Low Belowground Biomass Research Articles

Seagrass space occupation efficiency is key for their role as ecosystem engineers and ecological indicators

Studies for the preservation of seagrass beds biotopes have met difficulties in establishing appropriate methods assessing their health. We tested the efficiency of space occupation by seagrasses scattered worldwide (dgrass index), which proved to be dependent on clonal growth form and morphometric plasticity. dgrass correlated with the above-ground to below-ground biomass ratio. However, the latter was misleading when high ratios resulted from low below-ground biomass. Nutrient Posphate-limitations were revealed in situations of theoretical Nitrogen-limitation. Enhanced nutrient supply benefitted seagrasses only up to a threshold after which it became detrimental. Better nurtured, healthier meadows with denser canopies increased the organic matter in the sediment and had associated greater abundances of benthic macrofauna. Hence, seagrass biotopes could benefit from moderate anthropogenic nutrient additions. However, organic matter above ≈6% and/or reduced riverine discharges (dams upstream and climate-change-related droughts) were detrimental to healthy meadows, jeopardizing ecosystem services such as macrofauna abundances and carbon sinks.

Fungal epiphytes differentially regulate salt tolerance of invasive Ipomoea cairica according to salt stress levels.

Fungal symbionts can improve plant tolerance to salt stress. However, the interaction of epiphytic Fusarium oxysporum and Fusarium fujikuroi with the tolerance of the invasive plant Ipomoea cairica against saline coastal habitats is largely unknown. This study aimed to investigate the interaction of the mixture of the two epiphytic fungi with salt tolerance of I. cairica. Surface-sterilized I. cairica cuttings inoculated (E+) and non-inoculated (E-) with the fungal mixture were cultivated with 2, 3, and 5 parts per thousand (PPT) of NaCl solutions to simulate mild, moderate, and severe salt stress, respectively. The hydroponic experiment showed that the growth inhibition and peroxidation damages of E+ and E- cuttings were aggravated with salinity. Noteworthily, E+ cuttings had higher peroxidase (POD) and catalase (CAT) activities, chlorophyll content, total biomass, aboveground biomass, total shoot length and secondary shoot number, but lower root-to-shoot ratio than E- cuttings under 2 and 3 PPT NaCl conditions. Moreover, E+ had higher superoxide dismutase (SOD) activity and proline content but lower belowground biomass and malondialdehyde (MDA) content than E- cuttings under 3 PPT NaCl condition. However, lower SOD, POD, and CAT activities, and chlorophyll content, but higher MDA content occurred in E+ cuttings than in E- cuttings under 5 PPT NaCl condition. These findings suggested that the mixture of the two epiphytic fungi increased salt tolerance of I. cairica mainly through increasing its antioxidation ability and chlorophyll stability under mildly and moderately saline conditions, but decreased salt tolerance of this plant in an opposite way under severely saline conditions.

Soil amendment interacts with invasive grass and drought to uniquely influence aboveground versus belowground biomass in aridland restoration

Water‐holding soil amendments such as super‐absorbent polymer (SAP) may improve native species establishment in restoration but may also interact with precipitation or invasive species such as Bromus tectorum L. (cheatgrass or downy brome) to influence revegetation outcomes. We implemented an experiment at two sites in Colorado, U.S.A., in which we investigated the interactions of drought (66% reduction of ambient rainfall), B. tectorum seed addition (BRTE, 465 seeds/m2), and SAP soil amendment (25 g/m2) on initial plant establishment and 3‐year aboveground and belowground biomass and allocation. At one site, SAP resulted in higher native seeded species establishment but only with ambient precipitation. However, by the third year, we detected no SAP effects on native seeded species biomass. Treatments interacted to influence aboveground and belowground biomass and allocation differently. At one site, a SAP × precipitation interaction resulted in lower belowground biomass in plots with SAP and drought (61.7 ± 7.3 g/m2) than plots with drought alone (91.6 ± 18.1 g/m2). At the other site, a SAP × BRTE interaction resulted in higher belowground biomass in plots with SAP and BRTE (56.6 ± 11.2 g/m2) than BRTE alone (35.0 ± 3.7 g/m2). These patterns were not reflected in aboveground biomass. SAP should be used with caution in aridland restoration because initial positive effects may not translate to long‐term benefits, SAP may uniquely influence aboveground versus belowground biomass, and SAP can interact with environmental variables to impact developing plant communities in positive and negative ways.

