Geographical Distribution Of Plants Research Articles

Impact of climate zone migration on geographical distribution of indigenous vegetation in Northeast China

Based on the relationship between climate and vegetation, this study uses the time lag of vegetation response to climate change, simulates the dynamic response process of different vegetation types to climate change, retrieves relevant literature and collates data, and deduces the actual occurrence and geographic distribution of vegetation under the current climate potential and future climate change scenarios. This experiment infer the adaptation relationship between plant geographical distribution and climatic conditions. The results show that the plants in Northeast China are generally more adaptable to climate change. The areas with poor adaptability are mainly at the junction of forest shrubs and grasslands. The geographical distribution of plants has changed, accounting for about 5%. The grassland ecosystem in the bush-grassland transition zone in the Greater Xing’an Mountains is also less adaptable to climate, accounting for about 35%. The vegetation in these areas tends to degenerate. The geographical distribution may change. The adjustment of plants in Northeast China to the future climate change is usually reasonable. 84% of the vegetation changes are positive changes. Especially in the eastern regions, the vegetation deduction conditions will be improved in the future, and the vegetation coverage in these regions may be improved. About 79% of the potential changes in vegetation can adapt to the future climate. Nevertheless, the grassland ecosystems in the Greater Xing’an Mountains and parts of Inner Mongolia are less adaptable to future climate change and tend to degrade. It provides new ideas for assessing vegetation adaptability or ecosystem adaptability. Research on the interaction between climate change and terrestrial ecosystems of different scales needs to be strengthened in the context of global change.

Alleviation of cold stress in vegetable crops

Low temperature is a major environmental factor that limits crop productivity of plants. Cold stress is a serious threat to the sustainability of crop yields. Low temperature has a huge impact on the survival and geographical distribution of plants. It negatively affects cellular components and metabolism, and temperature extremes impose stresses of variable severity that depend on the intensity and duration of the stress. Low temperature (less than minimum) leads to chlorosis, necrosis, membrane damage, changes in cytoplasm viscosity, and changes in enzyme activities leading to death of plant. Cold stress disrupts the integrity of intracellular organelles, leading to the loss of compartmentalization. It also causes reduction and impairing of photosynthesis, protein assembly and general metabolic processes. Moreover, cold stress during anthesis induces flower dropping, sterility of pollen, pollen tube distortion, ovule abortion and reduced fruit set, which leads to declined growth and lower yield. A number of approaches are being used to mitigate the deleterious effects of cold stress which threatens the successful vegetable crop production, application of plant growth regulators (salicylic acid, abscisic acid, jasmonic acid, Gibberellin and brassinosteroids) and unitization of genetics tools and plant breeding is one of the strategies to alleviate the low temperature stress in vegetable crops. Plant growth regulators play a greater role in improving the cold stress tolerance. In this paper, the effects of cold stress on vegetable growth, productivity and physiological activities were discussed, and some effective techniques for the mitigation of cold stress that help sustainable vegetable production under fluctuating climate is presented.

NATURAL VEGETATION DISTRIBUTION AND CLIMATE ECOLOGY PREDICTION BASED ON GEOGRAPHIC INFORMATION SYSTEM

The global climate change, especially global warming, has seriously affected our living environment and the terrestrial biosphere. The typical consequences include biosystem destruction, crop failure and the rise of sea level. Therefore, a growing attention has been paid to quantify the relationship and mutual influence between vegetation and climate in the recent decade. In this paper, the vegetation distribution across China is digitized using the geographic information system (GIS) software. The raster data on the distribution of geographical spaces were obtained for 198 species of plants, including 92 species of arbor, 48 species of herbaceous plants and 46 species of shrubs. Besides, the Kriging interpolation was adopted to disclose the relationships between the geographical distribution of plants and different climate factors. The research results show that the selected climate factors can be widely applied to plant and climate prediction models, and used to forecast the response of vegetation to global climate change. The research findings provide reference and theoretical support to the research on natural vegetation distribution and climate ecology prediction.

