Thesis (Ph.D. Chemistry)--University of Waikato, 2007. / Includes bibliographical references. Also available via the World Wide Web.

Thesis (Ph. D.)--University of New South Wales, 2001. / Also available online.

The aboveground and belowground productivity of forest systems are interlinked through complex feedback loops involving tree, soil and environmental factors. With a predicted significant change in environmental conditions through the enhanced greenhouse effect, it is important to understand the response of forest systems to these new conditions. An increase in atmospheric CO2 is predicted to increase photosynthesis, and therefore whole plant productivity at the individual tree level. However this increase in photosynthesis may result in greater requirements for nutrients, particularly nitrogen (N). In order to acquire any additional available N, trees may respond by increasing their proportional allocation of C belowground to the root system. This study aimed to quantify the belowground C allocation in a mature forest system consisting of a single species on a single site, but with different levels of water and nutrient stress. The belowground carbon dynamics of a range of irrigated and fertilized Pinus radiata stands in Australia were investigated during 1992 and 1993. Belowground carbon allocation was estimated using the model proposed by Raich and Nadelhoffer (1989) where belowground C allocation is the difference between soil respiration and carbon input through litterfall, plus coarse root production and an adjustment for any change in soil and litter layer carbon pools. This model is best described by the equation: Belowground C = Csoilresp ?? Clitterfall + Ccoarseroot+ ???Cforest floor+ ???Csoil Soil respiration, measured using a modified soda lime absorption method either every 2 weeks or every 4 weeks for 2 years, showed a range in daily soil C flux from 137 ?? 785 mgCO2.m-2.h-1. Soil respiration showed seasonal trends with summer highs and winter lows. Limited fine root biomass data could not indicate a strong relationship between measured soil respiration and fine root (&gt2mm diameter) biomass. Fifty three percent of the variation in soil respiration measurements in irrigated treatments was explained by a linear relationship between soil respiration, and soil temperature at 0.10 m depth and litter moisture content. In non-irrigated treatments, 61% of the variation in soil xix respiration measurements was explained by a linear relationship between soil temperature at 1 cm depth and soil moisture content. Inter-year variation was considerable with annual soil respiration approximately 20% lower in 1993 compared with 1992. Annual soil C flux was calculated by linear interpolation and ranged from 3.4 ?? 11.2 tC ha-1 across the treatments. Soil C pools remained unchanged over 10 years between 1983 and 1993 for all combinations of irrigated and fertilized stands, despite significant aboveground productivity differences over the decade. Measurements of standing litter showed a change between 1991 and 1993 for only 2 out of the 10 treatments. These two treatments had belowground C allocation estimated both with and without an adjustment for a change in standing litter. Annual litterfall C ranged almost four fold from 0.6 ?? 2.2 tC ha-1 between the treatments in 1992 and 1993, and fell within the ranges of measured litterfall over 10 years at the field site. Again inter-year variation was large, with the 1993 litterfall values being approximately 97% greater across all treatments compared with 1992 values. Belowground carbon allocation was calculated using C fluxes measured at the field site, and ranged 3 fold from 4.4 ?????? 12.9 tC ha-1 between the treatments during 1992 and 1993. In 1993 the belowground C allocation was approximately 30% lower across all treatments compared with 1992 calculations. This was due to an approximate 23% reduction in annual soil C flux, a 97% increase in litterfall C and an 18% reduction in coarse root production between 1992 and 1993. The field site was N limited, and differences in belowground C allocation could be shown across irrigated treatments with different N limitations. As N availability increased belowground C allocation was decreased in the irrigated treatments. It was difficult to determine differences in belowground C allocation caused by water stress as the effects of water and N limitation were confounded. An increase in N availability generally indicated an increase in coarse root and litterfall C production, which were reflected in increased aboveground productivity. In high N treatments the coarse root fraction of belowground C allocation comprised approximately 50% of the total belowground C allocation, whereas in the N stressed treatments coarse roots only comprised 20% of the total belowground allocation The mechanistic model BIOMASS was used to estimate annual gross primary productivity (GPP) for the different treatments at the field site. BIOMASS estimated GPPs of between 30-38 tC ha-1 for the different treatments during 1992 and 1993. The measured belowground carbon allocation ranged from 16 ?? 40 % of simulated GPP, with the lower proportion allocated belowground in the irrigated and high fertility stands. Aboveground competition through the absence of thinning also appeared to reduce allocation belowground in non- irrigated stands. A direct trade off between bole and belowground C could not be demonstrated, unless data were separated by year and by the presence or absence of irrigation. Where data were separated in this manner, only three data points defined the reasonably strong, negative relationship between bole and belowground C. The value of this relationship is highly questionable and should be interpreted with caution. Thus a decrease in belowground C allocation may not necessarily indicate a concomitant increase in bole C allocation. Inter-year variation in a number of C pools and fluxes measured at the field site was at least as great as the variation between stands having different water and N limitation. Extrapolation of belowground productivity estimates from a single years data should be undertaken cautiously. The work undertaken in this study indicated that for a given forest stand in a given soil type, an increase in N availability reduced the absolute and relative C allocated belowground. However this decrease in C belowground may not directly translate as an increase in stem growth or increased timber production. Forest productivity in an enhanced greenhouse environment is likely to result in an increased allocation of C belowground due to increased N limitation, unless adequate N is present to support a more active canopy. Further work is required to more fully understand the dynamics of the belowground system in a changing environment. However further research should focus on mature forest systems in order to isolate the impacts of natural ageing changes from perturbation effects on the forest system. This would be best undertaken in long term monitoring sites where a C history of the stand may be available.

