Removal of Dibenzofuran, Dibenzo-p-Dioxin, and 2-Chlorodibenzo-p-Dioxin from Soils Inoculated with Sphingomonas sp. Strain RW1

Removal of dibenzofuran, dibenzo-p-dioxin, and 2-chlorodibenzo-p-dioxin (2-CDD) (10 ppm each) from soil microcosms to final concentrations in the parts-per-billion range was affected by the addition of Sphingomonas sp. strain RW1. Rates and extents of removal were influenced by the density of RW1 organisms. For 2-CDD, the rate of removal was dependent on the content of soil organic matter (SOM), with half-life values ranging from 5.8 h (0% SOM) to 26.3 h (5.5% SOM).     

Comparison of Soil Organic Matter in Created, Restored and Paired Natural Wetlands in North Carolina

Soil organic matter (SOM) content is a key indicator of soil quality and is correlated to a number of important soil processes that occur in wetlands such as respiration, denitrification, and phosphorus sorption. To better understand the differences in the SOM content of created (CW), restored (RW), and paired natural wetlands (NWs), 11 CW/RW-NW pairs were sampled in North Carolina. The site pairs spanned a range of hydrogeomorphic (HGM) subclasses common in the Coastal Plain. The following null hypotheses were tested: (1) SOM content of paired CW/RWs and NWs are similar; (2) SOM content of wetlands across different HGM subclasses is similar; and (3) interactions between wetland status (CW/RW vs. NW) and hydrogeomorphic subclass are similar. The first null hypothesis was rejected as CW/RWs had significantly lower mean SOM (11.8 ± 3.9%) than their paired NWs (28.98 ± 8.0%) on average and at 10 out of the 11 individual sites. The second and third null hypotheses were also rejected as CW/RWs and NWs in the non-riverine organic soil flat subclass had significantly higher mean SOM content (31.08 ± 14.2%) than the other three subclasses (8.18 ± 2.5, 11.18 ± 8.2, and 10.38 ± 4.2%). Individual sites within this fourth subclass also had significantly different SOM content. This indicated that it would be inappropriate to include the organic soil flat subclass with either the riverine or non-riverine mineral soil flat subclasses when considering restoration guidelines. These results also suggested that if there is a choice in mitigation options between restoration or creation, wetlands should be restored rather than created, especially those in the non-riverine organic soil flat subclass.     

Degradation of Mono-chlorinated Dibenzo-p-Dioxins by Janibacter sp. Strain YA Isolated from River Sediment

Strain YA was newly isolated from an enrichment culture of river sediment and was identified as Janibacter sp. It was able to utilize dibenzofuran as the sole source of carbon and energy. Strain YA degraded > 90% of 1-chloro-dibenzo-p-dioxin (1-CDD) and > 80% of 2-chloro-dibenzo-p-dioxin in 18 hours with each initial concentration at 40 mg/L. A novel metabolite, 2-chloro-2′,6-dihydroxydiphenylether, was observed in 1-CDD degradation. From the metabolites detected by gas chromatography–mass spectrometry, strain YA was supposed to have at least two types of oxidation pathways in 1-CDD degradation.     

Eighty years of maize breeding alters plant nitrogen acquisition but not rhizosphere bacterial community composition

Background and aims

Phosphorus (P) availability is crucial for forest ecosystem productivity and soil organic matter (SOM) is an important source for P. This study was conducted to reveal carbon (C), nitrogen (N) and P distributions in functional SOM fractions. We hypothesised that (1) most of the organic P (P_org) is part of the particulate SOM, (2) particulate SOM stores increasing share of P with decreasing soil P content and (3) the C:P_org ratio of mineral-associated SOM is smaller than that of particulate SOM.

Methods

We analysed soil samples from five temperate forest sites (Fagus sylvatica) under different geological parent material with a wide range of total P concentrations. Density fractionation was used to separate free light fraction (fLF), particulate SOM occluded within soil aggregates (occluded light fraction; oLF), and mineral associated SOM (heavy fraction; HF). We determined the mass balance of P in these fractions, in addition to the C and N concentrations. Additionally, the P speciation of the topsoil was analysed by X-ray absorption near edge structure (XANES) spectroscopy at the P K-edge.

