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Berlin Brandenburg

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  • 1
    In: New Phytologist, September 2013, Vol.199(4), pp.1034-1044
    Description: Where and how fast does water flow from soil into roots? The answer to this question requires direct and in situ measurement of local flow of water into roots of transpiring plants growing in soil. We used neutron radiography to trace the transport of deuterated water (D2O) in lupin (Lupinus albus) roots. Lupins were grown in aluminum containers (30 × 25 × 1 cm) filled with sandy soil. D2O was injected in different soil regions and its transport in soil and roots was monitored by neutron radiography. The transport of water into roots was then quantified using a convection–diffusion model of D2O transport into roots. The results showed that water uptake was not uniform along roots. Water uptake was higher in the upper soil layers than in the lower ones. Along an individual root, the radial flux was higher in the proximal segments than in the distal segments. In lupins, most of the water uptake occurred in lateral roots. The function of the taproot was to collect water from laterals and transport it to the shoot. This function is ensured by a low radial conductivity and a high axial conductivity. Lupin root architecture seems well designed to take up water from deep soil layers.
    Keywords: Axial Water Flux ; Deuterated Water ; Diffusional Permeability ; Lupin ; Neutron Radiography ; Radial Water Flux ; Root Water Uptake
    ISSN: 0028-646X
    E-ISSN: 1469-8137
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  • 2
    In: Global Change Biology, July 2018, Vol.24(7), pp.2810-2817
    Description: Nitrogen (N) fertilization is an indispensable agricultural practice worldwide, serving the survival of half of the global population. Nitrogen transformation (e.g., nitrification) in soil as well as plant N uptake releases protons and increases soil acidification. Neutralizing this acidity in carbonate‐containing soils (7.49 × 10 ha; ca. 54% of the global land surface area) leads to a CO release corresponding to 0.21 kg C per kg of applied N. We here for the first time raise this problem of acidification of carbonate‐containing soils and assess the global CO release from pedogenic and geogenic carbonates in the upper 1 m soil depth. Based on a global N‐fertilization map and the distribution of soils containing CaCO, we calculated the CO amount released annually from the acidification of such soils to be 7.48 × 10 g C/year. This level of continuous CO release will remain constant at least until soils are fertilized by N. Moreover, we estimated that about 273 × 10 g CO‐C are released annually in the same process of CaCO neutralization but involving liming of acid soils. These two CO sources correspond to 3% of global CO emissions by fossil fuel combustion or 30% of CO by land‐use changes. Importantly, the duration of CO release after land‐use changes usually lasts only 1–3 decades before a new C equilibrium is reached in soil. In contrast, the CO released by CaCO acidification cannot reach equilibrium, as long as N fertilizer is applied until it becomes completely neutralized. As the CaCO amounts in soils, if present, are nearly unlimited, their complete dissolution and CO release will take centuries or even millennia. This emphasizes the necessity of preventing soil acidification in N‐fertilized soils as an effective strategy to inhibit millennia of CO efflux to the atmosphere. Hence, N fertilization should be strictly calculated based on plant‐demand, and overfertilization should be avoided not only because N is a source of local and regional eutrophication, but also because of the continuous CO release by global acidification. The nitrification process as well as plants nitrogen (N) uptake releases protons and increases soil acidification. Neutralizing this acidity in carbonate‐containing soils leads to release of 7.48 × 10 g CO‐C/year until soils are fertilized by N. N fertilization in carbonate‐free soils on the other hand, decreases pH and necessitates liming. Dissolution of lime in the same process releases about 273 × 10 g CO‐C/year. These two CO sources correspond to 3% of global CO emissions by fossil fuel combustion or 30% of CO by land‐use changes. Hence, N fertilization should be plant‐demand to inhibit millennial CO efflux.
    Keywords: Co 2 Efflux ; Global Acidification Assessment ; Global Warming ; Mitigation Policy ; Nitrogen Fertilization ; Soil Acidification Mechanisms ; Soil Inorganic Carbon
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 3
    Language: English
    In: Plant physiology, October 2014, Vol.166(2), pp.487-99
    Description: Our understanding of soil and plant water relations is limited by the lack of experimental methods to measure water fluxes in soil and plants. Here, we describe a new method to noninvasively quantify water fluxes in roots. To this end, neutron radiography was used to trace the transport of deuterated water (D2O) into roots. The results showed that (1) the radial transport of D2O from soil to the roots depended similarly on diffusive and convective transport and (2) the axial transport of D2O along the root xylem was largely dominated by convection. To quantify the convective fluxes from the radiographs, we introduced a convection-diffusion model to simulate the D2O transport in roots. The model takes into account different pathways of water across the root tissue, the endodermis as a layer with distinct transport properties, and the axial transport of D2O in the xylem. The diffusion coefficients of the root tissues were inversely estimated by simulating the experiments at night under the assumption that the convective fluxes were negligible. Inverse modeling of the experiment at day gave the profile of water fluxes into the roots. For a 24-d-old lupine (Lupinus albus) grown in a soil with uniform water content, root water uptake was higher in the proximal parts of lateral roots and decreased toward the distal parts. The method allows the quantification of the root properties and the regions of root water uptake along the root systems.
