Responses Of Different Species Research Articles

Oribatid mite communities on lichens in heavily contaminated post-smelting dumps.

In this study, we examined oribatid fauna of strongly contaminated post-smelting dumps (southern Poland) that exist in the substrate and are associated with the most frequent lichen, Cladonia rei. Due to artificial origin of the substrate and the extremely high contamination with heavy metals, the studied dumps are unique in Europe in terms of unfavourable life conditions. In total, 2,936 specimens of Oribatida, representing 50 oribatid species, were sampled on 10 dumps and a reference site. Thalli of C. rei act as an island for soil oribatid mites on extremely contaminated post-smelting dumps. Both abundance and species richness of oribatid fauna collected from C. rei thalli were significantly greater than those recorded in the dump's substrate. The pool of oribatid species that was able to persist in extremely high doses of heavy metals was comparatively broad. However, only one species, Tectocepheus velatus, was able to achieve high abundances on all dumps. Three different responses of species (tolerant, sensitive, and indifferent) to heavy-metal contamination were recognised. Redundancy analysis indicated that highly increased levels of heavy metals, as well as K content, C/N ratio, and pH value, were the main factors that influence the composition and distribution of species. The concentrations of heavy metals (both essential elements (zinc) as well as xenobiotics (lead, cadmium) in T. velatus from the most contaminated dumps were not increased compared with those observed in moderately contaminated soils.

Are plant-soil feedback responses explained by plant traits?

Plant-soil feedbacks can influence plant growth and community structure by modifying soil biota and nutrients. Because most research has been performed at the species level and in monoculture, our ability to predict responses across species and in mixed communities is limited. As plant traits have been linked to both soil properties and plant growth, they may provide a useful approach for an understanding of feedbacks at a generic level. We measured how monocultures and mixtures of grassland plant species with differing traits responded to soil that had been conditioned by model grassland plant communities dominated by either slow- or fast-growing species. Soils conditioned by the fast-growing community had higher nitrogen availability than those conditioned by the slow-growing community; these changes influenced future plant growth. Effects were stronger, and plant traits had greater predictive power, in mixtures than in monocultures. In monoculture, all species produced more above-ground biomass in soil conditioned by the fast-growing community. In mixtures, slow-growing species produced more above-ground biomass, and fast-growing species produced more below-ground biomass, in soils conditioned by species with similar traits. The use of a plant trait-based approach may therefore improve our understanding of differential plant species responses to plant-soil feedbacks, especially in a mixed-species environment.

Biodiversity acts as insurance of productivity of bacterial communities under abiotic perturbations.

Anthropogenic disturbances are detrimental to the functioning and stability of natural ecosystems. Critical ecosystem processes driven by microbial communities are subjected to these disturbances. Here, we examine the stabilizing role of bacterial diversity on community biomass in the presence of abiotic perturbations such as addition of heavy metals, NaCl and warming. Bacterial communities with a diversity gradient of 1-12 species were subjected to the different treatments, and community biomass (OD600) was measured after 24 h. We found that initial species richness and phylogenetic structure impact the biomass of communities. Under abiotic perturbations, the presence of tolerant species in community largely contributed in community biomass production. Bacterial diversity stabilized the biomass across the treatments, and differential response of bacterial species to different perturbations was the key reason behind these effects. The results suggest that biodiversity is crucial for maintaining the stability of ecosystem functioning and acts as ecological insurance under abiotic perturbations. Biodiversity in natural ecosystems may also uphold the ecosystem functioning under anthropogenic disturbance.

Cryptogamic community structure as a bioindicator of soil condition along a pollution gradient.

