Years Of Enrichment Research Articles

Effects of elevated CO 2 concentration on rhizodeposition from Lolium perenne grown on soil exposed to 9 years of CO 2 enrichment

The effects of enriched CO 2 atmosphere on partitioning of recently assimilated carbon were investigated in a plant-soil-microorganism system in which Lolium perenne seedlings were planted into cores inserted into the resident soil within a sward that had been treated with elevated CO 2 for 9 consecutive years, under two N fertilisation levels (Swiss FACE experiment). The planted cores were excavated from the ambient (35 Pa pCO 2) and enriched (60 Pa pCO 2) rings at two dates, in spring and autumn, during the growing season. The cores were brought back to the laboratory for 14C labelling of shoots in order to trace the transfer of recently assimilated C both within the plant and to the soil and microbial biomass. At the spring sampling, high N supply stimulated shoot and total dry matter production. Consistently, high N enhanced the allocation of recently fixed C to shoots, and reduced it to belowground compartments. Elevated CO 2 had no consequences for DM or the pattern of C allocation. At the autumn sampling, at high N plot, yield of L. perenne was stimulated by elevated CO 2. Consistently, 14C was preferentially allocated aboveground and, consequently belowground recent C allocation was depressed and rhizodeposition reduced. At both experimental periods, total soil C content was similar in all treatments, providing no evidence for soil carbon sequestration in the Swiss Free Air CO 2 Enrichment experiment (FACE) after 9 years of enrichment. Recently assimilated C and soil C were mineralised faster in soils from enriched rings, suggesting a CO 2-induced shift in the microbial biomass characteristics (structure, diversity, activity) and/or in the quality of the root-released organic compounds.

Impact of elevated atmospheric CO2 on forest floor respiration in a temperate pine forest

The effects of elevated atmospheric CO2 (CO2e) on soil respiration were evaluated using inverse models and static chamber measurements collected over 4.5 years in a maturing loblolly pine forest. The chamber measurements of forest floor CO2 efflux showed that the flux enhancement increased progressively, reaching 1.4 after 3 years, but declined thereafter to 1.10 at the end of the study. The subsurface CO2 concentration measurements show that the difference in mean annual concentration gradient between ambient and enriched plots initially increased, and then stabilized after 2 years of enrichment. However, concomitant soil moisture increases in the enriched plots reduced the soil diffusivity, especially over the last 2 years. These two observations, in combination with inverse model calculations, suggest a decline in subsurface CO2 production over the last 2 years. Enhancement in photosynthesis has declined after 4.5 years of enrichment (remaining ∼40% higher than ambient photosynthesis), and the increase in production and respiration alone cannot account for the excess carbon uptake. Thus this modeling approach would suggest that non‐gaseous carbon is accumulating belowground. However, we have not been able to measure significant changes in soil organic carbon or fine root biomass. These results, in the context of other forest floor flux studies and the carbon budget at the site, suggest a lack of closure in the carbon budget under elevated atmospheric CO2.

Cognitive experience and its effect on age-dependent cognitive decline in beagle dogs.

Test-sophisticated beagle dogs show marked age sensitivity in a size discrimination learning task, with old and senior dogs performing significantly more poorly than young dogs. By contrast, age differences in learning were not seen in dogs naive with respect to neuropsychological test experience. These results indicate that old animals benefit less from prior cognitive experience than young animals, which is an example of an age-dependent loss in plasticity. This finding also suggests that behaviorally experienced animals are a more useful model of human cognitive aging than behaviorally naïve animals. We also looked at the effect of a program of behavioral enrichment in aged dogs. One year of enrichment did not lead to significant differences, but after 2 years the behaviorally enriched group performed significantly better than the control group. The effect after 2 years indicates that a prolonged program of cognitive enrichment can serve as an effective intervention in aged dogs. These findings demonstrate that cognitive abilities in aged animals can be modified by providing behavioral experience, indicating that cognitive abilities remain moderately plastic, even in very old animals.

Elevated atmospheric CO2 alters wood production, wood quality and wood strength of Scots pine (Pinus sylvestris L) after three years of enrichment

AbstractScots pine (Pinus sylvestris L.) trees were grown in open top chambers for three years under ambient and elevated CO2 concentrations. The trees were aged 3 y at the beginning of the CO2 exposure, and the effects of the treatment on total stem volume, stem wood biomass, wood quality and wood anatomy were examined at the end of the exposure. The elevated CO2 treatment lead to a 49% and 38% increase in stem biomass and stem wood volume, respectively. However, no significant effects of the elevated CO2 treatment on wood density were observed, neither when green wood density was estimated from stem biomass and stem volume, nor when oven‐dry wood density was measured on small wood samples. Under elevated CO2 significantly wider growth rings were observed. The effect of elevated CO2 on growth ring width was primarily the result of an increase in earlywood width. Wood compression strength decreased under elevated CO2 conditions, which could be explained by significantly larger tracheids and the increased earlywood band, that has thinner walls and larger cavities. A significant decrease of the number of resin canals in the third growth ring was observed under the elevated treatment; this might indicate that trees produced and contained less resin, which has implications for disease and pest resistance. So, although wood volume yield in Scots pine increased significantly with elevated CO2 after three years of treatment, wood density remained unchanged, while wood strength decreased. Whilst wood volume and stem biomass production may increase in this major boreal forest tree species, wood quality and resin production might decrease under future elevated CO2 conditions.

