title: Water relations and carbon dioxide exchange of epiphytic lichens in the Namib fog desert

authors: Lange, Otto L.

subjects: dew

abstract: Although there is only negligible rainfall, frequent nocturnal fog, dew and high air humidity support a luxurious lichen vegetation in the coastal zone of the central NamibDesert (Namibia). In earlier publications, we have studied ecophysiological performance of a series of epilithic and terrestrial lichens. Here, we have extended this work to three epiphytic species (Heterodermia namaquana, Ramalina lacera, and Xanthoria turbinata) that inhabit the sparse perennial shrubs growing in this area. Our intention, monitoring lichen CO₂ exchange, their waterrelations and microclimate conditions, was to determine the functional mechanisms that allow these epiphytes to exist under the special conditions of a fogdesert. Measurements were conducted mainly during the spring season.
The epiphyticlichens showed response patterns very similar to the epilithic and epigaeic species at the same site. Their metabolism was activated through moistening by dew and/or fog during the night and, in the very early morning, they exhibited the typical brief peak of net photosynthesis (NP) between sunrise and desiccation. The thalli were almost completely dry for the remainder of the day. Average duration of the positive NP during the morning peak was about 3 h. Dew condensation, alone, resulted in activation that provided 58–63% of integrated carbon income (ΣNP) as compared to fog (plus dew). In the late afternoon, there was a tendency for hydration to increase again, due to water vapour uptake at higher air humidity, and this allowed on some days a brief additional period of very low rates of photosynthesis shortly before sunset.
Light response of photosynthesis showed “sun-plant” characteristics with saturation around 1000 μmol m⁻² s⁻¹ photosynthetically active photon flux density (PPFD). Light compensation point (LCP) of CO2exchange after sunrise was highly dependent on actual water content (WC) for X. turbinata: at low hydration it was ca. 10 μmol m⁻² s⁻¹ PPFD whilst, at high WC, it was almost 80 μmol m⁻² s⁻¹ PPFD. In contrast, LCP of R. lacera was almost independent of WC. This phenomenon was probably due to differences in thallus structure.
Maximal attained NP and daily ΣNP both showed a saturation-type response to previous maximal nocturnal WC. Neither parameter was increased substantially when higher maximal thallus WCs were produced by experimental moistening in the night. All three species, despite their different morphologies, performed optimally at the highest nocturnal moistening achieved by natural fog and were not able to make use of higher hydration.
The three studied epiphytes were similar in their chlorophyll-related rates of NP. Due to lower chlorophyll content, dry weight and carbon-related NP of X. turbinata was only about one-third of that of the other two species. The average carbon income on days with fog and/or dew hydration during the spring season amounted to 2.4 and 2.1 mgC (gC)⁻¹ day⁻¹ (related to thallus carbon content) for H. namaquana and R. lacera, respectively. This primary production was of similar magnitude to those found for the terrestrial species at the same site.

text: Water relations and carbon dioxide exchange of epiphytic lichens in the Namib fog desert Although there is only negligible rainfall, frequent nocturnal fog, dew and high air humidity support a luxurious lichen vegetation in the coastal zone of the central NamibDesert (Namibia). In earlier publications, we have studied ecophysiological performance of a series of epilithic and terrestrial lichens. Here, we have extended this work to three epiphytic species (Heterodermia namaquana, Ramalina lacera, and Xanthoria turbinata) that inhabit the sparse perennial shrubs growing in this area. Our intention, monitoring lichen CO₂ exchange, their waterrelations and microclimate conditions, was to determine the functional mechanisms that allow these epiphytes to exist under the special conditions of a fogdesert. Measurements were conducted mainly during the spring season.
The epiphyticlichens showed response patterns very similar to the epilithic and epigaeic species at the same site. Their metabolism was activated through moistening by dew and/or fog during the night and, in the very early morning, they exhibited the typical brief peak of net photosynthesis (NP) between sunrise and desiccation. The thalli were almost completely dry for the remainder of the day. Average duration of the positive NP during the morning peak was about 3 h. Dew condensation, alone, resulted in activation that provided 58–63% of integrated carbon income (ΣNP) as compared to fog (plus dew). In the late afternoon, there was a tendency for hydration to increase again, due to water vapour uptake at higher air humidity, and this allowed on some days a brief additional period of very low rates of photosynthesis shortly before sunset.
Light response of photosynthesis showed “sun-plant” characteristics with saturation around 1000 μmol m⁻² s⁻¹ photosynthetically active photon flux density (PPFD). Light compensation point (LCP) of CO2exchange after sunrise was highly dependent on actual water content (WC) for X. turbinata: at low hydration it was ca. 10 μmol m⁻² s⁻¹ PPFD whilst, at high WC, it was almost 80 μmol m⁻² s⁻¹ PPFD. In contrast, LCP of R. lacera was almost independent of WC. This phenomenon was probably due to differences in thallus structure.
Maximal attained NP and daily ΣNP both showed a saturation-type response to previous maximal nocturnal WC. Neither parameter was increased substantially when higher maximal thallus WCs were produced by experimental moistening in the night. All three species, despite their different morphologies, performed optimally at the highest nocturnal moistening achieved by natural fog and were not able to make use of higher hydration.
The three studied epiphytes were similar in their chlorophyll-related rates of NP. Due to lower chlorophyll content, dry weight and carbon-related NP of X. turbinata was only about one-third of that of the other two species. The average carbon income on days with fog and/or dew hydration during the spring season amounted to 2.4 and 2.1 mgC (gC)⁻¹ day⁻¹ (related to thallus carbon content) for H. namaquana and R. lacera, respectively. This primary production was of similar magnitude to those found for the terrestrial species at the same site.