Results

The fLF contained 18–54% and the oLF 1–15% of total P (P_tot). High percentage of P in these light fractions was associated to soil minerals. Phosphorous in particulate SOM within aggregates tend to increase with decreasing soil P. The HF containing mineral-associated OM, comprised 38–71% of P_tot and their C:P_org ratios were consistently lower than those of the fLF irrespective of the P status of the soil.

Conclusions

We show that all three functional SOM fractions contain variable amount of both organic and inorganic P species. The free light fraction shows no response to changing P stocks of soils.. Despite physically protected particulate SOM, oLF, becomes increasingly relevant as P cache in soils with declining P status.

     

Effect of surfactant on the estimation by solid phase microextraction of bioavailable pyrene in soil samples

This study was focused on the effect of the presence of surfactant on the bioremediation efficacy and sensitivity of solid phase microextraction (SPME) in the pyrene-contaminated soil. Soils with 1.3 and 7.6% soil organic matter (SOM) were tested for biodegradation by microorganisms and extracted by aqueous solutions of the matrix used for SPME. For the biodegradation test, the presence of Triton X-100 at 5× CMC (critical micelle concentration) significantly enhanced pyrene removal for soil with lower SOM content (1.3%). However, this removal was insignificant for soil with higher SOM content (7.6%). The results may suggest that 5× CMC was not sufficient to improve significantly pyrene desorption for soil with higher SOM content. For the bioavailability test, in the absence of Triton X-100, SPME estimation of bioavailability in soils with indigenous or seeded microorganisms had an error range within 15%. However, with addition of Triton X-100, SPME estimations showed a significant decline (41 and 77%), in relation to their predicted values, for soil samples with SOM of 1.3 and 7.6%, respectively. The main reason for this underestimation is that micelle formation from the application of surfactant impacted the concentration of dissolved pyrene, rather than competitive site occupation between pyrene and surfactant molecules for SPME fiber. Thus, if soil samples contain surfactant, SPME would significantly underestimate bioavailability and risk level of PAH-contaminated sites.     

Components of forest soil CO2 efflux estimated from Δ14C values of soil organic matter

Aims

The partitioning of the total soil CO₂ efflux into its two main components: respiration from roots (and root-associated organisms) and microbial respiration (by means of soil organic matter (SOM) and litter decomposition), is a major need in soil carbon dynamics studies in order to understand if a soil is a net sink or source of carbon.

Methods

The heterotrophic component of the CO₂ efflux was estimated for 11 forest sites as the ratio between the carbon stocks of different SOM pools and previously published (Δ¹⁴C derived) turnover times. The autotrophic component, including root and root-associated respiration, was calculated by subtracting the heterotrophic component from total soil chamber measured CO₂ efflux.

Results

Results suggested that, on average, 50.4 % of total soil CO₂ efflux was derived from the respiration of the living roots, 42.4 % from decomposition of the litter layers and less than 10 % from decomposition of belowground SOM.

Conclusions

The Δ¹⁴C method proved to be an efficient tool by which to partition soil CO₂ efflux and quantify the contribution of the different components of soil respiration. However the average calculated heterotrophic respiration was statistically lower compared with two previous studies dealing with soil CO₂ efflux partitioning (one performed in the same study area; the other a meta-analysis of soil respiration partitioning). These differences were probably due to the heterogeneity of the SOM fraction and to a sub-optimal choice of the litter sampling period.     

Metabolism of polychlorinated dibenzo-p-dioxins by rat liver microsomes.

The in vitro metabolism of several chlorinated dibenzo-p-dioxin congeners (PCDDs) was studied using rat liver microsomes as a source of CYP 1 enzymes. The reactions were kinetically first order in both enzyme and substrate and showed a general trend toward decreasing reactivity with increasing chlorination. Michaelis-Menten kinetics were followed for 1-chlorodibenzo-p-dioxin (1-CDD); the reactivity of the enzyme preparation toward 1-CDD exactly paralleled its activity toward 7-ethoxyresorufin. The unreactive congeners 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD) and 2,2'-dichlorobiphenyl (2,2'-DCB) acted as competitive inhibitors toward 1-CDD, with inhibition constants in the micromolar range, similar to the value of the Michaelis constant of 1-CDD. The inhibitory potency of furafylline, a mechanism-based inhibitor that is selective for CYP 1A2, declined in the order acetanilide (standard) > 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) > 1-CDD. We conclude that 1-CDD and 1,2,3,4-TCDD are oxidized almost exclusively by CYP 1A1, whereas 2,3,7,8-TCDD and 1,2,4,7,8-PeCDD are oxidized mainly by CYP 1A2. 1,2,3,7,8-PeCDD was oxidized too slowly for us to reach any conclusion about the P450 isozyme responsible.     

