The Roles of Competition and Facilitation in Producing Zonation Along an Experimental Flooding Gradient: A Tale of Two Tails with Ten Freshwater Marsh Plants

2021 ◽  
Author(s):  
Daniel Campbell ◽  
Paul Keddy
Keyword(s):  
Full Range ◽  
Stress Gradient ◽  
Freshwater Marsh ◽  
Freshwater Wetlands ◽  
Physical Factors ◽  
Flooding Stress ◽  
Flood Duration ◽  
Growing Seasons ◽  
Emergent Plants ◽  
Flooding Duration

Abstract Plant zonation is conspicuous in wetlands. The cause is frequently assumed to be the direct physiological effects of physical factors (termed ‘stress’), however many experiments show that competition and facilitation also cause zonation patterns. We conducted a field experiment with freshwater marsh emergent plants to test the causes of zonation along a single stress gradient: flooding duration. We constructed an experimental wetland with ten flooding levels to ensure that the environmental conditions represented the full range of potential flooding levels, from never flooded to continually flooded. We planted ten common marsh plants with varied ecology along the flooding duration gradient. We grew them alone and in mixture for three years and measured changes in the minimum and maximum limits, the mode and the range of distribution, and interaction importance. The mode of distribution did not shift, whether species were grown alone or with neighbours. We found strong effects of competition under low flooding stress. We found no effects from facilitation under high flooding stress. Flooding duration alone controlled the lower limits of plants. The effects of competition were intense enough to eliminate half of the species within three growing seasons. Our experiment showed that competition and physical stresses, but not facilitation, controls the zonation of emergent macrophytes along a flooding duration gradient, at least in freshwater wetlands. Models guiding wetland restoration need to include competition as well as flood duration as causal factors, but not facilitation.

scholarly journals Facilitation Effects of Haloxylon salicornicum Shrubs on Associated Understory Annuals, and a Modified “Stress-Gradient” Hypothesis for Droughty Times

Plants ◽  
2020 ◽  
Vol 9 (12) ◽  
pp. 1726
Author(s):  
Nasr H. Gomaa ◽  
Ahmad K. Hegazy ◽  
Arafat Abdel Hamed Abdel Latef
Keyword(s):  
Species Richness ◽  
Water Availability ◽  
Stress Gradient ◽  
Growing Season ◽  
Annual Species ◽  
Negative Effects ◽  
Growing Seasons ◽  
Dry Seasons ◽  
The Impact ◽  
Haloxylon Salicornicum

Perennial shrub-annual plant interactions play key roles in desert regions influencing the structure and dynamics of plant communities there. In the present study, carried out in northwestern Saudi Arabia, we examined the effect of Haloxylon salicornicum shrubs on their associated understory annual species across four consecutive growing seasons, along with a record of the seasonal rainfall patterns. We measured density and species richness of all the annual species in permanent quadrats located beneath individual shrubs, as well as in the spaces between shrubs. During wet growing season H. salicornicum shrubs significantly enhanced the density and species richness of sub-canopy species, whereas in the relatively dry seasons they exerted negative effects on the associated species. In all growing seasons, the presence of shrubs was associated with enhanced soil properties, including increased organic carbon content, silt + clay, and levels of nutrients (N, P and K). Shrubs improved soil moisture content beneath their canopies in the wet growing season, while in the dry seasons they had negative effects on water availability. Differences in effects of H. salicornicum on understory plants between growing seasons seem due to the temporal changes in the impact of shrubs on water availability. Our results suggest the facilitative effects of shrubs on sub-canopy annuals in arid ecosystems may switch to negative effects with increasing drought stress. We discuss the study in light of recent refinements of the well-known “stress-gradient hypothesis”.

scholarly journals Effects of Carbon Addition on Dissimilatory Fe(III) Reduction in Freshwater Marsh and Meadow Wetlands

2018 ◽  
Vol 10 (11) ◽  
pp. 4309 ◽  
Author(s):  
Xiaoyan Zhu ◽  
Yuxiang Yuan ◽  
Ming Jiang
Keyword(s):  
Iron Reduction ◽  
Reduction Rate ◽  
Negative Relationship ◽  
Sanjiang Plain ◽  
Freshwater Marsh ◽  
Freshwater Wetlands ◽  
Natural Environments ◽  
Carbon Addition ◽  
Soil Slurry ◽  
The Sanjiang Plain

