A leakiness index for assessing landscape function using remote sensing

The cover, number, size, shape, spatial arrangement and orientation of vegetation patches are attributes that have been used to indicate how well landscapes function to retain, not ‘leak’, vital system resources such as rainwater and soil. We derived and tested a directional leakiness index (DLI) for this resource retention function. We used simulated landscape maps where resource flows over map surfaces were directional and where landscape patch attributes were known. Although DLI was most strongly related to patch cover, it also logically related to patch number, size, shape, arrangement and orientation. If the direction of resource flow is multi-directional, a variant of DLI, the multi-directional leakiness index (MDLI) can be used. The utility of DLI and MDLI was demonstrated by applying these indices to three Australian savanna landscapes differing in their remotely sensed vegetation patch attributes. These leakiness indices clearly positioned these three landscapes along a function-dysfunction continuum, where dysfunctional landscapes are leaky (poorly retain resources). This revised version was published online in July 2006 with corrections to the Cover Date.     

Validation of a multiplex PCR assay to detect Babesia spp. and Anaplasma marginale in cattle in Uruguay in the absence of a gold standard test

Detection of bovine Babesia spp. and Anaplasma marginale is based on the reading of Giemsa-stained blood or organ smears, which can have low sensitivity. Our aim was to improve the detection of bovine Babesia spp. and A. marginale by validating a multiplex PCR (mPCR). We used 466 samples of blood and/or organs of animals with signs and presumptive autopsy findings of babesiosis or anaplasmosis. The primers in our mPCR amplified the rap-1a gene region of Babesia bovis and B. bigemina, and the msp-5 region of A. marginale. We used a Bayesian model with a non-informative priori distribution for the prevalence estimate and informative priori distribution for estimation of sensitivity and specificity. The sensitivity and specificity for smear detection of Babesia spp. were 68.6% and 99.1%, and for A. marginale 85.6% and 98.8%, respectively. Sensitivity and specificity for mPCR detection for Babesia spp. were 94.2% and 97.1%, and for A. marginale 95.2% and 92.7%, respectively. Our mPCR had good accuracy in detecting Babesia spp. and A. marginale, and would be a reliable test for veterinarians to choose the correct treatment for each agent.     

Bradyarrhythmia in an anaesthetised, elderly, hypertensive cat

A 14-year-old neutered male domestic shorthaired cat was presented to the University Veterinary Centre Sydney for evaluation and treatment of dental disease. This cat developed an unusual bradyarrhythmia under anaesthesia. The possible causes and treatment of the dysrythmia are discussed.     

Roots in irrigated clay soils: Measurement techniques and responses to rootzone conditions

Summary This paper reviews research carried out at the Griffith Laboratory in Australia over the last decade on techniques for, and results of, observations of roots in irrigated clay soils. Our results emphasise the adaptability of root systems to rootzone conditions. Experiences with techniques for observing roots non-destructively in the field and both non-destructively and destructively in lysimeters are described. We concluded that the minirhizotron technique, applied in the field, was unreliable under our conditions. Horizontal root observation tubes were used in lysimeters to measure root length density (RLD) and to assess whether roots were clumped together or randomly distributed. Destructive sampling and measurement of RLD was used to establish a theoretical relationship between root intercept counts along the tubes and RLD. The application of image analysis to both destructive and non-destructive sampling in the lysimeters is outlined. The non-destructive lysimeter studies showed that roots were significantly clumped. Analysis of root intercept and root hole counts on the faces of sample cubes taken from the lysimeters showed root distribution was anisotropic over the whole soil profile for both safflower and wheat. There were many more roots and root holes present in the sampled soil cubes than was indicated by independent sampling for washed out RLD. Safflower appeared to have a faster turnover of roots than did wheat or maize. Lysimeters, equipped with horizontal root observation tubes, enabled studies to be made of many factors affecting root growth. Soils affect where and how fast roots grow, although there is also a strong species interaction. For example, soybean roots proliferated above a fresh water table in one soil but not in another; wheat had little tendency to proliferate above the water table in either soil. In wet soils, roots cease to grow once soil oxygen levels decrease below 10 mg O₂ l _soil ^-1 . This level should form the basis for soil drainage criteria. In drying soils, roots will grow successively into soil regions containing soil water: the level of adaptation being determined by soil conditions, crop growth stage and level of evaporative demand. The methods of root observation used in our studies have given quantitative assessment of root distribution. However, further research is needed to link horizontal and vertical root distribution and root adaptation more strongly to crop development and soil conditions.     

