title: Nutritional niche separation in coexisting bog species demonstrated by ¹⁵N-enriched simulated rainfall

authors: Clarkson, Beverley R.

subjects: niche separation

abstract: Empodisma minus and Sporadanthus ferrugineus (both Restionaceae) coexist in New Zealand raised bogs, yet Sporadanthus have significantly more depleted ¹⁵N natural abundance signatures than coexisting Empodisma. Their root systems are spatially separated with Empodisma having a thick surface layer of about 50 mm of cluster roots overlying the deeper Sporadanthus roots. We hypothesized this root displacement allows Empodisma to preferentially access the primary N input from rainfall, thus establishing niche separation, and tested this using tracer stable isotopes. We aerially applied 1.6 mmol m⁻² of ¹⁵N as (NH₄)₂SO₄ chased by deionized water to simulate a rainfall event of 34 L m⁻². Root/peat matrix cores were harvested after 5 h and analysed for ¹⁵N uptake. Approximately 80% of the tracer applied was recovered in the cores, with 90% of this recovered in the upper Empodisma cluster root layer. Seven weeks after application, young shoots of Empodisma were significantly enriched (mean δ15N = +7.21‰; reference = −0.42‰), whereas those of coexisting Sporadanthus were not (mean δ15N = −2.76‰; reference = −4.24‰). However, we were unable to quantify the ¹⁵N uptake because of the dilution effect of the large biomass. We calculated the contribution of biological nitrogen fixation as a possible alternative source of N in achieving niche separation. The acetylene reduction assay showed minor amounts of nitrogenase activity are associated with Empodisma and Sporadanthus roots (equivalent to 0.045 ± 0.019 and 0.104 ± 0.017 kg N ha⁻¹ year⁻¹respectively). Our results suggest that the species acquire nutrients from different rooting zones, with Empodisma accessing nutrients at the surface from rainfall and Sporadanthus accessing nutrients from mineralization in deeper peat layers. Such niche differentiation probably facilitates species coexistence and may provide a mechanism for slowing the rate of competitive displacement during long-term succession.

text: Nutritional niche separation in coexisting bog species demonstrated by ¹⁵N-enriched simulated rainfall Empodisma minus and Sporadanthus ferrugineus (both Restionaceae) coexist in New Zealand raised bogs, yet Sporadanthus have significantly more depleted ¹⁵N natural abundance signatures than coexisting Empodisma. Their root systems are spatially separated with Empodisma having a thick surface layer of about 50 mm of cluster roots overlying the deeper Sporadanthus roots. We hypothesized this root displacement allows Empodisma to preferentially access the primary N input from rainfall, thus establishing niche separation, and tested this using tracer stable isotopes. We aerially applied 1.6 mmol m⁻² of ¹⁵N as (NH₄)₂SO₄ chased by deionized water to simulate a rainfall event of 34 L m⁻². Root/peat matrix cores were harvested after 5 h and analysed for ¹⁵N uptake. Approximately 80% of the tracer applied was recovered in the cores, with 90% of this recovered in the upper Empodisma cluster root layer. Seven weeks after application, young shoots of Empodisma were significantly enriched (mean δ15N = +7.21‰; reference = −0.42‰), whereas those of coexisting Sporadanthus were not (mean δ15N = −2.76‰; reference = −4.24‰). However, we were unable to quantify the ¹⁵N uptake because of the dilution effect of the large biomass. We calculated the contribution of biological nitrogen fixation as a possible alternative source of N in achieving niche separation. The acetylene reduction assay showed minor amounts of nitrogenase activity are associated with Empodisma and Sporadanthus roots (equivalent to 0.045 ± 0.019 and 0.104 ± 0.017 kg N ha⁻¹ year⁻¹respectively). Our results suggest that the species acquire nutrients from different rooting zones, with Empodisma accessing nutrients at the surface from rainfall and Sporadanthus accessing nutrients from mineralization in deeper peat layers. Such niche differentiation probably facilitates species coexistence and may provide a mechanism for slowing the rate of competitive displacement during long-term succession.

