John Finnan

Bundle Sheath Leakiness and Light Limitation during C4 Leaf and Canopy CO2 Uptake

Perennial species with the C4 pathway hold promise for biomass-based energy sources. We have explored the extent that CO2 uptake of such species may be limited by light in a temperate climate. One energetic cost of the C4 pathway is the leakiness (ϕ) of bundle sheath tissues, whereby a variable proportion of the CO2, concentrated in bundle sheath cells, retrodiffuses back to the mesophyll. In this study, we scale ϕ from leaf to canopy level of a Miscanthus crop (Miscanthus × giganteus hybrid) under field conditions and model the likely limitations to CO2 fixation. At the leaf level, measurements of photosynthesis coupled to online carbon isotope discrimination showed that leaves within a 3.3-m canopy (leaf area index = 8.3) show a progressive increase in both carbon isotope discrimination and ϕ as light decreases. A similar increase was observed at the ecosystem scale when we used eddy covariance net ecosystem CO2 fluxes, together with isotopic profiles, to partition photosynthetic and respiratory isotopic flux densities (isofluxes) and derive canopy carbon isotope discrimination as an integrated proxy for ϕ at the canopy level. Modeled values of canopy CO2 fixation using leaf-level measurements of ϕ suggest that around 32% of potential photosynthetic carbon gain is lost due to light limitation, whereas using ϕ determined independently from isofluxes at the canopy level the reduction in canopy CO2 uptake is estimated at 14%. Based on these results, we identify ϕ as an important limitation to CO2 uptake of crops with the C4 pathway.

A time-concentration study on the effects of ozone on spring wheat (Triticum aestivum L.). 1. Effects on yield

Abstract Spring-sown wheat ( Triticum aestivum L., cv. ‘Promessa’) was grown in open-top chambers and ambient-air plots at a site in the southeast of Ireland, and exposed to different concentrations of ozone in a 3-year study carried out from 1991 to 1993. The treatments used in the study were charcoal-filtered air, non-filtered air and non-filtered air to which extra ozone was added. Additional ozone was added to the treatments either as short-term high-concentration exposures or as long-term low-concentration exposures. Air filtration had no significant effect on grain yield, indicating that ambient levels of ozone over the experimental period in the study area did not have the potential to decrease the yield of spring wheat crops. Additional ozone exposures with higher peak concentrations had the most detrimental effect on grain yield. Short-term fumigation with ambient ozone plus 50 parts per billion (p.p.b.) in 1991 resulted in a 53% reduction in grain yield. In 1992 a similar cumulative exposure but with ambient ozone plus 25 p.p.b. applied over a longer time interval increased grain yield by 17%. In 1993 these observations were confirmed when an ozone exposure with higher peak concentrations significantly reduced grain yield, while an identical exposure with lower peak concentrations had no effect. Changes in grain yield were primarily the result of changes in grain filling. They were accompanied by changes in protein percentage as well as in the percentage of small, improperly filled grains. The results suggest that increased emphasis should be given to peak concentrations in the assessment of ozone effects on vegetation.

Morphological and physiological traits for higher biomass production in perennial rhizomatous grasses grown on marginal land

A widespread criticism of growing energy crops is that they displace much needed food crops and cause upward pressure on food prices. One solution is the use of marginal land that is unfavourable for food production and is currently underutilized. However, the yield of crops growing on marginal land is reduced because they are subjected to a range of abiotic stresses such as extremes of temperature and rainfall and edaphic factors such as increased soil salinity. Therefore, to achieve acceptable economic returns on the use of this land it will be necessary to, on the one hand improve management practices and on the other to select for plant genotypes which are able to tolerate and potentially overcome the stressful conditions they are exposed to. Here, we review the morphological and physiological traits of perennial rhizomatous grasses that could be modified to overcome these stresses and to maximize biomass production on marginal land. The traits include aspects of crop phenology, canopy and leaf photosynthesis, biomass partitioning, nutrient and water use efficiency and heat, cold and salt tolerance. It is proposed that newly developed biotechnological methods combined with high‐throughput plant phenotyping offer opportunities to rapidly select new genotypes that could achieve economic yields on large areas of marginal land.

