Water Level Treatments Research Articles

Rewet without regret? Nutrient dynamics in fen peat exposed to different rewetting degrees

All over the world, peatlands have been drained, often for agricultural purposes, resulting in CO2 emissions, soil subsidence and biodiversity loss. To combat these negative effects, drained peatlands are being rewetted, but knowledge of the effects of rewetting on peat biogeochemistry is still incomplete, especially since a variety of rewetting methods and rewetting degrees exists. We conducted a mesocosm experiment in which we exposed 100 intact agricultural fen peat cores (80 cm, 20 cm Ø) to five different water levels (0, 20, 40, 60 cm and variable—surface), two nutrient application levels to mimic continued agricultural use, and two water origins. Over an eight-month period, we harvested above-ground plant biomass five times and sampled pore water at two depths each month. Samples were analysed for nutrients. Our results show increased phosphate and ammonium availability upon fully rewetting (0 cm—surface) and less so under partially rewetted circumstances (20 cm—surface). Above-ground biomass was strongly affected by nutrient application, especially in the high water level treatments. Vegetation was primarily N-limited, and N in the vegetation decreased with increasing water levels, indicating stronger nitrogen limitation upon rewetting. We conclude that nature restoration under fully rewetted conditions will likely be challenging as a result of the large release of nutrients from the system which may also affect surrounding nature areas. Furthermore, we conclude that partial rewetting combined with low-intensity agricultural use can be a solution to slow down the adverse effects of drainage, although this will lead to decreased agricultural production.

Comparative flooding tolerance of Typha latifolia and Phalaris arundinacea in wetland restoration: Insights from photosynthetic CO2 response curves, photobiology and biomass allocation

Tall helophytes such as Typha latifolia and Phalaris arundinacea often rapidly colonise after rewetting of former agricultural soil and are therefore often the first plants to contribute to the soil carbon pool. In this study we carried out a mesocosm experiment where these two species grew at three different water levels relative to the soil surface (−15 cm, 0 cm, +15 cm). After eight weeks' growth, measurements of photosynthetic CO2-response curves, stomatal conductance and chlorophyll fluorescence of photosystem II were carried out to detect flooding stress. After 10 weeks’ growth, the plants were harvested and biomass production, biomass allocation and specific leaf area were determined. T. latifolia had a higher and more stable photosynthetic performance across all water level treatments, which resulted in an overall higher aboveground and belowground production than P. arundinacea. In contrast, Vcmax and Jmax decreased by 41 % and 42 %, respectively from drained to flooded conditions with signs of flooding stress as impairment of the photosynthetic apparatus. Moreover, increasing water level resulted in maintenance of aboveground organs for P. arundinacea but a decrease in allocation to belowground organs. P. arundinacea did not invest in a higher specific leaf area to counter the decreased photosynthesis under flooding. From −15 cm to 0 cm water levels, P. arundinacea showed a 68 % reduction in belowground biomass, which has negative implication for carbon retention immediately after rewetting. In contrast, recolonization of T. latifolia is likely to be a suitable contributor to the soil carbon pool due to its stable physiology and high above- and belowground biomass production at all water depths, and also likely under natural water level fluctuations. We showed that even though both species are generally considered wetland plants, they are likely to support considerably different photosynthetic carbon assimilation and soil carbon sequestration rates.

Carbon limitation and aluminium toxicity prevents dominance of Crassula helmsii on weakly buffered soils

Invasions of the aquatic weed Crassula helmsii pose a serious threat to native vegetation of soft water lakes, which increases the need for understanding the factors that regulate the success or failure of C. helmsii. Creating favorable conditions for native species seems promising to control C. helmsii, as previous research indicated that C. helmsii is a poor (root) competitor. We studied the development of C. helmsii growing together with the native Littorella uniflora (biomass, cover, tissue nutrient composition) at two different calcareous poor soil types (organic/acid, mineral/buffered) and under two different water tables (not inundated, submerged) in a greenhouse experiment. We found that when growing under submerged conditions, C. helmsii coexisted with L. uniflora and other native species without becoming dominant due to carbon limitation in the water layer. In contrast, we found that C. helmsii can easily become dominant over L. uniflora when growing on desiccated buffered fen soils with moderate nutrient availability. On the acidic/organic soils, C. helmsii development was poor and die-off was observed under both water level treatments, probably induced due to aluminum toxicity under a low acidity. These results indicate that creating oligotrophic and carbon-poor conditions are required for controlling C. helmsii. Restoration measures can preferably be taken before the onset of the rainy season and/or be followed by maintenance of a temporal artificial high water table to stimulate carbon limitation. Liming more or less organic shores could alleviate aluminum toxicity under acidic conditions which can potentially stimulate the development of C. helmsii.