Effects of soil flooding, sunlight and herbivory on seedlings of Annona glabra and Pachira aquatica in a tropical swamp

Wetland seedlings, in addition to dealing with the effects of flooding, must gain access to sunlight and avoid herbivore damage in order to establish. Understanding the effects of environmental factors on seedling growth and how plants modify their functional traits in response to them, is a challenge of wetland ecology. We evaluated the effects of different conditions of soil flooding (flooded and mesic), sunlight (closed and no canopy) and herbivory (presence and absence) on the survival, growth, and morphological traits of Annona glabra and Pachira aquatica seedlings, two dominant woody species of Neotropical swamps. We had eight experimental treatments with five replicates each. Our results showed that the survival of both species was high and was not affected by soil flooding, sunlight and herbivory. However, these factors affected plant growth rates. In general, the highest growth rates were observed in the treatment with high sunlight, mesic soil and herbivore exclusion. Both species displayed higher leaf biomass allocation under closed than under no canopy. Furthermore, under closed canopy conditions both species produced relatively more slender and taller stems, which may allow them to intercept light more efficiently. Also, both species showed low belowground biomass allocation in flooded soils, probably as a consequence of a high anoxic condition. Our results confirmed that soil flooding, sunlight and herbivory are important factors that influence the growth patterns of A. glabra and P. aquatica seedlings, but they do not affect seedling survival. This information may help resource managers to identify high-quality sites that deserve to be protected. Also, the knowledge on species responses to different environmental conditions may be useful in restoration programs for tropical swamp forests.

Early growth interactions between a mangrove and an herbaceous salt marsh species are not affected by elevated CO2 or drought

Increasing atmospheric carbon dioxide (CO2) concentrations are likely to influence future distributions of plants and plant community structure in many regions of the world through effects on photosynthetic rates. In recent decades the encroachment of woody mangrove species into herbaceous marshes has been documented along the U.S. northern Gulf of Mexico coast. These species shifts have been attributed primarily to rising sea levels and warming winter temperatures, but the role of elevated CO2 and water availability may become more prominent drivers of species interactions under future climate conditions. Drought has been implicated as a major factor contributing to salt marsh vegetation dieback in this region. In this greenhouse study we examined the effects of CO2 concentration (∼380 ppm, ∼700 ppm) and water regime (drought, saturated, flooded) on early growth of Avicennia germinans, a C3 mangrove species, and Spartina alterniflora, a C4 grass. Plants were grown in monocultures and in a mixed-species assemblage. We found that neither species responded to elevated CO2 over the 10-month duration of the experiment, and there were few interactions between experimental factors. Two effects of water regime were documented: lower A. germinans pneumatophore biomass under drought conditions, and lower belowground biomass under flooded conditions regardless of planting assemblage. Evidence of interspecific interactions was noted. Competition for aboveground resources (e.g., light) was indicated by lower S. alterniflora stem biomass in mixed-species assemblage compared to biomass in S. alterniflora monocultures. Pneumatophore biomass of A. germinans was reduced when grown in monoculture compared to the mixed-species assemblage, indicating competition for belowground resources. These interactions provide insight into how these species may respond following major disturbance events that lead to vegetation dieback. Site variation in propagule availability and physico-chemical conditions will determine plant community composition and structure following such disturbances when these two species co-occur.

