Nitrogen Source Preference and Growth Carbon Costs of Leucaena leucocephala (Lam.) de Wit Saplings in South African Grassland Soils

Leucaena leucocephala (Fabaceae) is native to Central America and has invaded many climatic regions of the tropics. In South Africa, the species is categorized as an emerging or incipient weed used as fodder, timber, firewood and in erosion control on degraded habitats. The species is common along the eastern subtropical regions of KwaZulu-Natal (KZN) Province, where it invades grasslands, savannas and edges of forests. Soils of these ecosystems are characterized as nutrient deficient and acidic. Using a pot trial, we determined the effects of the nutrient addition treatments on microbial symbiosis, N nutrition and biomass accumulation of L. leucocephala under greenhouse conditions. After 180 days of growth, plants were harvested, and their utilization of N derived from the atmosphere and from the soil was quantified through determination of δ15N values. L. leucocephala maintained growth and N nutrition by relying on both atmospheric- and soil-derived N across all soil treatments. The NDFA was significantly higher in high P (N1 + P, N2 + P and N3 + P) soils. L. leucocephala was able to nodulate with intermediate and fast-growing strains from the Mesorhizobium and Rhizobium genus in N2 + P grown plants. This shows that L. leucocephala possesses traits that are successful in acquiring nutrients, especially in nutrient limited conditions, by establishing plant symbiosis with multiple bacteria and relying on extracting N from the soil and from the atmosphere through the symbiosis.

Fit for 55 could weaken EU industrial competitiveness

Significance Further strengthening of the EU Emissions Trading System (ETS), combined with phasing out free allocations and introducing a Carbon Border Adjustment Mechanism (CBAM), looks likely to expose European industry to upward cost pressures at a time when they need capital to invest in emergent low-carbon industrial processes. Impacts 'Carbon leakage' remains a big concern: while relocation usually has multiple motivations, it may well increase as EU carbon costs rise. Supply chain pressures look likely to push costs up both for EU industry and the renewables sector. Major investment opportunities exist in the areas of renewable energy and alternative fuels infrastructure.

Development of a Solar Park Carbon Calculator (SPCC) to assist deployment decisions

<p>Following the Paris agreement, many nations have committed to targets of net zero emissions, resulting in a significant increase in low-carbon energy generation. Recent improvements in the cost and efficiency of photovoltaic (PV) technology have made their deployment cheaper than new coal and gas fired power stations in a number of regions, with the uptake of PV projected to surpass fossil fuels by 2035. Large-scale, ground-mounted systems are likely to constitute a considerable portion of this expansion, with the International Energy Agency suggesting that 69% of new capacity additions in 2021 will be utility scale deployments (although some of this may be building-mounted). Despite the expansion of ground-mounted solar parks and the knowledge that land use change is a greater threat to nature than climate change, there is very little understanding of the environmental implications. In particular, the effect on ecosystem carbon cycling, and thus the decarbonisation attraction of the technology, is unknown. Whilst the carbon impacts of the technological components have been relatively well resolved, the true carbon costs cannot be determined without quantifying the impacts on land carbon. Here, we present a solar park carbon calculator (SPCC) that quantifies the full suite of solar park carbon impacts.</p><p>The SPCC provides information on the technological and environmental carbon flows, drawing on established quantifications of carbon costs for system components, operation, and land management. Key components include the emissions factors for production of panels and mounts, machinery related emissions and the associated carbon flows of ground disturbances, before and after park construction. The SPCC is applied to a case-study solar park, providing insight into the dominant carbon flows and payback time in light of grid electricity carbon intensities. Ultimately, the SPCC can help inform solar park developer decisions in order to minimise carbon costs and maximise carbon sequestration.</p>

Symbionts in Mucuna pruriens stimulate plant performance through Nitrogen fixation and improved Phosphorus acquisition

Aims South Africa is mainly dominated by savanna and grasslands ecosystems which have been previously reported to be acidic and nutrient deficient, specifically with regards to phosphorus (P) and nitrogen (N). Mucuna pruriens (L.) DC, commonly known as velvet bean, is an indigenous legume in most African countries and has been reported to withstand these adverse soil conditions. The legume is used in many countries of the world for their medicinal value as well as for soil fertilization purposes. Although there are reports on M. pruriens growth and establishment in nutrient stressed ecosystems, no investigation has been conducted on M. pruriens symbiotic interactions, N source preference and associated growth carbon costs when subjected to P deficiency. In this study, we determined the impact of microbial symbionts on N nutrition and growth carbon costs of M. pruriens under P deficiency. Methods Microbe inoculation soils were collected from four geographical distinct KwaZulu-Natal locations. Thereafter, seeds were germinated in these natural soils and in early stages of nodule development, then seedlings were transferred in sterile quartz sand and supplied with Long Ashton nutrient media with varying P concentrations. Important Findings The 16S RNA sequence results revealed that M. pruriens was nodulated by Burkholderia sp., Paenibacillus sp., and Bacillus irrespective of P concentrations. Even though P deficiency resulted in decreased overall biomass/growth, the root biomass, nodule number and carbon costs increased. In addition, low P supplied saplings showed the highest AM fungi percentage root colonization. In M. pruriens, nitrogen derived from atmosphere had a positive correlation with P level and the saplings had a dual reliance on atmospheric derived N and soil derived N with increased reliance on soil N in low P supplied plants. Therefore, M. pruriens exhibited different morphological and microbial symbiosis when subjected to P deficiency.