Application of chlorophyll fluorescence imaging technique in analysis and detection of chilling injury of tomato seedlings

Low temperature is one of the main environmental factors limiting plant geographical distribution and crop production. Chilling injury is a stress caused by low, nonfreezing temperatures (0–12 °C). Since chilling injury is an important facility agriculture problem in northeast China regions, we aimed to study a suitable method for evaluate the potential of chlorophyll fluorescence imaging for the detection of chilling injury in tomato Seedlings. Here, four types of chlorophyll fluorescence image features were used to study and analyze chilling injury classes: chlorophyll fluorescence parameter values, histograms, textures and color descriptions. The Pearson correlations of the features in each type were calculated, and eligible features were input into BPNN model to identify chilling injury classes of leaf. Our results reveal six fluorescence parameter values of Y (II), qP, qL, Y (NPQ), Y (NO) and Fv/Fm can be used to evaluate the chilling injury classes of tomato seedlings. The identification accuracy rate of training set was 90.3%, and that of the validation set was 90%. The Skewness of the gray histogram features and standard deviation of entropy of the texture can be used to evaluate the chilling injury classes of tomato seedlings. The identification accuracy rates of training sets were 88.1% and 72.6%, respectively, and that of the validation set were 82.5% and 61.7%, respectively. The B, b and L/b of the color descriptor features can also be used to evaluate the chilling injury classes of tomato seedlings. The identification accuracy rates of the training sets were 89.8%, 91.9% and 90.1%, respectively, and that of the validation sets were 87.5%, 90.8% and 90.0%, respectively. Our research showed that the best recognition accuracy was b and L/b of the color descriptor features, as well as fluorescence parameter values, and the recognition accuracy are all more than 90%. Therefore, chlorophyll fluorescence imaging was recommended for the detection of chilling injury classes of tomato seedlings under low temperature stress, and had a good evaluation effect. The data reported in this manuscript should foster new research method for the detection of the chilling injury classes and have considerable prospects for non-destructive diagnosis of plant chilling injury.

Comparative proteomics and gene expression analyses revealed responsive proteins and mechanisms for salt tolerance in chickpea genotypes

BackgroundSalinity is a major abiotic stress that limits the growth, productivity, and geographical distribution of plants. A comparative proteomics and gene expression analysis was performed to better understand salinity tolerance mechanisms in chickpea.ResultsTen days of NaCl treatments resulted in the differential expression of 364 reproducible spots in seedlings of two contrasting chickpea genotypes, Flip 97-43c (salt tolerant, T1) and Flip 97-196c (salt susceptible, S1). Notably, after 3 days of salinity, 80% of the identified proteins in T1 were upregulated, while only 41% in S2 had higher expression than the controls. The proteins were classified into eight functional categories, and three groups of co-expression profile. The second co-expressed group of proteins had higher and/or stable expression in T1, relative to S2, suggesting coordinated regulation and the importance of some processes involved in salinity acclimation. This group was mainly enriched in proteins associated with photosynthesis (39%; viz. chlorophyll a-b binding protein, oxygen-evolving enhancer protein, ATP synthase, RuBisCO subunits, carbonic anhydrase, and fructose-bisphosphate aldolase), stress responsiveness (21%; viz. heat shock 70 kDa protein, 20 kDa chaperonin, LEA-2 and ascorbate peroxidase), and protein synthesis and degradation (14%; viz. zinc metalloprotease FTSH 2 and elongation factor Tu). Thus, the levels and/or early and late responses in the activation of targeted proteins explained the variation in salinity tolerance between genotypes. Furthermore, T1 recorded more correlations between the targeted transcripts and their corresponding protein expression profiles than S2.ConclusionsThis study provides insight into the proteomic basis of a salt-tolerance mechanism in chickpea, and offers unexpected and poorly understood molecular resources as reliable starting points for further dissection.

Transcriptome sequencing and functional analysis of Sedum lineare Thunb. upon salt stress

Soil salinization is one major constraint to plant geographical distribution, yield, and quality, and as an ideal plant for the "greening" of flat-roofed buildings, Sedum lineare Thunb. has strong tolerance against a variety of environmental adversities including salinity with the underlying mechanism still remaining unknown. In this study, we performed de novo transcriptome sequencing on leaf and root samples of NaCl-treated S. lineare Thunb. and identified 584 differentially expressed genes (DEGs), which were further annotated by gene function classification and pathway assignments using the public data repositories. In addition to the increased gene expression level verified by qRT-PCR, the elevated activities of the corresponding enzymes were also demonstrated for peroxidase (POD), glutathione peroxidases (GPX), and cysteine synthase (CSase) in the NaCl-treated roots. Furthermore, two highly inducible genes without known functions related to salt tolerance were selected to be overexpressed and tested for their effects on salt tolerance in the model plant, Arabidopsis thaliana. Upon 150mM NaCl treatment, 35S:SlCXE but not 35S:SlCYP72A transgenic Arabidopsis seedlings exhibited improved salt resistance as shown by the increased seed germination rates and longer primary roots of transgenic seedlings when compared to wild-type plants. Taken together, this work laid a foundation for a better understanding of the salt adaptation mechanism of S. lineare Thunb. and genes identified could serve as useful resources for the development of more salt-tolerant varieties of other species through genetic engineering.

