Riparian Plant Research Articles

Phenotypic plasticity and genetic diversity elucidate rarity and vulnerability of an endangered riparian plant

AbstractEnvironmental change, accelerated by anthropogenic activities, threatens many species and can be especially challenging for rare species given their potentially limited capacity for migration and adaptation relative to more common species. The ability to acclimate via phenotypic plasticity could provide an important path to species persistence in the face of such change. We investigated the responses of an endangered plant species endemic to a highly dynamic riparian habitat in southeastern Tennessee, USA, and its most widespread congener to environmental change to elucidate their current statuses and future vulnerability. Specifically, we compared the population‐ and species‐level plasticity of rarePityopsis ruthiiand commonP. graminifoliato contrasting light, temperature, and water conditions in a growth chamber experiment to evaluate their potential to acclimate to environmental change. Contrary to our expectations,P. ruthiihad greater phenotypic plasticity than its common congener in response to both altered light and water availability. But this plasticity was not associated with increased fitness, suggesting that it was not adaptive. Concurrently, we genotyped these individuals at nine putatively neutral microsatellite loci to contrast genetic diversity across the range of each species. As expected,P. ruthiiexhibited reduced genetic diversity relative to its more common congener. Overall, our findings accord with the narrow range and current habitat specificity ofP. ruthii, especially its tolerance of highly variable water, and highlight its potential vulnerability to future environmental change.

Environmental injustice and Escherichia coli in urban streams: Potential for community‐led response

AbstractEscherichia coli are fecal indicator bacteria that reach waterbodies through aging and failing infrastructure in cities. Exposure to pathogens in untreated sewage can result in gastrointestinal disease, which frequently goes unreported. In the United States, the Clean Water Act regulates point source discharges of sewage and treated wastewater, but fecal indicator bacteria remain the second leading cause of river impairment. The burden of this contamination is not equitably distributed, with Black, Indigenous, and communities of color suffering from a disproportionate burden of untreated and overflowing waste and subsequent health impacts. Regulatory failures, and even abandonment, along with the exclusion of people of color from the mainstream environmental movement, mean that new approaches are needed to help communities empower themselves to address contamination. Community‐led groups that engage residents in addressing issues within and beyond regulatory frameworks have used approaches including trash traps, riparian planting and restoration, and community‐led monitoring. Mycofiltration, or the use of fungi to filter pollutants from water, is an emerging and understudied method of remediating E. coli. The low cost of mycofilter installation and maintenance may give agency to communities that have been unduly burdened with sewage contamination to diminish harmful exposures in the near term, even as they continue working toward longer‐term regulatory fixes. Continued research is needed to fully understand how different species of mycelium work under varying hydrologic conditions, including in‐field installations, along with long‐term monitoring and community acceptance to understand the efficacy and the potential impact of this strategy.

Functional Trait Diversity Shapes the Biomass in the Dam-Induced Riparian Zone

The construction of dams has caused a serious decline in riparian ecosystem functioning and associated services. It is crucial to assess the response of riparian plant communities to flooding stress for their conservation. Functional traits composition, functional diversity, and species diversity are commonly used to investigate the effect of abiotic stress on ecosystem functioning and services (i.e., biomass). Yet, how the functional traits respond to the flooding stress along a dam-induced riparian habitat remains unclear, and how biodiversity affects biomass still exists controversy. Accordingly, this study investigated the response strategies of functional traits subjected to the flooding stress and its correlation with aboveground biomass (AGB) in the water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR). We found that leaf traits and root traits showed a significant response to elevation, whereas they demonstrated different distribution patterns. Leaf traits showed acquisitive-conservative-acquisitive resource strategies along the flooding stress, while root traits shifted from species conservative resource to acquisitive resource strategies. AGB was found to be positively related to the community weighted mean (CWM) trait values for leaf dry matter content (LDMC) and negatively related to specific leaf area (SLA), but the AGB showed no relationship with the root traits. AGB accumulated greatly in the intermediate species diversity, and we also found a significant relationship between functional diversity and biomass within threshold values. Additionally, Rao’s exerted the most significant influence on the biomass, suggesting that the functional diversity index is a better indicator of biomass variation. The results obtained only partly supported the “mass ratio hypothesis” in leaf traits and mainly supported the “niche complementarity hypothesis”, which suggested that these two theories are not mutually exclusive at the early stage of vegetation community succession with an unstable community structure in dam-regulated riparian zones.

