1,721,079 research outputs found
Spatial and temporal dynamics of hotspots of enzyme activity in soil as affected by living and dead roots-a soil zymography analysis
No full textHotspots of enzyme activity in soil strongly depend on carbon inputs such as rhizodeposits and root detritus. In this study, we compare the effect of living and dead Lupinus polyphyllus L. roots on the small-scale distribution of cellulase, chitinase and phosphatase activity in soil. Soil zymography, a novel in situ method, was used to analyze extracellular cellulase, chitinase and phosphatase activity in the presence of i. living L. polyphyllus roots prior to shoot cutting and ii. dead/dying roots 10, 20 and 30 days after shoot cutting. After shoot cutting, cellulase and chitinase activities increased and were highest at the root tips. The areas of high cellulase and phosphatase activity extend up to 55 mm away from the root. Moreover, we observed microhotspots of cellulose, chitinase, and phosphatase activity up to 60 mm away from the next living root. The number and activity of microhotspots of chitinase activity was maximal 10 days after shoot cutting. The study showed that young root detritus stimulates enzyme activities stronger than living roots. Soil zymography allowed identification of microhotspots of enzyme activity up to several cm away from living and dying roots, which most likely were caused by arbuscular mycorrhizal fungi
Distribution of microbial- and root-derived phosphatase activities in the rhizosphere depending on P availability and C allocation - Coupling soil zymography with C-14 imaging
No full textDespite its importance for terrestrial nutrient and carbon cycling, the spatial organization of microbial activity in soil and in the rhizosphere is poorly understood. We related carbon allocation by roots to distribution of acid and alkaline phosphatase activity in the rhizosphere of Lupinus albus L To do so, we further developed soil zymography - an in situ method for the analysis of the two-dimensional distribution of enzyme activity in soil - integrating fluorescent substrates. Soil zymography was combined with C-14 imaging, a technique that gives insights into the distribution of photosynthates after labeling plants with C-14. Both acid and alkaline phosphatase activity were up to 5.4-times larger in the rhizosphere than in the bulk soil. While acid phosphatase activity (produced by roots and microorganisms) was closely associated with roots, alkaline phosphatase activity (produced only by microorganisms) was more widely distributed, leading to a 2.5-times larger area of activity of alkaline than of acid phosphatase. These results indicate a spatial differentiation of different ecophysiological groups of organic P mineralizing organisms. The spatial differentiation could be either between microorganisms and L albus or between microorganisms that produce exclusively alkaline phosphatases on the one hand, and L albus and root associated microorganisms that produce acid phosphatases on the other hand. The spatial separation of different organic P mineralizing organisms might alleviate a potential competition between them. While alkaline phosphatase activity strongly decreased with P fertilization, acid phosphatase activity was not affected by fertilization, suggesting that alkaline phosphatase-producing microorganisms react more strongly to it than other organic P mineralizing organisms. Alkaline phosphatase activity was high in parts of the rhizosphere where relatively little recent photosynthates were allocated, indicating that rhizodeposition and the activity of alkaline phosphatase-producing microorganisms are not directly related. Our study indicates, first, a spatial differentiation of organic P mineralization by various ecophysiological groups that react differently to inorganic P fertilization and second, that rhizodeposition and alkaline phosphatase-producing microorganisms were not directly related. Finally, we conclude that soil zymography with fluorescent substrates is a very promising approach for studying the distribution of a broad range of extracellular enzymes at microscales. (C) 2013 Elsevier Ltd. All rights reserved.German Research Foundation [SP-1389, SPP 1685
Microbial respiration per unit biomass increases with carbon-to-nutrient ratios in forest soils
No full textThe ratio of carbon-to-nutrient in forest floors is usually much higher than the ratio of carbon-to-nutrient that soil microorganisms require for their nutrition. In order to understand how this mismatch affects carbon (C) cycling, we investigated the respiration rate per unit soil microbial biomass the metabolic quotient (qCO(2)) - in relation to the soil carbon-to-nitrogen (C:N) and carbon-to-phosphorus (C:P) ratio in temperate forests. For this purpose, cores of beech, spruce, and mixed spruce-beech forest soils were cut into slices of 1 cm from the litter layer down to 5 cm in the mineral soil, and the relationship between the qCO(2) and the soil C:N and the soil C:P ratio was analyzed. We found that the qCO(2) was positively correlated with soil C:N ratio in spruce soils (R = 0.72), and with the soil C:P ratio in beech (R = 0.93), spruce (R = 0.80) and mixed forest soils (R = 0.96). We also observed a close correlation between the qCO(2) and the soil C concentration in all three forest types. Yet, the qCO(2) decreased less with depth than the C concentration in all three forest types, suggesting that the change in qCO(2) is not only controlled by the soil C concentration. We conclude that microorganisms increase their respiration rate per unit biomass with increasing soil C:P ratio and C concentration, which adjusts the substrate to their nutritional demands in terms of stoichiometry. (C) 2014 Elsevier Ltd. All rights reserved
