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1.
Net primary production was measured in three characteristic salt marshes of the Ebre delta: anArthrocnemum macrostachyum salt marsh,A. macrostachyum-Sarcocornia fruticosa mixed salt marsh andS. fruticosa salt marsh. Above-ground and belowground biomass were harvested every 3 mo for 1 yr. Surface litter was also collected from each plot. Aboveground biomass was estimated from an indirect non-destructive method, based on the relationship between standing biomass and height of the vegetation. Decomposition of aboveground and belowground components was studied by the disappearance of plant material from litter bags in theS. fruticosa plot. Net primary production (aboveground and belowground) was calculated using the Smalley method. Standing biomass, litter, and primary production increased as soil salinity decreased. The annual average total aboveground plus belowground biomass was 872 g m−2 in theA. macrostachyum marsh, 1,198 g m−2 in theA. macrostachyum-S. fruticosa mixed marsh, and 3,766 g m−2 in theS. fruticosa biomass (aboveground plus belowground) was 226, 445, and 1,094 g m−2, respectively. Total aboveground plus below-ground net primary production was 240, 1,172, and 1,531 g m−2 yr−1. There was an exponential loss of weight during decomposition. Woody stems and roots, the most recalcitrant material, had 70% and 83% of the original material remaining after one year. Only 20–22% of leafy stem weight remained after one year. When results from the Mediterranean are compared to other salt marshes dominated by shrubbyChenopodiaceae in Mediterranean-type climates, a number of similarities emerge. There are similar zonation patterns, with elevation and maximum aboveground biomass and primary production occurring in the middle marsh. This is probably because of stress produced by waterlogging in the low marsh and by hypersalinity in the upper marsh.  相似文献   

2.
From January 1987 to February 1988 the annual biomass cycle and demography of the seagrass Zostera marina were assessed in San Quintin Bay, a shallow coastal lagoon on the Pacific coast of Baja California, Mexico. Shoot density and aboveground biomass were sampled monthly along two intertidal transects parallel to the shore. Belowground biomass was sampled every 2 mo. Shoot density differed between transects, ranging from 929±71 (SE) in July to 279 ±80 shoots m−2 in December, at the deeper transect (I). At the shallow transect (II) there was not a significant difference through time, and a mean of 737 shoots m−2 was calculated. Lateral shoots were present year round and represented between 1% and 30% of total density at transect I and between 3% and 25% at transect II. Reproductive shoots were present from March to September at both transects, with a density range of 77±28 shoots m−2 (March) to 9±3 shoots m−2 (September), and represented 5% of total shoot density. Neither aboveground biomass nor LAI (Leaf Area Index) differed between transects, with values ranging between 77±14.5 g dry wt m−2 (October 1987) and 13±2.4 g dry wt m−2 (February 1988) for aboveground biomass, and between 0.6±0.2 m2 leves m−2 substrate (January) and 2.7±0.3 m2 leaves m−2 substrate (September) for LAI. Neither root biomass nor rhizome biomass differed between transects, or as a function of time; the mean value for roots was 17 g dry wt m−2 and for rhizomes 29 g dry wt m−2. Belowground biomass represented 54% of total biomass. We found a significant correlation between aboveground biomass and LAI (r=0.949 for transect I, and 0.926 for transect II) as well as between total biomass (aboveground and belowground) and LAI (r=0.814), which allows us to consider using LAI as a predictor of these variables. Biomass changes were related to changes in shoot weight (r=0.676 at transect I; 0.582 at transect II), more than to changes in shoot number. Water temperature was found to be the driver of biomass changes in the aboveground compartment.  相似文献   