This study aims to determine changes in the structure of cryptogamic vegetation of poor psammophilous grassland along a pollution gradient near a zinc smelter to evaluate the potential of species assemblages as bioindicators of soil condition. Lichens and bryophytes were examined in study plots along six transects in four distance zones, and the physicochemical properties of corresponding soil samples were analysed. Four different responses of species to substrate contamination were identified, with a distinct group of species resistant to and favoured by metal contamination. Although species richness decreases as one approaches the smelter, the gradual replacement of certain sensitive species by resistant ones was observed along the pollution gradient. The results enabled us to develop a useful tool to diagnose strongly polluted sites. Two different cryptogamic assemblages of well-recognised key species characteristic for strongly polluted and lightly polluted sites were distinguished. We conclude that cryptogamic community structure clearly corresponds to the degree of soil contamination, thus demonstrating high bioindicative value. The study confirmed the high relevance of the community approach in metal pollution biomonitoring.

The effect of mixtures on colonisation of leaf litter decomposing in a stream and at its riparian zone

Abstract. The effect of mixing litter on decomposition and colonisation has been the focus of many studies carried independently in terrestrial and aquatic ecosystems. Those studies are carried out in different regions, use different experimental protocols and methodologies for the assessment of additive or non-additive effects, and the conclusions on the effect of mixtures vary accordingly. In this study I tested the hypothesis, via a short-term decomposition experiment, that, when using the same experimental protocol, mixtures have similar additive effects on decomposition and associated biota in a stream and at its riparian zone. The effect of mixing litter was assessed by comparing values in mixtures with the average of single species, alder and poplar (method 1); comparing the value of a species in mixture with the value of that species alone (method 2); and by a graphical analysis of the average difference between observed and expected values and the 95% confidence intervals (method 3). Method 1 was the most conservative, detecting non-additive effects on macroinvertebrate abundance only; method 2 detected non-additive effects on both dry mass remaining and ergosterol, with differential responses of the leaf species and the habitat; and method 3 detected non-additive effects on all variables except ergosterol and percentage detritivore abundance and also identified different responses of the leaves exposed in the terrestrial and the aquatic habitats. These results show that (i) the methodology used to detect the effects of mixtures deeply influences the results obtained, and may partially explain the diversity of responses available in literature; and (ii) the effect of mixtures may differ in the stream and at the riparian area. However, the findings of the present work should be assessed in a larger-scale experiment in order to generalise the effects of mixing litter on terrestrial and aquatic habitats.

Cheetahs and wild dogs show contrasting patterns of suppression by lions.

Top predators can dramatically suppress populations of smaller predators, with cascading effects throughout communities, and this pressure is often unquestioningly accepted as a constraint on mesopredator populations. In this study, we reassess whether African lions suppress populations of cheetahs and African wild dogs and examine possible mechanisms for coexistence between these species. Using long-term records from Serengeti National Park, we tested 30 years of population data for evidence of mesopredator suppression, and we examined six years of concurrent radio-telemetry data for evidence of large-scale spatial displacement. The Serengeti lion population nearly tripled between 1966 and 1998; during this time, wild dogs declined but cheetah numbers remained largely unchanged. Prior to their local extinction, wild dogs primarily occupied low lion density areas and apparently abandoned the long-term study area as the lion population 'saturated' the region. In contrast, cheetahs mostly utilized areas of high lion density, and the stability of the cheetah population indicates that neither high levels of lion-inflicted mortality nor behavioural avoidance inflict sufficient demographic consequences to translate into population-level effects. Population data from fenced reserves in southern Africa revealed a similar contrast between wild dogs and cheetahs in their ability to coexist with lions. These findings demonstrate differential responses of subordinate species within the same guild and challenge a widespread perception that lions undermine cheetah conservation efforts. Paired with several recent studies that document fine-scale lion-avoidance by cheetahs, this study further highlights fine-scale spatial avoidance as a possible mechanism for mitigating mesopredator suppression.

