxyl polyoxyethylene], Newman Crop Spray 11E™ [paraffinic oil], Nu-Film P [poly-1-p menthene], and Spray Gard [di-1-p menthene]) on reducing salt spray injury on two woody species, evergreen oak (Quercus ilex L.) and laurel (Prunus laurocerasus L.). Irrespective of species, the film-forming polymers Nu-Film-P and Spay Gard did not provide any significant degree of protection against salt spray damage irrespective of concentration (1% or 2%) applied as measured by leaf chlorophyll concentrations, photosynthetic efficiency, visual leaf necrosis, foliar sodium and chloride content, and growth (height, leaf area). The film-forming polymer Newman Crop Spray 11E™ provided only 1-week protection against salt spray injury. The film-forming polymer Bond provided a significant (P < 0.05) degree of protection against salt spray injury 3 months after application as manifest by higher leaf chlorophyll content, photosynthetic efficiency, height and leaf area, and lower visual leaf necrosis and foliar Na and Cl content compared with nontreated controls. In conclusion, results indicate that application of a suitable film-forming polymer can provide a significant degree of protection of up to 3 months against salt spray injury in evergreen oak and laurel. Results also indicate that when applied at 1% or 2% solutions, no problems associated with phytotoxicity and rapid degradation on the leaf surface exist.

Acclimation of photosynthesis to elevated CO2 in onion (Allium cepa) grown at a range of temperatures

Onion (Allium cepa) was grown in the field within temperature gradient tunnels (providing about -2.5degreesC to +2.5degreesC from outside temperatures) maintained at either 374 or 532 mumol mol(-1) CO2. Plant leaf area was determined non-destructively at 7 day intervals until the time of bulbing in 12 combinations of temperature and CO2 concentration. Gas exchange was measured in each plot at the time of bulbing, and the carbohydrate content of the leaf (source) and bulb (sink) was determined. Maximum rate of leaf area expansion increased with mean temperature. Leaf area duration and maximum rate of leaf area expansion were not significantly affected by CO2. The light-saturated rates of leaf photosynthesis (A(sat)) were greater in plants grown at normal than at elevated CO2 concentrations at the same measurement CO2 concentration. Acclimation of photosynthesis decreased with an increase in growth temperature, and with an increase in leaf nitrogen content at elevated CO2. The ratio of intercellular to atmospheric CO2 (C-i/C-a ratio) was 7.4% less for plants grown at elevated compared with normal CO2. A(sat) in plants grown at elevated CO2 was less than in plants grown at normal CO2 when compared at the same C-i Hence, acclimation of photosynthesis was due both to stomatal acclimation and to limitations to biochemical CO2 fixation. Carbohydrate content of the onion bulbs was greater at elevated than at normal CO2. In contrast, carbohydrate content was less at elevated compared with normal CO2 in the leaf sections in which CO2 exchange was measured at the same developmental stage. Therefore, acclimation of photosynthesis in fully expanded onion leaves was detected despite the absence of localised carbohydrate accumulation in these field-grown crops.

Evaluation of film forming polymers to control apple scab (Venturia inaequalis (Cooke) G. Wint.) under laboratory and field conditions

A detached leaf bioassay was used to determine the influence of several film forming polymers and a conventional triazole fungicide on apple scab (Venturia inaequalis (Cooke) G. Wint.) development under laboratory in vitro conditions, supported by two field trials using established apple cv. Golden Delicious to further assess the efficacy of foliar applied film forming polymers as scab protectant compounds. All film forming polymers used in this investigation (Bond, Designer, Nu-Film P, Spray Gard, Moisturin, Companion PCT12) inhibited germination of conidia, subsequent formation of appressoria and reduced leaf scab severity using a detached leaf bioassay. Regardless of treatment, there were no obvious trends in the percentage of conidia with one to four appressoria 5 days after inoculation. The synthetic fungicide penconazole resulted in the greatest levels of germination inhibition, appressorium development and least leaf scab severity. Under field conditions, scab severity on leaves and fruit of apple cv. Golden Delicious treated with a film forming polymer (Bond, Spray Gard, Moisturin) was less than on untreated controls. However, greatest protection in both field trials was provided by the synthetic fungicide penconazole. Higher chlorophyll fluorescence Fv/Fm emissions in polymer and penconazole treated trees indicated less damage to the leaf photosynthetic system as a result of fungal invasion. In addition, higher SPAD values as measures of leaf chlorophyll content were recorded in polymer and penconazole treated trees. Application of a film forming polymer or penconazole resulted in a higher apple yield per tree at harvest in both the 2005 and 2006 field trials compared to untreated controls. Results suggest application of an appropriate film forming polymer may provide a useful addition to existing methods of apple scab management. (C) 2008 Elsevier Ltd. All rights reserved.