Increase in iron-bound organic carbon content under simulated sea-level rise: A “marsh organ” field experiment

Rising sea levels have increased the risk of intense flooding in tidal wetlands, potentially leading to rises in soil iron-bound organic carbon (Fe-OC) contents by inhibiting microbial activity. However, flooding-induced Fe-OC accumulation may be attenuated by root activities of tidal wetland plants, which remains under-investigated in tidal wetlands. Here we established manipulative “marsh organ” filed experiments with soils collected from an oligohaline tidal wetland and introduced the indigenous plant species Phragmites australis (Cav.) Trin. ex Steud. These “marsh organ” mesocosms were then subjected to three flooding water-level treatments over a period of 3.5 years. Overall, root biomass, root porosity, and rhizosphere ferric iron-to-ferrous iron [Fe(III):Fe(II)] ratio increased with flooding levels, indicating that enhanced flooding promotes root oxygen loss of tidal wetland plants. The abundances of Fe-oxidizing bacteria (Gallionella) and Fe-reducing bacteria (Geobacter) increased, whereas the abundance of sulfate-reducing bacteria (dsrA gene) decreased with increased flooding, indicating a diversion of Fe from Fe-sulfur associations towards microbially-mediated Fe redox cycling. The soil organic carbon (SOC) pool did not change with increased flooding; however, the Fe-OC-to-SOC ratio (fFe-OC) increased from 9 to 18%. The fFe-OC was strongly related to soil amorphous Fe(III) concentrations and the activities of soil C-acquiring enzymes, both of which were affected by rhizosphere Fe(III):Fe(II) ratios. Thus, increased root oxygen loss, along with enhanced flooding, facilitated increases in amorphous Fe(III) concentrations and C-acquiring enzyme activity. Increased soil amorphous Fe(III) concentrations further promoted Fe-OC accumulation, whereas increased soil C-acquiring enzyme activities reduced the labile organic C pool. Overall, the dominance of the Fe-OC pool increased under enhanced flooding, owing to increased oxygen loss from the roots. Therefore, we outlined that soil C stability will increase in tidal wetland ecosystems that are exposed to future sea-level rise.

Evaluation of water depth and inundation duration on Typha domingensis sustainability in the Everglades Stormwater treatment areas: A test cell study

Typha domingensis is a dominant plant species in the Everglades Stormwater Treatment Areas, freshwater wetlands constructed to reduce phosphorus (P) levels in stormwater runoff prior to discharge into the Everglades. Water depth and duration of inundation can negatively affect the health of these plants. To determine the effect of water depth and inundation duration, Typha plants were grown in this study in a series of 15 test cells, 0.2 ha in area, and exposed to five water-depth treatments over 10 months: control (40 cm), shallow (61 cm), moderate (84 cm), deep (104 cm) and extremely deep (124 cm). Mean adult Typha densities declined from 14.1 shoots m−2 in the control to 10.9 and 10.5 shoots m−2 in the deep and extremely-deep treatments, respectively. However, only mean juvenile Typha densities were significantly different among water-level treatments, declining from 3.2 juveniles m−2 in the control to 1.2 and 0.6 juveniles m−2 in the deep and extremely-deep treatments, respectively. Typha leaf elongation rate (LER) was significantly higher in the deeper treatments, with the highest rates measured during the active growing season (July to October). LER increased from 6.84 cm day−1 during June baseline measurements to 8.89 cm day−1 in the deeper treatments after eight weeks of continuous inundation. Typha showed morphological plasticity to adapt to deep water through changes in morphology and biomass allocation. Typha grew significantly taller and heavier to adapt to deep-water conditions and facilitate gas exchange between the above and belowground tissues. Ramet height of Typha harvested at the end of the study averaged 343 and 374 cm in the deep and extremely-deep treatments, respectively, compared to 285 cm in the control. Likewise, the weight of individual adult ramets was significantly greater in the deeper treatments (256 g ramet−1) compared to the control (123 g ramet−1). Although none of the water-level treatments resulted in a total collapse of their Typha populations, increased LER in the deeper treatments resulted in less structural support in stems, causing substantial Typha lodging when water levels were lowered at the end of the study. These findings provide valuable insight into the effect of different water-level inundations on plant responses and overall health of Typha populations in the STAs.