Bottom‐up manipulations alter the community structures of galling insects and gall morphs on Neoboutonia macrocalyx trees in a moist tropical rainforest

Abstract The effects of bottom‐up forces on the community structure of tropical insect gallers and within species variation in gall morphotype assemblages are not well understood. We tested the roles of increased nutritional quality and density of host plants with respect to structuring the galling insect communities and gall morphotype assemblages on Neoboutonia macrocalyx trees in Uganda. Plant nutritional quality and resource concentration were manipulated with four levels of fertilization and the group size of trees, respectively. After applying these treatments in May 2011, gallers established naturally on experimental replicates. Five months later, we sampled gallers and recorded their numbers and the different morphotypes. We analyzed the effects of treatments on the structures of galler communities and gall morphotype assemblages. We recorded 5237 individuals, representing four galler species. One species, Cecidomyiid leaf galler, was represented by three morphologically distinct galls. Fertilization, host tree density and their interactions significantly changed the structures of galler species communities and gall morphotype assemblages. The results of the present study demonstrate the important role of bottom‐up factors in structuring galler communities and the gall morphotype assemblages. These changes are likely caused by differential responses of different galler species and gall morphs to plant quality or quantity changes.

Changes in dimensional stability of Pinus roxburghii sarg. and Mangifera indica L. woods after retification

The present study was conducted to investigate the influence of heat treatment temperature and duration on the dimensional stability of chir pine (Pinus roxburghii Sarg.) and mango (Mangifera indica L.) wood. For this purpose, wood was heated at different temperatures for periods of 4, 8 and 12 h in an inert atmosphere. Differential responses of both wood species to different parameters, namely, volumetric swelling and shrinkage, water absorption and equilibrium moisture content (EMC) at different relative humidities, were observed. Results revealed that increase of heat treatment temperature in conjunction with time leads to a significant drop in the shrinkage of mango wood, whereas a reverse trend prevailed in chir pine until 210°C for 12 h treatment. Least values of EMC were recorded for chir pine and mango wood treated at 190 and 210°C for 4 h respectively. Further, increase in temperature and/or time of treatment significantly decreased the water absorption capacity of mango wood.

Iron addition as a measure to restore water quality: Implications for macrophyte growth

Eutrophication of shallow lakes in North-West Europe has resulted in cyanobacterial blooms, turbid water, and a decline in submerged macrophytes. Even though external inputs of phosphorus (P) are declining, internal loading of P from the sediment may delay the recovery of these aquatic ecosystems. Iron can be a useful chemical binding agent to combat internal P loading in shallow lakes, but may potentially be harmful for macrophyte growth. We tested whether iron addition as a restoration measure harms the growth of submerged macrophytes. We hypothesized that this depends on the iron dosage and the rooting strategy of the macrophytes. We experimentally tested the effects of Fe (FeCl3) on the submerged macrophytes Potamogeton pectinatus L. and Elodea nuttallii (Planch.) H. St. John. Iron was dosed at a concentration of 20gFem−2 and 40gFem−2 to the surface water or to both the surface water and sediment. E. nuttallii growth was not affected by iron addition, whereas P. pectinatus growth significantly decreased with increasing iron concentrations. Nonetheless, biomass of both species increased in all treatments relative to starting conditions. During the experiment, propagules sprouted from a propagule bank in the sediment including species with a high conservation value and this spontaneous emergence was not influenced by increasing iron concentrations. We conclude that adding iron(III)chloride in dosages of 20–40gm−2 may reduce growth of some macrophyte species, but does not prevent overall macrophyte recovery. It may however affect macrophyte community composition due to differential responses of macrophyte species to iron addition.