Phosphorus mineralization can be driven by microbial need for carbon
No full textDespite the importance of phosphorus (P) mineralization to maintain soil fertility, little is known about the mechanisms that regulate microbial P mineralization. We tested the hypothesis that microbial P mineralization can be driven by microbial need for carbon (C). For this purpose, net microbial uptake kinetics of C-14 and P-33 from glucose-6-phosphate were studied in a Leptosol depending on availability of C, nitrogen (N), and P. After 60 h of incubation, 16.4% of the C-14 from glucose-6-phosphate was recovered in the microbial biomass, while P-33 incorporation into the microbial biomass was a third less. The higher net uptake of C-14 than of P-33 from the glucose-6-phosphate indicates that soil microorganisms use the organic moiety of phosphorylated organic compounds as a C source, but only use a small proportion of the P. Hence, they mineralize P without incorporating it. Our finding that the net uptake of C-14 and P-33 in the soils amended with inorganic P did not differ from the control treatment indicates that P mineralization was not driven by microbial need for P but rather for C. In a second experiment with three temperate forest soils we found that the activity of C-14 from glucose-6-phosphate in soil solution decreased faster than the activity of P-33 from glucose-6-phosphate. This might suggest that higher net uptake of C than of P from glucose-6-phosphate can also be observed in other temperate forest soils differing in C, N, and P contents from the Leptosol of the main experiment. In conclusion, the experiments show that microbial P mineralization can be a side-effect of microbial C acquisition from which plants potentially can benefit. (C) 2013 Elsevier Ltd. All rights reserved
Carbohydrates, carbon and nitrogen in soils of a marine and a brackish marsh as influenced by inundation frequency
No full textMarshes on the southern North Sea coast store large amounts of organic matter (OM). The objective of this study was to investigate the effect of inundation frequency on carbohydrates, organic carbon (OC), inorganic carbon (IC) and nitrogen (N) in a marine and a brackish marsh. To gain insights into the origin of OC in the marshes we used monosaccharides as biomarkers. We studied soils in a marine and a brackish marsh along a gradient of inundation frequency. It was found that TOC and N stocks in soils of a marine and a brackish marsh increased with decreasing inundation frequency. Concentrations of carbohydrates were significantly higher in the topsoils of the marine marsh than of the brackish marsh. In the upper mid-zone of the marine marsh, which is inundated by the sea approximately 20-times a year, carbohydrate stocks were up to 2.4-times higher than in the upper mid-zone of the brackish marsh with the same inundation frequency. Differences in carbohydrate concentrations can be attributed to differences in the abundance of fine and medium roots in these soils. In the daily-inundated soils of both marshes we observed high hexose-to-pentose ratios, indicating a microbial origin of the carbohydrates, while the hexose-to-pentose ratios were significantly lower in the middle and upper zone of the two marshes, indicating a high proportion of plant-derived carbohydrates. This study shows that monosaccharides are useful biomarkers to explore the origin of OM in coastal soils. (c) 2012 Elsevier Ltd. All rights reserved
Soil zymography - A novel in situ method for mapping distribution of enzyme activity in soil
No full textRecently, there has been growing interest in the spatial distribution of microbial activity in soil; however, methods for analysis of spatial distribution of microbial activity and for localization of hotspots of enzyme activity in soil are limited. Here were present an in situ zymography technique for localization and quantification of enzyme activities in soil by means of thin gels with embedded substrates. After incubation, the substrate remaining in the gel is colored and quantified using calibration curves and digital image analysis. So far, zymography has mostly been used to localize enzymatic activity in electrophoresis gels and in tissue sections. In this study we developed a zymography technique for analysis of the two-dimensional distribution of enzyme activities in soil. The technique was applied to map and quantify protease and amylase activity in the rhizosphere of lupine (Lupinus polyphyllus) grown in rhizoboxes. Highest activities, of up to 46 ng mm(-2) of the soil surface h(-1) for the protease and of up to 0.90 mu g mm(-2) h(-1) for the amylase were found in close association with roots. Since zymography is an in situ method that does not require destruction of soil structure, it likely pictures enzyme activities more realistically than standard enzyme assays. In conclusion, soil in situ zymography offers a promising tool for mapping distributions of enzyme activities in soils in a work- and cost-efficient way. (C) 2012 Elsevier Ltd. All rights reserved
Microbial gross organic phosphorus mineralization can be stimulated by root exudates - A P-33 isotopic dilution study
