Abiotic Inputs Research Articles

Geochemical Characteristics of Mesoproterozoic Source Rocks in North China: Insights for Organic Matter Enrichment and Thermal Evolution

In recent years, the exploration of oil and gas in China’s Precambrian strata has garnered significant attention, leading to notable advancements in exploration play assessment. However, there is a dearth of published literature on Proterozoic source rocks’ organic sources, sedimentary environments, marine hydrochemistry, and other attributes. This study focuses on investigating potential source rocks within the Hongshuizhuang and Xiamaling Formations in the Jibei Depression of North China. A comprehensive analysis was conducted to evaluate hydrocarbon generation characteristics, using hydrocarbon biomarkers and polar compounds as geochemical indicators for precursor biota and maturity levels. The results indicate high organic matter abundance with predominantly type I-II1 organic matter composition in the studied source rocks. These samples are at an immature–low mature stage, with the potential for primarily generating aromatic crude oil. The parent material is mainly attributed to lower aquatic organisms, such as bacteria and algae. The sedimentary environment exhibits marine facies, characterized by high evaporation rates, salinity levels, and strong euxinic conditions, that led to sulfur incorporation into the organic matter matrix. It should be noted that correlations between biomarker parameters and maturity may not be fully applicable to ancient source rocks; however, the methyldibenzothiophene ratio (MDR) demonstrates a strong correlation with Tmax. The compounds and their total monoisotope ions abundance (TMIA) were primarily identified and analyzed using FT–ICR MS. It was observed that these compounds were influenced by the depositional environment and organic matter maturity. Importantly, it was clearly demonstrated that the DBE and carbon number range of CH compounds gradually increased with maturity, due to the removal of N, S, and O functional groups. Specifically, N1 compounds predominantly consisted of carbazoles with short alkyl side chains which readily converted into N1Ox compounds. On the other hand, O1 compounds mainly comprised benzofurans with low abundance, indicating a reducing sedimentary environment, as suggested by their low TMIA values. Furthermore, S1 compounds were primarily thiophenes whose DBE range and carbon number increased with maturity, possibly suggesting an abiotic input of inorganic sulfur. Notably, the maturity indices (MAT) proved suitable for Mesoproterozoic source rocks while exhibiting strong linear relationships.

Spatial range, temporal span, and promiscuity of CLE-RLK signaling.

CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) signaling through receptor-like kinases (RLKs) regulates developmental transitions and responses to biotic and abiotic inputs by communicating the physiological state of cells and tissues. CLE peptides have varying signaling ranges, which can be defined as the distance between the source, i.e., the cells or tissue that secrete the peptide, and their destination, i.e., cells or tissue where the RLKs that bind the peptide and/or respond are expressed. Case-by-case analysis substantiates that CLE signaling is predominantly autocrine or paracrine, and rarely endocrine. Furthermore, upon CLE reception, the ensuing signaling responses extend from cellular to tissue, organ and whole organism level as the downstream signal gets amplified. CLE-RLK-mediated effects on tissue proliferation and differentiation, or on subsequent primordia and organ development have been widely studied. However, studying how CLE-RLK regulates different stages of proliferation and differentiation at cellular level can offer additional insights into these processes. Notably, CLE-RLK signaling also mediates diverse non-developmental effects, which are less often observed; however, this could be due to biased experimental approaches. In general, CLEs and RLKs, owing to the sequence or structural similarity, are prone to promiscuous interactions at least under experimental conditions in which they are studied. Importantly, there are regulatory mechanisms that suppress CLE-RLK cross-talk in vivo, thereby eliminating the pressure for co-evolving binding specificity. Alternatively, promiscuity in signaling may also offer evolutionary advantages and enable different CLEs to work in combination to activate or switch off different RLK signaling pathways.

Integrated pest and pollinator management – expanding the concept

The objective of integrated pest and pollinator management (IPPM) is to co‐manage for pest control and pollination goals. Departing from the well‐established concept of integrated pest management, we include pollinator management in a hierarchical decision support system of management actions. We depict this support system as an IPPM pyramid. Priority is given to proactive measures at the base of the pyramid, which are undertaken through landscape and crop field management of mobile organisms, primarily arthropods. Farther up the pyramid, practices in the form of reactive use of biotic and abiotic inputs should align with basal actions. The goal of IPPM is to minimize trade‐offs, and to maximize co‐benefits and synergies between pest and pollinator management. We contend that IPPM has the potential to contribute to sustainable pest control and crop pollination, as well as provide broader environmental benefits.

