Limitations of soil microbial biomass carbon as an indicator of soil pollution in the field

The size of the soil microbial biomass carbon (SMBC) has been proposed as a sensitive indicator for measuring the adverse effects of contaminants on the soil microbial community. In this study of Australian agricultural systems, we demonstrated that field variability of SMBC measured using the fumigation-extraction procedure limited its use as a robust ecotoxicological endpoint. The SMBC varied up to 4-fold across control samples collected from a single field site, due to small-scale spatial heterogeneity in the soil physicochemical environment. Power analysis revealed that large numbers of replicates (3-93) were required to identify 20% or 50% decreases in the size of the SMBC of contaminated soil samples relative to their uncontaminated control samples at the 0.05% level of statistical significance. We question the value of the routine measurement of SMBC as an ecotoxicological endpoint at the field scale, and suggest more robust and predictive microbiological indicators.

Satellite evidence of harmful algal blooms and related oceanographic features in the Bohai Sea during autumn 1998

Harmful algal blooms (HABs) are truly global marine phenomena of increasing significance. Some HAB occurrences are different to observe because of their high spatial and temporal variability and their advection, once formed, by surface currents. A serious HAB occurred in the Bohai Sea during autumn 1998, causing the largest fisheries economic loss. The present study analyzes the formation, distribution, and advection of HAB using satellite SeaWiFS ocean color data and other oceanographic data. The results show that the bloom originated in the western coastal waters of the Bohai Sea in early September, and developed southeastward when sea surface temperature (SST) increased to 25-26 °C. The bloom with a high Chl-a concentration (6.5 mg m-3) in center portion covered an area of 60 × 65 km2. At the end of September, the bloom decayed when SST decreased to 22-23 °C. The HAB may have been initiated by a combination of the river discharge nutrients in the west coastal waters and the increase of SST; afterwards it may have been transported eastward by the local circulation that was enhanced by northwesterly winds in late September and early October.

Treatment of shrimp farm effluent with omnivorous finfish and artificial substrates

Long-term environmental sustainability and community acceptance of the shrimp farming industry in Australia requires on-going development of efficient cost-effective effluent treatment options. In this study, we aimed to evaluate the effectiveness of a shrimp farm treatment system containing finfish and vertical artificial substrates (VAS). This was achieved by (1) quantifying the individual and collective effects of grey mullet (Mugil cephalus L.) and VASs on water and sediment quality, and (2) comparing the retention of N in treatment systems with and without the presence of finfish (M. cephalus and the siganid Siganus nebulosus (Quoy & Gaimard)), where light was selectively removed. Artificial substrates were found to significantly improve the settlement of particulate material, regardless of the presence of finfish. Mullet actively resuspended settled solids and reduced the production of nitrate when artificial substrates were absent. However, appreciable nitrification was observed when mullet were present together with artificial substrates. The total quantity of N retained by the mullet was found to be 1.8– 2.4% of the incoming pond effluent N. It was estimated that only 21% of the pond effluent N was available for mullet consumption. When S. nebulosus was added, total finfish N retention increased from 1.8% to 3.9%, N retention by mullet also improved (78±16 to 132±21-mg N day−1 before and after siganid addition respectively). Presence of filamentous macroalgae (Enteromorpha spp.) was found to improve the removal of N from pond effluent relative to treatments where light was excluded. Denitrification was also a significant sink for N (up to 24% N removed). Despite the absence of algal productivity and greater availability of nitrate, denitrification was not higher in treatments where light was excluded. Mullet were found to have no effect on the rates of denitrification but significantly reduced macroalgal growth on the surface of the water. When mullet were absent, excessive macroalgal growth led to reduced dissolved oxygen concentrations and nitrification. This study concludes that the culture of mullet alone in shrimp farm effluent treatment systems does not result in significant retention of N but can contribute to the control of macroalgal biomass. To improve N retention and removal, further work should focus on polyculturing a range of species and also on improving denitrification.

