The role of organic amendments to soil for crop protection: Induction of suppression of soilborne pathogens

Application of external organic inputs to soils can be considered as one of the most ancient strategies in agriculture, and it has been commonly used since the very beginning of human-based agricultural practices. During all this time, application of several organic matters to agricultural soils has demonstrated their benefit to plants and soils. Organic amendments have proved to be useful in recovering soil properties, improving soil quality and, in some cases, can be directly involved in providing beneficial effects to plants. All these obtained effects finally lead to an increase in crop protection and sustainability. One most expected effect caused by the application of organic amendments, is the suppression of a wide range of soilborne pathogens (mainly bacterial and fungal pathogens) due to the induction of physicochemical and biological changes in soils. In order to get insight into the nature of the induced soil suppression of soilborne plant pathogens, the analysis of the physical, chemical and the microbial changes, pointed to the key role of beneficial activities produced by soil microorganisms finally adapted to the environmental changes produced by the influence of organic amendments. As shown in the case studies reported here, participation of soil microbes specifically selected after organic amendment is crucial in the control of fungal soilborne diseases. Moreover, the development of “omics” approaches allowed these recent studies to go one step further, revealing the main actors involved in the induced soil suppressiveness and their activities. Thus “omics” techniques will help to understand the soil and its microbiome as a whole system, and to assign the important roles of its biological components.     

Biochar co-compost improves nitrogen retention and reduces carbon emissions in a winter wheat cropping system

Organic amendments, such as compost and biochar, mitigate the environmental burdens associated with wasting organic resources and close nutrient loops by capturing, transforming, and resupplying nutrients to soils. While compost or biochar application to soil can enhance an agroecosystem's capacity to store carbon and produce food, there have been few field studies investigating the agroecological impacts of amending soil with biochar co-compost, produced through the composting of nitrogen-rich organic material, such as manure, with carbon-rich biochar. Here, we examine the impact of biochar co-compost on soil properties and processes by conducting a field study in which we compare the environmental and agronomic impacts associated with the amendment of either dairy manure co-composted with biochar, dairy manure compost, or biochar to soils in a winter wheat cropping system. Organic amendments were applied at equivalent C rates (8 Mg C ha⁻¹). We found that all three treatments significantly increased soil water holding capacity and total plant biomass relative to the no-amendment control. Soils amended with biochar or biochar co-compost resulted in significantly less greenhouse gas emissions than the compost or control soils. Biochar co-compost also resulted in a significant reduction in nutrient leaching relative to the application of biochar alone or compost alone. Our results suggest that biochar co-composting could optimize organic resource recycling for climate change mitigation and agricultural productivity while minimizing nutrient losses from agroecosystems.     

Soil initial bacterial diversity and nutrient availability determine the rate of xenobiotic biodegradation

Understanding the relative importance of soil microbial diversity, plants and nutrient management is crucial to implement an effective bioremediation approach to xenobiotics-contaminated soils. To date, knowledge on the interactive effects of soil microbiome, plant and nutrient supply on influencing biodegradation potential of soils remains limited. In this study, we evaluated the individual and interactive effects of soil initial bacterial diversity, nutrient amendments (organic and inorganic) and plant presence on the biodegradation rate of pyrene, a polycyclic aromatic hydrocarbon. Initial bacterial diversity had a strong positive impact on soil biodegradation potential, with soil harbouring higher bacterial diversity showing ~ 2 times higher degradation rates than soils with lower bacterial diversity. Both organic and inorganic nutrient amendments consistently improved the degradation rate in lower diversity soils and had negative (inorganic) to neutral (organic) effect in higher diversity soils. Interestingly, plant presence/type did not show any significant effect on the degradation rate in most of the treatments. Structural equation modelling demonstrated that initial bacterial diversity had a prominent role in driving pyrene biodegradation rates. We provide novel evidence that suggests that soil initial microbial diversity, and nutrient amendments should be explicitly considered in the design and employment of bioremediation management strategies for restoring natural habitats disturbed by organic pollutants.     