Biotic Energy Flow Passing through the Microbial Trophic Web in the Pelagic Zone of Lake Ecosystems

An algorithm of a dynamic mass-balance model emulating the biotic energy flow in a planktonic community with the involvement of microbial organisms has been developed. The abiotic input parameters of the model are the latitude, mean depth of the water body, total phosphorus content, and water color. The model makes it possible to forecast the biomass and production of key plankton groups. It is shown that the food-base production for fish and their growth are determined by the degree of protozoan plankton involvement in the trophic web.

Abiotic Input of Fixed Nitrogen by Bolide Impacts to Gale Crater During the Hesperian: Insights From the Mars Science Laboratory

AbstractMolecular hydrogen (H2) from volcanic emissions is suggested to warm the Martian surface when carbon dioxide (CO2) levels dropped from the Noachian (4100 to 3700 Myr) to the Hesperian (3700 to 3000 Myr). Its presence is expected to shift the conversion of molecular nitrogen (N2) into different forms of fixed nitrogen (N). Here we present experimental data and theoretical calculations that investigate the efficiency of nitrogen fixation by bolide impacts in CO2‐N2 atmospheres with or without H2. Surprisingly, nitric oxide (NO) was produced more efficiently in 20% H2 in spite of being a reducing agent and not likely to increase the rate of nitrogen oxidation. Nevertheless, its presence led to a faster cooling of the shock wave raising the freeze‐out temperature of NO resulting in an enhanced yield. We estimate that the nitrogen fixation rate by bolide impacts varied from 7 × 10−4 to 2 × 10−3 g N·Myr−1·cm−2 and could imply fluvial concentration to explain the nitrogen (1.4 ± 0.7 g N·Myr−1·cm−2) detected as nitrite (NO2−) and nitrate (NO3−) by Curiosity at Yellowknife Bay. One possible explanation is that the nitrogen detected in the lacustrine sediments at Gale was deposited entirely on the crater's surface and was subsequently dissolved and transported by superficial and ground waters to the lake during favorable wet climatic conditions. The nitrogen content sharply decreases in younger sediments of the Murray formation suggesting a decline of H2 in the atmosphere and the rise of oxidizing conditions causing a shortage in the supply to putative microbial life.

Comparisons of south Florida’s seawall and natural mangrove stands reveal similar structural attributes

Mangroves are an exceptional group of facultative halophytic trees within tropical and subtropical regions whose structural complexity is derived from the interplay of biotic and abiotic inputs, or energy signatures, which serve as a proxy for their ecosystem function. Mangroves were originally classified into six distinct community types existing in natural landscapes; absent of artificial structures or urban influence. Advancements in the use of mangroves as green infrastructure have resulted in a growing interest in understanding the ecological importance of mangrove stands associated with artificial structures. The question remains as to whether urban mangroves growing alongside hardened barriers (seawalls) differ from the community types originally described, and if so, to what extent does the urban landscape affect their structure and associated function. In order to answer this question, we compared seawall and natural mangrove stands with respect to their relative species contributions to stand complexity, tree diameter, height, leaf size, root density, diameter and tree height size classes, complexity index, and mean stand diameter. Results of this investigation revealed few differences between the structural characteristics of seawall and natural mangrove stands in south Florida and the Neotropical region. These findings bolster the importance of urbanized mangroves, their ecological function, and support the need to incorporate mangroves as part of the urban landscape.

Impacts of the agricultural transformation of the Canadian Prairies on grassland arthropods

AbstractThe prairie grasslands have been transformed to become the primary source of agricultural production in Canada. Soon after its establishment, the Biological Survey of Canada recognised the urgent need to document the arthropods of the prairie grasslands, especially in the few pristine remnants. Although this initiative has yielded considerable progress in documenting the species present in the Prairies Ecozone, comprehensive ecological studies are sparse. Landscape effects on arthropods are well studied elsewhere, but no equivalent studies have been published for the Canadian Prairies. Crop rotation varies landscape composition annually, changes host plant resources in fields, and interacts with other agricultural inputs to disturb pest and beneficial arthropods. Despite only a handful of studies on grazing, there is an emerging pattern: moderate grazing increases arthropod diversity and benefits certain arthropod guilds. Abiotic inputs elicit variable responses from different arthropod taxa; Carabidae (Coleoptera) are best studied, with some information available for ants (Hymenoptera: Formicidae) and aquatic arthropods. Biotic inputs include arthropods released for biocontrol of weed and insect pests; evidence indicates that biocontrol agents of insects have a greater potential for impact on native communities of arthropods. The studies reviewed here reveal important trends and research gaps to be addressed in the future.