3.
Seasonal variation patterns of aboveground and belowground biomass, net primary production, and nutrient accumulation were assessed inAtriplex portulacoides L. andLimoniastrum monopetalum (L.) Boiss. in Castro Marim salt marsh, Portugal. Sampling was conducted for five periods during 2001–2002 (autumn, winter, spring, summer, and autumn). This study indicates that both species have a clear seasonal variation pattern for both aboveground and belowground biomass. Mean live biomass was 2516 g m−2 yr−1 forL. monopetalum and 598 g m−2 yr−1 forA. portulacoides. Peak living biomass, in spring for both species, was three times greater in the former, 3502 g m−2 yr−1, than in the latter, 1077 g m−2 yr−1. For both the Smalley (Groenendijk 1984) and Weigert and Evans (1964) methods, productivity ofL. monopetalum (2917 and 3635 g m−2 yr−1, respectively) was greater than that ofA. portulacoides (1002 and 1615 g m−2 yr−1, respectively). Belowground biomass ofL. monopetalum was 1.7 times greater than that ofA. portulacoides. In spite of this, the root:shoot ratio forA. monopetalum to aerial components. Leaf area index was similar for both species, but specific leaf area ofA. portulacoides was twice that ofL. monopetalum. The greatest nutrient contents were found in leaves. Leaf nitrogen content was maximum in summer for both species (14.6 mg g−1 forA. portulacoides and 15.5 mg g−1 forL. monopetalum). Leaf phosphorus concentration was minimum in summer (1.1 mg g−1 inA. portulacoides and 1.2 mg g−1 inL. monopetalum). Leaf potassium contents inA. portulacoides were around three times greater than inL. monopetalum. Leaf calcium contents inL. monopetalum were three times greater than inA. portulacoides. There was a pronounced seasonal variation of calcium content in the former, while in the latter no clear variation was registered. Both species exhibited a decrease in magnesium leaf contents in the summer period. Mangamese content inL. monopetalum leaves was tenfold that inA. portulacoides. Seasonal patterns of nutrient contents inA. portulacoides andL. monopetalum suggest that availability of these elements was not a limiting factor to biomass production.  相似文献   

4.
Mortality, litter fall, and patterns of stem growth were examined in Rhizophora- and Ceriops-dominated forests located upstream and downstream in four tidally dominated creeks within a beach reef embayment on the northern Great Barrier Reef coast. Although patterns of stem densities, basal area, and diameter-at-breast height (DBH) between upstream–downstream sites and creeks were inconsistent, aboveground biomass, wood production, litter fall, and aboveground net primary productivity (ANPP) were greater in the Rhizophora-dominated forests. Incremental growth of stems (SI, cm year−1) was slow compared to other mangroves, declining among species as follows: Rhizophora stylosa (mean = 0.080) > Bruguiera exaristata (0.066) = Xylocarpus australasicus (0.064) = Ceriops australis (0.056); SI was greater upstream than downstream, possibly due to nutrient inputs from upland sugarcane cultivation. The DBH of dead trees were less than the DBH of live trees, suggesting natural mortality, which was greatest for X. australasicus (annual rate = 3.27%), followed by B. exaristata (0.84%), C. australis (0.48%), and R. stylosa (0.33%). Rates of litter fall were seasonal and equivalent to those measured in other mangroves, but rates of ANPP were, on average, low in most plots. Salinity was likely the main factor limiting growth as correlations of salinity with tree growth and production were negative. Nutrients may have also played a key regulatory role, with positive correlations between mangrove production and N and P content of soils and leaves and the comparatively low nutrient content of these sandy soils. The low ratio of wood to litter production suggests that these forests are in a mature stage of development.  相似文献   

