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Biochar may be potentially used as a rhizobial carrier due to its specific chemical compositions and surface properties, but the relationship between these properties and rhizobial survival rate is largely unknown. Here, we analysed the physicochemical characteristics and carrier potential of six types of biochars made from various feedstocks at 600 °C using slow pyrolysis method, and results were compared with conventional carrier material peat. Liquid suspension of Bradyrhziobium japonicum CB1809 was used to inoculate all the carrier materials. Shelf life and survival rate was determined via colony forming unit (CFU) method for up to 90 days under two storage temperature conditions (28 °C and 38 °C). The determined physicochemical characteristics of biochars were categorized into major elements, trace elements, relative ratios, surface morphology, functional groups, and key basic properties; and their interaction to shelf life was analysed using hypothesis-oriented structure equation modelling (path analysis). Results revealed that different types of biochars had different capacity to impact on shelf life due to their different physicochemical properties. Among all biochars pine wood BC was the most suitable carrier with the highest counts of 10.11 Log 10 CFU g

Changes in fire regime and soil temperatures will be simultaneous symptoms of climate change in many regions around the world, yet very few studies have investigated how these factors will interact to affect soil carbon (C) cycling. Interacting effects of fire regime and temperature on soil C cycling processes might constitute an important but poorly-understood feedback to the global climate system. Using soils from one of the world's longest running prescribed fire trials in eastern Australia, we investigated the effect of fire regime on the rate, energetic efficiency, and temperature sensitivity of soil heterotrophic respiration and associated properties across a range of incubation temperatures (15 °C, 25 °C, and 35 °C). Levels of total, labile, soluble, and microbial biomass C were 32%, 59%, 64%, and 38% lower, respectively, in biennially-burned (2yB) soils than in soils that had not been exposed to fire since 1969 (NB soils). Moreover, while rates of heterotrophic respiration did not vary among NB, 2yB or quadrennially-burned (4yB) soils during the 55-day incubation period, values of qCO2 (which are inversely related to microbial energetic efficiency) were 59.8% higher in 2yB soils than in NB soils. This suggests that biennial-burning is associated with soil conditions that promote energetic inefficiency in the microbial community and highlights the role of environmental stress as a determinant of respiratory responses to fire regime. Respiration temperature sensitivity (i.e. Q10 values) of 2yB soils was 86% greater than that of 4yB soils at the temperature range of 15–25 °C. This effect was absent at the temperature range of 25–35 °C and in soils to which labile C levels had been boosted through glucose addition. This pattern in Q10 values might be attributed to low quality soil organic matter in 2yB soils in combination with mechanisms associated with microbial community structure. Together these results enhance our understanding of C cycling in fire-affected soils and suggest a potentially important positive feedback between fire, climate change, and the terrestrial C cycle that warrants further investigation.

High sodicity and Low nutrient retention in bauxite-processing residue sand (BRS) disposal areas restrict sustainable vegetation management in this highly alkaline environment. Although previous investigations have reported the beneficial effect of organic amendments on BRS rehabilitation, little is known about the underlying mechanisms of this complicated process, particularly after supplementary leaching of biochar amended BRS. We have investigated the coupled effect of supplementary leaching process, biochar [aged acidic (AC) vs alkaline pine (PC)] amendment and di-ammonium phosphate (DAP) fertilisation on rhizosphere nutrient dynamic and ryegrass performance in a 116-day glasshouse study. Biochar amendment in DAP + PC and DAP + AC treatments significantly increased and decreased pH (0.3–0.5 units) in all BRS rhizosphere and root-free zones, respectively. The application of alkaline and acidic biochars to BRS have reduced ammonia volatilisation (25–80%) and increased nitrogen retention (9–72%) in comparison with DAP treatment. Supplementary leaching had no significant effect on BRS rhizosphere pH, but reduced the EC values by ca. 62% in biochar-amended treatments. The leachates’ pH remained unchanged (ca. 8) throughout the experiment, while their EC reduced in AC (6 folds) and PC (9 folds) amended treatments, with lower reduction in rhizosphere than root-free zones. The interaction of applied biochars and plant roots generally decreased nutrient leaching from rhizosphere in comparison with root-free zones. Sodium was the dominant cation in the leachate of all treatments and cumulative abundance of exchangeable cations were in the order of Na+ > Ca2+ > K+ > Mg2+ > Al3+. The reduction of BRS salinity has increased plant biomass (ca. 47%) in biochar amended treatments by improving the capacity of fresh BRS rhizosphere for plant establishment.

Low nitrogen (N) content and retention in bauxite-processing residue sand (BRS) disposal areas pose a great challenge to the establishment of sustainable vegetation cover in this highly alkaline environment. The budget and fate of applied N in BRS and its potential environmental impacts are largely unknown. We investigated the effect of combined application of biochars [aged acidic (AC) vs alkaline pine (PC)] and di-ammonium phosphate (DAP) fertiliser on ammonia (NH3) volatilisation, nitrous oxide (N2O) emission and N retention in a 116-day glasshouse study. The application of AC to BRS decreased pH (≈0.5 units) in BRS, while PC biochar increased pH (≈0.3 units). The application of AC reduced NH3 volatilisation by ca. 80%, while PC by ca. 25%. On the other hand, the AC treatment increased N2O emission by 5 folds. However, the N loss via N2O emission in the AC treatment only accounted for ca. 0.4% of applied N. The reduction in BRS pH and increased retention of mineral N due to the presence of oxygen-containing (phenolic and carboxylic) functional groups in AC may be responsible for reduced NH3 volatilisation and increased N2O emission. This study has highlighted the potential of biochar (particularly aged biochar) in improving N retention and minimising environmental impacts in highly alkaline environments.

Biochar amendment has been proposed as a strategy to improve soil quality and mitigate climate change. Yet the extent and regulating mechanisms of soil nitrous oxide (N2O) emission in response to amendment of biochars derived from different feedstock have not been clearly demonstrated. A 12-month field trial was conducted to study the impact of two distinct biochar feedstocks (pine chip and peanut shell, at 10 and 30 t ha−1) with (+N) and without nitrogen (N) (−N) fertilization on soil N dynamics, N2O emissions, plant performance and microbial gene abundance. The cumulative N2O emissions varied greatly with biochar feedstock and application rate, and N fertilization. Pine biochar (at 30 t ha−1) significantly increased N2O emissions (by 48%) compared to control under −N, while peanut shell biochar (at 30 t ha−1) significantly increased N2O emissions (by 131%) compared to control under +N. Overall, biochar amendments had no impact on soil mineral N (NH4+ and NO3−) under both −N and +N. Under −N, biochar amendments showed no effect on plant yield, whereas under +N yield was significantly improved by 25–27% from pine biochar treatments. Under +N, only pine biochar (at 10 t ha−1) significantly increased plant N uptake (by 47%), and only peanut shell biochar (at 30 t ha−1) significantly enhanced soil AOB, narG, nirS and nosZ gene abundance. Increased soil N2O emission under −N from pine biochar amendment is likely to be regulated by improved water retention. However, increases in N2O emission from peanut shell biochar under +N could be driven by its large N inputs, labile organic C concentration and the increased soil pH which might largely facilitate biotic processes as evidenced by higher narG, nirS and AOB gene abundance. Positive feedback to N2O emission by biochar application revealed from this study is inconsistent with many current biochar studies, showing that caution should be exercised when considering use of biochar to mitigate N2O emission.

Soil labile organic carbon (C) and nitrogen (N) pools play a central role in nutrient cycling, while fire is a key driver of biogeochemical cycle, shaping ecosystem structure and functioning. However, how soil labile organic C and N responds to the long-term repeated prescribed fire is largely unknown. In this study, a prescribed fire field experiment in a wet sclerophyll forest established in 1972 in southeast Queensland was used to evaluate the long-term impacts of different fire frequency regimes on labile organic C and N measured by different extraction methods. The fire frequency regimes included long unburnt (NB), burnt every two years (2yrB) and burnt every four years (4yrB). Results revealed that the 2yrB treatment had significantly lower C and N concentrations in hot water and K2SO4 extracts and in density fractions (LFD 1.6) compared with the NB treatment. Concentrations of carbohydrate-C in hot water extracts and acid soluble and insoluble organic matter-C in cold-water extracts followed a similar trend. The maximum reduction was observed for carbohydrate‑C (72%) and the hot water extractable N (54%) in the 2yrB treatment compared with the NB treatment, showing these parameters are most sensitive indicators. However, there was no significant difference in most of the above parameters between the 4yrB and the NB treatments, indicating that less frequent fire (4yrB) allows the ecosystem to have sufficient time to recover from fire disturbance and may be a sustainable practice for fire management in this wet sclerophyll forest ecosystem.

