Reconstruction of the carbon balance for microsites in a boreal oligotrophic pine fen, Finland

 Carbon dioxide (CO₂) exchange was studied at flark (minerotrophic hollow), lawn and hummock microsites in an oligotrophic boreal pine fen. Statistical response functions were constructed for the microsites in order to reconstruct the annual CO₂ exchange balance from climate data. Carbon accumulation was estimated from the annual net CO₂ exchange, methane (CH₄) emissions and leaching of carbon. Due to high water tables in the year 1993, the average carbon accumulation at the flark, Eriophorum lawn, Carex lawn and hummock microsites was high, 2.91, 6.08, 2.83 and 2.66 mol C m^–2, respectively, and for the whole peatland it was 5.66 mol m^–2 year^–1. During the maximum primary production period in midsummer, hummocks with low water tables emitted less methane than predicted from the average net ecosystem exchange (NEE), while the Carex lawns emitted slightly more. CH₄ release during that period corresponded to 16% of the contemporary NEE. Annual C accumulation rate did not correlate with annual CH₄ release in the microsites studied, but the total community CO₂ release seemed to be related to CH₄ emissions in the wet microsites, again excluding the hummocks. The dependence of CO₂ exchange dynamics on weather events suggests that daily balances in C accumulation are labile and can change from net carbon uptake to net release, primarily in high hummocks on fens under warmer, drier climatic conditions. Received: 16 August 1996 / Accepted: 30 November 1996     

The uptake of and structural changes induced by trichloroacetic acid in the needles of Scots pine seedlings

The uptake of trichloroacetic acid (TCA) and structural changesinduced in the needles of Scots pine (Pinus sylvestris L.) seedlingswere studied. Two exposure set-ups, a root route and an atmosphericroute through the surfaces simulating the wet deposition offog, were used. Both set-ups included two dose levels and correspondingcontrol treatments. The temperature and the relative humidityin the climate chambers were adjusted to represent the conditionsof June–July in a subarctic area in central Finland. Theseedlings were exposed three times a week for two months. Theresults showed that the uptake of TCA in needles occurred bothvia roots and via needle surface. However, most of the TCA viathe atmospheric route was absorbed on the surface of the needles.The structural responses in pine needles depended partly onthe treatment method: TCA applied via the atmospheric routedisintegrated the structures of the epicuticular waxes and thatof the stomatal cells, which was not seen in the exposures viaroots. A common feature was the decrease in size of the chloroplastsin concert with the increasing TCA concentrations inside theneedles. Key words: Pinus sylvestris L., climate chamber, effects, microscopic structure, secondary pollutant, TCA, trichloroacetic acid     

Trophic interactions in rockpool food webs: regulation of zooplankton and phytoplankton by Notonecta and Daphnia

We studied trophic interactions in experimental rockpools with three different food web structures: phytoplankton and small-bodied zooplankton; phytoplankton, small-bodied zooplankton and Daphnia ; and phytoplankton, small-bodied zooplankton, Daphnia and Notonecta . Nutrients, primary productivity, chlorophyll a and zooplankton species composition and biomass were measured over eight weeks.
2. Daphnia had a negative impact on other zooplankton and reduced the phytoplankton biomass and primary productivity. In the absence of Daphnia , small-bodied zooplankton species were abundant, in particular cyclopoid copepods. Concentrations of dissolved nutrients were lower and the standing crop of primary producers was higher when Daphnia was absent.
3. The presence of the invertebrate predator Notonecta produced a top-down effect which was similar to that reported for planktivorous fish, i.e. a selective reduction of daphnids followed by an increase of small-bodied zooplankton species and phytoplankton biomass.
4. The study showed that consumer regulation of Daphnia by Notonecta and of algae by Daphnia are important, but also demonstrated that trophic level biomasses were controlled by a combination of predation and resource limitation.     

Short-term recovery of benthos following disturbance from stream habitat rehabilitation

The recovery of benthic macroinvertebrates after disturbance from stream rehabilitation was studied in the River Livojoki, northern Finland. The stream that had been channelized for log transport was rehabilitated on 1 July 1992 by digging holes and inserting boulders. We measured habitat characteristics and sampled benthic animals before and after rehabilitation, including an unrehabilitated control site. The immediate effect of rehabilitation was a slight decrease in the abundances of benthic insects. Recolonization occurred rapidly, within 10 days. Disturbance of the rehabilitation did not have a detectable effect on the macroinvertebrate community. Most species-level changes and community patterns reflected seasonal life history events. Timing of such rehabilitation work can be critical for the recovery rate, which depends on the colonization abilities of the species present after disturbance. We suggest that many disturbances (including minor floods and moderate rehabilitation procedures) may have only small, short-term effects on benthic communities. We emphasize the importance of considering seasonality in studies of disturbance in streams.     

Seasonal physiological responses and biomass growth in a bioenergy crop (<Emphasis Type="Italic">Phalaris arundinacea</Emphasis> L.) under elevated temperature and CO<Subscript>2</Subscript>, subjected to different water regimes in boreal conditions

We investigated the seasonal variability of effects of elevated temperature (+3.5°C), CO₂ elevation (700 μmol mol⁻¹) and varying water regimes (high to low water content) on physiological responses and biomass growth of reed canary grass (Phalaris arundinacea L., local field-grown cultivar) grown in a boreal environment. In controlled environment greenhouses, various physiological and growth parameters of grass, i.e., light-saturated net photosynthetic rates (P _nmax), water use efficiency (WUE) and optimal photochemical efficiency of photosystem II (F _v/F _m), and leaf area development and biomass of plant organs (leaf, stem, coarse, and fine root) were measured. During the early measurement periods, elevated temperature enhanced leaf photosynthesis and above-ground biomass of reed canary grass; however, this resulted in earlier senescence and lower biomass at the end of measurement period, compared to ambient temperature. This effect was more pronounced under water limitation. Elevated CO₂ enhanced P _nmax, WUE, and leaf area and total plant biomass (above- and below-ground) over growing season. The explanation for imbalance between stimulated photosynthesis and increase in above-ground biomass was that CO₂ enrichment causes a greater increase in the plant’s root system. The combination of elevated temperature and CO₂ slightly increases the growth of plant. Adequate water availability favored photosynthesis and biomass growth of reed canary grass. The temperature- and drought-induced stresses were partially mitigated by elevated CO₂. Other cultivars should be tested in order to identify those that are better adapted to elevated temperatures and CO₂ and variable water levels.