year: 2009

title: Aspects of the ecology of black beetle (Heteronychus arator (F.), Coleoptera: Dynastinae)

authors: King, Peter Douglas

abstract: The study included laboratory and field studies of the ecology of the black beetle (Heteronychus arator F.) pre-adult and adult stages and field studies of population dynamics. The objectives were to understand population change and regulation, particularly in relation to host plant species and explore the possibilities of the prediction of outbreaks in order to rationalise the use of control strategies.
Whereas eggs were relatively tolerant to a range of soil moisture conditions, first instar larvae were very susceptible to extremes in soil moisture. In comparison to temperate scarabs, relatively high temperatures were necessary for optimum egg viability, larval feeding, utilisation, growth and survival. Adult oviposition preference, fecundity and survival, and larval food consumption, growth and survival were all influenced by the pasture plant species eaten. All grass species tested with the exception of phalaris were favourable for population growth while phalaris and the legumes tested were unfavourable.
The dynamic nature of the life cycle, the relatively low population densities and dispersal of adults made estimation of populations with reasonable levels of precision difficult. Life tables were constructed which quantified individual and generation mortalities, and identified the key factors causing population change. These were variation in natality, summer mortality and/or winter.- spring disappearance. Significant relationships were found between key mortalities and the level of population development which in turn was related to spring and summer temperatures.
Two very different types of population dynamics were evident. Populations in paspalum pastures which are tolerant to feeding damage were relatively stable. These pastures act as refuge areas during adverse climatic conditions. In contrast, population development was more rapid and large population decreases occurred between autumn and spring in ryegrass based pastures which were less tolerant of damage. Ryegrass based pastures appear to be favourable habitats during spring and summer only, and adult immigration in the spring is necessary for populations to reach high levels. Since spring migration only occurs in warm years, outbreaks in ryegrass based pasture are sporadic.
A population model was constructed which used mean daily air temperatures in September, October and November to simulate population densities over a 23 year period from temperature records. The prediction of high population numbers showed good correlation with years of previous outbreaks. Some density dependence was found to be necessary in the model for paspalum pasture indicating the occurrence of population regulation. It was concluded that except in years of high population numbers, population regulation does not occur in ryegrass based pastures.
Rationalisation of control strategies was discussed in the light of the differences in the two types of population dynamics and the prediction of outbreaks.
This research has revealed the necessity for a well designed population study in order to understand the manner in which mortalities operate and the way they affect numbers. As the first attempt at a quantitative ecological study of black beetle, the results have provided some understanding of black beetle ecology and suggested further areas for investigation.

text: Aspects of the ecology of black beetle (Heteronychus arator (F.), Coleoptera: Dynastinae) The study included laboratory and field studies of the ecology of the black beetle (Heteronychus arator F.) pre-adult and adult stages and field studies of population dynamics. The objectives were to understand population change and regulation, particularly in relation to host plant species and explore the possibilities of the prediction of outbreaks in order to rationalise the use of control strategies.
Whereas eggs were relatively tolerant to a range of soil moisture conditions, first instar larvae were very susceptible to extremes in soil moisture. In comparison to temperate scarabs, relatively high temperatures were necessary for optimum egg viability, larval feeding, utilisation, growth and survival. Adult oviposition preference, fecundity and survival, and larval food consumption, growth and survival were all influenced by the pasture plant species eaten. All grass species tested with the exception of phalaris were favourable for population growth while phalaris and the legumes tested were unfavourable.
The dynamic nature of the life cycle, the relatively low population densities and dispersal of adults made estimation of populations with reasonable levels of precision difficult. Life tables were constructed which quantified individual and generation mortalities, and identified the key factors causing population change. These were variation in natality, summer mortality and/or winter.- spring disappearance. Significant relationships were found between key mortalities and the level of population development which in turn was related to spring and summer temperatures.
Two very different types of population dynamics were evident. Populations in paspalum pastures which are tolerant to feeding damage were relatively stable. These pastures act as refuge areas during adverse climatic conditions. In contrast, population development was more rapid and large population decreases occurred between autumn and spring in ryegrass based pastures which were less tolerant of damage. Ryegrass based pastures appear to be favourable habitats during spring and summer only, and adult immigration in the spring is necessary for populations to reach high levels. Since spring migration only occurs in warm years, outbreaks in ryegrass based pasture are sporadic.
A population model was constructed which used mean daily air temperatures in September, October and November to simulate population densities over a 23 year period from temperature records. The prediction of high population numbers showed good correlation with years of previous outbreaks. Some density dependence was found to be necessary in the model for paspalum pasture indicating the occurrence of population regulation. It was concluded that except in years of high population numbers, population regulation does not occur in ryegrass based pastures.
Rationalisation of control strategies was discussed in the light of the differences in the two types of population dynamics and the prediction of outbreaks.
This research has revealed the necessity for a well designed population study in order to understand the manner in which mortalities operate and the way they affect numbers. As the first attempt at a quantitative ecological study of black beetle, the results have provided some understanding of black beetle ecology and suggested further areas for investigation.