Nitrogen (N) bioavailability is one of the main limiting factors for microbial activity and vegetation establishment in bauxite-processing residue sand (BRS). Although beneficial effects of biochar on reducing N loss in the early stages of BRS rehabilitation have been observed previously, the underlying mechanisms of this complicated process, particularly the interactions between applied biochar and the plant rhizosphere is largely unknown. This glasshouse study (116 days), investigated the coupled effects of biochar and water stress on N bioavailability in the rhizosphere of ryegrass (Lolium rigidum) grown in BRS amended with di-ammonium phosphate (DAP) fertiliser (at rates of 0 or 2.7 t ha−1) with and without biochar amendment. The applied biochar was characterised as either aged acidic (AC) or alkaline pine (PC) and was mixed with BRS at a rate of 5% v/v under four moisture regimes (50%, 40%, 20% and 7.5% water holding capacity). Amending BRS with AC and PC biochars increased NH4 + retention and decreased cumulative NH3 volatilization within both the rhizosphere and root-free zones compared with fertiliser only treatment. These effects were more pronounced for the AC than PC biochar, suggesting that aged acidic biochar has the great potential for use in rapid establishment of vegetation in BRS disposal areas. The biochar amendment increased cumulative nitrous oxide emissions compared with DAP only treatment, with no significant differences among different moisture regimes. The Control and 20% water holding capacity (WHC) treatment showed the highest dissolved organic carbon (DOC) concentrations compared with other treatments and moisture regimes in the ryegrass rhizosphere, while the highest dissolved organic N concentration were observed in the DAP + AC treatment. Reducing moisture levels below 20% WHC generally decreased microbial biomass carbon (MBC) concentrations and activity in both the rhizosphere and root-free zones of all treatments, while total N generally decreased as moisture levels decreased from 50% to 7.5% WHC. Plant took up more N in the DAP + AC treatment compared with DAP + PC and DAP only treatments, while increasing water stress generally resulted in decreased aboveground biomass. © 2018

Soil fungi play an important role in agricultural ecosystems, yet the understanding of the responses of fungi community and function to different fertilization is limited. Here we report the responses of fungal communities and functions to 34 years of application of inorganic fertilizer (NPK), rice straw combined with inorganic fertilizer (NPKS), and no fertilizer (CK). The fungal communities were identified by Illumina high-throughput sequencing and the functional groups were inferred with FUNGuild. Three predominant Phyla of Ascomycota, Basidiomycota, Zygomycota were identified in three treatments. A significantly lower proportion of Ascomycota (47%) but higher relative abundance of Basidiomycota (28%) were observed in the NPKS treatment compared with the CK (71% and 14%, respectively). A low proportion of Basidiomycota (10%), and no significant changes in Ascomycota (74%) were found in the NPK treatment in comparison to the CK (14% and 71%, respectively). The relative abundance of Zygomycota in the NPKS (8%) and NPK (9%) treatments were significantly higher than in the CK (5%). Diversity analysis showed that indexes including Shannon, Simpson, Chao 1 and ACE all significantly declined in NPK but increased in NPKS compared with CK. FUNGuild revealed that symbiotrophic fungi in the NPKS treatment (8%) were significantly higher than in the NPK (3%) and CK (3%) treatments, and dominated by the genera Redeckera and Tricholoma, the species Trichoderma atroviride and the order Scleroderma. However, a higher proportion of pathotrophic fungi in the NPK treatment (19%) were detected than in the NPKS (11%) and CK (10%) treatments, and dominated by the species Schizangiella serpentis. Redundancy analysis (RDA) showed that fungal community structure and function were more strongly related to moisture, EC and porosity in the soil. We suggest that the sole application of inorganic fertilizer results in great changes in fungal community composition and the hazard of excess growth of pathogenic fungi, whereas combined organic fertilizer and rice straw is beneficial to maintain a healthy ecological environment and the diversity of fungal communities in paddy soil.

Organic amendments are mostly carried out on the soil surface layer to mitigate the decline in sugarcane soil health, however, the effects of subsoil application of composts on soil carbon (C) and nutrient dynamics and sugarcane yield are largely unknown. A 4 years field trial was conducted at Maryborough, Australia, to investigate the effects of subsoil application of compost on soil C and N cycling, associated biological processes and sugarcane productivity. The trial included four subsoil (ca. 25 cm) amendment treatments of control (CK, without amendment); gypsum (GP); compost (CP); and mineral fertilizer (FE). Overall, the compost treatment increased concentrations of soil NH4+-N by 30% and NO3−-N by 40% at subsoil (10–25 cm) amendment layer. Soil microbial biomass C and N at the 0–10 cm depth were also significantly higher in the compost treatment than the other treatments. The CO2 respiration in the compost and fertilizer treatments, were significantly higher than in the control and gypsum treatments at the subsoil amendment depth. The compost treatment had greater β–glucosidase activities than other treatments at the 10–25 cm soil depth. In addition, subsoil application of compost increased inputs of hot water extractable organic C (HWEOC) by 30% and N (HWETN) by 70% at the application depth, but did not affect total soil C and N contents. The HWEOC and HWETN pools were positively related to the cumulative sugarcane yield during the 4 years cropping cycle. The subsoil application of compost increased the supply of organic C and N for microbial community, enhanced nutrient cycling processes, improved soil environmental conditions and soil health for sugarcane growth and thus increased sugarcane productivity.

Soil organic phosphorus (P) dynamics is proposed to vary across regions. However, it remains unclear how it is driven by regional variations in environmental conditions. This study examined the variations in the amount and forms of organic P in the top 10 cm of mineral soils in natural broadleaved forests along a latitudinal gradient (18.4–40.8°N) and their environmental drivers. Soil organic P amount (total Po) was expressed in both absolute (i.e. the concentration) and relative (i.e. the proportion of total Po to total P) terms, and soil organic P forms was represented by the proportion of non-residual Po (to total Po) quantified using a modified Hedley P fractionation procedure. Soil total Po amount in both absolute and relative terms were lower at the low-latitude site (18.4°N) than at the high-latitude sites (25.6–40.8°N) and predominantly positively determined by soil total P. The proportion of non-residual Po significantly increased with decreasing latitude and was primarily negatively affected by soil pH, highlighting a strong pH effect on soil organic P forms. Both the amount and forms of soil organic P were also considerably affected by climate (i.e. precipitation and temperature) and some other soil properties (e.g. cations and organic carbon). Latitudinal variations in climate affected soil total Po concentration largely through their effects on soil total P, organic C, and P sorption capacity, however they affected soil organic P forms mainly through their effects on soil pH and also via soil cations, organic C, and P saturation status.

Low phosphorus (P) solubility in soil limits primary productivity in terrestrial ecosystems worldwide. However, our understanding about drivers of soil P solubility is still incomplete. This study examined the levels of water soluble inorganic P (Pi) and organic P (Po) in soils under mature subtropical forests in China, and how they can be influenced by three low-molecular organic acids (LOAs, i.e. citric, malic and oxalic acids) and key soil properties (e.g. organic C concentration). Water soluble Pi (mean 0.05 mg kg− 1) and Po (0.32 mg kg− 1) in the soils studied were generally low, compared to in many other areas of the world. While all three LOAs significantly solubilized P from the soils studied as a whole, the solubilized amount varied greatly among soils and also varied largely with the type of LOA and P forms. Solubilized Po by the three LOAs were > 2.5 times of the solubilized Pi. Soluble total P (Pi + Po) increased in the order of oxalic acid

There is little doubt that 'rock phosphate' reserves are decreasing, with phosphorus (P) peak to be reached in the coming decades. Hence, removal and recovery of phosphorus (P) from alternative nutrient-rich waste streams is critical and of great importance owing to its essential role in agricultural productivity. Adsorption technique is efficient, cost-effective, and sustainable for P recovery from waste streams which otherwise can cause eutrophication in receiving waters. As selective P sorption using rare earth elements (REE) are gaining considerable attention, this review extensively focuses on P recovery by utilising a range of REE-incorporated adsorbents. The review briefly provides existing knowledge of P in various waste streams, and examines the chemistry and behaviour of REE in soil and water in detail. The impact of interfering ions on P removal using REE, adsorbent regeneration for reuse, and life cycle assessment of REE are further explored. While it is clear that REE-sorbents have excellent potential to recover P from wastewaters and to be used as fertilisers, there are gaps to be addressed. Future studies should target recovery and reuse of REE as P fertilisers using real wastewaters. More field trials of synthesized REE-sorbents are highly recommended before practical application.

