Plant diversity increases soil microbial activity and soil carbon storage

Plant diversity strongly influences ecosystem functions and services, such as soil carbon storage. However, the mechanisms underlying the positive plant diversity effects on soil carbon storage are poorly understood. We explored this relationship using long-term data from a grassland biodiversity experiment (The Jena Experiment) and radiocarbon (14C) modelling. Here we show that higher plant diversity increases rhizosphere carbon inputs into the microbial community resulting in both increased microbial activity and carbon storage. Increases in soil carbon were related to the enhanced accumulation of recently fixed carbon in high-diversity plots, while plant diversity had less pronounced effects on the decomposition rate of existing carbon. The present study shows that elevated carbon storage at high plant diversity is a direct function of the soil microbial community, indicating that the increase in carbon storage is mainly limited by the integration of new carbon into soil and less by the decomposition of existing soil carbon

Plant Diversity Surpasses Plant Functional Groups and Plant Productivity as Driver of Soil Biota in the Long Term

One of the most significant consequences of contemporary global change is the rapid decline of biodiversity in many ecosystems. Knowledge of the consequences of biodiversity loss in terrestrial ecosystems is largely restricted to single ecosystem functions. Impacts of key plant functional groups on soil biota are considered to be more important than those of plant diversity; however, current knowledge mainly relies on short-term experiments.We studied changes in the impacts of plant diversity and presence of key functional groups on soil biota by investigating the performance of soil microorganisms and soil fauna two, four and six years after the establishment of model grasslands. The results indicate that temporal changes of plant community effects depend on the trophic affiliation of soil animals: plant diversity effects on decomposers only occurred after six years, changed little in herbivores, but occurred in predators after two years. The results suggest that plant diversity, in terms of species and functional group richness, is the most important plant community property affecting soil biota, exceeding the relevance of plant above- and belowground productivity and the presence of key plant functional groups, i.e. grasses and legumes, with the relevance of the latter decreasing in time.Plant diversity effects on biota are not only due to the presence of key plant functional groups or plant productivity highlighting the importance of diverse and high-quality plant derived resources, and supporting the validity of the singular hypothesis for soil biota. Our results demonstrate that in the long term plant diversity essentially drives the performance of soil biota questioning the paradigm that belowground communities are not affected by plant diversity and reinforcing the importance of biodiversity for ecosystem functioning

Belowground biomass productivity from the Jena Experiment (Main Experiment, year 2007)

This data set contains measurements of belowground biomass productivity, i.e. coarse and fine root biomass production (N-concentration of the fine roots are attached to this dataset as well). Data presented here is from the Main Experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the Main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained in general by bi-annual weeding and mowing. Since 2010, plots were weeded three times per year. In July 2007, five soil cores with a 4.8 cm diameter per plot were removed to 30 cm depth. The removed soil was replaced by root-free soil from the field site. The ingrowth cores were removed in June 2008 and cut with scissors until root fragments were < 1 cm in length. For root washing, a 210 g subsample of the bulk material was taken and soaked in water. The soil was removed from the roots by rinsing over a sieve with 0.5 mm mesh width. Then, organic debris and remaining soil particles were removed by hand. The remaining roots were dried at 70 °C and weighed. In 2008, ingrowth cores were separated in depth increments of 0-5, 5-10, 10-20 and 20-30 cm depth. Roots were seperated in coarse (diameter > 2 mm) and fine roots before cutting the bulk material. Fine roots were grinded in a ball mill and 20 mg of the grinded material was used to determine N-concentration of the fine roots with VarioMax CNS (Elementar)

Standing belowground plant biomass from the Jena Experiment (Main Experiment, year 2008)

This data set contains measurements of standing belowground plant biomass. Data presented here is from the Main Experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the Main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained in general by bi-annual weeding and mowing. Since 2010, plots were weeded three times per year. In 2008, standing root biomass was sampled in June. Three soil cores with a 4.8 cm diameter per plot were taken to 30 cm depth and pooled plot-wise. The cores were immediately stored cool until further handling. The bulk material of the pooled cores was weighed and cut with scissors to 2 mm) and fine roots before cutting the bulk material

