Showing papers by "Karin Müller published in 2016"

Metagenomic analysis of microbial consortia enriched from compost: new insights into the role of Actinobacteria in lignocellulose decomposition

Abstract: Compost habitats sustain a vast ensemble of microbes specializing in the degradation of lignocellulosic plant materials and are thus important both for their roles in the global carbon cycle and as potential sources of biochemical catalysts for advanced biofuels production. Studies have revealed substantial diversity in compost microbiomes, yet how this diversity relates to functions and even to the genes encoding lignocellulolytic enzymes remains obscure. Here, we used a metagenomic analysis of the rice straw-adapted (RSA) microbial consortia enriched from compost ecosystems to decipher the systematic and functional contexts within such a distinctive microbiome. Analyses of the 16S pyrotag library and 5 Gbp of metagenomic sequence showed that the phylum Actinobacteria was the predominant group among the Bacteria in the RSA consortia, followed by Proteobacteria, Firmicutes, Chloroflexi, and Bacteroidetes. The CAZymes profile revealed that CAZyme genes in the RSA consortia were also widely distributed within these bacterial phyla. Strikingly, about 46.1 % of CAZyme genes were from actinomycetal communities, which harbored a substantially expanded catalog of the cellobiohydrolase, β-glucosidase, acetyl xylan esterase, arabinofuranosidase, pectin lyase, and ligninase genes. Among these communities, a variety of previously unrecognized species was found, which reveals a greater ecological functional diversity of thermophilic Actinobacteria than previously assumed. These data underline the pivotal role of thermophilic Actinobacteria in lignocellulose biodegradation processes in the compost habitat. Besides revealing a new benchmark for microbial enzymatic deconstruction of lignocelluloses, the results suggest that actinomycetes found in compost ecosystems are potential candidates for mining efficient lignocellulosic enzymes in the biofuel industry.

Influence of pyrolysis temperature on lead immobilization by chemically modified coconut fiber-derived biochars in aqueous environments

Abstract: Biochar has received widespread attention as an eco-friendly and efficient material for immobilization of toxic heavy metals in aqueous environments. In the present study, three types of coconut fiber-derived biochars were obtained by pyrolyzing at three temperatures, i.e., 300, 500, and 700 °C. In addition, nine types of biochars were prepared by chemical modification with ammonia, hydrogen peroxide, and nitric acid, respectively, which were used to investigate changes in physico-chemical properties by inter alia, Fourier transformation infrared spectrophotometry (FTIR), scanning electron microscope (SEM), and BET specific surface area analysis. Batch sorption experiments were carried out to determine the sorption capacity of the biochars for lead (Pb) in aqueous solutions. Results showed that the cation exchange capacity of biochar pyrolyzed at 300 °C and modified with nitric acid increased threefold compared to the control. Loosely corrugated carbon surface and uneven carbon surface of the biochar pyrolyzed at 300 °C were produced during ammonia and nitric acid modifications. Removal rate of Pb by the coconut biochar pyrolyzed at 300 °C and modified with ammonia was increased from 71.8 to 99.6 % compared to the untreated biochar in aqueous solutions containing 100 mg L−1 Pb. However, chemical modification did not enhance adsorption of Pb of the biochars pyrolyzed at higher temperatures (e.g., 500 or 700 °C), indicating that resistance of biochars to chemical treatment increased with pyrolysis temperature.

Magnesium Alleviates Adverse Effects of Lead on Growth, Photosynthesis, and Ultrastructural Alterations of Torreya grandis Seedlings

Abstract: Magnesium (Mg2+) has been shown to reduce the physiological and biochemical stress in plants caused by heavy metals. To date our understanding of how Mg2+ ameliorates the adverse effects of heavy metals in plants is scarce. The potential effect of Mg2+ on lead (Pb2+) toxicity in plants has not yet been studied. This study was designed to clarify the mechanism of Mg2+-induced alleviation of lead (Pb2+) toxicity. Torreya grandis (T. grandis) seedlings were grown in substrate contaminated with 0, 700 and 1400 mg Pb2+ per kg-1 and with or without the addition of 1040 mg kg-1 Mg2+. Growth parameters, concentrations of Pb2+ and Mg2+ in the plants’ shoots and roots, photosynthetic pigment, gas exchange parameters, the maximum quantum efficiency (Fv/Fm), root oxidative activity, ultrastructure of chloroplasts and root growth were determined to analyze the effect of different Pb2+ concentrations in the seedlings as well as the potential ameliorating effect of Mg2+ on the Pb2+ induced toxicity. The growth of T. grandis seedlings cultivated in soils treated with 1400 mg kg-1 Pb2+ was significantly reduced compared with that of plants cultivated in soils treated with 0 or 700 mg kg-1 Pb2+. The addition of 1040 mg kg-1 Mg2+ improved the growth of the Pb2+-stressed seedlings, which was accompanied by increased chlorophyll content, the net photosynthetic rate and Fv/Fm, and enhanced chloroplasts development. In addition, the application of Mg2+ induced plants to accumulate five times higher concentrations of Pb2+ in the roots and to absorb and translocate four times higher concentrations of Mg2+ to the shoots than those without Mg2+ application. Furthermore, Mg2+ addition increased root growth and oxidative activity, and protected the root ultrastructure. To the best of our knowledge, our study is the first report on the mechanism of Mg2+-induced alleviation of Pb2+ toxicity. The gener¬ated results may have important implications for understanding the physiological interactions between heavy metals and plants, and for successful management of T. grandis plantations grown on soils contaminated with Pb2+.

