Realised Niche Shifts, Rapid Evolution and Phenotypic Plasticity in Introduced Plants

<p>Recent biological invasions provide a unique opportunity to examine how species may adapt to novel conditions over relatively short time frames. Introduced species may respond to novel environmental conditions in the new range via rapid evolution, phenotypic plasticity, or the rapid evolution of phenotypic plasticity. However, the prevalence of these different mechanisms in introduced species remains unclear. In this thesis, I explore how introduced plant species may adjust their phenotype when introduced to a new range. First, I tested for evidence of phenotypic change through time in key morphological traits (plant height, leaf area, leaf shape, and leaf mass per unit area), using historic herbarium records for 34 plants introduced to Australia and New Zealand. Thirty-two out of 94 trait-species combinations showed evidence for change through time. The rate and direction of trait change was variable across species and the local climate. One possibility is that species introduced to a new range exhibit different trait responses depending on the relative difference in environment between the native and introduced range. To investigate this, I quantified climatic niche shifts in introduced species relative to their native range. I then predicted trait change through time from the magnitude and direction of climate niche shift in a meta-regression. This is the first study to simultaneously assess trait change in multiple introduced species in relation to a shift in their realised niche. Overall, climate niche shifts did not predict trait change through time, suggesting that climate may not be the predominant driver of trait change in plants introduced to Australia and New Zealand. Alternatively, the combined uncertainty and the mismatch in spatial scales that may arise when combining these two methods could mask any underlying patterns in plant trait responses to the new environment. It has been hypothesised that introduced species may respond to a sudden change in environment, by rapidly selecting for an increase in phenotypic plasticity. I tested for a difference in phenotypic plasticity between the native and introduced ranges of a beach daisy, Arctotheca populifolia. Contrary to my expectations, A. populifolia has shown a loss of phenotypic plasticity in as little as 80 years since its introduction to Australia. When using a meta-analysis to test for an overall difference in plasticity across multiple traits, I found that the current practice of calculating an effect size of an effect size (Hedges’ d) can lead to misleading results. I demonstrate how this issue arises when calculating a difference in Hedges’ d between two populations with different standard deviations. I propose an alternative way to calculate Hedges’ d to give a more accurate reflection of the difference in plasticity between ranges. Finally, I combine different lines of evidence from the previous chapters in a case study to explore how A. populifolia has changed since its introduction to Australia, and examine any discrepancies between the results. A glasshouse experiment revealed distinct trait differences between native and introduced populations of A. populifolia, which were not reflected in trait change through time inferred from herbarium specimens. Additionally, measured trait differences between ranges in the glasshouse experiment better reflected a niche shift into wetter climate, than the predicted trait change through time from herbarium specimens. This suggests that trait differences determined in glasshouse or common garden experiments, may be a more suitable approach to assess trait change in relation to a realised niche shift than using herbarium specimens.</p>

Realised Niche Shifts, Rapid Evolution and Phenotypic Plasticity in Introduced Plants

