Friday, December 2, 2016

Biomass in Response to Warming

Robert D. Hollister and Kathryn Flaherty published an article, Above- and Below-Ground Plant Biomass Response to Experimental Global Warming in Northern Alaska. The study area took place in northern Alaska, which consists of long cold winters and short cool summers. Their study area had 24 plots, and experimental warming was done by over-top chambers, which are basically small smaller forms of greenhouses. Biomass was harvested in early August of 1999, and they measured plant biomass after 3 or 4 years of experimental warming. Soil was extracted by cutting it into 10cm3 cubes, which would serve as an “index” for the actual mass of the plants. Overall there was less above-ground biomass and more below ground in the plots that were warmed. However, all of the data as a whole was not significant enough to support that warming changed the above/below ground ratio, possibly suggesting that the vegetation is resistant to short term warming. 
 Hollister, Robert D., and Kathryn J. Flaherty. “Above- and below-Ground Plant Biomass Response to Experimental Warming in Northern Alaska.” Applied Vegetation Science, vol. 13, no. 3, 2010, pp. 378–387.

Friday, November 18, 2016

Snow Depth Effects on Nitrogen Mineralization and Plants

Andrew P. Borner, Knut Keilland, and Mairlyn D. Walker conducted a study as part of the International Tundra Experiment (ITEX) to research the effects that increased winter snow depth and decreased growing seasons had on the phenology of four species of tundra plants, and the nitrogen availability of snowbed communities. They found that snow depth had an effect on the first day that it was snow free in spring while also affecting bud break, and flowering. However, snow depth had no effect on plant development. Timing and amount of N mineralization were also affected by snow depth. N mineralization of deeper snow depth occurred during winter, where ambient snow zones occurred in the spring. Overall more snowfall and a longer duration would have minor effects on plant phenological development and large effects on N cycling patterns.    

Borner, Andrew P. et al. “Effects of Simulated Climate Change on Plant Phenology and Nitrogen Mineralization in Alaskan Arctic Tundra.” Arctic, Antarctic, and Alpine Research, vol. 40, no. 1, 2008, pp. 27–38.

Friday, November 11, 2016

Leaf Nutrition in Response to Warming and Deeper Snow

Leaf Mineral Nutrition of Arctic Tundra Plants in Response to Warming and Deeper Snow in Northern Alaska by Welker, Fahnestock, Sullivan, and Chimner studied climate change factors under different conditions. They studied warming and snow accumulation independently and together to see how it would affect leaf carbon, lead nitrogen, and leaf C:N for vegetation in wet and dry tundra in Northern Alaska. They found that moist tundra responded with a 25% increase in leaf N. Wet tussock tundra plants showed greater sensitivity to the climate change scenarios with reduced leaf C, increase N, and reduced C:N. Overall deeper snow made for higher N mineralization, and that plant leaves with both deeps now and higher temperatures had higher N. With the higher N availability from both climate scenarios plant photosynthesis increases. When the lower C is combined with the higher N it causes lower C:N from climate change, which can then lead to trophic problems such as higher forage digestibility and decomposition. An increased decomposition could mean increased N in soils for plants.

Friday, October 28, 2016

Shrub Growth and Global Warming in Tundra Ecosystem

Climate warming has been an ongoing concern for every ecosystem. Michael N. Weintraub and Joshua P. Schimel studied certain effects of global warming in the Tundra ecosystem and its relationship to carbon. In their article Nitrogen Cycling and the Spread of Shrubs Control Changes in the Carbon Balance of Arctic Tundra Ecosystems, they observe how global warming could be causing carbon loss by speeding up the decomposition of soil organic matter(SOM). Nitrogen release from the SOM could then be causing more plant growth. Weintraub and Schimel were concerned that since each plant has a different limit for nitrogen uptake, it could affect carbon cycling. In their studies they found shrubs are growing more predominant with global warming. This is because woody plants have the highest C:N ratio of most plants, therefore they decompose slowly. They found that the species type had more of an effect on N uptake than the N form. Wienshraub and Schimel found significant differences between shrubs and other tundra plants, such as carbon storage, litter decomposition, and the timing of N uptake by the plants.

