Photosynthetic resource-use efficiency and demographic variability in desert winter annual plants

We studied a guild of desert winter annual plants that differ in long-term variation in per capita reproductive success (lb, the product of per capita survival from germination to reproduction, l, times per capita reproduction of survivors, b) to relate individual function to population and community dynamics. We hypothesized that variation in lb should be related to species' positions along a trade-off between relative growth rate (RGR) and photosynthetic water-use efficiency (WUE) because lb is a species-specific function of growing-season precipitation. We found that demographically variable species have greater RGR and greater leaf carbon isotope discrimination (Delta, a proxy inversely related to WUE). We examined leaf nitrogen and photosynthetic characteristics and found that, in this system, variation in Delta is a function of photosynthetic demand rather than stomatal regulation of water loss. The physiological characteristics that result in low Delta in some species may confer greater photosynthetic performance during the reliably moist but low temperature periods that immediately follow winter rainfall in the Sonoran Desert or alternatively during cool periods of the day or early growing season. Conversely, while species with high Delta and high RGR exhibit low leaf N, they have high biomass allocation to canopy leaf area display. Such trait associations may allow for greater performance during the infrequent conditions where high soil moisture persists into warmer conditions, resulting in high demographic variance. Alternatively, high variance could arise from specialization to warm periods of the day or season. Population dynamic buffering via stress tolerance (low RGR and Delta) correlates negatively with buffering via seed banks, as predicted by bet-hedging theory. By merging analyses of population dynamics with functional trait relationships, we develop a deeper understanding of the physiological, ecological, and evolutionary mechanisms involved in population and community dynamics.     

Reproductive biology and biochemical composition of the brooding echinoid <Emphasis Type="Italic">Amphipneustes lorioli</Emphasis> on the Antarctic continental shelf

The bathyal West Antarctic Peninsula (WAP) shelf experiences intense seasonal variability in primary production, with summer phytoplankton blooms yielding intense pulse of phytodetritus to shelf sediments. Echinoderms form a conspicuous proportion of the deposit-feeding megabenthos on the shelf and of these Amphipneustes lorioli was the most abundant irregular echinoid. To explore the reproductive response of A. lorioli to this seasonal production cycle, A. Lorioli was sampled at one location on the WAP shelf during four separate cruises between March 2000 and March 2001. Reproductive patterns were determined by histological analyses of gonad tissue, and elemental (CHN) analyses were used to estimate the nutritional and energetic status of the body tissues. Histological analysis of the brooding echinoid A. lorioli suggested a quasi-continuous gametogenic pattern in both the ovaries and the testes. Biochemical analysis of the gonads and the gut tissues were consistent with a continuous gametogenic cycle, showing no significant changes in the biochemical composition of the tissues among seasons. Size-frequency distributions of the embryo and juvenile echinoids within the adults’ brood pouches revealed a synchronous recruitment of embryos and juveniles in specific cohorts between different adult specimens. Whilst this occurrence of different cohorts of the developing brood may be an adaptation to limited brood space, there may also be an external factor influencing the synchrony between adult individuals. Nonetheless, a continuous gametogenic cycle and the lack of seasonal variation in the biochemical composition of gonad and gut tissues suggest that this deposit-feeding irregular urchin is exploiting a persistent sediment food bank in WAP shelf sediments throughout much of the year.     

High accuracy in situ radiometric mapping

In situ and airborne gamma ray spectrometry have been shown to provide rapid and spatially representative estimates of environmental radioactivity across a range of landscapes. However, one of the principal limitations of this technique has been the influence of changes in the vertical distribution of the source (e.g. 137Cs) on the observed photon fluence resulting in a significant reduction in the accuracy of the in situ activity measurement. A flexible approach for single gamma photon emitting radionuclides is presented, which relies on the quantification of forward scattering (or valley region between the full energy peak and Compton edge) within the gamma ray spectrum to compensate for changes in the 137Cs vertical activity distribution. This novel in situ method lends itself to the mapping of activity concentrations in environments that exhibit systematic changes in the vertical activity distribution. The robustness of this approach has been demonstrated in a salt marsh environment on the Solway coast, SW Scotland, with both a 7.6 cm x 7.6 cm NaI(Tl) detector and a 35% n-type HPGe detector. Application to ploughed field environments has also been demonstrated using HPGe detector, including its application to the estimation of field moist bulk density and soil erosion measurement. Ongoing research work is also outlined.     

