35 research outputs found
Microbial functionality as affected by experimental warming of a temperate mountain forest soil—A metaproteomics survey
Soil microbes play an important role in terrestrial carbon (C) cycling, but their functional response to global warming remains yet unclear. Soil metaproteomics has the potential to contribute to a better understanding of warming effects on soil microbes as proteins specifically represent active microbes and their physiological functioning. To quantify warming effects on microbial proteins and their distribution among different functional and phylogenetic groups, we sampled forest soil that had been artificially warmed (+4 °C) during seven consecutive growing seasons and analyzed its metaproteomic fingerprint and linked to soil respiration as a fundamental ecosystem service. Bacterial protein abundances largely exceeded fungal abundances at the study site but protein abundances showed only subtle differences among control and warmed soil at the phylum and class level, i.e. a temperature-induced decrease in Firmicutes, an increase in Agaricomycetes and Actinobacteria, and a decrease in the Asco/Basidiomycota ratio. Community function in warmed soil showed a clear trend towards increased proteins involved in microbial energy production and conversion, related to the increased CO2 efflux from warmed soil as a result of stress environmental conditions. The differences in community function could be related to specific phyla using metaproteomics, indicating that microbial adaptation to long-term soil warming mainly changed microbial functions, which is related to enhanced soil respiration. The response of soil respiration to warming (+35% soil CO2 efflux during sampling) has not changed over time. Accordingly, potential long-term microbial adaptations to soil warming were too subtle to affect soil respiration rates or, were overlaid by other co-varying factors (e.g. substrate availability)
Amplitude and frequency of wetting and drying cycles drive N and NO emissions from a subtropical pasture
This study investigated the effects of irrigation frequency on N and NO emissions from an intensively managed pasture in the subtropics. Irrigation volumes were estimated to replace evapotranspiration and were applied either once (low frequency) or split into four applications (high frequency). To test for legacy effects, a large rainfall event was simulated at the end of the experiment. Over 15 days, 7.9 ± 2.7 kg N + NO-N ha was emitted on average regardless of irrigation frequency, with NO accounting for 25% of overall N + NO. Repeated, small amounts of irrigation produced an equal amount of N + NO losses as a single, large irrigation event. The increase in NO emissions after the large rainfall event was smaller in the high-frequency treatment, shifting the NO/(NO + N) ratio towards N, indicating a treatment legacy effect. Cumulative losses of NO and N did not differ between treatments, but higher CO emissions were observed in the high-frequency treatment. Our results suggest that the increase in microbial activity and related O consumption in response to small and repeated wetting events can offset the effects of increased soil gas diffusivity on denitrification, explaining the lack of treatment effect on cumulative NO and N emissions and the abundance of N cycling marker genes. The observed legacy effect may be linked to increased mineralisation and subsequent increased dissolved organic carbon availability, suggesting that increased irrigation frequency can reduce the environmental impact (NO), but not overall magnitude of NO and N emissions from intensively managed pastures
Quicklime application instantly increases soil aggregate stability
Agricultural intensification, especially enhanced mechanisation of soil management, can lead to the deterioration of soil structure and to compaction. A possible amelioration strategy is the application of (structural) lime. In this study, we tested the effect of two different liming materials, ie limestone (CaCO3) and quicklime (CaO), on soil aggregate stability in a 3-month greenhouse pot experiment with three agricultural soils. The liming materials were applied in the form of pulverised additives at a rate of 2 000 kg ha1. Our results show a significant and instantaneous increase of stable aggregates after quicklime application whereas no effects were observed for limestone. Quicklime application seems to improve aggregate stability more efficiently in soils with high clay content and cation exchange capacity. In conclusion, quicklime application may be a feasible strategy for rapid improvement of aggregate stability of fine textured agricultural soils.(VLID)224292
Effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N-turnover, the NO reductase-gene nosZ and NO:N partitioning from agricultural soils
Nitrification inhibitors (NIs) have been shown to reduce emissions of the greenhouse gas nitrous oxide (NO) from agricultural soils. However, their NO reduction efficacy varies widely across different agro-ecosystems, and underlying mechanisms remain poorly understood. To investigate effects of the NI 3,4-dimethylpyrazole-phosphate (DMPP) on N-turnover from a pasture and a horticultural soil, we combined the quantification of N and NO emissions with N tracing analysis and the quantification of the NO-reductase gene (nosZ) in a soil microcosm study. Nitrogen fertilization suppressed nosZ abundance in both soils, showing that high nitrate availability and the preferential reduction of nitrate over NO is responsible for large pulses of NO after the fertilization of agricultural soils. DMPP attenuated this effect only in the horticultural soil, reducing nitrification while increasing nosZ abundance. DMPP reduced NO emissions from the horticultural soil by >50% but did not affect overall N + NO losses, demonstrating the shift in the NO:N ratio towards N as a key mechanism of NO mitigation by NIs. Under non-limiting NO availability, the efficacy of NIs to mitigate NO emissions therefore depends on their ability to reduce the suppression of the NO reductase by high NO concentrations in the soil, enabling complete denitrification to N
Resistant Soil Microbial Communities Show Signs of Increasing Phosphorus Limitation in Two Temperate Forests After Long-Term Nitrogen Addition
A closeup study of early beech litter decomposition: potential drivers and microbial interactions on a changing substrate
