Changes In Community Biomass Research Articles

Phytoplankton Community Responses to Interactions Between Light Intensity, Light Variations, and Phosphorus Supply

In a changing world, phytoplankton communities face a large variety of challenges including altered light regimes. These alterations are caused by more pronounced stratification due to rising temperatures, enhanced eutrophication, and browning of lakes. Community responses toward these effects can emerge as alterations in physiology, biomass, biochemical composition, or diversity. In this study, we addressed the combined effects of changes in light and nutrient conditions on community responses. In particular, we investigated how light intensity and variability under two nutrient conditions influence (1) fast responses such as adjustments in photosynthesis, (2) intermediate responses such as pigment adaptation and (3) slow responses such as changes in community biomass and species composition. Therefore, we exposed communities consisting of five phytoplankton species belonging to different taxonomic groups to two constant and two variable light intensity treatments combined with two levels of phosphorus supply. The tested phytoplankton communities exhibited increased fast reactions of photosynthetic processes to light variability and light intensity. The adjustment of their light harvesting mechanisms via community pigment composition was not affected by light intensity, variability, or nutrient supply. However, pigment specific effects of light intensity, light variability, and nutrient supply on the proportion of the respective pigments were detected. Biomass was positively affected by higher light intensity and nutrient concentrations while the direction of the effect of variability was modulated by light intensity. Light variability had a negative impact on biomass at low, but a positive impact at high light intensity. The effects on community composition were species specific. Generally, the proportion of green algae was higher under high light intensity, whereas the cyanobacterium performed better under low light conditions. In addition to that, the diatom and the cryptophyte performed better with high nutrient supply while the green algae as well as the cyanobacterium performed better at low nutrient conditions. This shows that light intensity, light variability, and nutrient supply interactively affect communities. Furthermore, the responses are highly species and pigment specific, thus to clarify the effects of climate change a deeper understanding of the effects of light variability and species interactions within communities is important.

Soil temperature effects on the structure and diversity of plant and invertebrate communities in a natural warming experiment.

Global warming is predicted to significantly alter species physiology, biotic interactions and thus ecosystem functioning, as a consequence of coexisting species exhibiting a wide range of thermal sensitivities. There is, however, a dearth of research examining warming impacts on natural communities.Here, we used a natural warming experiment in Iceland to investigate the changes in above‐ground terrestrial plant and invertebrate communities along a soil temperature gradient (10°C–30°C).The α‐diversity of plants and invertebrates decreased with increasing soil temperature, driven by decreasing plant species richness and increasing dominance of certain invertebrate species in warmer habitats. There was also greater species turnover in both plant and invertebrate communities with increasing pairwise temperature difference between sites. There was no effect of temperature on percentage cover of vegetation at the community level, driven by contrasting effects at the population level.There was a reduction in the mean body mass and an increase in the total abundance of the invertebrate community, resulting in no overall change in community biomass. There were contrasting effects of temperature on the population abundance of various invertebrate species, which could be explained by differential thermal tolerances and metabolic requirements, or may have been mediated by changes in plant community composition.Our study provides an important baseline from which the effect of changing environmental conditions on terrestrial communities can be tracked. It also contributes to our understanding of why community‐level studies of warming impacts are imperative if we are to disentangle the contrasting thermal responses of individual populations.

Global Warming Impacts on Alpine Vegetation Dynamic in Qinghai-Tibet Plateau of China

This study is to illustrate alpine vegetation dynamics in Qinghai-Tibetan Plateau of China from simulated filed experimental climate change, vegetation community dynamic simulation integrated with scenarios of global temperature increase of 1 to 3°C, and simulated regional alpine vegetation distribution changes in responses to global warming. Our warming treatment increased air temperatures by 5°C on average and soil temperatures were elevated by 3°C at 5 cm depth. Above- ground biomass of grasses responded rapidly to the warmer conditions whereby biomass was 25% greater than that of controls after only 5 wk of experimental warming. This increase was accompanied by a simultaneous decrease in forb biomass, resulting in almost no net change in community biomass after 5 wk. Under warmed conditions, peak community bio-mass was extended into October due in part to continued growth of grasses and the postponement of senescence. The Vegetation Dynamic Simulation Model calculates a probability surface for each vegetation type, and then combines all vegetation types into a composite map, determined by the maximum likelihood that each vegetation type should distribute to each raster unit. With scenarios of global temperature increase of 1°C to 3°C, the vegetation types such as Dry Kobresia Meadow and Dry Potentilla Shrub that are adapted to warm and dry conditions tend to become more dominant in the study area.

Changes in Community Biomass along Snow-melting Gradient in Alpine Meadow*

In an alpine snowf ield on the eastern Qinghai-Tibetan Plateau,three sites were chosen along snow-melting gradient for this study,and the environmental factors and biomass of these sites were measured and compared. The result indicated that the snow melting time,soil water content and amplitude of diurnal temperature variance at soil surface were signif icantly different in the three sites,while no signif icant differences in soil nutrient contents (total N,total P,total K,soluble N,soluble P) and pH were found. From early-to late-melting sites,aboveground biomass,total biomass and ratio of below-to aboveground biomass increased,but underground biomass decreased. Comparison with late-melting site,the aboveground biomass in early-melting site largely distributed in a range of 0～10 cm above ground,indicating that plants in the early-melting site were shorter than those in the late-melting site. Unlike the aboveground biomass,the underground biomass in the early-melting site almost distributed evenly in soil at different depths. Underground biomass in the late-melting site mainly distributed in a layer of 0～10 cm below ground. All the results suggested that the changing trend of biomass was principally affected by soil water content and diurnal soil surface temperature variance in each site. Fig 5,Tab 2,Ref 33