    Keywords: Models, Biological ; Plant Roots -- Metabolism ; Radiography -- Methods ; Water -- Metabolism
    ISSN: 00320889
    E-ISSN: 1532-2548
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  • 4
    Language: English
    In: Soil Biology and Biochemistry, May 2016, Vol.96, pp.229-237
    Description: The rhizosphere, the small soil volume that surrounds and is influenced by plant roots, is one of the most dynamic biological interfaces on Earth. Enzymes, produced by both roots and microorganisms, are the main biological drivers of SOM decomposition. soil zymography was applied to test hypotheses that 1) the spatial pattern of rhizosphere activity is enzyme-specific and 2) the distribution of enzyme activity along the roots is dependent on root system and plant species. Lentil ( ) and maize ( L.), two species with contrasting root physiology, were chosen to test their effects on spatial distribution of activities of β-glucosidase, cellobiohydrolase, leucine-aminopeptidase and phosphatase. The extent of the rhizosphere for each enzyme and plant species was estimated as a function of distance from the root. For the first time, we demonstrated plant-specific patterns of exoenzyme distribution: these were uniform along the lentil roots, whereas in the rhizosphere of maize, the enzyme activities were higher at the apical or proximal root parts. We conclude that the shape and extent of the rhizosphere for enzyme activities is plant species specific and varies due to different rhizosphere processes (e.g. root exudation) and functions (e.g. nutrient mobilization abilities). The extension of enzyme activity into the rhizosphere soil was minimal (1 mm) for enzymes responsible for the C cycle and maximal (3.5 mm) for enzymes of the phosphorus cycle. This should be considered in assessments and modeling of rhizosphere extension and the corresponding effects on soil properties and functions.
    Keywords: Rhizosphere Extent ; Spatial Pattern ; Enzyme Distribution ; Soil Zymography ; Lentil and Maize ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 5
    Language: English
    In: Agriculture, Ecosystems and Environment, 15 January 2018, Vol.252, pp.93-104
    Description: The Tibetan Plateau hosts the world’s largest alpine pastoral ecosystems, dominated by the endemic sedges and . Owing to the very harsh environment and also to soil nitrogen (N) and phosphorus (P) limitations, these pastoral ecosystems are very sensitive to disturbances (e.g. anthropogenic activities and climate change) and recover extremely slowly. Overgrazing on the Tibetan Plateau has caused severe degradation of vegetation and soils in the last 30–50 years. For the first time, for pastures in Tibetan Plateau, we have summarized and generalized the consequences of pasture degradation for soil organic carbon (SOC) and nutrient (N, P) stocks, and evaluated the main biotic and abiotic mechanisms of their loss. Based on 44 literature studies as well as own data, we demonstrated that 42% of SOC stocks were lost, relative to non-degraded pastures. These SOC losses are similar to the decreases in N stocks (-33%), and aboveground (-42%) and belowground (-45%) plant biomass. Although P losses are lower (-17%), its precipitation reduces its availability for plants. These losses are in fact underestimates, since undisturbed natural sites no longer exist on the Tibetan Plateau. The losses are much higher in the upper 10 cm and in some areas extend to complete removal of soil cover. This has dramatic repercussions for local livestock, human populations and river pollution. While some rehabilitation projects have shown positive outcomes, the complete recovery of degraded pastures (e.g. soil fertility, ecosystem stability) is infeasible, because of very slow pedogenic processes, slow vegetation restoration, as well as continuously increasing anthropogenic pressure and climate change. Considering the rapid losses of SOC and nutrients, and the very slow recovery potential, Tibetan pastures in some regions may disappear in the next few decades without proper and effective recovery strategies.