Hybrid physiological models are being increasingly used to assess productivity, carbon sequestration, water and nutrient use and environmental impacts of management decisions. Users include forest managers, politicians, environmental agencies and scientists. However a wider use of these models has been prevented as a result of an incomplete understanding of the mechanisms regulating carbon allocation, nutrient availability in soils and nutrient uptake by trees. On-going innovation in clonal forestry, genetic improvement and vegetation management techniques is also poorly represented in hybrid models. This thesis examines means to represent nutrition and genotype-nutrition interactions in productivity physiological hybrid models. Nutrient limitations and growth differences between genotypes were hypothesized to operate through key physiological processes: photosynthesis, carbon allocation and nutrient internal cycling. In order to accomplish the aims of the study both greenhouse and field experimentation were carried out. In a first experiment, responses of photosynthesis (A) to intercellular CO₂ concentration (Ci) were measured in a fast- and a slow-growing clone of Pinus radiata D. Don cultivated in a greenhouse in a factorial combination of nitrogen and phosphorus supply, and analyzed using the biochemical model of leaf photosynthesis described by Farquhar et al. (1980). There were significant positive linear relationships between the parameters, Vcmax, Jmax, Tp and both foliar nitrogen (Na) and phosphorus (Pa) concentration on an area basis. The study showed that the effects of nitrogen and phosphorus supply on photosynthesis were statistically independent and that the photosynthetic behaviour of the two clones was equivalent. In a similar study, gas exchange and chlorophyll fluorescence were simultaneously measured to determine internal transfer conductance (gm) based on the "constant J method". Transfer conductance may pose significant limitations to photosynthesis which may be differentially affected by nutrition and genotype in Pinus radiata. Values of gm were similar to those of stomatal conductance (gs) and their ratio (gm / gs) was not influenced by nutrient supply or clone being on average (±1 SE) 1.22 ±0.04. Relative mesophyll limitations (LM, 16%) to photosynthesis were marginally greater than those imposed by stomata (LS, 13%), and together smaller than the relative limitations posed to photosynthesis by biochemical processes (LB, 71%). The CO₂ concentration in the intercellular air spaces (Ci) was (±1 SE) 53 ±3 µmol mol-1 lower than in the atmosphere (Ca) while CO₂ concentration in the chloroplasts (Cc) was (±1 SE) 48 ±2 µmol mol-1 less than Ci. Values of LS, LM and LB and CO₂ diffusion gradients posed by gs (Ca-Ci) and gm (Ci-Cc) did not change with nutrient supply or clone. In a third experiment, one-year old Pinus radiata cuttings from four genotypes were cultivated in silica sand with a factorial combination of nitrogen (N0=1.43 and N1=7.14 mM) and phosphorus (P0=0.084 and P1=0.420 mM) supply for 24 months. N supply was enriched with ¹⁵N to 2.5⁰/₀₀ (labelled N) during the first year, then plants transferred to clean sand and cultivated for another year with ¹⁵N at levels close to natural abundance (0.3664899 atom percent ¹⁵N, δ¹⁵N 0.5115 ⁰/₀₀) provided by the source of N in nutrient solution applied during the second year. Recovery of labelled and unlabelled N was used to estimate N remobilization. N remobilization scaled with plant growth, N content and N and P supply. In relative terms, 65% of all stored N was remobilized in the high-nutrient supply regime compared to 42-48% at lower N and P addition rates. Most N remobilization occurred during spring-summer (77%), coincidently with the largest proportion of needle development (80%), indicating that N remobilization was driven by sink-strength. Foliage was by far the main source for internal cycling while roots were the main sink (40%). Clones exhibited differences in N remobilization