Species removal and experimental warming in a subarctic tundra plant community

Neighbor interactions are likely to play an important role in subarctic plant communities. We conducted experiments in Interior Alaska in which we crossed species removal with greenhouse warming manipulations. We examined changes in community biomass, and in plant survival and growth of individual species in response to experimental warming and to: (1) removal of whole species versus an equivalent amount of biomass across many species, and (2) removal of subdominant (locally common) versus minor (locally uncommon) plants. Community biomass indicated compensation in growth after removal of minor species and after biomass removal without elimination of entire species, but under-compensation after removal of subdominants. Growth and survival of individual species showed facilitation between some species. Warming increased growth of dominant vascular plants, but at the same time reduced survival, and these impacts were greater for larger, more mesic species than for the smaller species associated with drier habitats. Growth of mosses was reduced by the warming. Removal effects did not differ between warming and ambient conditions. The results indicate that common species are able to reduce resources for others (competitive effect) and increase their growth after neighbor removal, whereas locally uncommon species are not able to respond rapidly to increased resources made available by neighbor removal. Therefore, the impact of the presence of common species on locally uncommon species was facilitative overall, but not vice versa. The balance between disturbances such as changes in temperature and species losses from the community will likely be crucial in determining shifts in subsequent community composition.

Effect of DNase and Antibiotics on Biofilm Characteristics

The role of extracellular DNA in the maintenance of biofilms formed by gram-positive and gram-negative bacteria was studied. This study evaluated all the bacterial strains that were tested for the presence of extracellular DNA with an average size of 30 kb in the matrix. Our results indicate changes in community biomass, architecture, morphology, and the numbers of CFU in the presence of DNase. This effect seems to be common to biofilms established by various unrelated gram-positive and gram-negative bacteria. The cleavage of extracellular DNA leads to the formation of an altered biofilm that permits the increased penetration of antibiotics. Thus, the addition of DNase enhances the effect of antibiotics, resulting in decreased biofilm biomass and numbers of CFU.

Species richness and susceptibility to heat and drought extremes in synthesized grassland ecosystems: compositionalvsphysiological effects

SummaryWe investigated effects of declining plant species richness (S) on resistance to extremes in grassland communities.Synthesized model ecosystems of differentS, grown outdoors in containers, were exposed to a stress peak combining heat and drought. The heat wave was induced experimentally by infrared irradiation in free air conditions.Before the heat wave, the more species‐rich communities produced more biomass as a result of a large and positive complementarity effect that outweighed a small negative selection effect.Water use during the heat wave was likewise enhanced byS, which could not be attributed to dominance of ‘water‐wasting’ species. Instead, water consumption at highSexceeded that expected from changes in community biomass and biomass composition. The observed enhancement of resource (water) acquisition under stress with increasingStherefore probably originated from complementarity.Despite enhanced water use in the more diverse communities, plant survival was significantly less, affecting all species alike. Physiological stress, recorded as photochemical efficiency of photosystem II electron transport, was significantly greater. Before the heat wave, the changes in biomass composition that coincided with increasingSdid not favour species that would later prove intrinsically sensitive or insensitive.Complementarity in resource use for biomass production had a cost in terms of reduced survival under stress, despite the likelihood of complementarity in water acquisition during exposure. The greater loss of individuals from the more diverse grasslands suggests enhanced risk of local extinction.

Species Diversity and Biomass Stability

With the current accelerating rate of biodiversity extinction, there is great interest in how species diversity influences ecosystem properties. In this article, we investigate the relationship between species diversity and the stability of community biomass in the face of stochastic perturbations of species' abundances. The model explicitly includes species' interactions. We show that the pattern of species' interactions affects whether the relationship between diversity and biomass stability is positive or negative. In particular, assumptions about community structure influence the relationship between species diversity and community biomass, which in turn influences the diversity-stability relationship. We also discuss the relationship between diversity and another type of stability, the proportional change in community biomass with the extinction or introduction of a species. Regardless of community type, diversity buffers the change in biomass when a species is added or removed.

Tibetan Alpine Tundra Responses to Simulated Changes in Climate: Aboveground Biomass and Community Responses

High-elevation ecosystems are predicted to be some of the terrestrial habitats most sensitive to changing climates. The ecological consequences of changes in alpine tundra environmental conditions are still unclear especially for habitats in Asia. In this study we report findings from a field experiment where an alpine tundra grassland on the Tibetan plateau (37'N, 101oE) was exposed to experimental warming, irradiance was lowered, and wind speed reduced to simulate a suite of potential changes in environmental conditions. Our warming treatment increased air temperatures by 5oC on average and soil temperatures were elevated by 3'C at 5 cm depth. Aboveground biomass of grasses responded rapidly to the warmer conditions whereby biomass was 25% greater than that of controls after only 5 wk of experimental warming. This increase was accompanied by a simultaneous decrease in forb biomass, resulting in almost no net change in community biomass after 5 wk. Lower irradiance reduced grass biomass during the same period. Under ambient conditions total aboveground community biomass increased seasonally from 161 g m-2 in July to a maximum of 351 g m-2 in September, declining to 285 g m-2 in October. However, under warmed conditions, peak community biomass was extended into October due in part to continued growth of grasses and the postponement of senescence. Our findings indicate that while alpine grasses respond favorably to altered conditions, others may not. And, while peak community biomass may actually change very little under warmer summers, the duration of peak biomass may be extended having feedback effects on net ecosystem CO2 balances, nutrient cycling, and forage availability.