year: 2007

title: Assessment for learning in design and technology: An ethnographic study in Mauritius state secondary schools

authors: Boodhoo, Chandan

subjects: Assessment for learning

abstract: Research advocates that it is the teacher’s role to support learners to take the next steps in their learning. ‘Assessment for learning’, considered as a bridge between teaching and learning, not only provides teachers with multiple possibilities to enhance students’ learning, but can also transform their own practice. Despite research interest in educational assessment, teachers’ ‘assessment for learning’ behaviours and perceptions are under-researched. This study investigated Design and Technology teachers’ ‘assessment for learning’ practices in state secondary schools in Mauritius since little is known about this context. A constructivist epistemology, naturalistic interpretative perspective and an ethnographic methodology was used to understand the participants’ ‘assessment for learning’ practices in their natural settings. The study was underpinned by sociocultural theory, Foucault’s and Bourdieu’s critical theories, and Bronfenbrenner’s ecological model as theoretical frameworks. A three-stage mixed methods research design was adopted, which involved multiple methods of data collection, including questionnaires, interviews and observations along with field notes and secondary documents. The participants involved were 29 Design and Technology teachers and 16 students (14-year-olds) from schools of three educational zones. The results of this study indicate that Design and Technology teachers did not enact ‘assessment for learning’ strategies to enhance their teaching and student learning. Despite the introduction of a new curriculum and the policy initiatives of the Mauritius Ministry of Education to adopt learner-centred approaches to assessment, Design and Technology teachers focused on syllabus coverage, using traditional assessment approaches and teaching students to sit for end-of-year examinations. The findings of this study have important implications for policymakers, teacher educators, principals and Design and Technology teachers. Key implications associated with ‘assessment for learning’ include the need to develop: teacher education programmes that cover concepts and theories, and evidence of best practice; and professional learning and development programmes that complement the national curriculum, and explore the relationships between beliefs and practices and influences of contextual factors.

text: Assessment for learning in design and technology: An ethnographic study in Mauritius state secondary schools Research advocates that it is the teacher’s role to support learners to take the next steps in their learning. ‘Assessment for learning’, considered as a bridge between teaching and learning, not only provides teachers with multiple possibilities to enhance students’ learning, but can also transform their own practice. Despite research interest in educational assessment, teachers’ ‘assessment for learning’ behaviours and perceptions are under-researched. This study investigated Design and Technology teachers’ ‘assessment for learning’ practices in state secondary schools in Mauritius since little is known about this context. A constructivist epistemology, naturalistic interpretative perspective and an ethnographic methodology was used to understand the participants’ ‘assessment for learning’ practices in their natural settings. The study was underpinned by sociocultural theory, Foucault’s and Bourdieu’s critical theories, and Bronfenbrenner’s ecological model as theoretical frameworks. A three-stage mixed methods research design was adopted, which involved multiple methods of data collection, including questionnaires, interviews and observations along with field notes and secondary documents. The participants involved were 29 Design and Technology teachers and 16 students (14-year-olds) from schools of three educational zones. The results of this study indicate that Design and Technology teachers did not enact ‘assessment for learning’ strategies to enhance their teaching and student learning. Despite the introduction of a new curriculum and the policy initiatives of the Mauritius Ministry of Education to adopt learner-centred approaches to assessment, Design and Technology teachers focused on syllabus coverage, using traditional assessment approaches and teaching students to sit for end-of-year examinations. The findings of this study have important implications for policymakers, teacher educators, principals and Design and Technology teachers. Key implications associated with ‘assessment for learning’ include the need to develop: teacher education programmes that cover concepts and theories, and evidence of best practice; and professional learning and development programmes that complement the national curriculum, and explore the relationships between beliefs and practices and influences of contextual factors.

year: 2018

title: How many deaths were caused by the Tarawera eruption?

authors: Lowe, David J.

abstract: Most texts and brochures describing the Tarawera eruption of 10 June, l 886, record that it resulted in about 150 fatalities (e.g., Scott & Nairn, 1989; Ansell & Taber, 1996). Indeed, a figure of 153 deaths is recorded at the excellent new visitors' centre at the Buried Village, Te Wairoa, and in a number of other contexts. Elsewhere, numbers ranging from as few as about one hundred to possibly 'thousands' of deaths have been suggested (e.g., Houghton & Johnston, 1999).

text: How many deaths were caused by the Tarawera eruption? Most texts and brochures describing the Tarawera eruption of 10 June, l 886, record that it resulted in about 150 fatalities (e.g., Scott & Nairn, 1989; Ansell & Taber, 1996). Indeed, a figure of 153 deaths is recorded at the excellent new visitors' centre at the Buried Village, Te Wairoa, and in a number of other contexts. Elsewhere, numbers ranging from as few as about one hundred to possibly 'thousands' of deaths have been suggested (e.g., Houghton & Johnston, 1999).

year: 2001