Spartina Stem Research Articles

Pore, live root and necromass quantification in complex heterogeneous wetland soils using X-ray computed tomography

Subsurface structures and especially the interactions between pores, roots and other organic matter elements have a strong impact on ecosystem functioning. Yet despite recent progress in the application of X-ray Computed Microtomography (µCT) to soil structure in agricultural science, applications to the more complex and heterogeneous substrates found in natural soils, specifically wetland soils, remain sparse. We apply X-ray µCT to a complex heterogenous soil and develop a robust segmentation method to quantify the pores, live roots and necromass. This approach significantly improves the detection of the organic matter elements, and gives us unprecedented detail and resolution in the segmentation of pores, live roots and necromass at a high spatial resolution (62.5 µm in this study). We identify several situations where pores and organic matter interact in the soil, including the disconnected air spaces (aerenchyma) that run within the Spartina stem and roots, tubular-shaped pores left behind by decaying roots, and lateral roots deploying within structural fragilities in the sediment. The capacity of X-ray µCT to distinguish the connected live root system from the necromass opens possibilities for applications to determine key wetland soil functions such as soil cohesivity, soil nutrient exchanges and soil carbon dynamics.

A new non-indigenous Crassostrea species in Southwest Atlantic salt marshes affects mortality of the cordgrass Spartina alterniflora

Biological invasions in marine and coastal systems may produce new trophic and nontrophic interactions influencing the structure of the invaded community. In the intertidal salt marshes of Samborombón Bay (36°19′20″S, 56°46′26″W; mouth of La Plata River; Argentina), there is a new non-indigenous oyster species, Crassostrea sp., which settles on the dominant smooth cordgrass Spartina alterniflora. Here, we analyzed if the oyster affects S. alterniflora. Sampling showed that density of live plant was similar across intertidal levels, but there were higher density of dead plant stems at low intertidal levels. This pattern coincides with higher density and larger shell size of Crassostrea sp. at the low intertidal where oysters are attached to the basal part of the plant stems. An experiment manipulating oysters attached to S. alterniflora stems and oyster mimics shows that Crassostrea sp. can indeed increase mortality of S. alterniflora. The negative effect of bivalves on plant could be because several oysters settle around the Spartina stem, and by growing during the year, strangle the plants increasing their mortality rate. Together, all these evidences strongly suggest that these non-indigenous oysters can control the lower intertidal level of plant distribution in this system.

Effect of Spartina anglica stems on near-bed hydrodynamics, sediment erodability and morphological changes on an intertidal mudflat

Our main objective was to investigate the effect of Spartina anglica stems on hydro- dynamics, sediment dynamics and their influence on seasonal morphological changes on the upper shore and salt marsh of an intertidal mudflat in the Tavy estuary (southwest England). On an inter- tidal transect, the greatest seasonal changes in sediment levels occurred at the seaward edge and lower part of the salt marsh, and on the lower shore mudflat, while the smallest changes occurred on the mid- and upper-shore mudflat. Flume studies demonstrated flow attenuation with increasing Spartina stem density, but this was accompanied by an increase in turbulent kinetic energy and bed shear stress (τ0). The critical erosion threshold (τe), however, remained relatively constant at 0.12 Pa. Field measurements showed that τ0 was well below τe under calm conditions. During periods of wind- wave activity, when daily mean wind speeds were >8 m s -1 , τ0 was greater than τe in the lower salt marsh for brief periods at the beginning and end of tidal inundation. At the seaward edge of the salt marsh, τ0 increased to 1.0 Pa and τ0 was greater than τe throughout the inundation period, causing significant sediment erosion. Wind-induced wave activity was the major driver of sediment erosion on soft muddy shores and this was enhanced by the interaction with S. anglica stems. The number of days per month with mean daily wind speeds >8 m s -1 was inversely related to changes in sediment levels at the seaward edge of the salt marsh. During the summer, winds were below this threshold, and there was gradual accretion. Results are discussed in the context of climate changes involving increased storminess leading to increased erosion. We show that the S. anglica salt marsh should not be considered a 'bio-stabiliser' of fine muddy sediment.

