For example, if CO 2 concentration becomes scarce e. The same result will occur if light energy becomes less available or less intense, the rate of photosynthesis will be slower despite the abundance of CO 2 and H 2 O.

Light becomes a limiting factor in photosynthesis when the plant is unable to collect light, for instance, due to shade resulting from the dense population of plants. The law of tolerance was developed in by American zoologist Victor Ernest Shelford.

It states that the success of an organism depends on a complex set of environmental conditions environmental factors. And that organism would have definite minimum , maximum , and optimum environmental factors that determine success. However, the tolerance ranges may vary within the same organism, for example depending on the life stage larval vs.

Density-dependent limiting factor refers to the factor restricting the size of a population based on density. A large, dense population are more strongly affected than a small or less dense population.

For example, a dense population would have higher demands for food and water compared to a small population. In this case, food and water supply is the limiting factor and it depends on density.

Disease as a factor is also density-dependent. It spreads faster in dense population than small ones. Density-independent limiting factor refers to the limiting factor that is not dependent on density.

The limiting factor can restrict population size independent of how dense the population is. For example, a catastrophic event, such as an earthquake or a volcanic eruption, could cause a population decline regardless of population density.

A single-limiting factor is when there is one factor that limits the system. A co-limiting factor is when a factor affects the population of organisms in an ecosystem indirectly but increases the limitation of the factor directly affecting the population.

In the law of the size of a population, a population will grow exponentially as long as the environment from where all individuals in that population are exposed to remains constant. However, there will come a time when the population will reach the maximum at which the environment can sustain. This is called the carrying capacity , the maximum load of the environment.

Carrying capacity is the number of individuals that an environment can sustain without ending in damage or destruction to the organisms and the environment. Thus, population size may increase until carrying capacity is met. Above this capacity, the population size will eventually decrease. The determiners of carrying capacity are limiting factors. The common limiting factors in an ecosystem are food, water, habitat, and mate. The availability of these factors will affect the carrying capacity of an environment.

Lewis, Jesse S. Biotic and abiotic factors are increasingly acknowledged to synergistically shape broad-scale species distributions. However, the relative importance of biotic and abiotic factors in predicting species distributions is unclear. In particular, biotic factors , such as predation and vegetation, including those resulting from anthropogenic land-use change, are underrepresented in species distribution modeling, but could improve model predictions.

Using generalized linear models and model selection techniques, we used estimates of population density of wild pigs Sus scrofa from 5 continents to evaluate the relative importance, magnitude, and direction of biotic and abiotic factors in predicting population density of an invasive large mammal with a global distribution.

Incorporating diverse biotic factors , including agriculture, vegetation cover, and large carnivore richness, into species distribution modeling substantially improved model fit and predictions. Abiotic factors , including precipitation and potential evapotranspiration, were also important predictors.

The predictive map of population density revealed wide-ranging potential for an invasive large mammal to expand its distribution globally. Our study demonstrates that the ongoing paradigm shift, which recognizes that both biotic and abiotic factors shape species distributions across broad scales, can be advanced by incorporating diverse biotic factors.

Owing to diverse abiotic stresses and global climate deterioration, the agricultural production worldwide is suffering serious losses. Breeding stress-resilient crops with higher quality and yield against multiple environmental stresses via application of transgenic technologies is currently the most promising approach.

Deciphering molecular principles and mining stress-associate genes that govern plant responses against abiotic stresses is one of the prerequisites to develop stress-resistant crop varieties. As molecular switches in controlling stress-responsive genes expression, transcription factors TFs play crucial roles in regulating various abiotic stress responses. Hence, functional analysis of TFs and their interaction partners during abiotic stresses is crucial to perceive their role in diverse signaling cascades that many researchers have continued to undertake.

Here, we review current developments in understanding TFs, with particular emphasis on their functions in orchestrating plant abiotic stress responses. Further, we discuss novel molecular mechanisms of their action under abiotic stress conditions. This will provide valuable information for understanding regulatory mechanisms to engineer stress-tolerant crops. Spatial variation in abiotic and biotic factors in a floodplain determine anuran body size and growth rate at metamorphosis.

