Plant roots are more important than temperature in modulating carbon release in a limed acidic soil

Lime is a common amendment to overcome soil acidity in agricultural production systems. However, plant root effects on lime and soil carbon (C) dynamics in acidic soils under varied temperature remain largely unknown. We monitored root effects of soybean on the fate of lime applied to an acidic soil at 20 and 30°C in growth chambers. Soil respired CO₂ was continuously trapped in columns without and with plants until the final stage of vegetative growth. Lime‐derived CO₂ was separated from total respired CO₂ based on δ¹³C measurements in CO₂. Leaching was induced at early and late vegetative growth stages, and the leachates were analysed for dissolved organic (DOC) and inorganic C (DIC) concentrations. Soil respiration significantly increased with lime addition at both temperatures (p < 0.001). The presence of soybean doubled the recovery of lime‐derived CO₂‐C at 20°C at the early growth stage; however, by the end of the experiment, the contribution of lime‐derived CO₂‐C to soil respiration was negligible in all treatments, indicating that the contribution of lime to soil respiration was shortlived. In contrast, DIC and DOC concentrations in leachates remained elevated with liming and were greater in the presence of soybean. We observed no main temperature effects and no interactive effects of temperature and soybean presence on lime‐derived CO₂‐C, DIC and DOC. These results highlight the role of plant‐modulated processes in CO₂ release and C leaching from lime in acidic soils, whereas an increase in temperature may be less important. Temperature and plant roots alter the rate of key processes controlling C dynamics in a limed acidic soil. Lime‐derived CO₂‐C, DIC and DOC increased more in the presence of plants than with increased temperature. Root effects are more important than temperature for inorganic and organic carbon dynamics in limed acidic soils.     

Subtropical plantations are large carbon sinks: Evidence from two monoculture plantations in South China

Quantifying the net carbon (C) storage of forest plantations is required to assess their potential to offset fossil fuel emissions. In this study, a biometric approach was used to estimate net ecosystem productivity (NEP) for two monoculture plantations in South China: Acacia crassicarpa and Eucalyptus urophylla. This approach was based on stand-level net primary productivity (NPP, based on direct biometric inventory) and heterotrophic respiration (R_h). In comparisons of R_h determination based on trenching vs. tree girdling, both trenching and tree girdling changed soil temperature and soil moisture relative to undisturbed control plots, and we assess the effects of corrections for disturbances of soil moisture and soil moisture on the estimation of soil CO₂ efflux partitioning. Soil microbial biomass and dissolved organic carbon were significantly lower in trenched plots than in tree girdled plots for both plantations. Annual soil CO₂ flux in trenched plots (R_h-t) was significantly lower than in tree-girdled plots (R_h-g) in both plantations. The estimates of R_h-t and R_h-g, expressed as a percentage of total soil respiration, were 58 ± 4% and 74 ± 6%, respectively, for A. crassicarpa, and 64 ± 3% and 78 ± 5%, respectively, for E. urophylla. By the end of experiment, the difference in soil CO₂ efflux between the trenched plots and tree-girdled plots had become small for both plantations. Annual R_h (mean of the annual R_h-t and R_h-g) and net primary production (NPP) were 470 ± 25 and 800 ± 118 g C m⁻² yr⁻¹, respectively, for A. crassicarpa, and 420 ± 35 and 2380 ± 187 g C m⁻² yr⁻², respectively, for E. urophylla. The two plantations in the developmental stage were large carbon sinks: NEP was 330 ± 76 C m⁻² yr⁻¹ for A. crassicarpa and 1960 ± 178 g C m⁻² yr⁻¹ for E. urophylla.     

Soils as carbon sinks: the global context

Abstract. Soil carbon sequestration could meet at most about one-third of the current yearly increase in atmospheric CO₂-carbon, but the duration of the effect would be limited, with significant impacts lasting only 20–50 years. Coupled with this limited duration, increases in population and per-capita energy demand mean that soil carbon sequestration could play only a minor role in closing the difference between predicted and target carbon emissions by 2100. However, if atmospheric CO₂ concentrations are to be stabilized at reasonable levels (450–650 ppm), drastic reductions in carbon emissions will be required over the next 20–30 years. Given this, carbon sequestration should form a central role in any portfolio of measures to reduce atmospheric CO₂ concentrations over this crucial period, while new energy technologies are developed and implemented. International agreements, such as the Kyoto Protocol, encourage soil carbon sequestration and could be used to formulate soil carbon sequestration polices. Such policies need to take account of other environmental impacts as well as political, economic and societal needs, so that they form part of a raft of measures encouraging sustainable development. Of the carbon sequestration options available, those of a 'win–win' nature, that is, those that increase carbon stocks at the same time as improving other aspects of the environment, and those that protect or enhance existing stocks ('no regrets' implementation) show the greatest promise in meeting these goals.     