Inability of yellow‐bellied toad to accelerate metamorphosis in desiccation conditions

AbstractMany amphibian species inhabit temporary aquatic habitats for reproduction to maximize larval growth under favorable conditions, but accelerate developmental rate to rapidly undergo metamorphosis under stress conditions when high desiccation risk exists. Desiccation affects different aspects of amphibian biology such as developmental rate, body size and mass, and growth rate. We studied the responses of yellow‐bellied toad (Bombina variegata) to different water levels (constant high, decreasing water level, and constant low water level) in the laboratory using individuals collected from natural ponds. To assess the effects of experimental pond drying, we investigated the effects on life‐history and morphological traits at metamorphosis as well as carry‐over effects on post‐metamorphic traits and locomotor performances. We found that B. variegata cannot accelerate developmental rate in response to pond drying. The metamorphs from decreasing and constant low water levels had similar size, mass, growth rate and body condition indices at metamorphosis, and all these traits were lower than in the constant high water level treatment. These changes in life‐history traits at metamorphosis did not affect tail shape although they had carry‐over effects on life‐history and morphological traits after metamorphosis. Post‐metamorphic individuals reared in desiccation treatments had similar but smaller lengths of femur and tibiofibula, but these changes did not have negative consequences on jumping performances. We show that responsiveness to pond drying of B. variegata is probably associated with maximum growth rate in favorable conditions and inability to increase growth rate as well as developmental rate in desiccation conditions. This resulted in prolonged developmental time to reach the minimum size and mass for metamorphosis.

Dual inoculation with rhizobia and arbuscular mycorrhizal fungus improves water stress tolerance and productivity in soybean

A glasshouse experiment was conducted to understand the influence of rhizobia, Bradyrhizobium liaoningense and an arbuscular mycorrhizal fungus, Ambispora leptoticha on growth and yield performance of soybean cultivars, MAUS 2 and MAUS 212 (drought susceptible) and DSR 12 (drought tolerant) under different levels of moisture stress conditions. Three different water levels [100%, 75% and 50% FC] with three microbial inocula (B. liaoningense, A. leptoticha and B. liaoningense + A. leptoticha) served as main treatments and the water level treatments were imposed 31–45 days after sowing. Various growth, physiological and microbial parameters were recorded besides analysing the samples for nutrients. The results showed that the plant growth parameters like biovolume index, total dry biomass, root volume and seed yield were significantly higher in dual inoculated plants in all the cultivars at all the moisture levels. There was an increase in mean seed weight by 88% and dry biomass by 58% in dual inoculated plants compared to uninoculated plants. Further physiological parameters and nutrients level improved significantly with dual inoculation under stress condition. However significant difference in recorded parameters was not observed in plants grown at 100% and 75% FC suggesting dual inoculation of B. liaoningense + A. leptoticha is beneficial when stress is severe in all the 3 cultivars. The microbial and nutrient parameters followed the same trend. Further of the two drought susceptible cultivars, MAUS 2 performed better compared to MAUS 212 in all the studied parameters under stress with dual inoculation. The results therefore signify the importance of rhizobia and mycorrhizal inoculation for imparting stress tolerance in soybean.

Determining Carbon Dioxide Emission Response in Soil Microcosms from a Shallow Mid-Atlantic Peatland: The Influence of Water Table Restoration