Body size at metamorphosis is a critical trait in the life history of amphibians. Despite the wide-spread use of amphibians as experimental model organisms, there is a limited understanding of how multiple abiotic and biotic factors affect the variation in metamorphic traits under natural conditions.

The aim of our study was to quantify the effects of abiotic and biotic factors on spatial variation in the body size of tadpoles and size at metamorphosis of the European common toad Bufo b. Our study population was distributed over the riverbed active tract and the fringing riparian forest of a natural floodplain.

The riverbed had warm ponds with variable hydroperiod and few predators, whereas the forest had ponds with the opposite characteristics. Spatial variation in body size at metamorphosis was governed by the interactive effects of abiotic and biotic factors. The particular form of the interaction between water temperature and intraspecific tadpole density suggests that abiotic factors laid the foundation for biotic factors : intraspecific density decreased growth only at high temperature.

Predation and intraspecific density jointly reduced metamorphic size. Interspecific density had a negligible affect on body size at metamorphosis, suggesting weak inter-anuran interactions in the larval stage. Population density at metamorphosis was about one to two orders of magnitudes higher in the riverbed ponds than in the forest ponds, mainly because of lower tadpole mortality.

Based on our results, we conclude that ponds in the riverbed appear to play a pivotal role for the population because tadpole growth and survival is best in this habitat. Abiotic stresses are major environmental factors that affect agricultural productivity worldwide. NAC transcription factors play pivotal roles in abiotic stress signaling in plants. As a staple crop, wheat production is severely constrained by abiotic stresses whereas only a few NAC transcription factors have been characterized functionally.

Localization assays revealed that TaNAC67 localized in the nucleus. Overexpression of TaNAC67 resulted in pronounced enhanced tolerances to drought, salt and freezing stresses, therefore it has potential for utilization in transgenic breeding to improve abiotic stress tolerance in crops. Plant WRKY transcription factors play a vital role in abiotic stress tolerance and regulation of plant defense responses.

Both genes were upregulated in response to abiotic stress. Next, we applied the same stressors to seedlings of T-DNA insertion wrky11 and 17 knock-out mutants single and double.

Under stress, the mutants exhibited slower germination and compromised root growth compared with the wild type. In most cases, double-mutant seedlings were more affected than single mutants. These results suggest that wrky11 and wrky17 are not strictly limited to plant defense responses but are also involved in conferring stress tolerance. All rights reserved. Inter-annual variability of carbon fluxes in temperate forest ecosystems: effects of biotic and abiotic factors.

Chen, M. Carbon dynamics in terrestrial ecosystems are influenced by both abiotic and biotic factors. Abiotic factors , such as variation in meteorological conditions, directly drive biophysical and biogeochemical processes; biotic factors , referring to the inherent properties of the ecosystem components, reflect the internal regulating effects including temporal dynamics and memory.

The magnitude of the effect of abiotic and biotic factors on forest ecosystem carbon exchange has been suggested to vary at different time scales.

In this study, we design and conduct a model-data fusion experiment to investigate the role and relative importance of the biotic and abiotic factors for inter-annual variability of the net ecosystem CO2 exchange NEE of temperate deciduous forest ecosystems in the Northeastern US.

We conducted a "transplant" modeling experiment, that is, cross- site and parameter simulations with different combinations of site meteorology and parameters. Using wavelet analysis and variance partitioning techniques, analysis of model predictions identifies both spatial variant and spatially invariant parameters.

Variability of NEE was primarily modulated by gross primary productivity GPP , with relative contributions varying from hourly to yearly time scales. The inter-annual variability of GPP and NEE is more regulated by meteorological forcing, but spatial variability in certain model parameters biotic response has more substantial effects on the inter-annual variability of ecosystem respiration Reco through the effects on carbon pools. Both the biotic and abiotic factors play significant roles in modulating the spatial and temporal variability in terrestrial carbon cycling in the region.