Combined application of plant residues and N fertilisers strongly affect soil mineral N dynamics and N2O emissions depending on the quality of the plant residues, their application methods and other management strategies. We investigated the effect of combined application of two vegetable plant residues (cauliflower and sweet corn) and 15N fertiliser on N dynamics and N2O emission in a glasshouse pot study. The experiment was conducted under two residue management practices (soil incorporation vs surface mulching) over 98 days with growing basil (Ocimum basilicum) plants. We also assessed the efficacy of applying the nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP) to the plant residues, for reducing N loss and mitigating N2O emissions. Application of plant residues, both on the soil surface or into soil, resulted in net N mineralisation and increased cumulative N2O emission compared with the application of N fertiliser alone. Soil surface mulching of sweet corn decreased total and residue-induced cumulative N2O emission compared with the incorporation method, while it showed opposite effect on N2O emissions from cauliflower residue. The application of DMPP with sweet corn residue reduced total, residue- and fertiliser-induced N2O emissions; however its application with cauliflower residue did not show any mitigating effect on the N2O emissions. The residue application methods and the use of DMPP did not significantly affect 15N recovery by the basil plants. In contrast, soil incorporation of these residues doubled the microbial immobilisation of applied 15N into soil organic matter. Linear regression analysis of N2O emission during the experimental period indicated that in the treatments without DMPP application, soil NO3--N concentration was the most important factor in controlling the magnitude of N2O emissions, while the application of DMPP changed the dominant regulating factor from NO3--N to NH4+-N concentration.

Agricultural activities in catchments can cause excessive nutrient loads in waterways. Catchment nitrogen (N) and phosphorus (P) flows may be intercepted and assimilated by riparian vegetation. While prior studies suggest that woody vegetation is preferable for reducing P loads, the question remains: is woody vegetation or grass cover more effective at reducing catchment N and P exports to waterways. To address this we investigated the relative importance of vegetation type, hydrologic and soil microbial processes on N and P losses from soil to a stream. The study involved the analysis of data from two soil microcosm experiments, and a field case study. We found P leaching loss from riparian zones depended significantly on vegetation type (woody vs. grass cover), with lower P exported from wooded riparian zones, irrespective of the scale of rainfall. For N leaching losses, the scale of rainfall had an effect. During high rainfall, vegetation type had a major effect on N leaching loss, with lower N exported from grassed verses wooded riparian zones. However, under low rainfall conditions, soil type and soil C and N stores, potential indicators of soil microbial activity, rather than vegetation cover, affected N leaching. It is hypothesized that soil microbes were reducing N removal under these conditions. We reason that nitrifiers may have played an important role in soil N cycling, as increased soil ammonium had a strong positive effect on nitrate leaching loads, mediated through soil nitrate stores. Whereas, N immobilization, via incorporation into microbial biomass, and denitrification processes appeared to be limited by C availability, with increased C associated with reduced N leaching. Overall, this study identified that N leaching losses from riparian zones appeared to be affected by two different processes, vegetative uptake and soil microbial processes, the relative importance of which was driven by hydrological conditions.

The aim of this study was to systemically evaluate how feedstock characteristics and temperature influence biochar evolution during pyrolysis and to establish their relationships with biochar potential for soil amendments. We produced four biochar thermosequences from oak, pine, sugarcane and peanut shell at twelve temperatures (350–900 °C), and characterised them by yield, proximate analysis, elemental analysis, pH, electrical conductivity (EC) and carbon (C) functional groups using FTIR and solid-state 13C CPMAS NMR spectroscopy, along with principal component and cluster analyses. The results showed that not all biochar properties changed consistently with increasing pyrolysis temperature during slow pyrolysis. The significant increase in biochar pH with increasing pyrolysis temperature, was only observed between 350 and 500 °C (p

Denitrification is one of the most important processes in the nitrogen (N) cycle due to its permanently removing excess N from ecosystems into the atmosphere. In practice, revegetation has employed to facilitate the process for preventing nitrogen from terrestrial into aquatic ecosystems, in particular in the terrestrial-aquatic ecotone (i.e., riparian zone). However, how revegetation drives the shift in the denitrifying bacterial community and consequently alters denitrification is still unclear. In this study, we investigated soil denitrifiers in three vegetation types with respective dominant species of trees, shrubs and herbs in the water-level-fluctuate-zone in the Three Gorges Reservoir, China. We hypothesized that revegetation affected the composition of denitrifiers. Results revealed that the functional gene composition in herb samples was well separated from that in tree samples, which was dependent on the interactions between plant traits (i.e., species number and diversity, root C:N ratio) and environmental factors (i.e., soil temperature and pH). Herb soils has more abundance of nirS and nirK genes and nirS gene diversity due to their higher species number, soil pH, soil organic C, TN, soil C:N ratio and root C:N ratio compared with the shrub and tree soils. Vegetation types did not significantly affect soil denitrification rate, which could be largely explained by the combined effects of plant attributes (species number, root organic C and root N), and soil pH. Our results have demonstrated that herb plantations could increase the abundance of soil denitrifiers through altering both the quantity and quality of SOC and soil pH.

A 49 week soil incubation study employing 15 recycled organic (RO) wastes was conducted to investigate relations (through Kendall correlation analysis) between plant available nitrogen (PAN) supply and soil recalcitrant carbon (C) parameters with those of the RO waste chemical properties as determined by wet chemistry and spectroscopic methods. The hot water extractable organic C to hot water extractable nitrogen (N) ratio (HWOC:HWN ratio) was often the highest correlating property for mineral N supply (mg mineral N kg dry waste − 1 ), while many of the 13 C NMR functional group parameters such as the aromatic C to N ratio, phenyl C to N ratio, and aryl C to carbonyl C ratio were also significantly correlated with mineral N supply. These functional group C properties were significantly correlated with mineral N release in the later phase of the incubation (i.e. 12–49 weeks), while HWOC:HWN ratio was highly correlated with the early period (0–2 weeks) but this period had a dominant influence on the total supply. The fore mentioned 13 C NMR functional group properties were also significantly correlated with recalcitrant C, but the fraction of total RO waste C as aromatic C (110–165 ppm) was the parameter most highly correlated with this property. Molecular C component composition had no predictive advantage over functional group data. Future work should focus on narrow classes of organic amendments for predictive correlations.