The effects of temperature and light integral on early vegetative growth and chlorophyll fluorescence of four contrasting genotypes of cacao (Theobroma cacao)

The effect of temperature on early vegetative growth, leaf chlorophyll fluorescence and chlorophyll content was examined on four genotypes of cacao (Amelonado, AMAZ 15–15, SCA 6 and SPEC 54/1). A controlled environment glasshouse was used to simulate the temperature conditions of three cacao-growing regions (Bahia, Brazil; Tafo, Ghana and Lower Perak, Malaysia) over the course of a year. Base temperatures calculated from increments in main stem growth varied from 18.6°C for AMAZ 15/15 to 20.8°C for SPEC 54/1. Temporal variation in Fv/Fm observed for two of the clones (SCA 6 and SPEC 54/1) in two of the compartments were correlated with temperature differences over time. Significant differences were also recorded between genotypes in leaf chlorophyll content. It was shown that variation over time in leaf chlorophyll content could be quantified accurately as a function of temperature and light integral. The results imply that genetic variability exists in cacao in response to temperature stress.

Comparison of the euryarchaeal microbial community in guts and food-soil of the soil-feeding termite Cubitermes fungifaber across different soil types

Termites are an important component of tropical soil communities and have a significant affect on the structure and nutrient content of soil. Digestion in termites is related to gut structure, gut physico-chemical conditions and gut symbiotic microbiota. Here we describe the use of 16S rRNA gene sequencing and Terminal-restriction Fragment Length Polymorphism (T-RFLP) analysis to examine methanogenic Archaea (MA) in the guts and food-soil of the soil-feeder Cubitermes fungifaber Sjostedt across a range of soil types. If they are strictly vertically inherited, then MA in guts should be the same in all individuals even if the soils differ across sites. In contrast, gut MA should reflect what is present in soil if populations are merely a reflection of what is ingested as the insects forage. We show clear differences between the euryarchaeal communities in termite guts and in food-soils from five different sites. Analysis of 16S rRNA gene clones indicated little overlap between the gut and soil communities. Gut clones were related to a termite-derived Methanomicrobiales cluster, to Methanobrevibacter and, surprisingly, to the haloalkaliphile Natronococcus. Soil clones clustered with Methanosarcina, Methanomicrococcus or Rice Cluster I. T-RFLP analysis indicated that the archaeal communities in the soil samples differed from site to site, whereas those in termite guts were similar between sites. There was some overlap between the gut and soil communities but these may represent transient populations in either guts or soil. Our data does not support the hypothesis that termite gut MA are derived from their food soil but also does not support a purely vertical transmission of gut microflora.

Comparison of Euryarchaea strains in the guts and food-soil of the soil-feeding termite Cubitermes fungifaber across different soil types

Termites are an important component of tropical soil communities and have a significant effect on the structure and nutrient content of soil. Digestion in termites is related to gut structure, gut physicochemical conditions, and gut symbiotic microbiota. Here we describe the use of 16S rRNA gene sequencing and terminal-restriction fragment length polymorphism (T-RFLP) analysis to examine methanogenic archaea (MA) in the guts and food-soil of the soil-feeder Cubitermes fungifaber Sjostedt across a range of soil types. If these MA are strictly vertically inherited, then the MA in guts should be the same in all individuals even if the soils differ across sites. In contrast, gut MA should reflect what is present in soil if populations are merely a reflection of what is ingested as the insects forage. We show clear differences between the euryarchaeal communities in termite guts and in food-soils from five different sites. Analysis of 16S rRNA gene clones indicated little overlap between the gut and soil communities. Gut clones were related to a termite-derived Methanomicrobiales cluster, to Methanobrevibacter and, surprisingly, to the haloalkaliphile Natronococcus. Soil clones clustered with Methanosarcina, Methanomicrococcus, or rice cluster I. T-RFLP analysis indicated that the archaeal communities in the soil samples differed from site to site, whereas those in termite guts were similar between sites. There was some overlap between the gut and soil communities, but these may represent transient populations in either guts or soil. Our data do not support the hypothesis that termite gut MA are derived from their food-soil but also do not support a purely vertical transmission of gut microflora.

Acclimation of photosynthesis to elevated CO2 in onion (allium cepa) grown at a range of temperatures