Johnson, A.M.; Atkinson, R.B.; Steven, J.C.; Whiting, G.; Napora, K.; Sharrett, L., and Mirda, C., 2022. Determining carbon dioxide emission response in soil microcosms from a shallow mid-Atlantic peatland: The influence of water table restoration. Journal of Coastal Research, 38(2), 261–268. Coconut Creek (Florida), ISSN 0749-0208. Determining carbon dioxide emission response in shallow microcosms from a shallow mid-Atlantic peatland: The influence of water table restoration. Peatlands provide ecosystem services such as pollution filtration, flood control, and carbon storage as these ecosystems contain 33% to 50% of the global soil carbon pool. Reestablishing soil saturation in degraded peatlands can limit microbial oxidation of organic matter; however, drainage history may alter soil saturation patterns and challenge restoration efforts. The purpose of this study was to investigate carbon emission response to water table restoration for two shallow peatlands including a Histosol and an Ultisol with divergent drainage histories. Soil cores were gathered from the top 22.5 cm of organic-rich surface horizons within Cavalier Wildlife Management Area in Chesapeake, Virginia. Cores were randomly assigned to four water level treatments that simulated restoration conditions, and carbon dioxide emissions were measured using an LI-6400XT portable open-flow photosynthesis system twice a week for 4 weeks. Despite higher organic matter content in the long-drained site, emissions (2.1 to 3.9 µmol CO2 m–2 s–1) were higher than at the historically less drained site (1.5 to 2.3 µmol CO2 m–2 s–1). Volumetric water content trends revealed that longer-drained soils retained lower water content within restoration treatments and were associated with higher carbon emissions. Restoration of long-drained peats in the mid-Atlantic region may require higher water tables than otherwise predicted to overcome a resistance to rewetting where limiting microbial soil respiration is a management objective.

Using dredged sediments to support wetland plant development in a constructed delta lake

Restoration efforts take place at large scales to improve the ecological value of degraded, modified river deltas. To anticipate on the implications of using dredged, estuarine sediment to restore wetlands in river deltas, we studied the development of Typha latifolia (cattail) and Phragmites australis (common reed) on two designated dredged sediments, virgin Holocene clay (clay) and eroded clay (mud), under different water levels (inundated, saturated, and moist) in a mesocosm experiment. The mud sediment contained about two times higher Fe, S, and P content and four times higher N-total content compared to clay sediment. The organic content was comparable for both sediments. Sediment type influenced germination and shoot growth of T. latifolia, which were both higher on clay compared to mud, but did not influence germination and initial growth of P. australis. Water level treatment effects on plant response were limited to inundation conditions only; this condition strongly reduced P. australis seedling and shoot development. Both species developed significantly more above- and belowground biomass when growing in mud compared to clay, however, their nutrient content was comparable on both sediment types. Overall, T. latifolia development was more strongly influenced by sediment composition compared to P. australis, but the latter species is more vulnerable to higher water levels during early stages of development. We conclude that both dredged sediment types are suitable as sediment for developing macrophyte vegetation.

Air Warming and Drainage Influences Soil Microarthropod Communities

The degradation of wetlands due to climate change is of critical concern to human beings worldwide. Little is known about the potential synergistic effects of simultaneous water level reduction and warming on the underground wetland ecosystems. We conducted a 5-month field experiment in the Sanjiang Plain, utilizing open-top chambers and water level automatic control systems to investigate such synergistic effects. Soil springtails (Collembola) and mites (Acari) in the top (0–20 cm) soil layers were sampled to calculate their density, diversity, and to screen for indicator species. Warming significantly influenced soil springtail communities, slightly increasing the total density and total abundance under the natural water level while reducing them under a constant water level. In addition, Anurida maritima and Vertagopus laricis, two indicators for the natural water level, had the highest densities in the natural water level treatment and under the combined treatment of warming and natural water level, respectively. Cheiroseius sinicus and Malaconothrus tardus had the highest densities in warming under the 0 cm water level, significantly higher than the other three treatments. This study also revealed the importance of maintaining fluctuating water levels for microarthropod communities influenced by global warming, providing a theoretical basis for water level control in wetland restoration.

Clonal performance of Scirpus yagara in multiple levels of substrate heterogeneity and submergence

Abstract Aims Environmental heterogeneity affects the performance of clonal aquatic plants. Few researchers integrated two aspects of heterogeneity into the study of clonal plant ecology. The aims of the present study are to (i) test whether different substrate heterogeneity and submergence exert similar effects on plant performance and (ii) explore the foraging behaviour. Methods In this study, Scirpus yagara was subjected to multiple levels of substrate heterogeneity and submergence. Substrate treatments included one homogeneous substrate and three heterogeneous substrates (two-patch, four-patch and eight-patch). Water level treatments included 0, 10 and 30 cm. Traits including ramet number, generation number, leaf number, bulb number, ramet height, culm length, rhizome length, clonal radius, spacer length, spacer thickness, total biomass, biomass of bulbs and biomass per bulb were measured. Important Findings Deeper water levels significantly reduced variables associated with growth such as ramet number, generation number, leaf number and bulb number, while substrate patchiness induced significant variations in traits such as spacer length and spacer thickness. Significant interactive effects of the two factors were found for ramet number, leaf number and spacer length. Scirpus yagara showed colonization towards the lake sediment patch in two-patch and four-patch substrates, and more structures were placed in the lake sediment patch. Especially for the two-patch substrate, all structures occupied the lake sediment patch. Two-sided intrusion was observed in the eight-patch substrate, which induced an even allocation of structures in different patches. The foraging behaviour was correlated with the patch size.