Differential physiological and metabolic response to low temperature in two zoysiagrass genotypes native to high and low latitude.

Low temperature is one of the important limiting factors for growing season and geographical distribution of plants. Zoysiagrass (Zoysia Willd) is one of the widely used warm-season turfgrass that is distribute in many parts of the world. Zoysaigrass native to high latitude may have evolved higher cold tolerance than the ones native to low latitude. The objective of this study was to investigate the cold stress response in zoysiagrass native to diverse latitude at phenotypic, physiological and metabolic levels. Two zoysiagrass (Z. japonica) genotypes, Latitude-40 (higher latitude) and Latitude-22 (lower latitude) were subjected to four temperature treatments (optimum, 30/25°C, day/night; suboptimum, 18/12°C; chilling, 8/2°C; freezing, 2/-4°C) progressively in growth chambers. Low temperature (chilling and freezing) increased leaf electrolyte leakage (EL) and reduced plant growth, turf quality, chlorophyll (Chl) content, photochemical efficiency (Fv/Fm) and photosynthesis (Pn, net photosynthetic rate; gs, stomatal conductance; intercellular CO2; Tr, transpiration rate) in two genotypes, with more rapid changes in Latitude-22. Leaf carbohydrates content (glucose, fructose, sucrose, trehalose, fructan, starch) increased with the decreasing of temperature, to a great extend in Latitude-40. Leaf abscisic acid (ABA), salicylic acid (SA) and jasmonic acid (JA) content increased, while indole-3-acetic acid (IAA), gibberellic acid (GA3) and trans-zeatin ribside (t-ZR) content decreased with the reduction of temperature, with higher content in Latitude-40 than in Latitude-22. Chilling and freezing induced the up-regulation of C-repeat binding factor (ZjCBF), late embryogenesis abundant (ZjLEA3) and dehydration-responsive element binding (ZjDREB1) transcription factors in two genotypes, whereas those genes exhibited higher expression levels in Latitude-40, particularly under freezing temperature. These results suggested that zoysiagrass native to higher latitude exhibited higher freezing tolerance may attribute to the higher carbohydrates serving as energy reserves and stress protectants that stabilize cellular membranes. The phytohormones may serve signals in regulating plant growth, development and adaptation to low temperature as well as inducing the up-regulated ZjCBF, ZjLEA3 and ZjDREB1 expressions thus result in a higher cold tolerance.

Tetraploid Carrizo citrange rootstock (Citrus sinensis Osb. × Poncirus trifoliata L. Raf.) enhances natural chilling stress tolerance of common clementine (Citrus clementina Hort. ex Tan)

Low temperatures can disturb the development, growth and geographic distribution of plants, particularly cold-sensitive plants in the Mediterranean area, where temperatures can reach seasonally low levels. In citrus crops, scion/rootstock combinations are used to improve fruit production and quality, and increase tolerance to biotic and abiotic stresses. In the last decade, several studies have shown that tetraploid citrus seedlings or rootstocks are more tolerant to abiotic stress than their respective diploid. The objective of this study was to test whether the use of tetraploid rootstocks can improve the chilling tolerance of the scion. We compared physiological and biochemical responses to low seasonal temperatures of common Clementine (Citrus sinensis Osb.×Poncirus trifoliata L. Raf.) grafted on diploid and tetraploid Carrizo citrange rootstocks, named C/2xCC and C/4xCC, respectively. During the coldest months, C/4xCC showed a smaller decrease in net photosynthesis (Pn), stomatal conductance (Gs), chlorophyll fluorescence (Fv/Fm), and starch levels, and lower levels of malondialdehyde and electrolyte leakage than C/2xCC. Specific activities of catalase (CAT), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) were higher in C/4xCC during the cold period, whereas chlorophyll, proline, ascorbate and hydrogen peroxide (H2O2) levels and superoxide dismutase (SOD) activity did not vary significantly between C/4xCC and C/2xCC throughout the study period. Taken together, these results demonstrate that tetraploid Carrizo citrange rootstock improves the chilling tolerance of common clementine (scion) thanks to a part of the antioxidant system.