A New Method of Estimating Groundwater Evapotranspiration at Sub-Daily Scale Using Water Table Fluctuations

Riparian ecosystems fundamentally depend on groundwater, and accurate estimations of groundwater evapotranspiration (ETG) are important for understanding ecosystem functionality and managing regional water resources. Over the past several decades, various methods have been proposed to estimate groundwater evapotranspiration based on water table fluctuations. However, the majority of methods cannot resolve sub-daily variations in ETG. In this study, we proposed a new hydraulic theory-based ETG estimation method at a sub-daily time scale. To evaluate its performance, we employed a variety of measurements (i.e., water table levels, latent heat flux and soil water contents) at a riparian forest (T. ramosissima) in Northwest China from 25 July to 10 October in 2017. The results indicated that the proposed method can successfully estimate ETG at both sub-daily (R2 = 0.75) and daily (R2 = 0.88) time scales, but the variations in the specific yield under different water table conditions should be carefully taken into account. In addition, we investigated the seasonal variations in water uptake source of the riparian plant, and found that it had strong plasticity in water usage during the study period. That is, it consumed approximately equal amounts of soil water and groundwater when soil moisture was available, and tended to consume more groundwater for survival as the soil moisture was depleted. To verify the seasonal patterns of the water uptake of the riparian forest, systematic isotope-based studies are needed in future study.

Using riparian plant species to locate the 1:2-year floodline on single channel rivers

Riparian zones can be characterised botanically into two main areas, a wet bank and a dry bank. These areas have been linked to the duration of inundation by river flow, the boundary between the two being the 1:2 year floodline. Therefore the wet bank is inundated regularly by small floods and the dry bank by larger, less frequent floods, and each may support one to a few distinct plant communities laterally up the bank. Understanding these plant distributions helps rehabilitation projects and Environmental Flow (EFlows) studies as it can inform re-vegetation strategies in the former and help understanding of the links between plants and the river’s flow regime in the latter. Systematic sampling and data analysis methods were developed for single channel rivers with relatively undisturbed natural vegetation to identify and locate the different plant communities in the riparian zone. Generic rules using distance and height from the water’s edge, rather than the presence or absence of plant species, were calculated to locate the communities. While these statistics were derived from the riparian vegetation along perennial Western Cape rivers, South Africa, the methods could be applied to other perennial single channel river anywhere.

The Healing Power of Clean Rivers: In Silico Evaluation of the Antipsoriatic Potential of Apiin and Hyperoside Plant Metabolites Contained in River Waters.

Humanity may benefit greatly from intact riverine ecosystems not only because they supply water to be used in the most common human activities, but also for the effects that clean rivers can have on human health. Herein, we used a computational approach to show that some phytochemicals produced by riparian plants as secondary metabolites, which are naturally released into river waters, can have therapeutic properties. These include antipsoriatic activities which we demonstrated in silico by modelling the interaction of apiin, guanosine and hyperoside, a few main river plant metabolites, with NF-kB, IL-17 and IL-36, which are recognized targets involved in psoriasis disease. In particular, we found that apiin and hyperoside are endowed with docking energies and binding affinities which are more favorable than the known reference inhibitors of the three protein targets whilst, in silico, guanosine shows comparable activity with respect to the inhibitors of IL-36 and NF-kB. The low skin permeation (logKp < −8) we predicted for apiin and hyperoside led us to hypothesize their possible utilization as topic antipsoriatic therapeutics, and in particular after PAINS (pan-assay interference compounds) score evaluation, we reached the conclusion that apiin, with no predicted tendency to react nonspecifically with the numerous targets involved in the biological cellular pathways, is particularly interesting for the desired therapeutic application.