Together, our study quantifies the relative importance of both, and calls for better understanding of them to better predict regional CO2. Woody-grass ratios in a grassy arid system are limited by multi-causal interactions of abiotic constraint, competition and fire.

We investigated abiotic and biotic factors influencing boundaries and habitat membership in grassland Triodia or 'spinifex' grassland -shrubland Acacia aneura or 'mulga' shrubland mosaics in semi-arid central Australia.

Our results showed that invasion of the shrubland swale by neighbouring grassland species is negated by abiotic limitations but competition limits shrubland invasion of the grassland dune. All species from both habitats had significantly reduced survival in the grassland dune in the presence of the dominant grass Triodia regardless of soil type or shade.

Further, the removal of the dominant grass allowed the shrubland dominant A. Seedling growth and sexual maturation of the shrubland dominant A. By contrast, rapid growth and seed set in the grassland shrubs facultative sprouters provides a solution to fire exposure prior to reproductive onset. In terms of landscape dynamics, we argue that grass competition and fire effects are important constraints on shrubland patch expansion, but that their relative importance will vary spatially throughout the landscape because of spatial and temporal rainfall variability.

Review of recent transgenic studies on abiotic stress tolerance and future molecular breeding in potato. Global warming has become a major issue within the last decade. Traditional breeding programs for potato have focused on increasing productivity and quality and disease resistance, thus, modern cultivars have limited tolerance of abiotic stresses.

The introgression of abiotic stress tolerance into modern cultivars is essential work for the future. Recently, many studies have investigated abiotic stress using transgenic techniques. This manuscript focuses on the study of abiotic stress, in particular drought, salinity and low temperature, during this century.

Dividing studies into these three stress categories for this review was difficult. Thus, based on the study title and the transgene property, transgenic studies were classified into five categories in this review; oxidative scavengers, transcriptional factors , and above three abiotic categories. The review focuses on studies that investigate confer of stress tolerance and the identification of responsible factors , including wild relatives.

From a practical application perspective, further evaluation of transgenic potato with abiotic stress tolerance is required. Although potato plants, including wild species, have a large potential for abiotic stress tolerance, exploration of the factors responsible for conferring this tolerance is still developing. Molecular breeding, including genetic engineering and conventional breeding using DNA markers, is expected to develop in the future.

Agler, Matthew T. Plant-associated microorganisms have been shown to critically affect host physiology and performance, suggesting that evolution and ecology of plants and animals can only be understood in a holobiont host and its associated organisms context. Host-associated microbial community structures are affected by abiotic and host factors , and increased attention is given to the role of the microbiome in interactions such as pathogen inhibition.

However, little is known about how these factors act on the microbial community, and especially what role microbe—microbe interaction dynamics play. We have begun to address this knowledge gap for phyllosphere microbiomes of plants by simultaneously studying three major groups of Arabidopsis thaliana symbionts bacteria, fungi and oomycetes using a systems biology approach. We evaluated multiple potential factors of microbial community control: we sampled various wild A.

Our results indicate that both abiotic factors and host genotype interact to affect plant colonization by all three groups of microbes. Considering microbe—microbe interactions, however, uncovered a network of interkingdom interactions with significant contributions to community structure.

By documenting these microbe—microbe interactions, we uncover an important mechanism explaining how abiotic factors and host genotypic signatures control microbial communities. Spatially dependent biotic and abiotic factors drive survivorship and physical structure of green roof vegetation. Plant survivorship depends on biotic and abiotic factors that vary at local and regional scales. This survivorship, in turn, has cascading effects on community composition and the physical structure of vegetation.