Effects of soil type on soybean crop water use in weighing lysimeters

Summary Different soils are known to affect the amount and distribution of both available water and roots. Optimising irrigation water use, especially when shallow water-tables are present requires accurate knowledge of the root zone dynamics. This study was conducted to determine the effect of two soil types on root growth, soil water extraction patterns, and contributions of a water-table to crop evaporation (E). Two weighing lysimeters (L1 and L2) with undisturbed blocks of soil were used. The soil in L1 had higher hydraulic conductivity and lower bulk density than that in L2. Well watered conditions were maintained by irrigation for the first 110 days from sowing (DFS). Root length density (RLD) was calculated from observations made in clear acrylic tubes installed into the sides of the lysimeters. Volumetric soil water contents were measured with a neutron probe. A water-table (EC = 0.01 S m^-1) was established 1 m below the soil surface 18 DFS. RLD values were greater in L1 than L2 at any depth. In L1, maximum RLD values (3 × 10⁴ m m^-3) were measured immediately above the water-table at physiological maturity (133 DFS). In L2, maximum RLD values (1.5 × 10⁴ m m^-3) were measured at 0.42 m on 120 DFS and few roots were present above the water-table. From 71 to 74 DFS, 55 and 64% of E was extracted from above 0.2 m for L1 and L2, respectively. In L2, extraction was essentially limited to the upper 0.4 m, while L1 extraction was to 0.8 m depth. Around 100 DFS the water-table contributed 29% (L1) and 7% (L2) of the water evaporated. This proportion increased rapidly as the upper soil layers dried following the last substantial irrigation 106 DFS. Over the whole season the water-table contributed 24% in L1 and 6.5% in L2 of total E.     

Salinity and sodicity effects on respiration and microbial biomass of soil

An understanding of the effects of salinity and sodicity on soil carbon (C) stocks and fluxes is critical in environmental management, as the areal extents of salinity and sodicity are predicted to increase. The effects of salinity and sodicity on the soil microbial biomass (SMB) and soil respiration were assessed over 12weeks under controlled conditions by subjecting disturbed soil samples from a vegetated soil profile to leaching with one of six salt solutions; a combination of low-salinity (0.5dSm⁻¹), mid-salinity (10dSm⁻¹), or high-salinity (30dSm⁻¹), with either low-sodicity (sodium adsorption ratio, SAR, 1), or high-sodicity (SAR 30) to give six treatments: control (low-salinity low-sodicity); low-salinity high-sodicity; mid-salinity low-sodicity; mid-salinity high-sodicity; high-salinity low-sodicity; and high-salinity high-sodicity. Soil respiration rate was highest (56–80mg CO₂-C kg⁻¹ soil) in the low-salinity treatments and lowest (1–5mg CO₂-C kg⁻¹ soil) in the mid-salinity treatments, while the SMB was highest in the high-salinity treatments (459–565mg kg⁻¹ soil) and lowest in the low-salinity treatments (158–172mg kg⁻¹ soil). This was attributed to increased substrate availability with high salt concentrations through either increased dispersion of soil aggregates or dissolution or hydrolysis of soil organic matter, which may offset some of the stresses placed on the microbial population from high salt concentrations. The apparent disparity in trends in respiration and the SMB may be due to an induced shift in the microbial population, from one dominated by more active microorganisms to one dominated by less active microorganisms.