The search for carbon sinks in the tropics

The study and modeling of the global C cycle have been dominated by the assumption that the atmosphere and the biota were in C steady state prior to the industrial revolution. This view led to the perception that most of the terrestrial biota was neutral with regards to the C concentration of the atmosphere. Recent evidence suggests that neither the atmosphere nor the biota were in C steady state prior to, or since, the industrial revolution. Therefore, it is now necessary to re-visit the role of natural processes in the global C cycle, study the C cycle in its totality, and focus attention on the magnitude of potential C sinks in ecosystems previously thought to be neutral with respect to atmospheric C. “An improved understanding of the CO₂ cycle is essential to predict the future rate of any atmospheric CO₂ increase and to plan eventually for an international CO₂ management strategy” Tans et al. (1990).     

Old soil carbon is more temperature sensitive than the young in an agricultural field

Changes in the carbon stock of soil in response to climate change would significantly affect the atmospheric carbon dioxide concentration and consequently climate. The isotopes of carbon provide a means to study the temperature sensitivities of different soil carbon fractions. Where C3 vegetation has changed for C4, soil organic matter (SOM) from the different origins have different ¹³C/¹²C ratios. Relying on this feature, we took soil samples from a control field and a field where ordinary grain (C3) vegetation was replaced by maize (C4), 5 years ago. We measured the respiration rate and the ¹³C/¹²C ratio of the CO₂ produced by the samples at different temperatures. Based on these measurements, we quantified that Q₁₀ was 3.4-3.6 for the total CO₂ production while it was 2.4-2.9 at 20 °C for the maize-derived young carbon and 3.6 for the older C3-derived carbon. Our results suggest that climatic warming will accelerate especially the decomposition of the large pool of old soil carbon in these fields.     

Soil nematode communities are ecologically more mature beneath late- than early-successional stage biological soil crusts

Biological soil crusts are key mediators of carbon and nitrogen inputs for arid land soils and often represent a dominant portion of the soil surface cover in arid lands. Free-living soil nematode communities reflect their environment and have been used as biological indicators of soil condition. In this study, we test the hypothesis that nematode communities are successionally more mature beneath well-developed, late-successional stage crusts than immature, early-successional stage crusts. We identified and enumerated nematodes by genus from beneath early- and late-stage crusts from both the Colorado Plateau, Utah (cool, winter rain desert) and Chihuahuan Desert, New Mexico (hot, summer rain desert) at 0–10 and 10–30 cm depths. As hypothesized, nematode abundance, richness, diversity, and successional maturity were greater beneath well-developed crusts than immature crusts. The mechanism of this aboveground–belowground link between biological soil crusts and nematode community composition is likely the increased food, habitat, nutrient inputs, moisture retention, and/or environmental stability provided by late-successional crusts. Canonical correspondence analysis of nematode genera demonstrated that nematode community composition differed greatly between geographic locations that contrast in temperature, precipitation, and soil texture. We found unique assemblages of genera among combinations of location and crust type that reveal a gap in scientific knowledge regarding empirically derived characterization of dominant nematode genera in deserts soils and their functional role in a crust-associated food web.     

A global synthesis reveals more response sensitivity of soil carbon flux than pool to warming

Journal of Soils and Sediments - Climate change continues to garner attention in the public sphere. Most recognize its potential to affect global carbon (C) dynamics in the biosphere. Many posit...     

Pyrogenic carbon soluble fraction is larger and more aromatic in aged charcoal than in fresh charcoal

Recent studies show that pyrogenic matter is one of the most stable compounds in the soil but less inert than previously expected. One potential pathway yielding losses from soil is solubilisation of pyrogenic compounds. In batch experiments, we estimated the proportion and molecular composition of soluble (<0.45 μm) and colloidal fractions (0.45-5 μm) extractable from a freshly pyrolysed charcoal and a 10 year old wildfire charcoal. These fractions represented a very small fraction (<2.7 g kg⁻¹) of chars. The benzene polycarboxylic acids (BPCA) pattern indicated that 40-55 times more condensed structures were released from the aged char than from the fresh char. This study shows that the soluble fraction of the char is small, and tends to increase with the residence time in the soil.     

