Functioning of terrestrial ecosystems of the Maritime Antarctic in a warmer climate

TY - THES

T1 - Functioning of terrestrial ecosystems of the Maritime Antarctic in a warmer climate

AU - Bokhorst, S.

N1 - 49 NIOO Thesis

PY - 2007/9/7

Y1 - 2007/9/7

N2 - Environmental change, as predicted by the Intergovernmental Panel on ClimateChange (IPCC), will entail increases in temperature for most parts of the earth.Predictions are that the temperature increase in the Arctic and Antarctic regions willbe highest of all on earth. As the mean summer temperature is around 0 ºC in PolarRegions, an increase of a few degrees, potentially may have a large effect ontemperature windows in which organisms and processes can operate. Due to theproximity to populous Northern Hemisphere continents, the major emphasis ofclimate change research to date has focused on the polar regions of the NorthernHemisphere. However, the Antarctic Peninsula region is also one of the three fastestwarming regions of the planet over the last 50 years. To better understand responsesof ecosystems on earth to climate change other regions have to be investigated aswell.Antarctic terrestrial ecosystems are one of the most extreme on Earth. Being thehighest, coldest and windiest continent, Antarctica places severe limits on life. Theorganisms living here are most likely at the edge of their survival abilities. Due to thelow temperatures, free water is only available during brief periods in summer whensnow and ice melts. This makes water the most limiting factors for survival in theAntarctic. The severe environmental conditions for life have resulted in relativeimpoverished vegetation types and soil arthropod communities. Changes intemperature, especially during the summer period, may have a large impact on growthand development of soil organisms, vegetation and processes. This makes Antarcticecosystems ideal for investigating climate change impacts.In the summer of 2003/04, Open Top Chambers (OTCs) were placed in contrastingcoastal communities along a latitudinal gradient; at the Falkland Islands, dwarf shruband grass-dominated communities, at Signy Island and Anchorage Island, moss andlichen-dominated communities were chosen. I investigated the response of soilarthropods, vegetation and decomposition to increasing temperatures generated by theOTCs. The latitudinal gradient was used as a proxy for extreme warming as apredicted result of environmental change. To better understand parts of the nutrientcycling within such communities, I investigated external nitrogen sources that mightbe used by the vegetation, as well as the food choice of soil arthropods.When conditions for water availability and temperature have been met, nitrogen tendsto become a major limiting factor on vegetation development in the Antarctic. Inchapter two, I describe potential external nitrogen sources for the three study sites inthis thesis. At the Falkland Islands, I was unable to conclude whether externalnitrogen sources play an important role for the vegetation. At Signy and AnchorageIsland, stable isotope analyses showed that vertebrate colonies highly influence thenitrogen brought in by the wind and this was reflected in the vegetation. However,some lichen species did not appear to be using this source of nitrogen but appeared tomake more use of precipitation.In the third chapter of this thesis I describe the feeding choice of the most abundantCollembola (springtail) on Anchorage Island. Preferred food choice by theCollembolan Cryptopygus antarcticus, was determined by combining food choiceexperiments in the lab with stable isotope analyses of field samples. The main dietappears to consist of alga and lichens.The response to warming of soil arthropods is described in chapter four. After twoyears of warming, the initial responses of arthropod abundance were low. However, inthe lichen community on Signy Island there was a decrease in Collembolanabundance, due to a combined effect of warming and a reduction in soil moisture. Thevegetation shows a similar pattern as described in chapter five. Here I found adecrease in vegetation cover in the same lichen community on Signy Island due to thewarming treatment. In the grass community at the Falkland Islands, there was also areduction in vegetation cover. A relative ‘dry’ summer resulted in a large overalldecrease but the warmed plots by OTCs showed an even larger reduction invegetation cover. The more densely vegetated communities at the three islands wereapparently better at buffering the vegetation and soil community to these smallincreases in temperature, as they showed no response. These results illustrate thevulnerability of such open vegetation types to a small increase in temperature.In chapter six I applied different methods to investigate the response of thedecomposition process to warming. The laboratory studies indicate a strong potentialresponse to increased temperatures. The field experiments showed a lower responseand this could have been a result of the relative low temperature increase by the OTCsbut perhaps more importantly a reduction in soil moisture. The decomposition processshows a great potential for response to increases in temperature. If the temperaturewill keep rising above the ones instigated in this study, larger responses are likely tobe expected but only if soil moisture will not be greatly affected.As a-biotic factors mainly govern life in the Antarctic, biotic interactions have notbeen extensively explored in the Antarctic. However, the biotic components inMaritime Antarctic ecosystems are likely to play some role of significance inecosystem processes as suggested in this thesis. The main focus of this thesis was toinvestigate the response of different parts of terrestrial ecosystem when temperatureswill keep rising in communities from the Falkland Islands and the Maritime Antarcticregion. The duration of my experiment was on a very short time-scale especiallyconsidering the ‘slow’ life cycles of most Antarctic organisms. Therefore, the largedifferences seen between my study islands were not greatly affected by the warmingtreatment. These differences do indicate that there is a potential for communitychange above as well as below ground. In the last chapter I have brought all thefindings together and provided an idea on what might happen with these Antarcticecosystems if the temperature will keep rising in the future. Based on what isdescribed in literature and by my own findings it is likely that open structuredcommunities will be negatively affected by temperature increases in the near future asthey have more difficulty in regulating soil moisture.

