title: Water relations and CO₂ exchange of the terrestrial lichen Teloschistes capensis in the Namib fog desert: Measurements during two seasons in the field and under controlled conditions

authors: Lange, Otto L.

subjects: lichen

abstract: Although the coastal zone of the Central Namib Desert (Namibia) has negligible rainfall, frequent fog, dew and high air humidity support a luxurious lichen flora. Large areas of soil crust communities are dominated by the multibranched, fruticose Teloschistes capensis interspersed by a (still indeterminable) Ramalina species. In earlier communications, based on field measurements in autumn, we began the analysis of functional mechanisms that allow these lichens to exist under the special conditions of a fog desert. We have extended this work by monitoring lichen CO₂ exchange and water relations in spring and by experiments under controlled conditions.


In both seasons, nocturnal hydration, by fog and/or dew, activated dark respiration of the lichens which was followed, after sunrise, by a short period of positive net photosynthesis (NP) that continued until metabolic inactivation occurred from desiccation. Dry thalli of T. capensis were able to reactivate NP through water vapour uptake alone, beginning at an air relative humidity of 82%, i.e. at a water potential of −26.3 MPa; the moisture compensation point during desiccation was at 13% thallus water content (WC, dry weight related). Optimal WC for photosynthesis was around 100%, and both species showed a large and extended suprasaturation depression of CO₂ assimilation. Light response showed “sun-plant” characteristics with saturation >1000 μmol m⁻²s⁻¹ photosynthetically active photon flux density (PPFD). However, due to rapid desiccation, the combination of light saturation with optimal WC very rarely occurred under field conditions. Light compensation point after sunrise was highly dependent on actual WC: at low hydration, it amounted to only ca. 10 μmol m⁻² s⁻¹ PPFD so that even the smallest levels of hydration could be used for carbon gain before desiccation took place again. This phenomenon was probably due to a hydration gradient in the thallus branches during transient moistening so that the outer photobiont layer was favoured in contrast to the internal mycobiont which remained dry longer and did not contribute respiratory CO₂ loss. Fully hydrated thalli had light compensation points around 50 μmol m⁻² s⁻¹ PPFD. Extended desiccation of 1–3 days had no impact on the magnitude and recovery of photosynthesis but, imposed desiccation of 10 days reduced NP in lab and field experiments and caused an extended period of recovery. “Resaturation respiration” was not detected in the field data, although it was present after experimental moistening of dry thalli.
In spring, the higher fog frequency and intensity increased maximal nocturnal WC, maximal attained NP as well as integrated daily carbon income (ΣNP) compared to the autumn measurements. NPmax and ΣNP depended on maximal nocturnal WC with a saturation-type response. In terms of carbon gain both species seem to be optimally adapted to nocturnal moistening up to 160% WC and were not able to make use of higher degrees of hydration, a feature that might well influence their habitat selection.

Maximal daily carbon-related ΣNP for T. capensis was 4.6 mgC (gC)⁻¹ day⁻¹. A rough estimate of the annual (projected) area-related carbon balance (photosynthetic income minus respiratory losses) based on published fog and dew frequencies and personal observations was 15–34 mgC m⁻² yr⁻¹.

text: Water relations and CO₂ exchange of the terrestrial lichen Teloschistes capensis in the Namib fog desert: Measurements during two seasons in the field and under controlled conditions Although the coastal zone of the Central Namib Desert (Namibia) has negligible rainfall, frequent fog, dew and high air humidity support a luxurious lichen flora. Large areas of soil crust communities are dominated by the multibranched, fruticose Teloschistes capensis interspersed by a (still indeterminable) Ramalina species. In earlier communications, based on field measurements in autumn, we began the analysis of functional mechanisms that allow these lichens to exist under the special conditions of a fog desert. We have extended this work by monitoring lichen CO₂ exchange and water relations in spring and by experiments under controlled conditions.


