Simulated Climate Change Conditions Research Articles

Mitigating water pollution in a Portuguese river basin under climate change through agricultural sustainable practices

Sustainable agricultural practices have been extensively used to reduce water pollution; however, the effectiveness of these practices may be significantly affected by climate change. In this study, we assess the effectiveness of sustainable agricultural practices in reducing sediment and nutrient export to rivers under future climate conditions, using the Soil & Water Assessment Tool in a Portuguese river basin exposed to high levels of agricultural pollution. In our study, filter strips demonstrated a significant mitigation effect on sediment and nutrient increases under simulated climate change conditions, with maximum sediment export depletion reaching 65% and the highest nutrient export depletion observed at 35%. The implementation of multiple sustainable practices resulted in the highest depletions, with a notable 71% depletion in sediment export and a 35% depletion in nutrient export. Additionally, our research underscores the crucial role of filter strips and multiple sustainable agricultural practices in mitigating the projected rise in nutrient concentrations during summer, given the effect of climate change on river discharge. Further studies exploring sustainable agricultural practices across different climates and watersheds can improve our understanding of their effectiveness for adaptation to climate change.

Effect of Dietary Supplementation with Lactiplantibacillus plantarum I On Queen Scallop Aequipecten opercularis Under Simulated Climate Change Conditions

Abstract This study examined the effects of dietary supplementation of queen scallop Aequipecten opercularis with an indigenous strain of lactic acid bacteria (LAB), Lactiplantibacillus plantarum I, previously isolated from its digestive tract, on gut microbial populations and growth rates during cultivation under simulated climate change conditions (pH 7.8, T = 16 ± 2 °C). After one month of feeding, the results showed a noticeable reduction in aquaculture diseases causing pathogens while maintaining sufficient viable Lpb. plantarum I cells. A higher pH and temperature resulted in higher growth rates, measured by the weight and length of scallops, compared to the control group. The results obtained shed light on the influence of the addition of lactic acid bacteria on the growth of bivalve mollusks under normal and climate change conditions, and provide control of pathogenic microorganisms. In the context of climate change, host-pathogen interactions need to be recognized and put under control by applying natural solutions to minimize the environmental footprint.

Effects of simulated climate change conditions of increased temperature and [CO2] on the early growth and physiology of the tropical tree crop, Theobroma cacao L.

Despite multiple studies of the impact of climate change on temperate tree species, experiments on tropical and economically important tree crops, such as cacao (Theobroma cacao L.), are still limited. Here, we investigated the combined effects of increased temperature and atmospheric carbon dioxide concentration ([CO2]) on the growth, photosynthesis and development of juvenile plants of two contrasting cacao genotypes: SCA 6 and PA 107. The factorial growth chamber experiment combined two [CO2] treatments (410 and 700p.p.m.) and three day/night temperature regimes (control: 31/22°C, control+2.5°C: 33.5/24.5°C and control+5.0°C: 36/27°C) at a constant vapour pressure deficit (VPD) of 0.9kPa. At elevated [CO2], the final dry weight and the total and individual leaf areas increased in both genotypes, while the duration for individual leaf expansion declined in PA 107. For both genotypes, elevated [CO2] also improved light-saturated net photosynthesis (Pn) and intrinsic water-use efficiency (iWUE), whereas leaf transpiration (E) and stomatal conductance (gs) decreased. Under a constant low VPD, increasing temperatures above 31/22 °C enhanced the rates of Pn, E and gs in both genotypes, suggesting that photosynthesis responds positively to higher temperatures than previously reported for cacao. However, dry weight and the total and individual leaf areas declined with increases in temperature, which was more evident in SCA 6 than PA 107, suggesting the latter genotype was more tolerant to elevated temperature. Our results suggest that the combined effect of elevated [CO2] and temperature is likely to improve the early growth of high temperature-tolerant genotypes, while elevated [CO2] appeared to ameliorate the negative effects of increased temperatures on growth parameters of more sensitive material. The evident genotypic variation observed in this study demonstrates the scope to select and breed cacao varieties capable of adapting to future climate change scenarios.