Quantitative differences in mitochondrial ultrastructure of a thiobiotic and an oxybiotic turbellarian

Specimens of the thiobiotic acoel Solenofilomorpha funilis Crezée, 1975 and the oxybiotic acoel Otocelis sp. were collected from Mount Desert Island, Maine, USA in spring and summer of 1982, and the ultrastructure and distribution of their mitochondria were compared. The volume density and the surface density of the mitochondria are significantly higher in the epidermis and parenchyma of S. funilis than in the corresponding tissues of Otocelis sp. Surface densities of mitochondrial cristae are higher in all tissues studied (epidermis, muscle, and parenchyma) of S. funilis than in Otocelis sp. The differences in mitochondrial ultrastructure of these two species suggest that mitochondria in anaerobic tissues differ in function from their aerobic counterparts.     

Some problems arising in analysis of large-scale animal irradiation experiments

This paper describes some of the problems that occur in experiments designed particularly to study the effects of irradiation. One of the purposes of such experiments is to provide data that allow an informed judgment on estimates of the risks for man after exposure to radiation.It is no trivial matter to establish whether exposure to agents, such as radiation, increases the probability of a tumor arising de novo or whether the effect is an advancement of the time of appearance of naturally occurring tumors. In many murine tumors, the problem of establishing which of these two possibilities is the case is increased by the high natural incidence. In order to interpret the data from carcinogenesis experiments, a knowledge of the natural history of the tumor of interest is necessary. In this paper we present data that help to elucidate the biology of lung tumors in hybrid B6CF₁/An1 mice.The rising incidence of many tumors late in life raises the question of whether a common systemic factor is involved. In experiments with female mice, relatively low doses of radiation may sterilize the ovary with subsequent hormonal imbalances that in turn may influence the appearance of tumors in a number of hormone-influenced tissues. We have found that radiation may increase not only the age-specific rates of tumors but also the probability of the number of different tumor types.The possibility of a lack of independence of the occurrences of different tumors complicates the data analysis. To answer some of the questions we have raised, it would be of considerable help to have data on the prevalence of tumors; however, such data usually involve serial killing which is costly. We have examined the possibility of obtaining prevalence data for lung tumors by the determination of the incidence of lung tumors in mice dying from causes other than lung tumors. There appears to be no difference in the prevalence of lung tumors determined by using either this approach or serial killing.     

Evaluation of an Infiltration Best Management Practice Utilizing Pervious Concrete1

Abstract: A pervious concrete infiltration basin was installed on the campus of Villanova University in August 2002. A study was undertaken to determine what contaminants, if any, were introduced to the soils underlying the site as a result of this best management practice (BMP). The average infiltration rate at the site is approximately 10^?4 cm/s. The drainage area (5,208 m²) consists of grassy surfaces (36%), standard concrete/asphalt (30%), and roof surfaces (30%) that directly connect to the infiltration beds via downspouts and storm sewers. Composite samples of infiltrated stormwater were collected from the vadose zone using soil moisture suction devices. Discrete samples were collected from a port within an infiltration bed and a downspout from a roof surface. Samples from 17 storms were analyzed for pH, conductivity, and concentrations of suspended solids, dissolved solids, chloride, copper, and total nitrogen. Copper and chloride were the two constituents of concern at this site. Copper was introduced to the system from the roof, while chloride was introduced from deicing practices. Copper was not found in porewater beneath 0.3 m and the chloride was not significant enough to impact the ground water. This research indicates that with proper siting, an infiltration BMP will not adversely impact the ground water.     

Transformative learning and adaptation to climate change in the Canadian Prairie agro-ecosystem

Agricultural production in the Canadian Prairies is expected to be negatively affected as climate change projections for the region indicate warmer temperatures, greater incidence and severity of extreme weather events, and reduced water availability and soil moisture. To understand climate change adaption, it is important to explore the learning process that underlies farmer’s adaptation practices in the region. Prairie farmers’ learning was analyzed using Transformative Learning Theory whereby learning is categorized into three types: instrumental, communicative, and transformative. All producers learned instrumentally to some degree, but farmers who placed less emphasis on maximizing economic returns generally showed secondary learning outcomes correlating economic and environmental benefits. Communicative learning was mainly limited to producer-producer dialogue to the exclusion of other organizational and institutional players in the agricultural system. Critical reflection was explored as an important precursor to transformative learning. Strong evidence of transformative learning was rare (observed in 11% of farmers), but indicators of transformative learning were diverse and was observed in 43% of farmers. Transformative learning is believed to be important for flexible decision-making and autonomous thinking, making it advantageous for responding to changing environmental conditions. The analysis shows that a large number of information sources, and communication of information in an experiential and observable way, is conducive to transformative learning. Adaptation to environmental uncertainty, resulting from changing climatic conditions, may be most effectively dealt with when individual farmers undergo transformative learning whereby underlying assumptions that govern actions, values, and claims to knowledge are questioned.     