A proposed framework for determining the environmental impact of replacing agricultural grassland with Miscanthus in Ireland

Energy crops offer an opportunity to substantially increase bioenergy resources which can replace rapidly depleting fossil fuel reserves and mitigate the effect of climate change. Energy crops are typically established within traditional agricultural systems such as tillage land or grassland. Associated land use conversion has environmental implications. The aim of this paper is to propose a framework to examine how such environmental implications can be assessed, based on (a) a Strategic Environmental Assessment (SEA) approach which considers potential impacts at different stages of a plan across a wide range of environmental receptors and (b) a literature review. The example we used was that of Miscanthus replacing grassland farming. This scenario is particularly relevant to Ireland, where over 90% of the agricultural land is permanent pasture, but is also applicable to grassland conversion throughout Europe and the United States. Two consecutive phases of land‐use change were identified for assessment, each with a distinct set of environmental impacts. The first was a transition phase, lasting from initial livestock clearance and grassland ploughing until the Miscanthus crop became established (2–3 years). The second phase was the mature crop phase, lasting up to 25 years. Miscanthus cultivation was more likely to impact negatively on the environment during the transition phase than the mature phase, primarily due to abrupt disturbance and the time required for a new equilibrium to establish. However, a literature review of the impact on the environmental receptors revealed that replacing Irish agricultural grassland with Miscanthus had the potential to improve biodiversity, water, air and soil quality, and climatic factors once the crop became established and reached maturity. In order to confirm these findings an appropriate monitoring programme involving objectives and indicators associated with each environmental receptor would need to be developed.

Workshop Approach To Developing Objectives, Targets And Indicators For Use In Sea

Strategic Environmental Assessment (SEA) is the process through which the impacts of plans and programmes on the environment are assessed. Objectives, targets and indicators are the tools through which these environmental impacts can be measured. The same objectives, targets and indicators may be used for all planning levels but it is also necessary to identify additional plan specific ones. We used a workshop based approach to provide an interface between planners and environmental scientists and to give examples of objectives, targets and indicators for biodiversity, water, air and climatic factors, which could be used in SEA for national, regional and local plans. In addition, we highlight the need for careful consideration during the selection process of these variables which will result in a more rigorous and robust SEA. This is a challenging process but once completed will maximise resources and reduce the workload later in the SEA process.

An evaluation of indices that describe the impact of ozone on the yield of spring wheat (Triticum aestivum L.)

Abstract A comparison of the performance of different ozone indices in exposure-response functions was made using crop yield and ozone monitoring data from spring wheat studies carried out within the framework of the European open-top chamber programme. Indices were calculated for a twelve-hour period (0900–2100 h, local time). An attempt was made to incorporate a measure of absorbed dose into current indices by weighting with simultaneous sunshine hour values. Both linear and Weibull models were fitted to the exposure-response data in order to evaluate index performance. Cumulative indices which employed continuous weighting functions (allometric or sigmoid) or which censored concentrations above threshold values performed best as they attributed increasing weight to higher concentrations. Indices which simply summed concentrations greater than or equal to a threshold value did not perform as well as equal weight was given to all concentrations greater than the threshold value. Model selection was found to be very important in determining the indices that best describe the relationship between exposure and response. In general weighting hourly ozone concentrations with the corresponding sunshine hour values in an attempt to incorporate this proposed measure of plant activity into current indices did not improve index performance. Ozone exposure indices accounted for a large proportion of the variability in data (91%) and it is suggested that a strong link exists between exposure and dose.

Economic Analysis of Manufacturing Costs of Pellet Production in the Republic of Ireland Using Non-Woody Biomass

An economic analysis of a non-woody biomass pelleting process was performed for conditions in the Republic of Ireland. The analysis considered the establishment, harvest, storage and drying costs of the feedstocks on-farm, together with transportation costs to the processing plant and the costs associated with the pelleting process. Capital and operating costs of the pelleting process were estimated at several plant capacities - 6t / h, 8t / h and 10t / h. The pellet production cost for the base case scenario of 8t / h was � 102 / t of pellets produced. By decreasing production capacity to 6t / h an increase in the production cost of � 10 / t was experienced while increasing capacity to 10t / h resulted in a decrease of � 6 / t in the production cost of pellets. The cost of the raw material is the largest cost component (66%) of the total pellet production cost. Other major cost factors include pelleting and cooling plant (11%), straw grinding plant (10%) and personnel costs (9%). Considering current energy prices the equivalent energy cost of � 7 / GJ (excluding profit margins) the potential production of non-woody biomass pellets competes favourably with oil and gas and was found to be economically viable.

