Timo Saarinen

Spatial and temporal performance of the miniface (free air CO2 enrichment) system on bog ecosystems in northern and central Europe

The Bog Ecosystem Research Initiative (BERI) projectwas initiated to investigate, at five climaticallydifferent sites across Europe, the effects of elevatedCO2 and N deposition on the net exchange ofCO2 and CH4 between bogs and the atmosphere,and to study the effects of elevated CO2 and Ndeposition on the plant biodiversity of bogcommunities. A major challenge to investigate theeffects of elevated CO2 on vegetation andecosystems is to apply elevated CO2concentrations to growing vegetation without changingthe physical conditions like climate and radiation.Most available CO2 enrichment methods disturb thenatural conditions to some degree, for instance closedchambers or open top chambers. Free Air CO2Enrichment (FACE) systems have proven to be suitableto expose plants to elevated CO2 concentrationswith minimal disturbance of their natural environment.The size and spatial scale of the vegetation studiedwithin the BERI project allowed the use of a modifiedversion of a small FACE system called MiniFACE. Thispaper describes the BERI MiniFACE design as well asits temporal and spatial performance at the five BERIfield locations. The temporal performance of theMiniFACE system largely met the quality criteriadefined by the FACE Protocol. One minute averageCO2 concentrations measured at the centre of thering stayed within 20% of the pre-set target for morethan 95% of the time. Increased wind speeds werefound to improve the MiniFACE systems temporalperformance. Spatial analyses showed no apparentCO2 gradients across a ring during a 4 day periodand the mean differences between each sampling pointand the centre of the ring did not exceed 10%.Observations made during a windy day, causing aCO2 concentration gradient, and observations madeduring a calm day indicated that short term gradientstend to average out over longer periods of time. On aday with unidirectional strong winds, CO2concentrations at the upwind side of the ring centrewere higher than those made at the centre and at thedownwind side of the ring centre, but the bell-shapeddistribution was found basically the same for thecentre and the four surrounding measurement points,implying that the short term (1 sec) variability ofCO2 concentrations across the MiniFACE ring isalmost the same at any point in the ring. Based on gasdispersion simulations and measured CO2concentration profiles, the possible interferencebetween CO2-enriched and control rings was foundto be negligible beyond a centre-to-centre ringdistance of 6 m.

Minor changes in vegetation and carbon gas balance in a boreal mire under a raised CO2 or NH4NO3 supply

AbstractIncreasing concentrations of carbon dioxide (CO2) in the atmosphere or continuous nitrogen (N) deposition might alter the carbon (C) cycle in boreal mires and thus have significant impacts on the development of climate change. The atmospheric impact of the C cycle in mires is twofold: C accumulation attenuates and CH4 release strengthens the natural greenhouse effect. We studied the effects of an increased supply of CO2 or NH4NO3 on the vegetation and annual CO2 exchange in lawns of a boreal oligotrophic mire in eastern Finland over a 2-year period. Ten study plots were enclosed with mini-FACE (Free Air Carbon Dioxide Enrichment) rings. Five plots were vented with CO2-enriched air (target 560 ppmv), while their controls were vented with ambient air; five plots were sprayed with NH4NO3, corresponding to a cumulative addition of 3 g N m−2 a−1, while their controls were sprayed with distilled water only. A raised NH4NO3 supply seemed to affect the composition of the moss layer. Raised CO2 did not affect the vegetation, but gross photosynthesis increased significantly. The change in net CO2 exchange depended on the annual weather conditions. Our results suggest that C accumulation may increase in wet years and compensate for the warming effect caused by the increase in CH4 release from this mire. In contrast, a relatively dry and warm growing period favors decomposition and can even make the CO2 balance negative. Along with the increased CH4 release under raised CO2, the decreased C accumulation then increases the radiative forcing of boreal mires.