Friday, October 21, 2016

Cyclical Patterns in Tundra Food Web

An article by Rolf A. Imes and Eva Fuglei, Trophic Interaction Cycles in Tundra Ecosystems and the Impact of Climate Change, looked at cyclical patterns they noticed between Arctic Foxes and Lemmings. Lemmings, small rodent like animals, reproduce under deep snow. They reproduce in a 4 year cycle, and this affects the population of Arctic foxes as they depend on the lemmings for food. Figure 1 and 2 show the population of Lemmings through several years and how they differ in different seasons and how the Arctic fox follows the 4 year cycle with lag years. This cycle also leads to the alternate theory hypothesis. This theory explains how predators such as the fox can find prey after peak years of their top prey. However, the cycle between Arctic Foxes and Lemmings isn’t the only cycle present in the tundra, other cycles can be seen in Plants such as sedges and dwarbs, or soil invertebrates. Reasons why the trophic interaction cycles occur are due to short growing seasons and simple food webs. As global warming occurs it is easy for the food web to be changed. For example, Red fox can begin to move in to the Arctic fox habitat and disrupt their feeding

Friday, September 30, 2016

Decadal Climate Warming in Arctic

CO2 fluxes during the summer in two arctic tundra ecosystems from 1960 to the end of 1998 and showing their results in their article, Acclimation of Ecosystem CO2 Exchange in the Alaskan Arctic in Response to Decadal Climate Warming. Arctic ecosystems have been thought to be net sinks due to cold temperatures and wet soils that reduce rates of decomposition of organic matter, but warming has stimulated rates of arctic ecosystem respiration more than primary production, which has caused a net loss of CO2 in Arctic and tundra ecosystems. Researchers measured the mean air temperature and precipitation over those 39 years to see the change in ambient temperature and surface water balance of coastal plains. “Although there was no significant temporal trend in precipitation, the surface water balance (P - PET) decreased by 2.6 mm yr-1 for the coastal plain and 6.7 mm yr-1 for interior regions (Fig. 2d). The increase in temperature and surface water deficit (P - PET) led to a change in the magnitude and direction of Arctic ecosystem net CO2 flux. For example, wet sedge ecosystems were net CO2 sinks of -25 g C m-2 yr -1 between 1970 and 1972 (negative values denote net ecosystem CO 2 uptake; Fig. 1a), while moist-tussock tundra ecosystems were reported to be net sinks of -120 g C m -2 yr-1 before 1976”(Oechel.) Near the early 1990’s wet sedge was a net source of CO2 on average of 25cm-2yr-1, while tussock tundra was losing 50-450g Cm-2yr-1. Recently net ecosystem CO2 flux of Arctic systems have acclimated to global warming, and net source activity during the summer has disappeared. Even though arctic ecosystems were considered net sinks during the summer, net losses of CO2 still occur over an annual period due to winter CO2 losses, therefore they are consider sources. This could imply that further climate change could aggravate CO2 emissions of arctic ecosystems.

Oechel, C Walter. “Acclimation of Ecosystem CO2 Exchange in the Alaskan Arctic in Response to Decadal Climate Warming.”Nature.406,pp.978-991,2000, 30 September 2016.

Friday, September 23, 2016

Tundra Permafrost: Old Carbon Release and Net Carbon Exchange

Biologists from Florida, California, and Alaska contributed to a study looking at carbon release and net carbon exchange from permafrost thaw in Tundra ecosystems in Alaska. They published their works in The Effect of Permafrost Thaw on Old Carbon Release and Net Carbon Exchange from Tundra. They state that “The rate of carbon release from permafrost soils is highly uncertain, but it is crucial for predicting the strength and timing of this carbon-cycle feedback effect, and thus how important permafrost thaw will be for climate change this century and beyond” (Schuur.) They measured net carbon exchange and radiocarbon age of ecosystem respiration experiencing permafrost thaw in an effort to see the effects of old carbon loss on ecosystem carbon balance. Methods included measuring ecosystem carbon at a site in Alaska where permafrost thaw had been documented since 1990.”At monthly intervals during the growing season, we also collected ecosystem respiration CO2 from dark chambers, as well as soil CO2 from soil profile gas wells, for Δ14C analysis. In the laboratory, CO2 was then purified and analysed for Δ14C using an accelerator mass spectrometer, while a subsample was analysed for δ13C using an isotope ratio mass spectrometer” (Schuur.) From this, radiocarbon was used to find the decomposition of old organic C in these permafrost soils. The permafrost temperature was taken at 30 meters deep on a north facing slope. 3 sites were monitored, minimal, moderate, and extensive, in regards to the amount of change of permafrost thaw based on factors such as ground subsidence and thaw depth. The tundra experienced net C uptake between June and August. Results of the overall experiment show that areas that had thawed decades earlier lost 78% more old carbon than minimal areas, which correlated with net ecosystem carbon release. “Our data document significant losses of soil carbon with permafrost thaw that, over decadal timescales, overwhelms increased plant carbon uptake at rates that could make permafrost a large biospheric carbon source in a warmer world” (Schuur.) Therefore over an extensive time, permafrost thaw can play a larger role in climate change.

Schuur, Edward. "The Effect of Permafrost Thaw on Old Carbon Release and Net Carbon Exchange from Tundra." Nature International Weekly Jounal of Science. N.p., 28 May 2009. Web. 22 Sept. 2016.