Influence of interactions between litter decomposition and rhizosphere activity on soil respiration and on the temperature sensitivity in a subtropical montane forest in SW China

Aims

The aims were to identify the effects of interactions between litter decomposition and rhizosphere activity on soil respiration and on the temperature sensitivity of soil respiration in a subtropical forest in SW China.

Methods

Four treatments were established: control (CK), litter removal (NL), trenching (NR) and trenching together with litter removal (NRNL). Soil CO₂ efflux, soil temperature, and soil water content were measured once a month over two years. Soil respiration was divided into four components: the decomposition of basic soil organic matter (SOM), litter respiration, root respiration, and the interaction effect between litter decomposition and rhizosphere activity. A two-factor regression equation was used to correct the value of soil CO₂ efflux.

Results

We found a significant effect of the interaction between litter decomposition and rhizosphere activity (R _INT) on total soil respiration, and R _INT exhibited significant seasonal variation, accounting for 26 and 31 % of total soil respiration in the dry and rainy seasons, respectively. However, we found no significant interaction effect on the temperature sensitivity of soil respiration. The temperature sensitivity was significantly increased by trenching compared with the control, but was unchanged by litter removal.

Conclusions

Though the interaction between litter decomposition and rhizosphere activity had no effects on temperature sensitivity, it had a significant positive effect on soil respiration. Our results not only showed strong influence of rhizosphere activity on temperature sensitivity, but provided a viable way to identify the contribution of SOM to soil respiration, which could help researchers gain insights on the carbon cycle.     

Integrated management systems and N fertilization: effect on soil organic matter in rice-rapeseed rotation

Aims

Understanding the effects of long-term crop management on soil organic matter (SOM) is necessary to improve the soil quality and sustainability of agroecosystems.

Method

The present 7-year long-term field experiment was conducted to evaluate the effect of integrated management systems and N fertilization on SOM fractions and carbon management index (CMI). Two integrated soil-crop system management (ISSM-1 and ISSM-2, combined with improved cultivation pattern, water management and no-tillage) were compared with a traditional farming system at three nitrogen (N) fertilization rates (0, 150 and 225 kg N ha^?1).

Results

Management systems had greater effects on SOM and its fractions than did N fertilization. Compared with traditional farming practice, the integrated management systems increased soil organic carbon (SOC) by 13 % and total nitrogen (TN) by 10 % (averaged over N levels) after 7 years. Integrated management systems were more effective in increasing labile SOM fractions and CMI as compared to traditional farming practice. SOC, TN and dissolved organic matter in nitrogen increased with N fertilization rates. Nonetheless, N addition decreased other labile fractions: particulate organic matter, dissolved organic matter in carbon, microbial biomass nitrogen and potassium permanganate-oxidizable carbon.

Conclusions

We conclude that integrated management systems increased total SOM, labile fractions and CMI, effectively improved soil quality in rice-rapeseed rotations. Appropriate N fertilization (N150) resulted in higher SOC and TN. Though N application increased dissolved organic matter in nitrogen, it was prone to decrease most of the other labile SOM fractions, especially under higher N rate (N250), implying the decline of SOM quality.     

