Bent Lorenzen

Are Phragmites-dominated wetlands a net source or net sink of greenhouse gases?

Phragmites australis wetlands act as a sink for greenhouse gases by photosynthetic assimilation of carbon dioxide (CO2) from the atmosphere and sequestration of the organic matter produced in the wetland soil. The wetlands also act as a source for greenhouse gases by emission of sediment-produced methane (CH4) to the atmosphere. In P. australis wetlands, the dominant mechanism of CH4 release to the atmosphere is internal gas transport in the plants, primarily by pressurized convective gas flow. The time periods of carbon fixation and CH 4 release therefore vary seasonally and diurnally. The balance between net CO2-assimilation and CH4 emission determines if a wetland can be regarded as a net sink or a net source of greenhouse gases, and hence, the function of the wetland in relation to global climate change. On an annual basis up to 15% of the net carbon fixed by the wetlands may be released to the atmosphere as CH 4. Because of the different infrared absorption characteristics and atmospheric longevity of CH4 and CO2, the warming effect of CH4 in the atmosphere is about 21 times higher on a mass basis than CO2 over a 100-year timescale. Thus, the immediate carbon balance, coupled with the different physical characteristics of the two gases, would suggest that although some wetlands function as a net sink for CO2, the wetlands still increase the greenhouse effect because of their release of CH4. However, the short adjustment time for CH4 in the atmosphere means that, over a longer time scale, the radiative forcing of CH4 is less relative to CO2 and the wetlands effectively become a sink for greenhouse gases. Wetlands may therefore be regarded as a source for greenhouse gases and so increase radiative forcing if evaluated on a short time scale (decades), but as a sink for greenhouse gases and thus attenuating radiative forcing if evaluated over longer time scales (>100 years).

Changes in leaf spectral properties induced in barley by cereal powdery mildew

Abstract Changes in spectral properties induced in barley leaves by cereal mildew were evaluated to identify important regions in the 400–1100 nm spectrum which can be used to detect infected barley leaves. Five spring barley lines grown in greenhouses were inoculated with mildew. During a 20-day period the directional spectral reflectance of the adaxial surface of the first leaf blades was recorded as well as the g d.wt. cm−2 leaf area, % water, and total chlorophyll content of the leaves. 1) The spectral reflectance of control leaves and inoculated resistant leaves was very similar throughout the experiment. 2) No changes in spectral reflectance from inoculated leaves were evident within the first 3 days following inoculation. 3) Six days after inoculation, the susceptible lines showed significantly higher reflectance in the visible (422–712 nm) wavelength region. 4) Ten days after inoculation, the susceptible lines showed significantly higher spectral reflectance between 400 and 1100 nm compared to control plants. 5) The differences in near infrared reflectance between control and infected plants observed were small and occurred several days later than changes in the visible region. 6) The differences in reflectance of blue and red wavebonds between control and inoculated plants were highly correlated to the cholorophyll content of infected leaves, r = 0.89 and 0.95, respectively. 7) Significant changes in spectral relectance of single leaves infected with mildew occur earlier in the visible region of the spectrum (400–706) than in the near infrared part of the spectrum.

CONTROLS ON SOIL CELLULOSE DECOMPOSITION ALONG A SALINITY GRADIENT IN A PHRAGMITES AUSTRALIS WETLAND IN DENMARK

Although soil organic matter decomposition is an important process determining nutrient transformations and availability in wetland ecosystems, few studies have attempted to assess which environmental factors are most important in controlling spatial differences in decomposition rates found along environmental gradients. Relative soil decomposition was determined in a Phragmites australis Cav. Trin ex Steudel dominated wetland in northern Jutland, Denmark along a natural salinity gradient, where nutrients, soil moisture, temperature and salinity among other factors also varied. Our objective was to identify which edaphic factors most limited rates of relative soil decomposition, as evaluated by measuring cellulose decomposition with the cotton strip technique. Replicate cotton strips were placed at seven marsh sites along the salinity gradient, and soil and interstitial water samples were collected and analyzed for major macro- and micronutrients (NH4‐N, NO3‐N, P, PO4, K, Mg, Ca, Na, S, Fe, Mn, Zn, Cu, Mo, B, Si), pH, Eh, conductivity, temperature, and soluble sulfides. Cellulose decomposition, expressed as cotton tensile strength loss (CTSL) per day, decreased with increasing salinity, except at the highest salinity site where a significant increase occurred. Mean CTSL values, averaged for each marsh site, varied 3-fold from 1.8 to 5.5% loss per day. Principal component and multiple regression analyses were used to prioritize the importance of the various factors that might control this spatial difference in CTSL rates. Although soil conductivity (salinity) accounted for the large percentage (45%) of the variation in the environmental data, soil fertility- and soil reduction-associated variables explained the greatest percentage (56%) of the spatial variation in cellulose decomposition. Univariate correlation analyses supported the conclusion that soil fertility, primarily inorganic nitrogen and phosphorus, is the major

