title: Macrophyte architecture affects the abundance and diversity of littoral microfauna

authors: Lucena-Moya, Paloma

subjects: zooplankton

abstract: We tested the hypothesis that structural complexity is an important factor influencing the abundance and taxon richness of microfauna (e.g., rotifers, copepods, cladocerans) in littoral habitats. Research on littoral microfauna has to date focused mainly on field observations, which commonly show microfauna have preference for some macrophytes over others. However, while such studies commonly conclude that macrophyte architecture is a major determinant of these variations, independent factors may also be responsible (e.g., differences in macrophyte ages, differences in macrophyte bed densities and the depth of the respective macrophyte beds sampled). We used artificial macrophytes with three levels of complexity to keep the surface area and mass of the substrate sampled constant, and to control for confounding factors not related to the complexity of the plants. Our results support the hypothesis that structural complexity is an important factor influencing abundance and taxon richness, independent of other potential confounding factors. Microfaunal (mainly rotifer) abundance and richness were generally greater on more complex artificial macrophytes, likely a result of more complex substrates (1) providing a greater variety of habitat, (2) supporting a greater concentration or variety of food and/or (3) affording greater protection against predators. Less mobile surface-associated (i.e., benthic/periphytic) taxa were found to discriminate among substrates, whereas the abundance and richness of planktonic species were not affected by complexity level. Relatively low abundances and taxon richness of microfauna recorded in control samples, which did not contain artificial macrophytes, supports the contention that vegetated areas sustain a higher abundance and variety of species than non-vegetated areas.

text: Macrophyte architecture affects the abundance and diversity of littoral microfauna We tested the hypothesis that structural complexity is an important factor influencing the abundance and taxon richness of microfauna (e.g., rotifers, copepods, cladocerans) in littoral habitats. Research on littoral microfauna has to date focused mainly on field observations, which commonly show microfauna have preference for some macrophytes over others. However, while such studies commonly conclude that macrophyte architecture is a major determinant of these variations, independent factors may also be responsible (e.g., differences in macrophyte ages, differences in macrophyte bed densities and the depth of the respective macrophyte beds sampled). We used artificial macrophytes with three levels of complexity to keep the surface area and mass of the substrate sampled constant, and to control for confounding factors not related to the complexity of the plants. Our results support the hypothesis that structural complexity is an important factor influencing abundance and taxon richness, independent of other potential confounding factors. Microfaunal (mainly rotifer) abundance and richness were generally greater on more complex artificial macrophytes, likely a result of more complex substrates (1) providing a greater variety of habitat, (2) supporting a greater concentration or variety of food and/or (3) affording greater protection against predators. Less mobile surface-associated (i.e., benthic/periphytic) taxa were found to discriminate among substrates, whereas the abundance and richness of planktonic species were not affected by complexity level. Relatively low abundances and taxon richness of microfauna recorded in control samples, which did not contain artificial macrophytes, supports the contention that vegetated areas sustain a higher abundance and variety of species than non-vegetated areas.

year: 2011

title: Photosynthesis and transpiration in a dry-land Pinus radiata forest

authors: Walcroft, Adrian S.

abstract: This thesis investigates biotic and abiotic regulation of photosynthesis and transpiration at the leaf and canopy scales in a dry-land Pinus radiata D. Don forest by combining gas exchange measurements with biophysical process-based models of photosynthesis, radiation transfer, and soil water balance.

Responses of photosynthesis to leaf intercellular CO₂ concentration in two-year old P. radiata seedlings were measured at a range of temperatures and leaf nitrogen concentrations in order to quantify parameters describing photosynthetic capacity and temperature response in a biophysical model of C₃ photosynthesis. Increasing leaf temperature from 8 °C to 30 °C caused a four-fold increase in Vcₘₐₓ the maximum rate of carboxylation (10.7 to 43.3 μmol m⁻² s⁻¹), and a three-fold increase in Jₘₐₓ, the maximum electron transport rate (20.5 to 60.2 μmol m⁻² s⁻¹). Foliar nitrogen concentration (N) varied between 0.36 mmol g⁻¹ and 1.27 mmol g⁻¹, and there were linear relationships between N and both Vcₘₐₓ and Jₘₐₓ. Measurements made throughout the crown of a forest tree, where N varied from 0.83 mmol g⁻¹ near the base to 1.54 mmol g⁻¹ near the leader, yielded similar relationships.

The leaf-level photosynthesis model was combined with a water balance model to successfully explain a seasonal pattern in stable carbon isotope composition (δ¹³C) measured within annual rings of P. radiata from two sites which differed markedly in annual water balance. Over two growing seasons there was good agreement between mean canopy-level cᵢ derived from the tree-ring δ¹³C data and modelled leaf-level cᵢ levels. The amplitudes of seasonal δ¹³C variation at the wet and dry sites were 1-2 %₀ and 4 %₀ respectively, and mean δ¹³C values from the wet site were 3 %₀ more ¹³C depleted than those from the dry site implying lower water-use efficiency (carbon assimilation per unit transpiration). Seasonal variation in carbon isotope discrimination of leaves in the canopy is therefore reflected directly in the δ¹³C of stem wood.