    Keywords: Tibetan Plateau ; Soil Organic Matter ; Pasture Degradation ; Soil Nutrients ; Carbon Sequestration ; Agriculture ; Environmental Sciences
    ISSN: 0167-8809
    E-ISSN: 1873-2305
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  • 6
    Language: English
    In: Soil Biology and Biochemistry, September 2017, Vol.112, pp.100-109
    Description: Manure is an important source of nutrients for plants and stimulates a wide range of enzyme-mediated microbial processes. Such stimulation, however, depends on manure distribution and the duration of its decomposition in soil. For the first time, we investigated the spatio-temporal patterns of enzyme activities as affected by manure application strategies: 1) Localized manure: manure application as a layer in the upper soil; 2) Homogenized manure: mixing manure throughout the soil; and 3) Control without manure. Tibetan barley was planted on soil managed with yak manure from the Tibetan Plateau. Soil zymography was used to visualize the two-dimensional distribution and dynamics of the activities of three enzymes responsible for cycling of carbon (β-glucosidase), nitrogen (N-acetylglucosaminidase) and phosphorus (phosphomonoesterase) over 45 days. The manure detritusphere increased enzyme activities relative to the control (which had only the rhizosphere effect of barley) and this stimulation lasted less than 45 days. Enzyme activities in the manure-induced hotspots were higher than on the barley rhizoplane, indicating that the detritusphere stimulated microbial activities more strongly than roots. Homogenized manure led to 3–29% higher enzyme activities than localized manure, but shoot and root biomass was respectively 3.1 and 6.7 times higher with localized manure application. Nutrients released by high enzyme activities within the whole soil volume will be efficiently trapped by microorganisms. In contrast, nutrients released from manure locally are in excess for microbial uptake and remain available for roots. Consequently, microorganisms were successful competitors for nutrients from homogeneous manure application, while plants benefited more from localized manure application. We conclude that localized manure application decreases competition for nutrients between the microbial community of manure and the roots, and thereby increases plant performance.
    Keywords: Manure Application Strategies ; Direct Zymography ; Tibetan Plateau ; Enzyme Activity Visualization ; Barley Roots ; Hordeum Vulgare ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 7
    Language: English
    In: Soil Biology and Biochemistry, March 2018, Vol.118, pp.69-78
    Description: The importance of root hairs and root radius for exudation and nutrient acquisition by plants is known mainly from nutrient solution studies. The effects of root hairs and root radius on the spatial distribution of enzyme activity in the rhizosphere of various plants are unknown. Four plants with contrasting root morphology (maize, wheat, lentil and lupine) were chosen to test the effects of root hairs and root radius on the spatial distribution of β-glucosidase, cellobiohydrolase, leucine aminopeptidase and acid phosphatase. We combined zymography with enzyme kinetics to evaluate the effects of root hairs on the rhizosphere extent and on substrate turnover. The extent of enzyme activity in the rhizosphere of four plants ranged from 0.55 to 2 mm. The extent of β-glucosidase was 1.5 times broader (1.2 mm versus 0.8 mm) and the substrate turnover was 2-fold faster around wheat root regions with hairs than hairless locations. The rhizosphere extent relative to root radius and the enzyme activity per root surface area were plant and enzyme specific: the rhizosphere extent was 1.5–2 times broader and the enzyme activity was 2–8-fold higher in wheat (with thin roots and long root hairs) compared to maize, lentil and lupine. The rhizosphere extent of acid phosphatase (1.1–2.0 mm) was 1.5–2-fold broader than that of other enzymes (0.5–1.0 mm). For the first time, we showed that the rhizosphere extent relative to root radius was 20–100% broader and enzyme activity per surface area was 4–7-fold higher around thin roots (wheat) than around thick roots (maize). Moreover, the rhizosphere extent relative to root radius was 10–30% broader and enzyme activity per root area was 2–7 times higher around roots with long and dense hairs (lupine) than around roots with short and sparse hairs (lentil). We conclude that root hairs and root radius shape the rhizosphere: root hairs contributed mainly to the rhizosphere extent, while root radius more strongly affected the enzyme activity per root surface area.
    Keywords: Rhizosphere Extent ; Enzyme Spatial Distribution ; Zymography ; Root Hairs ; Root Radius ; Nutrient Mobilization ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 8
    Language: English
    In: Journal of Plant Nutrition and Soil Science, April 2014, Vol.177(2), pp.227-236
    Description: The ability of plants to extract water from soil is controlled by the water‐potential gradient between root and soil, by the hydraulic conductivity of roots, and, as the soil dries, by that of the soil near the roots (rhizosphere). Recent experiments showed that the rhizosphere turned hydrophobic after drying and it remained temporarily dry after rewetting. Our objective was to investigate whether rhizosphere hydrophobicity is associated with a reduction in root water uptake after drying and rewetting. We used neutron radiography to trace the transport of deuterated water (DO) in the roots of lupines growing in a sandy soil. The plants were grown in aluminum containers (28 × 28 × 1 cm) filled with a sandy soil. The soil was initially partitioned into different compartments using a 1‐cm layer of coarse sand (three vertical × three horizontal compartments). We grew plants in relatively moist conditions (0.1 1–0.5 h. We conclude that a reduction in hydraulic conductivity occurred during drying and persisted after rewetting. This reduction in conductivity could have occurred in roots, in the rhizosphere, or more likely in both of them.
