F. García-Orenes

Changes in soil microbial community structure influenced by agricultural management practices in a mediterranean agro-ecosystem.

Agricultural practices have proven to be unsuitable in many cases, causing considerable reductions in soil quality. Land management practices can provide solutions to this problem and contribute to get a sustainable agriculture model. The main objective of this work was to assess the effect of different agricultural management practices on soil microbial community structure (evaluated as abundance of phospholipid fatty acids, PLFA). Five different treatments were selected, based on the most common practices used by farmers in the study area (eastern Spain): residual herbicides, tillage, tillage with oats and oats straw mulching; these agricultural practices were evaluated against an abandoned land after farming and an adjacent long term wild forest coverage. The results showed a substantial level of differentiation in the microbial community structure, in terms of management practices, which was highly associated with soil organic matter content. Addition of oats straw led to a microbial community structure closer to wild forest coverage soil, associated with increases in organic carbon, microbial biomass and fungal abundances. The microbial community composition of the abandoned agricultural soil was characterised by increases in both fungal abundances and the metabolic quotient (soil respiration per unit of microbial biomass), suggesting an increase in the stability of organic carbon. The ratio of bacteria:fungi was higher in wild forest coverage and land abandoned systems, as well as in the soil treated with oat straw. The most intensively managed soils showed higher abundances of bacteria and actinobacteria. Thus, the application of organic matter, such as oats straw, appears to be a sustainable management practice that enhances organic carbon, microbial biomass and activity and fungal abundances, thereby changing the microbial community structure to one more similar to those observed in soils under wild forest coverage.

Microbial recolonization and chemical changes in a soil heated at different temperatures

Samples of a Mediterranean forest soil were exposed in a muffle furnace to seven temperatures (100–700°C) for 15 min to simulate different fire intensities. Heated soils were incubated for 100 days after re-inoculation with fresh unheated soil. Immediately after heating, the extractable organic C increased with the heating temperature, reaching a maximum at 400°C. This increase in extractable organic C and nutrients in soils heated below 400°C allowed a rapid recolonization of bacteria, increasing the basal respiration. During the 100-day incubation, the cumulative values of basal respiration and carbon mineralization rates generally followed a double exponential equation in unheated and heated samples. Heating at 200°C caused a reduction of 99.6% for fungi (measured as culturable fungal propagules), which showed lower recolonization capacity than that of bacteria. Heating also caused a decrease in the organic C content of the soils, especially for the highest temperatures. As a consequence, the microbial biomass carbon recovery was short lived in heated soils. The varied effects of heating and incubation on the inorganic and organic nitrogen changes, available nutrients and metabolic quotients are also discussed. This study demonstrates that changes in soils exposed to comparatively high temperatures (>500°C) have a particularly strong impact on microbial population.

Different Patterns of Aggregate Stability in Burned and Restored Soils

The merits of soil aggregate stability determination by rainfall simulator method were studied. This method is based on the supposition that in standard conditions aggregate breakdown is proportional to the kinetic energy of the rainfall applied. We compared three experiments using four different soils. Two of the experiments were in controlled conditions and the other at field conditions. In one of the laboratory experiments we applied sewage sludge to a degraded soil from a semiarid climate. In the other laboratory experiment a forest soil was heated to 200°C, 400°C and 600°C, and we studied the effect of heat and loss of organic matter in soil aggregation. In the third experiment, carried out in the field, we studied the response of two soils affected by forest fire in different intensities. Aggregate stability percentage and organic matter content of soils were determined to establish trends between these parameters. Aggregate stability in soils subjected to rainfall simulation was used as an indicator for potential degradation or restoration processes of the soils. In some burned soils positive and negative relationships were obtained between aggregate stability percentage and organic matter soil contents due to heat-aggregation processes. It showed that the aggregate stability percentage method based on disruptive energy of a rainfall simulator could not always be used as an index of degradation or restoration of soils or both.