Ecosystem Development After Mangrove Wetland Creation: Plant–Soil Change Across a 20-Year Chronosequence

Mangrove wetland restoration and creation efforts are increasingly proposed as mechanisms to compensate for mangrove wetland losses. However, ecosystem development and functional equivalence in restored and created mangrove wetlands are poorly understood. We compared a 20-year chronosequence of created tidal wetland sites in Tampa Bay, Florida (USA) to natural reference mangrove wetlands. Across the chronosequence, our sites represent the succession from salt marsh to mangrove forest communities. Our results identify important soil and plant structural differences between the created and natural reference wetland sites; however, they also depict a positive developmental trajectory for the created wetland sites that reflects tightly coupled plant-soil development. Because upland soils and/or dredge spoils were used to create the new mangrove habitats, the soils at younger created sites and at lower depths (10–30?cm) had higher bulk densities, higher sand content, lower soil organic matter (SOM), lower total carbon (TC), and lower total nitrogen (TN) than did natural reference wetland soils. However, in the upper soil layer (0–10?cm), SOM, TC, and TN increased with created wetland site age simultaneously with mangrove forest growth. The rate of created wetland soil C accumulation was comparable to literature values for natural mangrove wetlands. Notably, the time to equivalence for the upper soil layer of created mangrove wetlands appears to be faster than for many other wetland ecosystem types. Collectively, our findings characterize the rate and trajectory of above- and below-ground changes associated with ecosystem development in created mangrove wetlands; this is valuable information for environmental managers planning to sustain existing mangrove wetlands or mitigate for mangrove wetland losses.     

Phytostabilization of Amended Soils Polluted with Trace Elements Using the Mediterranean Shrub: Rosmarinus Officinalis

We evaluate the mid-term effects of two amendments and the establishment of R. officinalis on chemical and biochemical properties in a trace element contaminated soil by a mine spill and the possible use of this plant for stabilization purposes. The experiment was carried out using containers filled with trace element polluted soil, where four treatments were established: organic treatment (biosolid compost, OAR), inorganic treatment (sugar beet lime, IAR), control with plant (NAR) and control without plant (NA). Amendment addition and plant establishment contributed to restore soil chemical (pH, total organic carbon, and water soluble carbon) and biochemical properties (microbial biomass carbon and the enzymatic activities: aryl-sulphatase and protease). The presence of rosemary did not affect soluble (0.01 M CaCl₂) Cd and Zn and decreased trace element EDTA extractability in amended soils. There were no negative effects found on plant growth and nutrient content on polluted soils (NAR, OAR, and IAR). Trace element contents were within normal levels in plants. Therefore, rosemary might be a reliable option for successful phytostablization of moderate trace element contaminated soils.     

Mid‐term effects on ecosystem services of quarry restoration with Technosols under Mediterranean conditions: 10‐year impacts on soil organic carbon and vegetation development

The use of Technosols for the restoration of limestone quarries overcomes the usual “in situ” scarcity of soil and/or its poor quality. The use of mine spoils, improved with mineral and/or organic amendments, could be an efficient and environmentally friendly option. Properly treated sewage sludge from urban wastewater treatment plants could be a suitable organic amendment and fertilizer (rich in N and P) whenever its pollutant burden is low (heavy metals and/or organic pollutants). Its appropriate use could improve essential soil physical and chemical properties and, therefore, promote key ecosystem services of restored areas, such as biomass production and carbon sequestration, as well as biodiversity and landscape recovery. However, the mid‐term impacts of these restoration practices on soil functioning and their services have rarely been reported in the available literature. In this study we assess the mid‐term effects (10 years) of the use of sewage sludge as a Technosol amendment on soil organic carbon (SOC), nutrient status, and plant development in several restored quarries. Soils restored using sewage sludge showed a threefold increase in SOC compared to the corresponding unamended ones, despite the moderate sludge dosage applied (below 50 tonnes/ha). Plant cover was also higher in amended soils, and recruitment was not affected by sludge amendment at these doses. This study demonstrates that, used at an appropriate rate, sewage sludge is a good alternative for the valorization of mine spoils in quarry restoration, improving some important regulatory ecosystem services such as carbon sequestration, without compromising woody plant encroachment.     

