Strukturelle und funktionelle Charakterisierung von mikrobiellen Gemeinschaften in ökologisch und konventionell bewirtschafteten Agrarböden

Soil samples from the DOK long-term field trial were investigated to study influences of different farming systems on structure and function of soil microbial communities. The DOK long-term field trial in Switzerland consists of plots managed bio-dynamically (D), bio-organically (O), conventionally (K) and of those which are managed conventionally but only receive mineral fertilizer (M). In spring 2003 soil samples from these differently managed plots were taken. All investigated fields were planted with winter wheat in 2003, but with different croppings in 2002: potato and maize cultivation, respectively. Analyses of phospholipid fatty acids (PLFA) and phospholipid etherlipids (PLEL) were carried out to determine bacterial, eukaryotic and archaeal phenotypic diversity. By combining this technique with isotope ratio mass spectrometry (GC/MS-C-IRMS) it was possible to analyse simultaneously 13C/12C ratios in PLFA and PLEL biomarkers for functional analyses of the soil microbiota. First results revealed differences in the total microbial biomass and community structure among the compared farming systems. Furthermore, the incorporation of the maize derived carbon could be detected in several PLFA at the natural abundance level. This may be an indication for the role of different microbial groups during organic matter degradation

Carbon allocation and carbon isotope fluxes in the plant-soil-atmosphere continuum: a review

The terrestrial carbon (C) cycle has received increasing interest over the past few decades, however, there is still a lack of understanding of the fate of newly assimilated C allocated within plants and to the soil, stored within ecosystems and lost to the atmosphere. Stable carbon isotope studies can give novel insights into these issues. In this review we provide an overview of an emerging picture of plant-soil-atmosphere C fluxes, as based on C isotope studies, and identify processes determining related C isotope signatures. The first part of the review focuses on isotopic fractionation processes within plants during and after photosynthesis. The second major part elaborates on plant-internal and plant-rhizosphere C allocation patterns at different time scales (diel, seasonal, interannual), including the speed of C transfer and time lags in the coupling of assimilation and respiration, as well as the magnitude and controls of plant-soil C allocation and respiratory fluxes. Plant responses to changing environmental conditions, the functional relationship between the physiological and phenological status of plants and C transfer, and interactions between C, water and nutrient dynamics are discussed. The role of the C counterflow from the rhizosphere to the aboveground parts of the plants, e.g. via CO<sub>2</sub> dissolved in the xylem water or as xylem-transported sugars, is highlighted. The third part is centered around belowground C turnover, focusing especially on above- and belowground litter inputs, soil organic matter formation and turnover, production and loss of dissolved organic C, soil respiration and CO<sub>2</sub> fixation by soil microbes. Furthermore, plant controls on microbial communities and activity via exudates and litter production as well as microbial community effects on C mineralization are reviewed. A further part of the paper is dedicated to physical interactions between soil CO<sub>2</sub> and the soil matrix, such as CO<sub>2</sub> diffusion and dissolution processes within the soil profile. Finally, we highlight state-of-the-art stable isotope methodologies and their latest developments. From the presented evidence we conclude that there exists a tight coupling of physical, chemical and biological processes involved in C cycling and C isotope fluxes in the plant-soil-atmosphere system. Generally, research using information from C isotopes allows an integrated view of the different processes involved. However, complex interactions among the range of processes complicate or currently impede the interpretation of isotopic signals in CO<sub>2</sub> or organic compounds at the plant and ecosystem level. This review tries to identify present knowledge gaps in correctly interpreting carbon stable isotope signals in the plant-soil-atmosphere system and how future research approaches could contribute to closing these gaps

Biowastes to augment the essential oil production of Leptospermum scoparium and Kunzea robusta in low-fertility soil