The influence of carbon costs and benefits on predicted vegetation behaviour along a precipitation gradient using the Vegetation Optimality Model

<p>Vegetation properties such as rooting depths and vegetation cover play a key role in coupling ecological and hydrological processes. These properties are however highly variable in space and/or time and their parametrization generally poses challenges for terrestrial biosphere models (Whitley et al., 2016). Models often use static values for dynamic vegetation properties or prescribe values based on observations, such as remotely sensed leaf area index. Here, vegetation optimality provides a way forward in order to predict such vegetation properties and their response to environmental change (Schymanski et al., 2015).</p><p>In this study, we explore the utility of a combined water-vegetation model, the Vegetation Optimality Model (VOM, Schymanski et al., 2009), to predict vegetation properties such as rooting depths, foliage cover, photosynthetic capacity and water use strategies. The VOM schematizes perennial trees and seasonal grasses each as a single big leaf with an associated root system and optimizes leaf and root system properties in order to maximize the Net Carbon Profit, i.e. the difference between the total carbon taken up by photosynthesis and all the carbon costs related to the construction and maintenance of the plant organs involved. The VOM was applied along the North-Australian Tropical Transect, which consists of six savanna sites equipped with flux towers along a strong rainfall gradient between 500 and 1700 mm per year. The multi-annual half-hourly measurements of evaporation and CO<sub>2</sub>-assimilation at the different sites were used here to evaluate the model.</p><p>The VOM produced similar or better results than more traditional models even though it requires much less information about site-specific vegetation properties. However, we found a persistent bias in the predicted vegetation cover. More detailed numerical experiments revealed a likely misrepresentation of the foliage costs in the model, which are based on a linear relation between leaf area and fractional vegetation cover. This finding, and the already favourable comparison with traditional models, implies that optimization of vegetation properties for Net Carbon Profit is a very promising approach for predicting the soil-vegetation-atmosphere exchange of water and carbon in complex ecosystems such as savannas.</p><p><strong>References<br></strong>Schymanski, S.J., Roderick, M.L., Sivapalan, M., 2015. Using an optimality model to understand medium and long-term responses of vegetation water use to elevated atmospheric CO2 concentrations. AoB PLANTS 7, plv060. https://doi.org/10.1093/aobpla/plv060</p><p>Schymanski, S.J., Sivapalan, M., Roderick, M.L., Hutley, L.B., Beringer, J., 2009. An optimality‐based model of the dynamic feedbacks between natural vegetation and the water balance. Water Resources Research 45. https://doi.org/10.1029/2008WR006841</p><p>Whitley, R., Beringer, J., Hutley, L.B., Abramowitz, G., De Kauwe, M.G., Duursma, R., Evans, B., Haverd, V., Li, L., Ryu, Y., Smith, B., Wang, Y.-P., Williams, M., Yu, Q., 2016. A model inter-comparison study to examine limiting factors in modelling Australian tropical savannas. Biogeosciences 13, 3245–3265. https://doi.org/10.5194/bg-13-3245-2016</p>

Householders’ readiness for demand-side response: A qualitative study of how domestic tasks might be shifted in time

Domestic demand-side response (DSR) involves having householders shift energy-consumptive behaviours forwards or backwards in time to avoid peak-demand periods. Time of Use tariffs, which vary the cost of energy depending on when it is used, are a proposed mechanism for DSR. However, we do not know which behaviours, if any, are amenable to being brought forward or postponed, nor what information people would need to do this. Here we presented people with hypothetical variable financial costs and, for the first time, carbon costs for future energy consumption. People's think-aloud decisions about when they would perform consumptive activities were qualitatively analysed. We show that non-daily high-consumption activities (e.g., ironing, vacuuming) are perceived as moveable in response to price changes or, notably, information about environmental consequences; but barriers to moving other activities, even in the face of higher costs or environmental harm, include household dynamics (difficulties negotiating consumption across cohabitants), social roles, community living (not wishing to disturb neighbours), lack of energy literacy and the routine nature of many tasks. This study provides a framework for understanding which behaviours might or might not be shifted and what guidance and information may be needed by householders if tariffs are to provide effective DSR.