Detecting soil and plant community changes in restored wetlands using a chronosequence approach

Wetland restoration aims to recreate or enhance valuable ecosystem services lost during wetland destruction. Regaining wetland ecosystem services depends on restarting basic wetland functions, like carbon (C) storage, which are unmeasured in many Wetlands Reserve Program (WRP) restoration sites. We collected soil and plant data from 17 WRP sites in western New York that were used for tillage or non-tillage agriculture and then actively restored as isolated depressional wetlands by excavating basins and disabling drainage systems. Sites had been restored for 0–15 years when sampled in August-October 2010. We analyzed data as chronosequences and tested whether soil and vegetation parameters in restored wetlands, over time, (1) departed from pre-restoration baselines, estimated using active agricultural fields paired to each WRP site, and (2) converged towards “natural” benchmarks, estimated from four naturally-occurring wetlands. Restored WRP soils remained similar to agricultural soils in organic matter, density, moisture, and belowground plant biomass across chronosequences, indicating negligible C storage and belowground development for 15 years following restoration. Soil changes were limited in sites restored after both tillage and non-tillage agriculture and throughout the upland meadow, emergent shoreline, and open-water habitat zones that characterize these sites. Many plant metrics like aboveground biomass matched natural wetlands within 15 years, but recovered inconsistently among tilled and untilled sites and across all habitat zones, suggesting land-use history impacts and/or zonation effects. Disparities in recovery times exists between vegetation, which can respond quickly to wetland restoration, and underlying soils, which show limited signs of recovery 15 years after being restored.     

Growth of Jatropha curcas on heavy metal contaminated soil amended with industrial wastes and Azotobacter. A greenhouse study

The aims of the study were to evaluate the effect of organic wastes (biosludge and dairy sludge) and biofertilizer (Azotobacter chroococcum) on the planting conditions of Jatropha curcas in metal contaminated soils. Results showed that the plants survival rate in heavy metal contaminated soil increased with addition of amendments. Treatment T6 (heavy metal contaminated soils+dairy sludge+biofertilizer) observed to be the best treatment for growth (height and biomass) as compared with the treatment T5 (heavy metal contaminated soils+biosludge+biofertilizer). In addition, organic amendments provided nutrients such as carbon, N, P and K to support plant growth and reduced the metal toxicity to plant. The present study showed that metal contaminated lands/soils could be suitably remediated by adapting appropriate measures.     

Woodchip and biochar amendments differentially influence microbial responses,but do not enhance plant recovery in disturbed semiarid soils

Restoration presents a global challenge in drylands (arid and semiarid ecosystems) where uses can range from exclusive conservation to open‐pit mining and restoration practices are constrained by scarce, unpredictable precipitation, and high ambient temperatures. Adding woodchip amendments to soils is a common strategy for mitigating soil degradation as amendments may enhance soil carbon and increase plant cover. We assessed the effect of surface or incorporated woodchip addition and incorporated wood‐derived biochar on soil carbon dynamics and microbial activities as well as plant cover in semiarid soils that had been removed and replaced. We found that woodchips at the soil surface increased soil organic carbon (SOC), and both surface and incorporated woodchips increased the dissolved organic carbon (DOC) content. The incorporation of woodchips inhibited plant cover yet increased soil CO₂ efflux and dissolved organic matter stoichiometry. Surface woodchips also significantly enhanced microbial activities but not plant cover. A significant amount of the soil efflux in response to incorporating woodchips was explained by plant cover and exoenzyme activities, but this was not the case for other amendment treatments. Biochar, thought to be more resistant to decomposition, neither stimulated nor reduced microbial activities or plant cover and did not influence SOC or DOC. Our findings demonstrate that the influence of woodchip amendments on microbial processes and soil carbon dynamics depends on the location of application and that coarse fast‐pyrolysis biochar has limited influence on soil processes over a 22‐month study in a water‐limited ecosystem.     

