Development of an epiphyte indicator of nutrient enrichment: A critical evaluation of observational and experimental studies

An extensive review of the literature describing epiphytes on submerged aquatic vegetation (SAV), especially seagrasses, was conducted in order to evaluate the evidence for response of epiphyte metrics to increased nutrients. Evidence from field observational studies, together with laboratory and field mesocosm experiments, was assembled from the literature and evaluated for a hypothesized positive response to nutrient addition. There was general consistency in the results to confirm that elevated nutrients tended to increase the load of epiphytes on the surface of SAV, in the absence of other limiting factors. In spite of multiple sources of uncontrolled variation, positive relationships of epiphyte load to nutrient concentration or load (either nitrogen or phosphorus) often were observed along strong anthropogenic or natural nutrient gradients in coastal regions. Such response patterns may only be evident for parts of the year. Results from both mesocosm and field experiments also generally support the increase of epiphytes with increased nutrients, although outcomes from field experiments tended to be more variable. Relatively few studies with nutrient addition in mesocosms have been done with tropical or subtropical species, and more such controlled experiments would be helpful. Experimental duration influenced results, with more positive responses of epiphytes to nutrients at shorter durations in mesocosm experiments versus more positive responses at longer durations in field experiments. In the field, response of epiphyte biomass to nutrient additions was independent of climate zone. Mesograzer activity was a critical covariate for epiphyte response under experimental nutrient elevation, but the epiphyte response was highly dependent on factors such as grazer identity and density, as well as nutrient and ambient light levels. The balance of evidence suggests that epiphytes on SAV will be a useful indicator of persistent nutrient enhancement in many situations. Careful selection of appropriate temporal and spatial constraints for data collection, and concurrent evaluation of confounding factors will help increase the signal to noise ratio for this indicator.     

Historical record of human impact in a lake of northern China: Magnetic susceptibility,nutrients, heavy metals and OCPs

The historical record (1859–2011) of magnetic susceptibility, total organic carbon, total nitrogen, δ¹³C_org, δ¹⁵N, As, Cd, Hg, Pb, and organochlorine pesticide (OCP) signatures in Baiyangdian Lake was used to analyze the water environmental changes due to human activities. The results indicate the following: the status of the lake approaches the background condition in 1859–1950s; the lake suffered increasing anthropogenic effects from the 1950s because of increasing human activities such as coal-fired power plant operations since 1958, fertilizer use in the agriculture and land transformation since the 1950s, steelmaking between the 1960s and 1970s, machinery manufacturing since the 1970s, use of petrol containing alky-lead since 1990; the lake has been in a contaminated condition since the 2000s. This study confirms that OCPs have been effectively controlled in the area, the level of nutrient and heavy metal pollution is increasing, coal-fired power plants are an important source of Hg, and the use of petrol containing alky-lead has accelerated the accumulation of Pb in the environment. The study indicates that magnetic susceptibility can be used as a rapid, simple, and non-destructive tool for assessment of organic and heavy metal pollution in the lake.     