Survivorship of native plant species is variable among populations planted in environmentally stressful habitats like urban roofs, but the degree to which factors at different spatial scales affect survivorship in urban systems is not well understood. We evaluated the effects of biotic and abiotic factors on survivorship, composition, and physical structure of two native perennial species assemblages, one characterized by a mixture of C 4 grasses and forbs Hempstead Plains, HP and one characterized by a mixture of C 3 grasses and forbs Rocky Summit, RS , that were initially sown at equal ratios of growth forms ; grass, N-fixing forb and non-N-fixing forb in replicate 2-m 2 plots planted on 10 roofs in New York City New York, USA.

While growing medium properties pH, nutrients, metals differed among roofs there was no correlation with survivorship. Percent cover and sward height increased with increasing survivorship. At low survivorship, cover of the HP assemblage was greater compared to the RS assemblage.

Sward height of the HP assemblage was about two times greater compared to the RS assemblage. These results highlight the effects of local biotic and regional abiotic drivers on community composition and physical structure of green roof vegetation. As a result, initial green roof plant. Unraveling the role of fungal symbionts in plant abiotic stress tolerance. Fungal symbionts have been found to be associated with every plant studied in the natural ecosystem, where they colonize and reside entirely or partially in the internal tissues of their host plant.

In mutualistic association fungal endophyte can enhance growth, increase reproductive success and confer biotic and abiotic stress tolerance to its host plant. Since abiotic stress such as, drought, high soil salinity, heat, cold, oxidative stress and heavy metal toxicity is the common adverse environmental conditions that affect and limit crop productivity worldwide.

It may be a promising alternative strategy to exploit fungal endophytes to overcome the limitations to crop production brought by abiotic stress. There is an increasing interest in developing the potential biotechnological applications of fungal endophytes for improving plant stress tolerance and sustainable production of food crops. Here we have described the fungal symbioses, fungal symbionts and their role in abiotic stress tolerance.

A putative mechanism of stress tolerance by symbionts has also been covered. Factors limiting sulfolane biodegradation in contaminated subarctic aquifer substrate. Sulfolane, a water-soluble organosulfur compound, is used industrially worldwide and is associated with one of the largest contaminated groundwater plumes in the state of Alaska. Despite being widely used, little is understood about the degradation of sulfolane in the environment, especially in cold regions.

We conducted aerobic and anaerobic microcosm studies to assess the biological and abiotic sulfolane degradation potential of contaminated subarctic aquifer groundwater and sediment from Interior Alaska. We also investigated the impacts of nutrient limitations and hydrocarbon co-contamination on sulfolane degradation. We found that sulfolane underwent biodegradation aerobically but not anaerobically under nitrate, sulfate, or iron-reducing conditions.

No abiotic degradation activity was detectable under either oxic or anoxic conditions. Our study is the first to investigate the sulfolane biodegradation potential of subarctic aquifer substrate and identifies several important factors limiting biodegradation rates.

We concluded that oxygen is an important factor limiting natural attenuation of this sulfolane plume, and that nutrient amendments are unlikely to accelerate biodegradation within in the plume, although they may biostimulate degradation in ex situ groundwater treatment applications. Future work should be directed at elucidating the identity of indigenous sulfolane-degrading microorganisms and determining their distribution and potential activity in the environment. A number of abiotic and biotic factors are known to regulate arthropod attraction, colonization, and utilization of decomposing vertebrate remains.

Such information is critical when assessing arthropod evidence associated with said remains in terms of forensic relevance. Interactions are not limited to just between the resource and arthropods. There is another biotic factor that has been historically overlooked; however, with the advent of high-throughput sequencing, and other molecular techniques, the curtain has been pulled back to reveal a microscopic world that is playing a major role with regards to carrion decomposition patterns in association with arthropods.

The objective of this publication is to review many of these factors and draw attention to their impact on microbial, specifically bacteria, activity associated with these remains as it is our contention that microbes serve as a primary mechanism regulating associated arthropod behavior.

Wheat is an important crop in the world. But most of the cultivars are salt sensitive, and often adversely affected by salt stress. WRKY transcription factors play a major role in plant responses to salt stress, but the effective salinity regulatory WRKYs identified in bread wheat are limited and the mechanism of salt stress tolerance is also not well explored.