Comparative growth and biomass allocation of two varieties of cat's claw creeper, Dolichandra unguis-cati (Bignoniaceae) in Australia

Introduced as an ornamental vine, cat's claw creeper Dolichandra unguis-cati (syn. Macfadyena unguis-cati) has invaded coastal and subcoastal areas of subtropical eastern Australia. Two varieties have been indentified, one of which ('short-pod') is found throughout south-eastern Australia, while the other ('long-pod') appears to be restricted to several sites in south-eastern Queensland. We compared the growth and biomass allocation patterns of the two varieties in the field over a 22-month period to determine if a higher growth rate and/or more efficient allocation of biomass may contribute to this disparity in distribution. The long-pod variety produced greater aboveground and total biomass than the short-pod variety in both riparian and non-riparian zones. Belowground the two varieties produced a similar number of tubers and overall biomass, though the long-pod variety allocated a smaller portion of its carbon belowground. High growth rates and greater biomass allocation aboveground are characteristic of invasive species, allowing them to outcompete and crowd out existing vegetation. There was no significant site by variety interaction, an indication of consistency in variety performance across riparian and non-riparian sites. Results from our study suggest that differences in growth and biomass allocations are unlikely to have contributed to the disparity in distribution of the two varieties. Despite currently occupying a relatively small range, the long-pod variety may be a more adept invader than the short-pod variety, and could become more prevalent in the future. © 2012 CSIRO.

Stunted cotton (Gossypium hirsutum L.) fully recovers biomass and yield of seed cotton after delayed root inoculation with spores of an arbuscular mycorrhizal fungus (Glomus mosseae)

In the northern grain and cotton region of Australia, poor crop growth after long periods of fallow, called 'long-fallow' disorder, is caused by a decline of natural arbuscular-mycorrhizal fungi (AMF). When cotton was grown in large pots containing 22 kg of Vertisol from a field recently harvested from cotton in Central Queensland, plants in pasteurised soil were extremely stunted compared with plants in unpasteurised soil. We tested the hypothesis that this extreme stunting was caused by the absence of AMF and examined whether such stunted plants could recover from subsequent treatment with AMF spores and/or P fertiliser. At 42 days after sowing, the healthy cotton growing in unpasteurised soil had 48% of its root-length colonised with AMF, whereas the stunted cotton had none. After inoculation with AMF spores (6 spores/g soil of Glomus mosseae) and/or application of P fertiliser (50 mg P/kg soil) at 45 days after sowing, the stunted plants commenced to improve about 25 days after treatment, and continued until their total dry matter and seed cotton production equalled that of plants growing in unpasteurised soil with natural AMF. In contrast, non-mycorrhizal cotton grown without P fertiliser remained stunted throughout and produced no bolls and only 1% of the biomass of mycorrhizal cotton. Even with the addition of P fertiliser, non-mycorrhizal cotton produced only 64% of the biomass and 58% of the seed cotton (lint + seed) of mycorrhizal cotton plants. These results show that cotton is highly dependent on AMF for P nutrition and growth in Vertisol (even with high rates of P fertiliser), but can recover from complete lack of AMF and consequent stunting during at least the first 45 days of growth when treated with AMF spores and/or P fertiliser. This corroborates field observations in the northern region that cotton may recover from long-fallow disorder caused by low initial levels of AMF propagules in the soil as the AMF colonisation of its roots increases during the growing season.

More fertile florets and grains per spike can be achieved at higher temperature in wheat lines with high spike biomass and sugar content at booting