The rapid increase in municipal sewage sludge production due to quick urbanization and economic development raised significant socio-economic and environmental issues in recent years. Although the increase in heavy metals' (HMs) immobilization through pyrolysis and hydrothermal carbonization (HTC) of municipal sewage sludge are reported in previous investigations, but there is still limited information available regarding the potential environmental risks associated with these processes. This study investigated the chemical speciation, bioavailability and eco-toxicity of HMs (Zn, Cu, Ni and Pb) in biochars (pyrolysis temperatures of 450 °C and 600 °C) and hydrochars (HTC temperature of 180 °C) produced from two sludge feedstocks (sludge cake and stabilized sewage sludge). The HTC generally resulted in higher char yield compared to pyrolysis process. The raw sewage samples showed a flat morphological surface texture, while HTC process increased the porosity and surface area of produced hydrochars. The pyrolysis process also increased the porous structures and surface morphology of biochars, with higher porosity in biochars produced at 600 °C. The pH value of hydrochars was significantly (P Cu > Pb > Ni, and with thermochemical processes the concentration of HMs increased in biochar and hydrochar products. The enrichment of HMs in all biochars was significantly (P

Bauxite residue sand (BRS) is the primary growth medium for rehabilitating Alcoa’s residue storage areas in south-west Western Australia. Successful revegetation of highly alkaline BRS can be hindered by its low nitrogen (N) use efficiency. Biochar, a carbon (C)-rich material, has been suggested to have the potential to improve water and nutrient retention in soil. However, little is still known about the effect of biochar amendment on N use efficiency in the alkaline BRS environment. This incubation study aimed to evaluate the impact of biochars with different characteristics on N retention and dynamics in BRS. The BRS (pH 9.5 after being pre-treated with 1% gypsum and leached with water) was amended with the acidic biochar (pH 3.86; AC, from wild fire) and alkaline biochars (pH 9.58–10.8; greenwaste, GW; Jarrah, JL; mallee, ML) at a rate of 10% (w/w). The N loss via NH 3 volatilization was much lower from the AC treatment (24% of di-ammonia phosphate (DAP)-N added) than the alkaline biochars treatments (76–80% of the DAP-N added). The AC treatment can retain about 73% of N added to BRS, compared with 4 + -N sorption capacity arising from the presence of a high density of the oxygen-containing functional groups on the surface of acidic biochar as revealed by the FTIR spectroscopy. These results imply acidic biochar can be used as an effective amendment for increasing N use efficiency by plants growing in alkaline BRS.

Char as a carbon-rich material, can be produced under pyrolytic conditions, wildfires or prescribed burn offs for fire management. The objective of this study was to elucidate mechanistic interactions of copper (Cu2+) and nickel (Ni2+) with different chars produced by pyrolysis (green waste, GW; blue-Mallee, BM) and forest fires (fresh-burnt by prescribed fire, FC; aged char produced by wild fire, AC). The pyrolytic chars were more effective sorbents of Cu2+ (∼11 times) and Ni2+ (∼5 times) compared with the forest fire chars. Both cross-polarization (CPMAS-NMR) and Bloch decay (BDMAS-NMR) 13C NMR spectroscopies showed that forest fire chars have higher woody components (aromatic functional groups) and lower polar groups (e.g. O-alkyl C) compared with the pyrolytic chars. The polarity index was greater in the pyrolytic chars (0.99–1.34) than in the fire-generated chars (0.98–1.15), while aromaticity was lower in the former than in the latter. Fourier transform infrared (FTIR) and Raman spectroscopies indicated the binding of carbonate and phosphate with both Cu2+ and Ni2+ in all chars, but with a greater extent in pyrolytic than forest fire-generated chars. These findings have demonstrated the key role of char's oxygen-containing functional groups in determining their sorption capacity for the Cu2+ and Ni2+ in contaminated lands.

Prescribed burning has been widely used in the management of forests for reducing wildfire risk, and can have significant effects on soil carbon (C) and nitrogen (N) pools and their temporal changes. This study aimed to investigate the impacts of different burning frequency regimes on the temporal dynamics of C and N in the topsoil and forest floors. The experimental site was a 39 year old wet scherophyll forest prescribed burning trial at Peachester, southeast Queensland, Australia, with treatments of no burning (NB) since 1969, 2 yearly burning (2yrB) and 4 yearly burning (4yrB) since 1972. Each of three burning treatments had four replications and these plots were randomly distributed over an area of the forest with similar vegetation and soil characteristics. Soil (0–10 cm) and forest floors were sampled monthly for 6 months prior to the next scheduled burning for both burning treatments to minimize the effects of fire recency. Prescribed burning significantly (P < 0.01) affected most C and N variables in both soils and forest floors. The 2yrB treatment had significantly lower (P < 0.01) soil total C, total C:N ratio, microbial biomass C (MBC) and N (MBN), MBC:MBN ratio, dissolved organic C (DOC) and N (DON), NO3−-N, inorganic N and L layer total N, DON and NO3−-N, compared with the NB and 4yrB treatments. However, there were no overall significant differences in these variables between the NB and 4yrB treatments. Sampling month significantly (P < 0.01) affected C and N variable in both soils and forest floors except for soil total C and N and F layer MBC. Temporal dynamics of most of these labile C and N variables were highly related to soil and forest floor moisture content, seven day mean air temperature (MAT) and cumulative rainfall prior to sampling date. However, fire effects were independent of sampling month, as there were no significant interactions between them for most response variables measured. This study has clearly demonstrated that more frequent burning (2 yr burning) had negative impact on soil and forest floor C and nutrient pools. Insignificant differences observed in soil C and N and forest floor N pools between less frequent burning (4yrB) and NB treatments highlighted that the prescribed burning at four year interval gave sufficient time for recovery of these soil and forest floor nutrients to pre-burn levels.

The magnitudes of nitrogen (N) mineralisation and nitrous oxide (N2O) emissions after the application of plant materials strongly depend on their quality. Despite the existence of some studies in this field, little is known about the underlying mechanisms and regulating factors of these processes, particularly for vegetable cropping systems. In this study, ten typical vegetable and/or vegetable farming rotation plant materials were finely ground, incorporated into the soil and incubated at 25 °C under fluctuating moisture conditions of 55–85% water-filled pore space (WFPS) without N (-N) or with N (+N) addition (100 mg N kg−1 soil as urea). The applied plant materials were characterised using solid state 13C nuclear magnetic resonance (NMR) spectroscopy and wet-chemical analysis. The dynamics of soil mineral N accumulation and N2O emissions were monitored over 169 days. Under the -N treatment, plant materials with total N (TN) contents ≥ 27 mg g−1 dry matter produced significantly higher cumulative N2O emissions than those with TN contents

In this study, the amounts of phosphorus (P) in nine types of biochar (one natural woody biochar and eight manufactured plant derived biochars) extractable by deionized water, 0.5 N NaHCO 3 (pH = 8.5) and 0.5 N H 2 SO 4 , respectively, and P adsorption on single biochar or soil/biochar mixtures were examined to investigate the potential effect and role of biochar in improving P availability in soils. Results indicated that biochars were able to bring available P into soils, but the amount and form of available P was dependent on biochar types. The results from P adsorption experiments (in phosphate solutions of 100 and 200 mg P L − 1 , respectively) revealed that not all the biochars showed favourable P retention abilities and the amount of P retained by each biochar varied with the P concentration in the solution used. Among the nine biochars studied, only biochar derived from Mallee ( Eucalyptus polybractea ) at 720 °C with a solid residence time of 20 min showed a high P retention ability. Soils amended with Mallee biochar (5% w/w) showed an increase in the P retention ability by 16% after treatment with 200 mg P L − 1 phosphate solution. 55% of the retained P on Mallee biochar was still available for plant uptake. Results from the kinetic study of P adsorption on Mallee biochar indicated that there were two stages in P adsorption on Mallee biochar, a rapid chemisorption stage followed by a surface-diffusion-controlled stage when the surface adsorption sites were saturated. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and attenuated total reflectance-Fourier transform infrared spectroscopy revealed that calcium carbonate was mainly responsible for P chemisorption on Mallee biochar.

Application of organic amendments (OAs), nutrients and gypsum to sodic subsoils is of great interest to improve soil functionality and crop yield. However, controversy remains about the impact of the priming effect (PE) on native soil organic carbon (SOC), and the mechanisms governing the dynamics of the PE by OAs (with variations in nutrient stoichiometry). To address these gaps in knowledge, this nine-month study applied C4-plant-derived OAs in a C3-plant-derived soil at 6.2 g C kg−1 soil, with and without the exogenous supply of nutrients (nitrogen and/or phosphorus) or gypsum. Across the treatments, the cumulative PE was between 135 and 475 mg CO2–C kg−1 soil over the nine months, equivalent to 2.3–8.2% of native SOC loss. In the first two months, the positive PE by the OAs could be attributed to co-metabolism and nitrogen (N) mining. These theories were supported by (i) the enhanced growth of microbial biomass associated with increased soil labile C (such as dissolved organic C); and (ii) the decreased soil mineral N availability, likely via microbial N immobilization, particularly with the inputs of sorghum stubble or sugarcane bagasse. Towards the end of the incubation, the relative PE (i.e., PE ÷ SOC mineralization in the control soil) was higher in the OA treatments (sorghum stubble and sugarcane bagasse) where nutrients were added to lower the C: nutrient stoichiometric ratios. These results support the theory of microbial stoichiometric decomposition of SOC, which may have become the dominant mechanism of PE over time. The application of gypsum, together with OAs (sorghum stubble or sugarcane bagasse), did not significantly change the magnitude or direction of the PE. In conclusion, the significant native SOC losses and N immobilization induced by the OAs, particularly where we balanced the nutrient stoichiometric ratios, indicate the vulnerability of subsoil SOC, and hence the potential of C sequestration in a sodic subsoil following the application of OAs may be limited.

