Identifying phenological functional types in savanna trees

Savannas are notable for the varied patterns of leaf display in the tree layer. Characterising this variation, and assessing the range of phenological strategies apparent in savanna ecosystems will be helpful for understanding savanna tree life-histories and their response to global change. We recorded leaf phenological metrics on a monthly basis for 28 woody species for one year in a semi-arid savanna at Nylsvley Nature Reserve, South Africa. Using these metrics four plant functional types were described: (1) evergreen species, which retained full canopy throughout the year; (2) semi-evergreen species, which lost a significant amount of canopy during the dry season, but not less than 60%; (3) obligate deciduous species in which the canopy was leafless for about 3 months during the dry season; and (4) rain-stimulated species, in which canopy flushing was driven by rainfall patterns. Of the 28 species, 18% were evergreen, 18% obligate deciduous, 32% semi-evergreen and 32% were rain-stimulated species. These results confirm that phenological strategies are variable in savannas, and highlight that there are numerous cues controlling the timing of leaf out and leaf drop. By defining distinct phenological strategies we can predict which plant functional types will have phenological cues that will be vulnerable to shifting climates.     

Activity of meadowfoam (Limnanthes alba) seed meal glucolimnanthin degradation products against soilborne pathogens

Meadowfoam (Limnanthes alba L.) is a herbaceous winter-spring annual grown as a commercial oilseed crop. The meal remaining after oil extraction from the seed contains up to 4% of the glucosinolate glucolimnanthin. Degradation of glucolimnanthin yields toxic breakdown products, and therefore the meal may have potential in the management of soilborne pathogens. To maximize the pest-suppressive potential of meadowfoam seed meal, it would be beneficial to know the toxicity of individual glucolimnanthin degradation products against specific soilborne pathogens. Meloidogyne hapla second-stage juveniles (J2) and Pythium irregulare and Verticillium dahliae mycelial cultures were exposed to glucolimnanthin as well as its degradation products. Glucolimnanthin and its degradation product, 2-(3-methoxyphenyl)acetamide, were not toxic to any of the soilborne pathogens at concentrations up to 1.0 mg/mL. Two other degradation products, 2-(3-methoxymethyl)ethanethioamide and 3-methoxyphenylacetonitrile, were toxic to M. hapla and P. irregulare but not V. dahliae. The predominant enzyme degradation product, 3-methoxybenzyl isothiocyanate, was the most toxic compound against all of the soilborne pathogens, with M. hapla being the most sensitive with EC(50) values (0.0025 ± 0.0001 to 0.0027 ± 0.0001 mg/mL) 20-40 times lower than estimated EC(50) mortality values generated for P. irregulare and V. dahliae (0.05 and 0.1 mg/mL, respectively). The potential exists to manipulate meadowfoam seed meal to promote the production of specific degradation products. The conversion of glucolimnanthin into its corresponding isothiocyanate should optimize the biopesticidal properties of meadowfoam seed meal against M. hapla, P. irregulare, and V. dahliae.     

Characterization of phytoecdysteroid glycosides in Meadowfoam (Limnanthes alba) seed meal by positive and negative ion LC-MS/MS

Meadowfoam ( Limnanthes alba) is an oilseed crop grown in western Oregon. The seed meal has potential value as a biopesticide due to glucosinolate degradation products and phytoecdysteroids, a group of polyhydroxylated triterpenoids with potent activities as arthropod molting hormones. Liquid chromatography in combination with tandem mass spectrometry operated in the precursor ion mode revealed the presence of four ecdysteroid glycosides in meadowfoam seed meal. The carbohydrate sequence and the identity of the ecdysteroid aglycones, ponasterone A and 20-hydroxyecdysone, were determined by product ion scanning. Ecdysteroids were detected in the negative ion mode as [M + formate] (-) ions, which yielded [M - H] (-) and alpha-cleavage fragments with retention of hydroxyl groups in MS/MS experiments (not seen in the positive ion mode), allowing the determination of the number of hydroxyl groups in the side chain and in the steroid ring system. MS/MS of glycoside ions ([MH] (+) or [M + formate] (-)) provided carbohydrate sequence information.     