Creating riverine wetlands: Ecological succession, nutrient retention, and pulsing effects

Successional patterns, water quality changes, and effects of hydrologic pulsing are documented for a whole-ecosystem experiment involving two created wetlands that have been subjected to continuous inflow of pumped river water for more than 10 years. At the beginning of the growing season in the first year of the experiment (1994), 2400 individuals representing 13 macrophyte species were introduced to one of the wetland basins. The other basin was an unplanted control. Patterns of succession are illustrated by macrophyte community diversity and net aboveground primary productivity, soil development, water quality changes, and nutrient retention for the two basins. The planted wetland continued to be more diverse in plant cover 10 years after planting and the unplanted wetland appeared to be more productive but more susceptible to stress. Soil color and organic content continued to change after wetland creation and wetlands had robust features of hydric soils within a few years of flooding. Organic matter content in surface soils in the wetlands increased by approximately 1% per 3-year period. Plant diversity and species differences led to some differences in the basins in macrophyte productivity, carbon sequestration, water quality changes and nutrient retention. The wetlands continued to retain nitrate–nitrogen and soluble reactive phosphorus 10 years after their creation. There are some signs that sediment and total phosphorus retention are diminishing after 10 years of river flow. Preliminary results from the beginnings of a flood pulsing experiment in the two basins in 2003–2004 are described for water quality, nutrient retention, aboveground productivity, and methane and nitrous oxide gaseous fluxes.     

Isolation and Partial Characterization of Bacterial Strains on Low Organic Carbon Medium from Soils Fertilized with Different Organic Amendments

A total of 720 bacterial strains were isolated from soils with four different organic amendment regimes on a low organic carbon (low-C) agar medium (10 µg C ml^?1) traditionally used for isolation of oligotrophs. Organic amendments in combination with field history resulted in differences in dissolved organic carbon contents in these soils. There were negative correlations between total and dissolved organic carbon content and the number of isolates on low-C agar medium, whereas these correlations were absent for bacterial strains isolated from the same soil on high-C agar medium (1,000 µg C ml^?1). Repeated transfers (up to ten times) of the isolates from low-C agar medium to fresh low- and high-C agar media were done to test for exclusive growth under oligotrophic conditions. The number of isolates exclusively growing under oligotrophic conditions dropped after each subsequent transfer from 241 after the first to 98 after the third transfer step. Identification on the basis of partial 16S rRNA gene sequences revealed that most of the 241 isolates (as well as the subset of 98 isolates) belong to widespread genera such as Streptomyces, Rhizobium, Bradyrhizobium, and Mesorhizobium, and the taxonomic composition of dominant genera changed from the first transfer step to the third. A selected subset of 17 isolates were further identified and characterized for exclusive growth on low-C agar medium. Two isolates continued to grow only on low-C agar medium up to the tenth transfer step and matched most closely with Rhizobium sullae and an uncultured bacterium on the basis of the almost full-length 16S rRNA gene. It was concluded that the vast majority of strains which are isolated on low-C agar media belong to the trophic group of microorganisms adapted to a “broad range” of carbon concentrations, including well-known and widespread bacterial genera. Oligotrophy is a physiological, not a taxonomic property, and can only be identified by cultural means so far. We showed that true oligotrophs that are unable to grow on high carbon media are rare and belong to genera that also contain broad-range and copiotrophic strains.     

Soil amendments promote denitrification in restored wetlands

Wetlands perform important ecosystem functions, including improvement of water quality through the process of denitrification. To offset the negative environmental impact of replacing wetlands with agriculture and development, the United States has a policy requiring that losses in wetland area are compensated for through wetland restoration elsewhere. However, these restored wetlands may require decades to achieve functional equivalency to natural wetlands. We evaluated the efficacy of using carbon amendments during restoration to promote denitrification potential in four restored wetlands in central New York State, United States. The amendments were straw, topsoil, and biochar, chosen to range along a gradient of carbon lability. Soil samples collected 6 years after restoration were analyzed for denitrification potential and associated soil properties, including soil carbon and nitrogen, pH, microbial biomass carbon and nitrogen, carbon lability, and potential net nitrogen mineralization and nitrification. Compared to unamended control plots, denitrification potential was approximately 3 times higher in straw‐amended plots, 8 times higher in topsoil‐amended plots, and 11 times higher in biochar‐amended plots. Denitrification potential positively correlated with both soil organic carbon and microbial biomass nitrogen, suggesting that the use of soil amendments in restorations can help stimulate the development of denitrification potential by facilitating the suite of carbon and nitrogen cycling processes that underlie this function. However, denitrification potential in a nearby natural reference wetland was at least 50 times higher than it was in the restored wetland plots, highlighting the limitations of using wetland restoration to compensate for the loss of natural wetlands.     