The operation of the Three Gorges Reservoir (TGR), the largest hydropower dam in the world, has triggered a dramatic shift in the flooding regimes of sites upstream of the reservoir. Little is known about how disrupted flooding regimes and consequent management approaches might affect the ecological and biogeochemical characteristics of riparian ecosystems. In this study, we evaluated the effects of disruptions to natural flooding regime on basic soil properties, soil nutrient and heavy metal levels, and key characteristics of riparian plant and soil microbial communities. To do this, we used an elevational gradient that encompassed four flooding duration zones (0 (i.e., control), 169, 237, 286 days of flooding per year on average). The disrupted flooding regimes were associated with levels of soil total N and P that were on average 17% and 24% lower, respectively, than those in the non-flooded areas. On the other hand, the concentrations of heavy metals (Hg, Pb, Cu, Zn and Mn) were higher in flood-affected areas than in the non-flooded areas. Increased flooding frequency was also associated with lower plant diversity and species richness relative to non-flooded areas. Thus, disruption of the natural flooding regime had strong and often negative consequences for the ecological and biogeochemical properties of the riparian ecosystems in our study. There was some evidence that riparian plant communities were able to partially recover from prior flooding during a single growing season, even after nine years of repeated flooding, and these recovery trajectories were associated with shifts in soil chemical properties during the same period. However, revegetation efforts had few effects on ecosystem properties or their recovery trajectories following flooding events, suggesting that natural regeneration could be a useful option for the management of these sites. We conclude that the unnatural flooding regimes associated with large scale reservoir development are likely to have profound impacts on the structure and functioning of riparian ecosystems, and these will pose a considerable challenge for environmental management and biodiversity conservation.

Prescribed fire is one of the most widely-used management tools for reducing fuel loads in managed forests. However the long-term effects of repeated prescribed fires on soil carbon (C) and nitrogen (N) pools are poorly understood. This study aimed to investigate how different fire frequency regimes influence C and N pools in the surface soils (0-10 cm). A prescribed fire field experiment in a wet sclerophyll forest established in 1972 in southeast Queensland was used in this study. The fire frequency regimes included long unburnt (NB), burnt every 2 years (2yrB) and burnt every 4 years (4yrB), with four replications. Compared with the NB treatment, the 2yrB treatment lowered soil total C by 44%, total N by 54%, HCl hydrolysable C and N by 48% and 59%, KMnO4 oxidizable C by 81%, microbial biomass C and N by 42% and 33%, cumulative CO2-C by 28%, NaOCl-non-oxidizable C and N by 41% and 51%, and charcoal-C by 17%, respectively. The 4yrB and NB treatments showed no significant differences for these soil C and N pools. All soil labile, biologically active and recalcitrant and total C and N pools were correlated positively with each other and with soil moisture content, but negatively correlated with soil pH. The C:N ratios of different C and N pools were greater in the burned treatments than in the NB treatments. This study has highlighted that the prescribed burning at four year interval is a more sustainable management practice for this subtropical forest ecosystem.

The amounts and forms of soil phosphorus (P) follow predictable patterns during long-term pedogenesis, but have rarely been examined along subtropical chronosequences. We quantified changes in soil nutrient stocks, foliar nutrient concentrations, and the chemical forms of soil P along the Cooloola chronosequence, a series of coastal dunes spanning ca. 500,000 years of pedogenesis in subtropical Queensland. The total P stock in the upper 30 cm of the soil profile declined continuously with soil age, from 229–237 kg ha − 1 on the youngest soils (40 years old) to 24–28 kg ha − 1 on the oldest soils (195–> 460 ka). In contrast, total carbon (C) and nitrogen (N) stocks increased initially along the chronosequence and then declined in the oldest soils. As a consequence, soil N:P ratios increased continually throughout the sequence, from ≤ 4 on the youngest soils to 27–30 on the oldest soils. This indication of increasing biological P stress and ultimately P limitation was further supported by a decline in foliar P concentrations and increasing foliar N:P ratios of two common plant genera along the chronosequence. Sequential P fractionation revealed that although all forms of P declined during pedogenesis, young soils contained low concentrations of primary mineral P and relatively high concentrations of occluded P associated with secondary minerals, suggesting that the parent sand originated from strongly-weathered continental soils. We conclude that the Cooloola chronosequence is an important example of long-term ecosystem development under a subtropical climate, although the pre-weathered nature of the parent sand indicates that the sequence represents a modification of the Walker and Syers model of P transformations during pedogenesis.

Stoichiometric ratios of leaf nitrogen (N) to phosphorus (P) have been used as a tool to characterize ecological problems and ecosystem productivity. This study used leaf N:P stoichiometry to assess nutrient limitation and productivity in alkaline bauxite-processing residue sand (BRS) vegetated with Lolium rigidum. Fresh BRS [amended with either greenwaste compost (BRSgc) or biochar (BRSbc)], and aged BRS [e.g. 5, 7, and 15 years under established rehabilitation (5, 7, and 15YrBRS)] were grown with L. rigidum for 3 months in a controlled environment. Leaf N:P ratios were positively correlated with the pH of growth media [freshly amended BRS (r = 0.66, P 5YrBRS (20.9) > 7YrBRS (19.0) > 15YrBRS (17.2)]. This suggests that when rehabilitated BRS becomes older, the leaf N:P ratio will shift towards the ratio of the reference sample (i.e. L. rigidum with adequate levels of N and P), demonstrating an improved plant N and P uptake in aged BRS-plant systems. Results highlight that leaf N:P ratios can effectively reflect N and P limitations to productivity in vegetated alkaline BRS, which can be a critical ecological indicator in such environment. These results however, have to be verified with other species (e.g. native shrubs and trees) used for plant establishment of alkaline BRS before using this indicator for assessing ecological rehabilitation performance.

The emission of nitrous oxide (N 2 O) from vegetable fields contributes to the global greenhouse gases budget. However, reliable estimation of N 2 O emissions from vegetable production in the word has been lack. Vegetable cropping systems are characterised with high N application rates, irrigation, intensive production and multiple planting-harvest cycles during the year. Improved understanding of the key factors controlling N 2 O production is critical for developing effective mitigation strategies for vegetable cropping systems under different climate, soil type and management practices. Based on a comprehensive literature review and data analysis, we estimated the global N 2 O emission from vegetable production using seasonal fertiliser-induced emission factors (EFs) and examined the relationship of the seasonal emissions and EFs to possible controlling factors. The global average seasonal EF for vegetable fields is around 0.94% of applied N fertiliser, which is very similar to the Intergovernmental Panel on Climate Change (IPCC) annual emission factor of 1.0% for all cropping systems. The total N 2 O emission from global vegetable production is estimated to be 9.5 × 10 7 kg N 2 O–N yr −1 , accounting for 9.0% of the total N 2 O emissions from synthetic fertilisers. Stepwise multiple regression analysis on the relationships of soil properties, climatic factors and N application rates to seasonal N 2 O emissions and N 2 O EFs showed that N fertiliser application rate is the main regulator of seasonal N 2 O emission from vegetable fields but the seasonal EFs are negatively related to soil organic carbon (SOC) content. In fields receiving ≥250 kg ha −1 N fertiliser, 67% (n = 23, P ≤ 0.01) of the variation in seasonal emissions can be explained by the combined effects of N application rate, mean water-filled pore space (WFPS) and air temperature, while 59% (n = 23, P ≤ 0.01) of the variation in seasonal EFs relates to temperature, mean WFPS and soil pH. The result also shows that in vegetable fields with mean seasonal air temperature higher than 14 °C, increases in SOC decrease the seasonal EF and total N 2 O emissions from fertiliser N.