<p>Recent biological invasions provide a unique opportunity to examine how species may adapt to novel conditions over relatively short time frames. Introduced species may respond to novel environmental conditions in the new range via rapid evolution, phenotypic plasticity, or the rapid evolution of phenotypic plasticity. However, the prevalence of these different mechanisms in introduced species remains unclear. In this thesis, I explore how introduced plant species may adjust their phenotype when introduced to a new range. First, I tested for evidence of phenotypic change through time in key morphological traits (plant height, leaf area, leaf shape, and leaf mass per unit area), using historic herbarium records for 34 plants introduced to Australia and New Zealand. Thirty-two out of 94 trait-species combinations showed evidence for change through time. The rate and direction of trait change was variable across species and the local climate. One possibility is that species introduced to a new range exhibit different trait responses depending on the relative difference in environment between the native and introduced range. To investigate this, I quantified climatic niche shifts in introduced species relative to their native range. I then predicted trait change through time from the magnitude and direction of climate niche shift in a meta-regression. This is the first study to simultaneously assess trait change in multiple introduced species in relation to a shift in their realised niche. Overall, climate niche shifts did not predict trait change through time, suggesting that climate may not be the predominant driver of trait change in plants introduced to Australia and New Zealand. Alternatively, the combined uncertainty and the mismatch in spatial scales that may arise when combining these two methods could mask any underlying patterns in plant trait responses to the new environment. It has been hypothesised that introduced species may respond to a sudden change in environment, by rapidly selecting for an increase in phenotypic plasticity. I tested for a difference in phenotypic plasticity between the native and introduced ranges of a beach daisy, Arctotheca populifolia. Contrary to my expectations, A. populifolia has shown a loss of phenotypic plasticity in as little as 80 years since its introduction to Australia. When using a meta-analysis to test for an overall difference in plasticity across multiple traits, I found that the current practice of calculating an effect size of an effect size (Hedges’ d) can lead to misleading results. I demonstrate how this issue arises when calculating a difference in Hedges’ d between two populations with different standard deviations. I propose an alternative way to calculate Hedges’ d to give a more accurate reflection of the difference in plasticity between ranges. Finally, I combine different lines of evidence from the previous chapters in a case study to explore how A. populifolia has changed since its introduction to Australia, and examine any discrepancies between the results. A glasshouse experiment revealed distinct trait differences between native and introduced populations of A. populifolia, which were not reflected in trait change through time inferred from herbarium specimens. Additionally, measured trait differences between ranges in the glasshouse experiment better reflected a niche shift into wetter climate, than the predicted trait change through time from herbarium specimens. This suggests that trait differences determined in glasshouse or common garden experiments, may be a more suitable approach to assess trait change in relation to a realised niche shift than using herbarium specimens.</p>

Seed Coating with Organomineral Fertilizer, an Alternative Method to Improve the Efficiency of Farming

Seed and fertilizer are two important farming inputs, which are commonly available and used separately. Combining both materials into a unit of fertilizer-coated seed may improve farming efficiency. However, the appropriate seed coating method must be found out, and this research was the first effort of finding the method. A glasshouse experiment was carried out to identify the growth and yield of the coated seeds of rice and groundnut with organomineral fertilizer in three different sizes, i.e., small (SS), medium (MS), and big sizes (BS). Four sets of experiments were prepared, two of those were for testing two varieties of rice and the others were for testing two varieties of groundnut. Each experiment was laid out in a complete randomized design; the treatment was the size of coated seeds (SS, MS, BS, and a control - uncoated seeds) in triplicates. Results reveal that the seed coating delayed the germination of rice seeds for 2 – 3 days and groundnut seeds for 7 – 16 days, suppressed the growth and yield of rice but improved the growth and yield of groundnut. The highest yield of groundnut was the grown groundnut from the small and medium sizes of coated seeds (weight ratios of 1:4 and 1:9). The reduces of growth and yield of rice were most probably due to the direct contact of the high concentration of nutrients, especially nitrogen, with the seeds. In conclusion, the seed coating with organomineral fertilizer was a potentially developed method to improve farming efficiency. Further efforts were needed to fix the composition of organomineral fertilizer, especially the type N substances used and the steps of applying the materials onto the seeds.

Contribution of Eelemental Sulfur to Soil Acidification, Fe Release and Uptake by corn (Zea mays L.)

Abstract—A glasshouse experiment was conducted to elucidate the effectiveness of elemental sulfur as a soil acidulates on solubility of soil Fe and it’s uptake by corn (Zea mays L.). Four rates of elemental sulfur, 0, 0.5, 1 and 2 g S kg-1 soil, incubated for 0, 20 and 40 days before corn plantation. The result showed that with one unit increase in S application rate the soil pH decreased about 1.52 units and the solubility of the Fe was significantly increased. The concentration of Fe in corn leaves and stem were increased with soil acidification from the background of 7.03 to 5.42 due to elemental sulfur application rate of 1 g S kg-1 soil. However, further soil acidification decreased Fe concentration in corn. Overall, application of elemental sulfur at a rate of 0.5 g S kg-1 soil is recommended to enhance corn performance by 45 percent without the risk of Fe toxicity for corn and the minimum Fe export to groundwater.