Biowastes are unwanted materials of biological origin. They include biosolids, dairy shed effluent, and sawdust. When applied to soil, biowastes can provide plant nutrients, but also introduce heavy metals, pathogens, or xenobiotics. Biowastes could improve degraded or low-fertility soils and generate revenue through the production of non-food products such as essential oils. We grew New Zealand native plants, mānuka (Leptospermum scoparium J.R. Forst & G. Forst) and kānuka (Kunzea robusta de Lange & Toelken) in series of greenhouse experiments in low-to-medium-fertility soils (Bideford clay loam, Lismore stony silt loam, and Pawson silt loam) amended with either biosolids (up to 13500 kg N ha⁻¹ equiv.), biosolids + sawdust (1:0.5–1250 kg N ha⁻¹ equiv.) and dairy shed effluent (200 kg N ha⁻¹ equiv.). Two types of biosolids from Kaikoura (KB) and Christchurch City Council (CB) were used in the experiments. CB (1500 kg N ha⁻¹ equiv.) and dairy shed effluent (200 kg N ha⁻¹ equiv.) increased the biomass of L. scoparium by up to 120% and 31%, and K. robusta by up to 170% and 34%, respectively. Adding sawdust to KB increased the biomass of L. scoparium and K. robusta although it offset the L. scoparium growth increase in the KB-only treatment. The growth response of K. robusta to biowastes was greater than L. scoparium with oil production in K. robusta increasing by up to 211% when 1500 kg N ha⁻¹ equiv. of CB was applied to Lismore stony silt loam. Generally, the treatments had a negligible effect on oil concentration in all the soil types, except for the KB + sawdust treatment, which increased the oil concentration by 82%. Most of the EOs’ major components were unaffected by biowaste addition in the soils, although some components increased in the Bideford clay loam following KB and KB + sawdust application. Biosolids increased foliar concentrations of Zn, Cu, and Cd, but these were below risk-threshold concentrations. Applying CB (up to 1500 kg N ha⁻¹ equiv.) to low-fertility soils is recommended to establish ecosystems dominated by L. scoparium and K. robusta that annually would produce ca. 100 kg ha⁻¹ of EOs worth US$ 26k and 24k, respectively. Adding sawdust to CB could have environmental benefits through reduction of N leaching. Field trials are warranted to elucidate critical ecological variables and production economics in biowaste management

Response of Leptospermum scoparium, Kunzea robusta and Pinus radiata to contrasting biowastes

The myrtaceae family has a cosmopolitan distribution and includes the Australasian native species Leptospermum scoparium (mānuka) and Kunzea robusta (kānuka), which are of economic interest for the production of high-value honey and essential oils. Potentially, these species could be established on low-fertility or degraded soils that have been amended with biowastes, including biosolids and sawdust. We aimed to determine the effect of these biowastes on nitrate leaching and the growth and chemical composition of these plant species compared to Pinus radiata (pine), a common forestry species. The addition of biosolids (1250 kg N ha⁻¹ equiv.) increased the total dry biomass of mānuka, kānuka, and pine by 117, 90, and 86% respectively. Mixing sawdust with biosolids stimulated growth of mānuka (52%), kānuka (121%) but not pine. Biosolids increased plant uptake of N, P, and trace elements, but not to levels of concern. Nitrate leaching from all treatments was negligible (<2 kg ha⁻¹)

The potential of L. scoparium, K. robusta and P. radiata to mitigate N-losses in silvopastural systems

Silvopastoral systems aim to enhance economic, cultural and social principles by sustainably combining forest management with agriculture. In these typically high-nitrogen (N) environments, plant species selection can profoundly influence N fluxes. For grazed pastures, plants may be exposed to urine patches that have received the equivalent of up to 1000 kg N ha⁻¹. We aimed to determine the growth and N fluxes in three potential trees that may be used in silvopastoral systems: L. scoparium, K. robusta and P. radiata. Plants were grown in a greenhouse lysimeter experiment, with controlled irrigation and temperature and exposed to N at rates of 200 kg ha⁻¹ equiv. for 15 weeks, followed by the addition of 800 kg ha⁻¹ N equiv, to simulate a urine patch. Urea produced a positive growth response of all plant species. Treatments containing L. scoparium and K. robusta leached lower amounts of nitrate (NO₃−) (2 kg ha⁻¹ NO₃−) compared to P. radiata (53 kg ha⁻¹). Measurements of N₂O over 20 days after the application of 800 kg N ha⁻¹ indicated an inhibitory effect of L. scoparium and K. robusta on denitrification, hence loss of N via N₂O. Both L. scoparium and K. robusta demonstrated that they have potential to reduce N-losses in silvopastural systems, while producing valuable biomass.Plant & Food Research (Blueskies fund) and Environmental Science and Research (Pioneer fund)

