Scolochloa Research Articles

Крупномасштабное картографирование растительности долины реки Пинеги (в окрестностях пос. Голубино, Архангельская область)

Geobotanical survey of floodplain natural complexes near gypsum outcrops in the Pinega river valley was done in 2015. Large-scale geobotanical map of the key polygon (scale 1 : 30 000) was composed. Typological units of vegetation were selected on the basis of the composition of dominant species and groups of indicator species. Homogeneous and heterogeneous territorial units of vegetation (serial series, combinations, environmental series) were used. 53 mapped unit types (25 homogeneous types and 28 heterogeneous types) were recognized. The floodplain vegetation consists of 17 homogeneous types of plant communities, 3 series, 14 combinations and 6 ecological series. The sites of old floodplain forests, such as willow forests with Urtica sondenii rare in the Arkhangelsk region and oxbow wet meadows with Scolochloa festucacea were identified.

Estimating the breakdown and accumulation of emergent macrophyte litter: A mass-balance approach

Abstract Litter accumulation within emergent macrophyte marshes may significantly influence abiotic conditions and biota but litter is rarely considered in emergent macrophyte studies. Litter is defined here as the standing and fallen dead plant material that can be collected using harvest methods in the field. Litter accumulation can be predicted by combining annual production with litter breakdown rates. Breakdown rates are typically measured using litter bag studies but these rates may also be measured using a mass-balance approach. A five year study conducted in Delta Marsh, Manitoba measured annual standing crop and harvested accumulated litter of Phragmites australis (Cav.) Trin., Typha glauca Godr., and Scolochloa festucacea (Willd.) Link. These species differ in their level of refractory material and hence the amount of litter that is expected to accumulate. Using annual estimates of standing crop and litter mass, a mass-balance model was used to estimate the litter breakdown rate for each species...

Habitat edges, within‐patch dispersion of hosts, and parasitoid oviposition behavior

Although density-edge effects are commonly reported, we have only scratched the surface in understanding the mechanisms underlying how habitat edges mediate species interactions. Here, I use a combination of field surveys and experiments to explore the linkages between the presence of host-plant edges (Scolochloa festucacea), the within-patch distribution of planthopper eggs (Delphacodes scolochloa), and the oviposition behavior of their egg parasitoids (Anagrus spp.). The field surveys revealed that densities of hosts and parasitoids at the edge were > or = 2.5 times lower than densities in the patch interior and that the effect was independent of patch size. As a consequence of its edge-avoidance behavior, host within-patch dispersion was significantly more aggregated in the presence, as compared to the absence, of an edge. Also, as patch size decreased, the proportion of the patch that was core (i.e., beyond the influence of the edge) decreased, and the degree of host aggregation increased. In a subsequent field experiment, I found that the dispersion of hosts affected Anagrus oviposition behavior only when hosts were present on islands with discrete edges. Under these circumstances, the proportion parasitized and per capita parasitized were 2.3 and 3.4 times higher, respectively, when hosts were clumped as compared to when hosts were uniformly or randomly distributed. Based on a laboratory experiment using small S. festucacea patches, I found that Anagrus had 40% shorter step lengths, spent 52% more time in the patch, and parasitized 84% more hosts when hosts were clumped as compared to uniformly distributed. These results were indicative of area-restricted search by Anagrus, which is an effective foraging strategy when hosts are clumped. This is the first study to demonstrate that predator foraging behavior in response to prey dispersion can be mediated by the presence of a patch edge. Also, because edge-averse behavior is commonly reported in the literature, an underappreciated effect of fragmentation on predator-prey interactions and stability could arise from edge-mediated effects on prey within-patch aggregation.

