Soil cellulase, chitinase, and protease activity in Eriophorum vaginatum tussock tundra at Eagle Summit, Alaska

Cellulase, chitinase, and protease activities were examined in Eriophorum vaginatum tussocks at Eagle Summit, Alaska. Changes in the activities were recorded for tussocks of differing relative plant composition. Highest total activity was found in tussocks with at least 50% (relative surface) cover by mycorrhizal colonized shrubs. Total enzyme activity declined in tussocks as the variety of plants decreased. The lowest enzyme activity was found in the moss dominated tussock. Changes in the nature of cellulose hydrolysis suggested that decomposition may be primarily regulated by litter composition in some cases and soil environment in others.     

Phenological observations of major plant growth forms and species in montane and Eriophorum vaginatum tussock tundra in central Alaska

The development stages of several tundra plant species were observed during the summers of 1977 and 1978 in different vegetation zones in a snow accumulation area and in tussock tundra. Leaf maturation and senescence tend towards synchrony regardless of the time of emergence from under the snow. Flowering stages are less synchronous and general than are the vegetation stages within a growth form.     

Microdistribution and water loss resistances of selected bryophytes in an Alaskan Eriophorum tussock tundra

Bryophyte species distributions were analyzed with respect to microtopography at an alpine tundra site in central Alaska which is dominated by tussocks of Eriophorum vaginatum . Bryophyte distributions were found to be significantly correlated with slope but not with azimuth. Different types of tussocks and hollows and mats between tussocks also supported different bryophyte floras. Water loss resistances of three species of moss did not account for differences in their distributions.     

Ecotypic differences in the phenology of the tundra species Eriophorum vaginatum reflect sites of origin

Eriophorum vaginatum is a tussock‐forming sedge that contributes significantly to the structure and primary productivity of moist acidic tussock tundra. Locally adapted populations (ecotypes) have been identified across the geographical distribution of E. vaginatum; however, little is known about how their growth and phenology differ over the course of a growing season. The growing season is short in the Arctic and therefore exerts a strong selection pressure on tundra species. This raises the hypothesis that the phenology of arctic species may be poorly adapted if the timing and length of the growing season change. Mature E. vaginatum tussocks from across a latitudinal gradient (65–70°N) were transplanted into a common garden at a central location (Toolik Lake, 68°38′N, 149°36′W) where half were warmed using open‐top chambers. Over two growing seasons (2015 and 2016), leaf length was measured weekly to track growth rates, timing of senescence, and biomass accumulation. Growth rates were similar across ecotypes and between years and were not affected by warming. However, southern populations accumulated significantly more biomass, largely because they started to senesce later. In 2016, peak biomass and senescence of most populations occurred later than in 2015, probably induced by colder weather at the beginning of the growing season in 2016, which caused a delayed start to growth. The finish was delayed as well. Differences in phenology between populations were largely retained between years, suggesting that the amount of time that these ecotypes grow has been selected by the length of the growing seasons at their respective home sites. As potential growing seasons lengthen, E. vaginatum may be unable to respond appropriately as a result of genetic control and may have reduced fitness in the rapidly warming Arctic tundra.     

Exsertion, elongation, and senescence of leaves of Eriophorum vaginatum and Carex bigelowii in Northern Alaska

The seasonal patterns of leaf exsertion, elongation, and senescence were described and compared for two of the most abundant graminoid species of Alaskan moist tussock tundra, Eriophorum vaginatum and Carex bigelowii . In addition the responses of both species to NPK fertilizer and to variation in site fertility (water track vs. non-track areas) were also assayed and compared. The research was done over two full growing seasons at two sites near Toolik Lake, Alaska, where other aspects of the ecology of both species have been the subject of intensive and ongoing research.
Both species showed the typical graminoid pattern of sequential leaf growth, in which the exsertion and elongation of new leaves is coincident with the senescence of old leaves. However, the rates of these processes were much slower and steadier in Eriophorum than in Carex , with much greater overlap in the life histories of individual leaf cohorts. The total and green leaf lengths of whole tillers in Eriophorum were also less variable over the entire year than in Carex . The conclusion is that leaf growth in Carex should depend more on external storage of carbon and nutrients than Eriophorum , with a much greater seasonal variation in demands on storage and retranslocation to and from leaves.
The effects of fertilizer and the water track on leaf growth dynamics and turnover rates were largely nonsignificant, despite major effects on total tiller size and productivity. This is in contrast to previous research on evergreen leaf dynamics, but similar to results of previous research on overall production and biomass regulation in Eriophorum . It is concluded that the graminoid response to increased nutrient availability in the Arctic is to dilute the greater amounts of nutrient uptake by greater growth, so that nearly the same metabolic homeostasis is achieved as under low nutrient availability, but at a higher biomass.     