Impacts of permafrost on above- and belowground biomass on the northern Qinghai-Tibetan Plateau

ABSTRACT Because permafrost is extremely sensitive to climate change, it is of great importance to understand the relationship between permafrost and vegetation biomass. This study aims to reveal the impacts of permafrost on above- and belowground vegetation biomass on the northern Qinghai-Tibetan Plateau. Soil temperature, moisture, active-layer thickness, vegetation coverage, aboveground biomass (AGB), belowground biomass (BGB), and soil organic carbon were investigated in the growing seasons during 2014–2016. The average AGB and BGB in the growing seasons were 0.036 and 0.83 g cm−2, respectively. The AGB was significantly positively correlated with BGB, soil moisture, and soil organic carbon content, but was significantly negatively correlated with mean annual ground temperature and active-layer thickness, suggesting that permafrost degradation can potentially decrease vegetation growth. The BGB was positively correlated with active-layer thickness and was negatively correlated with soil moisture. This study suggests that permafrost degradation can decrease the soil moisture on the northern Qinghai-Tibetan Plateau and thus decrease AGB. The decreased soil moisture can also lead to lower BGB, while the vegetation in drier soils tends to have higher BGB to access more water resources for plant growth.

Effects of aboveground herbivory on plants with long-term belowground biomass storage

Plant tolerance to herbivory is contingent on multiple traits and adaptive mechanisms, which makes it a complex response with ecological implications. In plants with long-term belowground storage, allocation of biomass to inaccessible parts belowground in response to folivory is a well-recognized tolerance mechanism. In temperate regions, spring growth from buried rootstock is common among winter deciduous plants and is often followed by regrowth after defoliation, both of which draws resources from the stored reserves. We developed a mathematical model to analyze this tolerance response in a winter deciduous plant with long-term belowground biomass when it is defoliated by a specialist insect folivore. The model explores how three closely associated traits—(1) belowground biomass allocation to roots, (2) spring utilization of stored reserves, and (3) post-defoliation regrowth capacity—modulate the persistence and dynamics of the plant and herbivore populations. Model results show that allocation to belowground storage is not only a critical component of tolerance but also influences the herbivore population dynamics in ways that depend on how and when plant biomass is allocated and used. Low belowground biomass allocation and high storage utilization combined with poor photosynthetic growth caused extirpation of the plant population by the defoliating insects. Stable coexistence of the plant at low biomass along with its specialist insect required a moderate amount of post-herbivory belowground allocation. High values of belowground biomass allocation, storage utilization, and photosynthetic growth resulted in sustained cycles of the herbivore and plant populations. Interestingly, utilization of stored reserves had conflicting influence on above and belowground biomass, and strongly affected herbivore population dynamics. Our model thus highlights the complexity of tolerance response when it involves multiple traits and mechanisms as evinced by winter deciduous plants. We close by discussing the implications of our findings for the contributions of defoliating insects to biocontrol programs.

Concentration is not enough to evaluate accumulation of heavy metals and nutrients in plants

Wetland plants produce high aboveground biomass and possess the ability to accumulate heavy metals and nutrients. This ability is used for phytoremediation purposes including removal of nutrients and heavy metals from polluted waters. The concentrations of heavy metals are usually much higher in the belowground then in aboveground biomass, especially in roots which are primary sites of uptake. This may lead to the conclusion that accumulation of heavy metals is higher in the belowground biomass. However, in case the aboveground is much higher than belowground biomass the accumulation could be higher in the aboveground biomass. Concentration of nitrogen and phosphorus is always higher in leaves than in stems. However, the stem biomass is often much higher in robust emergent species such as Phragmites australis and therefore, more nutrients can be stored in stems. The examples shown in this communication clearly reveal that to evaluate properly the accumulation of heavy metals and nutrients in particular plant compartment biomass amount must be taken into consideration. In the first study, concentrations of Cd, Cr and Hg in Phalaris arundinacea belowground/aboveground biomass were 150/80μg/kg, 5420/228μg/kg and 38/18μg/kg. The high aboveground biomass (1196g/m2) and low belowground biomass (244g/2) resulted in much higher accumulation of Cd and Hg in aboveground biomass (96μg/m2 and 21.2μg/m2, respectively) than in belowground biomass (36μg/m2 and 9.3μg/m2, respectively). Only for chromium, belowground accumulation (1312μg/m2) was higher than aboveground accumulation (272μg/m2). In the second study, both nitrogen and phosphorus concentrations were higher (26.7mg/g and 749mg/kg, respectively) in leaves than in stems (8.2mg/g and 534mg/kg, respectively) of P. australis. The higher biomass of stems (1835g/m2) than leaves (967g/m2) resulted in higher accumulation of nitrogen but lower accumulation of phosphorus in leaves as compared to stems.