Onion (Allium cepa) was grown in the field within temperature gradient tunnels (providing about -2.5 degrees C to +2.5 degrees C from outside temperatures) maintained at either 374 or 532 mumol mol (-1) CO2. Plant leaf area was determined non-destructively at 7 day intervals until the time of bulbing in 12 combinations of temperature and CO2 concentration. Gas exchange was measured in each plot at the time of bulbing, and the carbohydrate content of the leaf (source) and bulb (sink) was determined. Maximum rate of leaf area expansion increased with mean temperature. Leaf area duration and maximum rate of leaf area expansion were not significantly affected by CO2. The light-saturated rates of leaf photosynthesis (A(sat)) were greater in plants grown at normal than at elevated CO2 concentrations at the same measurement CO2 concentration. Acclimation of photosynthesis decreased with an increase in growth temperature, and with an increase in leaf nitrogen content at elevated CO2. The ratio of intercellular to atmospheric CO2 (C-i/C-a ratio) was 7.4% less for plants grown at elevated compared with normal CO2. A(sat) in plants grown at elevated CO2 was less than in plants grown at normal CO2 when compared at the same C-i Hence, acclimation of photosynthesis was due both to stomatal acclimation and to limitations to biochemical CO2 fixation. Carbohydrate content of the onion bulbs was greater at elevated than at normal CO2. In contrast, carbohydrate content was less at elevated compared with normal CO2 in the leaf sections in which CO2 exchange was measured at the same developmental stage. Therefore, acclimation of photosynthesis in fully expanded onion leaves was detected despite the absence of localised carbohydrate accumulation in these field-grown crops.

Free atmospheric CO2 enrichment increased above ground biomass but did not affect symbiotic N2-fixation and soil carbon dynamics in a mixed deciduous stand in Wales

Through increases in net primary production (NPP), elevated CO2 is hypothesizes to increase the amount of plant litter entering the soil. The fate of this extra carbon on the forest floor or in mineral soil is currently not clear. Moreover, increased rates of NPP can be maintained only if forests can escape nitrogen limitation. In a Free atmospheric CO2 Enrichment (FACE) experiment near Bangor, Wales, 4 ambient CO2 and 4 FACE plots were planted with patches of Betula pendula, Alnus glutinosa and Fagus sylvatica on a former arable field. Four years after establishment, only a shallow L forest floor litter layer had formed due to intensive bioturbation. Total soil C and N contents increased irrespective of treatment and species as a result of afforestation. We could not detect an additional C sink in the soil, nor were soil C stabilization processes affected by FACE. We observed a decrease of leaf N content in Betula and Alnus under FACE, while the soil C/N ratio decreased regardless of CO2 treatment. The ratio of N taken up from the soil and by N2-fixation in Alnus was not affected by FACE. We infer that increased nitrogen use efficiency is the mechanism by which increased NPP is sustained under elevated CO2 at this site.

Water reuse for irrigation in Jordan: plant beneficial nutrients, farmers’ awareness and management strategies

The reuse of treated wastewater (reclaimed water) is particularly well suited for irrigated agriculture as it often contains significant quantities of plant essential nutrients. This work has shown that reclaimed water in Jordan can have adequate concentrations of potassium, phosphate, sulphate and magnesium to meet all or part of the crop’s requirements. To fully benefit from these inputs farmers must have an awareness of the water quality and reduce the application of chemical fertilisers accordingly. Interviews with farmers have shown that 75 per cent of farmers indirectly using reclaimed water are aware of the nutrients. Farmers’ decision making as to the application of chemical fertilisers appears to be influenced by a range of factors which include the type of crops being cultivated, the provision of training on nutrient management and the availability of information on the nutrient content of the reclaimed water.

The determination of total nitrogen and total phosphorus concentrations in freshwaters from land use, stock headage and population data: testing of a model for use in conservation and water quality management

1. Nutrient concentrations (particularly N and P) determine the extent to which water bodies are or may become eutrophic. Direct determination of nutrient content on a wide scale is labour intensive but the main sources of N and P are well known. This paper describes and tests an export coefficient model for prediction of total N and total P from: (i) land use, stock headage and human population; (ii) the export rates of N and P from these sources; and (iii) the river discharge. Such a model might be used to forecast the effects of changes in land use in the future and to hindcast past water quality to establish comparative or baseline states for the monitoring of change. 2. The model has been calibrated against observed data for 1988 and validated against sets of observed data for a sequence of earlier years in ten British catchments varying from uplands through rolling, fertile lowlands to the flat topography of East Anglia. 3. The model predicted total N and total P concentrations with high precision (95% of the variance in observed data explained). It has been used in two forms: the first on a specific catchment basis; the second for a larger natural region which contains the catchment with the assumption that all catchments within that region will be similar. Both models gave similar results with little loss of precision in the latter case. This implies that it will be possible to describe the overall pattern of nutrient export in the UK with only a fraction of the effort needed to carry out the calculations for each individual water body. 4. Comparison between land use, stock headage, population numbers and nutrient export for the ten catchments in the pre-war year of 1931, and for 1970 and 1988 show that there has been a substantial loss of rough grazing to fertilized temporary and permanent grasslands, an increase in the hectarage devoted to arable, consistent increases in the stocking of cattle and sheep and a marked movement of humans to these rural catchments. 5. All of these trends have increased the flows of nutrients with more than a doubling of both total N and total P loads during the period. On average in these rural catchments, stock wastes have been the greatest contributors to both N and P exports, with cultivation the next most important source of N and people of P. Ratios of N to P were high in 1931 and remain little changed so that, in these catchments, phosphorus continues to be the nutrient most likely to control algal crops in standing waters supplied by the rivers studied.