Climatic change and its ecological implications at a subantarctic island

Summary Marion Island (47°S, 38°E) has one of the most oceanic climates on earth, with consistently low air temperatures, high precipitation, constantly high humidity, and low incident radiation. Since 1968 mean surface air temperature has increased significantly, by 0.025° C year^–1. This was strongly associated with corresponding changes in sea surface temperature but only weakly, or not at all, with variations in radiation and precipitation. We suggest that changing sealevel (atmospheric and oceanic) circulation patterns in the region underlie all of these changes. Sub-Antarctic terrestrial ecosystems are characterized by being species-poor and having a simple trophic structure. Marion Island is no exception and a scenario is presented of the implications of climatic change for the structure and functioning of its ecosystem. Primary production on the island is high and consequently the vegetation has a large annual requirement for nutrients. There are no macroherbivores and even the insects play only a small role as herbivores, so most of the energy and nutrients incorporated in primary production go through a detritus, rather than grazing, cycle. Ameliorating temperatures and increasing CO₂ levels are expected to increase productivity and nutrient demand even further. However, most of the plant communities occur on soils which have especially low available levels of nutrients and nutrient mineralization from organic reserves is the main bottleneck in nutrient cycling and primary production. Increasing temperatures will not significantly enhance microbially-mediated mineralization rates since soil microbiological processes on the island are strongly limited by waterlogging, rather than by temperature. The island supports large numbers of soil macro-arthropods, which are responsible for most of the nutrient release from peat and litter. The activities of these animals are strongly temperature dependent and increasing temperature will result in enhanced nutrient availability, allowing the potential for increased primary production due to elevated temperature and CO₂ levels to be realized. However, housemice occur on the island and have an important influence on the ecosystem, mainly by feeding on soil invertebrates. The mouse population is strongly temperature-limited and appears to be increasing, possibly as a result of ameliorating temperatures. We suggest that an increasing mouse population, through enhanced predation pressure on soil invertebrates, will decrease overall rates of nutrient cycling and cause imbalances between primary production and decomposition. This, along with more direct effects of mice (e.g. granivory) has important implications for vegetation succession and ecosystem structure and functioning on the island. Some of these are already apparent from comparisons with nearby Prince Edward Island where mice do not occur. Other implications of climatic change for the island are presented which emphasize the very marked influences that invasive organisms have on ecosystem structure and functioning. We suggest that changing sealevel circulation patterns, by allowing opportunities for colonization by new biota, may have an even more important influence on terrestrial sub-Antarctic ecosystems than is suggested merely on the basis of associated changes in temperature or precipitation.     

Abiotic stresses increase plant regeneration ability

In disturbed habitats, vegetative regeneration is partly ruled by plant reserves and intrinsic growth rates. Under nutrient-limiting conditions, perennial plants tend to exhibit an increased allocation to storage organs. Under mechanically stressful conditions, plants also tend to increase allocation to below-ground biomass and storage organs. We tested whether those stresses acting differently on plants (nutrient level versus mechanical forces) led to similar effect on storage organs and regeneration ability. We measured, for an aquatic plant species, (1) the size and allocation to storage organs (stems) and (2) the regeneration ability of the storage organs. Plant stems were collected in 4 habitats ranked along a nutrient stress gradient, and having encountered null versus significant mechanical stress (flowing water). All stems were placed in similar neutral conditions and left for a period of 6 weeks before measuring their survival and growth. Dry mass allocation to the storage organ (stem) was higher in stressful habitats. Moreover, stress encountered by plants before the experiment significantly affected regeneration: stems of previously stressed plants (i.e. plants that had grown in nutrient-poor or mechanically stressful habitats) survived better than unstressed ones. Stems of plants having encountered mechanical stress before the experiment had increased growth in nutrient-rich habitats but reduced growth in the poorest habitats. These results demonstrate that regeneration could rely on the level of stress previously encountered by plants. Stress could lead to greater regeneration ability following mechanical failure. The possible mechanisms involved in these results are discussed.     

Performance of an ecological treatment system at three strengths of dairy wastewater loading

Ecological treatment systems, which rely on renewable resources, have successfully treated municipal and industrial effluents with reduced costs compared to conventional methods, but their capacity to treat dairy wastewater is unknown. In order for ecological treatment systems to be practical for agriculture they must be able to treat a significant portion of a dairy's daily wastewater production. In this study, the impact of three strengths of dairy wastewater on effluent water quality was assessed. Three ratios of wastewater and city water—(1) one part wastewater:three parts city water, (2) one part wastewater:one part city water, and (3) two parts wastewater:one part city water—were each pumped into an ecological treatment system. Influent and effluent water samples were analyzed for PO₄-P, TP, TN, NH₄-N, NO₃-N, total suspended solids (TSS), and carbonaceous biochemical oxygen demand (CBOD₅). Influent dairy wastewater volumetric loading rates were much greater than those of municipal wastewater. Regardless of influent wastewater strength, concentrations of all measured variables were significantly reduced between the influent and effluent of the ecological treatment system. At the lowest wastewater strength, PO₄-P was reduced 39%, TN 83%, and NH₄-N 89%, while at the highest wastewater strength, PO₄-P was reduced 41%, TN 79%, and NH₄-N 70%. Increased wastewater strength required greater aerobic treatment volume to reduce concentrations of NH₄-N and CBOD₅.     

