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1.
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
2.
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
3.
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
4.
David A. Tomasko 《Estuaries and Coasts》1992,15(2):214-217
Shoal grass, Halodule wrightii, exhibited different morphologies when growing in a monospecific meadow compared to plants growing under a canopy of turtle grass, Thalassia testudinum. When growing under a turtle grass canopy, shoal grass had longer internodes, less frequent branching, and lower aboveground to belowground biomass ratios than when growing in a monospecific meadow. Aquarium studies approximated the observed phenomena in the field study. Rhizome growth of sprigs of shoal grass (mm d?1) was greater for plants grown under 35% light reduction caused by blades of turtle grass than for sprigs grown under ambient light. Sprigs grown under 35% light reduction caused by neutral density screens had rhizome growth rates lower than controls. Greater rhizome growth rates of sprigs grown under turtle grass blades were due to increased internode distances, rather than increased rates of shoot formation. The environmental factor responsible for inducing morphological changes in shoal grass appears to be the ratio between red and far-red light. This ratio declines as light passes through a canopy of blades of turtle grass. 相似文献
5.
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
6.
The response of deltaic emergent marsh vegetation to increases in precipitation was examined over a 14-mo period at three
sites in the lower Nueces Estuary in south Texas. At all three sites, significant changes in plant biomass, percent cover,
and allocation of aboveground and belowground tissues were associated with more than double the rainfall in late winter and
early spring 1992 compared to the previous year and the 50-yr average for this region. Water column salinities, which ranged
from 10‰ to 35‰ at all three sites in 1991, remained below 10‰ through August 1992. Significant changes in marsh vegetative
structure included decreases in bare space, increases in the percent cover and aboveground biomass of a relatively less salt
tolerant halophytes (Borrichia frutescens), and significant increases in root:shoot ratios inB. frutescens, Batis maritima andSuaeda linearis (inSalicornia virginica root:shoot ratios decreased significantly). Higher precipitation generally led to an overall increase in the biomass of most
marsh perennials, but these increases were not statistically significant. For one species,Lycium carolinianum, additional rainfall extended its growing season through August 1992, 2 mo longer than in the previous year. The expansion
(+58%) ofB. frutescens at one site was also coincident with the significant loss ofB. maritima, whose cover decreased nearly 20%. In an ecological context, these responses suggest that precipitation events in arid environments
may be considered a major physical disturbance that can result in large changes in the composition and relative abundance
of emergent vascular plants over a relatively short period. The long-term significance of these changes is unknown and demonstrates
the value of ecological studies that are conducted over several years for a more complete understanding of the dynamic processes
that regulate marsh productivity. 相似文献
7.
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
8.
Monica Goigel Turner 《Estuaries and Coasts》1987,10(1):54-60
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
9.
Alana Hanson Roxanne Johnson Cathleen Wigand Autumn Oczkowski Earl Davey Erin Markham 《Estuaries and Coasts》2016,39(5):1376-1385
Coastal wetlands, well recognized for their ecosystem services, have faced many threats throughout the USA and elsewhere. While managers require good information on the net impact of these combined stressors on wetlands, little such information exists. We conducted a 4-month mesocosm study to analyze the multiple stressor effects of precipitation changes, sea level rise, and eutrophication on the salt marsh plant Spartina alterniflora. Pots containing plants in an organic soil matrix were positioned in tanks and received Narragansett Bay (RI, USA) water. The study simulated three precipitation levels (ambient daily rain, biweekly storm, and drought), three levels of tidal inundations (high (15 cm below mean high water (MHW)), mean (MHW), and low (15 cm above MHW)), and two nutrient enrichment levels (unenriched and nutrient-enriched bay water). Our results demonstrate that storm and drought stressors led to significantly less above- and belowground biomass than those in ambient rain conditions. Plants that were flooded at high inundation had less belowground biomass, fine roots, and shoots. Nutrients had no detectable effect on aboveground biomass, but the enriched pots had higher stem counts and more fine roots than unenriched pots, in addition to greater CO2 emission rates; however, the unenriched pots had significantly more coarse roots and rhizomes, which help to build peat in organogenic marshes. These results suggest that multiple stressors of altered precipitation, sea level rise, and nutrient enrichment would lead to reduced marsh sustainability. 相似文献
10.