5.
Phragmites expansion rates (linear at 1–3% yr−1) and impacts of this expansion on high marsh macroinvertebrates, aboveground production, and litter decomposition fromPhragmites and other marsh graminoids were studied along a polyhaline to oligohaline gradient. These parameters, and fish use of creeks and high marsh, were also studied inPhragmites control sites (herbicide, mowing, and combined herbicide/mow treatments).Phragmites clones established without obvious site preferences on oligohaline marshes, expanding radially. At higher salinities,Phragmites preferentially colonized creekbank levees and disturbed upland borders, then expanded into the central marsh. Hydroperiods, but not salinities or water table, distinguishedPhragmites-dominated transects. Pooled samples ofPhragmites leaves, stems, and flowers decompose more slowly than other marsh angiosperms;Phragmites leaves alone decompose as or more rapidly than those of cattail. AbovegroundPhragmites production was 1,300 to 2,400 g m−2 (about 23% of this as leaves), versus 600–800 g m−2 for polyhaline to mesohaline meadow and 1,300 g m−2 for oligohaline cattail-sedge marsh. Macroinvertebrates appear largely unaffected byPhragmites expansion or control efforts; distribution and densities are unrelated to elevation or hydroperiod, but densities are positively related to litter cover. Dominant fish captured leaving flooded marsh wereFundulus heteroclitus andAnguilla rostrata; both preyed heavily on marsh macroinvertebrates.A. rostrata andMorone americana tended to be more common inPhragmites, but otherwise there were no major differences in use patterns betweenPhragmites and brackish meadow vegetation. SAV and macroalgal cover were markedly lower within aPhragmites-dominated creek versus one withSpartina-dominated banks. The same fish species assemblage was trapped in both plus a third within the herbicide/mow treatment. Fish biomass was greatest from theSpartina creek and lowest from thePhragmites creek, reflecting abundances ofF. heteroclitus. Mowing depressedPhragmites aboveground production and increased stem density, but was ineffective for control.Phragmites, Spartina patens, andJuncus gerardii frequencies after herbicide-only treatment were 0.53-0.21; total live cover was <8% with a heavy litter and dense standing dead stems. After two growing seasonsAgrostis stolonifera/S. patens/J. gerardii brackish meadow characterized most of the herbicide/mow treatment area;Phragmites frequency here was 0.53, contributing 3% cover. Both values more than doubled after four years; a single treatment is ineffective for long-termPhragmites control.  相似文献   

6.
Sulfate reduction rates were measured over the course of a year in the sediments of aJuncus roemerianus marsh located in coastal Alabama. Sulfate reduction rates were typically highest in the surface 0–2 cm and at depths corresponding to peak belowground biomass of the plants. The highest volume-based sulfate reduction rate measured was 1,350 μmol liter-sediment−1 d−1 in September 1995. Areal sulfate reduction rates (integrated to 20 cm depth) were strongly correlated to sediment temperature and varied seasonally from 15.2 mmol SO 4 2− m−2 d−1 in January 1995 to 117 mmol SO 4 2− m−2 d−1 in late August 1995. Despite high sulfate reduction rates porewater dissolved sulfide concentrations were low (<73 μM), indicating rapid sulfide oxidation or precipitation. Sulfate depletion data indicated that net oxidation of sediment sulfides occurred in March through May, following a period of infrequent tidal flooding and during a period of high plant production. Porewater Fe(II) reached very high levels (maximum of 969 μM; mean for all dates was 160 μM), particularly during periods of high sulfate reduction. The annual sulfate reduction rate integrated over the upper 20 cm of sediment was 22.0 mol SO 4 2− m−2 yr−1, which is among the highest rates measured in a wetland ecosystem. Based on literature values of net primary production inJ. roemerianus marshes, we estimate that an amount equivalent to 16% to 90% of the annual belowground production may be remineralized through sulfate reduction.  相似文献   

7.
The responses of Spartina alterniflora above- and belowground biomass to various combinations of N, P, and Fe were documented in a 1-year field experiment in a Louisiana salt marsh. Five levels of N additions to 0.25 m2 plots resulted in 18% to 138% more live aboveground biomass compared to the control plots and higher stem densities, but had no effect on the amount of live belowground biomass (roots and rhizomes; R&R). There was no change in the aboveground biomass when P or Fe was added as part of a factorial experiment of +P, +N, and +Fe additions, but there was a 40% to 60% decrease in the live belowground biomass, which reduced the average R&R:S ratio by 50%. The addition of various combinations of nutrients had a significant affect on the belowground biomass indicating that the addition of P, not N, eased the need for root foraging activity. The end-of-the-growing-season N:P molar ratios in the live above- and belowground tissues of the control plot was 16.4 and 32.7, respectively. The relative size of the belowground standing stocks of N and P was higher than in the aboveground live tissues, but shifted downwards to about half that in fertilized plots. We conclude that the aboveground biomass was directly related to N availability, but not P, and that the accumulation of belowground biomass was not limited by N. We suggest that the reduction in belowground biomass with increased P availability, and the lower absolute and relative belowground standing stocks of P as plant tissue N:P ratios increased, is related to competition with soil microbes for P. One implication for wetland management and restoration is that eutrophication may be detrimental to long-term salt marsh maintenance and development, especially in organic-rich wetland soils.  相似文献   