Response of dark respiration to temperature in Eriophorum vaginatum from a 30-year-old transplant experiment in Alaska

Background: In the Arctic region, temperature increases are expected to be greater under anticipated climate change than the global average. Understanding how dark respiration (R_d) of common Arctic plant species acclimates to changes in the environment is therefore important for predicting changes to the Arctic carbon balance.

Aims: The aim of this study is to investigate the influence of genotype and growing environment on R_d, the temperature response (Q₁₀) of R_d, and foliar N (N_leaf) of the Arctic sedge Eriophorum vaginatum.

Methods: We measured R_d, and determined its Q₁₀ and N_leaf of E. vaginatum populations that were reciprocally transplanted 30 years previously along a latitudinal transect of 370 km in northern Alaska.

Results: R_d and Q₁₀ did not differ among populations (ecotypes) of E. vaginatum, but the local environment had a significant effect on both variables. R_d as well as N_leaf was higher in northern, colder sites, while Q₁₀ was lower there.

Conclusions: R_d in the different populations of E. vaginatum is a very plastic trait and controlled by growing environment, as is N_leaf. The lower Q₁₀ values in the northern sites were most likely a consequence of substrate inhibition of R_d at higher temperatures.     

Temperature effect on growth rates of Eriophorum vaginatum roots

Summary Root growth rates of the sedge Eriophorum vaginatum L. were studied under controlled environmental conditions. The air temperature was maintained constant at 15°C while the root temperatures varied in 5°C intervals between 2° and 37° C (12° C excluded). Root growth rates of 1.2 mm d^-1 at 2°, 20.4 mm d^-1 at 32° C and 10.1 mm d^-1 at 37° C were recorded. A Q₁₀ of 3.2 was calculated for the temperature range from 7° to 27° C. Root growth rates at temperatures above 17° C declined after one week of growth. The degree of decline was proportional to the applied root temperature. Depletion of available nonstructural carbohydrate was the probable cause for this decline.     

Northward displacement of optimal climate conditions for ecotypes of Eriophorum vaginatum L. across a latitudinal gradient in Alaska

Plants are often genetically specialized as ecotypes attuned to local environmental conditions. When conditions change, the optimal environment may be physically displaced from the local population, unless dispersal or in situ evolution keep pace, resulting in a phenomenon called adaptational lag. Using a 30‐year‐old reciprocal transplant study across a 475 km latitudinal gradient, we tested the adaptational lag hypothesis by measuring both short‐term (tiller population growth rates) and long‐term (17‐year survival) fitness components of Eriophorum vaginatum ecotypes in Alaska, where climate change may have already displaced the optimum. Analyzing the transplant study as a climate transfer experiment, we showed that the climate optimum for plant performance was displaced ca. 140 km north of home sites, although plants were not generally declining in size at home sites. Adaptational lag is expected to be widespread globally for long‐lived, ecotypically specialized plants, with disruptive consequences for communities and ecosystems.     

Growth and tillering patterns within tussocks of Eriophorum vaginatum

Growth patterns were investigated for Eriophorum vaginatum tussocks from disturbed and undisturbed tussock tundra at two sites in Alaska. Total basal area of tussocks decreased with increased cryoturbation but mean basal area per tussock did not. Flowering was observed in tussocks of significantly smaller size on disturbed compared to undisturbed tundra. For tussocks with < 10% cover by shrubs and moss, number of tillers per tussock was linearly related to tussock diameter in most disturbed and undisturbed sites. Exceptions occurred in an area that had been bladed with a bulldozer 7 yr before our survey where tiller number increased as the square of diameter and in an area with much frost activity where tiller number was not emulated with diameter. The ratio of daughter tillers to adult tillers decreased with diameter in disturbed tundra, whereas the trend was less pronounced in undisturbed tundra.
Microsuccession in undisturbed tussock tundra was investigated by sampling tussocks with different amounts of shrub and moss cover for number of daughter tillers per adult tiller, weight per tiller, percent nitrogen, and percent phosphorus. Small tussocks without cover by other species and large, partially covered tussocks were not significantly different by any measures, but tussocks that were almost completely buried had significantly (p < 0.05) lower values of tillering index, weight per tiller, and percent phosphorus.     

Reproductive effort in cotton grass tussock tundra

Eriophorum vaginatum ssp. spissum is a dominant plant species of undisturbed cotton grass tussock tundra in Alaska. It also quickly invades and dominates recently disturbed sites. The hypothesis tested in this research was that the success of E. vaginatum on disturbed sites might be achieved through a higher allocation of biomass to reproductive structures relative to other tundra species. Reproductive allocation of tundra plants in general also was compared with plants of the temperate zone. The results indicate that E. vaginatum is about average among the common tundra species in terms of total reproductive allocation, allocation to seeds, and the proportion of total reproductive allocation that is accounted for by viable seeds. Tundra species, on a relative basis, allocate less biomass to all reproductive structures than temperate species but not necessarily less biomass to the output of viable seeds.     