In both seasons, nocturnal hydration, by fog and/or dew, activated dark respiration of the lichens which was followed, after sunrise, by a short period of positive net photosynthesis (NP) that continued until metabolic inactivation occurred from desiccation. Dry thalli of T. capensis were able to reactivate NP through water vapour uptake alone, beginning at an air relative humidity of 82%, i.e. at a water potential of −26.3 MPa; the moisture compensation point during desiccation was at 13% thallus water content (WC, dry weight related). Optimal WC for photosynthesis was around 100%, and both species showed a large and extended suprasaturation depression of CO₂ assimilation. Light response showed “sun-plant” characteristics with saturation >1000 μmol m⁻²s⁻¹ photosynthetically active photon flux density (PPFD). However, due to rapid desiccation, the combination of light saturation with optimal WC very rarely occurred under field conditions. Light compensation point after sunrise was highly dependent on actual WC: at low hydration, it amounted to only ca. 10 μmol m⁻² s⁻¹ PPFD so that even the smallest levels of hydration could be used for carbon gain before desiccation took place again. This phenomenon was probably due to a hydration gradient in the thallus branches during transient moistening so that the outer photobiont layer was favoured in contrast to the internal mycobiont which remained dry longer and did not contribute respiratory CO₂ loss. Fully hydrated thalli had light compensation points around 50 μmol m⁻² s⁻¹ PPFD. Extended desiccation of 1–3 days had no impact on the magnitude and recovery of photosynthesis but, imposed desiccation of 10 days reduced NP in lab and field experiments and caused an extended period of recovery. “Resaturation respiration” was not detected in the field data, although it was present after experimental moistening of dry thalli.
In spring, the higher fog frequency and intensity increased maximal nocturnal WC, maximal attained NP as well as integrated daily carbon income (ΣNP) compared to the autumn measurements. NPmax and ΣNP depended on maximal nocturnal WC with a saturation-type response. In terms of carbon gain both species seem to be optimally adapted to nocturnal moistening up to 160% WC and were not able to make use of higher degrees of hydration, a feature that might well influence their habitat selection.

Maximal daily carbon-related ΣNP for T. capensis was 4.6 mgC (gC)⁻¹ day⁻¹. A rough estimate of the annual (projected) area-related carbon balance (photosynthetic income minus respiratory losses) based on published fog and dew frequencies and personal observations was 15–34 mgC m⁻² yr⁻¹.

year: 2006

title: A study of the relationships between climate and stable isotope ratios in tree rings

