Water and salt movement in soil driven by crop roots: a controlled column study

Water deficit and salt accumulation in soil presents serious problems to crop production in semi-arid regions. These problems depend on the active transpiration stream and the selective absorption of ions by crop roots. In this study, a large sized soil column system was used to examine the dynamics of water and ion transport and salt accumulation in soil layers. Special reference was placed on the effects of the active and selective absorption by roots of different crops (i.e., corn plants, sunflower plants and no plants). The column system was equipped with on-line systems for the control of groundwater level. Soil water content sensors enabled time-course evaluations of the volumetric water content and hence upward flux of the groundwater in the soils at different depths. Furthermore, the distribution and accumulation of ions in soil layers, plant organs and xylem sap were analyzed using ion chromatography. In this column experiment, diurnal and longer term changes in water movement and ion accumulation in soil, affected by root absorption characteristics of plants, were evaluated quantitatively. The results demonstrated that the column system was applicable for the quantitative analysis of the effects of root absorption by different crops on water deficit and salinization in soils.     

Expression of EGFP driven by BmNPV orf4 promoter, a novel immediate early promoter

Bombyx mori nucleopolyhedrovirus (BmNPV) orf4 has been shown to be expressed at very early stage of Bm-NPV infection cycle. In this study, using transient expression experiment, we demonstrated for the first time that orf4 promoter is an immediate early promoter, indicating that orf4 may play a role in the immediate-early stage of BmNPV infection. Moreover, with the recently developed Bac-to-Bac/BmNPV baculovirus expression system and a modified pFast-Bac1 whose polyhedrin promoter was replaced with orf4 promoter, a recombinant bacmid baculovirus expressing enhanced green fluorescent protein (EGFP) under the control of orf4 promoter in Bombyx mori (Bm) cells was successfully constructed. The result not only showed that the polyhedrin promoter can be replaced easily with other promoters to direct the expression of foreign genes by using this novel system but also laid the foundation for the rescue experiment of orf4 deletion mutant.     

Variation in life-cycle between three rare and endangered floodplain violets in two regions: implications for population viability and conservation

We studied the demography of Viola elatior, V. pumila, and V. stagnina, three rare and endangered Central European floodplain species, to (i) analyse variation in life-cycles among congeners and between regions (Dyje-Morava floodplains, Czech Republic; Upper Rhine, Germany), (ii) to define sensitive stages in the life-cycles, and (iii) to identify possible threats for population viability and species conservation. Matrix models were based on the fate of marked individuals from a total of 27 populations over two years. We analysed population growth rate (λ), stage distribution, net reproductive rate (R ₀), generation time, age at first reproduction, and elasticity and calculated a life table response experiment (LTRE). Most populations were declining and λ did not differ between species or regions during the observed interval. Despite higher probabilities for survival and flowering in the Dyje populations, R ₀ was higher in the Rhine populations. Also other demographic traits showed consistent differences between regions and/or species. Complex life-cycles and large variation in λ precluded unequivocal identification of sensitive stages or vital rates for conservation. Variation between regions may be a consequence of differences in habitat quality. Our results suggest that deterministic processes such as reduced management, succession, habitat destruction, and lack of disturbance through reduced or eliminated flooding present the strongest threat for the viability and persistence of populations of the three floodplain violets as compared with stochastic processes. However, the persistent seed bank of the species may buffer populations against environmental variation and represents a reservoir for recovery after resumption of suitable land-use management.     