Wood bison population recovery and forage availability in northwestern Canada

Forage availability was assessed to determine sustainable stocking rates for eight broadly defined vegetation types (Treed Uplands, Treed Lowlands, Mixed Tall Shrub/Sedge, Closed-canopied Willow, and Open-canopied Willow, Meadow, Wetland Grass, Wetland Sedge) for use by wood bison ( Bison bison athabascae), a threatened subspecies, in the Canadian boreal forest of northern Alberta. Clip plots ( n = 108) were used to sample peak availability of herbs and current annual growth of Salix spp. in late summer. Graminoid wetlands dominated by Carex atherodes, Carex aquatilis, Carex utriculata, Scolochloa festucacea, or Calamagrostis stricta produced 1975–4575 kg ha −1 of fair to good quality forage, whereas treed stands produced <250 kg ha −1 of forb-dominated forage (>85% content), which was below a published 25% foraging efficiency threshold of 263 kg ha −1 for bison. Upland forests that dominate the region produced ≤1 animal unit day (AUD) of forage per hectare in summer. Most forest understory plants were of poor forage value, suggesting the potential sustainable stocking rate of such areas was actually ≤0.3 AUD ha −1, with even lower rates during winter due to snow cover. Herbaceous wetlands contained ∼78 AUD ha −1 of forage, but were considered largely unavailable in summer because of flooding and soft organic soils that make access difficult. Conversion of prime foraging habitat to agricultural land, forest expansion due to fire control, and a warmer and wetter climatic regime after the mid-1900s likely contributed to a regional reduction in carrying capacity. It is hypothesized that substantial recovery of the wood bison population toward historical levels will be constrained in northern Alberta by the availability of summer forage, and the limited extent of graminoid wetlands that provide winter foraging habitat.

Description, Life History, and Parasitism of a New Species of Delphacid Planthopper (Hemiptera: Fulgoroidea)

Delphacodes scolochloa Cronin & Wilson (Hemiptera: Fulgoroidea) is a newly discovered delphacid planthopper that feeds and oviposits exclusively on the stems of sprangletop, Scolochloa festucacea (Willd.) Link (Poaceae: Pooidae), in the prairie pothole region of northeastern North Dakota. D. scolochloa is bivoltine. It is also wing dimorphic, but populations are composed predominantly of flightless brachypters. Macropters incur a substantial cost in terms of reduced longevity and fecundity relative to brachypters. The parasitoid complex attacking D. scolochloa consists of two egg parasitoids, Anagrus nigriventris Girault and Anagrus columbi Perkins (Hymenoptera: Mymaridae), and one undescribed dryinid. The proportion of eggs parasitized averages 21%, and egg parasitization is density independent.

Macroflora in Lake Ülemiste (Estonia) – changes and the impact of environmental factors

The changes in the macroflora observed over the last 100 years in Lake Ulemiste in the vicinity of Tallinn and the impact of environmental factors are reported. Lake Ulemiste has supplied the city of Tallinn with water since the 14th century, but the treatment of water did not start until 1927. The macroflora of Lake Ulemiste has been studied four times during the 20th century: in 1908, 1968, 1979, and 2000, with additions in 2004. The extent of macrophyte cover and the maximum width of the zone of macrophytes have reduced in the course of 100 years. While the species composition has not changed in most of the lake, the relationships between dominating species have altered. In 2000, Phragmites australis was the predominant species in the lake, whereas Scolochloa festucacea was the main dominant in 1908. The widely fluctuating water level, as well as steadily increasing mean annual water level since the beginning of the 1960s, favoured a decline in the macrophyte community by the end of the 20th century.

Scolochloa festucacea (Poaceae)in Hungary

Király, G.: Scolochloa festucacea (Poaceae) in Hungary. — Willdenowia 35: 259–263. — ISSN 0511-9618; © 2005 BGBM Berlin-Dahlem. doi:10.3372/wi.35.35205 (available via http//dx.doi.org/)The discovery of the circumboreal grass Scolochloa festucacea in Hungary, which is also its first known locality in the entire Carpathian Basin, is documented. Only one population was found, near Földsziget in the western fen basin of the Hanság region in NW Hungary. The locality, where it grows as a dominant, stand-forming species in an area of c. 10 hectare, is one of the low elevation refugia of the boreal flora in Central Europe, indicating the relict character of its Hungarian occurrence.

Chironomidae (diptera) responses to the experimental flooding of prairie marshes

This study examined chironomid responses to the flooding of ten drained experimental marshes in Delta Marsh, Manitoba, Canada. Emergence traps were used to monitor chironomid emergence from three vegetation types (Symphyotrichum ciliatum, Scolochloa festucacea, and Schoenoplectus tabernaemontani) flooded at two water depths (shallow: 20–40 cm, deep: 50–70 cm) over a four-year period. The greatest number (7,651 m−2 yr−1) and biomass (20.3 g m−2 yr−1) of chironomids emerged from Schoenoplectus-deep sites in the fourth year of flooding. Numbers, biomass, and size classes of emerging chironomids were similar over the four years from the Symphyotrichum habitat. However, chironomid emergence from Scolochloa and Schoenoplectus habitats was dominated initially by the smallest size class but shifted steadily toward production of much larger species over the four-year experiment. The production of chironomids as a potential food resource for waterfowl was high from the Symphyotrichum habitat during all four years of flooding, but emergence from the Scolochloa and Schoenoplectus habitats did not reach comparable levels until the third or fourth year.