蚂蚁筑巢对西双版纳热带森林土壤微生物生物量碳及熵的影响

蚂蚁筑巢能够改变热带森林土壤理化环境,从而对土壤微生物生物量碳及熵的时空动态产生重要影响.本研究以西双版纳高檐蒲桃热带森林群落为对象,采用氯仿熏蒸法对蚂蚁巢地和非巢地土壤微生物生物量碳及熵时空动态进行测定.结果表明: 1)蚁巢地平均微生物生物量碳及熵(1.95 g·kg^-1,6.8%)显著高于非巢穴(1.76 g·kg^-1,5.1%);蚁巢地和非蚁巢地土壤微生物生物量碳呈单峰型时间变化趋势,而土壤微生物熵呈“V”型变化格局.2)蚁巢地和非巢地土壤微生物生物量碳及熵均具有明显的垂直变化:微生物生物量碳随土层加深显著降低,微生物熵则沿土层加深显著升高,但蚁巢微生物生物量碳及熵的垂直变化较非巢穴显著. 3)蚂蚁筑巢引起了巢内水分和温度的显著改变,进而影响土壤微生物生物量碳及熵的时空动态.土壤水分分别解释微生物生物量碳及熵的66%～83%和54%～69%,而土壤温度分别解释土壤微生物生物量碳及熵的71%～86%和67%～76%. 4)蚂蚁筑巢引起土壤理化性质变化对土壤微生物生物量碳和熵产生重要影响.蚁巢土壤微生物生物量碳与土壤有机碳、温度、全氮、含水率呈极显著正相关,与容重、硝态氮,水解氮呈显著正相关,与土壤pH呈极显著负相关;除土壤微生物熵与pH呈显著正相关外,与其他土壤理化指标均呈显著负相关.土壤总有机碳、全氮和温度对微生物生物量碳的贡献最大,而土壤总有机碳和全氮对微生物熵的负作用最小.因此,蚂蚁筑巢能够显著改变微生境(如土壤水分与温度)及土壤理化性质(如总有机碳及全氮),进而调控热带森林土壤微生物生物量碳及熵的时空动态.     

Long‐term influence of fallen logs on patch formation and their effects under contrasting grazing regimes

Patchiness is a critical functional feature of arid lands, increasing productivity and diversity, but there is little information on the long‐term dynamics of patch formation. While plant‐created heterogeneity is widespread, grazing reduces plant density, hence removing patchiness. Patchiness is also associated with fallen logs and it is particularly important to assess this association in grazed areas, as there are few patches which are not created by living plants. We studied differences in soil nutrient content and soil seed bank associated with the presence of logs in the long ungrazed Koonamore Vegetation Reserve and an adjacent heavily grazed paddock in chenopod shrublands of South Australia. We studied soil properties associated with fallen logs of unknown age, and others known to have persisted for up to 78 years. Logs acted as traps for soil nutrients and seeds. Organic carbon was higher in soils associated with logs, and also higher inside the reserve than in the grazed paddock. Propagule number and species richness were higher next to logs than in open spaces and viable seeds were in much higher abundance next to logs in the grazed paddock than any other site. Increased time in situ of a log had a relatively small effect on soil organic carbon and total nitrogen. Logs act as resource traps which may enhance the diversity of the system, and may be particularly important for maintaining patches of resources in areas of severe grazing damage. Hence, their preservation should be incorporated into management schemes. [Correction added on 3 March 2015, after online publication: The following parts in the abstract have been edited. ‘Organic carbon and total nitrogen were higher in soils associated with logs’ has been corrected to ‘Organic carbon was higher in soils associated with logs’, and ‘had a relatively small effect on soil organic carbon, total nitrogen and available potassium’ has been corrected to ‘had a relatively small effect on soil organic carbon and total nitrogen’.]     