No full textPhosphorus (P) is one of the most important nutrients for plant growth. While most studies on microbial P mobilization, i.e. on mineralization of organic P and solubilization of inorganic P, focus on mycorrhiza, P mobilization by non-mycorrhizal microorganisms in soil is little explored. In this study we address the question whether root exudates stimulate organic P mineralization by non-mycorrhizal microorganisms. A P-33 isotopic dilution approach was applied to investigate microbial gross P mineralization in top- and subsoil horizons of three forest soils differing in P concentrations (Leptosol, Podzol, and Cambisol). To simulate the effects of root exudates on microbial gross P mineralization, glucose, alanine, and methionine were added in rhizosphere-relevant concentrations (12 mg carbon (C) g(-1) soil organic C). Based on P-33 isotopic dilution we showed that glucose and alanine addition increased gross P mineralization rates up to a factor of 20 and 31, respectively. In contrast, methionine had little effect on microbial gross P mineralization rates. Phosphatase activity was increased most strongly due to the addition of alanine and glucose by factors of up to 6 and 4, respectively. Fifteen days after addition of artificial root exudates, microbial P concentrations and P-33 recovery in the microbial biomass were only slightly and not consistently changed. In conclusion, the results show that alanine and glucose can stimulate microbial gross P mineralization and phosphatase activity, and that structure and stoichiometry of root exudates significantly shape the extent of stimulation of microorganisms. Our study indicates that stimulation of non-mycorrhizal microorganisms by root exudates might be an important strategy of plants to increase the availability of P in soils. (C) 2013 Elsevier Ltd. All rights reserved.DAA
Changes in soil organic matter quality during sea-influenced marsh soil development at the North Sea coast
No full textSalt marsh soils sequester large amounts of organic matter (OM). The question we address in this study is how OM quality changes during initial soil development in salt marshes. To answer this question, we studied soils at six sites at the German North Sea coast. At each site, three zones - low, mid, and high marsh - that differ in inundation frequency were analyzed. We found that organic carbon (OC) and nitrogen (N) contents increased significantly with decreasing inundation frequency at all sites, while inorganic carbon contents decreased. delta C-13 signatures of the OC strongly decreased at all sites from low to high marsh (from -153 to -21.5 parts per thousand), indicating a decrease in the proportion of marine-derived OC. The decrease in sea-derived OC was associated with an increase in C/N ratio, which can be attributed to the difference in the C/N ratios between sea- and land-derived OM inputs. Increases in OC and N contents in the bulk soils during soil development resulted from increases of the OC content in the coarse size fraction (>200 mu m), and were associated with increases in the content of hot water extractable C and N (C-hwe and N-hwe). The proportion of OM found in the fraction <2 mu m decreased with soil development. The delta C-13 signature of the OC sequestered in this fraction decreased from -20.6 to -24.0 parts per thousand. The smaller decrease in the delta C-13 signatures of the OC in the fraction <2 mu m compared to the delta C-13 signatures of the OC in the bulk soils indicates that the OC is relatively rigidly bound to the minerals in this fraction. The low delta C-13 signatures of OC stored in the fraction <2 mu m indicates that OM in this fraction is mainly of terrestrial origin. In conclusion, this study shows that OM contents and the proportion of relatively labile OM increases during initial marsh soil development due to inputs of terrestrial OC. (C) 2013 Elsevier B.V. All rights reserved
Temperature- and moisture-dependent soil water repellency induced by the basidiomycete Agaricus bisporus
No full textSoil water repellency (SWR) has been reported to regularly occur in many soils under various climatic conditions. Despite the commonness of this soil property the mechanisms leading to the occurrence of SWR are largely unknown. The aim of this experiment was to test the hypothesis that the basidiomycete Agaricus bisporus promotes SWR, and that this fungal-induced SWR is dependent on soil moisture and temperature. We report that A. bisporus strongly induces SWR. We further show that the water content during the cultivation of A. bisporus on soil as well as drying temperature of the soil after the incubation experiment significantly affected SWR. Water drop penetration time (WDPT) of the soil ranged from 0.5s in the samples cultivated at high soil water content (20%, w/w) and subsequently freeze dried, to more than 162 min in the soils that were kept at the low water content (13.8%, w/w) and were subsequently dried at 80 degrees C. These findings show that fungal activity potentially can promote dramatic SWR. The strong increase in SWR clue to heating of the soil to 80 degrees C supports the view that SWR can be caused by a rearrangement of organic substances. For this reason, we discuss surface-active proteins produced by basidiomycetes as potential drivers of the SWR observed in our experiment. (C) 2011 Elsevier GmbH. All rights reserved
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