8.
The monthly variations of below- and aboveground biomass of Spartina alterniflora were documented for a south Louisiana salt marsh from March 2004 to March 2005, and in March 2006 and 2007. The annual production rate above- and belowground was 1821 and 11,676 g m?2, respectively (Smalley method), and the annual production rate per biomass belowground was 10.7 g dry weight?1, which are highs along the latitudinal distributions of the plant’s range. The average root + rhizome/shoot ratio (R&R/S) was 2.6:1, which is lower than the R&R/S ratios of 4 to 5.1 reported for Spartina sp. marshes in the northeastern US. The belowground biomass increased from July to September and fluctuated between October and November, after which it declined until February when the growing season began. The belowground biomass was dominated by rhizomes, which declined precipitously in spring and then rose to a seasonal high in the month before declining again as the late summer rise in inflorescence began. Over half of the root biomass in a 30-cm soil profile was in the upper 10 cm, and in the 10- to 20-cm profile for rhizomes. The maximum March biomass above- and belowground was four to five times that of the minimum biomass over the four sampling years. The net standing stock (NSS) of N and P in live biomass aboveground compared to that in the belowground biomass was about 1.7 times higher and equal, respectively, but the NSS of N and P for the live + dead biomass was about six times higher belowground. The average nitrogen/phosphorous molar ratios of 16:1 aboveground is in agreement with the often tested N limitation of biomass accumulation aboveground, whereas the 37:1 belowground ratio suggests that there is an influence of P on R&R foraging for P belowground. Some implications for management and restoration are, in part, that salt marshes should be evaluated and examined using information on the plant’s physiology and production both below- and aboveground.  相似文献   

9.
This study was carried out to evaluate the seasonal variations of seaweed biomass and species composition at six different sites along the coastal areas in Bushehr Province. Sampling depths varied among sites, from 0.3 to 2.0 m below mean sea level. A total of 37 (i.e., 10 Chlorophyta, 12 Phaeophyta and 15 Rhodophyta) seaweed species were collected. Studies were conducted for quantifying the seaweeds during four seasons from October 2008 until July 2009. During present research, Ulva intestinalis and Cladophora nitellopsis of green, Polycladia myrica, Sirophysalia trinodis and Sargassum angustifolium of brown and Gracilaria canaliculata and Hypnea cervicornis of red seaweeds showed highest biomass in coastal areas of Bushehr Province. The Cheney‘s ratio of 2.1 indicated a temperate algal flora to this area. All sites exhibited more than 50% similarity of algal species, indicating a relatively homogenous algal distribution. Total biomass showed the highest value of 3280.7 ± 537.8 g dry wt m − 2 during summer and lowest value of 856.9 ± 92.0 g dry wt m − 2 during winter. During this study, the highest and lowest seaweed biomass were recorded on the site 2 (2473.7 ± 311.0 g dry wt m − 2) and site 5 (856.7 ± 96.8 g dry wt m − 2), respectively.  相似文献   