Native plant restoration combats environmental change: development of carbon and nitrogen sequestration capacity using small cordgrass in European salt marshes

Restoration of salt marshes is critical in the context of climate change and eutrophication of coastal waters because their vegetation and sediments may act as carbon and nitrogen sinks. Our primary objectives were to quantify carbon (C) and nitrogen (N) stocks and sequestration rates in restored marshes dominated by Spartina maritima to provide support for restoration and management strategies that may offset negative aspects of eutrophication and climate change in estuarine ecosystems. Sediment C content was between ca. 13mgCg(-1)and sediment N content was ca. 1.8mgNg(-1). The highest C content for S. maritima was recorded in leaves and stems (ca. 420mgCg(-1)) and the lowest in roots (361 ± 4mgCg(-1)). S. maritima also concentrated more N in its leaves (31 ± 1mgNg(-1)) than in other organs. C stock in the restored marshes was 29.6tCha(-1); ca. 16% was stored in S. maritima tissues. N stock was 3.6tNha(-1), with 8.3% stored in S. maritima. Our results showed that the S. maritima restored marshes, 2.5years after planting, were sequestering atmospheric C and, therefore, provide some mitigation for global warming. Stands are also capturing nitrogen and reducing eutrophication. The concentrations of C and N contents in sediments, and cordgrass relative cover of 62%, and low below-ground biomass (BGB) suggest restored marshes can sequester more C and N. S. maritima plantations in low marshes replace bare sediments and invasive populations of exotic Spartina densiflora and increase the C and N sequestration capacity of the marsh by increasing biomass production and accumulation.

Cutting affects growth of Potamogeton lucens L. and Potamogeton compressus L

Effects of cutting on the growth of Potamogeton lucens L. and Potamogeton compressus L. were studied indoor under experimental conditions. Plants were cut every time they reached the water surface, applying three depth treatments at which the plants were cut; halfway down the water column, at three-quarters down the water column and at the sediment–water interface. For both species short term negative effects of cutting on biomass production and survival were observed. P. lucens seemed to be the more tolerant species as only below-ground biomass was significantly lower when cutting biomass at the sediment–water interface together with a downward trend in shoot biomass at increasing cutting depth. The low below-ground biomass (less than 20% of that in the controls) was caused by the death of most plants in this treatment. P. compressus was more vulnerable with every treatment resulting in significantly lower below-ground and green shoot biomass production. The lowest biomass for P. compressus was observed when plants were cut at the sediment–water interface with values more than 80% lower compared to the controls, while cutting halfway and at three-quarters resulted in values 30–50% lower compared to the controls. Long term effects of cutting on P. lucens might occur through decreased development of the rhizome network. Long term effects on reproduction of P. compressus might be expected as flowering decreased when cut at the sediment–water interface, while turion formation only occurred in the uncut controls. Additionally, the decreased biomass production by P. compressus may lead to a competitive disadvantage in the field as fast-growing, disturbance tolerant species such as Elodea nuttallii (Planch.) St. John may outcompete the species. Creating patchiness in mowing height and frequency or applying a mowing regime that leads to reduced biomass development while species still survive might create opportunities to both maintain the water transporting function of drainage ditches while preserving the species in the system.