capacity, but these differences were completely explained by the size of the N pool before remobilization took place, indicating that N remobilization performance was similar among clones. In a fourth study, four clones were cultivated in silica sand with a factorial combination of nitrogen and phosphorus supply for ten months, and patterns of carbon allocation examined using a carbon balance approach. Gross-primary productivity (GPP) scaled mainly with nitrogen but also with phosphorus supply. The fraction of GPP (GPP = ANPP + APR + TBCA) allocated to above-ground components (ANPP) increased with N and P supply at the expense of total-below ground C allocation (TBCA) with no apparent effect on the fraction of GPP partitioned to above-ground plant respiration (APR). Carbon use efficiency (NPP:GPP) scaled with nutrient supply, being 0.42 in the low-nutrient supply regime compared to 0.51 in the high-nutrient supply regime, suggesting that in poor fertility environments a larger proportion of the C budget is respired compared to the net productivity. Fast-growing clones allocated about 2-4% more carbon to above-ground components (ANPP) at the expense of carbon allocated below-ground (TBCA) with no effect on carbon respired above-ground (APR), indicating that faster-growing genotypes allocate more carbon to leaf area which may compound and increase overall GPP over time. The field component of this thesis was conducted in a subset of locations where ENSIS (formerly New Zealand Forest Research Institute) had established trials to test the influence of species, soil disturbance and plant nutrition on sustainability indicators. Plots were small in size (3 m × 3 m) with trees spaced at 0.5 m × 0.5 m (40 000 trees ha-1) with nine measurement trees surrounded by a two-row buffer. All sites were planted in winter 2001 and harvested in spring 2005. The aim of this pilot study was to examine patterns of carbon allocation during the fourth year after planting in control and fertilized mini-plots of Pinus radiata in five sites with contrasting climate and soil conditions in the South Island of New Zealand. The study showed that the fraction of gross-primary productivity allocated belowground increased as the soil C:N ratio increased. However, these results should be interpreted with caution due to the unusual nature of the trial and the reduced number of sites studied. Two existing physiological models were selected for the discussion in this thesis (3-PG, Landsberg and Waring 1997; canopy net carbon exchange model, Whitehead et al. 2002). Potential improvements for the nutritional component of 3-PG comprise: accounting for reductions in carbon use efficiency (NPP:GPP) in poor-fertility environments, adding a preliminary fertility modifier (FN, 0-1) driven by soil C : N ratio and soil N, adding a preliminary relationship between carbon allocation to roots and the soil C : N ratio and representing faster-growing genotypes by increasing their leaf area but not their photosynthetic performance. The canopy net carbon exchange model (NCE) combines the coupled model of leaf photosynthesis - stomatal conductance described by Leuning (1995) with canopy structure and a water balance model to scale carbon assimilation from leaves to canopies. Potential improvements to account for nutrient deficiencies in the leaf model by Leuning (1995), comprise using nutrient ratios to discriminate nitrogen (Na/Pa < 23 mol mol-1) from phosphorus deficiencies (Na/Pa > 23 mol mol-1), adding relationships between photosynthetic model parameters Vcmax and Jmax to Pa, and correcting the estimation of photosynthetic parameters Vcmax and Jmax by accounting for transfer conductance (gm). The canopy net carbon exchange model may be also modified to account for carbon-use efficiency, carbon allocation to roots and genotype in a similar form to that proposed for 3-PG. The results previously outlined provide a preliminary framework to represent tree and soil nutrition in physiological hybrid productivity models.