The Effects of Edaphic Factors on Riparian Plants in the Middle and Lower Reaches of the Hanjiang River, China.

It is important to understand the interactions between soil and plant in riparian zones to ensure ecosystem function. The effects of edaphic factors on plant composition and species diversity were investigated in the middle and lower reaches of the Hanjiang River (MLHR), China. A total of 154 species of herbs were recorded, and vegetation was divided into 32 clusters according to a two-way indicator species analysis (TWINSPAN). Cynodon dactylon and Paspalum distichum were the most common clusters, accounting for 22.7% and 12.5% of total samples, respectively. Hydric and mesic species were dominant in the first and second transects, with mesophytes dominating the third and fourth transects. First transects situated were mainly composed of perennials and annuals, respectively. Perennials in second transects were present in 83% of sites, and perennials in the third and fourth transects were present in 86% of the sites. Margalef richness index (Dma), Simpson dominance diversity index (D), Shannon–Wiener diversity index (H) and Pielou evenness index (Jsw) were higher in the first transects in some sites. The redundancy analysis (RDA) results indicated that soil moisture content was the dominant factor affecting hydrophilic vegetation types, and total nitrogen (TN) and soil organic matter (SOM) were the most critical factors affecting plant life history types and species diversities in this area.

Climate‐induced plasticity in leaf traits of riparian plants

AbstractAimLeaf litter inputs from riparian vegetation and its decomposition play a key role in energy and nutrient transfer in many stream ecosystems. Instream leaf litter decomposition is driven by both leaf traits and environmental conditions. Therefore, understanding and predicting leaf trait variation under current environmental changes and their putative interactive effects on stream food webs is a critical challenge. Most studies have focussed on the assumed higher interspecific leaf trait variability, with little research addressing an intraspecific perspective.LocationAndalusia, Spain.MethodsWe assessed the relative effects of climate and soil conditions on the plasticity of leaf traits of four common woody riparian species in permanent low‐order Mediterranean streams across a wide aridity gradient. We used a space‐for‐time substitution approach to predict leaf trait changes and consequences for stream food webs in a future climate change scenario.ResultsOverall, we found that aridity had a major influence on leaf trait plasticity but with opposite patterns depending on plant functional type, although soil was the strongest predictor in some cases. Results indicated that leaf quality—linked to palatability and decomposability—of Alnus glutinosa, Salix atrocinerea and Rubus ulmifolius (deciduous/semi‐deciduous) will decrease with forecasted aridification, whereas the palatability of the evergreen Nerium oleander will increase. We observed higher trait plasticity than interspecific variation for leaf P, Ca and Mg concentrations and C:P ratio.Main conclusionsOur findings suggest a decrease of intraspecific leaf quality in riparian deciduous species with global warming in a relatively short term. In a longer term, this may merge with the forecasted dieback of deciduous species in riparian corridors of temperate climate zones. These changes have the potential to significantly impair ecosystem functioning of Mediterranean mountain streams currently under deciduous gallery forests.