Threatened dry grasslands in the continental boreal forests of Wood Buffalo National Park: commentary

There are three primary types of graminoid-dominated communities in or near Wood Buffalo National Park, Canada: freshwater meadows and marshes composed of Calamagrostis canadensis (Michx.) Beauv., Carex atherodes Spreng., Carex aquatilis Wahlenb., Scolochloa festucacea (Willd.) Link, and Poa L.; saline meadows composed of Hordeum jubatum L., Puccinellia nuttalliana (Schult.) A.S. Hitchc.,Agropyron trachycaulum (Link) Malte, Calamagrostis stricta (Timm) Koeler, and Calamagrostis inexpansa A. Gray; and dry grasslands composed of Agropyron trachycaulum, Stipa L., Carex siccata Dewey, Carex obtusata Lilj., and Koeleria macrantha (Ledeb.) J.A. Schultes f. Except for the Peace Point area, it is not known whether dry grasslands have declined in areal extent. Including various wetlands under "dry grasslands", and concluding that these areas no longer support dry grassland is misleading. Dry grasslands exist in Wood Buffalo National Park, but most graminoid-dominated communities in the park are, and have been, freshwater and saline meadows and marshes. A clear understanding of the ecological factors operating in these different ecosystems is critical to informed management.Key words: fire, grassland, prairie, vegetation, wetland, Wood Buffalo National Park.

Decomposition of emergent macrophyte roots and rhizomes in a northern prairie marsh

Dry mass, nitrogen and phosphorus content in belowground litter of four emergent macrophytes ( Typha glauca Godr., Phragmites australis (Cav.) Trin., Scolochloa festucacea (Willd.) Link and Scirpus lacustris L.) were followed for 1.2 years in a series of experimental marshes, Delta Marsh, Manitoba. Litter bags containing roots and rhizome materials of each species were buried in unflooded soil, or soil flooded at three water depths (1–30, 31–60, > 60 cm). There were few differences in dry mass loss in unflooded or flooded soils, and depth of flooding also had little effect on decomposition rates. In the flooded sites, Scolochloa and Phragmites roots lost more mass (48.9–63.8% and 59.2–85.5%, respectively) after 112 days than Typha and Scirpus (36.3–43.6 and 37.0–47.2%, respectively). These differences continued through to the end of the study, except in the shallow sites where Scirpus roots lost more mass and had comparable mass remaining as Scolochloa and Phragmites. In the unflooded sites, there was little difference between species. All litters lost nitrogen (22.9–90.0%) and phosphorus (46.3–92.7%) during the first 112 days, then levels tended to remain constant. Decay rates for our belowground root and rhizome litters were comparable to published literature values for aboveground shoot litter of the same species, except for Phragmites roots and rhizomes which decomposed at a faster rate (− k = 0.0014−0.0032) than shoots (− k = 0.0003−0.0007, [van der Valk, A.G., Rhymer, J.M., Murkin, H.R., 1991. Flooding and the decomposition of litter of four emergent plant species in a prairie wetland. Wetlands 11, 1–16]).

Seasonal flooding, nitrogen mineralization and nitrogen utilization in a prairie marsh

Flooding can be an important control of nitrogen (N) biogeochemistry in wetland ecosystems. In North American prairie marshes, spring flooding is a dominant feature of the physical environment that increases emergent plant production and could influence N cycling. I investigated how spring flooding affects N availability and plant N utilization in whitetop (Scolochloa festucacea) marshes in Manitoba, Canada by comparing experimentally spring-flooded marsh inside an impoundment with adjacent nonflooded marsh. The spring-flooded marsh had net N mineralization rates up to 4 times greater than nonflooded marsh. Total growing season net N mineralization was 124 kg N ha−1 in the spring-flooded marsh compared with 62 kg N ha−1 in the nonflooded marsh. Summer water level drawdown in the spring-flooded marsh decreased net N mineralization rates. Net nitrification rates increased in the nonflooded marsh following a lowering of the water table during mid summer. Growing season net nitrification was 33 kg N ha−1 in the nonflooded marsh but < 1 kg N ha−1 in the spring-flooded marsh. Added NO3 −1 induced nitrate reductase (NRA) activity in whitetop grown in pot culture. Field-collected plants showed higher NRA in the nonflooded marsh. Nitrate comprised 40% of total plant N uptake in the nonflooded marsh but <1% of total N uptake in the spring-flooded marsh. Higher plant N demand caused by higher whitetop production in the spring-flooded marsh approximately balanced greater net N mineralization. A close association between the presence of spring flooding and net N mineralization and net nitrification rates indicated that modifications to prairie marshes that change the pattern of spring inundation will lead to rapid and significant changes in marsh N cycling patterns.