Trifluralin-induced chlorosis in soybeans (Glycine max (L.) Merr.) grown on clayey,high pH soils

Summary The cause of leaf chlorosis, frequently observed on soybeans (Glycine max (L.) Merr.) grown on high pH soils of the Mississippi Blackland Prairie, is thought to be low Fe availability and restricted rooting. Three greenhouse experiments were conducted using two soils, Sumter, a Rendollic Eutrocrept and Okolona, a Typic Chromudert; nine soybean cultivars differing in Feefficiency; and trifluralin (α-α-α-trifluoro-2,6-dinitro-N, N-di-propyl-p-toludine). Trifluralin at rates greater than 0.56 kg/ha caused chlorosis which was more severe on the Sumter, a soil low in available Fe. Fe-efficient cultivars were more resistant to the chlorosis induced by trifluralin than the Fe-inefficient cultivars. It was concluded that the chlorosis is an Fe deficiency caused by reduced uptake. The herbicide-induced chlorosis can be avoided by proper dosage and placement of the herbicide.     

Micronutrient availability to cereals from calcareous soils

Summary The mechanism of higher grain production of wheat (Triticum aestivum L.) by four tillage methods was explored on a sandy calcareous soil of Sahl-Al Jafara, Libya, during the year 1976–77. Tillage methods increased grain yield and dry matter weight at the boot stage in the order of no-tillage<rotovator=disc plough < subsoiler. Rotovation to 15 cm and disc ploughing to 25 cm depth enhanced grain production mainly by eliminating weed competition. In both the cases, roots penetrated < 25 cm where plough-pan existed.Further yield increases by 50 cm deep subsoiling seems to be mainly explained by N and Cu rise in plants from their marginal to optimum levels and by reduction of Mn deficiency in plant shoots. Penetration of roots beyond the 25 cm plough-pan apparently resulted in higher absorption of these nutrients from leached or native soil supplies. Subsoiling also resulted in greater Zn concentration in plant shoots which, under marginal to deficient conditions, will also increase grain production.     

Effect of long-term NPK application on secondary and micro nutrient contents ofCoffea canephora Pierre

Summary The Ca, Mg, S, Mn and Cu contents in leaves ofCoffea canephora trees selected in 64 plots under a 4×4×2 NPK trial were determined after seven years of fertilizer application. It was observed that NPK applications increased Mn uptake, P application increased the uptake of Cu, Ca and S while application of N and K did not enhance the uptake of Cu, Mg, Ca and S. It was shown that as a result of NPK applications, Ca and Mg had become deficient in coffee leaves, which corroborates earlier findings based on soil analysis.     

M(en)TORship lessons on life and death by the integrated stress response

Cells employ pro-survival and pro-adaptive pathways to cope with different forms of environmental stress. When stress is excessive, and the damage caused by it is unsustainable, cells engage pro-death pathways, which are in place to protect the host from the deleterious effects of harmed cells. Two important pathways that determine the balance between survival and death of stressed cells are the integrated stress response (ISR) and the mammalian target of rapamycin (mTOR), both of which converge at the level of mRNA translation. The two pathways have established avenues of communication to control their activity and determine the fate of stressed cells in a context-dependent manner. The functional interplay between the ISR and mTOR may have significant ramifications in the development and treatment of human diseases such as diabetes, neurodegeneration and cancer.