Subjective resource value and shell abandoning behavior in hermit crabs

Understanding the factors that motivate animals to hold or abandon a valuable resource is a central goal of behavioral ecology, the study of which will grow more important in the face of increasingly frequent extreme events. We compared the shell-abandoning behavior of the sympatric hermit crabs Clibanarius antillensis and Pagurus criniticornis in response to simulated burial and entrapment by rocks and other debris. While these hazards are relatively common in dynamic intertidal habitats, the frequency and severity of such disturbance are increasing due to human activity. While both species exhibited shell-abandoning behavior in response to experimental burial, it was far more prevalent for the soft-bottom dwelling species P. criniticornis (90%) when compared to the rocky bottom inhabitant C. antillensis (55%). Simulated entrapment experiments highlighted further differences in species response, with the decision to abandon domicile shells again far more common for P. criniticornis (80%) than it was for C. antillensis (10%). Given the tendency for P. criniticornis to abandon its shell, we subsequently focused on this species to test specific hypothesis about subjective resource value in hermit crabs. There was no difference in the tendency for this species to abandon optimal or sub-optimal (poorly-fitting) shells when faced with the immediate and potentially fatal risk of burial. This contrasted the response seen under conditions of entrapment, whereby individuals inhabiting sub-optimal shells abandoned them more rapidly and in greater numbers than those inhabiting optimal shells. Combining these two outcomes, we suggest that hermit crabs subjectively assess shell-value and respond according to the nature of the disturbance and its associated risks (i.e., high-value shells are abandoned in minutes under conditions of burial; but are held for hours under the less severe conditions of entrapment). In effect, the results show that extrinsic environmental cues can be just as important to decision making processes as those intrinsic cues that govern an animal's physiological condition. The contrasting behavior of the two hermit crabs to the movement of mud and other debris may lead to a higher survivorship of P. criniticornis than C. antillensis where activities such as dredging and harbor construction are intensifying along developing coastlines.

A flamelet-based a priori analysis on the chemistry tabulation of polycyclic aromatic hydrocarbons in non-premixed flames

In this paper, the chemical response of different species to turbulent effects is investigated in the context of one-dimensional laminar non-premixed flamelets. Turbulent effects are modeled as abrupt changes in the scalar dissipation rate. One-dimensional unsteady flamelet calculations assuming unity-Lewis number for all species are performed for an ethylene/air configuration. From the time-evolution of the species mass fractions, it is found that transient effects are not substantial for radicals such as OH and H, and species such as CO,CO2 and C2H2, consistent with their small characteristic chemical time scales. The steady state flamelet assumption for these species is well justified and their mass fractions can be pre-tabulated using the steady state flamelet solutions legibly. On the other hand, aromatic species are characterized by relatively slow chemistry, and substantial transient effects are observed for these species. The evolution of their mass fractions and chemical source terms are studied through a reaction flux analysis. Specifically for Polycyclic Aromatic Hydrocarbons (PAH), the chemical production terms are found to be linearly proportional to the mass fraction of smaller aromatic species, and the chemical consumption terms are found to be linearly proportional to their own mass fractions. Based on the unsteady flamelet results, the validity of various existing flamelet-based pre-tabulation methods is examined, and a new linear relaxation model is proposed for PAH. The proposed relaxation model is validated through the unsteady flamelet formulation, and results are compared against full chemistry calculations.

Temporal patterns in immunity, infection load and disease susceptibility: understanding the drivers of host responses in the amphibian‐chytrid fungus system

Summary Many pathogens infect a wide range of host species. However, variation in the outcome of infection often exists amongst hosts and is shaped by intrinsic host traits. For example, contact with pathogens may trigger changes in hosts directed toward preventing, fighting, or tolerating infection. Host responses to infection are dynamic; they change over time and vary depending on health, condition and within the context of the environment. Immunological defences are an important class of responses that mediate host–pathogen dynamics. Here, we examined temporal patterns of immunity in two amphibian species, Pacific tree frogs (Pseudacris regilla) and Cascades frogs (Rana cascadae), exposed to control conditions or experimental inoculation with the emerging infectious fungal pathogen, Batrachochytrium dendrobatidis (Bd). For each species, we compared bacterial killing ability of blood and differential white blood cell counts at four different time‐points after pathogen inoculation. We also quantified infection load over time and monitored survival. We detected qualitative and quantitative differences in species responses to Bd. Pseudacris regilla exhibited an increase in infection load over time and 16% of Bd‐exposed animals died during the experiment. Tree frogs lacked robust treatment differences in immune responses, but Bd‐exposed P. regilla tended to display weaker bacterial killing responses than unexposed control animals. Neutrophil counts did not vary consistently with treatment and lymphocytes tended to be less abundant in Bd‐exposed animals at the later sampling time‐points. In contrast, Bd‐exposed R. cascadae exhibited a decrease in infection load over time and no mortality occurred in the Bd treatment. Bd‐exposed Cascades frogs showed stronger bacterial killing responses and an elevated number of neutrophils in blood when compared with control animals, and both responses were upregulated within 48 h of pathogen exposure. Lymphocyte counts did not vary significantly with treatment. Although only statistically significant in Cascades frogs, neutrophil:lymphocyte ratios showed a trend of being elevated in Bd‐exposed animals of both species and are indicative of pathogen‐induced physiological stress. Our results suggest that variation in systemic immunological responses of two syntopic amphibian species is associated with and may contribute to differential patterns of survival and infection load during exposure to the chytrid fungus. Species variation in immunological responses as soon as 48 h after pathogen exposure suggests that initial host–pathogen interactions may set the stage for subsequent infection and disease progression. Variation in host responses can drive disease dynamics and comparative studies of host responses to pathogens are critical for making predictions about pathogen emergence, spread and persistence.