Heavy metals in Phalaris arundinacea growing in a constructed wetland treating municipal sewage

Constructed wetlands with horizontal subsurface horizontal flow are commonly used for treatment of municipal sewage and are well monitored for removal of organics, suspended solids, nutrients and bacteria. However, the information on removal of heavy metals and their sequestration in plants growing there is very limited. The present study deals with sequestration of six heavy metals in Phalaris arundinacea growing in a constructed wetland treating municipal sewage in the Czech Republic during the period 2004–2008. The aboveground biomass of Phalaris arundinacea is higher that the average Phalaris biomass in other Czech constructed wetlands and also as compared to natural stands. Contrary to natural stands, the root to shoot (R/S) ratio is lower than 1.0 and varied between 0.34 and 0.68 with a mean value of 0.49. For all studied heavy metals the concentrations are the highest in the roots while in other parts, i.e. leaves, stems, rhizomes and flowers, the concentrations usually do not differ significantly. Because of low belowground biomass, the standings stocks are higher aboveground for Zn, Cd, Pb and Cu with copper standing stock being significantly higher than belowground. On the other hand, for Cr and Ni the belowground standing stocks were significantly higher than aboveground because of very high Cr and Ni concentrations in the roots. In most cases the concentrations found in our study are within the order of magnitude as compared to results from other constructed wetlands and natural stands. Heavy metal aboveground standing stocks represented between 1.6% (Cr) and 15.1% (Cd) of the annual metals inflow with an average value of 6.5%. The amount of heavy metals sequestered in the aboveground biomass accounted for between 3.7% (Zn) and 38.4% (Cd) of the heavy metal removal in the filtration beds with an average value of 13.2%.

Responses of eelgrass Zostera marina seedlings to reduced light

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 223:133-141 (2001) - doi:10.3354/meps223133 Responses of eelgrass Zostera marina seedlings to reduced light Joanne C. Bintz1,*, Scott W. Nixon2 1Ocean Studies Board, National Academy of Sciences, 2101 Consitution Av. NW, HA 470, Washington, DC 2041, USA 2Graduate School of Oceanography, University of Rhode Island, PO Box 200, South Ferry Road, Narragansett, Rhode Island 02882, USA *E-mail: jbintz@nas.edu ABSTRACT: We subjected seedlings of Zostera marina L. to High (72%), Medium (23%), and Low (10%) daily irradiance (mean daily PAR of 24.4, 7.9, and 3.3 E m-2 d-1 respectively) over 12 wk. We measured plant response in terms of survivorship, lateral shoot production, morphology, growth rate, photosynthesis and respiration, and leaf pigment concentration. Decreasing the light available to eelgrass seedlings from 72 to 23% resulted in a reduction of lateral shoot formation, lower plant biomass, and longer and wider leaves. Shoot area, growth rate, and pigment concentrations remained similar. A reduction of incident light to 10% decreased survival to 74% and had a negative effect on shoot growth, size, and above- and belowground biomass. Pigment concentrations increased with respect to seedlings raised at medium light. In general, the responses of seedlings to reduced light are similar to those reported for mature Z. marina. Rapid expansion of seedling patches can only occur at irradiance levels greater than 7.9 E m-2 d-1. Morphological changes resulting from exposure to mean daily PAR levels of less than 8 E m-2 d-1 such as thinner leaves and low belowground biomass, have serious implications for decreased seedling survival in the field. KEY WORDS: Eelgrass · Seagrass seedlings · Light · Zostera marina · Shade adaptation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 223. Online publication date: November 28, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Modification of sediments and macrofauna by an invasive marsh plant

Invasive grasses have recently altered salt marsh ecosystems throughout the northern hemisphere. On the eastern seaboard of the USA, Phragmites australis has invaded both brackish and salt marsh habitats. Phragmites australis influence on sediments and fauna was investigated along a salinity and invasion-age gradient in marshes of the lower Connecticut River estuary. Typical salinities were about 19–24 ppt in Site I, 9–10 ppt in Site II and 5–7 ppt in Site III. Strongest effects were evident in the least saline settings (II and III) where Phragmites has been present the longest and exists in monoculture. Limited influence was evident in the most saline region (I) where Phragmites and native salt marsh plants co-occur. The vegetation within Phragmites stands in tidal regions of the Connecticut River generally exhibits taller, but less dense shoots, higher above-ground biomass, and lower below-ground biomass than does the un-invaded marsh flora. There were lower sediment organic content, greater litter accumulation and higher sediment chlorophyll a concentrations in Phragmites- invaded than un-invaded marsh habitat. Epifaunal gastropods (Succinea wilsoni and Stagnicola catascopium) were less abundant in habitats where Phragmites had invaded than in un-invaded marsh habitat. Macro-infaunal densities were lower in the Phragmites-invaded than un-invaded habitats at the two least saline sites (II and III). Phragmites stands supported more podurid insects, sabellid polychaetes, and peracarid crustaceans, fewer arachnids, midges, tubificid and enchytraeid oligochaetes, and greater habitat-wide taxon richness as measured by rarefaction, than did the uninvaded stands. The magnitude and significance of the compositional differences varied with season and with site; differences were generally greatest at the oldest, least saline sites (II and III) and during May, when faunal densities were higher than in September. However, experimental design and the 1-year study period precluded clear separation of salinity, age, and seasonal effects. Although structural effects of Phragmites on salt marsh faunas are evident, further investigation is required to determine the consequences of these effects for ecosystem function.