Soil type and water level treatments influence peatland CO2 efflux in simulated restoration

Peatlands are characterized by accumulation of organic matter primarily in response to soil anoxia and soil saturation. In the Cavalier Wildlife Management Area (CWMA) of southeastern Virginia, weirs were installed within ditches in an effort to restore peatlands. The purpose of this research was to determine the water levels that restore soil respiration functions and encourage carbon dioxide (CO2) sequestration. Core microcosms of two soil types (histosol and ultisol) were collected and established in the laboratory with differing water level treatments with simulated depth to water table. Incubations continued for 1 month and CO2 emission rates of the soil cores were measured twice per week using a portable photosynthesis instrument. Results from a mixed linear model and Tukey post-hoc tests demonstrated water level treatments were inversely correlated to CO2 emissions regardless of soil type and that the ultisol soil type exhibited lower percent volumetric water content and higher CO2 emissions overall. This suggests that higher water tables suppress CO2 emissions and can increase carbon sequestration, and that natural resource managers should evaluate soil types when establishing restoration and carbon sequestration goals, as soil types have differing responses to hydrologic restoration.

Impact of Water Level on Species Quantity and Composition Grown from the Soil Seed Bank of the Inland Salt Marsh: An Ex-Situ Experiment

The near elimination of inland salt marshes in Central Europe occurred throughout the 19th and 20th centuries, and the currently remaining marshes exist in a degraded condition. This work examines the impact of groundwater level on the growth of plants from a seed bank obtained from a degraded salt marsh in proximity to still existing one through an ex-situ experiment. An experimental tank was set up with the sample seed bank experiencing differing levels of water level. There were 1233 specimens of 44 taxa grown from the seed bank, of which 5 species were abundant, and 10 species are considered as halophytes. Only Lotus tenuis from halophytes was more abundant, and only five species of halophytes were represented by more than three individuals. The water level has a significant impact on the number of species (based on linear regression analysis) as well as species distribution among different water level treatments (a non-metric multidimensional analysis (nMDS) followed by linear regression). The results show a strong negative relationship between the average water level and the number of species. The water level did not affect the species composition of halophytes, but differences in individual species abundances were found among the halophytes. The species Bupleurum tenuissimum, Crypsis schoenoides, Melilotus dentatus, and Plantago maritima grew on the drier and non-inundated soils. Tripolium pannonicum, Spergularia maritima, and Lotus tenuis grew on both wet and dry soils. Trifolium fragiferum and Bolboschoenus maritimus were found in places with water stagnant at the soil level. Pulicaria dysenterica grew in inundated soil.

Impact of different Irrigation Levels and Foliar Spraying with some Potassium Forms on Growth and Productivity of Garlic (Allium sativum L.) تأثیر مستویات الری المختلفة والرش الورقی ببعض صور البوتاسیوم على نمو وإنتاجیة الثوم

A strip-plot experiment was carried out during the two winter seasons of 2018/2019 and 2019/2020 at a private farm located in Demiana village, Belqas District, Dakahlia Governorate, Egypt. This study aimed to investigate the impact irrigation water levels and some potassium forms on garlic (cv. Balady) vegetative growth, water relations and leaves pigments, bulbs physical and chemical quality as well as yield and its components. Irrigation water level treatments were 50%, 75% and 100% full irrigation and different potassium forms (without, potassium citrate, potassium nitrate and potassium thiosulfate) at concentration of 1000 ppm as foliar spray. Results showed that all studied traits of garlic were significantly decreased with water irrigation deficit except electorate leakage, leaves and cloves dry matter, net ratio percentage, water use efficiency for fresh and cured yield and loss weight percent were improved. The highest values of all characters were achieved by potassium thiosulfate. However, the best values for leaves and cloves dry matter and loss weight percentage exhibited by potassium citrate. In addition, the most promising results were obtained from garlic plants treated with potassium thiosulfate interacted with full irrigation treatment which followed by the interaction treatment of full irrigation level with potassium citrate. It can be recommend treating garlic plants with potassium thiosulfate (1000 ppm) to improve yield and water use efficiency. As well as, potassium citrate (1000 ppm) to increase cloves dry matter and eliminate weight loss of cured yield of garlic bulbs under different irrigation levels.