Primary production and management of seasonally flooded prairie marshes harvested for wild hay

Experimental spring-flooded and nonflooded water regimes were applied to prairie marshes dominated by whitetop grass (Scolochloa festucacea) in Manitoba, Canada, to examine their effects on aboveground and belowground primary production and to evaluate flooding management for wild hay production. Spring flooding increased marsh aboveground and belowground production. Annual and perennial forbs comprised a greater portion of aboveground production in nonflooded marsh. Two methods (soil coring and ingrowth into mesh bags) showed earlier commencement of belowground growth and greater belowground production in flooded marsh. Higher rhizome ingrowth in flooded marsh indicated that spring flooding increased plants' ability to replenish belowground reserves. The percentage of plant production allocated aboveground was greater in flooded marsh, but shifts in allocation were small compared with the absolute increases in production caused by flooding and could not account for the observed differences in aboveground production between flooding regimes. The strong plant growth response to flooding indicates that management that conserves or mimics the natural spring-flooded hydrologic regime can increase whitetop forage production and control invasion by undesirable species. Key words: belowground, hydrologic regime, prairie marsh, primary production, rhizomes, roots.

Effects of prolonged flooding on the distribution and biomass of emergent species along a freshwater wetland coenocline

Water levels were raised 1 m for two years in 10 cells of an experimental wetland complex located in the Delta Marsh, Manitoba, Canada. The mean area covered by each of the 5 dominant emergent species in these cells declined significantly during the first year of flooding. There was no significant difference in the total acreage of ?mergents between flooding years. Three species were completely {Carex atherodes Spreng, Scolochloa festucacea (Willd.) Link) or almost {Scirpus lacustris L. spp. glaucus (Sm.) Hartm.) eliminated from the cells. Typha glauca Godr. and Phragmites australis (Cav.) Trin. still covered in the second year of flooding about 40 and 25%, respectively, of the area that they had occupied in the cells in the preflooding year. The mean elevation at which the two surviving species were found both increased 0.1 and 0.2 m over preflooding elevations during the first and second year of flooding, respectively. There is no evidence that during the flooding years any species migrated upslope toward more optimal water depths. Aboveground standing crop for all five species declined significantly during the first year of flooding, but was not significantly different between the two flooding years. Total belowground biomass did not differ between spring and fall, but declined significantly (about 20%) during the first year of flooding and remained about at that level during the second year. In the spring following the two years of flooding, mean total belowground biomass was only 40 g m-2, less than 10% of the belowground biomass dur ing the preflooding year.

Hydrologic control of litter decomposition in seasonally flooded prairie marshes

The effect of seasonal inundation on the decomposition of emergent macrophyte litter (Scolochloa festucacea) was examined under experimental flooding regimes in a northern prairie marsh. Stem and leaf litter was subjected to six aboveground inundation treatments (ranging from never flooded to flooded April through October) and two belowground treatments (nonflooded and flooded April to August). Flooding increased the rate of mass loss from litter aboveground but retarded decay belowground. Aboveground, N concentration decreased and subsequently increased earlier in the longer flooded treatments, indicating that flooding decreased the time that litter remained in the leaching and immobilization phases of decay. Belowground, both flooded and nonflooded litter showed an initial rapid loss of N, but concentration and percent of original N remaining were greater in the nonflooded marsh throughout the first year. This suggested that more N was immobilized on litter under the nonflooded, more oxidizing soil conditions. Both N concentration and percent N remaining of belowground litter were greater in the flooded than the nonflooded marsh the second year, suggesting that N immobilization was enhanced after water-level drawdown. These results suggest different mechanisms by which flooding affects decomposition in different wetland environments. On the soil surface where oxygen is readily available, flooding accelerates decomposition by increasing moisture. Belowground, flooding creates anoxic conditions that slow decay. The typical hydrologic pattern in seasonally flooded prairie marshes of spring flooding followed by water-level drawdown in summer may maximize system decomposition rates by allowing rapid decomposition aboveground in standing water and by annually alleviating soil anoxia.