Ecological restoration of bauxite residue storage areas is a great challenge due to the inherently hostile characteristics (high alkalinity, high salinity and poor nutrient availability). Nitrogen (N) availability and microbial functionality are crucial indicators for successfully restoring ecosystem functions of bauxite residue storage areas. This study examined the pathway and dynamics of 15 N-labeled fertilizer [e.g., ammonium sulphate (AS), potassium nitrate (KN), glycine (GL)] and the role of ammonia oxidizing archaea (AOA) and bacteria (AOB) in bauxite residue sand (BRS) amended with greenwaste compost (BRSGC) and without organic amendment (BRSNA) grown with Hardenbergia violacea and Lolium rigidum . 15 N losses via volatilization and leaching from applied 15 N fertilizer were higher in AS (49–50%) and GL (42–47%) compared to KN (38–44%) treatment under BRSNA. 15 N losses via these pathways however, were significantly ( P 15 N recovered in BRSGC (34–57%) was significantly higher compared with BRSNA ( 15 N fertilizers by plants was consistently higher in BRSNA for both plants (KN > AS > GL) compared with BRSGC, suggesting an increased sorption or immobilization of applied 15 N by greenwaste compost. Significant relationships observed between the AOB abundance under AS and GL treated BRS and 15 N uptake by plants and extractable 15 NO 3 –N indicated that AOB plays a significant role in the transformation of 15 N and uptake by plants. These results have important implications for developing improved nutrient management strategies and ecological rehabilitation prescriptions in alkaline BRS storage areas.

To examine the potential impact of plant species richness on ecosystems, we studied non-additive effects of different plant litters on the biodegradation rate of dissolved organic matter (DOM) when mixing plant leaf-derived DOM derived from different plant species. A full factorial biodegradation experiment (31 possible singular and multiple combinations of five litter type-derived DOM sources) was conducted using plant litters from the five most abundant plant species in a subtropical watershed ecosystem, from which dissolved organic carbon (DOC) disappearance was measured. Loss of DOC over time was considered biodegradable DOC. We tested whether DOM diversity, measured as source species richness and composition, would affect biodegradation rates. Overall, we found significant non-additive (synergistic) effects of DOM diversity on biodegradation rates of DOM, which were explained both by plant species richness and composition. Across all treatments, a significantly higher biodegradation rate was correlated with the presence of DOM from higher nitrogen (N) containing plant litters; conversely, the presence of lower N decreased these rates. The N content and chemical characteristic of DOM might influence the magnitude of the synergistic effect. Our results suggest that loss of plant litter species diversity would not affect DOC biodegradation rate, provided that at least two species are conserved. However, the variability in DOC biodegradation rate across the treatments decreased with increased DOM diversity at three incubation time points. Our results also indicate that in an ecosystem with low plant biodiversity, loss of key species such as Lophostemon confertus could reduce the synergistic effects on DOC biodegradation rate.

Integrated rice-shrimp ponds (IRSPs) are common in areas of Southeast Asia where saltwater intrudes into rice fields in the dry season, enabling rice production in the wet season, and shrimp farming in the dry season or throughout the year. Previous research has highlighted that IRSPs have periods of low dissolved oxygen concentrations which may have a critical effect on shrimp survival. To understand the causes of low dissolved oxygen, this study examined oxygen fluxes at two IRSPs in Ca Mau Province, Vietnam during a two-year period (two wet seasons and two dry seasons). Sediment oxygen demand (SOD) incubations and whole-system oxygen flux measurements were conducted and compared with a range of water and sediment parameters to explain drivers for low oxygen concentrations. A high percentage of oxygen demand at a whole pond scale was from the sediment; hence SOD drove low oxygen concentrations in the water column. SOD rates were significantly positively correlated with chlorophyll a concentrations in the water column. These findings suggested that algal production in the water column, rather than benthic algal production, or other organic loading, provided an organic carbon source driving SOD. Oxygen demand was much higher than oxygen production within the IRSPs, indicating high bacterial activity and low algal production. This study has shed new light on the importance of SOD in driving oxygen drawdown in IRSPs and improving shrimp survival requires new management approaches to reduce the negative effect of SOD.

Using solid state 13C NMR data and elemental composition in a molecular mixing model, we estimated the molecular components of the organic matter in 16 recycled organic (RO) wastes representative of the major materials generated in the Sydney basin area. Close correspondence was found between the measured NMR signal intensities and those predicted by the model for all RO wastes except for poultry manure char. Molecular nature of the organic matter differed widely between the RO wastes. As a proportion of organic C, carbohydrate C ranged from 0.07 to 0.63, protein C from

Few studies have examined the long-term responses of soil labile organic carbon (C) and nitrogen (N) and microbial activities to climate change in semiarid and arid regions. Here we investigated soil extractable organic carbon (EOC) and nitrogen (EON), microbial biomass and microbial metabolic activities at two depths of 0–10 and 10–20 cm in response to single and combined effects of warming and increased precipitation in a semiarid grassland of northern China since April 2005. Soil EOC and EON pools were measured using KCl and hot water extractions, and microbial metabolic activities were measured using MicroResp. Results showed that warming had no effects on EOC, EON and microbial biomass C (MBC) and N (MBN) in the two extracts as well as the ratio of MBC to MBN at the two depths, but increased precipitation significantly increased MBC, MBN, EON and microbial quotient at the 0–10 cm depth. Warming significantly decreased microbial metabolic activities at both soil depths, but significantly increased microbial metabolic diversity (H) and evenness (E) at the 10–20 cm depth. Increased precipitation significantly decreased microbial metabolic activities, but significantly increased H and E at the two depths. Warming and increased precipitation significantly interacted to affect microbial metabolic activities at the two depths as well as H and E at the 10–20 cm depth. Redundancy analysis determined that microbial quotient, i.e., the ratio of MBC to total C, pH and NH 4 + –N greatly accounted for the variances in the soil microbial metabolic profiles, but the ratio of EOC to EON, moisture and microbial quotient largely accounted for the variances in the soil microbial metabolic profiles specifically at the 10–20 cm depth, implying that microbial physiology such as microbial quotient rather than the amounts of labile organic C and N pools exerted more influence on driving the patterns of microbial metabolic profiles. Our results indicated that soil EOC and EON, microbial biomass and microbial metabolic activities at the two depths differentially responded to warming and increased precipitation in this semiarid region.

Understanding nutrient dynamics in non-typical soil materials such as bauxite-processing residue sand (pH > 10; EC > 30 dS m −1 ) is critical for developing fertilizer strategies and evaluating ecological restoration performance. Indices relating nitrogen (N) concentration in soil to plant N uptake are well-established for natural soils but their application to non-typical soils has received little attention. This study investigated a range of soil-based methods [i.e. 2 M KCl extractable inorganic N (NH 4 + , NO 3 − ), potentially mineralizable nitrogen (PMN), and 0.01 M CaCl 2 extractable N] to identify their suitability for describing soil–plant N relations in highly alkaline bauxite-processing residue sand. Nitrogen availability indices were measured under laboratory (pot trial) and field conditions. Pot trial was established using residue sand that had been amended (10%, v/v, basis) with various organic (greenwaste compost, biochar and biosolids) and inorganic (zeolite) materials. Both the field study and pot trial showed that 2 M KCl extractable NO 3 − -N was most highly correlated with plant biomass N compared with the other N availability indices. Findings from this study suggest that 2 M KCl extractable NO 3 − -N can be used as a soil quality indicator in developing fertilizer management strategies and assessing ecological status of the residue storage areas.