Over-expression of TaWRKY93 in Arabidopsis thaliana enhanced salt NaCl , drought, low temperature and osmotic mannitol stress tolerance, mainly demonstrated by transgenic plants forming longer primary roots or more lateral roots on MS plates supplemented with NaCl and mannitol individually, higher survival rate under drought and low temperature stress.

Further, transgenic plants maintained a more proline content, higher relative water content and less electrolyte leakage than the wild type plants. The transcript abundance of a series of abiotic stress-related genes was up-regulated in the TaWRKY93 transgenic plants.

In summary, TaWRKY93 is a new positive regulator of abiotic stress, it may increase salinity, drought and low temperature stress tolerance through enhancing osmotic adjustment, maintaining membrane stability and increasing transcription of stress related genes, and contribute to the superior agricultural traits of SR3 through promoting root development. It can be used as a candidate gene for wheat transgenic engineering breeding against abiotic stress.

Effects of abiotic factors on ecosystem health of Taihu Lake, China based on eco-exergy theory. A lake ecosystem is continuously exposed to environmental stressors with non-linear interrelationships between abiotic factors and aquatic organisms.

Ecosystem health depicts the capacity of system to respond to external perturbations and still maintain structure and function. In this study, we explored the effects of abiotic factors on ecosystem health of Taihu Lake in , China from a system-level perspective. Spatiotemporal heterogeneities of eco-exergy and specific eco-exergy served as thermodynamic indicators to represent ecosystem health in the lake.

The results showed the plankton community appeared more energetic in May, and relatively healthy in Gonghu Bay with both higher eco-exergy and specific eco-exergy; a eutrophic state was likely discovered in Zhushan Bay with higher eco-exergy but lower specific eco-exergy. Gradient Boosting Machine GBM approach was used to explain the non-linear relationships between two indicators and abiotic factors.

This analysis revealed water temperature, inorganic nutrients, and total suspended solids greatly contributed to the two indicators that increased.

However, pH rise driven by inorganic carbon played an important role in undermining ecosystem health, particularly when pH was higher than 8.

This implies that climate change with rising CO2 concentrations has the potential to aggravate eutrophication in Taihu Lake where high nutrient loads are maintained.

Using thermodynamics to assess biotic and abiotic impediments to root water uptake. Root water uptake has been the subject of extensive research, dealing with understanding the processes limiting transpiration and understanding strategies of plants to avoid water stress. Many of those studies use models of water flow from the soil through the plant into the atmosphere to learn about biotic and abiotic factors affecting plant water relations.

One important question in this context is to identify those processes that are most limiting to water transport, and specifically whether these processes lie within the plant or the soil? Here, we propose to use a thermodynamic formulation of root water uptake to answer this question. The method allows us to separate the energy exported at the root collar into a sum of energy fluxes related to all processes along the flow path, notably including the effect of increasing water retention in drier soils.

Evaluation of the several contributions allows us to identify and rank the processes by how much these impede water flow from the soil to the atmosphere. The application of this approach to a complex 3-dimensional root water uptake model reveals insights on the role of root versus soil resistances to limit water flow. We investigate the efficiency of root water uptake in an ensemble of root systems with varying root hydraulic properties.

While root morphology is kept the same, root radial and axial resistances are artificially varied. Starting with entirely young systems uptake roots, high radial, low axial conductance we increasingly add older roots transport roots, high axial, low radial conductance to improve transport within root systems. This yields a range of root hydraulic architectures, where the extremes are limited either by radial uptake capacity or low capacity to transport water along the root system. We model root water uptake in this range of root systems with a 3-dimensional root water uptake model in two different soils, applying constant flux boundary conditions in a dry down experiment and.

Enhancing crop resilience to combined abiotic and biotic stress through the dissection of physiological and molecular crosstalk. Plants growing in their natural habitats are often challenged simultaneously by multiple stress factors , both abiotic and biotic. Research has so far been limited to responses to individual stresses, and understanding of adaptation to combinatorial stress is limited , but indicative of non-additive interactions.