A canopy photosynthesis model was developed by combining the leaf-level model with a model of canopy radiation transfer, and used as a framework to analyse a field experiment designed to quantify the response of photosynthesis and tree growth to a long-term reduction in illuminated leaf area. Shading the lower crown of two young forest trees reduced absorbed radiation and canopy photosynthesis by 11 and 9 % respectively in the first year. Nitrogen was translocated from current year foliage below the shade cloth to that above, and carbon partitioning to the branches increased at the expense of stem growth. In the second year, the effect of the shading on absorbed radiation, canopy photosynthesis and tree growth was less due to a reduction in shaded foliage proportional to total leaf area. Additionally, a prolonged period of soil water deficit during the summer of year 2 reduced photosynthesis, stomatal conductance and growth similarly in both shaded and control trees. Models which scale up processes from the leaf-level to the canopy can provide a framework to analyse and interpret field experiments.

text: Photosynthesis and transpiration in a dry-land Pinus radiata forest This thesis investigates biotic and abiotic regulation of photosynthesis and transpiration at the leaf and canopy scales in a dry-land Pinus radiata D. Don forest by combining gas exchange measurements with biophysical process-based models of photosynthesis, radiation transfer, and soil water balance.

Responses of photosynthesis to leaf intercellular CO₂ concentration in two-year old P. radiata seedlings were measured at a range of temperatures and leaf nitrogen concentrations in order to quantify parameters describing photosynthetic capacity and temperature response in a biophysical model of C₃ photosynthesis. Increasing leaf temperature from 8 °C to 30 °C caused a four-fold increase in Vcₘₐₓ the maximum rate of carboxylation (10.7 to 43.3 μmol m⁻² s⁻¹), and a three-fold increase in Jₘₐₓ, the maximum electron transport rate (20.5 to 60.2 μmol m⁻² s⁻¹). Foliar nitrogen concentration (N) varied between 0.36 mmol g⁻¹ and 1.27 mmol g⁻¹, and there were linear relationships between N and both Vcₘₐₓ and Jₘₐₓ. Measurements made throughout the crown of a forest tree, where N varied from 0.83 mmol g⁻¹ near the base to 1.54 mmol g⁻¹ near the leader, yielded similar relationships.

The leaf-level photosynthesis model was combined with a water balance model to successfully explain a seasonal pattern in stable carbon isotope composition (δ¹³C) measured within annual rings of P. radiata from two sites which differed markedly in annual water balance. Over two growing seasons there was good agreement between mean canopy-level cᵢ derived from the tree-ring δ¹³C data and modelled leaf-level cᵢ levels. The amplitudes of seasonal δ¹³C variation at the wet and dry sites were 1-2 %₀ and 4 %₀ respectively, and mean δ¹³C values from the wet site were 3 %₀ more ¹³C depleted than those from the dry site implying lower water-use efficiency (carbon assimilation per unit transpiration). Seasonal variation in carbon isotope discrimination of leaves in the canopy is therefore reflected directly in the δ¹³C of stem wood.

A canopy photosynthesis model was developed by combining the leaf-level model with a model of canopy radiation transfer, and used as a framework to analyse a field experiment designed to quantify the response of photosynthesis and tree growth to a long-term reduction in illuminated leaf area. Shading the lower crown of two young forest trees reduced absorbed radiation and canopy photosynthesis by 11 and 9 % respectively in the first year. Nitrogen was translocated from current year foliage below the shade cloth to that above, and carbon partitioning to the branches increased at the expense of stem growth. In the second year, the effect of the shading on absorbed radiation, canopy photosynthesis and tree growth was less due to a reduction in shaded foliage proportional to total leaf area. Additionally, a prolonged period of soil water deficit during the summer of year 2 reduced photosynthesis, stomatal conductance and growth similarly in both shaded and control trees. Models which scale up processes from the leaf-level to the canopy can provide a framework to analyse and interpret field experiments.

year: 1998

title: Maori & Psychology Research Unit annual report 2007

authors: Rua, Mohi

subjects: Maori and Psychology Research Unit

abstract: Annual report of the Maori and Psychology Research Unit (MPRU) 2007. The unit was established in August of 1997. The unit is designed to provide a catalyst and support network for enhancing research concerning the psychological needs, aspirations, and priorities of Maori people. The MPRU is well situated to draw together skilled and experienced interdisciplinary research groups by networking and establishing working relationships with staff and students within the Faculty of Arts and Social Sciences, the University, and the wider community.

text: Maori & Psychology Research Unit annual report 2007 Annual report of the Maori and Psychology Research Unit (MPRU) 2007. The unit was established in August of 1997. The unit is designed to provide a catalyst and support network for enhancing research concerning the psychological needs, aspirations, and priorities of Maori people. The MPRU is well situated to draw together skilled and experienced interdisciplinary research groups by networking and establishing working relationships with staff and students within the Faculty of Arts and Social Sciences, the University, and the wider community.

year: 2008