Modelling the effects of stranding on the Atlantic salmon population in the Dale River, Norway

Rapid dewatering in rivers as a consequence of hydropower operations may cause stranding of juvenile fish and have a negative impact on fish populations. We implemented stranding into an Atlantic salmon population model in order to evaluate long-term effects on the population in the Dale River, Western Norway. Furthermore, we assessed the sensitivity of the stranding model to dewatered area in comparison to biological parameters, and compared different methods for calculating wetted area, the main abiotic input parameter to the population model. Five scenarios were simulated dependent on fish life-stage, season and light level. Our simulation results showed largest negative effect on the population abundance for hydropeaking during winter daylight. Salmon smolt production had highest sensitivity to the stranding mortality of older juvenile fish, suggesting that stranding of fish at these life-stages is likely to have greater population impacts than that of earlier life-stages. Downstream retention effects on the ramping velocity were found to be negligible in the stranding model, but are suggested to be important in the context of mitigation measure design.

A conceptual framework to describe the ecology of fragmented landscapes and implications for conservation and management.

The study of the ecology of fragmented landscapes has been dominated by two assumptions: the unique unidirectional path from larger to smaller fragments and the negligible role of fragment species on fragment properties. An accurate conceptualization of fragmented landscapes requires consideration of the age and origin of the fragments, i.e., direct fragmentation or reverse fragmentation (generation or increase of vegetated fragments by colonization), and the habitat modifications of fragment species (autogenic processes). Colonization and autogenic processes alter the fragments' composition and function. Fragment metrics affect colonization. Autogenic processes are antagonized by disturbances and modulated by abiotic inputs. Fragment alterations by autogenic processes may explain the continuous species substitution detected in some fragments or the species persistence in others. Reverse fragmentation, a natural process in commonly disturbed landscapes, challenges the avoidance-of-habitat disturbance as the ultimate strategy for biodiversity conservation and stresses the importance of pioneer species that promote succession as resilience elements in fragmented landscapes. Among-fragment diversity, generated by local disturbances, can be essential for the resilience of fragmented landscapes, suggesting that conservation and habitat utilization can be complementary processes. Traditional agroforestry systems that depend on disturbance, fragmentation, colonization, and autogenic processes may provide important insights into fragmentation ecology.

Integrating agricultural and environmental sustainability across generations: the never-ending quest for the golden fleece

Dynamic agricultural sustainability strongly depends on a reliable energy resource that is capable of maintaining order in an open (agro-eco-) system at the expense of the order of the environment. In this article, the integrative and complex challenges of combining efficient farming with environmental upgrading are analysed. Farming should be practiced within an appropriate, though moving agro-climax, the impact of which has become more important than that of the remaining natural ecosystems. Efficient use of resources and energy is not only important during the concentration phase of farming, but even more important during the dilution phase. The best way of improving the eco-capacity of farming systems is to increase the vitality of the agrosphere i.e. assimilation capacity of abiotic inputs necessary for crop intensification. This will require hands-on guidelines for the farmer amongst which integrated plant nutrition and the integration of organic and inorganic fertilisation will allow both sustainable and intensive production systems. The intergenerational adoption of the latter will be proof of their sustainable character. World agriculture faces new challenges today, among which are: 1) a growing population that needs to be fed,2) a decrease in the availability of prime agricultural land,3) competition for key resources such as labour, water, and land with other economic sectors such as cities and mining,4) competing uses for agricultural products, for example fuel,5) growing awareness of the general public regarding sustainability of agriculture production and hence,6) necessary improvements to the biodiversity and ecosystem functions in agriculture.

Study on Material Input of Coal Mines Production

Based on the MIPS method, material input model of raw coal production was built. Taking two coal groups which were typical as investigation object, the material input coefficients of groups raw coal production were calculated. The results showed that the air input of unit raw coal was about 0.03t/t whatever it is open pit or underground mine for two groups. The water input of underground mine was slightly high above open pit mine and the average was 6.69t/t. The solid abiotic material input of open pit mine which was about 8.45t/t was far above underground mine which was about 1.36t/t. In the all full production mines of two groups, the water input proportion was biggest in unit raw coal production and the average was about 68.21%.The solid abiotic material input accounted for 31.49% while air was just about 0.3%.