Copper: An alternative to mercury; more effective than zirconium in Kjeldahl digestion of ecological materials

Abstract

Copper sulfate as a catalyst in Kjeldahl digestion of selected ecological materials has been demonstrated to be effective when a salt/acid ratio of 1 g/mL is used. Copper sulfate in combination with zirconium sulfate is no more effective than copper sulfate alone.     

Bacterial communities are more dependent on soil type than fertilizer type, but the reverse is true for fungal communities

The soil microbial community is strongly influenced by a wide variety of factors, such as soil characteristics and field management systems. In order to use biological indicators based on microbial community structure, it is very important to know whether or not these factors can be controlled. The present study aimed to determine whether soil type or fertilization has a greater influence on the soil microbial community based on denaturing gradient gel electrophoresis (DGGE) analysis of 12 experimental field plots containing four different soil types, Cumulic Andosol, Low-humic Andosol, Yellow Soil and Gray Lowland Soil, kept under three different fertilizer management systems since 2001 (the application of chemical fertilizer, the application of rice husk and cow manure, and the application of pig manure). Bacterial DGGE analysis using 16S rRNA genes and fungal DGGE analysis using 18S rRNA genes revealed that the bacterial community was related to the soil type more than the fertilization; however, the fungal community was related to the fertilization more than the soil type. These results might suggest that the fungal community is easier to control by fertilization than the bacterial community. Thus, we propose that indicators based on the fungal community might be more suitable as microbial indicators for soil quality.     

Manipulating biotic carbon sources and sinks for climate change mitigation: Can science keep up with practice?

The potential for natural C sinks to be manipulated by human means to mitigate climate change has been discussed in the environmental literature for more than a decade. There now appears to be little doubt that changes in global land-use and land management practices could significantly slow the accumulation of CO₂ in the atmosphere. As a result, some forward-thinking companies and governmental bodies are acting now upon the biotic mitigation literature by developing actual mitigation projects. It is now national policy in the United States to encourage such activities. The future of C offsets, however, is unclear, due in large measure to lagging scientific knowledge. Large-scale private action likely will await regulatory signals that action will be accepted as a legitimate mitigation measure, perhaps providing retroactive regulatory credit, a source of tradeable emission entitlements, or credit against yet-to-be-established C taxes. The practical potential of most biotic mitigation approaches is unknown, and the entire concept remains subject to political challenge domestically and abroad. The ability to predict C benefits of individual mitigation projects is often tenuous and subject to debate. To allow expansion of C offset practices as quickly as possible, and hopefully to fund projects with many ancillary environmental and economic benefits, policymakers and project developers desperately need physical and social science data to be provided in a useable form.     

Workshop summary statement: Terrestrial bioshperic carbon fluxesquantification of sinks and sources of CO2

Understanding the role of terrestrial ecosystems in the global carbon (C) cycle has become increasingly important as policymakers consider options to address the issues associated with global change, particularly climate change. Sound scientific theories are critical in predicting how these systems may respond in the future, both to climate change and human actions. In March 1993, 60 scientists from 13 nations gathered in Bad Harzburg, Germany, to develop a state-of-the-science assessment of the present and likely future C fluxes associated with the major components of the earth's terrestrial biosphere. In the process, particular emphasis was placed on the potential for improving C sinks and managing long-term C sequestration. The majority of the week's work was conducted in eight working groups which independently considered a particular biome or subject area. The working groups considered: the Global Carbon Cycle; Boreal Forests and Tundra; Temperate Forests; Tropical Forests; Grasslands, Savannas and Deserts; Land and Water Interface Zones; Agroecosystems; and Biomass Management. This paper presents a brief overview of their major conclusions and findings. In addition, Table 1 brings together the best estimates from each group as to the current magnitude and estimated future direction of changes in the terrestrial C fluxes.     

Why understanding the natural sinks and sources of CO2 is important: A policy analysis perspective

The mechanisms that regulate the concentration of carbon dioxide in the atmosphere, the carbon cycle, is an integral part of the analysis of the greenhouse issue. The present understanding of the carbon cycle is inadequate to the purpose of assessing the relationship between future anthropogenic emissions and concentrations of atmospheric CO₂. The most important problem is that natural science cannot presently explain the relationship between present and past anthropogenetic emissions and concentrations. Sinks for CO₂ are inadequate to explain present and past dispositions of emissions. This deficiency in scientific understanding leads to uncertainty in the analysis of potential future emissions and atmospheric CO₂ accumulation, and to uncertainty in the specification of other policy analysis instruments such as global warming potential coefficients.     