Pressures on Boreal Riparian Vegetation: A Literature Review

Riparian zones are species-rich and functionally important ecotones that sustain physical, chemical and ecological balance of ecosystems. While scientific, governmental and public attention for riparian zones has increased over the past decades, knowledge on the effects of the majority of anthropogenic disturbances is still lacking. Given the increasing expansion and intensity of these disturbances, the need to understand simultaneously occurring pressures grows. We have conducted a literature review on the potential effects of anthropogenic pressures on boreal riparian zones and the main processes that shape their vegetation composition. We visualised the observed and potential consequences of flow regulation for hydropower generation, flow regulation through channelisation, the climate crisis, forestry, land use change and non-native species in a conceptual model. The model shows how these pressures change different aspects of the flow regime and plant habitats, and we describe how these changes affect the extent of the riparian zone and dispersal, germination, growth and competition of plants. Main consequences of the pressures we studied are the decrease of the extent of the riparian zone and a poorer state of the area that remains. This already results in a loss of riparian plant species and riparian functionality, and thus also threatens aquatic systems and the organisms that depend on them. We also found that the impact of a pressure does not linearly reflect its degree of ubiquity and the scale on which it operates. Hydropower and the climate crisis stand out as major threats to boreal riparian zones and will continue to be so if no appropriate measures are taken. Other pressures, such as forestry and different types of land uses, can have severe effects but have more local and regional consequences. Many pressures, such as non-native species and the climate crisis, interact with each other and can limit or, more often, amplify each other’s effects. However, we found that there are very few studies that describe the effects of simultaneously occurring and, thus, potentially interacting pressures. While our model shows where they may interact, the extent of the interactions thus remains largely unknown.

Evaluating the different methods for estimating groundwater evapotranspiration using diurnal water table fluctuations

Riparian ecosystems fundamentally depend on groundwater, and thus accurate estimates of daily groundwater evapotranspiration rate (ETg) is curial for understanding the interactions between groundwater and vegetation. Up to now, various methods (i.e., White, 1932; Hays, 2003; Soylu et al., 2012) have been proposed to estimate daily ETg using the water table fluctuations. The objective of this paper was to evaluate and compare their performances under various water table conditions in field environments. For this purpose, we employed a variety of measurements (i.e., water table levels, latent heat flux and soil water contents) at a riparian forest (T. ramosissima) in Northwest China in 2017. Our results showed that the White method is suitable for use during the water table declining periods. Also, the selected time intervals could have impacts on the estimations of ETg. The Soylu method and the Hays method performed well under various water table conditions. Thus, it seems that the Hays and Soylu methods are more suitable for long-term ETg estimates in field environments. In addition, the percentage of plant transpired water from groundwater varied during the growing seasons. The riparian plants mainly use soil water during the early growing stages, and it tended to use groundwater during the late growing stages. In the future, more isotope-based studies were needed to verify the seasonal patterns of water uptake of the riparian forest.

The role of fine root morphology in nitrogen uptake by riparian plants

The role of fine root morphology in nitrogen uptake by riparian plants

Shifts from native to non-native riparian plant communities analyzed using hierarchical phytosociological data

Shifts from native to non-native riparian plant communities analyzed using hierarchical phytosociological data

Study on the Phenological Period of Riparian Plants in the Kalban River in Rainy Season

Study on the Phenological Period of Riparian Plants in the Kalban River in Rainy Season

An ecological water replenishment model of urban lake riparian plant restoration based on the groundwater–vegetation interactions

Ecological water replenishment is an effective method that can ensure the urban lake riparian plant restoration. Here, a coupled one-dimensional model was developed to simulate the plant restoration under the ecological water replenishment and the groundwater–vegetation interactions in the urban lake. Meanwhile, the habitat suitability rate was used to show the degree of the plant restoration. The simulation results revealed three characteristic zones of plant restoration along a cross-bank section under the combined effect of ecological water replenishment method and evapotranspiration: (1) an air-limiting zone at the lake bank where plant restoration was limited by air scarcity in the soil due to water replenishment; (2) a plant growth zone near the bank, which is the core zone of plant restoration that urban lake managers can consider; (3) a water-limiting zone far from the bank where the plant restoration was limited by water scarcity in the soil. Urban lake managers should give priority to control the initial water level in each cycle when ensuring the plant restoration. When the actual conditions were difficult to control the initial water level in each cycle, the replenishment cycle could be controlled to improve the plant restoration degree. These findings demonstrated that the interplays of ecological and hydrological processes in urban lake marshes, and provided a management model tool for urban lake managers facing riparian plant restoration problems.