Interactions between snow, canopy, and vegetation in a boreal coniferous forest

Background: Snow is known to have a major impact on the distribution of plants in arctic and alpine ecosystems; however, its impact on understorey vegetation in boreal forests is little reported. Aims: To study the effects of trees on the distribution of snow and examine the small-scale spatial relation between snow distribution and ground vegetation. Methods: Detailed spatial variation in snow depth and summer precipitation, canopy dimensions and locations of individual trees, and ground vegetation cover were observed in a coniferous forest, and the spatial correlations between these variables were examined. Results: Spatial patterns of snow remained unchanged throughout the winter and across two different winters. Snow depth showed significant correlations with different tree influence indices calculated based on the distance to the trunk, height, diameter or canopy extent. Dwarf shrub cover correlated positively with snow, and moss cover correlated negatively with the tree influence indices. The highest covers of Vaccinium myrtillus, V. vitis-idaea and Hylocomium splendens were observed on patches with thick snow cover. Linnaea borealis, in contrast, was absent from these patches. Pleurozium schreberi and Dicranum polysetum were most abundant on patches with moderate snow. Conclusions: Trees do not only affect ground vegetation through competition, but also have indirect effects associated with uneven snow cover. Our results suggest that, like arctic and alpine species, boreal forest understorey species show differences in their snow affinity.

Overwintering of Vaccinium vitis-idaea in two sub-Arctic microhabitats: a reciprocal transplantation experiment

Northern plants have to cope with a wide range of overwintering conditions, as the depth and physical properties of snow show high spatial variation in the Arctic. The overwintering of lingonberry (Vaccinium vitis-idaea) was studied in a reciprocal transplantation experiment between two sub-Arctic microhabitats in northern Finland. The experiment was set up in the autumn, and physiological traits related to overwintering were measured at the time of snowmelt in the following spring. The origin of the plants was not a significant source of variation for most of the traits measured, whereas major differences were observed between the two sites. Plants that overwintered at an exposed site above the treeline showed high relative winter damage, assessed by the electrolyte leakage of the leaves. No severe winter damage was observed in the plants that overwintered under a moderate snowpack at a sheltered birch forest site. These plants were able to maintain their photosynthetic capacity through the winter. A low capacity of photosystem II and a very low capacity of CO2 uptake were characteristic of the exposed site, where low temperatures and high irradiation predominate during late winter. However, photosynthetic capacity was recovered within a few days when the plants were kept under favourable conditions after the field experiment. The content of nonstructural carbohydrates was low, probably because of high respiratory losses under the snow. This short-term study suggests that lingonberry, which occupies a wide range of microhabitats in the present climate, may thrive even if the overwintering conditions change as a result of climatic warming.

Shoot density of Carex rostrata Stokes in relation to internal carbon:nitrogen balance.

Abstract Initiation of new shoots originating from basal meristems of older shoots of Carex rostrata was studied in relation to the internal carbon/nitrogen balance. In a greenhouse experiment, individual shoots with a vigorous formation of a new shoot contained the highest concentrations of free amino acids (FAA) and the lowest concentrations of total nonstructural carbohydrates (TNC), resulting in a low TNC/FAA ratio. Thus shoots with high availability of nitrogenous compounds in relation to carbohydrates started growing a new shoot. The results suggest that TNC/FAA ratios could affect shoot densities. Field measurements supported this view: TNC/FAA ratios were lower in a mesotrophic site with a high density of shoots than in an oligotrophic site with a low density of shoots. Compared with roots, TNC/FAA ratios of shoots seemed to be more decisive both in the greenhouse experiment and in the field. In the greenhouse experiment, initiation of new shoots was measured in fragmented shoots of Carex having no intraclonal connections. Even if physiological integration was lacking due to fragmentation, shoot initiation was efficiently controlled in relation to the internal carbon/nitrogen balance.

ROS signalling in a destabilised world: A molecular understanding of climate change

Climate change results in increased intensity and frequency of extreme abiotic and biotic stress events. In plants, reactive oxygen species (ROS) accumulate in proportion to the level of stress and are major signalling and regulatory metabolites coordinating growth, defence, acclimation and cell death. Our knowledge of ROS homeostasis, sensing, and signalling is therefore key to understanding the impacts of climate change at the molecular level. Current research is uncovering new insights into temporal-spatial, cell-to-cell and systemic ROS signalling pathways, particularly how these affect plant growth, defence, and more recently acclimation mechanisms behind stress priming and long term stress memory. Understanding the stabilising and destabilising factors of ROS homeostasis and signalling in plants exposed to extreme and fluctuating stress will concomitantly reveal how to address future climate change challenges in global food security and biodiversity management.