Sources of nitrite in a permanent grassland soil

The objective of this study was to separate the observed nitrite (NO₂^–) concentration in a permanent grassland soil into process‐specific subpools. A laboratory experiment was carried out where either the nitrate and/or ammonium pool was labelled with ¹⁵N at 60 atom % excess. The main N transformations that occurred in this experiment were analysed with a ¹⁵N tracing model extended with a NO₂^– submodel. Techniques that have been used to date have been only able to identify NO₂^– subpools related to nitrification (NO₂^–_nit) and denitrification (NO₂^–_den). With the analysis presented here, we were able to quantify the size of an additional NO₂^– pool in the soil related to organic N turnover (NO₂^–_org). All transformations related to NO₂^– turnover of the three subpools occurred simultaneously. After non‐linear parameter optimization the model predicted that on average NO₂^–_den, NO₂^–_nit and NO₂^–_org pools contributed 57, 33 and 10% to the total soil NO₂^– concentration. The finding that heterotrophic processes can contribute to the NO₂^– dynamics in permanent grassland soils might also have important implications for the understanding of gaseous N production that are tightly linked to NO₂^– turnover. Further work is needed to find out how important the conversion of organic N to NO₂^– is in other soil‐based ecosystems and to identify the microbial groups responsible for this process.     

Technique for rapid, small-scale analysis of vitamin C levels in fruit and application to a tomato mutant collection

We present a technique for easy, rapid analysis of both total and reduced forms of vitamin C in fruits using microplates and a plate reader. This technique has been compared with a spectrofluorometric technique classically used for assaying vitamin C in fresh tomato. We have applied these methods to a population of 118 tomato mutant lines and controls in search of variability for this trait. Six lines, identified as having high vitamin C levels, and four lines having low vitamin C levels have been chosen for further study. The vitamin C levels have been compared with sugar concentration, dry matter content, fruit weight, titratable acidity, and firmness. The correlations that often exist in tomato varieties between sugar and vitamin C content (positive correlation) or fruit weight and vitamin C content (negative correlation) can be uncoupled in the lines selected for further analysis.     

Discriminating soil crust type,development stage and degree of disturbance in semiarid environments from their spectral characteristics

Biological soil crusts (BSCs) are increasingly recognized as common features in arid and semiarid ecosystems and play an important role in the hydrological and ecological functioning of these ecosystems. However, BSCs are very vulnerable to, in particular, human disturbance. This results in a complex spatial pattern of BSCs in various stages of development. Such patterns, to a large extent, determine runoff and erosion processes in arid and semiarid ecosystems. In recent years, visible and near infrared (Vis‐NIR) diffuse reflectance spectroscopy has been used for large‐scale mapping of the distribution of BSCs. Our goals were (i) to demonstrate the efficiency of Vis‐NIR spectroscopy in discriminating vegetation, physical soil crusts, various developmental stages of BSCs, and various types of disturbance on BSCs and (ii) to develop a classification system for these types of ground cover based on Vis‐NIR spectroscopy. Spectral measurements were taken of vegetation, physical crusts and various types of BSCs prior to, and following, trampling or removal with a scraper in two semiarid areas in SE Spain. The main spectral differences were: (i) absorption by water at about 1450 nm, more intense in the spectra of vegetation than in those of physical crusts or BSCs, (ii) absorption features at about 500 and 680 nm for the BSCs, which were absent or very weak for physical crusts, (iii) a shallower slope between about 750 and 980 nm for physical crusts and early‐successional BSCs than for later‐successional BSCs and (iv) a steeper slope between about 680 and 750 nm for the most developed BSCs. A partial least squares regression‐linear discriminant analysis of the spectral data resulted in a reliable classification (Kappa coefficients over 0.90) of the various types of ground cover and types of BSC disturbance. The distinctive spectral features of vegetation, physical crusts and the various developmental stages of BSCs were used to develop a classification system. This will be a promising tool for mapping BSCs with hyperspectral remote sensing.     