The progress of dissimilatory iron(III) reduction is widespread in natural environments, particularly in anoxic habitats; in fact, wetland ecosystems are considered as “hotspots” of dissimilatory Fe(III) reduction. In this study, we conducted soil slurry and microbial inoculation anaerobic incubation with glucose, pyruvate, and soluble quinone anthraquinone-2,6-disulphonate (AQDS) additions in freshwater marsh and meadow wetlands in the Sanjiang Plain, to evaluate the role of carbon addition in the rates and dynamics of iron reduction. Dissimilatory Fe(III) reduction in marsh wetlands responded more quickly and showed twice the potential for Fe(III) reduction as that in meadow wetland. Fe(III) reduction rate in marsh and meadow wetlands was 76% and 30%, respectively. Glucose had a higher capacity to enhance Fe(III) reduction than pyruvate, which provides valuable information for the further isolation of Fe reduction bacteria in pure culture. AQDS could dramatically increase potential Fe(III) reduction as an electron shuttle in both wetlands. pH exhibited a negative relationship with Fe(III) reduction. In view of the significance of freshwater wetlands in the global carbon and iron cycle, further profound research is now essential and should explore the enzymatic mechanisms underlying iron reduction in freshwater wetlands.

Implications of methane emissions in biogeochemical budgeting: A study from a eutrophic tropical lake of South India

2020 ◽  
Author(s):  
Revathy Das ◽  
Appukuttan Pillai Krishnakumar ◽  
Krishnan AnoopKrishnan ◽  
Vivekanandan Nandakumar
Keyword(s):  
Plant Biomass ◽  
Regional Scale ◽  
Temporal Variations ◽  
Physical Factors ◽  
Growing Seasons ◽  
Littoral Zones ◽  
Flux Measurements ◽  
The Mean ◽  
Spatio Temporal ◽  
Lake Systems

<p>Greenhouse gases (GHGs), especially, methane (CH<sub>4</sub>) emissions from the littoral zones of the lakes play an important role in regional biogeochemical budgets. Only a few studies are available in literature highlighting the direct flux measurements of CH<sub>4   </sub>from the aquatic systems. In the present study, an attempt has been made to quantify the spatio-temporal variations of CH<sub>4</sub> efflux and the key physical factors controlling the emission rate, from the vegetated littoral zones of lake Vellayani (5.55Km<sup>2</sup>), located in the urbanized area of Thiruvananthapuram city, Kerala, South-West India. CH<sub>4</sub> efflux were collected from different vegetations in littoral zones, using a static chamber, during the peak growing seasons from March to October in 2016 and further analyses were carried out by using Gas Chromatograph (PE Clarus 500, PerkinElmer, Inc.). The mean efflux rate of CH<sub>4   </sub>from the emergent plant species (Phragmites australis and Typha spp.) was 114.4 mg CH<sub>4</sub> m<sup>-2</sup>h<sup>-1</sup>; while, in the floating leaved species (Nymphaea spp. and Nelumbo Spp.), it <sub>  </sub>was   observed to be 32.6 mgCH<sub>4</sub> m<sup>-2</sup>h<sup>-1</sup>. The results reveal that CH<sub>4</sub> efflux in the zone of emergent vegetation was significantly higher than the floating-leaved zone indicating the importance of plant biomass and standing water depths for the spatial variations of CH<sub>4 </sub>efflux. However, no significant temporal variations were noticed in the physical factors during the peak growing seasons. These results indicate that the vegetated littoral zones of lake, especially the emergent plant zones were supersaturated with CH<sub>4</sub>, facilitating the production of carbon for CH<sub>4</sub> emission<sub>,</sub> but also enable the release of CH<sub>4 </sub>by the diffusion from the intercellular gas lacunas. We conclude that the atmospheric CH<sub>4</sub> emissions will be affected by the growth of exotic species in the lake systems and may be the reason for enhancing the climate warming in local/regional scale.</p>

Methane flux from beds of Baumea arthrophylla (Nees) Boeckeler and Triglochin procerum R. Br. at Bool Lagoon, South Australia

1994 ◽  
Vol 45 (8) ◽  
pp. 1543 ◽  
Author(s):  
KL Muller ◽  
GG Ganf ◽  
PI Boon
Keyword(s):  
South Australia ◽  
Methane Flux ◽  
Methanogenic Bacteria ◽  
Freshwater Wetlands ◽  
Sediment Surface ◽  
Major Pathway ◽  
Emergent Plants ◽  
Oxidation Of Methane ◽  
Methane Fluxes ◽  
Time Of Year