The Impact of Corn Residue Removal on Soil Aggregates and Particulate Organic Matter

Removal of corn (Zea mays L.) stover as a biofuel feedstock is being considered. It is important to understand the implications of this practice when establishing removal guidelines to ensure the long-term sustainability of both the biofuel industry and soil health. Aboveground and belowground plant residues are the soil’s main sources of organic materials that bind soil particles together into aggregates and increase soil carbon (C) storage. Serving to stabilize soil particles, soil organic matter (SOM) assists in supplying plant available nutrients, increases water holding capacity, and helps reduce soil erosion. Data obtained from three Corn Stover Regional Partnership sites (Brookings, SD; Morris, MN; and Ithaca, NE) were utilized to evaluate the impact of removing corn stover on soil physical properties, including dry aggregate size distribution (DASD), erodible fraction (EF), and SOM components. Each site consisted of a combination of three residue removal rates (low—removal of grain only, intermediate—approximately 50 % residue removal, and high—maximum amount of residue removal). Results showed that the distribution of soil aggregates was less favorable for all three locations when residue was removed without the addition of other sources of organic matter such as cover crops. Additionally, we found that when residue was removed and the soil surface was less protected, there was an increase in the EF at all three research sites. There was a reduction in the EF for both the Brookings, SD, and Ithaca, NE sites when cover crops were incorporated or additional nitrogen (N) was added to the system. Amounts of SOM, fine particulate organic matter (fPOM), and total particulate organic matter (tPOM) consistently decreased as greater amounts of residue were removed from the soil surface. Across these three locations, the removal of crop residue from the soil surface had a negative impact on measured soil physical properties. The addition of a cover crop or additional N helped reduce this impact as measured through aggregate size distribution and EF and SOM components.     

Soil organic matter accounting in the carbon footprint analysis of the wine chain

Purpose

Concerns about global warming led to the calculation of the carbon footprint (CF) left by human activities. The agricultural sector is a significant source of greenhouse gas (GHG) emissions, though cropland soils can also act as sinks. So far, most LCA studies on agricultural products have not considered changes in soil organic matter (SOM). This paper aimed to: (1) integrate the Hénin–Dupuis SOM model into the CF study and (2) outline the impacts of different vineyard soil management scenarios on the overall CF.

Methods

A representative wine chain in the Maremma Rural District, Tuscany (Italy), made up of a cooperative winery and nine of its associated farms, was selected to investigate the production of a non-aged, high-quality red wine. The system boundary was established from vineyard planting to waste management after use. The functional unit (FU) chosen for this study was a 0.75-L bottle of wine, and all data refer to the year 2009. The SOM balance, based on Hénin–Dupuis’ equation, was integrated and run using GaBi4 software. A sensitivity analysis was performed, and four scenarios were developed to assess the impact of vineyard soil management types with decreasing levels of organic matter inputs.

Results and discussion

SOM accounting reduced the overall CF of one wine bottle from 0.663 to 0.531 kg CO₂-eq/FU. The vineyard planting sub-phase produced a loss of SOM while, in the pre-production and production sub-phases, the loss/accumulation of SOM was related to the soil management practices. On average, soil management in the production sub-phase led to a net accumulation of SOM, and the overall vineyard phase was a sink of CO₂. Residue incorporation and grassing were identified as the main factors affecting changes in SOM in vineyard soils.

Conclusions

Our results showed that incorporating SOM accounting into the wine chain’s CF analysis changed the vineyard phase from a GHG source to a modest net GHG sink. These results highlighted the need to include soil C dynamics in the CF of the agricultural product. Here, the SOM balance method proposed was sensitive to changes in management practices and was site specific. Moreover, we were also able to define a minimum data set for SOM accounting. The EU recognises soil carbon sequestration as one of the major European strategies for mitigation. However, specific measures have yet to be included in the CAP 2020. It would be desirable to include soil in the new ISO 14067—Carbon Footprint of Products.     

