Oliver Dilly

Bacterial diversity in agricultural soils during litter decomposition

ABSTRACT Denaturing gradient gel electrophoresis (DGGE) of amplified fragments of genes coding for 16S rRNA was used to study the development of bacterial communities during decomposition of crop residues in agricultural soils. Ten strains were tested, and eight of these strains produced a single band. Furthermore, a mixture of strains yielded distinguishable bands. Thus, DGGE DNA band patterns were used to estimate bacterial diversity. A field experiment performed with litter in nylon bags was used to evaluate the bacterial diversity during the decomposition of readily degradable rye and more refractory wheat material in comparable luvisols and cambisols in northern, central, and southern Germany. The amount of bacterial DNA in the fresh litter was small. The DNA content increased rapidly after the litter was added to the soil, particularly in the rapidly decomposing rye material. Concurrently, diversity indices, such as the Shannon-Weaver index, evenness, and equitability, which were calculated from the number and relative abundance (intensity) of the bacterial DNA bands amplified from genes coding for 16S rRNA, increased during the course of decomposition. This general trend was not significant for evenness and equitability at any time. The indices were higher for the more degradation-resistant wheat straw than for the more easily decomposed rye grass. Thus, the DNA band patterns indicated that there was increasing bacterial diversity as decomposition proceeded and substrate quality decreased. The bacterial diversity differed for the sites in northern, central, and southern Germany, where the same litter material was buried in the soil. This shows that in addition to litter type climate, vegetation, and indigenous microbes in the surrounding soil affected the development of the bacterial communities in the litter.

Microbial biomass content, basal respiration and enzyme activities during the course of decomposition of leaf litter in a black alder (Alnus glutinosa (L.) Gaertn.) forest

Abstract Decomposition of leaf litter from a black alder (Alnus glutinosa (L.) Gaertn.) forest on a fen (peat soil) in Northern Germany was studied at two sites within the forest. The ‘wet’ site was adjacent to a lake and soil was water-saturated throughout most of the year. In contrast, the other site was substantially drier, especially in summer and therefore called the ‘dry’ site. The pH (H2O) value of the topsoils (horizon below litter) at the wet and dry site was 6.0 and 3.5, respectively. The litter consisted mainly of alder leaves and decomposed at different rates at the two sites. After 12 months, about 40% of the initial litter was decomposed at the dry site compared to 90% at the wet site. The water content of the litter varied seasonally, particularly at the dry site. The pH of the litter was similar to or higher than that in the underlying topsoil and decreased at the dry site after 18 months. The total C content in residual material did not change during the course of decomposition. The microbial biomass content was, with some irregularities, similar throughout the first months and then continually declined. Basal respiration decreased from an initial value of approximately 700 to 100 μg CO2 g−1 dry litter h−1 after 17 months. β-Glucosidase activity also continuously decreased during litter decomposition; protease activity decreased initially but then tended to increase. The metabolic quotient declined during the course of litter decomposition from a relatively high value to a value almost typical for soils. This decline indicates an increase in the C utilization efficiency of the microbial community as well as a shift from a zymogenous to an autochthonous microflora. Regression analyses were performed to determine correlations between properties and to evaluate factors controlling the decomposition process.

Soil microbial eco-physiology as affected by short-term variations in environmental conditions

Short-term variations in abiotic and biotic environmental conditions modify microbial metabolism. These effects were studied in an arable soil during the oat straw decomposition. Cumulative CO2 evolution was significantly higher when soil was subjected weekly to drying‐ rewetting cycles (DR) or had been initially fertilised with nitrogen (þ N, as NH4NO3) in comparison to samples incubated at constant conditions (CC). The microbial metabolic quotient (respiration rate per unit microbial C) of DR and þN exceeded CC by approximately 100‐ 150%, indicating that variable water availability and improved N availability induced a higher activity level of the microbial biomass. In addition, the metabolic-responsive microbial communities, calculated by the ratio of microbial C estimated by substrate-induced respiration to fumigation ‐ extraction technique, increased from 1.0 to approximately 1.3 after 7 weeks for DR and þ N, but remained essentially at 1.0 for CC and control. A high abundance of soil nematodes significantly affected respiration rate, metabolic-responsive biomass and metabolic quotient during the early stages of decomposition. We concluded that short-term variation in environmental conditions promoted decomposition processes by influencing the physiology of soil microorganisms and increasing the metabolic-responsive biomass. Such a stimulated microbial metabolism seems to be unspecific due to stressing environmental conditions. The role of the interacting fauna such as nematodes varied during decomposition. q 2002 Elsevier Science Ltd. All rights reserved.