Litter pool sizes, decomposition, and nitrogen dynamics in Spartina alterniflora-invaded and native coastal marshlands of the Yangtze Estuary

Past studies have focused primarily on the effects of invasive plants on litter decomposition at soil surfaces. In natural ecosystems, however, considerable amounts of litter may be at aerial and belowground positions. This study was designed to examine the effects of Spartina alterniflora invasion on the pool sizes and decomposition of aerial, surficial, and belowground litter in coastal marshlands, the Yangtze Estuary, which were originally occupied by two native species, Scirpus mariqueter and Phragmites australis. We collected aerial and surficial litter of the three species once a month and belowground litter once every 2 months. We used the litterbag method to quantify litter decomposition at the aerial, surficial and belowground positions for the three species. Yearly averaged litter mass in the Spartina stands was 1.99 kg m(-2); this was 250 and 22.8% higher than that in the Scirpus (0.57 kg m(-2)) and Phragmites (1.62 kg m(-2)) stands, respectively. The litter in the Spartina stands was primarily distributed in the air (45%) and belowground (48%), while Scirpus and Phragmites litter was mainly allocated to belowground positions (85 and 59%, respectively). The averaged decomposition rates of aerial, surficial, and belowground litter were 0.82, 1.83, and 1.27 year(-1) for Spartina, respectively; these were 52, 62 and 69% of those for Scirpus litter at corresponding positions and 158, 144 and 78% of those for Phragmites litter, respectively. The differences in decomposition rates between Spartina and the two native species were largely due to differences in litter quality among the three species, particularly for the belowground litter. The absolute amount of nitrogen increased during the decomposition of Spartina stem, sheath and root litter, while the amount of nitrogen in Scirpus and Phragmites litter declined during decomposition for all tissue types. Our results suggest that Spartina invasion altered the carbon and nitrogen cycling in the coastal marshlands of China.

THE PACE OF ECOSYSTEM DEVELOPMENT OF CONSTRUCTED SPARTINA ALTERNIFLORA MARSHES

Ecological attributes were measured along a chronosequence of 1‐ to 28‐yr‐old, constructed Spartina alterniflora marshes to identify trajectories and rates of ecosystem development of wetland structure and function. Attributes related to biological productivity and diversity (Spartina, epiphytic and sediment algae, benthic invertebrates), soil development (sediment deposition, organic C, N, P, organic matter quality), and microbial processes (C mineralization) were compared among eight constructed marshes and eight paired natural reference marshes. Most ecological attributes developed in a predictable manner over time, and most achieved equivalence to natural marshes 5–15 yr after marsh construction. An exception was soil organic C and N pools (0–30 cm) that, after 28 yr, were significantly lower in constructed marshes. Development of habitat structure (Spartina stem height and density) and biodiversity (algae and invertebrates) developed concurrently with functional characteristics such as biomass, chlorophyll a, and invertebrate density. Processes related to hydrology, sediment deposition and soil C and N accumulation, developed almost instantaneously with the establishment of Spartina, and young (1‐ to 3‐yr‐old), constructed marshes trapped sediment and sequestered N at higher rates than comparable reference marshes. Development of heterotrophic activity (C mineralization, invertebrate density) was strongly linked to surface (0–10 cm) soil organic C content. Ecosystem development of constructed (and natural) salt marshes depended on a minimum of 100 g N/m2 (0.05–0.1% N) to support emergent vegetation and 1000 g C/m2 (0.5–1% C) to sustain the heterotrophic community.

Food, density, and microhabitat: factors affecting growth and recruitment potential of juvenile saltmarsh fishes

The relationships among microhabitat use, food habits, conspecific density and recent growth rate for estuarine-dependent juvenile spotted seatrout, Cynoscion nebulosus, and red drum, Sciaenops ocellatus, were studied to determine how nursery habitat influences early growth. Juvenile spotted seatrout and red drum were quantified along the marsh-edge ecotone from multiple drop samples, and their immediate environments characterized by a suite of physical and chemical variables along with substrate type and Spartina stem density. Recent daily growth of individual fish was modeled in a series of multiple regression analyses that considered the relative contributions of food, microhabitat, and conspecific density. The spotted seatrout model (p 0.0001) included five independent variables, otolith radius, temperature, salinity, depth and substrate, and explained 63.3% of the variation in daily growth. All variables were significant (p > 0.05), and all regression slopes were positive. Fish size (as estimated by otolith radius) accounted for most of the variance in the spotted seatrout (60.2%) and red drum (44.8%) models, while the remaining environmental variables were significant and responsible for 7.7 and 18.5%, respectively. Density variables were not selected for either model, suggesting that density-dependence was not an important influence on recent daily growth. Generally, physico-chemical variables such as temperature, salinity, and dissolved oxygen contributed more to growth than diet or extrinsic factors such as grass stem density.