Is subcritical water repellency an issue for efficient irrigation in arable soils

Abstract: In New Zealand a resurgence of irrigation development is underway. Considerable effort is focused on developing efficient irrigation technology to maximise production per unit of applied water while ensuring minimal environmental impacts. Most New Zealand pastoral soils have the potential to develop soil water repellency (WR). Its occurrence limits water infiltration, leads to ponding of water on the soil and may enhance runoff and macropore flow. Some limited New Zealand research has shown that subcritical WR may also be common, where water infiltration is impeded by WR and water absorption into the storage pores of the soil matrix may be restricted even though the soils appear to wet readily. The objective of this research was to assess the potential of arable soils to develop WR and to analyse potential tillage effects. Soil cores were collected from the 0–5 cm depth across the three dominant soil orders used for arable production in the Canterbury region, four common tillage practices and histories, as well as from two long-term tillage trials. At each site, duplicate soil cores were collected to compare the infiltration of water to ethanol using tension disc infiltrometers. Ethanol infiltration is not affected by repellent substances, so it is used as the reference infiltration liquid to assess the degree to which water infiltration is retarded. Our results showed that subcritical WR developed in arable soils irrespective of soil order. We found significantly higher WR with decreasing tillage intensity for the long-term tillage trial. In contrast, no such significant trend was found in the regional survey, which similarly only considered sites with known long-term tillage history. It is possible that any potential effect of tillage intensity on WR was masked by confounding site or soil factors in the survey. Tillage effects on subcritical WR were shown not to persist upon change of tillage system. Our results indicate that soil management affects the degree of subcritical WR and the resultant inhibition of early-time infiltration dynamics. Hydrological significance of the results was shown by comparing actual and potential short-term infiltration, showing that suboptimal infiltration into subcritical water-repellent soils limited soil wetting and water storage efficiency. Further research is recommended that develops soil and irrigation management practices that minimise the occurrence of subcritical WR and assist in capturing more water, resulting in increased irrigation efficiencies and reduced water footprints.

Land use affects soil organic carbon of paddy soils: empirical evidence from 6280 years BP to present

Abstract: Submerged rice cultivation has been practiced in China for 7000 years. Empirical evidence on changes of soil organic carbon (SOC) contents in paddy soils over this historical time period is scarce. Therefore, a field study was conducted to investigate the effect of submerged rice cultivation on the accumulation and preservation of SOC in paddies. Two buried ancient paddy profiles (6280 years BP, named P-01 and P-03) in the Yangtze Delta of eastern China were excavated to illustrate the development of SOC contents in soils during the evolution of paddies under anthropogenic land use and environmental changes from the prehistoric period to the present time. Trends in SOC concentrations, total nitrogen concentrations, and stable carbon isotope ratio were identified for different points in time. Accumulation of organic carbon was found in the paddy soil layers of P-01 at 100–174 cm depth. This site was taken under submerged rice cultivation in about 6280 years BP. The average SOC concentration in the prehistoric paddy topsoil in 100–130 cm depth was 1.27 %, which is seven times higher than that in the adjacent uncultivated land at 103–130 cm depth of P-03. This implies that the paddy soil has experienced substantial CO2 sequestration under submerged management during that time. By about 3320 years BP, organic carbon contents were halved, potentially due to marine inundation by sea level rise. Up to the year 2003, the SOC contents in all horizons in the present time paddy soil have increased, especially in the surface layer, indicative of continuous rice cultivation. However, due to rapid urbanization and industrialization, the cultivation of paddies in eastern China has gradually been discontinued leading to the loss of SOC stocks of approximately 10 % in a 6-year interval (from 2003 to 2009). A significant relationship between SOC and rice phytolith contents was found in the paddy soil horizons of P-01 (r = 0.71, p < 0.01) and P-03 (r = 0.72, p < 0.01), suggesting that phytolith-occluded organic carbon could be used as a biomarker to ascertain the development of SOC in the evolution of rice paddies over the past 6000 years. Submerged rice cultivation led to a noticeable accumulation of SOC in paddies. Phytolith-occluded organic carbon could be used as a biomarker to monitor changes of OC contents in paddy soils.

Quantifying the potential contribution of soil carbon to orchard carbon footprints

Abstract: Increasing soil carbon is promoted to growers as a means of increasing soil function and mitigating climate change. However, the importance of soil carbon is not yet fully acknowledged in life cycle assessment guidelines. Because of their perennial nature and deep rooting systems, orchards have the potential to increase subsoil carbon stocks below 0.3 m depth. Quantifying soil carbon stocks at the orchard scale, however, requires sampling protocols that incorporate the spatial variability of carbon in orchards. We have investigated soil carbon stocks to 1 m depth in apple orchards in Australia and New Zealand and found that total carbon stocks were maintained over four to 12 years. Orchard floor management practices can create a spatial distribution of shallow soil carbon stocks, and we observed a trend for decreasing surface-soil carbon stocks under the alley. Additionally, we determined soil carbon stocks to 9 m depth in a New Zealand kiwifruit orchard and calculated an increase of 190 t C ha-1 after 30 years compared with that in the nearby pasture soil that was the antecedent land-use. This increase in soil carbon equates to 42% of the carbon footprint of New Zealand kiwifruit on United Kingdom supermarket shelves. Therefore, accurately quantifying soil carbon stock changes under orchard systems presents a potential opportunity to reduce horticultural carbon footprints.