Selecting tree species to restore forest under climate change conditions: Complementing species distribution models with field experimentation

The long-term success of forest restoration programs can be improved using climate-based species distribution models (SDMs) to predict which tree species will tolerate climate change. However, as SDMs cannot estimate if species will recruit at these habitats, determining whether their predictions apply to early life-cycle stages of trees is critical to support such a usage. For this, we propose sowing seeds of the focal tree species under the current climate and simulated climate change conditions in target restoration sites. Thus, using of SDMs to design climate-adaptive forest restoration programs would be supported if the differences in habitat occupancy probabilities of species they predict between the current and future climate concurs with the observed differences in recruitment rates of species when sowed under the current climate and simulated climate change conditions. To test this hypothesis, we calibrated SDMs for Vachellia pennatula and Prosopis laevigata, two pioneer tree species widely recommended to restore human-degraded drylands in Mexico, and transferred them to climate change scenarios. After that, we applied the experimental approach proposed above to validate the predictions of SDMs. These models predicted that V. pennatula will decrease its habitat occupancy probabilities across Mexico, while P. laevigata was predicted to keep out their current habitat occupancy probabilities, or even increase them, in climate change scenarios. The results of the field experiment supported these predictions, as recruitment rates of V. pennatula were lower under simulated climate change than under the current climate, while no differences were found for the recruitment rates of P. laevigata between these environmental conditions. These findings demonstrate that SDMs provide meaningful insights for designing climate-adaptive forest restoration programs but, before applying this methodology, predictions of these models must be validated with field experiments to determine whether the focal tree species will recruit under climate change conditions. Moreover, as the pioneer trees used to test our proposal seem to be differentially sensitive to climate change, this approach also allows establishing what species must be prescribed to restore forests with a view to the future and what species must be avoided in these practices.

Future Climate Change Conditions May Compromise Metabolic Performance in Juveniles of the Mud Crab Scylla serrata

Research characterising the effects of future climate change on the marine environment remains heavily focussed on that of temperate regions and organisms. Furthermore, little is known of these effects on the early life stages of many marine species. Tropical regions are already experiencing an increase in sea surface temperature and decrease in sea surface salinity, conditions favoured by pathogenic bacteria such as Vibrio spp. The early life stages of crabs are known to be particularly vulnerable to both the direct physiological effects of climate change and exposure to harmful microorganisms, yet there are limited data on these effects on juveniles of many tropical crustacean species. This study assessed the metabolic responses of mud crab (Scylla serrata) juveniles to warming and/or freshening in the presence or absence of pathogenic bacteria in southwest India. Juvenile crabs were exposed to either ambient (28 °C/30 PSU) or one of three projected climate change regimes (28 °C/20 PSU (freshening), 32 °C/30 PSU (warming), 32 °C/20 PSU (warming + freshening)) for 10 days, in either the presence or absence of the pathogenic bacteria Vibrio parahaemolyticus. Results show that simulated climate change conditions, especially freshening, caused a significant increase in oxygen consumption rates (MO2), and that these were further increased when juveniles were exposed to V. parahaemolyticus. These results suggest that the effects of future climate change conditions could have significant implications for the conservation of wild stocks and commercial farming of this species in South Asia.

Recruitment of pioneer trees with physically dormant seeds under climate change: the case of Vachellia pennatula (Fabaceae) in semiarid environments of Mexico.

Most tree species native to arid and semiarid ecosystems produce seeds with physical dormancy, which have impermeable coats that protect them from desiccation and prevent germination when the environmental conditions are unfavorable for seedling establishment. This dormancy mechanism may confer some degree of tolerance to seeds facing warmer and drier conditions, as those expected in several regions of the world because of climate change. Scarification of these seeds (removal of protective coats) is required for stimulating germination and seedling development. However, as scarification exposes seeds to the external environmental conditions, it can promote desiccation and viability loss in the future. To test these hypotheses, we performed field experiments and sowed scarified and unscarified seeds of a pioneer tree native to semiarid ecosystems of Mesoamerica (Vachellia pennatula) under the current climate and simulated climate change conditions. The experiments were conducted at abandoned fields using open-top chambers to increase temperature and rainout shelters to reduce rainfall. We measured microenvironmental conditions within the experimental plots and monitored seedling emergence and survival during a year. Air temperature and rainfall in climate change simulations approached the values expected for the period 2041-2080. Seedling emergence rates under these climatic conditions were lower than under the current climate. Nevertheless, emergence rates in climate change simulations were even lower for scarified than for unscarified seeds, while the converse occurred under the current climate. On the other hand, although survival rates in climate change simulations were lower than under the current climate, no effects of the scarification treatment were found. In this way, our study suggests that climate change will impair the recruitment of pioneer trees in semiarid environments, even if they produce seeds with physical dormancy, but also indicates that these negative effects will be stronger if seeds are scarified.