The Change Characteristics and Interactions of Soil Moisture and Temperature in the Farmland in Wuchuan County, Inner Mongolia, China

Soil moisture and temperature are both significant factors for crop growth and development. They are also the main influencing factors of regional climate change. In the context of climate change, the relationship between soil moisture and soil temperature is not only important for explaining the mechanism of moisture and temperature interaction, but also provides scientific suggestions for agricultural production. Since the accurate measurement of soil moisture and temperature is difficult, their relationship remains poorly understood. Here, based on real-time field observation in a potato field in Wuchuan County, Inner Mongolia, China, the change characteristics of soil moisture and temperature under different water level treatments were analyzed, and their relationships were disclosed. The results show that there was an inverse proportional relationship between soil moisture and temperature. With an increase of soil moisture, soil temperature decreased. The basic relation between soil moisture and temperature took the form of reciprocal functions (Q = 4.2 × 103 V × (0.2 + W) × ΔT). The decline of soil moisture in the farmland will increase the soil temperature and has a negative impact on land–atmosphere interactions. The results can provide important insight into regional climate change mechanisms.

Temperature and water-level effects on greenhouse gas fluxes from black ash (Fraxinus nigra) wetland soils in the Upper Great Lakes region, USA

Forested black ash (Fraxinus nigra) wetlands are an important economic, cultural, and ecological resource in the northern Great Lake States, USA, and are threatened by the invasive insect, emerald ash borer (Agrilus planipennis Fairmmaire [EAB]). These wetlands are likely to experience higher water tables and warmer temperatures if they are impacted by large-scale ash mortality and other global change factors. Therefore, it is critical to understand how temperature, hydrology, and their interaction affect greenhouse gas fluxes in black ash wetland soils. In order to predict potential ecosystem changes, we sampled and incubated intact soil cores containing either mineral or organic (peat) soils from two black ash wetlands, monitored soil oxidation-reduction potential (Eh), and measured the efflux of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) at two water-level treatments nested in three temperature treatments, 10 °C, 15 °C, or 20 °C. The water-level treatments were either saturated or drawdown, designed to mimic wetlands impacted or not impacted by EAB. Mean CO2 fluxes increased with increasing temperature but did not vary significantly by soil type or water-level. Peat soil had 60 to 135 times significantly greater CH4 flux in the saturated treatment and had minimal N2O loss across all treatments, while mineral soils had 8 to 43 times significantly greater N2O flux in the saturated treatment, and minimal CH4 loss across all treatments. Gas fluxes generally increased and had greater variation with increasing temperature. The drawdown treatment resulted in significantly higher Eh during unsaturated periods in both soil types, but the response was more variable in the peat soil. Our findings demonstrate potential indirect effects of EAB in black ash wetlands, with implications for ecosystem functions associated with C and N cycling.

Propagule types and environmental stresses matter in saltmarsh plant restoration

Restoration of degraded saltmarshes has attracted global attention, which makes disentangling the factors that determine target species success critically important. The pioneer plant Scirpus mariqueter in the Yangtze River estuary saltmarshes is rapidly declining due to plant invasion. It needs to be protected and restored, but the effects of environmental factors and propagule types on its restoration success are unclear. We examined the environmental niche of three propagule types (seedlings, corm shoots and plantlets) of Scirpus mariqueter under water level, salinity and nitrogen treatments in a greenhouse experiment. We found that water level was the most critical environmental factor limiting plant performance, followed by salinity. Nitrogen addition inhibited propagule growth in intermediate water level and salinity treatments. There were significant three-way interactions between water level, salinity, and nitrogen addition: Scirpus mariqueter performed best in treatments of low salinity + low to intermediate water levels + high nitrogen. Corm shoots outperformed plantlets and seedlings. Our results suggest that planting corm shoots under intermediate salinity and high water level conditions will enhance the restoration success of Scirpus mariqueter in the saltmarshes of the Yangtze River Estuary.