WASTEWATER TREATMENT IN CONSTRUCTED REED BEDS IN DENMARK — STATE OF THE ART

Since 1983 more than 130 reed bed systems have been constructed in Denmark. All systems are designed as subsurface flow systems which are thought to pass wastewater horizontally through the macrophyte rhizosphere. The reed bed systems vary in area between 100 and 13,000 m2, but most systems are less than 1,000 m2. Most of the systems treat domestic sewage. In this paper, the state of the art of the Danish systems is evaluated. Data on design, loading characteristics and inlet and effluent quality control analyses from the systems, are presented. In addition, data on soil composition (texture, content of Ca, Fe and Al) from 42 of the systems are presented in order to evaluate the performance of the systems in relation to growth media composition. Extensive investigations have been carried out in five systems, including depth-fractionated soil analyses, vegetation cover and distribution of below-ground biomass. The water retention time in two of the systems has been elucidated by tracer experiments. In general the Danish constructed reed beds can meet the official requirements for BOD5 (20 mg l-1) and suspended solids (20 mg l-1). The removal efficiencies for nitrogen and phosphorus, however, are generally poor (25-50%). The data indicate that the major removal process for nutrients is sedimentation within the beds. Low hydraulic conductivity of the bed substrate is found to be the main problem for sufficient treatment performance in Danish constructed reed beds. The design of the Danish constructed reed beds has only been slightly modified during the years 1983-90 in order to decrease surface run-off, and to improve water distribution in the soil body of the systems. Possible design changes for improving the treatment efficiency in macrophyte-based wastewater treatment systems could be identified by studying those which work most efficient efficiently.

Seed germination of two Everglades species, Cladium jamaicense and Typha domingensis

The germination requirements of Cladium jamaicenseCrantz and Typha domingensisPers. were studied under controlled conditions in the laboratory. Treatments included six temperature regimes, (constant temperatures of 15 20, 25, 30C, and two fluctuating day : night temperature regimes of 25 : 10C and 30 : 20C), two light levels (14 : 10 h light : dark photoperiod and 24 h dark environment), two substrates (peat and water) and two O2 levels (atmospheric and low (4.34%) O2 concentration) using a complete randomized block design. The average incubation period needed for seeds to germinate was shorter for T. domingensis (1.1‐19.5 days) than for C. jamaicense (26‐46 days) and the final germination percentage was higher for T. domingensis than for C. jamaicense (85 vs. 42 %). Cladium jamaicenseonly germinated with fluctuating temperatures whereas T. domingensisgerminated at all temperature regimes. Light was required for T. domingensisseeds to germinate, whereas C. jamaicensecould germinate at a reduced rate in the dark. Peat substrate had a positive effect on germination in both species. Peat substrate shortened the incubation period for seeds of both species, enhanced germination of T. domingensis, especially at low temperatures, and enhanced germination of C. jamaicense in the dark. Low oxygen availability did not influence the germination of C. jamaicense but enhanced germination of T. domingensisat low temperatures. Although the two species differ significantly in their germination requirements and responses to specific environmental conditions, germination of both these species was enhanced by environmental conditions typical of exposed water saturated mudflats or sediment surfaces. Typha domingensisproduces a large number of small seeds, which do not germinate when covered by sediment. In contrast, C. jamaicenseproduces fewer and larger

Die-back of Phragmites australis : influence on the distribution and rate of sediment methanogenesis

Methanogenesis was measured during the summer of 1994, in sediment coresand bulk samples from a Phragmites australis wetland in northern Jutland,Denmark. We compared sediment from healthy reed and dying-back reed, andan open lagoon resulting from die-back. Cores revealed variability withdepth and between sites, with the highest rates coinciding with layers oforganic gyttja, and negligible methane production from the underlying sandbase. Methanogenesis rates in the lagoon and die back sites were higher(up to 100–150 nmol h-1 g-1dry wt. sediment) than in the healthy reed (50–80 nmolh-1 g-1), with the highest rates being recordedfrom May to July. At these times, methanogenesis was markedly temperature-limited; samples incubated at 30 °C anon-limiting temperature, gave rates as high as 200–400nmol h-1 g-1 for the lagoon and die-backareas and 150 nmol h-1 g-1 for the healthyarea. Addition of 8 mM acetate and H2/CO2headspace suggested that both acetate-fermenting andCO2-reducing bacteria were present. Acetate additions suggested some co-limitation by substrate availability, with acetate limitation occurring in the healthy site during July and in the die-back site during August. Lower rates during August, especially in the healthy area, were associated with low water levels which resulted in more oxidized sediments. The data reveal highly variable methanogenesis in the sediment which, when considered with sediment depths, indicates that sites of Phragmites die-back have significantly greater rates of anaerobic mineralization than surrounding healthy wetland, and may be intense sources of methane.