Comparison of phosphite application methods for control of Phytophthora cinnamomi in threatened communities

Stem injection, high and low-volume aerial spray and stem spray using Pentra-bark® and Pulse® as bark penetrants were compared to determine whether application method could increase the effectiveness of phosphite in inhibiting colonisation by Phytophthora cinnamomi. Phosphite stem injection and stem spray inhibited P. cinnamomi more effectively than aerial application. In contrast, low-volume aerial phosphite spray showed the least effectiveness. Colonisation in B. attenuata was significantly reduced by stem spray of phosphite alone at 400 g/L and phosphite at ≥200 g/L when combined with Pentra-bark® or Pulse®. For B. baxteri, colonisation of P. cinnamomi was significantly reduced by stem spray of phosphite alone at ≥200 g /L and by phosphite ≥100 g /L when combined with Pentra-bark® and phosphite at ≥200 g /L combined with Pulse®. Stem spray did not significantly control of colonisation in L. inermis var. inermis. Only stem injection overcame the ineffectiveness of phosphite application in L. inermis var. inermis previously recorded. Different responses of species to phosphite application highlights the need to assess effectiveness at the species level.

Pesticide-induced release from competition among competing Aedes aegypti and Aedes albopictus (Diptera: Culicidae).

Competitive interactions between mosquitoes Aedes aegypti (L.) and Aedes albopictus (Skuse) may depend on environmental conditions. Pesticides may alleviate density-dependent competition for limited food, and a differential species response to sublethal concentrations may modify interspecific competition. We tested the hypothesis that exposure to malathion alters interspecific resource competition between these two species. In the absence of malathion, Ae. aegypti survivorship and per capita rate of population change were negatively affected by increasing densities of Ae. albopictus. However, the asymmetrical negative effect ofAe. albopictus on Ae. aegypti was eliminated in the presence of malathion. In addition, the presence of malathion resulted in shorter development time compared with the controls. The relative importance of pesticide-mediated coexistence in nature has not been evaluated, so its role in mediating coexistence is unclear; however, these findings underscore the potential of environmental concentrations of malathion, and perhaps other pesticides to facilitate coexistence between species.

Tree-growth responses across environmental gradients in subtropical Argentinean forests

Subtropical forests in montane ecosystems grow under a wide range of environmental conditions. However, little is known about the growth responses of subtropical trees to climate along ecological gradients. To assess how, and to what extent climate controls tree growth, we analyzed tree responses to climate for 15 chronologies from 4 different species (Schinopsis lorentzii, Juglans australis, Cedrela lilloi, Alnus acuminata) across a variety of environments in subtropical forests from northwestern Argentina (22–28°S, 64–66°W). Using correlation and principal component analysis, site and species differences in tree-growth responses to precipitation and temperature were determined along the elevation gradient from the dry-warm Chaco lowlands to the wet-cool montane Yungas. Our results show that species responses differ according to the severity in climate conditions along the elevation gradient. At sites with unfavorable conditions, mainly located at the extremes of the environmental gradient, responses of different species to climate variations are similar; in contrast, at sites with relatively mild conditions, tree growth displays a large variety of responses reflecting differences in both local environmental conditions and species physiology. Our research suggests that individualistic responses to environmental variability would determine differences in the type and timing of the responses of dominant trees to climate, which ultimately may shift species’ assemblages in montane subtropical regions of South America under future climate changes.