Epiphytic Nitrogen Fixation Associated with Standing Dead Shoots of Smooth Cordgrass, Spartina alterniflora

N2 fixation associated with the epiphytic community on standing dead Spartina alterniflora shoots was examined in both a natural and transplanted salt marsh in North Carolina. Acetylene reduction (AR) assays were conducted over a 24-mo period to estimate N2 fixation rates on standing dead stems and leaves. In the natural salt marsh, mean AR rates ranged from 0.5 nmol C2H4 cm−2 h−1 to 14 nmol C2H4 cm−2 h−1, while in the transplanted marsh mean AR rates ranged from 1 nmol C2H4 cm−2 h−1 to 33 nmol C2H4 cm−2 h−1. Diel AR activity of epiphytic communities in both marshes varied seasonally. Midday incubations yielded higher AR rates than nighttime incubations in the spring, while midday incubations in late summer and fall generally yielded AR rates equal to or lower than nighttime incubations. Desiccation during low tides occasionally repressed AR activity, although AR rates quickly rebounded with wetting. AR activity was localized in the epiphytic community, rather than in the underlying Spartina stem material. Based on the measured AR rates and the density of standing dead stems, the annual input of new N to the natural salt marsh via epiphytic N2 fixation is estimated to be 2.6 g N m−2 yr−1. The estimate of annual input of new N to the transplanted marsh is 3.8 g N m−2 yr−1. These estimates should be added to previous estimates of N2 fixation in marsh sediments to estimate the total contribution of new nitrogen to salt marsh nitrogen budgets.

Notes on Sample Size Requirements in Morphological Plant Ecology

between Spartina stem borers, by means of murder. Ecology 64:770-778. Whitham, T. G. 1978. Habitat selection by Pemphigus aphids in response to resource limitation and competition. Ecology 59:1164-1176. 1979. Territorial behaviour ofPemphigus gall aphids. Nature 279:324-325. twe n Spartina stem borers, by means of murder. Ecol64:7 0-778. itham, T. G. 1978. Habit t selection by Pemphigus aphids response to resource limitation and competition. Ecology

Weak Competition among Spartina Stem Borers, by Means of Murder

We examined co—occurrence among five species of insect larvae that bore the stems of salt marsh cordgrass, Spartina alterniflora, in northwest Florida. Statistical analysis of 5400 stems at three different sites revealed fewer empty stems, more stems containing one species, and fewer stems containing two or more species than one would expect if individuals were arranged randomly and independently. Particular interspecific co—occurrences at individual sites were significantly rarer than expected for 6 of the 10 possible species pairs. This deficiency in species co—occurrences is likely a result of direct interspecific aggression and murder of larvae within stems, as demonstrated in laboratory experiments. However, we detected no obvious decreases in population densities or alteration of stem section occupancy patterns due to competition. Thus, although interspecific competition occurs, it does not play a critical role in structuring this community.

Polychlorinated biphenyl uptake and translation by Spartina alterniflora loisel

This paper presents the findings of initial investigation of the role of Spartina alterniora Loisel. in the movement of chlorinated hydrocarbons. 14C-polychlorinated biphenyls and technical Aroclor® 1254 were used for the determinations. The findings demonstrate that Spartina accumulates 14C-radioactivity from sand and organic mud soil systems treated with 14C-PCB's. These findings also demonstrate that this plant has the capacity to accumulate 14C-radioactivity to levels elevated above that in the treated soil. Other experiments with Aroclor® 1254 demonstrate that cogeners of Aroclor® 1254 are present in Spartina stem and root extracts. These experiments also suggest that the chlorinated hydrocarbon uptake process is modulated by the plant and that this results in selective cogener uptake. The selectivity appears to be for the lesser chlorinated components of the commercial mixture. Overall, this study suggests that Spartina may act as an initial vector for mobilization of sediment bound chlorinated hydrocarbons to the estuarine food chain.