authors: Grinsted, Martin James

abstract: The main objectives of this work were to find out: 
(a) how the stable isotope ratios in wood constituents such as cellulose and lignin vary with changing climate;
(b) whether such variations can be applied to the study of past climate. 
Initially rings from a New Zealand grown Pinus radiata (Monterey pine) were studied since this is a complacent tree which grows throughout the year and hence over a wide temperature range.
In order to accurately determine the stable isotope ratios in wood components the following techniques were developed:
(a) the preparation of wood constituents on a small scale;
(b) the determination of δD values in waters;
(c) the determination of δD values in plant materials;
(d) the determination of δ¹³C values in plant materials.
Several possible methods for measuring D/H ratios for cellulose are discussed. It was decided to use a technique which involves heating cellulose with a standard water to fix the D/H ratio of the exchangeable hydrogens. Using this method relative δD values have been determined to a precision of ± 0.9°/οο (1 σ). The δ¹³C method was developed so that the ¹³C content of cellulose and lignin samples could be determined to ± 0. 04°/οο (1 σ).
A new procedure for determining δ values from raw mass spectrometer results is outlined. 
δD determinations on cellulose samples from three growth rings in a specimen of Pinus radiata show that the non-exchangeable hydrogens of cellulose are more than 20°/οο depleted in the summer as compared with the winter. These δD values appear to vary with the annual temperature cycle, but in the opposite sense to that expected from thermodynamic considerations. δ¹⁸ο determinations on the same samples show a summer/winter variation of about 2°/οο and in the opposite direction to the summer/winter variation in the δD determinations.
The δD results from Pinus radiata cellulose are compared with δD determinations on cellulose from other trees. 
It is concluded that all the measurements to date suggest that an increase in temperature results in a decrease in the D/H ratio of the non-exchangeable hydrogens in cellulose. The results imply a temperature coefficient of about - 3°/oo per °C, which is opposite to that found for precipitation (+ 5. 6°/oo per °C). This temperature effect will only be useful for past climate studies if δD variations due to meteoric and/or leaf transpiration changes can be corrected for. This may be possible using δ¹⁸o determinations. 
A new model to explain the effects of environmental changes on the magnitude of carbon isotopic fractionation in C₃ plants is presented and discussed. 
δ¹³C determinations on both cellulose and lignin from the same Pinus radiata that was used for the δD determinations show an enrichment of about 2°/oo in summer wood as compared with winter wood. This summer/winter variation is probably mainly due to changes in air temperature affecting the magnitude of carbon isotope fractionation during photosynthesis. The lignin variations are similar, but significantly displaced in time with respect to the cellulose variations. This is probably the result of secondary lignification. 
δ¹³C values for cellulose prepared from individual rings in a sample of dendrochronologically dated Pseudotsuga menziesii (Douglas fir) are compared with meteorological observations during growth. A correlation between the δ¹³C values and mean late spring/early summer temperature is discussed. The temperature coefficient for this correlation is + 0.22°/oo per °C, which is in good agreement with the Pinus radiata results.
Similar determinations on individual rings from Pinus radiata are difficult to interpret in terms of climatic changes because of a relatively large depletion in ¹³C towards the centre of the tree studied. A similar depletion in ¹³C was observed for cellulose prepared from a carbon-14 dated Agathis australis (New Zealand kauri) which grew during the last 1000 years. However, no such “age” effect was observed when δ¹³C values were determined for cellulose samples prepared from two dendrochronologically dated Pinus longaeva (Bristlecone pine) trees which also grew during the last 1000 years. 
The short-term fluctuations in the cellulose δ¹³C curve for Agathis australis are probably temperature related, and therefore represent a record of warm and cold periods in New Zealand’s climate. This record is discussed together with information available from other sources. It is concluded that the fluctuations in New Zealand’s climate during the last millennium were basically similar to those in the climate of North-western Europe. 
The δ¹³C variations in Pinus longaeva cellulose appear to be climate related, although in the opposite sense to the Agathis australis variations. These δ¹³C variations in lower forest border Pinus longaeva significantly correlate with upper tree line ring width variations for the same species. It is proposed that changing water stress is the underlying cause of the δ¹³C variations. If this is the case, the correlation may be the result of a correspondence between periods of water stress at the lower forest border and warm periods at the upper tree line.
It is concluded that ¹³C/¹²C ratios in both cellulose and lignin vary with changing climate. Results from Pinus radiata and Pseudotsuga menziesii indicate a temperature dependence of about + 0.21°/oo per °C. However, other results from Pseudotsuga menziesii and Pinus longaeva indicate that, in some situations, this effect is dominated by a larger and opposite effect, attributed in this work to water stress.
Thus there is little doubt that δ¹³C variations in the wood components from each tree ring sequence studied reflect climatic changes in that particular area. For some trees the effect of plant physiological changes on such variations is little understood. At present, those trees growing in exposed situations with a plentiful water supply appear to hold most promise for elucidating past climate data from measurements of ¹³C/¹²C ratios.