Impacts of climate change on forests in different climatic zones and their implications on sustainable development

Atmospheric and meteorological data collected during the last few decades show clear evidence thatglobal climate is undergoing a long-term change. Increasing atmospheric concentrations of greenhousegases (i.e. CO" CH4, NO, and CFCs) and the consequent warming of the atmosphere are clearfeatures of' long-term climate change. Because of their long life span, these changes in climate areIikely to influence the functioning and productivity offorest ecosystems. The objective of this reviewis to predict the impacts of climate change on forests on the basis of experimental results on key plantphysiological and ecological processes.There is clear experimental evidence that increasing atmospheric CO2 (C ) increases photosynthesisand biomass production of forests. However, the magnitude of growth shmulation is likely to varywith temperature. The highest increases in productivity are expected to occur in the cooler and moistclimatic zones while the productivity increases would be lowest or absent in the warmer and drierzones. It is highly probable that the species composition offorests in all climatic zones would changebecause of the differential response of different plants species to increases in Ca and temperature.There is clear evidence that the underlying physiology of all plant species become relatively droughttolerant with increasing C . Hence, there is a possibility that in areas which are not deforested due tohuman population pressure, the existing forests would spread beyond their present boundaries withlowland evergreen forests extending to relatively drier, sub-humid climates and dryland deciduousforests extending to relatively semi-arid climates.Climate change induced changes in forests will definitely trigger changes in soil and in the complexnetwork of organisms that inhabit forests. While the inputs of carbon and nutrients to the soil throughIitter fall and root exudates are Iikely to increase with increasing Ca' soil organic matter decompositionwould also increase with increasing soil temperatures. Photosynthesis in a future high CO, environmentwill produce plant tissues with higher carbohydrates, but lower nitrogen. This will affect tlie populationsof organisms which feed on plants. Therefore, the climate change induced changes in forests couldcause wide ranging and complex secondary and tertiary effects on the whole forest ecosystem.It is well-established that management of forest resources is a vital component of sustainabledevelopment. Therefore, understanding and identifying the impacts of climate change on forestecosystems would be essential in formulating rational forest management strategies to achieve longtermsustainable development.

The Influence of Variable Rainfall Frequency on Germination and Early Growth of Shade-Tolerant Dipterocarp Seedlings in Borneo

Climate change induced alterations to rainfall patterns have the potential to affect the regeneration dynamics of plant species, especially in historically everwet tropical rainforest. Differential species response to infrequent rainfall may influence seed germination and seedling establishment in turn affecting species distributions. We tested the role of watering frequency intervals (from daily to six-day watering) on the germination and the early growth of Dipterocarpaceae seedlings in Borneo. We used seeds that ranged in size from 500 to 20,000 mg in order to test the role of seed mass in mediating the effects of infrequent watering. With frequent rainfall, germination and seedling development traits bore no relationship to seed mass, but all metrics of seedling growth increased with increasing seed mass. Cumulative germination declined by 39.4% on average for all species when plants were watered at six-day intervals, and days to germination increased by 76.5% on average for all species from daily to six-day intervals. Final height and biomass declined on average in the six-day interval by 16% and 30%, respectively, but the percentage decrease in final size was greater for large-seeded species. Rooting depth per leaf area also significantly declined with seed mass indicating large-seeded species allocate relatively more biomass for leaf production. This difference in allocation provided an establishment advantage to large-seeded species when water was non-limiting but inhibited their growth under infrequent rainfall. The observed reduction in the growth of large-seeded species under infrequent rainfall would likely restrict their establishment in drier microsites associated with coarse sandy soils and ridge tops. In total, these species differences in germination and initial seedling growth indicates a possible niche axis that may help explain both current species distributions and future responses to climate change.