Downslope fertilizer movement in arctic tussock tundra

Slow release fertilizer pellets (NPK) were spread in June and July 1985, on the frost surface under an 8–20 cm thick layer of thawed tundra in the northern foothills of the Brooks Range, Alaska. The fertilizer was applied at a rate of 3.8 kg N, 1.2 kg P₂O₅, and 2.4 kg K to two, 10 × 0.75 m tussock bands. These bands were placed parallel to the contour lines in the middle of a uniform 10° slope. The purpose of the experiment was to test the hypothesis that fertilizer moves at a measurable rate downslope, affecting the vegetation in its course. The results support this hypothesis. One year after fertilizer application, plants collected 2 to 6 m downslope from the fertilizer band had significantly larger leaves and significantly higher nitrogen and phosphorus concentrations than those upslope from fertilizer application. It is concluded that nutrient-releasing tundra perturbations affect the downslope tundra vegetation.     

In vitro-regenerated wetland sedge Eriophorum vaginatum L. is genetically stable

Eriophorum vaginatum L. is a promising species for phytostabilization, restoration, or creation of wetlands, because it can survive in cold, nutrient-poor, or metal-contaminated soils. However, its propagation on a large scale is problematic due to the infrequent production of viable seeds, seed dormancy, and the limitations of reproduction by rhizomes. A technique to rapidly and effectively produce large quantities of outplanting stock of this species was sought. Seeds of E. vaginatum were cultured on Murashige and Skoog (MS) medium supplemented with plant growth regulators at different concentrations. The highest regeneration rate was obtained on MS medium supplemented with 2.26???M 2,4-dichlorophenoxyacetic acid (2,4-D) and 2.32???M kinetin (KIN) for callus induction, and 17.76???M BA (6-benzylaminopurine) for shoot regeneration as well as when 2.26???M 2,4-D and 4.65???M KIN was added to the callus-induction medium, and 8.88???M or 17.76???M BA to the shoot-regeneration medium. The regenerated shoots were rooted on MS medium without growth regulators and acclimatized in a greenhouse. Genetic stability of the in vitro regenerants was determined using flow cytometry and random amplified polymorphic DNA. Cytometric analysis revealed that the nuclear DNA content was similar in all plant materials and amounted to about 0.8?pg/2C. The PCR amplification products were monomorphic in callus-derived plants and similar to plants grown in a field. Lack of genome size variation and polymorphism within the regenerants indicates that the detailed E. vaginatum micropropagation protocol allows the production of a large number of genetically stable plants.     

Competition for nitrogen in a tussock tundra ecosystem

Summary The objective was to measure the competition for nitrogen among vascular plants, mosses, and soil microbes along a continuum of nitrogen availability, induced by carbon and nitrogen amendments, in a tussock tundra ecosystem.¹⁵N was used as a tracer. Vascular plants showed an increasing¹⁵N recovery with increasing time and with increasing nitrogen availability; the latter suggests that nitrogen was limiting vascular plant growth. Green mosses took up¹⁵N initially, but showed no significant trends with either treatment or time. There was a higher¹⁵N recovery in the soil insoluble compartment for the carbon-amended treatment than in the nitrogen-amended treatments; this suggested that carbon as an energy source limited microbial activity. After two months, the relative¹⁵N recovery fell in the order: soil microbes (79%)>vascular plants (16%) >green mosses (2%).     

Seasonal root growth in the arctic tussock tundra

Summary The quantity of growing root tips per unit of soil volume was analyzed in a central Alaskan tussock tundra site. By June 10, the aboveground fraction of the vegetation had initiated the flush of spring growth and flowering while less than 5 active root tips cm^-3 were found. By June 25 this value had increased to 30 root tips cm^-3. Similar values in July were followed by a complete cessation of root growth after the first week of August. By then, leaf senescence had also become visible. In the spring, low root temperatures were responsible for the time lag between shoot growth initiation and the beginning of root growth. In early August, root growth stopped in spite of adequate soil temperatures and accumulated carbohydrate for root growth. It is proposed that use of reserve carbohydrate for root growth in August would compromise the flush of spring growth in the following year.     