Radiometric estimation of biomass and nitrogen content of barley grown at different nitrogen levels

Abstract Field measurements of red (655 nm) and near-infrared (NIR: 805 nm) canopy reflectance from barley grown at different nitrogen levels are related to changes in biomass accumulation and total nitrogen content of the plant material. Crop biomass and the NIR reflectance or the NIR/red index are highly correlated. The variation in reflectance and index accounted for by the biomass is between 93 and 99 per cent. In the different nitrogen treatments the percentage nitrogen content of the crop is negatively correlated with the biomass accumulation, and the nitrogen content declines in a exponential manner. The correlation coefficient between plant nitrogen content and biomass declines from −0·99 to −0·92 with increasing nitrogen application rates. However, at any given chronological age the total plant nitrogen content and the accumulated biomass are strongly correlated in a curvilinear manner. Hence on each sampling date the NIR and NIR/red reflectance are closely related to percentage plant nitrogen in...

Nutrient and growth responses of cattail (Typha domingensis) to redox intensity and phosphate availability

BACKGROUND AND AIMS In the Florida Everglades, the expansion of cattail (Typha domingensis) into areas once dominated by sawgrass (Cladium jamaicense) has been attributed to altered hydrology and phosphorus (P) enrichment. The objective of this study was to quantify the interactive effects of P availability and soil redox potential (Eh) on the growth and nutrient responses of Typha, which may help to explain its expansion. METHODS The study examined the growth and nutrient responses of Typha to the interactive effects of P availability (10, 80 and 500 microg P L(-1)) and Eh level (-150, +150 and +600 mV). Plants were grown hydroponically in a factorial experiment using titanium (Ti(3+)) citrate as a redox buffer. KEY RESULTS Relative growth rate, elongation, root-supported tissue/root ratio, leaf length, lateral root length and biomass, as well as tissue nutrient concentrations, were all adversely affected by low Eh conditions. P availability compensated for the negative effect of low Eh for all these variables except that low P stimulated root length and nutrient use efficiency. The most growth-promoting treatment combination was 500 microg P L(-1)/ + 600 mV. CONCLUSIONS These results, plus previous data on Cladium responses to P/Eh combinations, document that high P availability and low Eh should benefit Typha more than Cladium as the growth and tissue nutrients of the former species responded more to excess P, even under highly reduced conditions. Therefore, the interactive effects of P enrichment and Eh appear to be linked to the expansion of Typha in the Everglades Water Conservation Area 2A, where both low Eh and enhanced phosphate availability have co-occurred during recent decades.

Growth and nutrient responses of Eloecharis cellulosa (Cyperaceae) to phosphate level and redox intensity.

Phosphorus (P) availability limits plant growth in many ecosystems. The ability of plants to explore for soil P is often impaired by nonresource stressors. Understanding the effects of these stressors on P acquisition in oligotrophic environments is critical in predicting species dominance. Growth and nutrient responses of Eleocharis cellulosa to redox intensity and phosphate level were evaluated under three redox potentials (Eh) and three phosphate (PO(4)) levels (P). Although low Eh (-150 mV) decreased root length at low P, Eh did not affect shoot height, relative growth rate (RGR), shoot elongation, photosynthesis, or biomass of E. cellulosa. Low PO(4) (10 μg P · L(-1)) strongly inhibited growth. Shoot height, RGR, elongation, photosynthesis, and biomass were lower at 10 μg P · L(-1) than at 80 or 500 μg P · L(-1). None of the growth variables, except the ratio of root-supported biomass to root biomass, significantly differed between the 80 and 500 μg P · L(-1) treatments. At low P, plants allocated relatively more biomass to roots than to shoots, compared to the medium and high P levels. Eleocharis cellulosa is well adapted to flooded conditions that lower soil Eh, and elevated PO(4) levels further promote its growth potential.

ROOT PHOSPHATASE ACTIVITY IN CLADIUM JAMAICENSE AND TYPHA DOMINGENSIS GROWN IN EVERGLADES SOIL AT AMBIENT AND ELEVATED PHOSPHORUS LEVELS

Activity of root phosphatase was examined in Cladium jamaicense (sawgrass) and Typha domingensis (cattail) grown under controlled conditions in Everglades peat with different inorganic P availabilities and flooding regimes. Cladium root phosphatase activity was significantly greater than for Typha when both were subjected to relatively low inorganic phosphorus concentrations (10 to 80 μg l−1) in the interstitial water, indicating a greater potential for Cladium to use organic phosphorus compounds as a phosphate source. When inorganic phosphorus concentration was elevated (500 μg l−1), internal root phosphate concentrations increased and root phosphatase activities decreased in both species to similar levels. Thus, root phosphatase activity in these species is induced by low ambient inorganic phosphate concentrations. The relatively greater ability of Cladium to hydrolyze organic phosphorus compounds indicates that it is physiologically better adapted to peat-based, low inorganic phosphorus conditions and helps explain this species’ historic dominance in peat-based Everglades soils.