典型矿冶区周边土壤微生物功能特征及影响因素

土壤微生物对重金属污染胁迫敏感,但在实际野外环境中,土壤微生物群落生态效应通常是污染胁迫和环境因素综合作用的结果。为探究重金属污染土壤中微生物群落生态效应发生变化的主控因素,本研究以湖南省某典型矿冶区周边不同土地利用类型土壤为研究对象,以土壤碳氮循环过程主要的微生物功能指标土壤微生物生物量碳(MBC)、基础呼吸(BR)、诱导呼吸(SIR)和硝化潜势(PNR)为生态效应终点,进行采样调查分析。结果表明: 土地利用类型对MBC、BR和SIR影响均不显著;研究区土壤微生物功能的主要影响因子包括CaCl₂提取态Pb(CaCl₂-Pb)含量与土壤有机质(SOM)含量。多元回归分析结果表明,在CaCl₂-Pb含量为0.004～13.14 mg·kg^-1及SOM含量为0.24%～4.34%的条件下,土壤CaCl₂-Pb和SOM含量可以共同解释土壤中BR、SIR和PNR总变异的39.8%～58.3%;中等含量下(SOM在1.70%～2.36%,CaCl₂-Pb在0.004～12.98 mg·kg^-1),土壤CaCl₂-Pb和SOM含量与BR、SIR和PNR的变化能够建立显著的暴露-效应关系,可以作为测定终点定量评价重金属污染对微生物群落功能的生态效应。     

Effects of agriculture and wetland restoration on hydrology, soils, and water quality of a Carolina bay complex

We compared hydrology, soils, and water quality of an agricultural field (AG), a two-year-old restored wetland (RW), and two reference ecosystems (a non-riverine swamp forest (NRSF) and a high pocosin forest (POC)) located at the Barra Farms Regional Wetland Mitigation Bank, a Carolina bay complex in Cumberland County, North Carolina. Our main objectives were to: 1) determine if the RW exhibited hydrology comparable to a reference ecosystem, 2) characterize the soils of the AG, RW, and reference ecosystems, and 3) assess differences in water quality in the surface outflow from the AG, RW, and reference ecosystems. Water table data indicated that the hydrology of the RW has been successfully reestablished as the hydroperiod of the RW closely matched that of the NRSF in 1998 and 1999. Jurisdictional hydrologic success criterion was also met by the RW in both years. To characterize soil properties, soil cores from each ecosystem were analyzed for bulk density (D_b), total carbon (C_t), nitrogen (N_t), and phosphorus (P_t), extractable phosphate (PO_4w), nitrogen (N_ex), and cations (Ca_ex, Mg_ex, K_ex, Na_ex), as well as pH. Bulk density, P_t, Ca_ex, Mg_ex, and pH were greatly elevated in the AG and RW compared to the reference ecosystems. Water quality monitoring consisted of measuring soluble reactive phosphorus (SRP), total phosphorus (TP), nitrate + nitrite (NOX), and total nitrogen (TN) concentrations in surface water from the AG, RW, and reference outflows. Outflow concentrations of SRP, TP, and NOX were highest and most variable in the AG, while TN was highest in the reference. This study suggested that while restoration of wetland hydrology has been successful in the short term, alteration of wetland soil properties by agriculture was so intense, that changes due to restoration were not apparent for most soil parameters. Restoration also appeared to provide water quality benefits, as outflow concentrations of SRP, TP, NOX, and TN were lower in the RW than the AG.     

Roles of shoots and roots in cadmium uptake and distribution in tubers of potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L)

Aims

We investigated whether density fractionation can be used to determine the distribution of organic phosphorus (OP) between free and mineral-associated soil organic matter (SOM).

Methods

We performed density fractionations using sodium polytungstate solution (specific gravity 1.6 g cm^?3) on 20 soils from UK semi-natural and pasture ecosystems, to obtain a light fraction (LF) and a heavy fraction (HF) for each soil. The fractions were quantified by weight, and analysed for organic carbon (OC), total N (TN), total P (TP), inorganic P (IP), and OP (by difference).

Results

Good recoveries of soil mass (96%), OC and TN (both ~ 90%) were obtained, but recovery of OP only averaged 56%. The average P:C ratio of HF SOM exceeded that of LF SOM by a factor of six, greater than the factor of two obtained for TN:OC. For the soils studied, the elements of SOM were predominantly in the HF, with averages of 75% for C, 82% for N, and 90% for P.

Conclusions

The incomplete recovery of OP demands further work. Nonetheless, the results show that HF SOM is much richer in P than LF SOM.