Standing belowground plant biomass from the Jena Experiment (Main Experiment, year 2004)

This data set contains measurements of standing belowground plant biomass. Data presented here is from the Main Experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the Main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained in general by bi-annual weeding and mowing. Since 2010, plots were weeded three times per year. In 2004, standing root biomass was sampled in September. Three soil cores with a 4.8 cm diameter per plot were taken to 30 cm depth and pooled plot-wise. The cores were immediately stored cool until further handling. The bulk material of the pooled cores was weighed and cut with scissors to 2 mm) and fine roots after root washing

Morphological root parameters of standing roots from the Jena Experiment (Main Experiment, year 2004)

This data set contains measurements of diameter of standing roots. Data presented here is from the Main Experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the Main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained in general by bi-annual weeding and mowing. Since 2010, plots were weeded three times per year. In September 2004, three soil cores with a 4.8 cm diameter per plot were taken to 30 cm depth. The bulk material of the pooled cores was cut with scissors to < 1 cm pieces. A subsample of 50 g was suspended in water and rinsed over a 0.5 mm screen. Roots collected in the screen were transferred into a water-filled clear acrylic tray and scanned. Mean diameter of the roots was determined by using WinRhizo (Regent Instruments, Quebec, Canada)

Morphological root parameters of newly formed roots from the Jena Experiment (Main Experiment, year 2003)

This data set contains measurements of morphological root parameters, i.e. length and diameter of newly built roots. Data presented here is from the Main Experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the Main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Since 2010, plots were weeded three times per year. In June 2003, five soil cores with a 4.8 cm diameter per plot were taken to 30 cm depth. The removed soil was replaced by root-free soil from the field site. In September 2003, the initially root-free ingrowth cores were removed and the holes were refilled with root-free soil until the following withdrawal in July 2004. To extract the newly formed roots, each ingrowth core was first weighed and carefully homogenized. A subsample of 50 g of soil was suspended in water and rinsed over a 0.5 mm screen. Roots collected in the screen were transferred into a water-filled clear acrylic tray and scanned. Total root length and mean diameter were determined by using WinRhizo (Regent Instruments, Quebec, Canada). Afterwards, root length density (cm root length per cm3 soil volume) was calculated

Belowground biomass productivity from the Jena Experiment (Main Experiment, year 2003)

This data set contains measurements of belowground biomass productivity, i.e. coarse and fine root biomass production (C- and N-concentration of the fine roots are attached to this dataset as well). Data presented here is from the Main Experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the Main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained in general by bi-annual weeding and mowing. Since 2010, plots were weeded three times per year. In June 2003, five soil cores with a 4.8 cm diameter per plot were removed to 30 cm depth. The removed soil was replaced by root-free soil from the field site. The ingrowth cores were removed in September 2003 and cut with scissors until root fragments were < 1 cm in length. For root washing, a 50 g subsample of the bulk material was taken and soaked in water. The soil was removed from the roots by rinsing over a sieve with 0.5 mm mesh width. Then, organic debris and remaining soil particles were removed by hand. The remaining roots were dried at 70 °C and weighed. In 2003, roots were seperated in coarse (diameter > 2 mm) and fine roots after root washing. After withdrawal of the ingrowth cores in September 2003, the holes were refilled with root-free soil, and the ingrowth cores were sampled again in July 2004. In 2003 and 2004, fine roots were grinded in a ball mill and 20 mg of the grinded material was used to determine C- and N-concentration of the fine roots with VarioMax CNS (Elementar)