Small mammal relative abundance within riparian ecosystems of the Blue Mountains

There is a growing interest and investment in restoring riparian areas in the Pacific Northwest to protect biodiversity and water quality, and to restore quality habitat for threatened fish species. However, these management activities change vegetation conditions and potentially impact terrestrial species in these ecosystems. Our objective was to estimate associations between small mammals and 4 broad cover types—conifers, shrubs, grasses, and forbs—in riparian areas within the Blue Mountains of northeast Oregon, USA. We estimated abundances and spatial association for 10 small mammal species using a multispecies hierarchical abundance model and mark-recapture data collected on 36 sites from 2014 to 2017. We predicted that forest-associated species would be more abundant with greater conifer cover, that increases in shrub cover would favor most species, and that increases in grass and forb cover would favor grassland-associated species. Yellow-pine chipmunks (Tamias amoenus) were positively associated with conifer cover, while long-tailed voles (Microtus longicaudus) and montane voles (Microtus montanus) were negatively associated with conifer cover. Associations with shrub cover were positive for bushy-tailed woodrats (Neotoma cinerea), deer mice (Peromyscus maniculatus), and yellow-pine chipmunks, but negative for montane voles. Bushy-tailed woodrats and montane voles were negatively associated with grass cover. This study is the first to characterize the riparian small mammal communities in this region and provides insights on the effects of restoration activities on riparian ecosystems in dry interior forests and grasslands. We suggest that riparian plantings, a ubiquitous restoration practice, will increase the relative abundances for some, but not all, small mammal species. We also demonstrate use of a new multi-species abundance model that can be a powerful tool for analyzing mark-recapture data because it allowed us to extend the scope of our analysis to data poor species by pooling information with data rich species.

Riparian plant species offer a range of organic resources to stream invertebrate communities through varied leaf breakdown rates

ABSTRACT Riparian plants provide an important source of energy for freshwater food webs through inputs of leaf litter. Planting riparian buffers with mixed species could enhance the detrital resource supply for invertebrates through varied leaf breakdown rates. To quantify leaf breakdown rates and invertebrate colonisation, we used leaves from eleven grass, shrub and tree species common along agricultural waterways in New Zealand. Breakdown of leaves immersed in a spring-fed stream differed significantly among species, being fastest for pasture grass (k = 0.0458 day−1) followed by broadleaf, pittosporum, willow, toetoe, poplar, gorse, Carex, eucalyptus, flax, and slowest for cabbage tree leaves (k = 0.0099 day−1). Invertebrate community composition did not differ between leaf species, but consumers were extremely abundant on some leaves (e.g. 51–83 Potamopyrgus snails g−1 pasture grass), indicating coarse detrital resources were in high demand for food or habitat. These breakdown rates could inform selection of riparian plant combinations that will enhance food availability for stream communities, especially continuity of supply, thereby contributing to waterway restoration.

Dam-induced difference of invasive plant species distribution along the riparian habitats

Riparian ecosystem is structurally unstable due to the frequent disturbances from water fluctuation. Moreover, dams on large rivers tend to trigger fundamental changes of the composition and structure of riparian plant communities, which provides high odds for invasive species to colonize. Yet, how the invasive species distribute along a dam-induced riparian habitat, and how the native species resist to plant invasion are still puzzles. In this study, we investigated spatial distribution of invasive floral species and its correlation with the distance from dam and the dam-triggered flooding stresses, as well as the resistance of native species to plant invasion in the water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) along the Yangtze River. By our investigation, a total of 43 alien plant species belonging to 14 families and 34 genera were found, including 20 existed and 23 newly discovered alien species recorded. Most of the new invasive species are annual herbs of the Asteraceae family. At the current successional stage, the new invasive species had not yet fully occupied the habitats of the existed invasive species. Longitudinally, number and coverages of the new invasive species showed an opposite distribution pattern to the existed invasive species, but vertically they demonstrated similar pattern. Currently, the new dominant invasive species are mainly concentrated at the intermediate elevation of WLFZ in the middle section of the reservoir, whereas the existed dominant invasive species have proliferated across the whole WLFZ. Additionally, native species showed a weak resistance to plant invasion, and water fluctuation along the elevation exerted the most significant influence on plant invasion. The results indicated that, after a decade of riparian community succession, the invasiveness of alien species remain persisted. The potential penetration site of the invasion may locate at the intermediate section along the vertical and longitudinal dimension.