Ex Ante Impact Assessment of Policies Affecting Land Use, Part A: Analytical Framework

Contemporary policy making calls for scientific support to anticipate the possible consequences of optional policy decisions on sustainable development. This paper presents an analytical framework for ex ante assessment of economic, social, and environmental impacts of policy driven land use changes that can be used as an aid to policy making. The tasks were to (1) link policy scenarios with land use change simulations, (2) link land use change simulations with environmental, social, and economic impacts through indicators, and (3) valuate the impacts in the context of sustainable development. The outcome was a basis for dialogue at the science-policy interface in the process of developing new policies on the European level that impact on land and land use. The analytical approach provides a logical thread for ex ante impact assessment within the context of sustainable development, land use multifunctionality, and land use change and it provides a thorough discussion of achievements and open challenges related to the framework. It concludes with considerations on the potential for using evidence based ex ante assessments in the process of policy development. The paper is complemented by a B-paper providing exemplary results from two applications of the framework: a financial reform scenario of the Common Agricultural Policy of the European Union, and a bioenergy policy scenario for the case of Poland (Helming et al. 2011).

Ex ante impact assessment of land use changes in European regions: the SENSOR approach

Land use includes those human activities that exhibit a spatial dimension and that change the bio-geophysical conditions of land. Land use policy making at European level aims at fostering sustainability pathways of natural resource use and rural development through the decoupling of economic growth from environmental degradation while supporting social cohesion in rural areas. Targeted policy making requires tools for the ex ante assessment of impacts of policy driven land use changes on sustainable development opportunities in European regions. These tools have to cover all relevant land use sectors and impact issues including their interrelations. They have to be spatially explicit, allow scenario analysis of possible future developments, be based on reproducible analyses, and be transparent and easy to use. The European Commission funded Integrated Project SENSOR is dedicated to develop such ex-ante Sustainability Impact Assessment Tools (SIAT) for land use in European regions. SIAT is designed as a meta modelling toolkit, in which global economic trend and policy scenarios are translated into land use changes at 1km2 grid resolution for the area of Europe. Based on qualitative and quantitative indicator analyses, impacts of simulated land use changes on social, environmental and economic sustainability issues are assessed at regional (NUTS2/3) scale. Valuation of these impacts is based on the concept of multifunctionality of land use. It is conducted through expert and stakeholder valuations leading to the determination of sustainability choice spaces for European regions. This paper presents the analytical approach in SENSOR and describes the impact assessment framework.

Microbial Energetics in Soils

Microbial communities in soil represent a high diversity and density of biotic interactions. Fungi and bacteria dominate the microbial biomass and the potential activity is generally restricted by low nutrient availability in soil. Fresh plant residues and exudates provide the main internal source of nutrients in natural ecosystems. Substrate input rapidly stimulates catabolic and anabolic processes leading to high metabolic and microbial quotients. The respiratory quotient is additionally increased under growth conditions. The interaction between respiration, microbial C and organic C content in soil is discussed with reference to an integrative energetic indicator for soil organic matter quality.

Soil microbial activities in Luvisols and Anthrosols during 9 years of region-typical tillage and fertilisation practices in northern Germany

In order to evaluate soil functions of contemporary agricultural management practices, the adjustment of microbial biomass and C and N mineralisation capacities was monitored during 9 years following the implementation of conventional and reduced tillage, and mineral N and pig slurry fertilisation systems. Soil microbial biomass content and microbial activities decreased continuously from initial values. The decrease was slowed by slurry application, compared to either no or mineral N fertilisation, and both slurry and mineral N application stimulated soil microbial activities in the long-term. There were no significant differences in microbiological characteristics between conventional and reduced tillage for the 0 to 30 cm soil depth but microbial biomass and activity were highest from 0 to 15 cm depth under reduced tillage. Changes in several microbial properties became evident when analysing the whole experiment of 9 years and the soil unit is also of importance as shown by higher microbial activity level in Anthrosols in comparison to Luvisols.