text: A study of the relationships between climate and stable isotope ratios in tree rings The main objectives of this work were to find out: 
(a) how the stable isotope ratios in wood constituents such as cellulose and lignin vary with changing climate;
(b) whether such variations can be applied to the study of past climate. 
Initially rings from a New Zealand grown Pinus radiata (Monterey pine) were studied since this is a complacent tree which grows throughout the year and hence over a wide temperature range.
In order to accurately determine the stable isotope ratios in wood components the following techniques were developed:
(a) the preparation of wood constituents on a small scale;
(b) the determination of δD values in waters;
(c) the determination of δD values in plant materials;
(d) the determination of δ¹³C values in plant materials.
Several possible methods for measuring D/H ratios for cellulose are discussed. It was decided to use a technique which involves heating cellulose with a standard water to fix the D/H ratio of the exchangeable hydrogens. Using this method relative δD values have been determined to a precision of ± 0.9°/οο (1 σ). The δ¹³C method was developed so that the ¹³C content of cellulose and lignin samples could be determined to ± 0. 04°/οο (1 σ).
A new procedure for determining δ values from raw mass spectrometer results is outlined. 
δD determinations on cellulose samples from three growth rings in a specimen of Pinus radiata show that the non-exchangeable hydrogens of cellulose are more than 20°/οο depleted in the summer as compared with the winter. These δD values appear to vary with the annual temperature cycle, but in the opposite sense to that expected from thermodynamic considerations. δ¹⁸ο determinations on the same samples show a summer/winter variation of about 2°/οο and in the opposite direction to the summer/winter variation in the δD determinations.
The δD results from Pinus radiata cellulose are compared with δD determinations on cellulose from other trees. 
It is concluded that all the measurements to date suggest that an increase in temperature results in a decrease in the D/H ratio of the non-exchangeable hydrogens in cellulose. The results imply a temperature coefficient of about - 3°/oo per °C, which is opposite to that found for precipitation (+ 5. 6°/oo per °C). This temperature effect will only be useful for past climate studies if δD variations due to meteoric and/or leaf transpiration changes can be corrected for. This may be possible using δ¹⁸o determinations. 
A new model to explain the effects of environmental changes on the magnitude of carbon isotopic fractionation in C₃ plants is presented and discussed. 
δ¹³C determinations on both cellulose and lignin from the same Pinus radiata that was used for the δD determinations show an enrichment of about 2°/oo in summer wood as compared with winter wood. This summer/winter variation is probably mainly due to changes in air temperature affecting the magnitude of carbon isotope fractionation during photosynthesis. The lignin variations are similar, but significantly displaced in time with respect to the cellulose variations. This is probably the result of secondary lignification. 
δ¹³C values for cellulose prepared from individual rings in a sample of dendrochronologically dated Pseudotsuga menziesii (Douglas fir) are compared with meteorological observations during growth. A correlation between the δ¹³C values and mean late spring/early summer temperature is discussed. The temperature coefficient for this correlation is + 0.22°/oo per °C, which is in good agreement with the Pinus radiata results.
Similar determinations on individual rings from Pinus radiata are difficult to interpret in terms of climatic changes because of a relatively large depletion in ¹³C towards the centre of the tree studied. A similar depletion in ¹³C was observed for cellulose prepared from a carbon-14 dated Agathis australis (New Zealand kauri) which grew during the last 1000 years. However, no such “age” effect was observed when δ¹³C values were determined for cellulose samples prepared from two dendrochronologically dated Pinus longaeva (Bristlecone pine) trees which also grew during the last 1000 years. 
The short-term fluctuations in the cellulose δ¹³C curve for Agathis australis are probably temperature related, and therefore represent a record of warm and cold periods in New Zealand’s climate. This record is discussed together with information available from other sources. It is concluded that the fluctuations in New Zealand’s climate during the last millennium were basically similar to those in the climate of North-western Europe. 
The δ¹³C variations in Pinus longaeva cellulose appear to be climate related, although in the opposite sense to the Agathis australis variations. These δ¹³C variations in lower forest border Pinus longaeva significantly correlate with upper tree line ring width variations for the same species. It is proposed that changing water stress is the underlying cause of the δ¹³C variations. If this is the case, the correlation may be the result of a correspondence between periods of water stress at the lower forest border and warm periods at the upper tree line.
It is concluded that ¹³C/¹²C ratios in both cellulose and lignin vary with changing climate. Results from Pinus radiata and Pseudotsuga menziesii indicate a temperature dependence of about + 0.21°/oo per °C. However, other results from Pseudotsuga menziesii and Pinus longaeva indicate that, in some situations, this effect is dominated by a larger and opposite effect, attributed in this work to water stress.
Thus there is little doubt that δ¹³C variations in the wood components from each tree ring sequence studied reflect climatic changes in that particular area. For some trees the effect of plant physiological changes on such variations is little understood. At present, those trees growing in exposed situations with a plentiful water supply appear to hold most promise for elucidating past climate data from measurements of ¹³C/¹²C ratios.

year: 1977

title: Kua Huri Taku Tira: The Rereahu Journey Towards Autonomy

authors: Crown, Jenny

subjects: autonomy

abstract: The establishment of the Native Land Court in Aotearoa New Zealand by the settler government caused much upheaval for tangata whenua. Traditional land tenure was interrupted by the colonised view of land ownership. Impetus to establish individual ownership of land was placed upon iwi and hapū Māori. This necessitated the iwi and hapū of the Rohe Pōtae to define their own individual boundaries within the autonomous region.