10.
Seasonal plant growth dynamics were followed for a year in undisturbed plots of tall and short formSpartina alterniflora Loisel. and in plots of short formS. alterniflora which were enriched with sewage sludge at a rate of 100 g dry sludge m?2wk?1, corresponding to a nitrogen enrichment of 2 g N m?2wk?1. Monthly determinations of aboveground live and dead biomass, density of live stems, the ratio of number of young shoots to total number of shoots, and belowground mass of macro-organic matter to a depth of 30 cm were made for each area. Sludge fertilization increased the live biomass of the short formS. alterniflora by up to 150% of the control live biomass, but had little effect on the dead biomass, stem density, or proportion of young shoots. There was a trend of increased amount of belowground macro-organic matter in fertilized compared to control plots during the last 6 months of the study. In all areas, there was a marked decrease in the proportion of young shoots from winter to early summer, followed by a rapid increase in the percent of young shoots from late summer to fall. Sampling of plots 7 and 20 months after termination of sludge enrichment showed higher plant biomass and % N content in surface soils, but no difference in N content of live plant tissue, in fertilized compared to unfertilized marsh. After 20 months, about half of the sludge nitrogen remaining in the soils of the fertilized plots had disappeared.  相似文献   

11.
Since its introduction in the early part of this century,Rhizophora mangle L. has spread extensively through most of the main islands of the Hawaiian Archipelago. We investigated the structural properties and estimated productivity of aR. mangle population at Nuupia Ponds Wildlife Management Area (NPWMA), on windward Oahu, where the mangroves were being controlled due to their propensity to overgrow archaeological sites and the habitat of endangered Hawaiian waterbirds. Mangroves within NPWMA were very dense (>24,000 trees ha−1) and most were relatively small (only 3.3% of the trees were ≥10 cm DBH). Mean basal area, aboveground biomass, and number of seedlings were all high, at 37.2 m2 ha−1, 279 t (dry wt) ha−1, and 121 m−2, respectively. The seedling, density may be particularly unusual and appears to be due to extremely high rates of propagule, production coupled with low rates of propagule predation. Stand productivity was estimated by stem growth (allometry), litterfall, and a light attenuation approach to determining net canopy photosynthetic production. All three methods yielded estimates that are higher than previously, reported forR. mangle and comparable with estimates of highly productiveRhizophora spp.-dominated stands in Australia and Asia. The high density, biomass, and productivity of this stand relative to stands within the species' native range may be due to a combination of favorable site conditions, lack of competition from other woody plants, and very low rates of herbivory and propagule predation.  相似文献   

12.
The size-fractionated phytoplankton biomass and primary production were investigated in four contrasting areas of Hong Kong waters in 2006. Phytoplankton biomass and production varied seasonally in response to the influence of the Pearl River discharge. In the dry season, the phytoplankton biomass and production were low (<42 mg chl m−2 and <1.8 g C m−2 day−1) in all four areas, due to low temperatures and dilution and reduced light availability due to strong vertical mixing. In contrast, in the wet season, in the river-impacted western areas, the phytoplankton biomass and production increased greater than five-fold compared to the dry season, especially in summer. In summer, algal biomass was 15-fold higher than in winter, and the mean integrated primary productivity (IPP) was 9 g C m−2 day−1 in southern waters due to strong stratification, high temperatures, light availability, and nutrient input from the Pearl River estuary. However, in the highly flushed western waters, chl a and IPP were lower (<30 mg m−2 and 4 g C m−2 day−1, respectively) due to dilution. The maximal algal biomass and primary production occurred in southern waters with strong stratification and less flushing. Spring blooms (>10 μg chl a L−1) rarely occurred despite the high chl-specific photosynthetic rate (mostly >10 μg C μg chl a −1 day−1) as the accumulation of algal biomass was restricted by active physical processes (e.g., strong vertical mixing and freshwater dilution). Phytoplankton biomass and production were mostly dominated by the >5-μm size fraction all year except in eastern waters during spring and mostly composed of fast-growing chain-forming diatoms. In the stratified southern waters in summer, the largest algal blooms occurred in part due to high nutrient inputs from the Pearl River estuary.  相似文献   