Predation on fungal and bacterial biomass in a soddy-podzolic soil amended with starch, wheat straw and alfalfa meal

The variation in bacterial, fungal and total microbial biomass and activity was studied together with the abundance of soil nematodes and microarthropods after the addition of substrates differing in nitrogen availability to a soddy-podzolic soil. The experiments were carried out in microcosms with native and defaunated soil to evaluate stimulatory and suppressive effects of the microfauna on soil micro-organisms. Predation by microfauna (nematodes) and mesofauna (microarthropods) reduced the microbial biomass and microbial respiration by approximately 25% after addition of nitrogen rich alfalfa meal. When starch and wheat straw were supplied, the microbial biomass and activity were stimulated by up to 30% by grazing. Thus, the effect of predation on the microbiota depended on the composition of the available substrates and available nitrogen seems to be an important factor controlling stimulation or suppression of soil micro-organisms by the soil fauna when fresh organic compounds are accessible. The presence of soil fauna stimulated bacteria and, thus, reduced the fungal/bacterial ratio during the course of decomposition. In contrast, the fungal/bacterial ratio declined due to decreasing fungal biomass in defaunated soil.

Microbial eco-physiology of degrading aral sea wetlands: Consequences for C-cycling

Abstract The effects of elevated salinity level on the physiology of microbial communities and C-cycling were evaluated in soils located in areas near the degraded Aral Sea. One site on a freshwater wetland (FW) and two sites on a salt water wetland on the eastern (EW) and northern shores (NW) with salt contents of 1.1, 34.3, and 78.9 g L-1, respectively, were selected. The total microbial biomass estimated by fumigation-extraction and the respiration rate were lower at the two sites with elevated salinity level (EW and NW) than in FW while the amount of extractable organic carbon (EOC) was higher. The EOC/biomass-C ratio as an index of carbon supply was highest in NW where the lowest microbial activity was detected, indicating the restriction of microbial metabolism. Thus elevated salinity level appeared to restrict microbial colonization of organic substrates and C transformation rate but to increase the amount of soil available C. Difference in precipitation (rain events) between 2002 and 2003 did not affect the respiration rate and surface CO2 flux in FW. In NW, the respiration rate increased by more than 5 times, suggesting that in the ecosystems with a high content of available C, elevated CO2 emissions may occur under changing environmental conditions.

Characteristics and energetic strategies of the rhizosphere in ecosystems of the Bornhöved Lake district

This paper reviews investigations on interactions between soil microbiota, and plants during the interdisciplinary program ‘Ecosystem research in the Bornhoved Lake district’; it deals with processes associated with the rhizosphere at four agricultural, and forest ecosystems. Emphasis was placed on a black alder forest representing the interface between terrestrial and aquatic ecosystems. In the alder forest, more than 96% of the alder roots were colonised by ectomycorrhizal fungi. The diversity and vitality of these mycorrhizal rootlets exhibited local differences being generally lower at a dystric-dry site compared to an eutric-wet site close to the lake. Bacterial populations typical of well-aerated arable soils and rhizosphere soils were detected in samples taken from the soil at the eutric-wet site although unfavourable anoxic conditions were assumed to occur near to the lake. The composition of the bacterial populations seems to be profoundly influenced by the plant. Furthermore, the Alnus‐Frankia-symbiosis showed a high spatial variability and was also more extensively established at the lake shore indicating both higher nitrogen requirement of the trees and higher energy supply for N 2-fixing actinomycetes by the tree. The high energy supply by the trees at the eutric-wet site could be confirmed by the soil carbon availability index. The role of plants on in situ soil respiration was estimated for agricultural and forest sites. The aggregated and modelled data for arable soil indicated that the respiration of roots and rhizosphere organisms contributed up to 40% of the total soil respiration during summer. An even higher contribution to soil respiration may have been derived from rhizomicrobial respiration in the alder forest. In conclusion, the amount of carbon delivered below ground seemed to be adjusted dependent on ecosystem type and environmental conditions. In particular, alder trees seemed to have established a beneficial environment for the microbiota in the rhizosphere.