The flux of methane from freshwater wetlands is likely to be influenced by the presence of emergent macrophytes. The plants generate an organic loading, which should increase methanogenesis, yet they also aerate the sediment, creating oxic zones inimical to the obligately anaerobic methanogenic bacteria and promoting the oxidation of methane by methanotrophic bacteria. Moreover, emergent plants can act as a conduit for methane to be vented to the atmosphere. Depth profiles of oxygen in beds of B. arthrophylla and T. procerum at Bool Lagoon, South Australia, showed that water at the sediment surface was anoxic during the night but became oxygenated during the latter part of the day. Redox profiles of the sediment gave values that ranged from -50 to +250 mV, indicating a sediment that was not highly reducing. Despite these conditions, the wetlands were sources of significant methane emissions, with total water-atmosphere fluxes ranging from < 0.0 t1o 1.05 mmol m-2 h-1. The presence of B. arthrophylla, but not that of T. procerum, affected the bubble concentration of methane in the sediments. Diel variations in ebullitive or total methane fluxes were not detected, but emissions varied according to water depth and time of year. Treatments that removed macrophytes reduced total methane fluxes to rates approximately equivalent to ebullition, indicating that the plants were acting as a major pathway for the release of methane to the atmosphere. The lack of a clear die1 pattern in emissions suggests that diffusion, rather than convective flow, is the mechanism for this flux through the plants.

scholarly journals Using Remote Sensing to Identify Drivers behind Spatial Patterns in the Bio-physical Properties of a Saltmarsh Pioneer

2019 ◽  
Vol 11 (5) ◽  
pp. 511
Author(s):  
B. Oteman ◽  
E.P. Morris ◽  
G. Peralta ◽  
T.J. Bouma ◽  
D. van der Wal
Keyword(s):  
Salt Marsh ◽  
Spatial Patterns ◽  
Salt Marshes ◽  
Spatial Organization ◽  
Minor Effect ◽  
Surface Reflectance ◽  
Area Index ◽  
Flood Duration ◽  
Wave Forcing ◽  
Flooding Duration

Recently, spatial organization in salt marshes was shown to contain vital information on system resilience. However, in salt marshes, it remains poorly understood what shaping processes regulate spatial patterns in soil or vegetation properties that can be detected in the surface reflectance signal. In this case study we compared the effect on surface reflectance of four major shaping processes: Flooding duration, wave forcing, competition, and creek formation. We applied the ProSail model to a pioneering salt marsh species (Spartina anglica) to identify through which vegetation and soil properties these processes affected reflectance, and used in situ reflectance data at the leaf and canopy scale and satellite data on the canopy scale to identify the spatial patterns in the biophysical characteristics of this salt marsh pioneer in spring. Our results suggest that the spatial patterns in the pioneer zone of the studied salt marsh are mainly caused by the effect of flood duration. Flood duration explained over three times as much of the variation in canopy properties as wave forcing, competition, or creek influence. It particularly affects spatial patterns through canopy properties, especially the leaf area index, while leaf characteristics appear to have a relatively minor effect on reflectance.

scholarly journals Colonization of Trees by Ambrosia Beetles (Coleoptera: Curculionidae: Scolytinae) Is Influenced by Duration of Flood Stress

2021 ◽  
Vol 114 (2) ◽  
pp. 839-847
Author(s):  
Michael E Reding ◽  
Christopher M Ranger ◽  
Peter B Schultz
Keyword(s):  
Callus Tissue ◽  
Flood Events ◽  
Ambrosia Beetles ◽  
Malus Domestica Borkh ◽  
Flood Duration ◽  
Cercis Canadensis ◽  
Flooding Duration ◽  
Time Periods ◽  
Xylosandrus Germanus ◽  
D Numbers

Abstract The ambrosia beetles Xylosandrus germanus (Blandford) and Xylosandrus crassiusculus (Motschulsky) bore into flood-stressed trees to establish colonies, but the influence of flooding duration on colonization is unknown. This relationship was examined by flooding trees for various time periods and evaluating colonization. In one experiment, X. germanus bored into 20 dogwood (Cornus florida L.) trees during a 3-d flood treatment. Ten trees dissected that season had no offspring present in tunnels; the remaining trees appeared healthy and bloomed the following spring. In another experiment, dogwood trees were flooded for 3 or 7 d and then dissected to assess colonization. The incidence of superficial (short unbranched) and healed (callus tissue in entrance) tunnels was greater in the 3-d trees, while the incidence of tunnels with X. germanus or offspring was greater in the 7-d trees. Four experiments (three in Ohio and one in Virginia) had flood treatments of 0 (nonflooded), 3, 5, 7, and 10 d. Numbers of tunnel entrances, tunnels with X. germanus, and incidence of tunnels with offspring or live foundresses tended to increase as flood duration increased on apple (Malus × domestica Borkh.), dogwood, and redbud (Cercis canadensis L.) in Ohio and redbud in Virginia. Nonflooded trees in Ohio had no boring activity, but ambrosia beetles bored into three nonflooded trees in Virginia. Indicators of unsuccessful colonization, such as superficial tunnels and healing, decreased as flood duration increased. These results suggest tree crops may recover from boring by ambrosia beetles following short-duration flood events, and not necessarily require culling.