Long-Term Effects of Irrigation with Waste Water on Soil AM Fungi Diversity and Microbial Activities: The Implications for Agro-Ecosystem Resilience

The effects of irrigation with treated urban wastewater (WW) on the arbuscular mycorrhizal fungi (AMF) diversity and soil microbial activities were assayed on a long-term basis in a semiarid orange-tree orchard. After 43 years, the soil irrigated with fresh water (FW) had higher AMF diversity than soils irrigated with WW. Microbial activities were significantly higher in the soils irrigated with WW than in those irrigated with FW. Therefore, as no negative effects were observed on crop vitality and productivity, it seems that the ecosystem resilience gave rise to the selection of AMF species better able to thrive in soils with higher microbial activity and, thus, to higher soil fertility.

Plant community influence on soil microbial response after a wildfire in Sierra Nevada National Park (Spain)

Plant community influence on microbial response after fire has been studied in a Sierra Nevada National Park area affected by a wildfire in 2005. Two different plant communities adapted to different altitudes were selected to analyse possible differences on soil microbial recolonisation process after fire, in oak forest and high mountain shrub communities. Microbial abundance, activity and community composition were monitored to evaluate medium-term changes. Microbial abundance was studied by mean of microbial biomass carbon and plate count methods; microbial activity was analysed by microbial respiration and bacterial growth while microbial community composition was determined by analysing phospholipid fatty acid pattern. Under unburnt conditions oak forest showed higher nutrient content, pH and microbial abundance and activity values than the high mountain shrubs community. Different parameters studied showed different trends with time, highlighting important changes in microbial community composition in high mountain shrubs from first sampling to the second one. Post-fire recolonisation process was different depending on plant community studied. Highlighting fungal response and microbial activity were stimulated in burnt high mountain shrubs community whilst it was negatively affected in oak forest. Fire induced changes in oak forest were almost neutralized 20months after the fire, while high mountain shrubs community still showed fire-induced changes at the end of the study.

Relationships between soil water repellency and microbial community composition under different plant species in a Mediterranean semiarid forest

Abstract Soil water repellency (SWR) can influence many hydrological soil properties, including water infiltration, uneven moisture distribution or water retention. In the current study we investigated how variable SWR persistence in the field is related to the soil microbial community under different plant species (P. halepensis, Q. rotundifolia, C. albidus and R. officinalis) in a Mediterranean forest. The soil microbial community was determined through phospholipid fatty acids (PLFA). The relationships between microbiological community structure and the soil properties pH, Glomalin Related Soil Protein (GRSP) and soil organic matter (SOM) content were also studied. Different statistical analyses were used: Principal Component Analysis (PCA), ANOVA, Redundancy Analysis and Pearson correlations. The highest concentrations of PLFA were found in the most water repellent samples. PCA showed that microorganism composition was more dependent of the severity of SWR than the type of plant species. In the Redundancy Analysis, SWR was the only significant factor (p<0.05) to explain PLFA distributions. The only PLFA biomarkers directly related to SWR were associated with Actinobacteria (10Me16:0, 10Me17:0 and 10Me18:0). All the results suggest that a strong dependence between SWR and microbial community composition.

The impact of post-fire salvage logging on microbial nitrogen cyclers in Mediterranean forest soil

Forest fires are a regular occurrence in the Mediterranean basin. High severity fires and post-fire management can affect biological, chemical and physical properties of soil, including the composition and abundance of soil microbial communities. Salvage logging is a post-fire management strategy, which involves the removal of burnt wood from land after a fire. The main objective of this work was to evaluate the impact of post-fire salvage logging and microaggregation on soil microbial communities, specifically on the abundance of nitrogen cyclers and, thus, the potential of the soil for microbial nitrogen cycling. The abundance of nitrogen cyclers was assessed by quantification of microbial nitrogen cycling genes in soil DNA, including nifH (involved in nitrogen fixation), nirS/K and nosZ (involved in denitrification), amoA-B and amoA-Arch (involved in bacterial and archaeal nitrification, respectively). It was demonstrated that salvage logging reduced bacterial load post-fire when compared to tree retention control and resulted in significant changes to the abundance of functional bacteria involved in nitrogen cycling. Microbial gene pools involved in various stages of the nitrogen cycle were larger in control soil than in soil subjected to post-fire salvage logging and were significantly correlated with organic matter, available phosphorous, nitrogen and aggregate stability. The microaggregate fraction of the soil, which has been associated with greater organic carbon, was shown to be a hotspot for nitrogen cyclers particularly under salvage logging. The impact of post-fire management strategies on soil microbial communities needs to be considered in relation to maintaining ecosystem productivity, resilience and potential impact on climate change.