Assessment and monitoring of soil quality using near-infrared reflectance spectroscopy (NIRS)

Soil degradation processes have dramatically increased in their extent and intensity over the last decades. Progressively, actions have been taken in order to evaluate and reduce the major threats that have already wreaked havoc on soil conditions. Efficient and standardized monitoring of soil conditions is thus required but soil quality research is facing an important technological challenge because of the number of properties involved in soil quality. The objective of the present review is to examine critically the suitability of near-infrared reflectance spectroscopy (NIRS) as a tool for soil quality assessment. We first detail the soil quality-related parameters (chemical, physical and biological) that can be predicted with NIRS through laboratory measurements. The ability of imaging NIRS (airborne or satellite) for mapping a minimum data set of soil quality is also discussed. Then we review the most recent research using soil reflectance spectra as an integrated measure of soil quality, from global site classification to the prediction of specific soil quality indices. We conclude that imaging NIRS enables the direct mapping of some soil properties and soil threats, but that further developments to solve several technological limitations identified are needed before it can be used for soil quality assessment. The robustness of laboratory NIRS for soil quality assessment allows its implementation in soil monitoring networks. However, its routine use requires the development of international soil spectral libraries that should become a priority for soil quality research.     

Soil Testing Bray-1 Phosphorus with Non-Reagent Grade Hydrochloric and Sulfuric Acids

Portable instruments have reduced on-site testing costs for soil pH and potassium in isolated locations. Acids could not be shipped to a remote Africa field laboratory. Bray-1 phosphorus (P) testing is difficult because hydrochloric (HCl) is required in the extraction solution and sulfuric acid (H₂SO₄) is used in color development stock solutions. Muriatic HCl acid and battery H₂SO₄ were available in a local stores. The objectives of this study were to evaluate the accuracy of P soil testing using diluted, non-reagent HCl for making modified Bray1-P extractant and non-reagent H₂SO₄ for color development. Experiment 1 was conducted with soil samples from fields using Sunnyside? and Klean Strip? HCl muriatic acids. Soil samples extracted with diluted reagent HCl were closely related to P results using diluted Klean Strip (R² = 0.96) and Sunnyside (R² = 0.84) HCl. In Experiment 2, two commercial brands of H₂SO₄ acid used to refill car battery cells were evaluated. Test results suggested that the battery H₂SO₄ acids are not suitable for making color development solution. In Experiment 3, a small battery powered spectrometer for P testing aquarium water was calibrated for soils. Samples from the Soil Science Society of America –North American Proficiency Testing program (NAPT) were tested with the meter and non-reagent HCl. Fiske-Subbarrow reducing agent and HCl were used in a variation procedure which does not require H₂SO₄ for color development. Eight of 10 samples tested proficient based on NAPT limits (2.5 x Median Absolute Deviation).     

Measuring Soil and Tissue Potassium with a Portable Ion-Specific Electrode in Cotton

Most laboratories make potassium (K) fertilizer recommendations based on field research calibrated with soil K from atomic absorption spectroscopy, flame emission spectroscopy, or inductively coupled plasma mass spectrometry. Information is needed to interpret readings from K⁺ meters on cotton. The objective was to compare soil and cotton plant sap potassium content from a Laqua Twin? K⁺ meter to results from standard tests. Aluminum sulfate solution was used with the meter to extract K from 10 soil samples from the North America Proficiency Testing program. A linear relationship (R² = 0.86) was found between K measured with a K⁺ meter and K measured with 138 labs using ammonium acetate or Mehlich-3. Using a factor of 1.4754 to adjust readings, fertilizer recommendations with the K⁺ meter were similar to results from atomic absorption spectroscopy. A linear relationship was found between petiole K measured in the lab and petiole sap measured with the K⁺ meter.