Population, Community, and Ecosystem Variates as Ecological Indicators: Phytoplankton Responses to Whole-Lake Enrichment

We quantified the reliability of phytoplankton population, community, and ecosystem variates as indicators of whole-lake enrichment. Variates with high sensitivity to perturbation and low background variability were assumed to be more reliable indicators than variates with low sensitivity or high variability. Our data set included weekly data in four lakes (three manipulated and one reference) during two pretreatment summers and two summers of enrichment. We determined background variability by evaluating change in each variate from year to year in the reference lake throughout the experiment and in each manipulated lake during the pretreatment period. We evaluated sensitivity to enrichment using the frequency of departure from expected conditions for each variate during the period of experimental enrichment. Using this information, we then (1) tested the expectation that species populations are more reliable indicators of perturbation than ecosystem variates (biomass, chlorophyll, and primary productivity), and (2) evaluated whether community variates (genera, taxonomic divisions, allometric variates, and community diversity) were reliable indicators of enrichment. Contrary to expectations from other perturbations, phytoplankton species populations were less reliable indicators of enrichment than community and ecosystem variates. Chlorophyll, species diversity, and species evenness were the most reliable indicators of enrichment: each changed significantly only during the first year of enrichment and only in the three enriched lakes. Simultaneous changes in multiple taxonomic divisions also signaled enrichment very reliably. In contrast, the frequency of significant changes in species populations differed little between the reference lake and the enriched lakes, even after experimental enrichment. Changes in species were difficult to detect reliably due to high background variability in all four lakes: most taxa were not present often enough during a single year to assess reliably whether they had increased or decreased compared to the previous years. Genera and allometric variates were also unreliable indicators due to high variability and moderate sensitivity, respectively. Reliable indicators of phytoplankton responses to enrichment were very different from reliable indicators of animal responses to toxic stressors, suggesting that it may be difficult to make generalizations regarding the use of population, community, and ecosystem variates as indicators of a wide array of perturbations.

Influence of trophic role and life-cycle duration on timing and magnitude of benthic macroinvertebrate response to whole-lake enrichment

Phosphorus and nitrogen additions over a 3-year period (1991-1993) significantly increased the abundance of most benthic macroinvertebrate taxa collected on artificial substrates in a small oligotrophic lake in insular Newfoundland relative to a nearby control lake. The speed and magnitude of response was related to both the trophic role and the life-cycle duration of the taxa. This created a response continuum with small, fast-growing herbivores such as sphaeriid clams and gastropods demonstrating more pronounced and more rapid abundance responses than longer lived detritivores such as Ephemeroptera, which, in turn, had quicker responses than long-lived predators. These observations support the hypothesis that these benthic communities are controlled by bottom-up resource processes during the initial years of enrichment and provide the basis for expecting future enhancement of benthivorous salmonid populations in the fertilized lake.

Effects of in situ nitrogen and phosphorus enrichment of the sediments on the seagrass Heterozostera tasmanica (Martens ex Aschers.) den Hartog in Western Port, Victoria, Australia

The rhizosphere of Heterozostera tasmanica (Martens ex Aschers.) den Hartog was enriched in situ with ammonium and/or phosphate at a rate of 100 g N · m −2 and 20 g P · m −2 each month from August (winter) through February (late summer) in a 2 × 2 factorial experiment. Ammonium enrichment resulted in increased levels of total nitrogen in the rhizomes (from 0.83 to 1.03% of dry wt) and leaves (from 1.63 to 1.82%) and caused a 20% increase in leaf growth rate. Phosphate enrichment resulted in increased levels of total phosphorus in the rhizomes (from 0.16 to 0.18%), but no increase in total phosphorus in the leaves nor any change in the leaf growth rate. Neither ammonium nor phosphate enrichment caused a change in above sediment standing crop or shoot density. It is suggested that nitrogen limits the growth rate of H. tasmanica plants in northern Western Port during spring and early summer, but that an increase of 5 to 100 times the control level of nitrogen and phosphorus in the rhizosphere of these plants appears to have little direct effect on their growth or on standing crop during the first year of enrichment.

Eutrophication of Lake 227 by Addition of Phosphate and Nitrate: the Second, Third, and Fourth Years of Enrichment, 1970, 1971, and 1972

Lake 227, a small lake with extremely low concentrations of dissolved inorganic carbon, was fertilized with PO4 and NO3 for 4 years, beginning in 1969. The additions increased natural inputs of phosphorus and nitrogen about five times.Phytoplankton standing crop increased nearly two orders of magnitude, and the Cryptophyceae and Chrysophyceae present in natural lakes of the area were replaced by Chlorophyta and Cyanophyta. The standing crop of phytoplankton per square meter was near the maximum which could theoretically be maintained by surface light, in spite of the low carbon concentrations. Added phosphate and nitrate were rapidly removed by phytoplankton, so that concentrations in the lake remained low.Almost all of the added nutrient was retained by the lake, in spite of relatively fast water renewal times. An average of 80% of the phosphorus income of the lake was sedimented. There was no return of phosphorus from sediments in spite of anoxic conditions in the hypolimnion.Photosynthesizing plankton reduced dissolved inorganic carbon concentrations severely, causing a flux of atmospheric CO2 into the lake. From 69 to 95% of the inorganic + particulate carbon supplied to the lake was from the atmosphere. Results demonstrate that low carbon concentrations do not hinder eutrophication if phosphorus and nitrogen supplies are adequate.