Growth and resource allocation of whitetop ( Scolochloa festucacea) along a water depth gradient

The above- and below-ground growth of the prairie marsh grass whitetop, Scolochloa festucacea (Willd.) Link, was studied along a gradient of water depth to investigate the importance of shifts in above- and below-ground biomass allocation in explaining observed patterns of above-ground biomass under different flooding regimes. In pot culture, above- and below-ground biomass values were similar between water depths of 15 cm below the soil surface (−15 cm), at the soil surface (0 cm) and 15 cm above the soil surface, but biomass declined with water depths greater than 15 cm. Whitetop allocated an increasing proporotion of total biomass to above-ground parts as water depths increased from −15 to 15 cm. In the field, above-ground biomass varied more in relation to changing water depths than below-ground biomass. Greater depth and duration of spring flooding increased both above- and below-ground biomass and relative biomass allocation to above-ground parts. The increase of total biomass that occurred with flooding was a more important influence on patterns of above-ground biomass than were shifts in relative biomass allocation.

Seasonal flooding, soil salinity and primary production in northern prairie marshes

Hydrologic regime is an important control of primary production in wetland ecosystems. I investigated the coupling of flooding, soil salinity and plant production in northern prairie marshes that experience shallow spring flooding. Field experiments compared whitetop (Scolochloa festucacea) marsh that was: (1) nonflooded, (2) flooded during spring with 25 cm water and (3) nonflooded but irrigated with 1 cm water · day-1. Pot culture experiments examined whitetop growth response to salinity treatments. The electrical conductivity of soil interstitial water (ECe) at 15 cm depth was 4 to 8 dS· m-1 lower in flooded marsh compared with nonflooded marsh during 2 years. Whitetop aboveground biomass in flooded marsh (937 g · m-2, year 1; 969 g · m-2, year 2) exceeded that of nonflooded marsh (117 g · m-2 year 1; 475 g · m-2, year 2). Irrigated plots had lower ECe and higher aboveground biomass than nonflooded marsh. In pot culture, ECe of 4.3 dS · m-1 (3 g · L-1 NaCl) reduced total whitetop biomass by 29 to 44% and ECe of 21.6 dS · m-1 (15 g · L-1 NaCl) reduced biomass by more than 75%. Large reductions of ECe and increases of whitetop growth with irrigation indicated that plants responded to changes in soil salinity and not other potential environmental changes caused by inundation. The results suggest that spring flooding controls whitetop production by decreasing soil salinity during spring and by buffering surface soils against large increases of soil salinity after mid-summer water level declines. This mechanism can explain higher marsh plant production under more reducing flooded soil conditions and may be an important link between intermittent flooding and primary production in other wetland ecosystems.

Water-depth tolerances of the dominant emergent macrophytes of the Delta Marsh, Manitoba

The growth (shoot height, cumulative shoot length, shoot density, above- and below-ground biomass) of seven emergent species growing at five different water depths was measured for 2 years. These species belonged to three different ecological classes: (i) upper marsh species (Carex atherodes, Scolochloa festucacea, and Phragmites australis) that occupy sections of the water-depth gradient that are only seasonally flooded in the Delta Marsh; (ii) lower marsh species (Typha glauca and Scirpus lacutris spp. glaucus) that occupy permanently flooded areas; and (iii) drawdown species (Scirpus lacustris spp. validus and Scirpus maritimus) that become established temporarily during drawdowns. Upper marsh species could not adjust their shoot length if they were growing in water deeper than 20 cm. Lower marsh species were able to do this in water up to 70 cm deep. All three types survived for 1 or 2 years in water too deep for long-term persistence. Scirpus species survived as tubers in areas with water too deep for them to grow. The distributions of the seven species in the experiments overlapped considerably, and all species cooccurred at water depths to 70 cm after 2 years of flooding. The predicted distribution in the four dominant species along a water-depth gradient were consistent with their actual distributions in the Delta Marsh, but their predicted distributions overlapped much more than is the case in the field. Key words: emergent vegetation, experiment, water-depth tolerance, plant growth, distributions.