    Keywords: Deuterated Water ; Hydrophobicity ; Mucilage ; Neutron Radiography ; Rhizosphere ; Root Water Uptake
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 9
    In: Journal of Experimental Botany, 2018, Vol. 69(5), pp.1199-1206
    Description: We showed that crown roots have a different capacity to transport water compared with seminal roots. Acknowledging such differences between root types is crucial to understand optimal root traits. The ability of plants to take up water from the soil depends on both the root architecture and the distribution and evolution of the hydraulic conductivities among root types and along the root length. The mature maize ( Zea mays L.) root system is composed of primary, seminal, and crown roots together with their respective laterals. Our understanding of root water uptake of maize is largely based on measurements of primary and seminal roots. Crown roots might have a different ability to extract water from the soil, but their hydraulic function remains unknown. The aim of this study was to measure the location of water uptake in mature maize and investigate differences between seminal, crown, and lateral roots. Neutron radiography and injections of deuterated water were used to visualize the root architecture and water transport in 5-week-old maize root systems. Water was mainly taken up by crown roots. Seminal roots and their laterals, which were the main location of water uptake in younger plants, made a minor contribution to water uptake. In contrast to younger seminal roots, crown roots were also able to take up water from their most distal segments. The greater uptake of crown roots compared with seminal roots is explained by their higher axial conductivity in the proximal parts and by the fact that they are connected to the shoot above the seminal roots, which favors the propagation of xylem tension along the crown roots. The deeper water uptake of crown roots is explained by their shorter and fewer laterals, which decreases the dissipation of water potential along the roots.
    Keywords: Crown Roots ; Diffusion–Convection Model ; Neutron Radiography ; Root Water Uptake ; Seminal Roots ; 〈Kwd〉 〈Italic Toggle="Yes"〉Zea Mays〈/Italic〉 〈/Kwd〉
    ISSN: 0022-0957
    E-ISSN: 1460-2431
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  • 10
    Language: English
    In: Plant and Soil, 2016, Vol.407(1), pp.161-171
    Description: Background and Aims Although maize roots have been extensively studied, there is limited information on the effect of root exudates on the hydraulic properties of maize rhizosphere. Recent experiments suggested that the mucilaginous fraction of root exudates may cause water repellency of the rhizosphere. Our objectives were: 1) to investigate whether maize rhizosphere turns hydrophobic after drying and subsequent rewetting; 2) to test whether maize mucilage is hydrophobic; and 3) to find a quantitative relation between rhizosphere rewetting, particle size, soil matric potential and mucilage concentration. Methods Maize plants were grown in aluminum containers filled with a sandy soil. When the plants were 3-weeks-old, the soil was let dry and then it was irrigated. The soil water content during irrigation was imaged using neutron radiography. In a parallel experiment, ten maize plants were grown in sandy soil for 5 weeks. Mucilage was collected from young brace roots growing above the soil. Mucilage was placed on glass slides and let dry. The contact angle was measured with the sessile drop method for varying mucilage concentration. Additionally, capillary rise experiments were performed in soils of varying particle size mixed with maize mucilage. We then used a pore-network model in which mucilage was randomly distributed in a cubic lattice. The general idea was that rewetting of a pore is impeded when the concentration of mucilage on the pore surface (g cm.sup.-2) is higher than a given threshold value. The threshold value depended on soil matric potential, pore radius and contract angle. Then, we randomly distributed mucilage in the pore network and we calculated the percolation of water across a cubic lattice for varying soil particle size, mucilage concentration and matric potential. Results Our results showed that: 1) the rhizosphere of maize stayed temporarily dry after irrigation; 2) mucilage became water repellent after drying. Mucilage contact angle increased with mucilage surface concentration (gram of dry mucilage per surface area); 3) Water could easily cross the rhizosphere when the mucilage concentration was below a given threshold. In contrast, above a critical mucilage concentration water could not flow through the rhizosphere. The critical mucilage concentration decreased with increasing particle size and decreasing matric potential. Conclusions These results show the importance of mucilage exudation for the water fluxes across the root-soil interface. Our percolation model predicts at what mucilage concentration the rhizosphere turns hydrophobic depending on soil texture and matric potential. Further studies are needed to extend these results to varying soil conditions and to upscale them to the entire root system.
    Keywords: Root mucilage ; Contact angle ; Maize ; Rhizosphere ; Hydrophobicity ; Pore-network model ; Neutron radiography
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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