Soil pH controls nitrification and carbon substrate utilization more than urea or charcoal in some highly acidic soils

Understanding the mechanism and key controlling factors of nitrification in highly acidic soils is important from both ecological and environmental perspectives. Many acid soils are also characterized by vegetation that produces polyphenolic and terpene compounds that inhibit microbial activity. We investigated the potentially ameliorative effects of lime, charcoal, and urea additions on soil nitrification and carbon substrate utilization (using the MicroResp method). Four soils were studied from widely different environments but with similar pH and inputs of phytochemicals to determine the relative effects of these potentially controlling factors. The addition of charcoal had no significant effect on net nitrification, but charcoal significantly increased soil basal respiration and altered C substrate utilization in the two Scottish soils. Urea greatly increased nitrification in both the Chinese soils, but there was no effect of urea on nitrification in the two Scottish soils. Lime application increased nitrification in all the soils except for the Chinese mixed forest soil. Multivariate analysis of the C source utilization data revealed that lime altered C substrate utilization more than urea or charcoal in these highly acidic soils. Our results suggest that acid-tolerant nitrifiers do exist in these soils and have potential for high activity, and pH (lime addition) and N-substrate (urea) most often increased nitrification. However, no single factor controlled nitrification in every soil, suggesting an interaction between abiotic and nitrifier community composition as a result of land use and soil type interactions.     

Bioorganic fertilizer maintains a more stable soil microbiome than chemical fertilizer for monocropping

Understanding the responses of soil microbiome composition to various farming practices is important for selecting suitable managements to maintain soil functions. In this study, the influences of heavy chemical fertilizer application (CF) and reduced chemical fertilizer supplemented with organic (OF) or bioorganic fertilizer (BF, BF = OF + Trichoderma) on composition of soil microbiome were investigated for monocropping cucumber systems using a five-season continuous pot experiment. The MiSeq sequencing data indicated that the CF treatment resulted in the lowest fungal diversity and the BF treatment resulted in a relatively higher one close to the initial soil (CK). The BF and OF treatments had similar impacts on the composition of bacterial community, and the CF treatment significantly reduced bacterial diversity. Although both OF and BF treatments had better plant growth responses, they had less disturbance on the composition of fungal community relative to the CF treatment. The BF treatment is more predictable than the other treatments for postponing fungal diversity as the inoculated fungal species significantly (p < 0.05) affected the fungal community. In conclusion, the combination of bioorganic fertilizers with reduced chemical fertilizer application can maintain a diverse soil microbiome in cucumber monocropping.     

Doing more good than harm - Building an evidence-base for conservation and environmental management

The problems of environmental change and biodiversity loss have entered the mainstream political agenda. Given the call from an increasingly influential environmental lobby for government and wider society to make both financial and personal sacrifices to address these problems, it seems likely that conservation biologists and environmental managers will be asked tough questions of the general form ‘are conservation interventions effective?’ and, ‘are they doing more good than harm?’ Science constantly advances and must remain open to challenge, but managers and policy formers require an interim product (an evidence-base) to underpin their current decision-making. The health services have been using the objective and transparent methodology of systematic review to summarise the evidence-base relating to the effectiveness of interventions. Environmental management has, up until now, had no formal shared evidence-base of this kind. Reviewing recent developments in evidence-based practice, this paper introduces a ‘systematic review’ section for this journal and argues that constructing an evidence-based framework for environment management is possible, the challenge is scaling it up to engage the global scientific community. We draw on the history of evidence-based healthcare, but also on the differences between healthcare and conservation, to set out the challenges in creating a Collaboration for Environmental Evidence that develops a library of systematic reviews on the effectiveness of conservation and environmental interventions.     

Future of land use in Australia: An economic perspective

It is proposed that the standard economist's model of optimum land use is extended to include the interaction with land cover and land condition. Such a model allows consideration of the influence of market factors and government policies and programmes on land use patterns and management practices, and the feedback effect on land cover and land condition. Recent developments in the approach to modelling land condition, which include the joint consideration of economic factors and physical processes, are discussed. Factors affecting the pattern of agricultural land use in Australia are then reviewed. The importance of considering economic and physical interactions when assessing land use patterns is increasingly being recognized in research and policy development. If research is to meet the needs of land managers in the future then economists and physical scientists will need to integrate their data modelling capabilities in order to address natural resource management issues.