Shifts in microbial stoichiometry upon nutrient addition do not capture growth-limiting nutrients for soil microorganisms in two subtropical soils
Microbial stoichiometry has become a key aspect in ecological research as shifts in microbial C:N, C:P and N:P ratios upon nutrient addition are presumed to give insight into relative nutrient limitations for soil microorganisms–with far-reaching implications for biogeochemical processes. However, this expectation has never been tested against direct methods of microbial growth responses to nutrient addition. We therefore manipulated a subtropical grassland and forest soil with multifactorial C-, N- and P-additions during 30 days to induce changes in limiting resources and evaluated the resulting soil microbial growth rates, microbial biomass stoichiometry, potential enzyme activities and microbial community composition. Our results show that microbial stoichiometric shifts upon nutrient addition ambiguously predict growth-limiting nutrients for soil microbes. For example, P- and NP-addition to the grassland soil significantly shifted the microbial N:P ratio, which suggests increased N- relative to P-limitation. Microbial growth responses however indicated that soil microbes remained C limited. The same applies for the forest soil, where P-, CN-, NP- and CNP-additions shifted the microbial N:P ratio, yet microbial growth remained C limited. This indicates that microorganisms can immobilize N and P for storage when C is the main limiting nutrient, and that intracellular storage of N and P is responsible for the observed shifts in microbial stoichiometry. Moreover, our data imply that shifts in microbial C:N ratios do not necessarily indicate shifts in microbial community composition and suggest that soil microorganisms–when subject to resource pulses–are stoichiometrically quite plastic
Lachgas und N2-Emissionen intensiv bewirtschafteter Weiden in den australischen Subtropen (Nitrous Oxide and N2 emissions from intensiveliy managed pastures in the Australian Subtropics in response to wetting and drying cycles)
Rainfall and irrigation cause denitrification losses in the form of nitrous oxide (N2O) and dinitrogen (N2) emissions from pasture soils. Nitrous oxide is a potent greenhouse gas, while total N2O and N2 emissions represent a loss of available nitrogen (N) from the soil. In situ measurements of both N2O and N2 are rare, despite their importance to N budgets and the greenhouse gas balance of agroecosystems. This paper presents our research on N2O and N2 emissions from dairy pastures in the Australian subtropics. A series of field studies examined factors determining the temporal and spatial distribution and magnitude of denitrification rates. Furthermore, measures to reduce denitrification losses were investigated that include fertilisation and irrigation. The data obtained provide the basis for predictions using simulation models that examine the long-term effects of agricultural practices on dairy pasture
Does Soil Contribute to the Human Gut Microbiome?
Soil and the human gut contain approximately the same number of active microorganisms, while human gut microbiome diversity is only 10% that of soil biodiversity and has decreased dramatically with the modern lifestyle. We tracked relationships between the soil microbiome and the human intestinal microbiome. We propose a novel environmental microbiome hypothesis, which implies that a close linkage between the soil microbiome and the human intestinal microbiome has evolved during evolution and is still developing. From hunter-gatherers to an urbanized society, the human gut has lost alpha diversity. Interestingly, beta diversity has increased, meaning that people in urban areas have more differentiated individual microbiomes. On top of little contact with soil and feces, hygienic measures, antibiotics and a low fiber diet of processed food have led to a loss of beneficial microbes. At the same time, loss of soil biodiversity is observed in many rural areas. The increasing use of agrochemicals, low plant biodiversity and rigorous soil management practices have a negative effect on the biodiversity of crop epiphytes and endophytes. These developments concur with an increase in lifestyle diseases related to the human intestinal microbiome. We point out the interference with the microbial cycle of urban human environments versus pre-industrial rural environments. In order to correct these interferences, it may be useful to adopt a different perspective and to consider the human intestinal microbiome as well as the soil/root microbiome as ‘superorganisms’ which, by close contact, replenish each other with inoculants, genes and growth-sustaining molecules
Soil quality increases with long-term chabazite-zeolite tuff amendments in arable and perennial cropping systems
The application of natural zeolites to improve soil quality and functioning has become highly popular, but we still miss information about the long-term effects on the soil due to its application. This study assesses the soil quality index (SQI) of three distinct agricultural soil systems 6–10 years after a single application of natural chabazite zeolite as a soil amendment. These soils exhibit different management practices: intensive arable (cereals), intensive perennial (pear) and organic perennial (olive). In the arable system, a zeolite application
dosage of 5, 10 and 15 kg m− 2 was tested and compared to unamended soil. In the two perennial systems, an application of 5 kg m− 2 was tested against untreated reference sols. A set of 25 soil physical, chemical and biological parameters linked to soil health and quality were analysed at each experimental site. The dataset was investigated through Principal Component Analysis (PCA) to calculate the soil quality index (SQI) using linear scoring.
In the arable-cereal field, the SQI doubled (0.3 to ca. 0.6 for all amendments) in chabazite-amended plots; a dose effect was not recognizable. In both perennial fields, the SQI was significantly higher in the chabaziteamended plots (5 kg m− 2) with similar increases as compared to the arable-cereal field. At each site, the indicators selected by the PCA were different, indicating that chabazite addition impacted soil quality differently in each cropping system. Overall, the results highlighted a significant increase in soil quality with chabazite amendment, which confirms its potential for increasing soil health in the long-term