Rafflesia spp.: propagation and conservation.

The propagation of Rafflesia spp. is considered to be important for future development of ornamental and other applications. Thus far, the only successful propagation technique has been grafting. This mini-review succinctly emphasizes what is known about Rafflesia species. Members of the genus Rafflesia (Rafflesiaceae), which are holoparasitic plants known to grow on a host vine, Tetrastigma sp., are widely spread from the Malayan Peninsula to various islands throughout Indonesia. The plant's geographical distribution as well as many other aspects pertaining to the basic biology of this genus have still not been studied. The young flower buds and flowers of wild Rafflesia hasseltii Suringar, Rafflesia keithii Meijer and Rafflesia cantleyi Solms-Laubach are used in local (Malaysia and Indonesia) traditional ethnomedicine as wound-healing agents, but currently no formal published research exists to validate this property. To maintain a balance between its ethnomedicinal and ornamental use, and conservation, Rafflesia spp. must be artificially cultivated to prevent overexploitation. A successful method of vegetative propagation is by host grafting using Rafflesia-impregnated Tetrastigma onto the stem of a normal Tetrastigma plant. Due to difficulties with culture contamination in vitro, callus induction was only accomplished in 2010 for the first time when picloram and 2,4-D were added to a basal Murashige and Skoog medium, and the tissue culture of holoparasitic plants continues to be extremely difficult. Seeds harvested from fertile fruit may serve as a possible method to propagate Rafflesia spp. This paper provides a brief synthesis on what is known about research related to Rafflesia spp. The objective is to further stimulate researchers to examine, through rigorous scientific discovery, the mechanisms underlying the ethnomedicinal properties, the flowering mechanisms, and suitable in vitro regeneration protocols that would allow for the fortification of germplasm conservation.

The effect of arginine pretreatment in the increase of cold tolerance in Pistacia vera L. in vitro

Low temperature is an important environmental stress that produces reactive oxygen species in plants and causes oxidative injuries and limits the survival, productivity and geographical distribution of plants across broad areas of the world. In vitro culture of plants such as pistachio which has high economic value is an effective technique to select fairly stress tolerant genotypes that could be grown in severe environmental conditions. Previously SNP was applied as an NO donor to counteract the effect of chilling stress whilethere are little information about exogenous arginine application as a precursor of NO in the possible antioxidative responses of plants against low temperature stress. In this study we have investigated the effect of arginine pretreatment on oxidative parameters of pistaciavera under cold stress and LNAME was used as nitric oxide synthase inhibitor in some treatment. Results showed that cold stress induced the increment of hydrogen peroxide, MDA and other aldehyde content, carbonyl groups and proline content. Cold stress also decreased the SOD, CAT,GPX and APX activity. Arg pretreatment decreased the lipid peroxidation, protein oxidation and hydrogen peroxide content while increased the activity of all antioxidant enzymes in plants which were under cold stress. Proline content decreased under Arg pretreatment. In this research in some parameters such as lipid peroxidation, Arg and Arg + LNAM pretreatment had the same effects and it seems that in these situations other pathways of Arg metabolism rather than NOS may be activated. However in the case of hydrogen peroxide, protein oxidation and anti-oxidative enzyme activity, the role of NO were more effective than other products because in the present of LNAME the effects of Arg on these parameters decreased significantly.

OsMsr9, a novel putative rice F-box containing protein, confers enhanced salt tolerance in transgenic rice and Arabidopsis

Salinity is a major environmental stress that limits agricultural production and geographical distribution of plants. In a previous study, it has been shown that OsMsr9 was induced by cold, drought and heat stresses. However, functions of OsMsr9 at physiological and molecular levels are still unknown. Here, we report that OsMsr9 plays roles in salt tolerance in plants. Quantitative real-time PCR (qPCR) analysis revealed that OsMsr9 was also rapidly and strongly induced by salt stress. Overexpression of OsMsr9 in Arabidopsis and rice showed enhanced salt stress tolerance displaying increased shoot and root elongation, higher survival rates in transgenic plants compared with wild type. OsMsr9 might act as a positive regulator of plant salt tolerance with reinforced expression of stress-related genes, such as RD29A, DREB2A and RAB18 in transgenic plants under salt conditions. Furthermore, transgenic plants accumulated more compatible solutes (proline and soluble sugar) and low level of malondialdehyde, alleviating the changes in reactive oxygen species. These results indicate that OsMsr9 could be a useful gene in developing transgenic crops with enhanced salt tolerance.