Organic amendment additions to rangelands: A meta‐analysis of multiple ecosystem outcomes

Interest in land application of organic amendments—such as biosolids, composts, and manures—is growing due to their potential to increase soil carbon and help mitigate climate change, as well as to support soil health and regenerative agriculture. While organic amendments are predominantly applied to croplands, their application is increasingly proposed on relatively arid rangelands that do not typically receive fertilizers or other inputs, creating unique concerns for outcomes such as native plant diversity and water quality. To maximize environmental benefits and minimize potential harms, we must understand how soil, water, and plant communities respond to particular amendments and site conditions. We conducted a global meta‐analysis of 92 studies in which organic amendments had been added to arid, semiarid, or Mediterranean rangelands. We found that organic amendments, on average, provide some environmental benefits (increased soil carbon, soil water holding capacity, aboveground net primary productivity, and plant tissue nitrogen; decreased runoff quantity), as well as some environmental harms (increased concentrations of soil lead, runoff nitrate, and runoff phosphorus; increased soil CO₂ emissions). Published data were inadequate to fully assess impacts to native plant communities. In our models, adding higher amounts of amendment benefitted four outcomes and harmed two outcomes, whereas adding amendments with higher nitrogen concentrations benefitted two outcomes and harmed four outcomes. This suggests that trade‐offs among outcomes are inevitable; however, applying low‐N amendments was consistent with both maximizing benefits and minimizing harms. Short study time frames (median 1–2 years), limited geographic scope, and, for some outcomes, few published studies limit longer‐term inferences from these models. Nevertheless, they provide a starting point to develop site‐specific amendment application strategies aimed toward realizing the potential of this practice to contribute to climate change mitigation while minimizing negative impacts on other environmental goals.     

The biogeochemistry of phosphorus after the first century of soil development on Rakata Island, Krakatau, Indonesia

This study examined the accumulation of organic carbon (C) and fractions ofsoil phosphorus (P) in soils developing in volcanic ash deposited in the1883 eruption of Krakatau. Organic C has accumulated at rates of 45 to 127g/m²/yr during 110 years of soil development, resulting inprofiles with as much as 14 kgC/m². Most soil P is found inthe HCl-extractable forms, representing apatite. A loss of HCl-extractableP from the surface horizons is associated with a marked accumulation ofNaOH-extractable organic P bound to Al. A bioassay with hill rice suggeststhat P is limiting to plant growth in these soils, perhaps as a result ofthe rapid accumulation of P in organic forms.     

Connecting carbon and nitrogen storage in rural wetland soil to groundwater abstraction for urban water supply

We investigated whether groundwater abstraction for urban water supply diminishes the storage of carbon (C), nitrogen (N), and organic matter in the soil of rural wetlands. Wetland soil organic matter (SOM) benefits air and water quality by sequestering large masses of C and N. Yet, the accumulation of wetland SOM depends on soil inundation, so we hypothesized that groundwater abstraction would diminish stocks of SOM, C, and N in wetland soils. Predictions of this hypothesis were tested in two types of subtropical, depressional‐basin wetland: forested swamps and herbaceous‐vegetation marshes. In west‐central Florida, >650 ML groundwater day^?1 are abstracted for use primarily in the Tampa Bay metropolis. At higher abstraction volumes, water tables were lower and wetlands had shorter hydroperiods (less time inundated). In turn, wetlands with shorter hydroperiods had 50–60% less SOM, C, and N per kg soil. In swamps, SOM loss caused soil bulk density to double, so areal soil C and N storage per m² through 30.5 cm depth was diminished by 25–30% in short‐hydroperiod swamps. In herbaceous‐vegetation marshes, short hydroperiods caused a sharper decline in N than in C. Soil organic matter, C, and N pools were not correlated with soil texture or with wetland draining‐reflooding frequency. Many years of shortened hydroperiod were probably required to diminish soil organic matter, C, and N pools by the magnitudes we observed. This diminution might have occurred decades ago, but could be maintained contemporarily by the failure each year of chronically drained soils to retain new organic matter inputs. In sum, our study attributes the contraction of hydroperiod and loss of soil organic matter, C, and N from rural wetlands to groundwater abstraction performed largely for urban water supply, revealing teleconnections between rural ecosystem change and urban resource demand.     