An understanding of processes regulating wheat floret and grain number at higher temperatures is required to better exploit genetic variation. In this study we tested the hypothesis that at higher temperatures, a reduction in floret fertility is associated with a decrease in soluble sugars and this response is exacerbated in genotypes low in water soluble carbohydrates (WSC). Four recombinant inbred lines contrasting for stem WSC were grown at 20/10 degrees C and 11 h photoperiod until terminal spikelet, and then continued in a factorial combination of 20/10 degrees C or 28/14 degrees C with 11 h or 16 h photoperiod until anthesis. Across environments, High WSC lines had more grains per spike associated with more florets per spike. The number of fertile florets was associated with spike biomass at booting and, by extension, with glucose amount, both higher in High WSC lines. At booting, High WSC lines had higher fixed C-13 and higher levels of expression of genes involved in photosynthesis and sucrose transport and lower in sucrose degradation compared with Low WSC lines. At higher temperature, the intrinsic rate of floret development rate before booting was slower in High WSC lines. Grain set declined with the intrinsic rate of floret development before booting, with an advantage for High WSC lines at 28/14 degrees C and 16 h. Genotypic and environmental action on floret fertility and grain set was summarised in a model.

Development and testing of allometric equations for estimating above-ground biomass of mixed-species environmental plantings

To quantify the impact that planting indigenous trees and shrubs in mixed communities (environmental plantings) have on net sequestration of carbon and other environmental or commercial benefits, precise and non-biased estimates of biomass are required. Because these plantings consist of several species, estimation of their biomass through allometric relationships is a challenging task. We explored methods to accurately estimate biomass through harvesting 3139 trees and shrubs from 22 plantings, and collating similar datasets from earlier studies, in non-arid (>300mm rainfallyear-1) regions of southern and eastern Australia. Site-and-species specific allometric equations were developed, as were three types of generalised, multi-site, allometric equations based on categories of species and growth-habits: (i) species-specific, (ii) genus and growth-habit, and (iii) universal growth-habit irrespective of genus. Biomass was measured at plot level at eight contrasting sites to test the accuracy of prediction of tonnes dry matter of above-ground biomass per hectare using different classes of allometric equations. A finer-scale analysis tested performance of these at an individual-tree level across a wider range of sites. Although the percentage error in prediction could be high at a given site (up to 45%), it was relatively low (<11%) when generalised allometry-predictions of biomass was used to make regional- or estate-level estimates across a range of sites. Precision, and thus accuracy, increased slightly with the level of specificity of allometry. Inclusion of site-specific factors in generic equations increased efficiency of prediction of above-ground biomass by as much as 8%. Site-and-species-specific equations are the most accurate for site-based predictions. Generic allometric equations developed here, particularly the generic species-specific equations, can be confidently applied to provide regional- or estate-level estimates of above-ground biomass and carbon. © 2013 Elsevier B.V.

Effects of externally supplied protein on root morphology and biomass allocation in Arabidopsis

Growth, morphogenesis and function of roots are influenced by the concentration and form of nutrients present in soils, including low molecular mass inorganic N (IN, ammonium, nitrate) and organic N (ON, e.g. amino acids). Proteins, ON of high molecular mass, are prevalent in soils but their possible effects on roots have received little attention. Here, we investigated how externally supplied protein of a size typical of soluble soil proteins influences root development of axenically grown Arabidopsis. Addition of low to intermediate concentrations of protein (bovine serum albumen, BSA) to IN-replete growth medium increased root dry weight, root length and thickness, and root hair length. Supply of higher BSA concentrations inhibited root development. These effects were independent of total N concentrations in the growth medium. The possible involvement of phytohormones was investigated using Arabidopsis with defective auxin (tir1-1 and axr2-1) and ethylene (ein2-1) responses. That no phenotype was observed suggests a signalling pathway is operating independent of auxin and ethylene responses. This study expands the knowledge on N form-explicit responses to demonstrate that ON of high molecular mass elicits specific responses.