Climatic niche shifts in the serpentine soil flora of California

Question Soil properties are known to have a profound effect on the geographic distribution of plants. Unusual soils seem to allow species to occur outside their ‘typical’ (realized) climatic niche. However, the generality of this pattern, and the mechanisms that drive it, are poorly known. Here, we focus on the tendency for some plant species to occur at unusually low elevations on infertile substrates, especially serpentine soils. We ask whether there is a flora-wide trend in the state of California toward lower elevations and warmer thermal limits on infertile serpentine soils than on other soils. Location State of California, USA. Methods We used herbarium data from 19 institutions. We only used species collected from both serpentine and non-serpentine soils. To focus on plant response to recent climate, we discarded records from before 1979. Finally, we discarded records that did not report latitude and longitude. The final data set consisted of 36 045 specimens representing 814 species. Latitude and longitude were used to infer elevation, temperature and soil type. We then developed a simulation modelling approach to test for significant differences in elevational and thermal distribution between serpentine and non-serpentine soils. Results Serpentine populations are found at lower elevations than non-serpentine populations, at both the low and high ends of elevation distributions (two tailed t-test, P < 0.01). This pattern is partially matched by temperature: both high and low temperature data indicate that serpentine populations are limited to less extreme temperatures than non-serpentine populations (two tailed t-test, P < 0.01). Conclusions We show that there is a flora-wide trend toward lower elevation limits on serpentine soils in the state of California. Temperature data suggest a slightly different pattern, with serpentine plants occupying more moderate temperatures. We suggest that this difference may be due to a decoupling of elevation and temperature in some parts of California. Overall, our results are consistent with two mechanisms of plant range limitation: (1) a biotic mechanism at lower elevations (high temperatures), where serpentine provides a refuge from competition; and (2) an abiotic limit at upper elevations (low temperatures), where the effect of cold is exacerbated by the infertility of serpentine.

Comparative transcriptome profiling of freezing stress responsiveness in two contrasting Chinese cabbage genotypes, Chiifu and Kenshin

Freezing stress is a major factor affecting plant growth, crop productivity, and the geographical distribution of plants. To identify freezing-responsive genes in Brassica rapa, we analyzed transcriptome profiles of two contrasting inbred lines with different geographic origins, Chiifu and Kenshin, in control and −4 °C-treated leaves. A total of 3,301 genes were differentially expressed between Chiifu and Kenshin upon freezing treatment. Among these, 67 and 1,633 genes were specifically expressed in Chiifu and Kenshin, respectively. An ortholog (BrTPP1) of Arabidopsis trehalose-6-phosphate phosphatase 1 (TPP1) was specifically and highly induced in Chiifu by freezing treatment. However, most cold-responsive genes, including CBF pathway-related genes, showed similar patterns of expression between Chiifu and Kenshin. Many genes involved in stress responses (i.e., to freezing temperatures) were intrinsically and specifically expressed in Chiifu, which is tolerant of freezing temperatures. The results suggest that the CBF pathway is not the main factor conferring freezing tolerance to Chiifu, but genes that are expressed prior to cold acclimation, along with other regulatory genes, may play important roles in freezing tolerance.

Discovering the alternation of generations in salps (Tunicata, Thaliacea): Adelbert von Chamisso’s dissertation “De Salpa” 1819 - its material, origin and reception in the early nineteenth century