Seed fate, seedling establishment and the role of propagule size in forest regeneration under climate change conditions

Climate change can affect tree recruitment altering post-dispersal seed fates and impairing seedling development, and these effects will be stronger at man-disturbed areas than beneath forest canopies. Seed biomass, however, positively influences tree recruitment processes and its relevance increases with environmental harshness. Therefore, this seed trait may become critical for forest regeneration under climate change scenarios. We experimentally tested these hypotheses with two Mexican oaks that dominate forests at sites where temperature will increase and rainfall will decrease in the next 20 years. At both experimental sites, we sowed acorns of varying biomass at forest understories and deforested areas under the current climate and simulated climate change conditions. We measured microclimate, incidence of seed parasitism by insects and fungi, germination, shoot emergence, and seedling survival and growth over a year. Temperature in climate change simulations was increased 2 °C and rainfall was reduced 17–18%, and this concurred with the near-term changes expected for both variables at the experimental sites. Climate change conditions intensified insect parasitism and decreased fungal infestation on seeds, but these effects were only found within forests and they did not relate with propagule size. Increased warming and drought reduced germination, shoot emergence, and seedling survival and growth at forests and deforested areas, but all these processes were positively related with seed biomass. Indeed, in an oak species, these relationships displaced towards bigger-sized seeds under climate change conditions. Our findings suggest that climate change can alter the intensity of seed-parasite interactions and impair tree establishment processes, also suggesting that this phenomenon will favor large-sized over small-sized seeds during recruitment of some tree species.

From the ground up: Building predictions for how climate change will affect belowground mutualisms, floral traits, and bee behavior

Climate change affects species and their interactions, resulting in novel communities and modified ecosystem processes. Through shifts in phenology and distribution, climatic change can disrupt interactions, including those between mutualists. Mutualisms influence the structure and stability of communities and can link species to a common fate. However, research on climate change has focused on pairwise mutualisms, neglecting the higher-order interactions that can arise when species interact with multiple mutualists. We explore the effects of climate change on tripartite interactions involving belowground mutualists, namely soil bacteria and fungi, flowering plants, and pollinators. We outline how climate change is predicted to affect the phenology and distribution of these belowground mutualists, emphasizing the consequent effects on host plant floral traits, plant-pollinator interactions, and bee behavior. We find evidence that warming, advanced snowmelt, and drought are likely to cause phenological and distributional shifts in soil microbes, leading to diminished mutualistic interactions with plants and symbiont switching. Consequently, shifts in flowering phenology, smaller floral displays, and lower quality floral rewards are expected, increasing foraging time and energy demands for bees and altering their floral preferences. Such costs could translate into reduced fitness and novel selection pressures for bees and flowering plants in the short term. We highlight knowledge gaps and ways forward, urging studies on microbe dispersal and phenological cues, experiments that manipulate soil microbe-host plant interactions under simulated climate change conditions, and large-scale field studies across environmental gradients, all with the goal of understanding how climate change will affect soil microbe-plant-pollinator mutualisms.

Modelling and validation of the spatial distribution of suitable habitats for the recruitment of invasive plants on climate change scenarios: An approach from the regeneration niche

The regeneration niche concept states that plant species only occur in habitats where the environmental conditions allow their recruitment. This study focuses on this concept and proposes a novel approach for modelling and experimentally validating the distribution of suitable habitats for the recruitment of invasive plants under the current and future climate. The biological invasion of the Peruvian peppertree (Schinus molle) in Mexico is used as practical example. The values of eight bioclimatic variables associated to sites in which young, naturally established seedlings and saplings were detected were used to model the current distribution of recruitment habitats. A machine-learning algorithm of maximum entropy (MaxEnt) was used to calibrate the model and its output indicated the distribution of occurrence probabilities of young peppertrees in Mexico under the current climate. This model was projected on climate change scenarios predicted for the middle of this century, which indicated that the cover of suitable recruitment habitats for this invasive species will shrink. To validate these predictions, field experiments were performed at three sites where the model predicted reduced occurrence probabilities of young peppertrees. In these experiments, emergence and survival rates of peppertree seedlings were assessed under the current climate and under simulated climate change conditions. As seedling emergence and survival rates were lower under simulated climate change conditions, the experiments validated the model predictions. These results supported our proposal, which combines modelling and experimental approaches to make accurate and valid predictions about the distribution of suitable recruitment habitats for invasive plants in a warmer and drier world.