Production of nitrous oxide (N2O) by anaerobic denitrification is one of the most important processes in the global nitrogen (N) cycle and has attracted recent attention due to its significant impacts on climatic change. Fire is a key driver of many ecosystem processes, however, how fire drives the shift in microbial community and thus alters nutrient cycling is still unclear. In this study, a 35-year-old repeated prescribed burning trial, with three treatments (no burning, 2 yearly burning and 4 yearly burning), was used to explore how the long-term repeated prescribed burning affects N2O flux, key soil properties (inorganic N, dissolved organic carbon (DOC) and N, pH, electrical conductivity (EC), moisture), denitrification gene abundance and their interactions. Soil samples were collected in January and April 2011. Quantitative real-time PCR was employed to quantify the gene copy number of target genes, including narG, nirK, nirS and nosZ. In situ N2O fluxes ranged from 0 to 8.8 g N2O–N ha−1 h−1 with an average of 1.47 g N2O–N ha−1 h−1. More frequent fire (2 yearly burning) significantly reduced soil N2O fluxes, availability of C and N substrates and moisture, but increased soil pH and EC compared with no burning and 4 yearly burning treatments. Fire treatments did not significantly affect the abundance of most denitrification genes. There were no significant differences in most parameters measured between the 4 yearly burning and no burning treatments, indicating microbial community function is not affected by less frequent (4 year interval) burning. Variation in the N2O fluxes among the treatments can largely be explained by soil substrate ( NO 3 − , DOC and total soluble nitrogen (TSN)) availability and soil environmental factors (pH, EC, and moisture), while the abundance of most denitrification genes were not related to the N2O fluxes. It is concluded that soil environmental factors rather than denitrification gene abundance control N2O fluxes in this wet sclerophyll forest in response to long-term repeated fires.

Few studies have conducted the responses of soil extracellular enzyme activities (EEA) to climate change, especially over the long term. In this study, we investigated the six-year responses of soil EEA to warming and increased precipitation in a temperate grassland of northern China at two depths of 0-10 and 10-20 cm. These extracellular enzymes included carbon-acquisition enzymes (β-glucosidase, BG), nitrogen-acquisition enzymes (N-acetylglucosaminidase, NAG; Leucine aminopeptidase, LAP) and phosphorus-acquisition enzymes (acid and alkaline phosphatases). The results showed that warming significantly increased acid phosphatase at the 0-10 cm depth and NAG at the 10-20 cm depth, but dramatically decreased BG and acid phosphatase in the subsurface. In contrast, increased precipitation significantly increased NAG, LAP and alkaline phosphatase in the surface and NAG, LAP and acid phosphatase in the subsurface. There was a significant warming and increased precipitation interaction on BG in the subsurface. Redundancy analysis indicated that the patterns of EEA were mainly driven by soil pH and NH(4)(+)-N and NO(3)(-)-N in the surface, while by NH(4)(+)-N and microbial biomass in the subsurface. Our results suggested that soil EEA responded differentially to warming and increased precipitation at two depths in this region, which may have implications for carbon and nutrient cycling under climate change.

Weed control is a key factor affecting early plant growth and establishment in revegetation projects in South-east Queensland of sub-tropical Australia. Costs associated with weed control are significant and methods which reduce establishment costs and effectively suppress weeds are of great interest. However, different methods may have implications for soil quality and fertility and require a detailed investigation. Understanding the response of soil organic matter (SOM) and microbial functional diversity to different weed control methods is crucial as they affect soil quality and nutrient availability. A field trial was established in South-east Queensland to identify the effects of three methods of weed control: (1) glyphosate, (2) a mixture of glyphosate and MCPA and (3) topsoil removal or scalping on SOM, microbial biomass, soil respiration, NH4+-N availability, potentially mineralisable N (PMN) and soil microbial community functional diversity (as assessed by carbon substrate utilisation using Biolog GN2 plates). The scalped area had lower SOM and microbial activity compared to the herbicide and control plots. There was no significant difference in water soluble organic carbon (WSOC), hot water extractable organic C (HWEOC), hot water extractable total N (HWETN) and microbial biomass C and N (MBC and MBN) between the herbicide and control plots, particularly at week 20. NH4+-N and PMN values were lower at week 20 than week 1 in the herbicide and scalping treatments. Week 20 was the end of the growing season and reduction in N availability may have been the result of decreasing temperature. Principal component analyses (PCA) from Biolog GN2 results indicated a separation in soil microbial community function in the scalped area compared to the other treatments which may have implications for soil properties in the long term. Scalping proved to be the most cost-effective method of site preparation, requiring fewer site visits for weed control compared to herbicide application. However, SOM was significantly affected by scalping due to topsoil removal and it may not be a sustainable practice in short rotation plantation establishment. Single herbicide application at field rates did not impact soil organisms but also failed to achieve proper weed control.

Ammonia-oxidizing bacteria (AOB) and archaea (AOA) are considered as the key drivers of global nitrogen (N) biogeochemical cycling. Responses of the associated microorganisms to global changes remain unclear. This study was to determine if there was a shift in soil AOB and AOA abundances and community structures under free-air carbon dioxide (CO₂) enrichment (FACE) and N fertilization in Duke Forest of North Carolina, by using DNA-based molecular techniques, i.e., quantitative PCR, restriction fragment length polymorphism (RFLP) and clone library. The N fertilization alone increased the abundance of bacterial amoA gene, but this effect was not observed under elevated CO₂ condition. There was no significant effect of the N fertilization on the thaumarchaeal amoA gene abundance in the ambient CO₂ treatments, while such effect increased significantly under elevated CO₂. A total of 690 positive clones for AOA and 607 for AOB were selected for RFLP analysis. Analysis of molecular variance (AMOVA) indicated that effects of CO₂ enrichment and N fertilization on the community structure of AOA and AOB were not significant. Canonical correspondence analysis also showed that soil pH rather than elevated CO₂ or N fertilization shaped the distribution of AOB and AOA genotypes. A negative linear relationship between the δ¹³C and archaeal amoA gene abundance indicated a positive effect of elevated CO₂ on the growth ammonia oxidizing archaea. On the other hand, the community structures of AOB and AOA are determined by the soil niche properties rather than elevated CO₂ and N fertilization.

The conservation farming systems coupled with stubble retention are now widely adopted in southern Australia to improve soil fertility. However, little information is available about the effects of winter crops on soil labile organic carbon (C) and nitrogen (N) pools, especially in an arid agricultural ecosystem. In this study, eight winter cover crop treatments were used to investigate their effects on soil labile organic C and N pools and microbial metabolic profiles and diversity in temperate Australia. These treatments included two legume crops (capello woolly pod vetch and field pea), four non-legume crops (rye, wheat, Saia oat and Indian mustard), and a mixture of rye and capello woolly pod vetch as well as a nil-crop control. At the crop flowering stage, soil and crop samples were collected from the field and we examined aboveground crop biomass, soil NH4+-N, NO3−-N, extractable organic C (EOC) and N (EON) concentrations using methods of 2 M KCl and hot water, microbial biomass, biologically active organic C (CBio), and substrate-induced respiration (SIR) using the MicroResp method. Results showed that the crop treatments had lower soil moisture content, NO3−-N and the ratios of EOC to EON, but higher pH, NH4+-N, EOC, EON, CBio, microbial metabolic diversity index (H) and evenness index compared with the control. There were no significant differences in microbial biomass C and N among the treatments. Although no pronounced differences in EOC and EON concentrations were found between the legumes and non-legumes, the legume treatments had lower SIR and higher H than the non-legume treatments. Principal component analysis showed that soil microbial metabolic profiles under the crops were different from those of the control, and the crop treatments had a clear separation along principal component 2. In addition, redundancy analysis showed that soil pH and moisture content were the most important influencing factors, along with EON and crop biomass, determining the patterns of microbial metabolic profiles under the crops.

Tree species have significant effects on the availability and dynamics of soil organic matter. In the present study, the pool sizes of soil dissolved organic matter (DOM), potential mineralizable N (PMN) and bioavailable carbon (C) (measured as cumulative CO2 evolution over 63 days) were compared in soils under three coniferous species - 73 year old slash (Pinus elliottii), hoop (Araucaria cunninghamii) and kauri (Agathis robusta) pines. Results have shown that dissolved organic N (DON) in hot water extracts was 1.5-1.7 times lower in soils under slash pine than under hoop and kauri pines, while soil dissolved organic C (DOC) in hot water extracts tended to be higher under slash pine than hoop and kauri pines but this was not statistically significant. This has led to the higher DOC:DON ratio in soils under slash pine (32) than under hoop and kauri pines (17). Soil DOC and DON in 2 M KCl extracts were not significantly different among the three tree species. The DOC:DON ratio (hot water extracts) was positively and significantly correlated with soil C:N (R2=0.886, Pb0.01) and surface litter C:N ratios (R2=0.768, Pb0.01), indicating that DOM was mainly derived from litter materials and soil organic matter through dissolution and decomposition. Soil pH was lower under slash pine (4.5) than under hoop (6.0) and kauri (6.2) pines, and negatively correlated with soil total C, C:N ratio, DOC and DOC:DON ratio (hot water extracts), indicating the soil acidity under slash pine favored the accumulation of soil C. Moreover, the amounts of dissolved inorganic N, PMN and bio-available C were also significantly lower in soils under slash pine than under hoop and kauri pines. It is concluded that changes in the quantity and quality of surface litters and soil pH induced by different tree species largely determined the size and quality of soil DOM, and plantations of hoop and kauri pine trees may be better in maintaining long-term soil N fertility than slash pine plantations.