Life history and population dynamics of whitetop ( Scolochloa festucacea) shoots under different levels of flooding and nitrogen supply

Tagged shoots of the perennial grass whitetop ( Scolochloa festucacea (Wild.) Link) were followed in a seasonally flooded prairie marsh at Delta, Manitoba, Canada, under different treatments of flooding and nitrogen (N) addition to examine how these factors influenced the timing and magnitude of shoot emergence, flowering and mortality. Deep flooding (10–20 cm of water during most of the growing season) increased the total number of shoots that emerged during early spring, the number and percentage of flowering shoots, and total biomass and net primary production compared with shallow flooding (flooded for only several days with less than 5 cm of water). Shoot emergence during July and August was high under deep flooding, but absent under shallow flooding. These new shoots produced during late summer under deep flooding accounted for 56% of the total difference in annual production of unfertilized marsh between shallow and deep flooding. Shoot mortality was low during early summer and increased during July and August at both levels of flooding. Shoot turnover was similar (19–22%) between flooding treatments in the absence of fertilization. Nitrogen increased shoot mortality under both levels of flooding, but effects were greater under shallow flooding and generally restricted to late summer. Nitrogen availability enhanced shoot growth, but did not change the basic pattern of shoot dynamics, indicating that environmental factors other than N availability were largely responsible for controlling differences in production between deep- and shallow-flooding regimes.

Flooding and the decomposition of litter of four emergent plant species in a prairie wetland

Changes in mass, N, and P for old and new litter of four emergent plant species (Scolochloa festucacea (Willdl.) Link,Phragmites australis (Cav.) Trin ex Steud.,Typha ×glauca Godr., andScirpus lacustris L. spp.glaucus (Sm.) Hartm.) were studied under two water-level regimes in a 10-cell experimental marsh complex in the Delta Marsh, Manitoba, Canada. In the normal regime, water levels were kept at the regulated water level for Lake Manitoba until the fall of 1981, while in the flooded or high-water regime, they were raised 1 m above the regulated level in the fall of 1980. In the spring of 1980, old litter (i.e., litter from the previous growing season) was placed in all ten cells of the complex, and in the fall of 1980, new litter (i.e., litter from the 1980 growing season) was placed in the same 10 cells. Litter ofS. festucacea had the highest mean decomposition rate (k=0.00171), followed byT. ×glauca (0.0131),S.l. glaucus (0.00126), andP. australis (0.00050). Mean decomposition rates were higher in the flooded treatment than in the normal treatment forP. australis andS. festucacea. Within water-level treatments, mass loss depended on initial litter age. The amount of N and P lost or gained by the end of 1981 varied with species, litter age, and water-level treatment.Scolochloa festucacea old and new litter had a lower percent N and P remaining in the flooded than in the normal water-level treatment. The percent N and P remaining in old litter ofP. australis andS.l. glaucus at the end of the study was higher than that in new litter regardless of water-level treatment. ForT. ×glauca, however, new litter had a higher percent of N and P remaining than old litter at the end of the study in both water-level treatments. Litter with lower initial N and P levels accumulated more N and P than did that with higher initial levels.

Effects of nutrients and water levels on emergent macrophyte biomass in a prairie marsh

Nitrogen and phosphorus fertilizers were added over two growing seasons to marshes dominated by whitetop grass (Scolochloa festucacea) or cattail (Typha glauca) in a prairie lacustrine marsh to assess nutrient limitation and the interaction of nutrient limitation with water depth. For each species, stands were selected at the deep and shallow extremes of its water depth range. Water levels were high during the first year of fertilization and low during the second year, exposing the fertilized stands to a variety of water depths. Nitrogen limited growth in whitetop and cattail marshes. Water level, by controlling whether the soil was flooded or the water table was below the soil surface, affected growth and the degree of nitrogen limitation. In whitetop marshes, nitrogen increased biomass more when the soil was flooded or when standing water was deeper and in cattail marshes, it increased biomass more under intermediate water depths (approximately 0–20 cm) than under more deeply flooded (20–40 cm) or dry conditions. Nitrogen reduced biomass in whitetop marshes the second year, apparently because growth was inhibited by fallen litter from the previous year. Nitrogen did not limit cattail marsh biomass in the driest locations during a year of low water levels. Phosphorus caused a small increase in growth of both species after 2 years. Changes of nitrogen limitation with flooding suggest that annual water level fluctuations, by creating alternating flooded and dry conditions, may influence the primary production of emergent macrophytes through effects on nitrogen cycling.