Effect of Temperature, Water Activity and Carbon Dioxide on Fungal Growth and Mycotoxin Production of Acclimatised Isolates of Fusarium verticillioides and F. graminearum.

Climate change is primarily manifested by elevated temperature and carbon dioxide (CO2) levels and is projected to provide suitable cultivation grounds for pests and pathogens in the otherwise unsuitable regions. The impacts of climate change have been predicted in many parts of the world, which could threaten global food safety and food security. The aim of the present work was therefore to examine the interacting effects of water activity (aw) (0.92, 0.95, 0.98 aw), CO2 (400, 800, 1200 ppm) and temperature (30, 35 °C and 30, 33 °C for Fusarium verticillioides and F. graminearum, respectively) on fungal growth and mycotoxin production of acclimatised isolates of F. verticillioides and F. graminearum isolated from maize. To determine fungal growth, the colony diameters were measured on days 1, 3, 5, and 7. The mycotoxins produced were quantified using a quadrupole-time-of-flight mass spectrometer (QTOF-MS) combined with ultra-high-performance liquid chromatography (UHPLC) system. For F. verticillioides, the optimum conditions for growth of fumonisin B1 (FB1), and fumonisin B2 (FB2) were 30 °C + 0.98 aw + 400 ppm CO2. These conditions were also optimum for F. graminearum growth, and zearalenone (ZEA) and deoxynivalenol (DON) production. Since 30 °C and 400 ppm CO2 were the baseline treatments, it was hence concluded that the elevated temperature and CO2 levels tested did not seem to significantly impact fungal growth and mycotoxin production of acclimatised Fusarium isolates. To the best of our knowledge thus far, the present work described for the first time the effects of simulated climate change conditions on fungal growth and mycotoxin production of acclimatised isolates of F. verticillioides and F. graminearum.

Changes in soil nematode abundance and composition under elevated [CO2] and canopy warming in a rice paddy field

Global climate change is characterized by enhanced atmospheric carbon dioxide concentration ([CO2]) and temperature, with unknown consequences for soil nematode communities. Soil nematode in response to elevated [CO2], warming and their interaction in paddy field remain largely unknown. Here we aimed to understand how factorial combinations of elevated [CO2] and canopy warming affect soil nematode in a rice paddy field. A rice paddy field was consistently treated with elevated [CO2] (500 ppm), canopy warming (+2 °C) or their combinations. Soil samples after a two-year treatment were collected during the rice growing season and nematode communities were extracted with a modified Baermann funnel extraction to examine the changes in nematode abundance and composition under climate change. Soil nematode communities were altered by elevated [CO2] and warming, but these responses were dependent on rice growing stages. When averaged over the four stages, total nematode abundances were increased by 31.5% under elevated [CO2], and by 25.7% under warming. Elevated [CO2] had no effect on nematode diversity, but slightly altered the composition of different trophic groups. In contrast, warming decreased nematode diversity, but increased plant parasite index, which was negative correlated with crop production. This was attributed to increases in the relative abundance of herbivores under simulated climate change conditions. Elevated [CO2] and warming had a positive effect on nematode abundance, but potentially reduced nematode diversity and soil health. These results suggest that multi-factors interactively affect the responses of soil nematode communities, which is important for food productivity under climate change.

Adaptive Diversity of Beech Seedlings Under Climate Change Scenarios.