year: 1979

title: Quantification of Nitro-toxins in Karaka (Corynocarpus laevigatus) Drupes

authors: MacAskill, Jessica Jane

abstract: The karaka (Corynocarpus laevigatus) is a tree native to New Zealand (NZ), found throughout the North and South Islands. Traditionally, many parts of the karaka were used by Māori, however the parts of the karaka of most interest are the berry and nut as they were valuable food sources, in particular the nut. Karaka was known to be a toxin-bearing food, however implementation of a traditional baking and soaking process meant that the nuts were left in states fit for consumption, more often than not. The nuts also had the benefit of being able to be stored for future use when other food sources were short in supply. Karaka was readily consumed up until the 1950s, after this consumption rates decreased rapidly, after the toxic effects were associated with the incorrect preparation of the nuts.

Studies on karaka have revealed that the toxicity of the nuts primarily arises from various nitropropanoyl glucopyranoses (NPGs), twelve of which have been detected in karaka. The quantity of these NPGs has been infrequently studied and it is often only one of the NPGs-karakin which is quantified, although it is believed the toxicity in nuts arises collectively from all of the NPGs. As a result, there is the need to be able to quantify the NPGs in karaka and look at potential toxin removal techniques. If toxin removal can be accomplished, there is the potential for karaka to be a marketable ‘traditional’ or ‘Kiwi’ food item. Additionally, the toxins removed as a by-product may prove to have their own potential commercial applications, for example as insecticides or repellents. 

Since all the NPGs are assumed to be toxic, a method was developed to quantify the total toxicity in the nuts. The method involves the release of NPA via acid hydrolysis of the nitropropanoyl ester groups of the NPGs. The NPA is then able to be measured and subsequently quantified using HPLC. The method incorporates a correction factor (CF) that was determined to give the original NPA content at a time of zero (NPA0), accounting for the unavoidable loss of NPA that arises from the hydrolysis method.

The average quantity of NPA in karaka nuts was found to range from 50.25 to 138.62 g kg-1 (dry weight) which is equivalent to 5.0 to 13.9%. These are much higher percentages than any previously reported because the method used in this study measured total NPA. Earlier methods measured a limited range of NPGs (often a single NPG) unhydrolysed and could have missed NPA arising from other compounds that contribute to total toxicity. Additionally, the concentrations of NPA in karaka nuts were influenced by a number of factors including intra and inter tree variation, storage conditions and ripeness. Although quantification was focused on determining NPA content in nuts, a test conducted also showed NPA to be present in increasingly lower levels in the berry flesh, shell and pellicle respectively. 