Salt marsh fucoid algae are a conspicuous component of north temperate marshes, yet comparatively little research has been
conducted to examine their ecological effects. We examined the influence of salt marsh fucoids on physical conditions and
the biotic community in a manipulative experiment conducted in a southern Maine back-barrier salt marsh. The biomass of salt
marsh fucoids was higher than that of aboveground Spartina alterniflora in the zone where we conducted the experiment. Average daytime temperatures at the sediment surface were significantly reduced
by the presence of salt marsh fucoids. Density and biomass of standing-dead S. alterniflora was significantly higher when salt marsh fucoids were removed. In contrast, the abundance of various species of epifauna
and infauna were significantly enhanced by the presence of salt marsh fucoids. A regional survey indicated that results from
the study site may be conservative because the biomass of salt marsh fucoids was lowest among other back-barrier marshes.
Salt marsh fucoids are little studied ecosystem engineers whose presence affects the microclimate and biotic community, especially
the animals that constitute the basal components of the salt marsh trophic relay. 相似文献
11.
Salt marshes respond to both slowly increasing tidal inundation with sea level rise and abrupt disturbances, such as storm-induced
wrack deposition. The effects of inundation pattern and wrack deposition have been studied independently but not in combination.
We manipulated inundation of tidal creek water and wrack presence individually and in combination, in two neighboring communities
within a Virginia high salt marsh during 1994 and 1995. The effects of these manipulations were assessed by measurements of
aboveground plant biomass. Altered inundation by itself produced little response in the various categories of plant biomass
measured. Wrack deposition affected all species (i.e., Juncus roemerianus, Spartina patens, and Distichlis spicata) showing a significant reduction in aboveground biomass, as expected. Recovery after wrack deposition was dependent on the
species. S. patens and D. spicata recovered from wrack deposition within one growing season, while J. roemerianus did not. Because the effects of wrack deposition greatly exceeded those of experimentally increased inundation, the possible
interactions between the two were masked. Increased inundation may have inhibited the colonization of bare areas by some species
after the removal of wrack from an area, although statistical significance at α=0.01 was not reached. Our results confirm
that wrack deposition can cause the redistribution of species within the high marsh community. Altered inundation may have
a greater effect on the re-establishment of the plant community after wrack deposition than it does without wrack deposition. 相似文献
12.
Our goal is to understand how removal regime and habitat type interact to influence removal success of a marine plant invader
and the subsequent potential for restoration. In particular, we investigate the management program designed to eradicate the
English cordgrass,Spartina anglica C. E. Hubbard, in marine intertidal habitats of Puget Sound, Washington, United States. Observational and manipulative experiments
were used to measure the regrowth (vegetative growth), reinvasion (seedling recruitment), and restoration potential (return
to native condition) of invaded habitats. Removal regime (consistent: yearly removal; interrupted: yearly removal with the
last year missed) and habitat type (low salinity marsh, mudflat, cobble beach, and high salinity marsh sites) were considered.
The response to removal regime was dramatic. Under consistent removal, cordgrass slowly declined but under interrupted removal,
there was substantial regrowth of the invader. This pattern results from the resiliency of belowground biomass and the subsequent
high aboveground productivity and seedling growth ofS. anglica. We also found that removal success depended on differences among sites that represent different habitat types. Cordgrass
regrowth and reinvasion were substantially higher in the low salinity marsh sites where soils have lower salinity. We also
found that at the low salinity marsh sites, some restoration of native plants and soil conditions was evident. At mudflat,
cobble beach, and high salinity marsh sites, colonization of native vascular plants and algae not normally present, in the
absence of the invasion, occurred. Whether these habitats will eventually revert back to the pre-invasion conditions over
a longer period of time is unknown. 相似文献
13.
We report the first data on belowground tissue mass and nitrogen (N) concentration forSpartina foliosa in southern California, assessing one natural and two constructed marshes on San Diego Bay. Biomass at the natural marsh was low compared to that of otherSpartina spp., but higher than values reported forS. foliosa in northern California. In sandy constructed marshes planted 5 and 10 years before this study,S. foliosa had lower belowground tissue N, lower N crop (%N×biomass), and shallower roots than in the adjacent natural marsh. We took advantage of a 2-yr, large-scale fertilization project being performed in the older constructed marsh and examined biomass and N storage after N additions. Although there was a trend toward N accumulation with fertilization, N crop remained at approximately 50% of natural marsh levels, unlike the large aboveground responses to N addition in our previous studies. Lower belowground reserves help to explain poor aerial growth in the created marshes and suggest the need for finer sediments (with greater potential for holding and supplying nutrients) to sustain (S. foliosa. While fine sediments are beginning to accumulate on the surface of the created marshes, vertical accretion is more likely to shift the plant community toward other species than to enhanceS. foliosa growth. We suggest salvaging and importing fine, organic marsh sediments or providing organic amendments to establish proper substrate conditions. Overexcavating and allowing fine sediments to accumulate remains an option, although the time scale is unpredictable due to the stochasticity of accretion events. 相似文献
14.
