Carex

Abstract: Species composition affects the carbon turnover and the formation and emission of the greenhouse gas methane (CH4) in wetlands. Here we investigate the individual effects of vascular plant species on the carbon cycling in a wetland ecosystem. We used a novel combination of laboratory methods and controlled environment facilities and studied three different vascular plant species (Eriophorum vaginatum, Carex rostrata and Juncus effusus) collected from the same wetland in southern Sweden. We found distinct differences in the functioning of these wetland sedges in terms of their effects on carbon dioxide (CO2) and CH4 fluxes, bubble emission of CH4, decomposition of C-14-labelled acetate into (CH4)-C-14 and (CO2)-C-14, rhizospheric oxidation of CH4 to CO2 and stimulation of methanogenesis through root exudation of substrate ( e. g., acetate). The results show that the emission of CH4 from peat - plant monoliths was highest when the vegetation was dominated by Carex (6.76 mg CH4 m(-2) h(-1)) than when it was dominated by Eriophorum (2.38 mg CH4 m(-2) h(-1)) or Juncus (2.68 mg CH4 m(-2) h(-1)). Furthermore, the CH4 emission seemed controlled primarily by the degree of rhizospheric CH4 oxidation which was between 20 and 40% for Carex but > 90% for both the other species. Our results point toward a direct and very important linkage between the plant species composition and the functioning of wetland ecosystems and indicate that changes in the species composition may alter important processes relating to controls of and interactions between greenhouse gas fluxes with significant implications for feedback mechanisms in a changing climate as a result. (Less)

Abstract: Grazed and ungrazed sites subjected to different fire frequencies were sampled on the Konza Prairie Research Natural Area in northeast Kansas after 4 years of bison grazing (1987-1991). The objective was to study effects of bison grazing on plant species composition and diversity components (plant species richness, equitability, and spatial heterogeneity) in sites of contrasting fire frequency. Cover and frequency of cool-season graminoids (e.g. Poa pratensis L., Agropyron smithii Rydb., Carex spp.) and some fortes (e.g. Aster ericoides [A. Gray] Howell, and Oxalis stricta L.) were consistently higher in sites grazed by bison than in ungrazed exclosures, whereas the dominant warm-season grasses (Andropogon gerardii Vitman, Sorghastrum nutans [L.] Nash, Panicum virgatum L., Schizachyrium scoparium [Michx.] Nash) and other forbs (e.g. Solidago missouriensis Nutt.) decreased in response to bison. Plant species diversity (H') and spatial heterogeneity in all areas sampled were significantly increased by bison. Increased heterogeneity and mean species richness in grazed prairie (40 species per sample site) compared to ungrazed prairie (29 species per site) were likely a result of greater microsite diversity generated by bison, whereas preferential grazing of the dominant grasses and concomitant increases in subordinate species resulted in an increase in equitability of species abundances. Species/area relationships indicated greater effects of bison on plant species richness with increasing sample area. Increases in plant diversity components associated with bison grazing were generally greater in annually burned than in 4-year burned sites. Effects of ungulate grazers on floristic diversity have important implications given recent evidence that plant species diversity and the compositional and production stability of grassland plant communities are positively related.

Abstract: We studied the effects of experimentally induced variation in leaf litter chemistry on leaf litter decomposition and leaf litter nutrient release of Carex species from habitats that differ in nutrient availability. Carex diandra, C. rostrata, and C. lasiocarpa are dominant in less productive mesotrophic fens, whereas C. acutiformis is dominant in more productive eutrophic fens. For each species, three types of litter were used: litter collected in the field (FLD); and litter from experimental populations grown at low (LN: 3.3 g N·m−2·yr−1) and high N supply (HN: 20.0 g N·m−2·yr−1). For all the litter chemistry parameters studied there were highly significant interactions between species and litter type. This implies that, due to differential plant-mediated controls on leaf litter chemistry, it is not always possible to predict changes in litter chemistry in response to increased nutrient supply. Litter decay was determined in a long-term (3 yr) field experiment using litter bags. The litter types of each species were incubated at their native growing sites. Contrary to what is generally found, the leaf litter decomposition rate of the species growing at the nutrient-poorest site (C. diandra) was higher than that of the species growing at the nutrient-richest site (C. acutiformis). Only for C. diandra and C. lasiocarpa was the decomposition rate of the litter from the HN treatment higher than that of the field litter. Thus, increased nutrient supply does not necessarily lead to higher litter decomposition rates. Nutrient controls on litter decay changed with time: initial litter decay (≤3 mo) was strongly controlled (high r2 values) by all P-related litter quality parameters, whereas long-term litter decay (>1 yr) was most strongly related with the phenolics : N ratio, the phenolics : P ratio, the lignin : N ratio, and the C:N ratio. Our data suggest that high levels of atmospheric N deposition, such as in the study area (The Netherlands), may lead to a relative shortage of P in the plant-derived substrates for bacteria and fungi. As a result, P-related litter chemistry parameters exert a strong influence on litter decay. Our data did not support the hypothesis that high-nutrient species increase nutrient cycling due to the production of easily decomposable litter with high rates of nutrient release. The leaf litter from Carex acutiformis, the species from the high-productivity fens, decomposed more slowly than that of the other species, immobilized more N and P and had a longer period of net N and P immobilization. However, this species has a higher litter production than the other species and thereby increases the rate of nutrient cycling. At the intraspecific level, increased nutrient supply led to lower amounts of immobilized N and P and faster N and P release from litter in most species, and thereby to a higher rate of nutrient cycling. This positive feedback between nutrient supply rate and the rate of nutrient cycling is reinforced by the increase in litter production in response to increased nutrient supply.

Abstract: (1) Field experiments were conducted to examine the response of mature plants to different edaphic conditions in a subarctic salt marsh. Five dominant perennial vascular species characteristic of distinct zones within the marsh were studied. The specific effects of salinity, waterlogging, and soil type were determined. (2) Results from a 2-year reciprocal transplant experiment demonstrated that Carex lyngbyaei, C. ramenskii and Poa eminens (species characteristic of less saline sites) were inhibited in the outer mudflat zone, where soil water salinity was highest (up to 35%S). The above-ground biomass of Puccinellia nutkaensis, a dominant species on the outer mudflat, was three to four times greater at more inland, drained sites; this species usually died in the waterlogged inner sedge marsh. Triglochin maritimum from the inner mudflat grew well in all sites to which it was transplanted. (3) When cultured for 8 weeks in pots of either peat or silt, all species grew best in the least saline (3 c1) waterlogged treatment. The growth of Puccinellia nutkaensis was greatly inhibited in peat; fertilization (N, P and K) overcame the inhibition. (4) The relative salt tolerance of each species corresponded with the soil salinity in its zone of occurrence, and may determine its seaward limit of distribution within the marsh. Where potential distributions overlap, as at most moderate and low salinity sites, biotic factors such as between-species competition may be more important in maintaining the observed zonation patterns. Puccinellia nutkaensis, in particular, appears to be restricted to the outer mudflat because it is a poor competitor in the inner mudflat and riverbank levee zones.