13.
Responses ofSpartina alterniflora marsh to combinations of feral horse grazing, clipping, simulated trampling, and a late winter burn were studied on Cumberland Island National Seashore, Georgia. Replicated 200-m2 plots were established and sampled bimonthly from July 1983 to November 1984. Clipping and trampling each reduced peak aboveground biomass by 20% in 1983 and 50% (clipping) and 55% (trampling) in 1984. A March burn reduced peak aboveground biomass by 35% in 1984. Trampling and burning earch reduced net aboveground primary production (NAPP) by 35%, but clipping did not reduce NAPP. Standing stocks of live rhizomes were correlated with aboveground biomass and were reduced with experimental treatments. Abundance of the periwinkle snail (Littorina irrorata) was also reduced. Horse grazing had a substantial impact on standing stocks and NAPP ofSpartina, but grazing was not uniform throughout the marsh. Moderately grazed plots had NAPP reduced by 25% compared to ungrazed plots. Heavily grazed plots had extremely low NAPP, and abovegroundSpartina never exceeded 40 g m?2 dry mass compared to 360 g m?2 within exclosures.  相似文献   

14.
High nitrogen (N) loading rates received by coastal bays can have deleterious effects on aquatic ecosystems. Salt marshes can intercept land-based N through seasonal plant uptake, denitrification, and burial. Salt marshes fringing Delaware’s Inland Bays are characterized by different plant species occurring in close proximity. To evaluate N pool retention and loss for the dominant plant species, we measured seasonal N concentration and pool size, N resorption efficiency, loss during decomposition, and soil N. Seasonal variation in N pools and fluxes differed among species. Seasonal differences in the total N pools of the herbaceous species were largely influenced by belowground fine root and dead macro-organic matter fluxes. N production rate estimates ranged from 18 g N m−2 year−1 aboveground for the high marsh shrub to 40.8 g N m−2 year−1 above- and belowground for the high marsh rush illustrating the importance of incorporating species-specific dynamics into ecosystem N budgets.  相似文献   

15.
The rapid proliferation of Phragmites australis in North America has challenged resource managers to curb its expansion and reduce the loss of functional tidal marsh. We investigated whether native plant competition could reduce the ability of Phragmites to invade a tidal marsh, and if plant diversity (species richness, evenness, and composition) altered the competitive outcome. Immature Phragmites shoots and four native halophytes were transplanted to small but dense field plots (~1,200 shoots m−2) comprising three community structure types (Phragmites alone, Phragmites + 1 native species, and Phragmites + 4 native species). Interspecific competition significantly reduced Phragmites aboveground biomass, shoot length production, density, and survival by approximately 60%. Additionally, plots planted with greater native diversity contained Phragmites with the lowest growth and survival, potentially indicating diversity-enhanced resource competition. Competition consistently reduced the growth of Phragmites even under favorable conditions: lack of strong tidal flooding stresses as well as elevated nutrient pools.  相似文献   

16.
Aboveground and belowground biomass ofSpartina alterniflora were harvested during the period of peak aerial biomass from six sites along a latitudinal gradient ranging from Georgia to Nova Scotia. An equation relating live aboveground to live belowground biomass for short-form plants was formulated, using data collected in Delaware marshes. When data from the other sites were substituted into the equation, the mean live belowground biomass it predicted was within 15% of the value determined by harvesting at four of the five sites. At all sites, short-form plant live belowground biomass was concentrated in the upper 10 cm. Dead belowground biomass was located mostly in the top 15 cm in southern marshes, but was more evenly distributed with depth in northern marshes. Results were more ambiguous for tall-form plants, probably because of greater spatial variability in biomass distribution, and greater seasonal biomass dynamics.  相似文献   

17.
Aboveground live standing crop of giant cutgrass (Zizaniopsis miliacea) populations in similar freshwater tidal and impounded nontidal marshes were almost identical (peaking at 1,039 g per m2 in each). The mortality, however, was greater in the tidal marsh resulting in significantly (95% level) greater annual production of aboveground cutgrass in the tidal (1,530±103 g per m2 per yr) than the impounded (1,172±88 g per m2 per yr) marsh, a 31% difference which we consider to be a measure of tidal subsidy. Belowground production also was found to average higher in the tidal marsh, but estimates were not as satisfactory as the aboveground results due to sampling difficulties. Combined annual above and belowground net production comes to an estimated 2,048 ±101 g per m2 per yr for the tidal and 1,481±219 for the impounded cutgrass marsh. The potential of freshwater tidal marshes for tertiary treatment of wastes is briefly discussed.  相似文献   