Comparing fixed and flexible stocking as adaptations to inter-annual rainfall variability in the extensive beef industry of northern Australia

2016 ◽  
Vol 38 (1) ◽  
pp. 85 ◽  
Author(s):  
Lester Pahl ◽  
Joe Scanlan ◽  
Giselle Whish ◽  
Robyn Cowley ◽  
Neil MacLeod
Keyword(s):  
Carrying Capacity ◽  
Rainfall Variability ◽  
Full Range ◽  
Herd Size ◽  
Annual Rainfall ◽  
Northern Australia ◽  
Beef Industry ◽  
Growing Seasons ◽  
Stocking Rates

Many beef producers within the extensive cattle industry of northern Australia attempt to maintain a constant herd size from year-to-year (fixed stocking), whereas others adjust stock numbers to varying degrees annually in response to changes in forage supply. The effects of these strategies on pasture condition and cattle productivity cannot easily be assessed by grazing trials. Simulation studies, which include feedbacks of changes to pasture condition on cattle liveweight gain, can extend the results of grazing trials both spatially and temporally. They can compare a large number of strategies, over long periods of time, for a range of climate periods, at locations which differ markedly in climate. This simulation study compared the pasture condition and cattle productivity achieved by fixed stocking at the long-term carrying capacity with that of 55 flexible stocking strategies at 28 locations across Queensland and the Northern Territory. Flexible stocking strategies differed markedly in the degree they increased or decreased cattle stocking rates after good and poor pasture growing seasons, respectively. The 28 locations covered the full range in average annual rainfall and inter-annual rainfall variability experienced across northern Australia. Constrained flexibility, which limited increases in stocking rates after good growing seasons to 10% but decreased them by up to 20% after poor growing seasons, provides sustainable productivity gains for cattle producers in northern Australia. This strategy can improve pasture condition and increase cattle productivity relative to fixed stocking at the long-term carrying capacity, and its capacity to do this was greatest in the semiarid rangeland regions that contain the majority of beef cattle in northern Australia. More flexible stocking strategies, which also increased stocking rates after good growing seasons by only half as much as they decreased them after poor growing seasons, were equally sustainable and more productive than constrained flexibility, but are often impractical at property and industry scales. Strategies with the highest limits (e.g. 70%) for both annual increases and decreases in stocking rates could achieve higher cattle productivity, but this was at the expense of pasture condition and was not sustainable. Constrained flexible stocking, with a 10% limit for increases and a 20% limit for decreases in stocking rates annually, is a risk-averse adaptation to high and unpredictable rainfall variability for the extensive beef industry of northern Australia.

Spatial variation in environmental characteristics of Atlantic salmon (Salmo salar) rivers

1998 ◽  
Vol 55 (S1) ◽  
pp. 267-280 ◽  
Author(s):  
Scott R Elliott ◽  
Treva A Coe ◽  
James M Helfield ◽  
Robert J Naiman
Keyword(s):  
Atlantic Salmon ◽  
Salmo Salar ◽  
Riparian Forest ◽  
Full Range ◽  
Anthropogenic Disturbances ◽  
Physical Factors ◽  
Physical Habitat ◽  
Atlantic Salmon Salmo Salar ◽  
Biological Variables ◽  
Rivers And Streams

Rivers and streams occupied by anadromous Atlantic salmon (Salmo salar) occur across a diverse array of landscapes. This article describes the general ecology of these rivers and streams, including many of the physical and biological variables that are important characteristics of all lotic systems. For analytical purposes, the geographic range of Atlantic salmon rivers is divided into five regions, based on geomorphology and climate. The physical habitat available to anadromous Atlantic salmon is diverse. The geology varies from granitic bedrock to volcanic and glacial substrates, which influence a broad array of other ecological variables, ranging from water chemistry to catchment morphology (e.g., river length). Flood regimes and system hydrology are dependent, as expected, on climate. Many of the catchments receive substantial precipitation in the form of snow; rivers in four of the five regions experience primarily spring freshets. Aquatic temperatures are also variable, representing close to the full range of thermal tolerance of S. salar, with lows just above 0°C in the northernmost latitudes to summer highs in western Europe approaching 25°C. Most rivers are best characterized as oligotrophic with relatively low annual primary productivity. However, physical factors such as availability of suitable spawning and rearing habitat, as well as aquatic temperature and flow regimes, may drive anadromous productivity. In general, most of the rivers have been modified by flow regulation and many suffer from impacts related to other anthropogenic disturbances, principally riparian forest clearing for agriculture, forestry, and urban development. We conclude that the rivers and streams occupied by anadromous Atlantic salmon are diverse across the species' range and have been heavily impacted by anthropogenic disturbances.

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