Wheat biomass and yield increased when populations of the root-lesion nematode (Pratylenchus thornei) were reduced through sequential rotation of partially resistant winter and summer crops

The root-lesion nematode, Pratylenchus thornei, can reduce wheat yields by >50%. Although this nematode has a broad host range, crop rotation can be an effective tool for its management if the host status of crops and cultivars is known. The summer crops grown in the northern grain region of Australia are poorly characterised for their resistance to P. thornei and their role in crop sequencing to improve wheat yields. In a 4-year field experiment, we prepared plots with high or low populations of P. thornei by growing susceptible wheat or partially resistant canaryseed (Phalaris canariensis); after an 11-month, weed-free fallow, several cultivars of eight summer crops were grown. Following another 15-month, weed-free fallow, P. thornei-intolerant wheat cv. Strzelecki was grown. Populations of P. thornei were determined to 150 cm soil depth throughout the experiment. When two partially resistant crops were grown in succession, e.g. canaryseed followed by panicum (Setaria italica), P. thornei populations were <739/kg soil and subsequent wheat yields were 3245 kg/ha. In contrast, after two susceptible crops, e.g. wheat followed by soybean, P. thornei populations were 10 850/kg soil and subsequent wheat yields were just 1383 kg/ha. Regression analysis showed a linear, negative response of wheat biomass and grain yield with increasing P. thornei populations and a predicted loss of 77% for biomass and 62% for grain yield. The best predictor of wheat yield loss was P. thornei populations at 0-90 cm soil depth. Crop rotation can be used to reduce P. thornei populations and increase wheat yield, with greatest gains being made following two partially resistant crops grown sequentially.

Growth analysis and biomass partitioning of Cyperus iria in response to rice planting density and nitrogen rate

Cyperus iria is a weed of rice with widespread occurrence throughout the world. Because of concerns about excessive and injudicious use of herbicides, cultural weed management approaches that are safe and economical are needed. Developing such approaches will require a better understanding of weed biology and ecology, as well as of weed response to increases in crop density and nutrition. Knowledge of the effects of nitrogen (N) fertilizer on crop-weed competitive interactions could also help in the development of integrated weed management strategies. The present study was conducted in a screenhouse to determine the effects of rice planting density (0, 5, 10, and 20 plants pot−1) and N rate (0, 50, 100, and 150 kg ha−1) on the growth of C. iria. Tiller number per plant decreased by 73–88%, leaf number by 85–94%, leaf area by 85–98%, leaf biomass by 92–99%, and inflorescence biomass by 96–99% when weed plants were grown at 20 rice plants pot−1 (i.e., 400 plants m−2) compared with weed plants grown alone. All of these parameters increased when N rates were increased. On average, weed biomass increased by 118–389% and rice biomass by 121–275% with application of 50–150 kg N ha−1, compared to control. Addition of N favored weed biomass production relative to rice biomass. Increased N rates reduced the root-to-shoot weight ratio of C. iria. Rice interference reduced weed growth and biomass and completely suppressed C. iria when no N was applied at high planting densities (i.e., 20 plants pot−1). The weed showed phenotypic plasticity in response to N application, and the addition of N increased the competitive ability of the weed over rice at densities of 5 and 10 rice plants pot−1 compared with 20 plants pot−1. The results of the present study suggest that high rice density (i.e., 400 plants m−2) can help suppress C. iria growth even at high N rates (150 kg ha−1).

Biomass for aviation fuel production in the Fitzroy Basin, Queensland: a preliminary assessment of native and plantation forest potential

SummaryThis scoping study assesses the contribution that woody biomass could make to feedstock supply for an aviation biofuel industry in Queensland. The inland 600?900 mm rainfall zone, including the Fitzroy Basin region, is identified as an area that is particularly worthy of closer study as it has potential for supply of woody biomass from existing native regrowth (brigalow and other species) as well as from new plantings. New analyses carried out for this study of Corymbia citriodora subsp. variegata trials suggest biomass plantings could produce harvestable yield of aboveground dry mass of about 85 t ha?1 over a 10-year rotation at relatively low-rainfall (600?750 mm mean annual precipitation) sites and about 115 t ha?1 at medium-rainfall (750?900 mm) sites. Estimates of productivity for native regrowth suggest potential productivity should be around 40 t ha?1 during the initial decade after clearing when systems are managed for bioenergy rather than grazing. In this paper, potential production systems are described, and sustainability issues are briefly considered. It is concluded that more detailed studies focused particularly on biomass production would be worthwhile, and further research requirements are briefly discussed.