The ability of beech (Fagus sylvatica L.) populations to adapt to the ongoing climate change is especially important in the southern part of Europe, where environmental change is expected to be more intense. In this study, we tested the existing adaptive potential of eight beech populations from two provenances in N.E. Greece (Evros and Drama) that show differences in their environmental conditions and biogeographical background. Seedling survival, growth and leaf phenological traits were selected as adaptive traits and were measured under simulated controlled climate change conditions in a growth chamber. Seedling survival was also tested under current conditions in the field. In the growth chamber, simulated conditions of temperature and precipitation for the year 2050 were applied for 3 years, under two different irrigation schemes, where the same amount of water was distributed either frequently (once every week) or non-frequently (once in 20 days). The results showed that beech seedlings were generally able to survive under climate change conditions and showed adaptive differences among provenances and populations. Furthermore, changes in the duration of the growing season of seedlings were recorded in the growth chamber, allowing them to avoid environmental stress and high selection pressure. Differences were observed between populations and provenances in terms of temporal distribution patterns of precipitation and temperature, rather than the average annual or monthly values of these measures. Additionally, different adaptive strategies appeared among beech seedlings when the same amount of water was distributed differently within each month. This indicates that the physiological response mechanisms of beech individuals are very complex and depend on several interacting parameters. For this reason, the choice of beech provenances for translocation and use in afforestation or reforestation projects should consider the small scale ecotypic diversity of the species and view multiple environmental and climatic parameters in connection to each other.

Community dynamics can modify the direction of simulated warming effects on crop yield.

Climate change affects agriculture through a range of direct and indirect pathways. These include direct changes to impacts of pests and diseases on crops and indirect effects produced by interactions between organisms. It remains unclear whether the net effects of these biotic influences will be beneficial or detrimental to crop yield because few studies consider multiple interactions within communities and the net effects of these on community structure and yield. In this study, we created two experimental grapevine communities in field cages, and quantified direct and indirect effects of key pest and disease species under simulated climate change conditions (elevated temperature and reduced humidity). We found that the net impact of simulated climate change on total yield differed for the two communities, with increased yield in one community and no effect in the other. These effects, and the interactions between pests and pathogens, may also have been affected by the prevailing abiotic conditions, and we discuss how these may contribute to our findings. These results demonstrate that future research should consider more of the interactions between key organisms affecting crops under varying abiotic conditions to help generate future recommendations for adapting to the effects of climate change.

Changes in nutrient uptake and utilization by rice under simulated climate change conditions: A 2-year experiment in a paddy field

Global climate change with elevated atmospheric CO2 concentration and temperature has been known impacting plant photosynthesis and grain yield in agroecosystems. However, how nutrient uptake and utilization by rice change under climate change stresses has been poorly addressed. An open-air field experiment was conducted to investigate the impacts of factorial combinations of CO2 enrichment (up to 500 ppm) and canopy warming (+2 °C) on nutrient concentration (PNC), accumulation (PNA) and utilization efficiency (NUE) for two cropping years in a paddy from southeast China. Plant samples of aboveground biomass were collected across the growing stages and grain yield measured at harvest. Compared to ambient condition, CO2 enrichment more or less decreased PNC of N, P and K, but unchanged PNA of N and P while increased aboveground biomass. In contrast, warming increased PNC of N, P and K respectively by 7.4%, 11.0% and 13.4% at the ripening stage, but decreased PNA of N, P and K respectively by 18.6%, 22.6% and 10.8% in 2013. Whereas, concurrent CO2 enrichment and warming unchanged PNC but slightly decreased PNA of N and K in both years. In addition, CO2 enrichment unchanged the apparent NUE, but increased NUE of N and K under concurrent warming in both years. Therefore, canopy warming may have impacted the rice response in NUE to CO2 enrichment as the change in PNA with concurrent CO2 enrichment and warming was in a similar trend to that with warming alone. Our findings suggest that nutrient uptake and utilization by rice are more impacted by warming compared with CO2 enrichment under the simulated climate change conditions. Therefore, simulated climate change experiments should be conducted regarding how simultaneous atmospheric CO2 enrichment and warming influences plant traits and functions in rice paddy, to provide a better understanding of agricultural production changes and sustainable nutrient management under future climate change.