Dry biomass and carbon sequestration in environmental plantings in the Midlands of Tasmania

SummaryEstimates of dry biomass and carbon sequestration were made for environmental plantings established in the harsh, dry agricultural landscapes of the Midlands of Tasmania. Plantings were designed to provide habitat connectivity for native wildlife. The dry biomass for 6‐year‐old woodland and riparian plantings was estimated to be 4.7 and 9.0 tonnes/ha, respectively. The carbon component of this biomass was estimated to be 2.4 and 4.5 tonnes/ha carbon, equivalent to 8.7 and 16.5 tonnes/ha carbon dioxide (CO2) sequestered, respectively. These are lower than previous estimates for plantings of the same age in the same landscape. This is largely due to lower planting densities of 200 stems/ha, and 883 stems/ha respectively, for woodland and riparian plantings, relative to comparable plantings (˜1,000 stems/ha). Further, a combination of extreme climatic events during early establishment and high heterogeneity in soil type and landscape position reduced performance in riparian plantings.

The role of plant functional traits and diversity in soil carbon dynamics within riparian agroforests.

Restoration of agricultural riparian buffers with trees (agroforestry) provides an elegant solution to enhance carbon storage while also augmenting local biodiversity. Yet the scope and role of riparian plant community diversity in key soil dynamics remain unresolved. Operationalizing riparian age (young [<10 yr] and mature [>30 yr] since establishment] and forest stand type (coniferous and deciduous dominant) to capture the potential extent of plant diversity, we measured plant functional trait diversity and community weighted mean trait values, microbial composition, abiotic soil conditions, and rates of soil CO2 efflux (mg CO2 -C m-2 h-1 ). We used piecewise structural equation modeling (SEM) to further refine the role of biotic indices (leaf, root, and microbial characteristics), and abiotic factors (soil physio-chemical metrics) on soil C cycling processes in riparian systems. We found significantly lower rates of CO2 efflux (F=8.47; p<.01) over one growing season and higher total soil C (F=3.46; p=.03) in mature buffers compared with young buffers. Using SEM, we describe influences on soil C content (marginal r2 =61) and soil CO2 efflux (marginal r2 =53). Within young buffers, soil C content was significantly predicted by fungal/bacterial ratio and root length density, whereas in mature buffers, tree leaf characteristics were associated with soil C content. Soil CO2 efflux was predicted by soil moisture, soil carbon content, and herbaceous root characteristics. Evidently, leaf and root functional traits in combination with broad soil parameters significantly describe soil C dynamics in the field; however, significant pathways are not the same throughout the life cycle of a riparian agroforest.

Analysing the distance decay of community similarity in river networks using Bayesian methods

The distance decay of community similarity (DDCS) is a pattern that is widely observed in terrestrial and aquatic environments. Niche-based theories argue that species are sorted in space according to their ability to adapt to new environmental conditions. The ecological neutral theory argues that community similarity decays due to ecological drift. The continuum hypothesis provides an intermediate perspective between niche-based theories and the neutral theory, arguing that niche and neutral factors are at the opposite ends of a continuum that ranges from competitive to stochastic exclusion. We assessed the association between niche-based and neutral factors and changes in community similarity measured by Sorensen’s index in riparian plant communities. We assessed the importance of neutral processes using network distances and flow connection and of niche-based processes using Strahler order differences and precipitation differences. We used a hierarchical Bayesian approach to determine which perspective is best supported by the results. We used dataset composed of 338 vegetation censuses from eleven river basins in continental Portugal. We observed that changes in Sorensen indices were associated with network distance, flow connection, Strahler order difference and precipitation difference but to different degrees. The results suggest that community similarity changes are associated with environmental and neutral factors, supporting the continuum hypothesis.