Regional adaptation improves the performance of grassland plant communities

Many plant species are adapted locally or regionally. Whether such individual species performance translates into effects at community and ecosystem levels has rarely been tested. Such tests are crucial, however, to predict ecosystem consequences of sowing seed mixtures for grassland restoration or hay production. We compared the performance of replicated sown plant communities of regional origin with the performance of four foreign communities consisting of the same grassland species but originating from distances up to 890 km from our experimental site. The regional communities performed better than foreign communities in plant cover and diversity but not in aboveground biomass production. Additionally, in communities based on regional seeds fewer unsown species occurred and less bare ground was left open for erosion. Variation in community performance among source regions was related to climatic differences rather than to geographic distance to source regions. Individual species performance only partly explained community patterns, highlighting the importance of community level experiments. Our results suggest that the use of regional seeds represents an important approach to improve sown managed grasslands.     

Independent evolution of leaf and root traits within and among temperate grassland plant communities

In this study, we used data from temperate grassland plant communities in Alberta, Canada to test two longstanding hypotheses in ecology: 1) that there has been correlated evolution of the leaves and roots of plants due to selection for an integrated whole-plant resource uptake strategy, and 2) that trait diversity in ecological communities is generated by adaptations to the conditions in different habitats. We tested the first hypothesis using phylogenetic comparative methods to test for evidence of correlated evolution of suites of leaf and root functional traits in these grasslands. There were consistent evolutionary correlations among traits related to plant resource uptake strategies within leaf tissues, and within root tissues. In contrast, there were inconsistent correlations between the traits of leaves and the traits of roots, suggesting different evolutionary pressures on the above and belowground components of plant morphology. To test the second hypothesis, we evaluated the relative importance of two components of trait diversity: within-community variation (species trait values relative to co-occurring species; α traits) and among-community variation (the average trait value in communities where species occur; β traits). Trait diversity was mostly explained by variation among co-occurring species, not among-communities. Additionally, there was a phylogenetic signal in the within-community trait values of species relative to co-occurring taxa, but not in their habitat associations or among-community trait variation. These results suggest that sorting of pre-existing trait variation into local communities can explain the leaf and root trait diversity in these grasslands.     

Constraints in the restoration of ecological diversity in grassland and heathland communities

Species-rich grassland and heathland communities still occur in low-intensity farming systems in many European countries. Gradually, such systems have either been abandoned or more intensively exploited, with a subsequent decrease in species numbers. Until recently, it was thought that restoration of these communities would be straightforward. However, abiotic constraints (with respect to eutrophication and acidification) have hampered restoration more than previously thought. Moreover, very recent research has revealed that biotic constraints can also be important: many plant species are not present in the soil seed bank and their dispersal is limited in the present fragmented landscape.     

Problems in heathland and grassland dynamics

A review of factors governing vegetation change in heathlands and grasslands is presented, with emphasis on soil factors. Climate, microclimate, fire, fauna, grazing by vertebrates, grazing by invertebrates, disease, dispersal, establishment, competition, allelopathy, stabilization, soil formation and podzolization are discussed with emphasis on inconsistencies and lacks in our present knowledge. Examples are mainly from NW European Calluna heath and related woodlands.Nomenclature follows Clapham, Tutin & Warburg (1962) for vascular plants; species not included in this work have authorities cited in the text.     

Winter photosynthetic activity of twenty temperate semi-desert sand grassland species

The winter photosynthetic activity (quantified by net CO(2) assimilation rates and chlorophyll (Chl) a fluorescence parameters) of 20 plant species (including two lichens and two mosses) of a Hungarian temperate semi-desert sand grassland was determined on one occasion per year in 1984, 1989 and 1994. Throughout winter, the overwintering green shoots, leaves or thalli were regularly exposed to below zero temperatures at night and daytime temperatures of 0-5 degrees C. In situ tissue temperature varied between -2.1 and +6.9 degrees C and the photosynthetic photon flux density (PPFD) between 137 and 351 micromol m(-2)s(-1). Under these conditions 18 of the grassland species exhibited photosynthetic CO(2) uptake (range: vascular plants ca. 0.2-3.8 micromol m(-2)s(-1), cryptogams 0.3-2.79 micromol kg(-1)s(-1)) and values of 0.9-5.1 of the Chl fluorescence decrease ratio R(Fd). In 1984, Festuca vaginata and Sedum sexangulare had net CO(2) assimilation at leaf temperatures of -0.85 to -1.2 degrees C. In 1989, all species except Cladonia furcata showed net CO(2) assimilation at tissue temperatures of 0 to +3.3 degrees C, with the highest rates observed in Poa bulbosa and F. vaginata. The latter showed a net CO(2) assimilation saturation at a PPFD of 600 micromol m(-2)s(-1) and a temperature optimum between +5 and +18 degrees C. At the 1994 measurements, the photosynthetic rates were higher at higher tissue water contents. The two mosses and lichens had a net photosynthesis (range: 1.1-2.79 micromol CO(2)kg(-1)s(-1)) at 2 degrees C tissue temperature and at 4-5 degrees C air temperature. Ca. 80% of the vascular grassland plant species maintained a positive C-balance during the coldest periods of winter, with photosynthetic rates of 1.5-3.8 micromol CO(2)m(-2)s(-1). In an extremely warm beginning March of the relatively warm winter of 2006/2007, the dicotyledonous plants had much higher CO(2) assimilation rates on a Chl (range 6-14.9 micromol g(-1)Chl s(-1)) and on a dry weight basis (9-48 micromol kg(-1)dw s(-1)) than in the cold winter of 1994. However, the assimilation rates of the three investigated cryptogams (Tortula and two Cladonia) and the two grasses Festuca and Poa were not affected by this increase. The results indicate that the photosynthetic activity of temperate semi-desert sand grassland species can help somewhat in slowing the general CO(2) rise in winter and function as a potential carbon sink of the investigated semi-desert Hungarian grassland species.     