Omics data analysis and functional characterization of individual genes has revealed a convergence of signaling pathways for abiotic and biotic stress adaptation. Taking into account that most data originate from imposition of individual stress factors , this review summarizes these findings in a physiological context, following the pathogenesis timeline and highlighting potential differential interactions occurring between abiotic and biotic stress signaling across the different cellular compartments and at the whole plant level.

Potential effects of abiotic stress on resistance components such as extracellular receptor proteins, R-genes and systemic acquired resistance will be elaborated, as well as crosstalk at the levels of hormone, reactive oxygen species, and redox signaling. Breeding targets and strategies are proposed focusing on either manipulation and deployment of individual common regulators such as transcription factors or pyramiding of non- negatively interacting components such as R-genes with abiotic stress resistance genes.

We propose that dissection of broad spectrum stress tolerance conferred by priming chemicals may provide an insight on stress cross regulation and additional candidate genes for improving crop performance under combined stress.

Validation of the proposed strategies in lab and field experiments is a first step toward the goal of achieving tolerance to combinatorial stress in crops. Flowering phenology, growth forms, and pollination syndromes in tropical dry forest species: Influence of phylogeny and abiotic factors. Analyses of the influence of temporal variation in abiotic factors on flowering phenology of tropical dry forest species have not considered the possible response of species with different growth forms and pollination syndromes, while controlling for phylogenetic relationships among species.

Here, we investigated the relationship between flowering phenology, abiotic factors , and plant functional attributes, while controlling for phylogenetic relationship among species, in a dry forest community in Mexico. We characterized flowering phenology time and duration and pollination syndromes of 55 tree species, 49 herbs, 24 shrubs, 15 lianas, and 11 vines.

We tested the influence of pollination syndrome, growth form, and abiotic factors on flowering phenology using phylogenetic generalized least squares. We found a relationship between flowering duration and time. Growth form was related to flowering time, and the pollination syndrome had a more significant relationship with flowering duration.

Flowering time variation in the community was explained mainly by abiotic variables, without an important phylogenetic effect. Flowering time in lianas and trees was negatively and positively correlated with daylength, respectively.

Functional attributes, environmental cues, and phylogeny interact with each other to shape the diversity of flowering patterns. Phenological differentiation among species groups revealed multiples strategies associated with growth form and pollination syndromes that can be important for understanding species coexistence in this highly diverse plant community. Relative contribution of biotic and abiotic factors to the population density of the cassava green mite, Mononychellus tanajoa Acari: Tetranychidae.

The cassava green mite, Mononychellus tanajoa, is a key pest of cassava, Manihot esculenta Crantz Euphorbiaceae , and it may be kept in check by naturally occurring predatory mites of the family Phytoseiidae.

In addition to predatory mites, abiotic factors may also contribute to regulate pest mite populations in the field. Here, we evaluated the population densities of both M.

The abiotic variables rainfall, temperature and relative humidity were also recorded throughout the cultivation cycle of cassava. We determined the relative importance of biotic density of E. The density of M. A hierarchical partitioning analysis revealed that most of the variance for the density of M.

We conclude that abiotic factors , especially rainfall, were the main mechanisms driving M. High temperatures and drought are critical abiotic factors that limit the production of grain legumes, especially in tropical countries.

Tepary bean Phaseolus acutifolius A. Gray is a species that is tolerant to high temperatures and drought. It is also closely related to common bean Phaseolus vu Top-down, bottom-up, middle-out and abiotic factors are usually viewed as main forces structuring biological communities, although assessment of their relative importance, in a single study, is rarely done.

Our analysis indicated that spatial structural factors like site and plot accounted for most of the community and population variation. We suggest that community and population structure were relatively uncoupled from the structuring influences of biotic and abiotic factors in this system because of high concentrations of resources that sustain high densities of infauna and limit exploitative competition.