Biowastes promote essential oil production on degraded soils

Biowastes (wastes of biological origin) can improve soil fertility but may render the land unsuitable for food production because they introduce contaminants, including heavy metals, pathogens and xenobiotics. We investigated whether sewage waste (pond sludge from Kaikoura and anaerobically-digested biosolids from Christchurch) and Dairy Shed Effluent (DSE) could improve degraded soils for the production of essential oils (EOs). We grew lavender (Lavandula angustifolia Mill.), rosemary (Rosmarinus officinalis L.) and thyme (Thymus vulgaris L.) in two greenhouse experiments in Lismore stony silt loam soil (LSL) amended with pond sludge or biosolids (500–4500 kg N ha⁻¹ equiv.) or DSE (200 kg N ha⁻¹ equiv.). Pond sludge application (2800 kg N ha⁻¹ equiv.) increased the biomass of L. angustifolia and T. vulgaris by 60 % and 62 %, respectively. Christchurch biosolids application up to 1500 kg N ha⁻¹ equiv. to L. angustifolia and R. officinalis increased the biomass of both plant species by up to 86 % and 80 %, respectively. The effect of treatments on EO concentration was insignificant in most cases except for DSE (200 kg N ha⁻¹ equiv.) and Christchurch biosolids at rates >1500 kg N ha⁻¹ equiv., which decreased the EO concentrations in R. officinalis and L. angustifolia. This decrease in EO concentration offset some of the increase in EO production resulting from the increased biomass of the biowaste-amended plants. The ideal EO production increase occurred when Christchurch biosolids were applied at 1500 kg N ha⁻¹ equiv. The benefits of biowaste additions to degraded soils are greater than would occur if they were added to high-fertility soils. Heavy metal concentrations in all treatments were below food safety standards. Biowastes could rebuild degraded soils and produce valuable EOs, thereby reducing the economic and environmental costs of biowaste disposal, while improving soil fertility and generating revenue from otherwise underproductive land

Changes in soil microbial communities as affected by intensive cattle husbandry

The present field study documents substantial changes in the soil microbial community (SMC) and organic matter (SOM) in an upland pasture soil resulting from 10 years of “cattle outdoor over-wintering practice”. Soils from a long-term investigated pasture area were compared under three different levels of cattle impact (SI – severe, MI – moderate, NI – no impact). Extended polar lipids analysis (PLA) confirmed a qualitatively new microbial community profile and a several-fold increase of the microbial biomass in the impacted soils (SI) compared to the control NI soil. The new SMC was derived from cattle intestine microorganisms, typical by increased content of archaeal phospholipid ether lipids and by new fatty acids indicative for bacterial and fungal fecal anaerobes. A quality of the SI-SOM, evaluated by the relative content of the pyrolytic fragments profile was more similar to the cattle excrements than to the MI and NI soils, and an organic carbon content of the SI soil was not more than three times higher in comparison to the control NI soil. The quality and quantity of the SOM as well as the SMC in both, the most impacted SI and the control NI soils, were stable in contrast to the moderately impacted MI soil. During the growing season, the MI soil lost 75% of the Corg and 65% of the soil microbial biomass that had accumulated during winter; its aromatic-rich-SOM showed transformation into SOM, enriched by N, P-organic derivates. This transformation was positively correlated to a significant recovery of the actinobacteria and reduction of anaerobic microorganisms during the vegetation season. Results in this study showed that the stability of the soil microbial changes due to the cattle outdoor over-wintering husbandry depended on the stability of the quantitative and qualitative changes of the SOM. © 2012 Published by Elsevier B.V

Production of biomass crops using biowastes on low-fertility soil: 1. Influence of biowastes on plant and soil quality

Land application of biosolids to low-fertility soil can improve soil quality by increasing concentrations of macronutrients and trace elements. Mixing biosolids with sawdust could reduce the risks of contaminant accumulation posed by rebuilding soils using biosolids alone. We aimed to determine the effects of biosolids and biosolids-sawdust on the plant quality and chemical composition of sorghum, rapeseed, and ryegrass. Plants were grown in a greenhouse over a 5-mo period in a low-fertility soil amended with biosolids (1250 kg N ha⁻¹), biosolids-sawdust (0.5:1), or urea (200 kg N ha⁻¹). Biosolids application increased the biomass of sorghum, rapeseed, and ryegrass up to 14.0, 11.9, and 4.1 t ha⁻¹ eq, respectively. Mixing sawdust with biosolids resulted in a growth response similar to biosolids treatments in rapeseed but nullified the effect of biosolids in sorghum. Urea fertilization provided insufficient nutrients to promote rapeseed growth and seed production, whereas seed yields after biosolids application were 2.5 t ha⁻¹. Biosolids and biosolids-sawdust application enhanced plant quality by increasing element concentrations, especially Zn, and potentially toxic elements (Cd, Cr, Ni) did not exceed food safety standards. An application of 50 t ha⁻¹ of biosolids, equivalent to 1250 kg N ha⁻¹, did not exceed current soil limits of Cu, Zn, and Cd and hence was effective in rebuilding soil without accumulating contaminants. The effect of mixing sawdust with biosolids varies with plant species but can further enhance plant nutrient quality in biomass and seeds, especially P, Cu, Zn, Mn, Fe, S, and Na