Farmers' perspectives for the development of a bioenergy industry in Ireland

A survey of Irish farmers was conducted to identify farmers’ opinions on energy crop production and to characterize potential adopters of energy crop cultivation in Ireland. One hundred and seventy‐two surveys were completed from 25 counties in Ireland. Miscanthus (48%) and grass (30%) were the preferred crops for adoption of energy crop production. Potential adopters described themselves as having a significantly greater level of knowledge of energy crop production compared with other respondents. The results indicate that lack of interest in adopting energy crop production may be due to lack of knowledge regarding the economic benefits of adoption and the variety of energy crops available for cultivation in Ireland. The establishment of long‐term contracts and government schemes were identified as important requirements for the development of bioenergy crop production in Ireland. Energy crop adoption was not limited to farmers undertaking specific farm enterprises. Farmers were motivated to adopt energy crop production for both economic and environmental benefits. These results are the first to provide valuable information on the perspectives of potential adopters of bioenergy crop production in Ireland for the promotion and implementation of a national bioenergy industry. Policy requirements and outreach strategies to encourage adoption of energy crops by agricultural producers are suggested.

The Effect of Elevated Levels of Carbon Dioxide on Potato Crops

SUMMARY Experiments, which have investigated the effect of elevated concentrations of atmospheric CO2 on the physiology, growth and yield of potato (Solanum tuberosum L.), are reviewed. These studies were conducted in controlled environment chambers, in glasshouses, in open top field chambers as well as using free air carbon dioxide (FACE) exposure systems. In general, photosynthesis is stimulated by elevated CO2 initially although long-term exposure leads to acclimation. The stomata of potato leaves partially close in response to elevated CO2 and starch granules build up in the chloroplasts. Although above- and below-ground biomass production is stimulated, accelerated senescence limits growth towards the end of the growing season exposure to elevated CO2 stimulates tuber yield, the magnitude of which depends on agronomic practise, cultivar choice and growing conditions. The beneficial effects of elevated CO2 may be reduced by interaction with other components of climate change, such as drought stress. Modelling of the effects of climate change on potato yield has predicted an increase in yields in northern Europe with little change in central and southern Europe. It is suggested that further research is needed to understand the reasons for photosynthetic acclimation, field trials are also needed to understand and quantify the interaction between elevated CO2 and drought stress.

The effect of harvest date and harvest method on the combustion characteristics of Miscanthus × giganteus

Miscanthus × giganteus is an energy crop with many attributes that make it a potential biofuel feedstock. This study examined the chemical composition of M. × giganteus stems cut at different dates throughout the spring harvest window (January, February and March) and either left in a swath or left flat in a thin layer on the ground and compared the composition to that of the standing crop collected on the same date in April (control). The research then examined the effect of cutting date on the chemical composition of whole plant M. × giganteus biomass (leaf and stem). The parameters examined in both parts of this experiment were lower heating value on a wet basis (LHVWB), ash, chlorine, potassium, nitrogen, sulphur, carbon and hydrogen content. The range of values recorded for the parameters from both aspects of this trial were LHVWB 4.84–11.87 MJ kg−1; ash 1.44–1.97%; Cl 0.07–0.23%; K 0.15–0.32%; N 0.28–0.39%; S 0.13–0.19%; C 46.75–50.00%; H 5.76–6.09%. The length of time that the M. × giganteus remained in the field after cutting affected the LHVWB (increased with time) of the stem biomass material. Cutting the biomass and leaving it in the field lowered the ash, Cl and C content of the stem material compared to that of the control which was cut and collected on the same date. No differences were observed for the other parameters. Date of harvest affected the LHVWB, Cl and C content which all improved with later cutting dates. Thus, combustion quality can be improved by delaying the harvest date or by cutting the crop and leaving it in the field for a period prior to collection. Choosing the correct combination of time and harvest method can therefore improve biomass fuel quality.