Effects of snowmelt on the springtime photosynthesis of the evergreen dwarf shrub Vaccinium vitis-idaea

Background: The dwarf shrub Vaccinium vitis-idaea has been found to retain its photosynthetic capacity under snow in winter. At snowmelt, the plants are exposed to low temperatures and full light, which may lead to the inhibition of photosynthesis. Aims: To examine the changes in the photosynthesis of V. vitis-idaea at snowmelt and to determine their temporal extent. Methods: The photosynthetic capacity and the energy conversion efficiency of photosystem II (F v/F m) were determined in a natural spring snowmelt setting in field conditions and by creating an artificial snowmelt gradient. Results: F v/F m decreased rapidly after snowmelt and remained low for several weeks in the spring. The photosynthetic capacity remained at pre-snowmelt levels at first, but started decreasing about a week after snowmelt. The depression of photosynthesis lasted for several weeks. Conclusions: The inhibition or downregulation of photosynthesis in V. vitis-idaea takes place at snowmelt, not at the onset of winter as it does in many evergreen conifers. The snow protects the plants from the harshest winter conditions and permits metabolic activity. If snow cover becomes more intermittent in the future, there may be longer periods of photoinhibition, which will affect the carbon balance of plants.

Potential energy surface for F2O

Abstract A curvilinear internal coordinate Hamiltonian is used to calculate variationally vibrational energy levels of F 2 O. The rotational motion is treated perturbatively by using theoretical expressions for α constants which describe the vibrational dependence of the rotational constants. Potential energy parameters are optimized with the nonlinear least-squares method. The potential energy surface obtained is in good agreement with a published ab initio surface.

Phenological responses to small-scale spatial variation in snowmelt timing reveal compensatory and conservative strategies in subarctic-alpine plants

Background: In tundra ecosystems, the adjustment of phenological events, such as bud burst, to snowmelt timing is crucial to the climatic adaptation of plants. Natural small-scale variations in microclimate potentially enable plant populations to persist in a changing climate. Aims: To assess how plant phenology responds to natural differences in snowmelt timing. Methods: We observed the timing of eight vegetative and reproductive phenophases in seven dwarf-shrub species in relation to differences in snowmelt timing on a small spatial scale in an alpine environment in subarctic Finland. Results: Some species and phenophases showed accelerated development with later snowmelt, thus providing full or partial compensation for the shorter snow-free period. Full compensation resulted in synchronous occurrence of phenophases across the snowmelt gradient. In other species, there was no acceleration of development. The timing of phenophases varied between two consecutive years and two opposing mountain slope aspects. Conclusions: The results have shown three distinct patterns in the timing of phenophases in relation to snowmelt and suggest alternative strategies for adaptation to snowmelt timing. These strategies potentially apply to other species and tundra ecosystems and provide a framework, enabling one to compare and generalise phenological responses to snowmelt timing under different future climate scenarios.

Can testate amoebae (protozoa) and other micro-organisms help to overcome biogeographic bias in large scale global change research?

To monitor global change, large scale long term studies are needed. Such studies often focus on vegetation, but most plant species have limited distribution areas. Micro-organisms by contrast are mostly cosmopolitan in their distributions. To study the relationships between organisation groups, we analysed the testate amoebae (Protozoa), vegetation, and water chemistry of five Sphagnum peatlands across Europe. Inter-site differences were more pronounced for the vegetation than for testate amoebae species assemblage. Testate amoebae represent a useful tool in multi-site studies and environmental monitoring of peatlands because: 1) the number of species is much higher than for plants, 2) most species are cosmopolitan and are therefore less affected by biogeographical distribution patterns than plants; thus differences in testate amoebae assemblages can be interpreted primarily in terms of ecology, 3) testate amoebae can be used to analyse and monitor small scale (cm) gradients that play a major role in the functioning of peatland ecosystems. We further studied the effect of elevated CO2 on microbial communities in the same peatlands. Elevated CO2 increased the biomass of heterotrophic bacteria and decreased the biomass of medium size protozoa (mostly small testate amoebae). These effects suggest changes in community functioning that may have feedback effects on other components of the ecosystem.