In situ Laser Raman Spectroscopy for Investigating SOFC Processes

The application of advanced diagnostic methods for monitoring cell characteristics of solid oxide fuel cells (SOFC) under real operating conditions can provide detailed information about the spatial distribution of cell properties in order to increase the fundamental understanding and to optimize the operational behavior. At high fuel utilization which is required for achieving high efficiency, strong concentration gradients of the fuel gas can occur which might detrimentally affect both performance and durability. To study inhomogeneous distributions of electrochemical and thermal cell properties during operation, DLR has developed spatially resolved diagnostic techniques such as segmented cell technology that allows for the determination of local current density and voltage, local impedance data, temperature distribution and local gas concentrations. To complement the existing diagnostic techniques, gas-phase laser Raman spectroscopy has recently been adopted to determine the concentrations of relevant gaseous species within the anode flow channel with high spatial and temporal resolution during operation at technically relevant operating conditions. A test rig has been built up which gives an optical access to the flow field of a SOFC cell setup through transparent windows in the furnace and using a transparent anode flow field entirely consisting of quartz glass. The Raman experiments were performed by means of a laser system using three double-pulse Nd:YAG lasers. The paper describes the experimental setup of gas-phase Raman spectroscopy measurements with an operating electrolyte-supported SOFC cell of a size of 50x50 mm2. At varying operating conditions with different fuel gas compositions, electrical loads and operating temperatures, Raman spectra were recorded and concentration profiles of gas species along the flow path in the anode were determined. The results obtained from Raman spectroscopy measurements are correlated with results from electrochemical characterization methods such as i-V characteristics and electrochemical impedance spectroscopy

Anwendung in-situ diagnostischer Methoden für die Untersuchung oxidkeramischer Brennstoffzellen

Für eine optimale Leistungsfähigkeit von Brennstoffzellen und möglichst geringe Degradation ist eine homogene elektrochemische Aktivität und Temperatur über den gesamten Bereich der Elektroden erwünscht, da eine inhomogene Stromdichte- und Temperaturverteilung zu einer verringerten Nutzung der Reaktanden führt, was sich in einem erniedrigten Wirkungsgrad niederschlägt. Auch die Langzeitstabilität von Zellkomponenten kann durch die ungleichmäßige Verteilung der elektrischen und thermischen Eigenschaften negativ beeinflusst werden. In-situ diagnostische Methoden können wertvolle Informationen liefern, um das Betriebsverhalten von SOFC-Zellen zu optimieren und Strategien zur Verminderung der Degradation zu entwickeln. Trotz der beträchtlichen experimentellen Schwierigkeiten, die mit der hohen Betriebstemperatur verbunden sind, ist es in den letzten Jahren gelungen, neuartige Analyseverfahren, wie ortsaufgelöste Messtechniken und bildgebende Verfahren, auch für die SOFC zu entwickeln und einzusetzen. Der Vortrag gibt einen Überblick über in-situ diagnostische Methoden, die beim DLR Stuttgart für die Untersuchung von SOFC-Zellen entwickelt wurden und eingesetzt werden. Es handelt sich dabei zum einen um ortsaufgelöste Messungen mit Hilfe segmentierter Zellen, wobei Strom-Spannungskennlinien, Impedanzspektroskopie, Gaschromatographie und Temperaturmessungen lokale Informationen über elektrochemische und thermische Eigenschaften der Zelle liefern. Mit dem aufgebauten Messsystem können realsystemnahe Effekte zeitlich und ortsaufgelöst gemessen und miteinander korreliert werden. Das Messsystem kann zur Aufklärung der Brenngasumsetzung entlang des Strömungswegs und zur Identifizierung der damit möglicherweise verbundenen korrosiven Bedingungen eingesetzt werden. Daneben kann es zur Optimierung des Strömungsdesigns und zur Untersuchung möglicher Effekte der Homogenisierung der Leistungsdichte- und Temperaturverteilung herangezogen werden. Zum anderen wurde kürzlich beim DLR ein Teststand mit einem transparenten optischen Zugang zum Anodengasverteiler aufgebaut, wodurch mittels Laser-Ramanspektroskopie die Konzentrationen von Gasspezies entlang eines Gaskanals mit hoher Ortsauflösung bestimmt werden können. Es werden beispielhaft Ergebnisse beider Analysenverfahren vorgestellt und die Potenziale sowie Grenzen der unterschiedlichen Techniken diskutiert