Contraception can Lead to Trophic Asynchrony between Birth Pulse and Resources

Abiotic inputs such as photoperiod and temperature can regulate reproductive cyclicity in many species. When humans perturb this process by intervening in reproductive cycles, the ecological consequences may be profound. Trophic mismatches between birth pulse and resources in wildlife species may cascade toward decreased survival and threaten the viability of small populations. We followed feral horses (Equus caballus) in three populations for a longitudinal study of the transient immunocontraceptive porcine zona pellucida (PZP), and found that repeated vaccinations extended the duration of infertility far beyond the targeted period. After the targeted years of infertility, the probability of parturition from post-treated females was 25.6% compared to 64.1% for untreated females, when the data were constrained only to females that had demonstrated fertility prior to the study. Estimated time to parturition increased 411.3 days per year of consecutive historical treatment. Births from untreated females in these temperate latitude populations were observed to peak in the middle of May, indicating peak conception occurred around the previous summer solstice. When the post-treated females did conceive and give birth, parturition was an estimated 31.5 days later than births from untreated females, resulting in asynchrony with peak forage availability. The latest neonate born to a post-treated female arrived 7.5 months after the peak in births from untreated females, indicating conception occurred within 24–31 days of the winter solstice. These results demonstrate surprising physiological plasticity for temperate latitude horses, and indicate that while photoperiod and temperature are powerful inputs driving the biological rhythms of conception and birth in horses, these inputs may not limit their ability to conceive under perturbed conditions. The protracted infertility observed in PZP-treated horses may be of benefit for managing overabundant wildlife, but also suggests caution for use in small refugia or rare species.

Genetic Interactions Between ArabidopsisDET1andUVH6During Development and Abiotic Stress Response

Plants must adapt to a variety of abiotic inputs, including visible light, ultraviolet (UV) light, and heat. In Arabidopsis thaliana, DE-ETIOLATED 1 (DET1) plays a role in visible light signaling, UV tolerance, and development. UV-HYPERSENSITIVE 6 (UVH6) mutants are UV and heat sensitive, as well as dwarf and pale, like det1. In this study, we examine the genetic interactions between these two genes. In dark-grown seedlings, uvh6 exhibits a weak de-etiolated phenotype but does not affect the stronger de-etiolated phenotype of det1. In the light, det1 is epistatic to uvh6 with regard to chlorophyll level, but their effect on all size parameters is additive and therefore independent. With regard to UV tolerance, det1 UV resistance is epistatic to uvh6 UV sensitivity. In heat stress experiments, det1 enhances heat-induced tissue damage in the uvh6 background but suppresses heat-induced growth inhibition. Thus, det1 acts epistatically to uvh6 with respect to de-etiolation, chlorophyll level, UV tolerance, and heat-induced growth inhibition, whereas det1 and uvh6 act additively to regulate plant size and heat-induced cell death. These data provide insight into interplay between light and heat signaling.

Conditions Under Which Nitrogen Can Limit Steady-State Net Primary Production in a General Class of Ecosystem Models

Human activity is drastically altering global nitrogen (N) availability. The extent to which ecosystems absorb additional N—and with it, additional CO2—depends on whether net primary production (NPP) is N-limited, so it is important to understand conditions under which N can limit NPP. Here I use a general dynamical model to show that N limitation at steady-state—such as in old-growth forests—depends on the balance of biotically controllable versus uncontrollable N inputs and losses. Steady-state N limitation is only possible when uncontrollable inputs (for example, atmospheric deposition) exceed controllable losses (for example, leaching of plant-available soil N), which is the same as when uncontrollable losses (for example, leaching of plant-unavailable soil N) exceed controllable inputs (biological N fixation). These basic results are robust to many model details, such as the number of plant-unavailable soil N pools and the number and type of N fixers. Empirical data from old-growth tropical (Hawai’i) and temperate (Oregon, Washington, Chile) forests support the model insights. Practically, this means that any N fixer—symbiotic or not—could overcome ecosystem N limitation, so understanding N limitation requires understanding controls on all N fixers. Further, comparing losses of plant-available N to abiotic inputs could offer a rapid diagnosis of whether ecosystems can be N-limited, although the applicability of this result is constrained to ecosystems with a steady-state N cycle such as old-growth forests largely devoid of disturbance.