Contrasting impacts of invasive engineers on freshwater ecosystems: an experiment and meta-analysis

Invasion by common carp (Cyprinus carpio) and red swamp crayfish (Procambarus clarkii) in shallow lakes have been followed by stable-state changes from a macrophyte-dominated clear water state to a phytoplankton-dominated turbid water state. Both invasive carp and crayfish are, therefore, possible drivers for catastrophic regime shifts. Despite these two species having been introduced into ecosystems world-wide, their relative significance on regime shifts remains largely unexplored. We compared the ecological impacts of carp and crayfish on submerged macrophytes, water quality, phytoplankton, nutrient dynamics, zooplankton and benthic macroinvertebrates by combining an enclosure experiment and a meta-analysis. The experiment was designed to examine how water quality and biological variables responded to increasing carp or crayfish biomass. We found that even at a low biomass, carp had large and positive impacts on suspended solids, phytoplankton and nutrients and negative impacts on benthic macroinvertebrates. In contrast, crayfish had a strong negative impact on submerged macrophytes. The impacts of crayfish on macrophytes were significantly greater than those of carp. The meta-analysis showed that both carp and crayfish have significant effects on submerged macrophytes, phytoplankton, nutrient dynamics and benthic macroinvertebrates, while zooplankton are affected by carp but not crayfish. It also indicated that crayfish have significantly greater impacts on macrophytes relative to carp. Overall, the meta-analysis largely supported the results of the experiment. Taken as a whole, our results show that both carp and crayfish have profound effects on community composition and ecosystem processes through combined consequences of bioturbation, excretion, consumption and non-consumptive destruction. However, key variables (e.g. macrophytes) relating to stable-state changes responded differently to increasing carp or crayfish biomass, indicating that they have differential ecosystem impacts.     

Spatial Variation in Lesser Prairie-Chicken Demography: A Sensitivity Analysis of Population Dynamics and Management Alternatives

ABSTRACT The lesser prairie-chicken (Tympanuchus pallidicinctus) is currently considered a candidate for protection under the Endangered Species Act. To identify potential limiting factors for lesser prairie-chicken populations, we developed an age-based matrix model of lesser prairie-chicken population dynamics to compare the relative importance of components of reproduction and survival, and determine if various management alternatives stabilize or increase rates of population change. We based our analyses on an intensive 6-year population study from which demographic rates were estimated for each age class in Kansas. We used deterministic models and elasticity values to identify parameters predicted to have the greatest effect on the rate of population change (λ) at 2 study sites. Last, we used life-stage simulation analysis to simulate various management alternatives. Lambda was <1 for both populations (site 1: λ = 0.54, site 2: λ = 0.74). However, we found differences in sensitivity to nest success and chick survival between populations. The results of the simulated management scenarios complemented the lower-level elasticity analysis and indicated the relative importance of female survival during the breeding season compared with winter. If management practices are only capable of targeting a single demographic rate, changes to either nest success or chick survival had the greatest impact on λ at site 1 and 2, respectively. Management that simultaneously manipulated both nest success and chick survival was predicted to have a greater effect on λ than changes in survival of adult females. In practice, our demographic analyses indicate that effective management should be based on habitat conservation measures to increase components of fecundity.     

Experimental warming causes rapid loss of plant diversity in New England salt marshes

Anthropogenic climate change is predicted to cause widespread biodiversity loss due to shifts in species' distributions, but these predictions rarely incorporate ecological associations such as zonation. Here, we predict the decline of a diverse assemblage of mid-latitude salt marsh plants, based on an ecosystem warming experiment. In New England salt marshes, a guild of halophytic forbs occupies stressful, waterlogged pannes. At three sites, experimental warming of < 4 °C led to diversity declines in pannes and rapid takeover by a competitive dominant, Spartina patens . In Rhode Island, near their southern range limit, pannes were more sensitive to warming than farther north, and panne area also declined in control plots over the three-season experiment. These results suggest that warming will rapidly reduce plant diversity in New England salt marshes by eliminating a high diversity zone. Biodiversity in zoned ecosystems may be more affected by climate-driven shifts in zonation than by individual species' distribution shifts.     