The exiled French nobleman Adelbert von Chamisso (1781–1838) is mostly known as a poet of the Romantic era in Germany, but less so as a keen and accurate naturalist. However, he was a much respected zoologist and botanist at his time. On board the Russian brig Rurik between 1815 and 1818 he explored some of the Pacific coasts and islands, from where he brought back rich collections of animals and plants, among them also salps (Tunicata) which he was one of the first to not only catch and preserve but observe, depict and describe in detail from living condition. Even more important than his collection of natural history objects (which subsequently mostly fell into oblivion in the museums) were Chamisso’s observations and insights in natural history. These include his findings in botanical taxonomy and geographical distribution of plants, but most eminent was his discovery of the alternation of generations in salps which was the first description of the phenomenon in the animal kingdom. Here we report first on the re-discovery of Chamisso’s original samples of salps from the Russian Rurik expedition. This material is nearly completely extant in the marine invertebrate collection of the Berlin Natural History Museum and was re-studied and compared to Chamisso’s original descriptions here for the first time since over a century. We then detail Chamisso’s observations on salps and their alternating generations, based on his own published accounts, in particular his dissertation of 1819, but also his article for the journal Isis in 1820. We add examples of the sketches found in an unpublished notebook and Chamisso’s original manuscript, made during or immediately after the Rurik circumnavigation, which we found in the archives of the Staatsbibliothek Berlin. We also discuss, presenting English translations of them, key passages of Chamisso’s original Latin account “De Salpa ”. Finally we look into the history of reception of Chamisso’s discovery and insight on salps during the first half of the nineteenth century (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Physiological and molecular changes in plants grown at low temperatures

Apart from water availability, low temperature is the most important environmental factor limiting the productivity and geographical distribution of plants across the world. To cope with cold stress, plant species have evolved several physiological and molecular adaptations to maximize cold tolerance by adjusting their metabolism. The regulation of some gene products represents an additional mechanism of cold tolerance. A consequence of these mechanisms is that plants are able to survive exposure to low temperature via a process known as cold acclimation. In this review, we briefly summarize recent progress in research and hypotheses on how sensitive plants perceive cold. We also explore how this perception is translated into changes within plants following exposure to low temperatures. Particular emphasis is placed on physiological parameters as well as transcriptional, post-transcriptional and post-translational regulation of cold-induced gene products that occur after exposure to low temperatures, leading to cold acclimation.

Life form and geographical distribution of plants in Posthband region, Khonj, Fars Province, Iran

A study was conducted to identify plant species, diversity, life form and relevant species to Mediterranean climate, Irano-Torunian and Sahara-Sindian in Postband region (N 27°58′4″–28°2′16″, E 53°17′34″−53°22′30″). In total, 95 species belonging to 29 families and 69 genera of flora were surveyed and identified from December 2006 to June 2008. Composite and Gramineae were important families in terms of species frequency. According to Raunkiaer’s system and using \( \hat \chi \)2 tests, the life-form spectrum showed that therophytes accounted for 47% of all species, and hemicryptophytes for 31%, phanerophytes for 12%, chamaeophyte for 7%, and cryptophytes for 3%. In geographical distribution, 29% species with the most frequency belonged to Irano-Torunian region. Results show that therophytes were more than normal spectrum and phaneropytes were less than normal spectrum, which was in agreement with data obtained in arid climate.

Distribution of the anther-smut pathogen Microbotryum on species of the Caryophyllaceae.

SummaryUnderstanding disease distributions is of fundamental and applied importance, yet few studies benefit from integrating broad sampling with ecological and phylogenetic data. Here, anther-smut disease, caused by the fungus Microbotryum, was assessed using herbarium specimens of Silene and allied genera of the Caryophyllaceae.A total of 42 000 herbarium specimens were examined, and plant geographical distributions and morphological and life history characteristics were tested as correlates of disease occurrence. Phylogenetic comparative methods were used to determine the association between disease and plant life-span.Disease was found on 391 herbarium specimens from 114 species and all continents with native Silene. Anther smut occurred exclusively on perennial plants, consistent with the pathogen requiring living hosts to overwinter. The disease was estimated to occur in 80% of perennial species of Silene and allied genera. The correlation between plant life-span and disease was highly significant while controlling for the plant phylogeny, but the disease was not correlated with differences in floral morphology.Using resources available in natural history collections, this study illustrates how disease distribution can be determined, not by restriction to a clade of susceptible hosts or to a limited geographical region, but by association with host life-span, a trait that has undergone frequent evolutionary transitions.