We can use soil mapping to gain a better understanding of the soil and how it varies in the landscape. Good quality data sets that represent the survey area are important to develop quantitative spatial models for soil mapping and to evaluate their outputs. Over the past three decades, scientists have become interested in rapid, non-destructive measurements of the soil using visible–near infrared (vis–NIR) (400–2500 nm) and mid infrared (mid-IR) (2500–25,000 nm) diffuse reflectance spectra. These spectra provide an integrative technique that measures the fundamental characteristics and composition of the soil, including colour, iron oxide, clay and carbonate mineralogy, organic matter content and composition, the amount of water present and particle size. If adequately summarised and exhaustively available over large areas, this information might be useful in situations where reliable, quantitative soil information is needed, such as agricultural, environmental and ecological modelling, or for digital soil mapping. The aims of this paper are to summarise the information content of vis–NIR spectra of Australian soils and to use a predictive spatial modelling approach to digitally map this information across Australia on a 3-arc second grid (around 90 m). We measured the spectra of 4606 surface soil samples from across Australia using a vis–NIR spectrometer. The soil information content of the spectra was summarised using a principal component analysis (PCA). We used model trees to derive statistical relationships between the scores of the PCA and 31 predictors that were readily available and we thought might best represent the factors of soil formation (climate, organisms, relief, parent material, time and the soil itself). The models were validated and subsequently used to produce digital maps of the information content of the spectra, as summarised by the PCA, with estimates of prediction error at 3-arc seconds pixel resolution. The most frequently used predictors at the continental scale were factors related to climate, parent material (and time), while at landscape and more local scales, they were factors related to relief, organisms and the soil. Finally, we use our maps for pedologic interpretations of the distribution of soils in Australia. Our results might be useful in situations requiring high-resolution, quantitative soil information e.g. in agricultural, environmental and ecologic modelling and for soil mapping and classification.

Successful soil organic matter (SOM) quality assessment is needed to improve our ability to manage forest soils sustainably. Our objective was to use a multivariate data set to determine whether the land use conversion from native forest (NF) to hoop pine plantation and the following rotation and site preparation practices had altered SOM quality at three adjacent sites of NF, first (1R) and second rotation (2R, including tree planting row (2R–T) and windrow of harvest residues (2R–W)) of hoop pine plantations in southeast Queensland, Australia. Cross-polarization magic angle spinning 13C nuclear magnetic resonance (CPMAS 13C NMR) spectroscopy and sequential hot water and acid hydrolysis were conducted on SOM fractions separated by wet-sieving and density fractionation procedures to characterize SOM quantitative and qualitative relevant parameters, including carbon (C) functional groups, C and nitrogen (N) contents, C/N ratios, and C and N recalcitrant indices. Analysis of variance (ANOVA) and principal component analysis (PCA) of these multivariate parameters together indicated a complicated interaction between physical protection and biochemical recalcitrance, making the land use and management induced changes of SOM quality more complex. Knowledge of PCA based on the refined set of 41 SOM quantitative and qualitative parameters identified that principal component 1 (PC1), which explained 55.7% of the total variance, was most responsible for the management induced changes in soil processes. This was reflected by the dynamics of SOM regarding the aspects of total stock, soil basal and substrate induced respirations, gross and net N mineralization and nitrification, and microbial biomass, microbial diversity of C utilization patterns. Further, the macroaggregates (F250–2000 μm) and the C/N ratio of acid extracts of SOM physical fractions, which represented the most informative and unique variables loading on PC1, might be the most promising physical and chemical measures for SOM quality assessment of land use and management impacts in subtropical Australian forests.

Soil physical structure causes differential accessibility of soil organic matter (SOM), including carbon (C) and nitrogen (N) pools, to decomposer organisms and is an important determinant of SOM storage. Physical fractionation method of SOM in conjunction with elemental as well as isotopic analyses (C, N, delta C-13, delta N-15) of those soil fractions are used in this study to determine the land use and management-induced changes of SOM and associated processes in three adjacent sites of native forest (NF), first (1R) and second rotation (2R, including tree planting row (2R-T) and windrow of harvest residues (2R-W)) of hoop pine plantations in southeast Queensland, Australia. The results suggest that there is a greater accumulation of C and N in the light fraction (LF) of NF site than that of plantation sites (1R and 2R), and the C and N losses following conversion from mixed species NF to the single-species plantation are attributed to the reduction in C and N stocks for all physical fractions separated by wet sieving. In contrast, the C and N losses induced by the rotation practices (e.g., between 1R and 2R-T) are attributed to the C and N decreases in the LF and macroaggregates (250-2000 mu m) only. The C and N increases upon the residue management (e.g., between 2R-W and 2R-T) are primarily attributed to the C and N increases in the LF and macroaggregates as well. Coupled with 30 soil chemical and biological parameters obtained in our previous studies, further principal component and multivariable regression analyses were conducted and the results showed that both the LF and macroaggregates were highly related to the status of C and N pools, the processes of N transformation and soil respiration, and the diversity of microbial communities, and thus could serve as diagnostic SOM fractions responsible for the changes of soil properties and processes within the tested ecosystem induced by the land uses and management practices. Knowledge of the interactive relationships between aggregate classes within SOM and soil chemical and biological processes in this study represents a further step towards diagnostically measuring and understanding important soil C and N processes in response to the land use and management changes in the soil ecosystems such as forests in subtropical Australia. (C) 2008 Elsevier B.V. All rights reserved.

The aims of this study were to: (1) assess the effects of mulching on labile soil organic matter (SOM) pools (water-soluble organic matter, WSOM; hot water extractable organic matter, HWEOM; microbial biomass, MB; acid hydrolysable organic matter, AHOM), microbial community functional diversity and soil nitrogen (N) transformations and (2) quantify the relationships among labile SOM pools, soil N transformations and microbial community functional diversity. Soil (0–10 cm) was collected from two hardwood plantations in subtropical Australia to which plant residues (1.57 kg m −1 , C/N ratio of 80) had previously been applied as mulch for 12 months. Both in southeast Queensland, Australia, one plantation was located in dry area (Pechey, average annual rainfall 851 mm) and the other at Proston, drier by comparison (average annual rainfall 613 mm). At both locations, soil WSOM-carbon (C), HWEOM-C, MB-C, and AHOM-C were significantly higher in the mulch treatment than in the non-mulch treatment. The soil microbial community functional diversity (Shannon's diversity index, H ′) measured by BIOLOG GN2 micro-plates was significantly greater in the mulch treatment than in the non-mulch treatment. The mulch treatment had significantly higher soil gross N mineralization and gross N immobilization rates than the non-mulch treatment. However, there was no significant difference in soil gross nitrification between the two treatments. Stepwise multiple regressions revealed that HWEOM-C had significant correlation with soil microbial functional diversity and explained more of the variation in microbial functional diversity than any other labile SOM pools. The MB-N explained more of the variations in gross N transformations than other labile SOM pools.

Soils from a long term experiment, established in 1972, incorporating replicated treatments of burning every 2 and 4 years with control plots were sampled in 2005 to determine the changes in microbial community structure, measured using phospholipid fatty acids (PLFAs) and functional diversity measured using multiple substrate induced respiration (SIR) tests (MicroResp™). Microbial biomass (total PLFA) in the 2 year burn treatments was 50% less than both the control and 4-year burn treatments. There was also concomitantly less respiratory activity which mirrored the known changes in soil C and substrate quality. Contrary to other studies soil bacterial PLFAs were reduced as much as fungal PLFAs in the 2-year burn and the short term (6 h) SIR of arginine, lysine, galactose and trehalose were significantly inhibited in the 2-year burn soils. The data suggest that a 4-year burn is a more sustainable practice for maintaining the original structure and function of the forest belowground ecosystem.