The aboveground and belowground productivity of forest systems are interlinked through complex feedback loops involving tree, soil and environmental factors. With a predicted significant change in environmental conditions through the enhanced greenhouse effect, it is important to understand the response of forest systems to these new conditions. An increase in atmospheric CO2 is predicted to increase photosynthesis, and therefore whole plant productivity at the individual tree level. However this increase in photosynthesis may result in greater requirements for nutrients, particularly nitrogen (N). In order to acquire any additional available N, trees may respond by increasing their proportional allocation of C belowground to the root system. This study aimed to quantify the belowground C allocation in a mature forest system consisting of a single species on a single site, but with different levels of water and nutrient stress. The belowground carbon dynamics of a range of irrigated and fertilized Pinus radiata stands in Australia were investigated during 1992 and 1993. Belowground carbon allocation was estimated using the model proposed by Raich and Nadelhoffer (1989) where belowground C allocation is the difference between soil respiration and carbon input through litterfall, plus coarse root production and an adjustment for any change in soil and litter layer carbon pools. This model is best described by the equation: Belowground C = Csoilresp ?? Clitterfall + Ccoarseroot+ ???Cforest floor+ ???Csoil Soil respiration, measured using a modified soda lime absorption method either every 2 weeks or every 4 weeks for 2 years, showed a range in daily soil C flux from 137 ?? 785 mgCO2.m-2.h-1. Soil respiration showed seasonal trends with summer highs and winter lows. Limited fine root biomass data could not indicate a strong relationship between measured soil respiration and fine root (&gt2mm diameter) biomass. Fifty three percent of the variation in soil respiration measurements in irrigated treatments was explained by a linear relationship between soil respiration, and soil temperature at 0.10 m depth and litter moisture content. In non-irrigated treatments, 61% of the variation in soil xix respiration measurements was explained by a linear relationship between soil temperature at 1 cm depth and soil moisture content. Inter-year variation was considerable with annual soil respiration approximately 20% lower in 1993 compared with 1992. Annual soil C flux was calculated by linear interpolation and ranged from 3.4 ?? 11.2 tC ha-1 across the treatments. Soil C pools remained unchanged over 10 years between 1983 and 1993 for all combinations of irrigated and fertilized stands, despite significant aboveground productivity differences over the decade. Measurements of standing litter showed a change between 1991 and 1993 for only 2 out of the 10 treatments. These two treatments had belowground C allocation estimated both with and without an adjustment for a change in standing litter. Annual litterfall C ranged almost four fold from 0.6 ?? 2.2 tC ha-1 between the treatments in 1992 and 1993, and fell within the ranges of measured litterfall over 10 years at the field site. Again inter-year variation was large, with the 1993 litterfall values being approximately 97% greater across all treatments compared with 1992 values. Belowground carbon allocation was calculated using C fluxes measured at the field site, and ranged 3 fold from 4.4 ?????? 12.9 tC ha-1 between the treatments during 1992 and 1993. In 1993 the belowground C allocation was approximately 30% lower across all treatments compared with 1992 calculations. This was due to an approximate 23% reduction in annual soil C flux, a 97% increase in litterfall C and an 18% reduction in coarse root production between 1992 and 1993. The field site was N limited, and differences in belowground C allocation could be shown across irrigated treatments with different N limitations. As N availability increased belowground C allocation was decreased in the irrigated treatments. It was difficult to determine differences in belowground C allocation caused by water stress as the effects of water and N limitation were confounded. An increase in N availability generally indicated an increase in coarse root and litterfall C production, which were reflected in increased aboveground productivity. In high N treatments the coarse root fraction of belowground C allocation comprised approximately 50% of the total belowground C allocation, whereas in the N stressed treatments coarse roots only comprised 20% of the total belowground allocation The mechanistic model BIOMASS was used to estimate annual gross primary productivity (GPP) for the different treatments at the field site. BIOMASS estimated GPPs of between 30-38 tC ha-1 for the different treatments during 1992 and 1993. The measured belowground carbon allocation ranged from 16 ?? 40 % of simulated GPP, with the lower proportion allocated belowground in the irrigated and high fertility stands. Aboveground competition through the absence of thinning also appeared to reduce allocation belowground in non- irrigated stands. A direct trade off between bole and belowground C could not be demonstrated, unless data were separated by year and by the presence or absence of irrigation. Where data were separated in this manner, only three data points defined the reasonably strong, negative relationship between bole and belowground C. The value of this relationship is highly questionable and should be interpreted with caution. Thus a decrease in belowground C allocation may not necessarily indicate a concomitant increase in bole C allocation. Inter-year variation in a number of C pools and fluxes measured at the field site was at least as great as the variation between stands having different water and N limitation. Extrapolation of belowground productivity estimates from a single years data should be undertaken cautiously. The work undertaken in this study indicated that for a given forest stand in a given soil type, an increase in N availability reduced the absolute and relative C allocated belowground. However this decrease in C belowground may not directly translate as an increase in stem growth or increased timber production. Forest productivity in an enhanced greenhouse environment is likely to result in an increased allocation of C belowground due to increased N limitation, unless adequate N is present to support a more active canopy. Further work is required to more fully understand the dynamics of the belowground system in a changing environment. However further research should focus on mature forest systems in order to isolate the impacts of natural ageing changes from perturbation effects on the forest system. This would be best undertaken in long term monitoring sites where a C history of the stand may be available.

ix, 177 leaves, [12] leaves of plates (some col.) : ill., maps, graphs, tables ; 31 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Entomology, 1980

Thesis (Ph.D.)--University of Melbourne, Dept. of Zoology, 1978. / Typescript (photocopy). Includes bibliographical references.

Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (p. 172-194). Also available via the World Wide Web.

Thesis (M.S.)--California Polytechnic State University, 2009. / Title from PDF title page; viewed on June 5, 2009. "May 2009." "In partial fulfillment of the requirements for the degree [of] Master of Science in Forestry Sciences." "Presented to the faculty of California Polytechnic State University, San Luis Obispo." Major professor: Walter R. Mark, Ph.D. Includes bibliographical references (p. 39-43). Also available on microfiche.

Thesis (Ph. D.)--Oregon State University, 1994. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.