In spite of its long history,Phragmites australis’ (Cav.) Trin ex Stuedel invasion in tidal marshes defies explanation. Initial establishment in these systems is particularly perplexing, because seedlings and rhizome fragments do not perform well in poorly drained saline environments. We tested the possibility that dispersal and burial of large rhizomes, periods of low salinity, and localized, well-drained areas facilitate initial establishment in brackish marshes. In a greenhouse we exposed large and small rhizomes to two drainage treatments: mimics of poorly-drained, high marsh interiors and mimics of well-drained, mosquito ditch banks. In well-drained treatments we exposed rhizomes to one of three salinity treatments: fresh, natural salinity regime of an invaded brackish water marsh, and a 2-wk freshwater window followed by a natural salinity regime. Small rhizone fragments did not emerge in saline treatments or treatments with high water tables, while emergence was spotty in well-drained freshwater treatments. Large rhizomes emerged only in well-drained, treatments. For large rhizomes, growth, survival, and clonal spread decreased when exposed to the natural salinity regime, but improved with exposure to the 2-wk freshwater window. These results suggest that dispersal and burial of larger rhizomes, well-drained features, and low salinity windows following dispersal improve the chances of successful establishment. These results help explain case-specific historical links between establishment and such human activities as hydrological alterations, construction activities, and lowered salinity. 相似文献
15.
The potential role of roots and rhizomes in structuring salt-marsh benthic communities 总被引：1，自引：0，他引：1
The density of the Carolina marsh clam,Polymesoda caroliniana (Bosc), was determined in three adjacent tidal marsh communities which differed only in plant species composition. Clam density was inversely related to the density (biomass) of plant roots and rhizomes in sediments and directly related to density of plant stems (numbers). Clam abundance was not related to the basal area of plant stems. Each plant community contained clams of various ages from juvenile to adult indicating continued recruitment and survival. These data suggest thatP. caroliniana is most abundant inJuncus roemerianus marshes because there are fewer roots and rhizomes (mean of 2.5 kg m?2) to hamper burrwing as compared toSpartina alterniflora andcynosuroides (5.1 and 6.3 kg m?2, respectively) dominated marshes. Salinity, floding frequency, distance from flooding water, and sediment type were essentially constant among the three plant communities. Root/rhizome density should be collected along with other environmental parameters during studies of benthic organisms on marshes because it potentially limits the occurrence or abundance of some species. 相似文献
16.
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
17.
Diana I. Montemayor Alejandro D. Canepuccia Jesus Pascual Oscar O. Iribarne 《Estuaries and Coasts》2014,37(2):411-420
Salt marsh zonation patterns generate different abiotic and biotic conditions that can accentuate species inherent differences in primary production and biomass. In South West Atlantic marshes, there are two Spartina species: Spartina alterniflora in the low intertidal and Spartina densiflora in the high intertidal. These two species are generally found in all marshes but with different dominance: In some marshes, the S. densiflora zone occupies higher extents, and in others, the S. alterniflora zone is the one that prevails. We found through field sampling that, in six studied marshes, there is greater S. densiflora live and total (i.e., dead+live) aboveground biomass (g m?2) in the marshes dominated by S. densiflora than in the ones dominated by S. alterniflora. Spartina alterniflora had similar aboveground biomass in the six marshes, regardless of the dominance of each species. When comparing the two Spartina species within each marsh, S. densiflora had greater live and total biomass in the marshes it dominates. In the marshes dominated by S. alterniflora, both species had similar live and total biomass. In all marshes, there was greater dead S. densiflora biomass. A multivariate analysis using selected abiotic factors (i.e., salinity, latitude, and tidal amplitude) showed that S. alterniflora aboveground biomass patterns are mainly correlated with salinity, while S. densiflora live biomass is mainly correlated with salinity and latitude, dead biomass with salinity and tidal amplitude, and total biomass with salinity alone. We conclude that in S. densiflora dominated marshes, the main processes of that species zone (i.e., nutrient accumulation) will be accentuated because of its higher biomass. We also conclude that climatic conditions, in combination with specific Spartina biotic and ambient abiotic parameters, can affect marsh ecological functions. 相似文献
18.
