Soil seed banks and restoration potential of tussock sedge meadows after farming in Changbai Mountain, China

Vast tracts of the wettest agricultural fields have been abandoned worldwide, hence knowledge of their restoration potential is becoming important. Soil seed banks can be important components of ecological restoration, particularly if the seeds of key structural dominants can survive periods of cultivation. In Changbai Mountain, China, we compared the seed banks and standing vegetation between natural sedge meadows and adjacent paddy fields under drained and flooded conditions. The tussock-forming sedge Carex schmidtii dominated plant communities in the natural sedge meadows. However, this key structural dominant species was not found in the paddy fields. Other important wetland species survived cultivation as seeds (e.g. Cyperus fuscus, Lythrum salicaria and Sagittaria trifolia). Species of various life history types require either drawdown (emergent; e.g. C. schmidtii) or flooding (e.g. Potamogeton pectinatus) for successful germination. This study indicates that the seed banks of farmed sedge meadows could contribute towards the establishment of new wetland vegetation assemblages. Active revegetation of sedge meadow, particularly the native tussock-forming Carex, and changes in environmental conditions are necessary to support the region’s biodiversity.

Microhabitat use by plateau pikas: living on the edge

Mammals rely on habitat resources for survival and reproduction. We studied microhabitats used by plateau pikas (Ochotona curzoniae) of the Qinghai-Tibetan Plateau. Microhabitat features used by pikas include sedge meadows that provide forage, burrows that provide safety from predators and cover for nests, degraded open-dirt patches, and edges between sedge meadow and open dirt patches that often have a “lip” between those microhabitats. We investigated the extent to which these edges might serve as a preferred pika microhabitat. GIS techniques were used to overlay individual pika home ranges, determined by focal and scan sampling, on a digitized map containing microhabitat features. Regions that contained multiple coinciding individual home ranges, referred to as overlap polygons, were categorized numerically based on the number of individual home ranges that overlapped each polygon. These overlap polygons were used as relative measures of pika activity. We tested the spatial relationship between pika activity and the microhabitat features of edges, burrows, and proportional area of sedge. There was a significant relationship between the number of pikas in an overlap polygon and the number of pikas in an adjacent polygon. This pattern was controlled statistically to test whether activity was influenced by the presence of potentially favorable microhabitat features. Most of the variation in number of pikas that overlapped a habitat polygon was associated with the relative amount of “edge microhabitat” between sedge meadow and degraded open dirt patches (Cohen’s effect size, f2 = 0.91). Neither burrow openings nor sedge had a strong influence on the number of pika home ranges that overlapped. The importance of microhabitat edges appeared high for plateau pikas.

Importance of tussocks in supporting plant diversity in Carex schmidtii Meinsh. wetlands

Tussocks created by Carex schmidtii in sedge meadows may be able to support biodiversity because of their structural complexity. Concerns about diversity loss and the potential to restore species-rich tussocks led us to investigate how tussocks foster high species richness and affect composition. We investigated vegetation in paired plots on and between tussocks of C. schmidtii, and measured environmental factors on and between tussocks. In all, 79 taxa were found in the sedge meadows. Species richness was higher on rather than between tussocks. During the growing season, the tops of tussocks were above the water level, whereas the area between tussocks was flooded. Soil temperature, organic carbon, soil total P and litter depth were higher on rather than between tussocks. Soil water content and soil total N were lower on than between tussocks. Species richness on tussocks increased with increasing tussock basal area, height and surface area. Based on canonical correspondence analysis, plant composition was mostly related to field water depth, organic carbon and tussock basal area. We conclude that tussocks enhance species richness by increasing surface area, and support a diversity of co-occurring species by creating at least two distinct microhabitats.

Phytocoenotic diversity and dynamics of the communities of association Caricetum gracilis Savich 1926 under the xerophytization of the Desna River floodplain

