Non-wetland Plants Research Articles

Trajectories of plant communities in Massachusetts, USA cranberry farms discontinued from agriculture

Retirement of cultivated croplands creates potential for ecosystem and wetland restoration, but vegetation and soil legacies of cropping influence the development of post-agriculture vegetation. In low-lying coastal watersheds of southeastern Massachusetts, cranberries (Vaccinium macrocarpon Aiton) are cultivated in commercial farm units that are diked, leveled and sanded beds created from historic wetlands. Current low cranberry prices and expanding cranberry production elsewhere now increase the likelihood of cranberry farmland retirement. We quantified the trajectories of plant species richness and cover, and plant characteristics (life form, native or non-native, wetland or non-wetland) in a chronosequence of cranberry farm beds that ranged from cultivated units to those retired from cropping and revegetated for 90 years with no post-cropping management. Species richness increased from active beds to 10–20 year-old beds and subsequently decreased. Post-retirement species richness was overwhelmingly dominated by native species. Shrub and tree richness and cover increased steadily over time. The richness of wetland, upland and facultative species all increased quickly after retirement and then declined in the oldest retired beds. The basal area and canopy cover of red maple (Acer rubrum) and pitch pine (Pinus rigida) increased over time. Vegetation followed a relatively consistent successional trajectory and the plant community after five to nine decades was predominantly forest and dominated by non-wetland plants. Encouragement of long-term persistence of greater diversity and cover of wetland plant species on retired cranberry farms will likely require active hydrological and soil modifications that decrease sand depth and raise water tables.

Global patterns of the leaf economics spectrum in wetlands

The leaf economics spectrum (LES) describes consistent correlations among a variety of leaf traits that reflect a gradient from conservative to acquisitive plant strategies. So far, whether the LES holds in wetland plants at a global scale has been unclear. Using data on 365 wetland species from 151 studies, we find that wetland plants in general show a shift within trait space along the same common slope as observed in non-wetland plants, with lower leaf mass per area, higher leaf nitrogen and phosphorus, faster photosynthetic rates, and shorter leaf life span compared to non-wetland plants. We conclude that wetland plants tend to cluster at the acquisitive end of the LES. The presented global quantifications of the LES in wetland plants enhance our understanding of wetland plant strategies in terms of resources acquisition and allocation, and provide a stepping-stone to developing trait-based approaches for wetland ecology.

Diversity patterns of seasonal wetland plant communities mainly driven by rare terrestrial species

In cleared landscapes, wetlands can represent important reservoirs of native plant diversity, which include terrestrial species. Depending on study aims, non-wetland plants might be removed before analysis, affecting conclusions around biodiversity and community structure. We compared the native plant communities of seasonal wetlands in a predominately agricultural landscape as defined geographically (including all species) with that of the obligate wetland assemblage. We were primarily concerned with determining how this design decision affects ecological and conservation conclusions. We analysed a survey database containing >12,900 flora records from South Australia, developing a new area-based method to remove sampling bias to include only wetlands with a near-complete census. We modelled occupancy, species-area relationships, β-diversity and nestedness under our contrasting community definitions. Terrestrial species were 57.4 % of total richness. Removing these species reduced wetland α-diversity by 45 %, but did not affect the scaling of richness with area (power-law species-area relationship z = 0.21 ± 0.01). Occupancies for wetland plants were relatively uniform, but were heavily dominated by rare (satellite) species when terrestrial plants were included, and this also increased β-diversity. Nestedness for terrestrial species occupancies was marginally lower than predicted under null models, suggesting that rare species often do not co-occur with common species. An implication of these occupancy patterns is that twice as many wetlands (and 50 % more wetland area) would be needed to include every native species within at least one wetland compared with wetland-only species.

Seeking a way to promote the use of constructed wetlands for domestic wastewater treatment in developing countries

The aim of this study was to evaluate the domestic wastewater treatment efficiency as well as the survivability of commercially valuable ornamental plants in subsurface flow wetlands (SSFW) for domestic wastewater (DWW) treatment in laboratory and pilot wetland studies. The laboratory scale study included five different species (Zantedeschia aethiopica, Strelitzia reginae, Anthurium andreanum, Canna hybrids and Hemmerocallis dumortieri) that were evaluated in horizontal flow subsurface treatment cells. All the plants survived during the 6-month experimental period demonstrating high wetland nutrient treatment efficiency. In order to validate and expand these preliminary results, a pilot-scale wetland study was carried out in SSFWs under two different flow regimes (horizontal and vertical flow). Four ornamental species were tested during a 1-year period: Zantedeschia aethiopica, Strelitzia reginae, Anthurium andreanum and Agapanthus africanus. The removal efficiencies were significantly higher in the vertical subsurface-flow constructed wetlands (VFCW) for all pollutants, except for nitrate (NO(3)-N), total nitrogen (TN) and total suspended solids (TSS). These results show that it is feasible to use select non-wetland plants with high market value in SSFWs without reducing the efficiency of the wastewater treatment system, although future work should continue in order to apply this technology in a large scale. The added value of floriculture in treatment wetlands can help to promote the use of constructed wetlands (CW) for domestic wastewater treatment in developing countries where economical resources are scarce and water pollution with DWW is common.

Measuring and interpreting respiratory critical oxygen pressures in roots.