Drought, cold and salinity are the major environmental stresses that limit agricultural productivity. NAC transcription factors regulate the stress response in plants. Pumpkin Cucurbita moschata is an important cucurbit vegetable crop and it has strong resistance to abiotic stress; however, the biological functions of stress-related NAC genes in this crop are largely unknown.

Transactivation assay in yeast cells revealed that CmNAC1 functions as a transcription activator, and its transactivation domain is located in the C-terminus. CmNAC1 was ubiquitously expressed in different organs, and its transcript was induced by salinity, cold, dehydration, H2O2, and abscisic acid ABA treatment.

Our results indicated that CmNAC1 is a critical factor in ABA signaling pathways and it can be utilized in transgenic breeding to improve the abiotic stress tolerance of crops. Earth, wind, and fire: Abiotic factors and the impacts of global environmental change on forest health. Trees do not just die; there is always a primary cause, and often contributing factors. Trees need adequate quantities of water, heat, light, nutrients, carbon dioxide, oxygen, and other abiotic resources to sustain life, growth, and reproduction.

When these factors are deficient or excessive, they cause mortality. According to the concept of baseline mortality Many plants respond to herbivory by releasing a specific blend of volatiles that is attractive to natural enemies of the herbivores. In corn Zea mays , this induced odor blend is mainly composed of terpenoids and indole. The induced signal varies with plant species and genotype, but little is known about the variation due to abiotic factors.

Here, we tested the effect of soil humidity, air humidity, temperature, light, and fertilization rate on the emission of induced volatiles in young corn plants.

Each factor was tested separately under constant conditions for the other factors. Light intensity had a dramatic effect. The emission of volatiles did not occur in the dark and increased steadily with an increase in the light intensity. An experiment with an unnatural light-dark cycle showed that the release was fully photophase dependent. Fertilization also had a strong positive effect; the emission of volatiles was minimal when plants were grown under low nutrition, even when results were corrected for plant biomass.

Changes in all abiotic factors caused small but significant changes in the relative ratios among the different compounds quality in the induced odor blends, except for air humidity. Hence, climatic conditions and nutrient availability can be important factors in determining the intensity and variability in the release of induced plant volatiles.

The wheat transcription factor , TabHLH39, improves tolerance to multiple abiotic stressors in transgenic plants. Although bHLH transcription factors play important roles regulating plant development and abiotic stress response and tolerance, few functional studies have been performed in wheat.

The TabHLH39 gene is located on wheat chromosome 5DL, and the protein localized to the nucleus and activated transcription. TabHLH39 showed variable expression in roots, stems, leaves, glumes, pistils and stamens and was induced by polyethylene glycol, salt and cold treatments. Further analysis revealed that TabHLH39 overexpression in Arabidopsis significantly enhanced tolerance to drought, salt and freezing stress during the seedling stage, which was also demonstrated by enhanced abiotic stress-response gene expression and changes to several physiological indices.

Therefore, TabHLH39 has potential in transgenic breeding applications to improve abiotic stress tolerance in crops. The importance of disturbance by fire and other abiotic and biotic factors in driving cheatgrass invasion varies based on invasion stage.

Disturbances create fluctuations in resource availability that alter abiotic and biotic constraints. Exotic invader response may be due to multiple factors related to disturbance regimes and complex interactions between other small- and largescale abiotic and biotic processes that may vary across invasion stages.

We explore how cheatgrass responds to both frequency and Watermelon Citrullus lanatus is one xerophyte that has relative higher tolerance to drought and salt stresses as well as more sensitivity to cold stress, compared with most model plants. These characteristics facilitate it a potential model crop for researches on salt, drought or cold tolerance.

These density-independent factors include food or nutrient limitation, pollutants in the environment, and climate extremes, including seasonal cycles such as monsoons. In addition, catastrophic factors can also impact population growth, such as fires and hurricanes. The quality of nutrients e. The lower the quality of the nutrients, the higher the environmental stress. In the freshwater Laurentian Great Lakes, particularly in Lake Erie, the factor limiting algal growth was found to be phosphorus.