Climatic signal in tree-ring chronologies of Cedrus deodara from Chitral Hindukush Range of Pakistan

Tree-rings are an important tool for the investigation of paleoclimatic records for regions or periods of time with no instrumental climatic data. However, the responses of different species and sites to various climatic parameters are unusual. In the present study, we developed tree-ring-width chronologies of Cedrus deodara from three different sites of Chitral Hindukush range of Pakistan. The study was conducted to understand tree-growth climate relationship and its applicability in proxy climate investigations. The chronologies covered the past 469 to 595 years, with a mean segment length (MSL) ranging from 148 to 223 years. Climatic data obtained from the three weather stations showed strong correlation and was found useful for tree-ring climate relationships. Correlation Function (CF) and Response Function (RF) analysis showed that spring precipitation (March–May) is a critical limiting factor for tree-ring growth, and temperature prior to November may also play a major role in affecting tree ring-growth. The results exposed that the three sites have continuous relationship indicated that only single species from different locations are affected by the same environmental variables and hence can be used in climate reconstruction in combination. The Cedrus deodara chronologies developed at different locations had several corresponding narrow and wide marker rings indicating a large macroclimatic response to regional climatic conditions. The current study suggests that the tree-rings of Cedrus deodara from the Chitral Hindukush range could be used to develop chronologies for the reconstruction of seasonal climatic variables.

English

Two wheat differing in salt sensivity, was examined for osmolyte contents and activities of a-amylase, b-amylase and a-glucosidase enzymes involved in seeds germination, in absence as well as in presence of 100, 150, 200 and 300 mM NaCl. The inhibitory effects of NaCl differed, depending on the species tested. In wild wheat specie (Triticum monococcum), with reduced germination percentage and lower relative water content, the increase in NaCl concentration resulted in the decrease in endogenous level of proline, total soluble carbohydrate and activities of the main enzymes involved in the germination process. In contrast, cultivated wheat specie (Triticum aestivum) seed in response to salt stress accumulated higher proline and total soluble carbohydrate concentrations which improved their water status and the enzyme activities involved in the germination process. Differential response of the different species of wheat to salt stress is governed by the accumulation of osmolytes in seeds. Key words: Salinity, amylases, glucosidases, wheat species.

Differential anatomical responses of tolerant and susceptible citrus species to the infection of ‘Candidatus Liberibacter asiaticus’

Citrus Huanglongbing (HLB) is becoming the most devastating citrus disease worldwide. Although no known HLB-resistant citrus species or varieties have been identified, some citrus accessions such as rough lemon are reportedly tolerant. To better understand the HLB tolerance or susceptibility mechanisms in citrus, comparative anatomical analyses of tolerant rough lemon and sensitive sweet orange seedlings in response to HLB-associated bacterium, ‘Candidatus Liberibacter asiaticus’, were performed on leaf, stem and root tissues using light microscopy and transmission electron microscopy. Phloem collapse, plugged sieve elements and accumulation of starch were observed in leaf petioles of symptomatic leaves from both HLB-diseased rough lemon and sweet orange, while not in the mock-inoculated controls. Interestingly, in symptomless leaves, significant anatomical changes (e.g. phloem cell collapse and starch accumulation) were found in HLB-diseased sweet orange, but not in rough lemon. Furthermore, starch depletion, phloem cell collapse and absence of phloem fibers were observed in secondary roots of only diseased sweet orange. In young green stems, a few plugged sieve elements were seen in both diseased rough lemon and sweet orange; whereas starch deposition only occurred in the latter. Taken together at the whole plant level, HLB infection induces fewer disruptive anatomical changes in rough lemon than in sweet orange. In particular, the absence of obvious changes in the rough lemon root system is suggested to be critical for sustaining plant growth after infection, and may contribute greatly to its HLB tolerance.