Ecological Efficiency Comparison of Fisheries Resources Utilization

The faster developing of fisheries activities could give some negative impacts for environment. The problems such as over-fishing, by-catch, habitat degradation, and fisheries management could be the main issues that developed with the activities of this sector. Coastal fisheries valued over-fishing, meanwhile high fisheries is not optimally utilized yet. For giving recommendation to develop fisheries need a holistic study. The beginning step is studying the comperazing of ecological efficiency between coastal – and high fisheries. The objective goal of this study is knowing the comperazing of ecological efficiency between coastal – and high fisheries in Sukabumi District. The method use MIPS (Material Input Per Service unit) that developed by Wuppertal Institute for Climate, Environmental, Energy (WI). The result of MIPS calculation show the different of ecological efficiency. For having 1 kg fresh fish from high fisheries and directly saled need the abiotic input 0,19 kg, biotic 1,26 kg, water 1,49 kg and air 0,03 kg, meanwhile for having 1 kg fresh fish from coastal fisheries and directly saled need the abiotic input 0,14 kg, biotic 1,33 kg, water 1,08 kg and air 0,04 kg. Averagely for having 1 kg fish from high fisheries need the material input of abiotic 0,35 kg, biotic 1,41 kg, water 2,89 kg and air 0,12 kg, meanwhile for having 1 kg fish from coastal fisheries need the material input of abiotic 0,27 kg, biotic 1,34 kg, water 1,95 kg and air 0,10 kg.

Prediction of street tree morphological parameters using artificial neural networks

Street trees positively affect the everyday life of city inhabitants and therefore successful management of this resource is important. A tree inventory is an essential first step towards this end, but this activity can be complex, costly and must be optimized. In order to reduce time and effort required for data acquisition either when using traditional field work or airborne laser systems, a method is proposed to predict the value of essential tree morphological parameters with surrogate variables and artificial intelligence multilayer perceptron networks (MLPs). To evaluate MLPs, seven different models were tested on Acer platanoides L., Acer saccharinum L., Celtis occidentalis L., Fraxinus pennsylvanica Marsh., Gleditsia triacanthos L., Tilia cordata Mill., and Ulmus pumila L. data sets. Three models were intended to predict diameter at breast height (DBH), annual DBH increment and crown volume with a minimal number of input measurements to be extracted from aerial LIDAR (Light Detection and Ranging) data. The last four were associated with traditional ground inventory methods and aimed to predict height, crown volume and their respective annual increments using less labour-intensive variables. The prediction performance was assessed with the Pearson r correlation coefficient, computed between the measured and estimated output values for each of the cross-validation test files per tree species and model. By using carefully selected biotic and abiotic input parameters, the prediction performance of multilayer perceptron showed robustness and precision despite different age–class distribution per species, dissimilar species morphological characteristics, uneven distribution of species within defined urban ecological zones, and varied abiotic growth conditions. More precisely, prediction coefficients were greater than 70% for all models with very small probability levels except for two predictions were input data exhibited strongly non-Gaussian distributions. Overall, the average prediction for all scenarios was 91%. Considering these results, it was found that prediction of DBH, annual DBH increment and crown volume is possible with limited aerial LIDAR laser information. Moreover, it was established that traditional field work effort can be further reduced by predicting the value of unmeasured morphological parameters within acceptable levels of precision. These findings can have an impact on future urban tree inventories. Depending on the number of trees to be measured, municipal administrations have the choice to use either airborne or traditional data acquisition methods. In both cases, this research proposes optimized procedures that may reduce the overall inventory costs.

Dimethylsulphide production in the Southern Ocean using a nitrogen-based flow network model and field measurements from ACE-1

Dimethylsulphide (DMS) has been implicated in climate change as a possible negative feedback to global warming, and several Models have been developed that simulate the production of DMS in the marine environment. The focus of this study is to improve the nitrogen based Gabric Model, using field data collected during the Southern Hemisphere First Marine Aerosol Characterisation Experiment (ACE-1) in the Southern Ocean in 1995. Two Model Runs (Series A and B) were carried out with six simulations of varying biotic and abiotic inputs applied over the voyage transect (41–48°S), reflecting Model default values or field values from the experiment. The abiotic inputs were time-step, dissolved dimethylsulphoniopropionate (DMSP) and DMS, and the biotic nitrogen inputs were from phytoplankton, bacteria, zooflagellates, large protozoa, micro and mesozooplankton. The focus of the abiotic assessment was nutrient (nitrate) uptake and dissolved DMSP and DMS output. Model output of the biotic compartments was assessed f...