Winter wheat water requirement and utilization efficiency under simulated climate change conditions: A Penman-Monteith model evaluation

Impact of climate change on water supply and use is a critical issue for dryland crop production. In this study is assessed the potential impact of atmospheric CO2 enrichment (500μmolmol−1, CE) and canopy warming (+2°C, WA) and their combination (CW) on crop water utilization efficiency (WUE) of winter wheat in an open-air field experiment from Southeast China. Micro-meteorological measurement and wheat growth under individual treatments over three executive years of 2012–2015 were used to estimate the crop water requirement (CWR) of wheat using an improved FAO Penman-Monteith equation. Overall, CO2 enrichment slightly decreased the CWR by 8.3%, and increased the WUE of grain production (WUEg) by 23.1%, averaged over the three years. In contrast, warming increased CWR by 19.6% but decreased WUEg by 27.9% over the period. Under CW treatment, however, CWR was increased by 3.1–15.8% but WUEg was decreased by 3.5–18.2% throughout three years. Clearly, the positive impact of CO2 enrichment on WUE was largely negated under canopy warming. Moreover, when assessing with individual year data, inter-annual variability of WUEg was insignificant under WA, smaller under CE but much higher under CW, compared to CK. These results indicated that an interaction by canopy warming overshadowed the potential increase in WUE with CO2 enrichment and enforced yearly fluctuation of the crop production under simulated climate change conditions. Therefore, improving water supply and management in agriculture should thus be endeavored to address the potential constraints with future trends of concurrent atmospheric CO2 enrichment and warming.

Dry-hot stress significantly reduced the nitrogenase activity of epiphytic cyanolichen

Nitrogen (N) fixed by epiphytic cyanolichens (i.e. lichens that contain cyanobacterial symbionts) is thought to be the most important resource of this nutrient in some natural forest ecosystems. Although a great deal of work has been carried out to evaluate the biomass of this group as well as its contribution to ecosystem N budgets, empirical studies are needed to confirm the N input responses by cyanolichens under climate change conditions (dry-hot stress) as well as to determine the factors that control this process. We simulated climate change conditions by transplanting Lobaria retigera, a common cyanolichen in the area, to lower elevations, and measured nitrogenase activity in response to warmer and drier conditions. In addition, we conducted a series of laboratory and greenhouse experiments to determine the dominant factors influencing nitrogenase activity in this species. The results of this study show that mean annual nitrogenase activity at the higher site was 1.5 and 2.4 times that at the simulated warmer and drier (middle and lower) sites, respectively. Combining laboratory experimental conclusions, we show that thallus water content is a key factor determining the nitrogenase activity of L. retigera in early transplantation while insufficient carbon storage resulting from a combination of warming and desiccation was likely responsible for reducing nitrogenase activity in later months of the transplant experiment. The results of this study imply that the negative impact of climate change (dry-hot stress) on ecosystems not only impacts the distribution and growth of species, but also nutrient circles and budgets.

Legacy effects of simulated short-term climate change on ammonia oxidisers, denitrifiers, and nitrous oxide emissions in an acid soil.

Although the effect of simulated climate change on nitrous oxide (N2O) emissions and on associated microbial communities has been reported, it is not well understood if these effects are short-lived or long-lasting. Here, we conducted a field study to determine the interactive effects of simulated warmer and drier conditions on nitrifier and denitrifier communities and N2O emissions in an acidic soil and the longevity of the effects. A warmer (+2.3°C) and drier climate (-7.4% soil moisture content) was created with greenhouses. The variation of microbial population abundance and community structure of ammonia-oxidizing archaea (AOA), bacteria (AOB), and denitrifiers (nirK/S, nosZ) were determined using real-time PCR and high-throughput sequencing. The results showed that the simulated warmer and drier conditions under the greenhouse following urea application significantly increased N2O emissions. There was also a moderate legacy effect on the N2O emissions when the greenhouses were removed in the urea treatment, although this effect only lasted a short period of time (about 60days). The simulated climate change conditions changed the composition of AOA with the species affiliated to marine group 1.1a-associated lineage increasing significantly. The abundance of all the functional denitrifier genes decreased significantly under the simulated climate change conditions and the legacy effect, after the removal of greenhouses, significantly increased the abundance of AOB, AOA (mainly the species affiliated to marine group 1.1a-associated lineage), and nirK and nosZ genes in the urea-treated soil. In general, the effect of the simulated climate change was short-lived, with the denitrifier communities being able to return to ambient levels after a period of adaptation to ambient conditions. Therefore, the legacy effect of simulated short-time climate change conditions on the ammonia oxidizer and denitrifier communities and N2O emissions were temporary and once the conditions were removed, the microbial communities were able to adapt to the ambient conditions.

Biotic nitrogen fixation in the bryosphere is inhibited more by drought than warming.

