Keith R. Edwards

A larger investment into exudation by competitive versus conservative plants is connected to more coupled plant–microbe N cycling

Plant–microbe interactions actively control nitrogen (N) cycling in the ecosystem. We hypothesize that the investment into exudation and the coupling of plant–microbe N cycling will be larger in competitive plants compared to the more conservative species. Root exudation of competitive (Glyceria maxima) and conservative (Carex acuta) plants was estimated by 13C-CO2 labeling. Seasonal changes in plant, microbial, and soil soluble N pools as well as potential net microbial N transformations were determined to interconnect the C and N cycling within grassland ecosystems dominated by these species. We showed that competitive Glyceria, as compared to conservative Carex, appears to affect soil N cycling through a more direct temporal and spatial influence on soil microbes due to a larger investment into root exudation. This makes the system highly dynamic, with faster soil N cycling and pronounced seasonal N redistribution between plants and microbes. The conservative Carex, irrespective of its larger root system, invested less C to exudation. In this case, the plant–microbe relationships appear to be less-coupled in time and space with the plant N supply likely relying mainly on the relatively slow microbial mineralization of organic matter than on rhizosphere priming effect. We showed that differences in soil N cycling associated with competitive versus conservative plants are closely connected with their different investments into root exudation, which govern the coupling of plant–microbe interactions in time and space.

The effect of nutrient level on plant structure and production in a wet grassland: a field study

Since the 1950s, agricultural intensification has affected the structure and functioning of ecological systems including wet grasslands. Our study site, a wet grassland near Třeboň, Czech Republic, was historically a sedge meadow, but increased nutrient additions, a long-lasting flood in 2002 and changed mowing patterns resulted in domination by Phalaris arundinacea. The aim of the study was to determine how different nutrient conditions may affect plant structure and production in a wet grassland used for hay production. Species composition and percent cover were determined from line intercepts. Aboveground biomass was harvested six times each in 2007 and 2008 and primary production then calculated. Ingrowth core bags were used to determine belowground production. Aboveground production was two times greater in the high nutrient versus the low nutrient area in both years, while belowground production was very similar. The high nutrient area was still dominated by P. arundinacea, but Carex gracilis was now a co-dominant in the low nutrient area. However, other factors, such as water level and mowing regime, may interact with nutrient level to govern wet grassland structure and function.

Landscape changes and their influence on the heterogeneity of landscape of the South Bohemian Region, the Czech Republic

Landscapes reflect both historic and current cultural and socio-economic activities of human societies. Accordingly, as human societies change, the landscape changes as well. Agriculture is the main driver of landscape changes in the Czech Republic. Therefore, it is necessary to devote special attention to agricultural practices and define simple but effective steps to improve landscape mosaics towards a sustainable development. In this study, regional information about historic changes in landscape structure was studied to (1) identify the trends in land use/cover development since 1940 to 2010 and (2) determine the impact of land use change on the resulting heterogeneity of the landscape. The overall purpose was to find areas of compromise which would allow strengthening of landscape structure and thus stabilize its functions. We specified trends of land use/cover development in 15 catchments with varying agriculture intensity. We digitalized aerial photographs from 1940, 1960, and 1990 and orthophotomaps from 2010. Then, we used a heterogeneity index to define landscape heterogeneity in all catchments and time horizons. The results of our research confirmed increasing tillage effort in intensively cultivated areas, support of secondary succession processes in marginalized areas, and overall increase in forest area. Our study found that simplification and homogenization of the landscape mosaic took place in all studied areas, with the steepest decline found in areas with high agriculture intensity. However, linear vegetation proved to be a suitable starting point for a targeted effort to increase heterogeneity and thus seemed to be crucial for sustainable development of landscape functions in agroecosystems.

Cotton-Grass and Blueberry have Opposite Effect on Peat Characteristics and Nutrient Transformation in Peatland

Peatlands are large repositories of carbon (C). Sphagnum mosses play a key role in C sequestration, whereas the presence of vascular plants is generally thought to stimulate peat decomposition. Recent studies stress the importance of plant species for peat quality and soil microbial activity. Thus, learning about specific plant–microbe–soil relations and their potential feedbacks for C and nutrient cycling are important for a correct understanding of C sequestration in peatlands and its potential shift associated with vegetation change. We studied how the long-term presence of blueberry and cotton-grass, the main vascular dominants of spruce swamp forests, is reflected in the peat characteristics, soil microbial biomass and activities, and the possible implications of their spread for nutrient cycling and C storage in these systems. We showed that the potential effect of vascular plants on ecosystem functioning is species specific and need not necessarily result in increased organic matter decomposition. Although the presence of blueberry enhanced phosphorus availability, soil microbial biomass and the activities of C-acquiring enzymes, cotton-grass strongly depleted phosphorus and nitrogen from the peat. The harsh conditions and prevailing anoxia retarded the decomposition of cotton-grass litter and caused no significant enhancement in microbial biomass and exoenzymatic activity. Therefore, the spread of blueberry in peatlands may stimulate organic matter decomposition and negatively affect the C sequestration process, whereas the potential spread of cotton-grass would not likely change the functioning of peatlands as C sinks.

The effect of macrophytes on retention times in a constructed wetland for wastewater treatment

Retention times of treated water in a constructed wetland (CW) with horizontal subsurface flow were determined both in the vegetative and non-vegetative periods of 2005. Tracer experiments were performed using fluorescein, an organic compound detectable at extremely low concentrations. Nominal and tracer retention times were determined and compared. Winter tracer retention time (TRT 194 h) and nominal retention time (nHRT 190 h) were nearly exactly equal, while summer TRT (335 h) was approximately twofold higher than nHRT (158 h). Residence time distribution function (RTD) was used to compare retention times obtained for the vegetative and non-vegetative periods. The obtained results document a significant influence of dense common reed vegetation on retention characteristics of the studied system. Common reed can convert a significant volume of water from liquid to gas via evapotranspiration (ET) and thus prolong water retention times in the system. This is very important both technically and ecologically. Longer retention times mean a longer time for microbiological decay of wastewater. Water converted from liquid to gas causes cooling of the microclimate, which is very important, especially in intensively cultivated areas with a lack of water.

Species effects and seasonal trends on plant efflux quantity and quality in a spruce swamp forest

AimsWe aimed to compare seasonal exudate quality and quantity between Sphagnum moss, Eriophorum vaginatum (graminoid) and Vaccinium myrtillus (ericoid shrub).MethodsExudates were collected in May, July and September 2014 using a culture-based method and characterized by total organic carbon (TOC) and nitrogen (TN) contents with exudation fluxes expressed on a root-mass basis. Organic acids, sugars and amino acids in the exudates were identified by ion exchange chromatography. C and N exudate fluxes, in situ exudation fluxes and exudate contribution to soil dissolved organic matter (DOM) were estimated. Differences in exudate biodegradability were assessed by 13C pulse labeling.ResultsE. vaginatum had the largest exudation fluxes, Sphagnum the lowest, and V. myrtillus intermediate, being the greatest in July. All species mostly exuded organic acids except Sphagnum in September when sugars (allose, xylose) and amino acids (cystine) dominated. Sphagnum exudates were more C-rich and less degradable than the vascular species exudates, which released both organic and inorganic N forms. E. vaginatum exudates were richer in amino acids and citrate especially in July. Exudates contributed up to 20% to soil DOM.ConclusionsPlant species composition greatly affects exudate quantity, quality and timing. Plant exudates represent considerable contributions to soil DOM.