     

黄土高原不同生态治理小流域土壤有机质、容重及黏粒含量的对比

为探讨不同生态治理小流域土壤性质的差异,本研究分别从坡向、坡位、区段和土层4个方面分析了人工刺槐林流域杨家沟(YJG)与封禁荒草地流域董庄沟(DZG)土壤有机质(SOM)、土壤容重(BD)和黏粒含量(CC)的空间分异.结果表明: YJG与DZG的SOM、BD、CC分别为12.78 g·kg^-1、1.24 g·cm^-3、19.2%与11.13 g·kg^-1、1.21 g·cm^-3、18.2%,前者均略高,但差异不显著.各指标均为东坡大于西坡;SOM和CC顺坡向下有增加趋势,BD变异最小;SOM由上游至下游呈增大趋势,BD和CC不断减小;由土表向下至60 cm土深,BD和CC不断增大,SOM不断减小.各指标的空间敏感性依次为CC＞SOM＞BD,空间因素的影响效用依次为土层＞区段＞坡向＞坡位.上游CC、中游BD和CC在两流域间的差异显著,各指标对坡位、区段、土层的敏感性均为YJG＜DZG.     

Annual burning of a tallgrass prairie inhibits C and N cycling in soil,increasing recalcitrant pyrogenic organic matter storage while reducing N availability

Grassland ecosystems store an estimated 30% of the world's total soil C and are frequently disturbed by wildfires or fire management. Aboveground litter decomposition is one of the main processes that form soil organic matter (SOM). However, during a fire biomass is removed or partially combusted and litter inputs to the soil are substituted with inputs of pyrogenic organic matter (py‐OM). Py‐OM accounts for a more recalcitrant plant input to SOM than fresh litter, and the historical frequency of burning may alter C and N retention of both fresh litter and py‐OM inputs to the soil. We compared the fate of these two forms of plant material by incubating ¹³C‐ and ¹⁵N‐labeled Andropogon gerardii litter and py‐OM at both an annually burned and an infrequently burned tallgrass prairie site for 11 months. We traced litter and py‐OM C and N into uncomplexed and organo‐mineral SOM fractions and CO₂ fluxes and determined how fire history affects the fate of these two forms of aboveground biomass. Evidence from CO₂ fluxes and SOM C:N ratios indicates that the litter was microbially transformed during decomposition while, besides an initial labile fraction, py‐OM added to SOM largely untransformed by soil microbes. Additionally, at the N‐limited annually burned site, litter N was tightly conserved. Together, these results demonstrate how, although py‐OM may contribute to C and N sequestration in the soil due to its resistance to microbial degradation, a long history of annual removal of fresh litter and input of py‐OM infers N limitation due to the inhibition of microbial decomposition of aboveground plant inputs to the soil. These results provide new insight into how fire may impact plant inputs to the soil, and the effects of py‐OM on SOM formation and ecosystem C and N cycling.     

Soil carbon pool structure and temperature sensitivity inferred using CO2 and 13CO2 incubation fluxes from five Hawaiian soils

We measured respiration and ¹³C values of respiredand soil carbon in long-term incubations of soils from two forests andthree pastures along an altitudinal gradient in Hawaii. CO₂fluxes early in the incubations decreased rapidly, and then stabilizedat approximately 20% of initial values for sevenmonths. We suggest that the rapid drop and subsequent stabilizationof respiration reflects a change in the dominant source of theCO₂ from labile (active) to much more recalcitrantpools of soil organic matter (SOM). Estimates of active SOM weremade by integrating all of the carbon respired in excess of thatattributable to respiration of the intermediate SOM pool; thesevalues ranged from 0.7–4.3% of total soil C.¹³C values for carbon respired from the pasturesoils showed that older, forest-derived C contributed an increasingfraction of total soil respiration with time. Initial and late-stagerespiration responded similarly to changes in temperature, suggestingthat intermediate SOM is as sensitive to temperature as the activefraction.     

Towards understanding the traits contributing to performance of pearl millet open-pollinated varieties in phosphorus-limited environments of West Africa

Background and aims

Arbuscular mycorrhizal (AM) hyphae represent an important route for input of plant-derived C to soil, but impacts of these inputs on microbial communities and processes are poorly understood. In this study we characterised pathways of C-flow through microbial communities associated with AM hyphae and quantified impacts on mineralisation of native SOM.