Abiotic conditions, neighbour interactions, and the distribution of Stipa tenacissima in a semiarid mountain range

Abiotic conditions and interactions among plants are important factors determining plant geographical distributions. With the aim of analyzing the distribution of a perennial grass species in a semiarid mountain range, we experimentally tested above- and belowground effects of shrubs on the grass along a gradient of aridity. We measured growth, physiology and reproductive output of Stipa tenacissima tussocks surrounded by intact or manipulated neighbour shrubs. Performance of Stipa improved under mesic conditions, but the net effect of shrubs on Stipa did not change along the gradient. Belowground, we did not find significant effects, suggesting belowground resource partitioning between tussocks and shrubs. Aboveground net effects of shrubs on Stipa were generally positive and independent from abiotic conditions. The improved performance of Stipa at the mesic end of gradient suggests that its absolute physiological optimum lies out of its realized range. Overall, the arid end of the geographical distribution of Stipa in this mountain range may be determined by environmental severity. The coincidence of the upper limit of Stipa with the lower tree limit suggests that the more mesic end of Stipa distribution may depend on other factors; most likely competition with trees, which, unlike shrubs, could be excluding Stipa tenacissima from forests.

Natural genetic variation in acclimation capacity at sub-zero temperatures after cold acclimation at 4 °C in different Arabidopsis thaliana accessions

Freezing tolerance is an important factor in the geographical distribution of plants and strongly influences crop yield. Many plants increase their freezing tolerance during exposure to low, nonfreezing temperatures (cold acclimation) and acclimation may continue at mild freezing temperatures in a process termed sub-zero acclimation. There is considerable natural variation in the cold acclimation capacity of Arabidopsis that has been used to study the molecular basis of this trait, but much less is known about the molecular basis of sub-zero acclimation. Freezing tolerance of detached leaves from the accessions C24, Columbia-0, Rschew, and Tenela was investigated using an electrolyte leakage assay. Sub-zero acclimation could be achieved by shifting plants from 4 °C to −3 °C, or by using detached leaves, either in the presence or absence of ice nucleation. The magnitude of the increase in freezing tolerance depended on both temperature and duration of sub-zero acclimation and while Columbia-0 showed no significant increase in freezing tolerance, the other three accessions increased their freezing tolerance significantly. The levels of several sugars that have been shown to be induced during cold acclimation at nonfreezing temperatures were not strongly changed during sub-zero acclimation and there was no correlation between the increases in freezing tolerance and sugar levels in the different accessions. Expression of the three cold induced CBF transcription factor genes and five of their representative target COR genes was moderately increased during sub-zero acclimation, but again there was no correlation to changes in freezing tolerance, indicating that the genetic and molecular basis of sub-zero acclimation is most likely different from that of cold acclimation at above freezing temperatures. Further studies will be needed to reveal novel signal transduction pathways and protective mechanisms important in sub-zero acclimation.

Chlorophyll fluorescence imaging accurately quantifies freezing damage and cold acclimation responses in Arabidopsis leaves

BackgroundFreezing tolerance is an important factor in the geographical distribution of plants and strongly influences crop yield. Many plants increase their freezing tolerance during exposure to low, nonfreezing temperatures in a process termed cold acclimation. There is considerable natural variation in the cold acclimation capacity of Arabidopsis that has been used to study the molecular basis of this trait. Accurate methods for the quantitation of freezing damage in leaves that include spatial information about the distribution of damage and the possibility to screen large populations of plants are necessary, but currently not available. In addition, currently used standard methods such as electrolyte leakage assays are very laborious and therefore not easily applicable for large-scale screening purposes.ResultsWe have performed freezing experiments with the Arabidopsis accessions C24 and Tenela, which differ strongly in their freezing tolerance, both before and after cold acclimation. Freezing tolerance of detached leaves was investigated using the well established electrolyte leakage assay as a reference. Chlorophyll fluorescence imaging was used as an alternative method that provides spatial resolution of freezing damage over the leaf area. With both methods, LT50 values (i.e. temperature where 50% damage occurred) could be derived as quantitative measures of leaf freezing tolerance. Both methods revealed the expected differences between acclimated and nonacclimated plants and between the two accessions and LT50 values were tightly correlated. However, electrolyte leakage assays consistently yielded higher LT50 values than chlorophyll fluorescence imaging. This was to a large part due to the incubation of leaves for electrolyte leakage measurements in distilled water, which apparently led to secondary damage, while this pre-incubation was not necessary for the chlorophyll fluorescence measurements.ConclusionChlorophyll fluorescence imaging is an alternative method to accurately determine the freezing tolerance of leaves. It is quick and inexpensive and the system could potentially be used for large scale screening, allowing new approaches to elucidate the molecular basis of plant freezing tolerance.