Rhizospheric exudation of Eriophorum vaginatum L. — Potential link to methanogenesis

Root exudates are a direct link between primary production in higher plants and methanogenesis. The relationship has been widely studied on rice paddies, but less is known about its role in wetlands populated by naturally occurring species. This study provides information about the amount and composition of root exudates produced by a widespread mire plant, Eriophorum vaginatum L. For this purpose, E. vaginatum plants were grown in quartz sand in pots from April to October, and root exudates were collected once a month by percolation of the cultivation substrate. In June and October, a set of plants was labelled with ¹⁴CO₂ for two days and subsequently harvested for the determination of dry weight and for root exudates collected by the dipping method. The study supports earlier findings that natural wetland plants can enhance methanogenesis in their rhizosphere via active and seasonally varying exudation, but that the amount of exuded carbon (C) is many times lower than that delivered via litter formation. At both harvests in June and October, the proportion of incorporated radioactivity in shoots, roots and exudates was 92–96%, 4–8%, and 0.2%, respectively. New C was primarily fixed in the metabolically important carbohydrates, as well as acid anions that composed the main compounds of the new exudates. However, microbes seemed to rapidly metabolise the exudates into other substances like acetate. This was the dominant compound in the rhizoplane and rhizosphere, and it was the only detected substance that occurred in higher amounts outside the roots than inside them. Further studies in the field, including the quantification of gaseous end products, are necessary to complete our understanding of the carbon cycling in E. vaginatum-soil-microbe-system.     

Climate and species affect fine root production with long-term fertilization in acidic tussock tundra near Toolik Lake,Alaska

Long-term fertilization of acidic tussock tundra has led to changes in plant species composition, increases in aboveground production and biomass and substantial losses of soil organic carbon (SOC). Root litter is an important input to SOC pools, although little is known about fine root demography in tussock tundra. In this study, we examined the response of fine root production and live standing fine root biomass to short- and long-term fertilization, as changes in fine root demography may contribute to observed declines in SOC. Live standing fine root biomass increased with long-term fertilization, while fine root production declined, reflecting replacement of the annual fine root system of Eriophorum vaginatum, with the long-lived fine roots of Betula nana. Fine root production increased in fertilized plots during an unusually warm growing season, but remained unchanged in control plots, consistent with observations that B. nana shows a positive response to climate warming. Calculations based on a few simple assumptions suggest changes in fine root demography with long-term fertilization and species replacement could account for between 20 and 39% of the observed declines in SOC stocks.     

The role of Eriophorum vaginatum in CH4 flux from an ombrotrophic peatland

Vegetation composition was found to be an important factor controlling CH₄ emission from an ombrotrophic peatland in the UK, with significantly greater (P < 0.01) CH₄ released from areas containing both Eriophorum vaginatumL. and Sphagnum, than from similar areas without E. vaginatum. Positive correlations were observed between the amount of E. vaginatum and CH₄ emission, with the best predictor of flux being the amount of below-ground biomass of this species (r ² = 0.93). A cutting experiment revealed that there was no significant difference (P > 0.05) in CH₄ flux between plots with E. vaginatum stems cut above the water table and plots with intact vegetation, yet there was a 56% mean reduction in CH₄ efflux where stems were cut below the water table (P < 0.05). The effect of E. vaginatum on CH₄ release was mimicked by the presence of inert glass tubes. These findings suggest that the main short-term role of E. vaginatum in the ecosystem is simply as a conduit for CH₄ release. The longer-term importance of E. vaginatum in controlling CH₄ fluxes through C substrate input was suggested by the positive correlation between the night-time CO₂ and CH₄ fluxes (r ² = 0.70), which only occurred when the vegetation was not senescent. This revised version was published online in June 2006 with corrections to the Cover Date.     

Summer temperature increase has distinct effects on the ectomycorrhizal fungal communities of moist tussock and dry tundra in Arctic Alaska

Arctic regions are experiencing the greatest rates of climate warming on the planet and marked changes have already been observed in terrestrial arctic ecosystems. While most studies have focused on the effects of warming on arctic vegetation and nutrient cycling, little is known about how belowground communities, such as fungi root‐associated, respond to warming. Here, we investigate how long‐term summer warming affects ectomycorrhizal (ECM) fungal communities. We used Ion Torrent sequencing of the rDNA internal transcribed spacer 2 (ITS2) region to compare ECM fungal communities in plots with and without long‐term experimental warming in both dry and moist tussock tundra. Cortinarius was the most OTU‐rich genus in the moist tundra, while the most diverse genus in the dry tundra was Tomentella. On the diversity level, in the moist tundra we found significant differences in community composition, and a sharp decrease in the richness of ECM fungi due to warming. On the functional level, our results indicate that warming induces shifts in the extramatrical properties of the communities, where the species with medium‐distance exploration type seem to be favored with potential implications for the mobilization of different nutrient pools in the soil. In the dry tundra, neither community richness nor community composition was significantly altered by warming, similar to what had been observed in ECM host plants. There was, however, a marginally significant increase in OTUs identified as ECM fungi with the medium‐distance exploration type in the warmed plots. Linking our findings of decreasing richness with previous results of increasing ECM fungal biomass suggests that certain ECM species are favored by warming and may become more abundant, while many other species may go locally extinct due to direct or indirect effects of warming. Such compositional shifts in the community might affect nutrient cycling and soil organic C storage.