The boreal forest is of particular interest to climate change research due to its large circumpolar distribution and accumulated soil carbon pool. Carbon uptake in this ecosystem is nitrogen (N)-limited, therefore factors affecting carbon or nitrogen dynamics in the boreal forest can have consequences for global climate. We used a 2-year field experiment to investigate the response of biotic nitrogen fixation by cyanobacteria associated with boreal forest bryophytes, in a factorial experiment combining simulated climate change with habitat fragmentation treatments. We simulated climate change conditions using open-top greenhouse chambers in the field, which increased mean and maximum temperatures, and created a precipitation gradient from ambient levels in the center to extreme drought conditions at the periphery of the chamber. The dry patches near the chamber walls exhibited almost no N-fixation, despite having similar densities of cyanobacteria (predominantly Stigonema sp.) as other patches. Rates of N-fixation were best explained by a model containing moisture, fragmentation, cyanobacteria density and time; warming was not a significant variable affecting N-fixation. There was no significant interaction between warming and fragmentation. These results suggest that cyanobacteria responded physiologically to drought by reducing N-fixation activity long before any changes in density. Ecosystem processes, such as N-fixation, can respond in the short term to environmental change much more rapidly than changes in the underlying community structure. Such rapid physiological responses may occur faster than demographic insurance effects of biodiversity.

Effect of Elevated Atmospheric CO2 and Temperature on the Disease Severity of Rocket Plants Caused by Fusarium Wilt under Phytotron Conditions.

The severity of F. oxysporum f.sp. conglutinans on rocket plants grown under simulated climate change conditions has been studied. The rocket plants were cultivated on an infested substrate (4 log CFU g-1) and a non-infested substrate over three cycles. Pots were placed in six phytotrons in order to simulate different environmental conditions: 1) 400–450 ppm CO2, 18–22°C; 2) 800–850 ppm CO2, 18–22°C; 3) 400–450 ppm CO2, 22–26°C, 4) 800–850 ppm CO2, 22–26°C, 5) 400–450 ppm CO2, 26–30°C; 6) 800–850 ppm CO2, 26–30°C. Substrates from the infested and control samples were collected from each phytotron at 0, 60 and 120 days after transplanting. The disease index, microbial abundance, leaf physiological performances, root exudates and variability in the fungal profiles were monitored. The disease index was found to be significantly influenced by higher levels of temperature and CO2. Plate counts showed that fungal and bacterial development was not affected by the different CO2 and temperature levels, but a significant decreasing trend was observed from 0 up to 120 days. Conversely, the F. oxysporum f.sp. conglutinans plate counts did not show any significantly decrease from 0 up to 120 days. The fungal profiles, evaluated by means of polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE), showed a relationship to temperature and CO2 on fungal diversity profiles. Different exudation patterns were observed when the controls and infested plants were compared, and it was found that both CO2 and temperature can influence the release of compounds from the roots of rocket plants. In short, the results show that global climate changes could influence disease incidence, probably through plant-mediated effects, caused by soilborne pathogens.

Bacteria Transport in a Soil-Based Wastewater Treatment System under Simulated Operational and Climate Change Conditions.

Bacteria removal efficiencies in a conventional soil-based wastewater treatment system (OWTS) have been modeled to elucidate the fate and transport of bacteria under environmental and operational conditions that might be expected under changing climatic conditions. The HYDRUS 2D/3D software was used to model the impact of changing precipitation patterns, bacteria concentrations, hydraulic loading rates (HLRs), and higher subsurface temperatures at different depths and soil textures. Modeled effects of bacteria concentration shows that greater depth of treatment was required in coarser soils than in fine-textured ones to remove . The initial removal percentage was higher when HLR was lower, but it was greater when HLR was higher. When a biomat layer was included in the transport model, the performance of the system improved by up to 12.0%. Lower bacteria removal (<5%) was observed at all depths under the influence of precipitation rates ranging from 5 to 35 cm, and 35-cm rainfall combined with a 70% increase in HLR. Increased subsurface temperature (23°C) increased bacteria removal relative to a lower temperature range (5-20°C). Our results show that the model is able to effectively simulate bacteria removal and the effect of precipitation and temperature in different soil textures. It appears that the performance of OWTS may be impacted by changing climate.