The effect of wood age on infection by Neonectria ditissima through artificial wounds on different apple cultivars

The age of apple wood may affect its susceptibility to European canker (Neonectria ditissima). Therefore, a glasshouse experiment was conducted with potted trees of six apple cultivars (‘Braeburn’, ‘Scilate’, ‘Fuji’, ‘Golden Delicious’, ‘Jonathan’ and ‘Royal Gala’) grafted onto two rootstocks (‘M793’ and ‘M9’) to study the effect of 3-, 2- or 1-year-old wood on incidence and disease progression following inoculation with conidia of N. ditissima. Initial analyses of cultivars on ‘M793’ showed a significant wood age effect on disease incidence and lesion length, which was similar to cultivars grafted on ‘M9’. Three-year-old wood developed more and longer lesions than either the 2- or the 1-year-old wood. A significant cultivar effect was observed with ‘Royal Gala’ developing more lesions than the other cultivars tested. More than half of asymptomatic wounds placed onto apple sap-amended water agar for pathogen isolation yielded N. ditissima.

Thermal treatment and leaching of biochar alleviates plant growth inhibition from mobile organic compounds

Recent meta-analyses of plant responses to biochar boast positive average effects of between 10 and 40%. Plant responses, however, vary greatly across systems, and null or negative biochar effects are increasingly reported. The mechanisms responsible for such responses remain unclear. In a glasshouse experiment we tested the effects of three forestry residue wood biochars, applied at five dosages (0, 5, 10, 20, and 50 t/ha) to a temperate forest drystic cambisol as direct surface applications and as complete soil mixes on the herbaceous pioneersLolium multiflorumandTrifolium repens. Null and negative effects of biochar on growth were found in most cases. One potential cause for null and negative plant responses to biochar is plant exposure to mobile compounds produced during pyrolysis that leach or evolve following additions of biochars to soil. In a second glasshouse experiment we examined the effects of simple leaching and heating techniques to ameliorate potentially phytotoxic effects of volatile and leachable compounds released from biochar. We used Solid Phase Microextraction (SPME)–gas chromatography–mass spectrometry (GC-MS) to qualitatively describe organic compounds in both biochar (through headspace extraction), and in the water leachates (through direct injection). Convection heating and water leaching of biochar prior to application alleviated growth inhibition. Additionally, growth was inhibited when filtrate from water-leached biochar was applied following germination. SPME-GC-MS detected primarily short-chained carboxylic acids and phenolics in both the leachates and solid chars, with relatively high concentrations of several known phytotoxic compounds including acetic acid, butyric acid, 2,4-di-tert-butylphenol and benzoic acid. We speculate that variable plant responses to phytotoxic organic compounds leached from biochars may largely explain negative plant growth responses and also account for strongly species-specific patterns of plant responses to biochar amendments in short-term experiments.

Thermal treatment and leaching biochar alleviates plant growth inhibition from mobile organic compounds

Recent meta-analyses of plant responses to biochar boast positive average effects of between 10 and 40 %. Plant responses, however, vary greatly across systems, and null or negative biochar effects are increasingly reported. The mechanisms responsible for such responses remain unclear. In a glasshouse experiment we tested the effects of three forestry residue wood biochars, applied at five dosages (0, 5, 10, 20, 50 t/ha) to a temperate forest drystic cambisol as direct surface applications and as complete soil mixes on the herbaceous pioneers Lolium multiflorum and Trifolium repens. Null and negative effects of biochar on growth were found in most cases. One potential cause for null and negative plant responses to biochar is plant exposure to mobile compounds produced during pyrolysis that leach or evolve following additions of biochars to soil. In a second glasshouse experiment we examined the effects of simple leaching and heating techniques to ameliorate potentially phytotoxic effects of volatile and leachable compounds released from biochar. We used Solid Phase Microextraction (SPME) – gas chromatography – mass spectrometry (GC-MS) to qualitatively describe organic compounds in both biochar (through headspace extraction), and in the water leachates (through direct injection). Convection heating and water leaching of biochar prior to application alleviated growth inhibition. Additionally, growth was inhibited when filtrate from water-leached biochar was applied following germination. SPME-GC-MS detected primarily short-chained carboxylic acids and phenolics in both the leachates and solid chars, with relatively high concentrations of several known phytotoxic compounds including acetic acid, butyric acid, bisphenol and benzonoic acid. We speculate that variable plant responses to phytotoxic organic compounds leached from biochars may largely explain negative plant growth responses and also account for strongly species-specific patterns plant responses to biochar amendments in short-term experiments.