AB - Environmental change, as predicted by the Intergovernmental Panel on ClimateChange (IPCC), will entail increases in temperature for most parts of the earth.Predictions are that the temperature increase in the Arctic and Antarctic regions willbe highest of all on earth. As the mean summer temperature is around 0 ºC in PolarRegions, an increase of a few degrees, potentially may have a large effect ontemperature windows in which organisms and processes can operate. Due to theproximity to populous Northern Hemisphere continents, the major emphasis ofclimate change research to date has focused on the polar regions of the NorthernHemisphere. However, the Antarctic Peninsula region is also one of the three fastestwarming regions of the planet over the last 50 years. To better understand responsesof ecosystems on earth to climate change other regions have to be investigated aswell.Antarctic terrestrial ecosystems are one of the most extreme on Earth. Being thehighest, coldest and windiest continent, Antarctica places severe limits on life. Theorganisms living here are most likely at the edge of their survival abilities. Due to thelow temperatures, free water is only available during brief periods in summer whensnow and ice melts. This makes water the most limiting factors for survival in theAntarctic. The severe environmental conditions for life have resulted in relativeimpoverished vegetation types and soil arthropod communities. Changes intemperature, especially during the summer period, may have a large impact on growthand development of soil organisms, vegetation and processes. This makes Antarcticecosystems ideal for investigating climate change impacts.In the summer of 2003/04, Open Top Chambers (OTCs) were placed in contrastingcoastal communities along a latitudinal gradient; at the Falkland Islands, dwarf shruband grass-dominated communities, at Signy Island and Anchorage Island, moss andlichen-dominated communities were chosen. I investigated the response of soilarthropods, vegetation and decomposition to increasing temperatures generated by theOTCs. The latitudinal gradient was used as a proxy for extreme warming as apredicted result of environmental change. To better understand parts of the nutrientcycling within such communities, I investigated external nitrogen sources that mightbe used by the vegetation, as well as the food choice of soil arthropods.When conditions for water availability and temperature have been met, nitrogen tendsto become a major limiting factor on vegetation development in the Antarctic. Inchapter two, I describe potential external nitrogen sources for the three study sites inthis thesis. At the Falkland Islands, I was unable to conclude whether externalnitrogen sources play an important role for the vegetation. At Signy and AnchorageIsland, stable isotope analyses showed that vertebrate colonies highly influence thenitrogen brought in by the wind and this was reflected in the vegetation. However,some lichen species did not appear to be using this source of nitrogen but appeared tomake more use of precipitation.In the third chapter of this thesis I describe the feeding choice of the most abundantCollembola (springtail) on Anchorage Island. Preferred food choice by theCollembolan Cryptopygus antarcticus, was determined by combining food choiceexperiments in the lab with stable isotope analyses of field samples. The main dietappears to consist of alga and lichens.The response to warming of soil arthropods is described in chapter four. After twoyears of warming, the initial responses of arthropod abundance were low. However, inthe lichen community on Signy Island there was a decrease in Collembolanabundance, due to a combined effect of warming and a reduction in soil moisture. Thevegetation shows a similar pattern as described in chapter five. Here I found adecrease in vegetation cover in the same lichen community on Signy Island due to thewarming treatment. In the grass community at the Falkland Islands, there was also areduction in vegetation cover. A relative ‘dry’ summer resulted in a large overalldecrease but the warmed plots by OTCs showed an even larger reduction invegetation cover. The more densely vegetated communities at the three islands wereapparently better at buffering the vegetation and soil community to these smallincreases in temperature, as they showed no response. These results illustrate thevulnerability of such open vegetation types to a small increase in temperature.In chapter six I applied different methods to investigate the response of thedecomposition process to warming. The laboratory studies indicate a strong potentialresponse to increased temperatures. The field experiments showed a lower responseand this could have been a result of the relative low temperature increase by the OTCsbut perhaps more importantly a reduction in soil moisture. The decomposition processshows a great potential for response to increases in temperature. If the temperaturewill keep rising above the ones instigated in this study, larger responses are likely tobe expected but only if soil moisture will not be greatly affected.As a-biotic factors mainly govern life in the Antarctic, biotic interactions have notbeen extensively explored in the Antarctic. However, the biotic components inMaritime Antarctic ecosystems are likely to play some role of significance inecosystem processes as suggested in this thesis. The main focus of this thesis was toinvestigate the response of different parts of terrestrial ecosystem when temperatureswill keep rising in communities from the Falkland Islands and the Maritime Antarcticregion. The duration of my experiment was on a very short time-scale especiallyconsidering the ‘slow’ life cycles of most Antarctic organisms. Therefore, the largedifferences seen between my study islands were not greatly affected by the warmingtreatment. These differences do indicate that there is a potential for communitychange above as well as below ground. In the last chapter I have brought all thefindings together and provided an idea on what might happen with these Antarcticecosystems if the temperature will keep rising in the future. Based on what isdescribed in literature and by my own findings it is likely that open structuredcommunities will be negatively affected by temperature increases in the near future asthey have more difficulty in regulating soil moisture.

M3 - PhD thesis

PB - VU University Press

CY - Amsterdam

ER -