Linking landscape history and dispersal traits in grassland plant communities

Dispersal limitation and long-term persistence are known to delay plant species’ responses to habitat fragmentation, but it is still unclear to what extent landscape history may explain the distribution of dispersal traits in present-day plant communities. We used quantitative data on long-distance seed dispersal potential by wind and grazing cattle (epi- and endozoochory), and on persistence (adult plant longevity and seed bank persistence) to quantify the linkages between dispersal and persistence traits in grassland plant communities and current and past landscape configurations. The long-distance dispersal potential of present-day communities was positively associated with the amounts of grassland in the historical (1835, 1938) landscape, and with a long continuity of grazing management—but was not associated with the properties of the current landscape. The study emphasises the role of history as a determinant of the dispersal potential of present-day grassland plant communities. The importance of long-distance dispersal processes has declined in the increasingly fragmented modern landscape, and long-term persistent species are expected to play a more dominant role in grassland communities in the future. However, even within highly fragmented landscapes, long-distance dispersed species may persist locally—delaying the repayment of the extinction debt.     

Variable sensitivity of plant communities in Iceland to experimental warming

Facing an increased threat of rapid climate change in cold‐climate regions, it is important to understand the sensitivity of plant communities both in terms of degree and direction of community change. We studied responses to 3–5 years of moderate experimental warming by open‐top chambers in two widespread but contrasting tundra communities in Iceland. In a species‐poor and nutrient‐deficient moss heath, dominated by Racomitrium lanuginosum, mean daily air temperatures at surface were 1–2°C higher in the warmed plots than the controls whereas soil temperatures tended to be lower in the warmed plots throughout the season. In a species‐rich dwarf shrub heath on relatively rich soils at a cooler site, dominated by Betula nana and R. lanuginosum, temperature changes were in the same direction although more moderate. In the moss heath, there were no detectable community changes while significant changes were detected in the dwarf shrub heath: the abundance of deciduous and evergreen dwarf shrubs significantly increased (>50%), bryophytes decreased (18%) and canopy height increased (100%). Contrary to some other studies of tundra communities, we detected no changes in species richness or other diversity measures in either community and the abundance of lichens did not change. It is concluded that the sensitivity of Icelandic tundra communities to climate warming varies greatly depending on initial conditions in terms of species diversity, dominant species, soil and climatic conditions as well as land‐use history.     

Large-scale manipulation of plant litter and fertilizer in a managed successional temperate grassland

Plant litter may play an important role in herbaceous plant communities by limiting primary production and influencing plant species richness. However, it is not known how the effect of litter interacts with fertilization. We tested for the role of litter and fertilization in a large-scale experiment to investigate effects on diversity and biomass of plant species, growth forms, native vs. non-native groups, and abiotic ecosystem components (e.g., soil moisture, PAR). We manipulated plant litter (removed vs. left in situ) and nutrient availability (NPK-fertilized vs. unfertilized) for 4 years in 314-m² plots, replicated six times, in an old-field grassland. While many of our species-level results supported previously published studies and theory, our plant group results generally did not. Specifically, grass species richness and forb biomass was not affected by either fertilization or plant litter. Moreover, plant litter removal significantly increased non-native plant species richness. Relative to native plant species, all of our experimental manipulations significantly increased both the biomass and the species richness of non-native plant species. Thus, this grassland system was sensitive to management treatments through the facilitation of non-native plant species. We coupled biotic and abiotic components within a nonmetric multidimensional scaling (NMS) analysis to investigate treatment effects, which revealed that specific treatments altered ecosystem development. These results suggest that fertilization and plant litter may have larger impacts on plant communities and on ecosystem properties than previously understood, underscoring the need for larger-scale and longer-term experiments.     