A large-scale dieback event struck marshes along the northwestern Gulf of Mexico coast during summer 2000, in apparent response to a prolonged and severe drought. Along the Louisiana coast, large areas of the dominant marsh species,Spartina alterniflora, turned brown, followed by death of at least the aboveground structures of entire plant mortality. Key ecological and genetic measures were studied in a dieback-affected marsh in southwest Louisiana (C83 marsh, Sabine National Wildlife Refuge), for which existed predieback ecologic and genetic datasets. Effects on genetic diversity only were studied in a second set of sites in southeastern Louisiana (near Bay Junop), where the dieback was more widespread. We hypothesized that stem density, live aboveground biomass, and genetic diversity would be significantly reduced compared to predieback conditions and to nearby unaffected marshes. Stem densities and biomass levels approached predieback conditions 14 months after first observance of the dieback in the Sabine marsh and were similar to or exceeded the same measures for a nearby unaffected marsh. DNA extracted from leaf samples in the Sabine and Bay Junop sites was used to construct genotype profiles using AFLPs and analyzed using the complement of Simpson’s Index (1-D), the richness measure G/N, average heterozygosity <H>, and the estimated proportion of polymorphic genes <P>. Genetic diversity was relatively unaffected by the dieback at either the Sabine or Bay Junop sites. Evidence from field observations and the results of the genetic analyses suggest that seedling recruitment is an important factor in the recovery of both the Bay Junop and C83 sites, although re-growth from surviving below-ground rhizomes appeared to dominate recovery at the latter site. Survival of below-ground structures, leading to the rapid recovery observed, indicates a high level of resilience of the Sabine marsh to drought-induced stress. Still, the genetic diversity ofS. alterniflora-dominated marshes may be promoted by occasional disturbance events, which produce open areas in which seedling recruitment can occur. 相似文献
19.
In Louisiana, salt marshes are being created in an effort to offset the large loss of such habitat that has occurred over the last 50 yr. Primary productivity is an important function and indicator of success for salt marsh creation and restoration projects. The aim of this study was to determine whether the aboveground and belowground productivity of the dominant salt marsh grassSpartina alterniflora in created marshes in southwest Louisiana began to approximate productivity levels in natural marshes, over time. Net annual aboveground primary productivity (NAPP) was measured by a harvest technique, while the ingrowth core method was used to estimate net annual belowground primary productivity (NBPP). NAPP levels were similar to those found in other, Louisiana salt marshes, while NBPP levels were similar to or higher than the reported range forS. alterniflora studied along the Atlantic and Gulf of Mexico coasts. NAPP tended to decrease as the created marshes aged, but the levels in the oldest, 19 year old, created marsh were still well above values measured in the, natural marshes. It was estimated that it would take 35 yr after marsh creation for NAPP in the created marshes to become equivalent to that in natural marshes. NBPP in the created marshes became equivalent to levels found in the natural marshes after 6–8 yr, but then belowground production increased with marsh age, reaching an asymptote that surpassed natural marsh levels. Equivalency in primary productivity has not been reached in these marshes. Elevation also affected productivity, as higher elevational sites with greater topographic heterogeneity had significantly lower aboveground and belowground biomass levels than those with elevations closer to mean sea level. This underscores the need to construct marshes so that their mean elevation and degree of topographic heterogeneity are similar to natural marshes. 相似文献
20.
Net annual primary production of a sedge Carex lyngbyei dominated tidal marsh in the Fraser River estuary, British Columbia, Canada was 634 g ash-free dry weight (AFDW) per m2 per yr (687 g dry weight per m2 per yr). Mean maximum shoot elongation during the short (May to August) growing season was 1.88 cm per day from overwintering shoots. The maximum aboveground standing crop of 690 g AFDW per m2 represented only 25% of the total below-ground biomass, which appears to be controlling most of the critical life history processes of the sedge marsh. An estimate of 14 percent of the aboveground standing crop was lost through leaching of dissolved organic carbon from the growting plant. Aboveground tissue losses, which were negligible during the growing season, occurred primarily via translocation in autumn and tidal export during the winter. In situ measurements showed that of the original maximum standing crop, approximately 38%, 37%, and 25% were lost by downward translocation, tidal export, and sediment burial, respectively. Based on changes in above and belowground nutrient pools, rapid spring (May to late June) uptake rates of 109 mg N per m2 per day and 23.0 mg P per m2 per day by shoots were followed by downward translocation rates of 44.8 mg N per m2 per day and 12.2 mg P per m2 per day during late June to the end of August. Aboveground leaching rates were estimated as 23.9 mg N per m2 per day and 7.8 mg P m2 per day and belowground uptake rates as 100 mg N per m2 per day and 26 mg P per m2 per day; root uptake occurred primarily after late June. Nutrient levels in decomposing litter more than doubled over the winter period showing a pattern of nutrient enrichment characteristic of marsh ecosystems. *** DIRECT SUPPORT *** A01BY023 00004 相似文献