Sawdust Addition Reduces the Productivity of Nitrogen‐Enriched Mountain Grasslands

Anthropogenic nutrient enrichment of mountain grasslands has boosted grasses and fast‐growing unpalatable plants at the expense of slow‐growing species, resulting in a significant loss in biodiversity. A potential tool to reduce nutrient availability and aboveground productivity without destroying the perennial vegetation is carbon (C) addition. However, little is known about its suitability under severe climatic conditions. Here, we report the results of a 3‐year field study assessing the effects of sawdust addition on soil nutrients, aboveground productivity, and vegetational composition of 10 grazed and ungrazed mountain grasslands. Of particular interest was the effect of C addition on grasses and on the tall unpalatable weed Veratrum album. After 3 years, soil pH, ammonium, and plant‐available phosphorus were not altered by sawdust application, and nitrate concentrations were marginally higher in treatment plots. However, the biomass of grasses and forbs (without V. album) was 20–25% lower in sawdust‐amended plots, whereas the biomass of V. album was marginally higher. Sawdust addition reduced the cover of grasses but did not affect evenness, vegetation diversity, or plant species richness, although species richness generally increased with decreasing biomass at our sites. Our results suggest that sawdust addition is a potent tool to reduce within a relatively short time the aboveground productivity and grass cover in both grazed and ungrazed mountain grasslands as long as they are not dominated by tall unpalatable weeds. The technique has the advantage that it preserves the topsoil and the perennial soil seed bank.     

Environmental limitation contributes to the differential colonization capacity of two forest herbs

Question: The recovery of forest plant communities in post‐agricultural landscapes is largely determined by dispersal constraints, but can environmental legacies of former land use additionally limit the recolonization of recent forests by forest herbs? Location: Ancient forest and recent forest on former heavily fertilized agricultural land (Muizenbos, northern Belgium). Methods: Seeds and adults of two forest herbs with similar life‐history traits, but contrasting colonization capacity – the fast‐colonizing Geum urbanum and the slow‐colonizing Primula elatior– were introduced into both ancient and recent forest sites. Soil conditions and plant tissue nutrient concentrations were measured to characterize habitat quality. To determine whether the introduced species could successfully establish and persist, we monitored recruitment, longevity and adult performance during 8 years in permanently marked plots. Results: Phosphorus availability was ten times higher in recent forest soils and was also reflected in the plant tissue samples. Species longevity was clearly lower in recent forest sites indicating higher turnover. The fast‐colonizing G. urbanum counterbalanced this lower longevity by new establishment, while the slow‐colonizing P. elatior dropped below the number of originally introduced individuals. Additionally, G. urbanum performed better in recent forest sites in contrast to P. elatior. Conclusions: Even when dispersal constraints of the slow‐colonizing forest herb P. elatior are eliminated through introduction, environmental conditions in recent forest sites additionally restrict its recruitment, longevity and performance. These experimental results suggest that environmental constraints may strengthen the differences in colonization capacity among forest herbs if slow dispersers also tend to be less likely to establish.     

Effects of herbivory and the season of disturbance on algal succession in a tropical intertidal shore,Phuket, Thailand

The effects of herbivory and the season of disturbance on species composition and algal succession were experimentally tested at a tropical intertidal shore, Phuket Island, Thailand. Dead coral patches were cleared of all organisms during both the dry and rainy seasons in order to study the effects of season on algal succession and cages were set up to exclude fish herbivory. Algal succession in this intertidal habitat showed a simple pattern and took a year from the early Ulva paradoxa C. Agardh stage to the late Polysiphonia sphaerocarpa Børgesen stage. The abundance of algae during succession was under the influence of seasonal change. U. paradoxa reproduced and recruited throughout the year. Caging effects did not apparently influence algal abundance, perhaps because resident herbivorous damselfishes excluded other herbivores from their territories and maintained their algal “farms”. Unexpectedly, the percent cover of Ulva in the caged plots was lower than in uncaged plots. This pattern may indicate that caging excluded damselfishes only, but allowed small herbivores that consumed substantial amounts of soft filamentous algae in the cages.