有机物料对污染土壤上水稻生长和重金属吸收的影响

采用盆栽试验,研究了施用有机碳源、菜籽饼和猪粪对污染土壤上水稻生长和重金属吸收特性的影响.结果表明： 施用菜籽饼和猪粪均能缓解重金属对水稻的毒害作用,促进水稻生长,显著增加地上部生物量和籽粒产量,降低糙米中重金属浓度;而有机碳源抑制水稻生长.与施用化肥相比,施用菜籽饼和猪粪处理的水稻籽粒产量分别增加128.3%和67.9%;施用菜籽饼处理的糙米Cd、Cu和Zn浓度分别降低47.6%、35.2%和21.5%,施用猪粪处理分别降低9.5%、21.2%和9.3%.土壤中DTPA提取态重金属浓度与水稻地上部生物量和重金属积累总量呈显著负相关.     

Temperature sensitivity of greenhouse gas production in wetland soils of different vegetation

Organic matter decomposition regulates rates of carbon loss (CO₂ and CH₄) in wetlands and has implications for carbon sequestration in the context of changing global temperature. Here we determined the influence of temperature and vegetation type on both aerobic and anaerobic decomposition of organic matter in subtropical wetland soils. As in many other studies, increased temperature resulted in higher rates of respiration and methanogenesis under both aerobic and anaerobic conditions, and the positive effect of temperature depended on vegetation (source of carbon substrate to soil). Under anaerobic incubations, the proportion of gaseous C (CO₂ and CH₄) lost as CH₄ increased with temperature indicating a greater sensitivity of methanogenesis to temperature. This was further supported by a wider range of Q₁₀ values (1.4–3.6) for methane production as compared with anaerobic CO₂ (1.3–2.5) or aerobic CO₂ (1.4–2.1) production. The increasing strength of positive linear correlation between CO₂:CH₄ ratio and the soil organic matter ligno-cellulose index at higher temperature indicated that the temperature sensitivity of methanogenesis was likely the result of increased C availability at higher temperature. This information adds to our basic understanding of decomposition in warmer subtropical and tropical wetland systems and has implications for C models in wetlands with different vegetation types.     

Organic matter and soil biota of upland wetlands in Taylor Valley,Antarctica

In January 2001, we surveyed streams and ponds above 300 m a.s.l. in Taylor Valley, South Victoria Land, Antarctica. One pond was examined in detail. Organic materials covered nearly 100% of the adjacent soil to 5–20 m from the shore, with intermittent patches to 80 m. Organic matter averaged 257 g C/m², and totaled 1,388 kg organic C on the soil around the pond. Soil-moisture content (0.56–12.41%) decreased with distance from shore, whereas pH (7.8–10.8) increased with distance. Electrical conductivity was lowest in the soils <10 m from the pond (416±94 µS/cm). Mineral soil organic C and total N concentrations were greatest between 10 and 30 m from the edge of the pond (1.21±0.37 and 0.13±0.05 mg/g soil, respectively). Soil invertebrates were present in only 50% of samples and included tardigrades, rotifers, and two nematodes, Scottnema lindsayae and Plectus antarcticus. A non-parametric, discriminant function analysis based on soil moisture, soil organic carbon, and electrical conductivity correctly predicted 87.0% of sites that had invertebrates and 70.8% of sites for which invertebrates were absent. Tardigrades, rotifers, and P. antarcticus were found only in the wettest soils nearest the pond whereas S. lindsayae was restricted to drier soils further from shore. Other ponds and streams also showed substantial accumulations of organic matter, suggesting that upland wetlands serve as resource islands in these polar deserts that provide a source of organic matter to nearby soils.