Functional redundancy in a clipping experiment on grassland plant communities

Functional redundancy predicts that some species may play equivalent roles in ecosystem functioning therefore conferring a kind of ‘insurance’ to perturbation when species richness is reduced, by the compensation of species of the same functional group on ecosystem processes. We evaluate functional redundancy on grassland plant communities by a removal experiment in which the evaluated treatments were: GG – clipping two graminoid species, FF – clipping two forb species, GF – clipping one graminoid and one forb species and Control – no removal. We tested the hypothesis that the above‐ground biomass removal of one species of each functional group would cause less change in the community composition (community persistence) and less decrease in biomass production than the above‐ground biomass removal of two species of the same functional group. Functional redundancy was corroborated for community persistence since treatments FG and C caused less change in community composition than treatments GG and FF, although no differences were found between treatments for above‐ground biomass. We verified that clipped species tend to be compensated by an increase in the percent cover of the remaining species of the same functional group. This work provides experimental evidence of early responses after plant clipping in small spatial scale of functional redundancy in naturally established grassland plant communities. We highlight redundancy as an intrinsic feature of communities insuring their reliability, as a consequence of species compensation within functional groups.     

Nitrogen competition between three dominant plant species and microbes in a temperate grassland

Background and aims

To test the hypothesis that dominant plant species could acquire different nitrogen (N) forms over a spatial scale and they also have the ability to compete for available N with microbes.

Methods

A short-term ¹⁵N labeling experiment was conducted in the temperate grassland ecosystem of North China in July of 2013. Three N forms (NO₃ ^? _, NH₄ ⁺ and glycine) labeled with ¹⁵N were injected into the two soil depths (0–5 and 5–15 cm) surrounding each plant to explore N acquisition by plants and microbes. Three dominant plant species (Artemisia frigida, Cleistogenes squarrosa and Artemisia capillaris) were investigated.

Results

Two hours after ¹⁵N labeling, all three dominant plant species absorbed both organic and inorganic N, but different patterns were observed at two soil depths. Uptake of NO₃ ^? was significantly higher at 0–5 cm than at 5–15 cm soil depth among all the dominant plant species. ¹⁵N recovery by microbes was significantly higher than plants. However, ¹⁵N recovery by plants showed different patterns over soil depths.

Conclusions

Dominant plant species in the temperate grassland have different patterns in acquisition of N added to soil in organic form and absorption of inorganic N, and microbes were more effectively than plants at competing for N in a short-term period.

     

Stability in temperate reef communities over a decadal time scale despite concurrent ocean warming

Despite increasing scientific and public concerns on the potential impacts of global ocean warming on marine biodiversity, very few empirical data on community-level responses to rising water temperatures are available other than for coral reefs. This study describes changes in temperate subtidal reef communities over decadal and regional scales in a location that has undergone considerable warming in recent decades and is forecast to be a 'hotspot' for future warming.
Plant and animal communities at 136 rocky reef sites around Tasmania (south-east Australia) were censused between 1992 and 1995, and again in 2006 and 2007. Despite evidence of major ecological changes before the period of study, reef communities appeared to remain relatively stable over the past decade. Multivariate analyses and univariate metrics of biotic communities revealed few changes with time, although some species-level responses could be interpreted as symptomatic of ocean warming. These included fishes detected in Tasmania only in recent surveys and several species with warmer water affinities that appeared to extend their distributions further south. The most statistically significant changes observed in species abundances, however, were not related to their biogeographical affinities. The majority of species with changing abundance possessed lower to mid-range abundances rather than being common, raising questions for biodiversity monitoring and management. We suggest that our study encompassed a relatively stable period following more abrupt change, and that community responses to ocean warming may follow nonlinear, step-like trajectories.     

Above- and belowground insect herbivores differentially affect soil nematode communities in species-rich plant communities