18.
Gulf sturgeon,Acipenser oxyrinchus desotoi, forage extensively in the Suwannee River estuary following emigration out of the Suwannee River, Florida. While in the estuary, juvenile Gulf sturgeon primarily feed on benthic infauna. In June–July 2002 and February–April 2003, random sites within the estuary were sampled for benthic macrofauna (2002 n = 156; 2003 n = 103). A mean abundance of 2,562 ind m−2 (SE ± 204) was found in the summer, with significantly reduced macrofaunal abundance in the winter (mean density of 1,044 ind m−2, SE ± 117). Benthic biomass was significantly higher in the summer with an average summer sample dry weight of 5.92 g m−2 (SE ± 0.82) compared to 3.91 g m−2 (SE ± 0.67) in the winter. Amphipods and polychaetes were the dominant taxa collected during both sampling periods. Three different estimates of food availability were examined taking into account principal food item information and biomass estimates. All three estimates provided a slightly different view of potential resources but were consistent in indicating that food resource values for juvenile Gulf sturgeon are spatially heterogeneous within the Suwannee River estuary.  相似文献   

19.
Burning has been employed as an oil spill remediation technique in coastal marshes, even though the combined and interactive effects of oil and burning on vegetation are poorly understood. Variation among clones of perennial marsh grasses in response to these perturbations is not known. We performed a greenhouse experiment designed to assess the effects of Venezuelan crude oil alone and of oil followed by burning on three clonal genets ofSpartina alterniflora. The fully-crossed 6-mo experiment involved five dosages of oil (0 l m−2, 4 l m−2, 8 l m−2, 16 l m−2, and 24 l m−2) and two burn treatments (burned or unburned) applied to ramets from three clones. All oil-only dosages reduced survival, but burning after oiling (oil + burn treatments) increased survival relative to oil-only groups in all except the highest two oil dosages. Higher oil-only treatments also reduced ramet densities and inhibited density increases over 6 mo. Burning after treatment with the 16 l m−2 oil concentration allowed increased production of new ramets, but burning exacerbated the negative impacts on ramet density at the oil concentration of 24 l m−2. At some intermediate oil dosages, burning remediated the negative effects of oil on aboveground biomass production and growth in height. There was a significant effect of oil-only treatments on numbers of flowering ramets produced, in which two clones responded with decreased flower production and one exhibited increased flowering. There was no main effect of oil + burn on flowering. There were significant among-clones differences in all response variables to one or both treatments. Our experiment demonstrates that burning of oiledS. alterniflora marshes may have little measurable effect at low levels of Venezuelan crude oil, can remediate the effects of oil at intermediate oil concentrations, but can increase the negative impacts at high concentrations of oil. These results indicate that oil spills have the potential to adversely affect genetic diversity inS. alterniflora populations by eliminating some sensitive clonal variants or changing the relative dominance of genets. These results suggest certain clones may be better suited for phytoremediation or restoration planting following oil spills.  相似文献   

20.
In the lower delta of the Paraná River, at the head of the Río de la Plata estuary (Argentina), we compared net aboveground primary production (NAPP) and soil properties of the dominant macrophyteScirpus giganteus (Kunth) in a floating and an attached marsh community. Both marshes are tidally influenced but in different ways. The floating marsh site is relatively isolated from tidal influences because its ability to float makes it resistant to overland flow and to sediment inputs from the estuary. The attached marsh lacks the capacity to float and receives sediment supplies from the estuary through overland flow. These hydrologic differences are reflected in lower mineral content in sediments of the floating marsh. Using a leaf tagging technique, estimated NAPP was 1,109 ± 206 g m−2 yr−1 for the floating marsh and 1,866 ±258 g m−2 yr−1 for the attached marsh. We attribute the lower NAPP of the floating marsh to isolation from sediment input from overland flow.  相似文献   

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