Methods

Continuous, steady-state ¹³CO₂ labelling was applied throughout the growth period (60 d) of Lolium perenne. Exclusion meshes were used to control access of roots and AM hyphae to soil, and plant-derived C was quantified within microbial PLFA and NLFA, and soil CO₂ efflux was partitioned into plant- and soil organic matter (SOM) derived components.

Results

Pathways of C-flow through hyphosphere and mycorrhizosphere communities were distinct, as was the fate of plant-derived C from AM hyphae accessing soil through 37 and 1 μm meshes. Mineralisation of native SOM was increased in all treatments, relative to unplanted controls, and this priming effect was largest for AM hyphae accessing soil through the 1 μm mesh size.

Conclusions

We demonstrated that AM hyphae can strongly increase mineralisation of native SOM and identified distinct pathways of C-flow through hyphosphere communities. Our results suggest that, in addition to affecting rates of litter decomposition, AM hyphae may have a significant influence on turnover of native SOM.

     

Comparison of methane, nitrous oxide fluxes and CO2 respiration rates from a Mediterranean cork oak ecosystem and improved pasture

Background and aims

During the recent decades, cork oak (Q. suber) mortality has been increasing in Mediterranean oak woodland endangering the economical and environmental sustainability of the “montado” ecosystem. This fact in combination with climate change and conversion of forestland to pasture may significantly affect the soil-atmosphere greenhouse gases (GHGs) exchange. Our study evaluates the impact of oak trees as compared to pasture on net ecosystem GHG (CH_4, N₂O, and CO₂) exchange as well as the main environmental factors influencing this exchange.

Methods

We used field chamber measurements for the collection of GHGs under three different conditions: 1) open area (OA), 2) under tree canopy area (UC) and 3) improved pasture (IP). Experiments were done under typical Mediterranean climate at central Portugal in 2010 and 2011.

Results

The UC had higher nitrification potential, soil C/N ratio, electrical conductivity, litter input and soil organic matter (SOM) than OA and IP. SOM positively correlated with soil CH₄ and N₂O fluxes but not with soil CO₂ respiration rates. Soil water content (SWC) drives both CH₄ and N₂O fluxes. Under certain conditions, when SWC reached a threshold (7 % for CH₄ and 3 % for N₂O) the result was net uptake and that net uptake increased with SWC. This was the case for the UC and OA. Conversely, for the IP soil water content above 4 % promoted net CH₄ release.

Conclusions

Our results show that cork oak influences soil properties and consequently GHGs fluxes. In the UC the input of litter for SOM together with soil moisture, favoured microbiological activity and related GHGs fluxes. Soil temperature is a secondary factor in the studied conditions. Our results also emphasized the potential impact posed by decreased cork oak tree density in the functioning of the “montado” ecosystem.     

Linking Above- and Belowground Responses to 16 Years of Fertilization,Mowing, and Removal of the Dominant Species in a Temperate Grassland

Species-rich oligotrophic meadows are affected by a wide range of management interventions that influence their functioning and capacity to deliver ecosystem services, but long-term studies on the above- and belowground adaptations to different management tools are still scarce. We focused on the interactive effects of NPK fertilization, mowing, and removal of the initially dominant species (Molinia caerulea) on plant, soil, and microbial responses in wet oligotrophic grassland in a 16-year full-factorial manipulative experiment. Changes in vegetation composition, soil pH, and nutrient availability were accompanied by altered microbial phospholipid fatty acid (PLFA) composition, whereas treatment effects on soil microbial biomass and carbon (C) mineralization were mainly related to changes in soil organic matter (SOM) content and nutrient availability. Fertilization decreased plant species richness aboveground and lowered SOM storage and microbial activity belowground. Mowing preserved high plant diversity and led to more efficient recycling of N within the grassland, whereas Molinia removal significantly affected only plant community composition. Mowing combined with fertilization maintained high species richness only in the short term. Belowground, mowing reduced N leaching from the fertilized system but did not prevent SOM depletion, soil acidification, and concomitant adverse effects on soil microbes. We conclude that annual mowing is the appropriate type of extensive management for oligotrophic species-rich meadows, but the concomitant nutrient depletion should not be compensated for by regular NPK fertilization due to its adverse effects on soil quality.