The paper presents the results of a comparative analysis of the floristic and phytocoenotic diversity within widespread association of acute sedge meadows Caricetum gracilis Savich 1926 in the floodplain of the Desna River (Bryansk and Smolensk regions, Russia). Available geobotanical data on Desna floodplain, collected in the last 40 years, allowed identifying the main dynamic trends in the syntaxonomical space. Based on 36 relevés made by the authors in 1975–1990 previously (Bulokhov, 2001) 3 subassociations, which communities were prevalent in the Desna valley, were established: Caricetum gracilis typicum, С. g. oenanthetosum aquaticae, С. g. beckmannietosum eruciformis. As a survey of the Desna floodplain in 2015–2018 showed, both flow decrease and drop in the level of spring flood and groundwater in the XXI century have led to a change in the appearance, floristic composition, and structure of acute sedge meadows. Xerophytization of the floodplain resulted in the disappearance of the С. g. oenanthetosum aquaticae and С. g. beckmannietosum eruciformis communities. Drying of typical habitats of moist acute sedge meadows became the background of the formation of diverse communities of other types in their place. In the coenoflors of these communities changes occurred at the class level from Phragmito-Magnocaricetea Klika in Klika et Novák 1941 to Molinio-Arrhenatheretea Tx. 1937. Two groups of communities have been formed. The first group is represented by syntaxa of the alliance Magnocaricion gracilis (class Phragmito-Magnocaricetea): Caricetum gracilis typicum with variant Achillea salicifolia as well as by the communities Lythrum salicaria, Calystegia sepium, Calamagrostis canescens. The share of the alliance characteristic species in their coenofloras is 54–64%, and Carex acuta, as a rule, dominates. The second group represents the communities of wet meadows (order Molinietalia caeruleae) of the class Molinio-Arrhenatheretea. The alliance Deschampsion cespitosae is established with subass. Poo palustris–Alopecuretum pratensis typicum (with three variants: Veronica longifolia, Hierochloё odorata, Galium physocarpum) and three communities (Cirsium arvense, Lysimachia vulgaris, Stachys palustris) The share of characteristic species of the order in their coenofloras is 58–95%. All communities and variants form series along the moisture gradient in habitats of acute sedge meadows. Communities Lythrum salicaria, Calystegia sepium, Calamagrostis canescens are distributed in the wettest and richest in mineral nitrogen habitats in the Middle Desna area, in the former long-flooded low-level floodplain. The other ones occur, first of all, in the Upper and Middle Desna areas on a short- and long-flooded floodplain of an average level. These communities are forming on moist and fresh soils. The variants and communities on the gradients of moisture and the richness of mineral nitrogen of the soil were ordinated using the ecological scales of H. Ellenberg et al. (1992). Serial communities form an ecological-dynamic sere on a humidity gradient, showing the direction of their dynamics. The same localization of studies carried out both in 1975–1990 and in 2015–2018 identified changes in vascular plant coenoflora of the ass. Caricetum gracilis for this period: from 62 species in 1975–1990 to 143 species in 2015–2018. There are three groups of species, which reflects these changes. Besides species affine to the class Phragmito-Magnocaricetea, numerous meadow herbs of the class Molinio-Arrhenatheretea appeared: Agrimonia eupatoria, Agrostis tenuis, Bromopsis inermis, Carex praecox, Dactilys glomerata, Dianthus deltoides, Elytrigia repens, Equisetum arvense, Festuca pratensis, Galium mollugo, Geranium pratense, Galium physocarpum, Hieracium umbellatum, Hierochloё odorata, Lathyrus pratensis, Odontites vulgaris, Poa pratensis, Potentilla argentea, Potentilla erecta, Phleum pratense, Vicia cracca. A complex of ruderal explerent and nitrophilous species with numerous alien ones has been formed: Bidens frondosa, Chamaenerion angustifolium, Cirsium arvense, Echinocystis lobata, Epilobium adenocaulon, E. collinum, E. pseudorubescens, E. tetragonum, Erigeron annuus, E. canadensis, Lactuca serriola, Linaria vulgaris, Senecio jacobaea, Sonchus arvensis. Most of these species are anemoсhores, and their presence in the sedge communities is associated with open site formation due to the soil drying between hummocks, as well as the destruction of sedge tussocks under drying and fire. Over the past decade invasive species Bidens frondosa, Erigeron annuus subsp. septentrionalis, E. canadensis,and Lactuca serriola have become an ordinary component of the Desna’s river valley flora. Trees and shrubs (Acer negundo, Betula pendula, Frangula alnus, Quercus robur, Rosa majalis, Salix cinerea, S. pentandra, Swida alba) enter into meadow communities because the lack of haymowing. The following changes in the life form spectrum took place due to the floodplain xerophytization and acute sedge meadow transformation: the proportion of long-rhizome species decreased, while that of rod-root, short-rhizome, and annuals increased; trees and shrubs appeared. Obvious also are changes in the ecobiomorphspectrum: the proportion of mesomorphic species increased, that of hygromophic and mesogygromorphic ones decreased; xero-mesomorphic plants appeared.

Controls on spatial and temporal patterns of soil nitrogen availability in a High Arctic wetland

Increased soil nutrient availability, and associated increase in vegetation productivity, could create a negative feedback between Arctic ecosystems and the climate system, reducing the contribution of Arctic ecosystems to future climate change. To predict whether this feedback will develop, it is important to understand the environmental controls over nutrient cycling in High Arctic ecosystems, and how they vary over space and time. This study explores the environmental controls over spatial patterns of soil nitrogen availability in a High Arctic wet sedge meadow and how they influence carbon exchange processes. Ion exchange resin membranes measured available inorganic nitrogen in soils throughout the growing season at a high spatial resolution, while environmental variables (e.g. active layer depth, soil temperature, soil moisture) and carbon flux measurements were taken at frequent intervals during the 2016 field season. Environmental measures correlated highly with total and late season nitrate levels (total season dry tracks nitrate R2 = 0.533, total season wet tracks nitrate R2 = 0.803, late season nitrate R2 = 0.622), with soil temperatures at 5 cm depth having the greatest effect. Soil available nitrate and ammonium correlated highly with total and early season gross primary productivity (total season wet tracks R2 = 0.685, early season dry tracks R2 = 0.788, early season wet tracks R2 = 0.785). Higher ammonium concentrations coincided with greater carbon dioxide uptake. Nitrate concentrations correlated strongly to soil moisture, but nitrate levels were much lower than ammonium concentrations, suggesting low rates of nitrification vs. mineralization. Similar patterns were observed regardless of whether the wet-sedge meadow was classified as wet or dry, but the relationships were always stronger in areas classified as wet, indicating the importance of moisture and water availability on abiotic processes in High Arctic wet sedge meadows. Topography played an important role in the movement and transport of water, which influenced how nutrients were cycled and moved within the wetland. Generally, the low-lying areas had the highest inorganic nitrogen concentrations. These results suggest that finer scale processes altering nitrogen availability may influence the overall carbon balance of wet sedge meadows in the High Arctic, and how these ecosystems may respond to changes in climate.