Assessment of promising agricultural management practices

iSQAPER project - Interactive Soil Quality Assessment in Europe and China for Agricultural Productivity and Environmental Resilience - aims to develop an app to advise farmers on selecting the best Agriculture Management Practice (AMPs) to improve soil quality. For this purpose, a soil quality index has to be developed to account for the changes in soil quality as impacted by the implementation of the AMPs. Some promising AMPs have been suggested over the time to prevent soil degradation. These practices have been randomly adopted by farmers but which practices are most used by farmers and where they are mostly adopted remains unclear. This study is part of the iSQAPER project with the specific aims: 1) map the current distribution of previously selected 18 promising AMPs in several pedo-climatic regions and farming systems located in ten and four study site areas (SSA) along Europe and China, respectively; and 2) identify the soil threats occurring in those areas. In each SSA, farmers using promising AMPs were identified and questionnaires were used to assess farmers perception on soil threats significance in the area. 138 plots/farms using 18 promising AMPs, were identified in Europe (112) and China (26).Results show that promising AMPs used in Europe are Crop rotation (15%), Manuring & Composting (15%) and Min-till (14%), whereas in China are Manuring & Composting (18%), Residue maintenance (18%) and Integrated pest and disease management (12%). In Europe, soil erosion is the main threat in agricultural Mediterranean areas while soil-borne pests and diseases is more frequent in the SSAs from France and The Netherlands. In China, soil erosion, SOM decline, compaction and poor soil structure are among the most significant. This work provides important information for policy makers and the development of strategies to support and promote agricultural management practices with benefits for soil quality.

Innovative Soil Management Practices (SMP) Assessment in Europe and China

(1) Instituto das Ciências Agrárias e Ambientais Mediterrânicas (ICAAM), University of Évora, Núcleo da Mitra Apartado 94 7006-554 Évora, Portugal (lbarao@uevora.pt), (2) 2 Centre for Development and Environment (CDE), University of Bern, Hallerstrasse 10, 2012 Bern, Switzerland, (3) University of Pannonia (UP), Deák F. u. 16., H-8360 Keszthely, Hungary, (4) Wageningen University (WU), The Netherlands, (5) Stichting Dienst Landbouwkundig Onderzoek (DLO), The Netherlands, (6) Gaec de la Branchette (GB), France, (7) Research Centre for Natural Resources, Environment and Society (CERNAS), College of Agriculture, Polytechnic Institute of Coimbra, Coimbra, Portugal, (8) University of Miguel Hernández (UMH), Spain, (9) Agricultural University Athens (AUA), Greece, (10) University of Ljubljana, Biotechnical Faculty, Jamnikarjeva 101, 1000 Ljubljana, Slovenia, (11) Institute for Soil Sciences and Agricultural Chemistry, Centre for Agricultural Research, Hungarian Academy of Sciences, Herman Ottó út. 15., H-1022 Budapest, Hungary, (12) National Research and Development Institute for Soil Science, Agrochemistry and Environmental Protection (ICPA), Romania, (13) Institute of Agrophysics, Polish Academy of Sciences, Doświadczalna 4, 20-290 Lublin, Poland, (14) Estonian University of Life Sciences, Institute of Agricultural and Environmental Sciences, Estonia, (15) 15 Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences (IARRP, CAAS), China, (16) Soil and Fertilizer Institute of the Sichuan Academy of Agricultural Sciences (SFI), China, (17) Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources (ISWC), China