Interactions between above‐ and belowground invertebrate herbivores alter plant diversity, however, little is known on how these effects may influence higher trophic level organisms belowground. Here we explore whether above‐ and belowground invertebrate herbivores which alter plant community diversity and biomass, in turn affect soil nematode communities. We test the hypotheses that insect herbivores 1) alter soil nematode diversity, 2) stimulate bacterial‐feeding and 3) reduce plant‐feeding nematode abundances. In a full factorial outdoor mesocosm experiment we introduced grasshoppers (aboveground herbivores), wireworms (belowground herbivores) and a diverse soil nematode community to species‐rich model plant communities. After two years, insect herbivore effects on nematode diversity and on abundance of herbivorous, bacterivorous, fungivorous and omni‐carnivorous nematodes were evaluated in relation to plant community composition. Wireworms did not affect nematode diversity despite enhanced plant diversity, while grasshoppers, which did not affect plant diversity, reduced nematode diversity. Although grasshoppers and wireworms caused contrasting shifts in plant species dominance, they did not affect abundances of decomposer nematodes at any trophic level. Primary consumer nematodes were, however, strongly promoted by wireworms, while community root biomass was not altered by the insect herbivores. Overall, interaction effects of wireworms and grasshoppers on the soil nematodes were not observed, and we found no support for bottom‐up control of the nematodes. However, our results show that above‐ and belowground insect herbivores may facilitate root‐feeding rather than decomposer nematodes and that this facilitation appears to be driven by shifts in plant species composition. Moreover, the addition of nematodes strongly suppressed shoot biomass of several forb species and reduced grasshopper abundance. Thus, our results suggest that nematode feedback effects on plant community composition, due to plant and herbivore parasitism, may strongly depend on the presence of insect herbivores.     

Flowering phenology in a species-rich temperate grassland is sensitive to warming but not elevated CO2

* Flowering is a critical stage in plant life cycles, and changes might alter processes at the species, community and ecosystem levels. Therefore, likely flowering-time responses to global change drivers are needed for predictions of global change impacts on natural and managed ecosystems. * Here, the impact of elevated atmospheric CO2 concentration ([CO2]) (550 micromol mol(-1)) and warming (+2 masculineC) is reported on flowering times in a native, species-rich, temperate grassland in Tasmania, Australia in both 2004 and 2005. * Elevated [CO2] did not affect average time of first flowering in either year, only affecting three out of 23 species. Warming reduced time to first flowering by an average of 19.1 d in 2004, acting on most species, but did not significantly alter flowering time in 2005, which might be related to the timing of rainfall. Elevated [CO2] and warming treatments did not interact on flowering time. * These results show elevated [CO2] did not alter average flowering time or duration in this grassland; neither did it alter the response to warming. Therefore, flowering phenology appears insensitive to increasing [CO2] in this ecosystem, although the response to warming varies between years but can be strong.     

Effects of long-term experimental warming on plants and soil microbes in a cool temperate semi-natural grassland in Japan

To clarify the effects of long-term warming on ecosystem matter cycling, we conducted an in situ 7-year experimental warming (2009–2015) using infrared heaters in a cool temperate semi-natural grassland in Japan. We measured plant aboveground biomass, soil total C and N, soil inorganic N (NH₄ ⁺-N and NO₃ ^?-N), and soil microbial biomass for 7 years (2009–2015). We also measured heterotrophic respiration for 2 years (2013–2014) and assessed net N mineralization and nitrification in 2015. We found that warming immediately increased plant aboveground biomass, but this effect ceased in 2013. However, the soil microbial biomass was continuously depressed by warming. Soil inorganic N concentrations in warmed plots substantially increased in the later years of the experiment (2013–2015) and the potential net N mineralization rate was also higher than in the earlier years. In contrast, heterotrophic respiration decreased with warming in 2013–2014. Our observations indicate that long-term warming has a contrasting effect on plants and soil microbes. In addition, the warming could have different effects on subterranean C and N cycling. To enhance the accuracy of estimation of future climate change, it is essential to continuously observe the warming effects on ecosystems and to focus on the change in subterranean C and N cycling.     

Limits to tree species invasion in pampean grassland and forest plant communities

Factors limiting tree invasion in the Inland Pampas of Argentina were studied by monitoring the establishment of four alien tree species in remnant grassland and cultivated forest stands. We tested whether disturbances facilitated tree seedling recruitment and survival once seeds of invaders were made available by hand sowing. Seed addition to grassland failed to produce seedlings of two study species, Ligustrum lucidum and Ulmus pumila, but did result in abundant recruitment of Gleditsia triacanthos and Prosopis caldenia. While emergence was sparse in intact grassland, seedling densities were significantly increased by canopy and soil disturbances. Longer-term surveys showed that only Gleditsia became successfully established in disturbed grassland. These results support the hypothesis that interference from herbaceous vegetation may play a significant role in slowing down tree invasion, whereas disturbances create microsites that can be exploited by invasive woody plants. Seed sowing in a Ligustrum forest promoted the emergence of all four study species in understorey and treefall gap conditions. Litter removal had species-specific effects on emergence and early seedling growth, but had little impact on survivorship. Seedlings emerging under the closed forest canopy died within a few months. In the treefall gap, recruits of Gleditsia and Prosopis survived the first year, but did not survive in the longer term after natural gap closure. The forest community thus appeared less susceptible to colonization by alien trees than the grassland. We conclude that tree invasion in this system is strongly limited by the availability of recruitment microsites and biotic interactions, as well as by dispersal from existing propagule sources.