Growth responses of eight wetland species to water level fluctuation with different ranges and frequencies.

Fluctuation range and frequency are two important components of water level fluctuation, but their effects on wetland plants have not been evaluated separately. We subjected eight wetland species to a control treatment with static water level and fluctuation treatments with different ranges or frequencies to examine their effects on plant growth. Acorus calamus, Butomus umbellatus and Iris wilsonii showed high survival rates in all treatments with various fluctuation ranges and frequencies. Their survival rates were higher at the medium fluctuation frequency than at the low and high frequencies, suggesting beneficial effects of the medium frequency. In the experiment comparing the fluctuation ranges, A. calamus and I. wilsonii could maintain the capacity for asexual propagation and accumulate higher biomass compared with the control plants, while biomass of the other six species dramatically decreased. In the experiment comparing fluctuation frequency, species with relatively high survival rates (≥ 50%) maintained or increased the capacity of asexual propagation, and A. calamus and I. wilsonii allocated relatively more biomass to roots, which may enhance plant growth and survival. In contrast, these species did not show increased biomass allocation to shoots in response to both fluctuation range and frequency, presumably because shoots are prone to mechanical damage caused by streaming floodwater. Taken together, biomass accumulation in roots rather than in shoots and the ability to asexually propagate are important for the survival of these species during water fluctuation.

Responses of two macrophytes of the genus Polygonum to water level fluctuations and interspecific competition

We assessed the zonation of two emergent macrophytes, Polygonum ferrugineum and Polygonum acuminatum, and experimentally tested the effects of water level fluctuations and competition on the growth of these two species. We modelled the abundance of both species as a function of depth using a Bayesian approach based on a 16-year dataset from a subtropical floodplain. Then, we designed a factorial experiment in which species were planted in monocultures and mixtures and subjected to three water level treatments (low, high and variable) for 30 days. All response variables and relative yields were analysed with a two-way ANOVA. The modelled data showed that the two species colonize different depths, with P. acuminatum colonizing shallower areas than P. ferrugineum. Biomass accumulation did not differ between species in monocultures, but P. acuminatum showed significantly higher shoot and internode lengths when it grew submerged, indicating different survival strategies between the two species. P. acuminatum resisted inundation through an escape strategy, elongating above the water surface, while P. ferrugineum did not show this strategy. In mixtures, P. acuminatum showed a significantly higher competitive ability than P. ferrugineum, indicating that the former species has advantages over the latter during the colonization phase. These results are consistent with our observational results because they show that P. acuminatum can dominate in shallower areas by having morphological adaptations to intermittent fluctuations in water level and a competitive advantage over P. ferrugineum.

Environmental resource deficit may drive the evolution of intraspecific trait variation in invasive plant populations

Intraspecific trait variation within natural populations (i.e. intra‐population trait variation, IPTV) is the basic source for selection and can have significant ecological consequences. Higher IPTV may increase a population's niche breath and benefit interspecies competition under a resource‐limited environment, thus affecting the ability of a species to move into novel habitats. However, the reciprocal influences of variation in environmental conditions and phenotypic trait expression in spreading plant populations are not clearly defined. We propose that during invasion, IPTV and its relative change in response to key resource enrichment may increase with the resource deficit of invaded sites, and that this relationship may facilitate plant invasions into resource‐limited environments. We analyzed the invasion trend, IPTV and its response to water enrichment, and moisture variability among populations of an annual grass Brachypodium hybridum in California, United States. We incorporated a genotyping‐by‐sequencing approach, a common garden experiment that had two water level treatments, and public plant and climate databases. Our hypothesis was supported by the observation that for populations that invaded sites with higher spring moisture deficit, both their seed biomass IPTV (for the water‐enriched treatment only) and relative change of the IPTV across water treatments were larger when examined in the common garden experiment. A generally north to south spreading direction was found in these B. hybridum populations, towards a drier and warmer climate exhibiting higher moisture deficit for plant growth. Our results suggest a role for interactions between IPTV (rather than trait means) and environmental resource availability in promoting plant invasions, providing new insights into the significance of IPTV in shaping plant geographic distributions.