Respiratory critical oxygen pressures (COPR) determined from O(2)-depletion rates in media bathing intact or excised roots are unreliable indicators of respiratory O(2)-dependency in O(2)-free media and wetlands. A mathematical model was used to help illustrate this, and more relevant polarographic methods for determining COPR in roots of intact plants are discussed. Cortical [O(2)] near the root apex was monitored indirectly (pea seedlings) from radial oxygen losses (ROL) using sleeving Pt electrodes, or directly (maize) using microelectrodes; [O(2)] in the root was controlled by manipulating [O(2)] around the shoots. Mathematical modelling of radial diffusive and respiratory properties of roots used Michaelis-Menten enzyme kinetics. Respiration declined only when the O(2) partial pressure (OPP) in the cortex of root tips fell below 0.5-4.5 kPa, values consistent with depressed respiration near the centre of the stele as confirmed by microelectrode measurements and mathematical modelling. Modelling predictions suggested that the OPP of a significant core at the centre of roots could be below the usual detection limits of O(2)-microelectrodes but still support some aerobic respiration. In O(2)-free media, as in wetlands, the COPR for roots is likely to be quite low, dependent upon the respiratory demands, dimensions and diffusion characteristics of the stele/stelar meristem and the enzyme kinetics of cytochrome oxidase. Roots of non-wetland plants may not differ greatly in their COPRs from those of wetland species. There is a possibility that trace amounts of O(2) may still be present in stelar 'anaerobic' cores where fermentation is induced at low cortical OPPs.

Model calculations on the relative importance of internal longitudinal diffusion for aeration of roots of non-wetland plants

A model is presented with which the contribution of longitudinal oxygen diffusion to total oxygen requirement of a root can be estimated. Oxygen transport in and respiration of the soil are taken into account. Given the air-filled root porosity, root diameter, coefficient of oxygen transfer between root and soil, root and soil respiration rate, and the coefficient for oxygen diffusion in the soil, the maximum length a root can attain with an adequate oxygen supply to the root tip can be calculated. Results show the importance of root porosity for root aeration, also in unsaturated soils. For thick roots (radius >0.03 cm), diffusion along the internal pathway can provide 50–75% of the total oxygen requirement even, at modest values of the root porosity.

The Effect of Hypoxia and Sulphide on Culture-Grown Wetland and Non-Wetland Plants

Pearson, J. and Havill, D. C. 1988. The effect of hypoxia and sulphide on culture-grown wetland and non-wetland plants. II. Metabolic and physiological changes.—J. exp. Bot. 39: 431-439. Two non-wetland (Agropyron pungens, Hordeum vulgare) and five wetland species (Oryza sativa, Aster tripolium, three Salicornia spp.) were grown in aerated, unaerated and sulphide-treated culture solution. Changes in the activity of alcohol dehydrogenase (ADH) and cytochrome oxidase (COase) in the roots were measured. In the non-wetland species, treatment with hypoxia or sulphide increased ADH activity by 900-1800%, whereas COase activity decreased by 80-92% of the aerated control. In the wetland species, except S. europaea which was not affected, hypoxia increased ADH activity by 350-550%, while COase activity was little affected. Generally, when treated with sulphide the activity of ADH increased to about 750% in most of the wetland species, but increases as low as 175% (S. europaea) and as high as 1400% (S.fragilis) were recorded. The effect of sulphide on the COase activity in the wetland plants was not as marked as in the non-wetland plants. The Salicornia spp. were the least affected by the sulphide treatment and they also had intrinsically higher levels of COase activity than the other species sampled. Of the wetland plants the Salicornia species had the lowest value for root aerenchyma, 3-6%. Therefore, there was no correlation between the possession of aerenchyma and the physiological changes measured. Measurement of malate, lactate and ethanol in roots of the first four species listed above gave no evidence for alternative anaerobic fermentation pathways. While in the flood-intolerant species, high ADH activities were not able to maintain the energy charge. It is suggested that maintenance of relatively high COase activity in wetland plants may help to 'scavenge' any available oxygen within roots and thus help reduce energy loss. Key words—Cytochrome oxidase, alcohol dehydrogenase, metabolic adaptation. Correspondence to: Department of Biology (Darwin Building), University College, Gower Street, London WC1E 6BT, U.K.

The Effect of Hypoxia and Sulphide on Culture-Grown Wetland and Non-Wetland Plants I: GROWTH AND NUTRIENT UPTAKE

Pearson, J. and Havill, D. C. 1988. The effect of hypoxia and sulphide on culture-grown wetland and non-wetland plants. I. Growth and nutrient uptake.—J. exp. Bot. 39: 363-374. The growth rates of two flood-intolerant (Agropyron pungens, Hordeum migare) and two flood tolerant plants (Oryza saliva, Aster tripolium) were compared after treatments in aerated, unaerated and unaerated plus sulphide, culture solution. Growth of the two flood-intolerant species was reduced 15-20 % by lack of aeration and 30-35 % by the sulphide treatment. Growth of the flood tolerant species was increased by 4-7 % when unaerated and decreased 10 % by the sulphide treatment. Of five macroand three micro-nutrients analysed in shoots and roots, no deficiency or increase in any single element could account for the reduction in growth rate of the flood intolerant plants. The treatment with sulphide increased the total sulphur in the tissues of the wetland more than in the non-wetland species. A large part of this increase can be accounted for by an increase in sulphate. By comparing the effects of both sulphate and sulphide on the activities of two enzymes of sulphur assimilation (ATP sulphurylase, O-acetylserine sulphydrylase) it was shown that sulphide uptake by roots does occur and that oxidation to sulphate is its most likely fate. Measurements of root aerenchyma showed no correlation between this and a species' growth rate when its roots were either unaerated or treated with sulphide. Similarly, there was no correlation between the extent of aerenchyma and the ability of a plant to oxidize sulphide within the root. Key words—Sulphide uptake, root aerenchyma, sulphide tolerance. Correspondence to: Department of Biology (Darwin Building), University College, Gower Street, London IVC1E 6BT, U.K.