Trends in Resin and KCl-extractable Soil Nitrogen Across Landscape Gradients in Taylor Valley, Antarctica

Previous descriptions of soils in the McMurdo Dry Valleys, Antarctica, have focused on the dominance of abiotic controls rather than on nutrient cycling. Although free-living N 2 -fixing and nitrifying microorganisms have been isolated in Antarctic soils, little is known about in situ nitrogen (N) cycling. We measured KCl-extractable NH 4 + and NO 3 - , as well as anion resin exchangeable NO 3 - , across sediment-soil transects and in two positions on a hill slope in Taylor Valley, Antarctica. These landscapes provide gradients of soil moisture, salinity, and texture that influence invertebrate communities and organic matter dynamics. Assuming an N cycle dominated by abiotic inputs, we hypothesized that inorganic N content would be predominantly comprised of NO 3 - and most strongly correlated to soil salinity, while NO 3 - flux (estimated by resin adsorption) would be most influenced by soil water content, salinity, and total soil NO 3 - concentrations. Our results were inconsistent with a physically dominated N cycle. In contrast to previous studies of Dry Valley soils, we found that NH 4 + made up a large proportion of inorganic N. Total KCl-extractable N was correlated most strongly with total soil N and soil moisture. The most saline soils in the swale of a hill slope had the highest concentrations of NO 3 - , but we found no overall correlation between soil salinity and resin-exchangeable NO 3 - or KCl-extractable N. Resin-extractable NO 3 - was most strongly correlated with total soil N, soil water content, and KCl-extractable NH 4 + , suggesting that accumulation of NO 3 - in resins was influenced by the mineralization of organic matter and not strictly by ionic migration, as an abiotic-based model may have predicted. We conclude that biological N cycling is significant in some Dry Valley soils and that the dominance of biological vs physical influences over N cycling is controlled in part by the availability of soil moisture and organic matter.

Atmospheric CO 2, climate change, and tree growth: a process model I. Model structure

Primary production of forest systems will be significantly changed as atmospheric CO 2 concentrations increase and climatic changes occur. This paper presents the structure of a process model to be used for predicting changes in tree seedling biomass accumulation associated with increases in CO 2 level and shifts in the abiotic environment. The model is a compartment representation of carbon flow that utilizes the processes of gross photosynthesis, stomatal conductance, growth and maintenance respiration, photosynthate allocation, and photosynthate conversion to biomass. The model is driven by abiotic submodels that provide high-resolution inputs obtained from standard meteorological stations. Independent data sets are used to evaluate the net photosynthesis portion of the model with respect to abiotic inputs; simulated and observed biomass accumulation are compared.

Evolution of nitrogen-fixing symbioses

SynopsisBecause of both the energy costs and the slowness of the reactions of the nitrogenase complex compared with those involving some form of combined nitrogen (oxidised or reduced), we argue that the evolution of nitrogen-fixing organisms required an environment which was very limited in combined nitrogen. This is thought to have occurred after phototrophy evolved, but before water was used as a hydrogen donor (and therefore oxygen was present in the atmosphere). After oxygenic photosynthesis evolved, the need for a high level of biological nitrogen-fixation remained, since abiotic inputs were insufficient to keep pace with the rapidly evolving biomass (flora and fauna). Symbiotic fixation probably first evolved in the form of casual associations between cyanobacteria and most other groups of plants. By inhabiting the sporophytic generation of evolving land plants (cycads in particular), protection against nitrogenase-inactivating oxygen and a more desiccating environment was achieved simultaneously.We envisage nodulated plants arising by the transfer ofnifgenes into tumour-forming bacteria. In the case of legumes, these would be ancestors of extant agrobacteria, which gain entry into their hostsviawounds. Co-evolution of symbionts from nitrogen-fixing tumours has taken several routes, leading to extant nodules differing in mode of infection, structure and physiology. Evolution towards optimisation of oxygen usage is continuing.Nitrogen-fixing symbiosis in animal systems is only advantageous in specialised ecological niches in which wood is the sole dietary intake. In the case of shipworms, the symbiosis has many of the advanced features associated with nitrogen fixing root nodules.