Evaluation of a Regional Monitoring Program’s Statistical Power to Detect Temporal Trends in Forest Health Indicators

Forests are socioeconomically and ecologically important ecosystems that are exposed to a variety of natural and anthropogenic stressors. As such, monitoring forest condition and detecting temporal changes therein remain critical to sound public and private forestland management. The National Parks Service’s Vital Signs monitoring program collects information on many forest health indicators, including species richness, cover by exotics, browse pressure, and forest regeneration. We applied a mixed-model approach to partition variability in data for 30 forest health indicators collected from several national parks in the eastern United States. We then used the estimated variance components in a simulation model to evaluate trend detection capabilities for each indicator. We investigated the extent to which the following factors affected ability to detect trends: (a) sample design: using simple panel versus connected panel design, (b) effect size: increasing trend magnitude, (c) sample size: varying the number of plots sampled each year, and (d) stratified sampling: post-stratifying plots into vegetation domains. Statistical power varied among indicators; however, indicators that measured the proportion of a total yielded higher power when compared to indicators that measured absolute or average values. In addition, the total variability for an indicator appeared to influence power to detect temporal trends more than how total variance was partitioned among spatial and temporal sources. Based on these analyses and the monitoring objectives of the Vital Signs program, the current sampling design is likely overly intensive for detecting a 5 % trend·year^?1 for all indicators and is appropriate for detecting a 1 % trend·year^?1 in most indicators.     

The Effectiveness of Asulam for Bracken (<Emphasis Type="Italic">Pteridium aquilinum</Emphasis>) Control in the United Kingdom: A Meta-Analysis

Bracken (Pteridium aquilinum) is a major problem for livestock-based extensive agriculture, conservation, recreation, and game management globally. It is an invasive species often achieving dominance to the detriment of other species. Control is essential to maintain plant communities such as grassland and lowland heath or if extensive grazing by domestic stock, particularly sheep, is to be viable on upland margins. Bracken is managed primarily by herbicide application or cutting but other techniques including rolling, burning, and grazing are also utilized. Here we evaluate the evidence regarding the effectiveness of asulam for the control of bracken. Thirteen studies provided data for meta-analyses which demonstrate that application of the herbicide asulam reduces bracken abundance. Subgroup analyses indicate that the number of treatments had an important impact, with multiple follow-up treatments more effective than one or two treatments. Management practices should reflect the requirement for repeated follow-up. There is insufficient available experimental evidence for quantitative analysis of the effectiveness of other management interventions, although this results from lack of reporting in papers where cutting and comparisons of cutting and asulam application are concerned. Systematic searching and meta-analytical synthesis have effectively demonstrated the limits of current knowledge, based on recorded empirical evidence, and increasing the call for more rigorous monitoring of bracken control techniques. Lack of experimental evidence on the effectiveness of management such as rolling or grazing with hardy cattle breeds contrasts with the widespread acceptance of their use through dissemination of experience.     

The importance of atmospheric deposition, charge and atomic mass to the dynamics of minor and rare elements in developing, ageing, and wilted leaves of beech (Fagus sylvatica L.)

The amounts of sixty elements in developing, maturing, senescent and wilting leaves, and in the wintering dead leaves attached to the branches, are reported for a beech (Fagus sylvatica) forest on mor Podzol in south Sweden, a site with no local sources of pollution or geological anomalies. The amounts (contents per leaf) of K (potassium), Rb (rubidium), Cs (caesium), Cu (copper) and P (phosphorus) were highest in young leaves, decreasing throughout the growing season and usually in the subsequent winter. The entirely opposite pattern with a continuous, mostly even increase of the amounts was measured with Be (beryllium), Ba (barium), Hg (mercury), Al (aluminium), Tl (thallium), Pb (lead), Bi (bismuth), V (vanadium), W (tungsten), As (arsenic), Sb (antimony), and Se (selenium). Amounts of rare-earth elements and some transition metals, such as Co (cobalt), Ti (titanium), and the actinides Th (thorium) and U (uranium) were more stable during the growing season, after an initial increase in early summer, but increased greatly in the winter. This winter increase in dead attached leaves has to be accounted for by uptake from long-distance transported constituents in dry and wet deposition. It was similar to deposition rate estimates using moss carpets from the same locality. A passive uptake was positively related to ionic charge and atomic mass. However, the amounts of several, mainly non-essential elements, such as Ni (nickel), Sc (scandium), Zr (zirconium), Cr (chromium), Ag (silver), and Cd (cadmium) were not much lower in the young or maturing leaves than in the wintered dead leaves of this deciduous (hardwood) forest and a proportion apparently originated from internal translocation in the trees. Seasonal fluxes or cycling of many of the scarce or rare elements reported here have never been studied before in forest ecosystems.