David Schindler and his colleagues at the Experimental Lakes Area Ontario, Canada demonstrated that phosphorus was the growth-limiting factor in temperate North American lakes using whole-lake treatment and controls Schindler This work encouraged the passage of the Great Lakes Water Quality Agreement of GLWQA — a reduction in phosphorus load from municipal sources was predicted to lead to a corresponding reduction in the total algal biomass and harmful cyanobacterial blue-green algae blooms McGuken ; Figure 3.

As annual phosphorus loads decreased in the mid s Dolan , there was some indication that Lake Erie was improving in terms of decreased total phytoplankton photosynthetic algae and cyanobacteria biomass Makarewicz Further improvement continued until the mid s, until an introduced species, the zebra mussel, began altering the internal phosphorus dynamics of the lake by mineralization excretion of digested algae Figure 3; Conroy et al.

C Change in Lake Erie seasonal average phytoplankton biomass in the central. Pollutants also contribute to environmental stress, limiting the growth rates of populations. Although each species has specific tolerances for environmental toxins, amphibians in general are particularly susceptible to pollutants in the environment. For example, pesticides and other endocrine disrupting toxins can strongly control the growth of amphibians Blaustein et al.

These chemicals are used to control agricultural pests but also run into freshwater streams and ponds where amphibians live and breed. They affect the amphibians both with direct increases in mortality and indirect limitation in growth, development, and reduction in fecundity. Rohr et al. These effects limit population growth irrespective of the size of the amphibian population and are not limited to pesticides but also include pH and thermal pollution, herbicides, fungicides, heavy metal contaminations, etc.

Environmental catastrophes such as fires, earthquakes, volcanoes and floods can strongly affect population growth rates via direct mortality and habitat destruction. A large-scale natural catastrophe occurred in when hurricane Katrina impacted the coastal regions of the Gulf of Mexico in the southern United States.

Katrina altered habitat for coastal vegetation by depositing more than 5 cm of sediment over the entire coastal wetland zone. In these areas, substantial improvement in the quality of wetlands for plant growth occurred after many years of wetland loss due to control of the Mississippi River flow Turner et al. At the same time, however, almost km 2 of wetland was destroyed and converted to open sea, completely eliminating wetland vegetation Day et al.

More recently the Gulf oil spill in has again impacted the coastal wetland vegetation. Though human derived, this large-scale environmental disaster will have long-term impacts on the population growth of not only vegetation but all organisms in the wetlands and nearshore regions of the Gulf of Mexico.

Blaustein, A. Ultraviolet radiation, toxic chemicals and amphibian population declines. Diversity and Distributions 9, — Clutton-Brock, T.

Sex differences in emigration and mortality affect optimal management of deer populations. Nature , — Conroy, J. Recent increases in Lake Erie plankton biomass: roles of external phosphorus loading and dreissenid mussels. Journal of Great Lakes Research 31 Supplement 2 , 89— Day, J. Restoration of the Mississippi delta: lessons from hurricanes Katrina and Rita. Science , — Gilg, O. Cyclic dynamics in a simple vertebrate predator-prey community.

Makarewicz, J. Phytoplankton biomass and species composition in Lake Erie, to Journal of Great Lakes Research 19, — McGucken, W. Rohr, J. Lethal and sublethal effects of atrazine, carbaryl, endosulfan, and octylphenol on the streamside salamander Ambystoma barbouri. Environmental Toxicology and Chemistry 22, — Schindler, D. Eutrophication and recovery in experimental lakes: implications for lake management. Sibley, R. Population growth rate and its determinants: an overview.

Philosophical Transactions of the Royal Society B , — Turner, R. Wetland Sedimentation from Hurricanes Katrina and Rita. Wauters, L. Effects of food availability and density on red squirrel Sciurus vulgaris reproduction.

Ecology 76, — Aging and Its Demographic Measurement.