Over one hundred years later, the New Zealand government were under pressure from the Māori community. Iwi and hapū were vociferous in their requirements. The returning of land and natural resources to Māori was of paramount importance. The implementation of the Māori Trust Board Act enabled iwi and hapū to establish governance entities which permitted access to government funding. These entities also provided a vehicle through which iwi could pursue cultural redress from the Crown. This was the only way forward – the way dictated by the Crown.

Devolution was to become a reality and a sign of the decolonisation process at play. Such would allow Māori to re-establish autonomy which had been lost over a century prior. Destructive notions such as marginalisation, disenfranchisement and displacement would be reversed and Māori would regain control over their own cultural practices, cultural resources and future. Under the Fourth Labour Government of New Zealand this became a reality for some iwi and hapū.

This thesis investigates the attempts made by the Rereahu iwi in securing such recognition. Interrogation into the many ways in which Rereahu has attempted to navigate the multiple political landscapes which still exist and continue to control iwi and hapū have been discussed. The study develops a theoretical framework of Māori wide concepts as applied through a Rereahu-centric lens. Thus, allowing for a balanced approach to the collection, collation and analysis of all evidence utilised in this thesis.

Key findings bring to light the effects colonisation has had and continues to have on Rereahu autonomy. The ways in which Rereahu has been misrepresented, and how Rereahu has responded to threats of colonisation in the 21st century are apparent. This thesis contributes new knowledge to the realm of academia through the experiences of the iwi Rereahu; and offers indigenous discourse regarding resilience and resistance.

The ongoing effects of colonisation being felt by the Rereahu iwi in this contemporary landscape are defined. It is an example of how the oppressed can easily become the oppressor. This thesis goes some way to highlighting the destructive nature of the Waitangi Tribunal process in regards to Rereahu. The knowledge presented in this thesis could be utilised by the Office of Treaty Settlements, education and health establishments, policy makers and the iwi of Rereahu in addressing and combating the negative effects created by the cycle of colonisation.

text: Kua Huri Taku Tira: The Rereahu Journey Towards Autonomy The establishment of the Native Land Court in Aotearoa New Zealand by the settler government caused much upheaval for tangata whenua. Traditional land tenure was interrupted by the colonised view of land ownership. Impetus to establish individual ownership of land was placed upon iwi and hapū Māori. This necessitated the iwi and hapū of the Rohe Pōtae to define their own individual boundaries within the autonomous region.

Over one hundred years later, the New Zealand government were under pressure from the Māori community. Iwi and hapū were vociferous in their requirements. The returning of land and natural resources to Māori was of paramount importance. The implementation of the Māori Trust Board Act enabled iwi and hapū to establish governance entities which permitted access to government funding. These entities also provided a vehicle through which iwi could pursue cultural redress from the Crown. This was the only way forward – the way dictated by the Crown.

Devolution was to become a reality and a sign of the decolonisation process at play. Such would allow Māori to re-establish autonomy which had been lost over a century prior. Destructive notions such as marginalisation, disenfranchisement and displacement would be reversed and Māori would regain control over their own cultural practices, cultural resources and future. Under the Fourth Labour Government of New Zealand this became a reality for some iwi and hapū.

This thesis investigates the attempts made by the Rereahu iwi in securing such recognition. Interrogation into the many ways in which Rereahu has attempted to navigate the multiple political landscapes which still exist and continue to control iwi and hapū have been discussed. The study develops a theoretical framework of Māori wide concepts as applied through a Rereahu-centric lens. Thus, allowing for a balanced approach to the collection, collation and analysis of all evidence utilised in this thesis.

Key findings bring to light the effects colonisation has had and continues to have on Rereahu autonomy. The ways in which Rereahu has been misrepresented, and how Rereahu has responded to threats of colonisation in the 21st century are apparent. This thesis contributes new knowledge to the realm of academia through the experiences of the iwi Rereahu; and offers indigenous discourse regarding resilience and resistance.

The ongoing effects of colonisation being felt by the Rereahu iwi in this contemporary landscape are defined. It is an example of how the oppressed can easily become the oppressor. This thesis goes some way to highlighting the destructive nature of the Waitangi Tribunal process in regards to Rereahu. The knowledge presented in this thesis could be utilised by the Office of Treaty Settlements, education and health establishments, policy makers and the iwi of Rereahu in addressing and combating the negative effects created by the cycle of colonisation.

year: 2019