Population Structure of Three Dominant Sedges under Muskox Herbivory in the High Arctic

We investigated population structure of Carex aquatilis ssp. stans, Carex membranacea, and Eriophorum angustifolium ssp. triste in ungrazed and grazed (by muskoxen) high arctic sedge meadow vegetation. Age structure, density, biomass, growth, and reproduction of tillers were compared between sites in 1995 and 1996. Tillers were considerably older in ungrazed vegetation relative to grazed vegetation. The density and biomass of C. stans were significantly greater in grazed vegetation than in ungrazed vegetation, whereas the density of C. membranacea and E. triste was the same but the biomass was lower relative to the ungrazed meadows. The grazed plants of all species reproduced earlier, but no seedlings were found in grazed vegetation, in contrast to ungrazed vegetation. Carex stans appears to gain competitive advantage over the other two species in grazed vegetation. This may be due to the larger belowground biomass, the high phenotypic plasticity in rhizome lengths and more persistent rhizome connections. E. triste may be the least buffered against grazing due to its lower belowground biomass and the early disintegration of rhizomes. On the other hand, E. triste allocates more to sexual reproduction than the two other species.

Biomass of Grazed, Burned, and Undisturbed Paramo Grasslands, Colombia. II. Root Mass and Aboveground:Belowground Ratio

In a Neotropical alpine grassland (pairamo) in the Colombian Central Cordillera, the root mass, root distribution, and aboveground: belowground (A:B) ratio were determined at four sites with different grazing and burning management. Compared to grasslands at other latitudes, pairamos have a relatively low belowground biomass and, due to the combination with a high aboveground biomass, a high A:B ratio. This is attributed to a low productivity and a lack of seasonality. Effects of grazing disturbance on the root system could be observed at a site without burning history, where the tussock grass vegetation was transformed into ground covering mats. Here, belowground biomass increased from 1.2 to 2.1 kg m-2, which was more concentrated in the upper 10 cm of the soil. An undisturbed and two other grazed sites did not show differences in root mass or distribution, in response to disturbance. Nevertheless, A:B ratios decreased clearly towards more managed sites, as a result of decreased aboveground biomass.

Field Water Relations of Sonoran Desert Annuals

Field water relations were examined in winter and summer annuals of the Sonoran Desert. Both groups were characterized by low belowground biomass allocation. Winter annuals had large interspecific variation in water relations parameters, but their leaves generally had high conductances of water vapor and high water potentials during early growth periods. These high values were very short—lived and were reduced by peak flowering periods. Summer annuals were measured midway through the growing season; their leaves showed less interspecific variability in water vapor conductances and had values similar to the winter annuals for this stage of the growing season. Midday and diurnal courses of photosynthesis in the winter annuals exhibited lower rates than values previously reported for plants grown under unlimited water and nutrient regimes in glasshouses. This was probably due to the decreased leaf water potentials and increased vapor pressure deficits present in field situation. Both the winter and the summer annuals showed a dichotomy among species in leaf water potentials, associated with either variations in soil water availability or the ability of leaves to adjust osmotically to decreased soil water availability. Although winter and summer annuals are ephemeral, some species are capable of tolerating low leaf water potentials and therefore are not drought evading in the traditional sense.