Nuts were subjected to various potential industrial processing techniques, treatment times and conditions, in order to determine their efficacy for toxin removal. Treatments included boiling, microwave cooking, soxhlet extraction, oven roasting, autoclaving and cold-water treatments. The efficiency of each treatment varied considerably, with both heat and water proving to be beneficial in toxin removal. However, treatments involving water were found to be more effective than heat treatments alone. Out of all treatment types, times and conditions tested, none were found to leave nuts with a NPA concentration lower than the estimated safe level of daily consumption for a 70 kg adult (< 1.75 mg). Additionally, only some of the treatments resulted in nuts being left in visually appealing states. At present, toxin removal by a single process in order to render karaka nuts safe to consume appears to be an impractical activity. However, if treatment protocols were combined and modified, there is the potential for the development of an effective detoxification process. Furthermore, tests on the treatment solutions revealed that NPA can be obtained in solution as a by-product of nut treatment; with cold-water proving to be more effective than treatments that also used heat. Obtaining NPA as a by-product of toxin removal in nuts appears to be a feasible option for a natural source of NPA.

text: Quantification of Nitro-toxins in Karaka (Corynocarpus laevigatus) Drupes The karaka (Corynocarpus laevigatus) is a tree native to New Zealand (NZ), found throughout the North and South Islands. Traditionally, many parts of the karaka were used by Māori, however the parts of the karaka of most interest are the berry and nut as they were valuable food sources, in particular the nut. Karaka was known to be a toxin-bearing food, however implementation of a traditional baking and soaking process meant that the nuts were left in states fit for consumption, more often than not. The nuts also had the benefit of being able to be stored for future use when other food sources were short in supply. Karaka was readily consumed up until the 1950s, after this consumption rates decreased rapidly, after the toxic effects were associated with the incorrect preparation of the nuts.

Studies on karaka have revealed that the toxicity of the nuts primarily arises from various nitropropanoyl glucopyranoses (NPGs), twelve of which have been detected in karaka. The quantity of these NPGs has been infrequently studied and it is often only one of the NPGs-karakin which is quantified, although it is believed the toxicity in nuts arises collectively from all of the NPGs. As a result, there is the need to be able to quantify the NPGs in karaka and look at potential toxin removal techniques. If toxin removal can be accomplished, there is the potential for karaka to be a marketable ‘traditional’ or ‘Kiwi’ food item. Additionally, the toxins removed as a by-product may prove to have their own potential commercial applications, for example as insecticides or repellents. 

Since all the NPGs are assumed to be toxic, a method was developed to quantify the total toxicity in the nuts. The method involves the release of NPA via acid hydrolysis of the nitropropanoyl ester groups of the NPGs. The NPA is then able to be measured and subsequently quantified using HPLC. The method incorporates a correction factor (CF) that was determined to give the original NPA content at a time of zero (NPA0), accounting for the unavoidable loss of NPA that arises from the hydrolysis method.

The average quantity of NPA in karaka nuts was found to range from 50.25 to 138.62 g kg-1 (dry weight) which is equivalent to 5.0 to 13.9%. These are much higher percentages than any previously reported because the method used in this study measured total NPA. Earlier methods measured a limited range of NPGs (often a single NPG) unhydrolysed and could have missed NPA arising from other compounds that contribute to total toxicity. Additionally, the concentrations of NPA in karaka nuts were influenced by a number of factors including intra and inter tree variation, storage conditions and ripeness. Although quantification was focused on determining NPA content in nuts, a test conducted also showed NPA to be present in increasingly lower levels in the berry flesh, shell and pellicle respectively. 

Nuts were subjected to various potential industrial processing techniques, treatment times and conditions, in order to determine their efficacy for toxin removal. Treatments included boiling, microwave cooking, soxhlet extraction, oven roasting, autoclaving and cold-water treatments. The efficiency of each treatment varied considerably, with both heat and water proving to be beneficial in toxin removal. However, treatments involving water were found to be more effective than heat treatments alone. Out of all treatment types, times and conditions tested, none were found to leave nuts with a NPA concentration lower than the estimated safe level of daily consumption for a 70 kg adult (< 1.75 mg). Additionally, only some of the treatments resulted in nuts being left in visually appealing states. At present, toxin removal by a single process in order to render karaka nuts safe to consume appears to be an impractical activity. However, if treatment protocols were combined and modified, there is the potential for the development of an effective detoxification process. Furthermore, tests on the treatment solutions revealed that NPA can be obtained in solution as a by-product of nut treatment; with cold-water proving to be more effective than treatments that also used heat. Obtaining NPA as a by-product of toxin removal in nuts appears to be a feasible option for a natural source of NPA.

year: 2013