Wet Climate Population Research Articles

The acclimation potential of Acacia longifolia to water stress: Implications for invasiveness

The ability of an invasive species to establish and spread to new areas may depend on its ability to tolerate a broad range of environmental conditions. Due to climate change, increasing occurrences of extreme events such as droughts are expected in the Mediterranean region and invasive species may expand if they cope with water stress. Limited information is available on the responses of Acacia longifolia, one of the most aggressive plant species in Portuguese coastal sand dune ecosystems, to prolonged water stress. In this study, we exposed A. longifolia plants from two distinct populations, one from the wet (northern) and another from the dry (southern) climate regions of Portugal, to drought conditions, and monitored morphological, physiological and biochemical responses. One-month-old seedlings were submitted to three different water treatments which involved watering twice a week, every 7 days and every 10 days, respectively, for three months, under controlled conditions. Overall, the progressive drought stress significantly affected most of the growth parameters considered, except the root:shoot ratio. Water stress also increased the uptake of ions (Ca2+, Mg2+, K+ and Na+) and N concentration. On the contrary, the C/N ratio decreased under water stress conditions. Isotopic analysis did not reveal significant differences in δ13C with water treatments but the same pattern was not observed in δ15N values. Compared with the wet climate population, the dry climate population showed somewhat differing responses to water stress, indicating a genetic difference between populations. These results provide insights into limitations and opportunities for establishment of A. longifolia in a drought-prone scenario.

Water deficit affects mesophyll limitation of leaves more strongly in sun than in shade in two contrasting Picea asperata populations

The aim of this study was to examine the response of internal conductance to CO(2) (g(i)) to soil water deficit and contrasting light conditions, and their consequences on photosynthetic physiology in two Picea asperata Mast. populations originating from wet and dry climate regions of China. Four-year-old trees were subjected to two light treatments (30% and 100% of full sunlight) and two watering regimes (well watered, drought) for 2 years. In both tested populations, drought significantly decreased g(i) and the net photosynthesis rate (A) and increased carbon isotope composition (delta(13)C) values in both light treatments, in particular in the sun. Moreover, drought resulted in a significantly higher relative limitation due to stomatal conductance (L(s)) in both light treatments and higher relative limitation due to internal conductance (L(i)) and abscisic acid (ABA) in the sun plants. The results also showed that L(i) (0.26-0.47) was always greater than L(s) (0.12-0.28). On the other hand, drought significantly decreased the ratio of chloroplastic to internal CO(2) concentration (C(c)/C(i)), photosynthetic nitrogen utilization efficiency (PNUE) and total biomass in the sun plants of the wet climate population, whereas there were no significant changes in these parameters in the dry climate population. Our results also showed that the dry climate population possessed higher delta(13)C values with higher ratio of internal conductance to stomatal conductance (g(i)/g(s)), suggesting that increasing the g(i)/g(s) ratio enhances water-use efficiency (WUE) in plants evolved in arid environments. Thus, we propose that the use of the g(i)/g(s) parameter to screen P. asperata plants with higher water deficit tolerance is certainly worthy of consideration. Furthermore, g(i) is an important variable, which reflects the population differences in PNUE, and it should thus be included in plant physiological investigations related to leaf economics.

Leaf morphological and physiological responses to drought and shade in two Populus cathayana populations

Cuttings from two contrasting Populus cathayana Rehder populations originating from Hanyuan (wet climate) and Ledu (dry climate) in western China were grown in a greenhouse to determine the effects of drought, shade and their interaction on the morphological and physiological traits of leaves. The dry climate population was more droughttolerant than the wet climate population, as indicated by smaller decreases in the leaf relative water content (RWC) and net photosynthetic rate (PN), as well as by greater increases in antioxidative enzyme activities and free proline content under drought. On the other hand, the negative effects of shade on leaf traits were more pronounced in the dry climate population, which suggested that the dry climate population was more light-demanding. In addition, moderate shade alleviated the drought stress of P. cathayana not only by improving the leaf RWC but also by maintaining the positive carbon balance. In contrast, severe shade aggravated drought stress as indicated by a pronounced decrease in leaf size, carbon and nitrogen contents, maximum PN, free proline content and antioxidative enzyme activities.

Physiological and proteomic responses of two contrasting Populus cathayana populations to drought stress

The acclimation of plants to water deficit is the result of many different physiological and biochemical mechanisms. To gain a better understanding of drought stress acclimation and tolerance mechanisms in Populus cathayana Rehder, we carried out an integrated physiological and comparative proteomic analysis on the drought stress responses of two contrasting populations originating from wet and dry regions in western China. The plantlets were subjected to continuous drought stress by withholding soil water content at 25% of field capacity (FC) for 45 days, while the control treatments were kept at 100% FC. Drought stress significantly inhibited plant growth, decreased net photosynthetic rate and stomatal conductance of leaves, increased the relative electrolyte leakage and malondialdehyde (MDA) content, and, at the same time, accumulated soluble sugars and free proline in both populations tested. The population from the dry climate region exhibited stronger tolerance to drought stress compared with the wet climate population. The proteomic analyses resulted in the identification of 40 drought-responsive proteins. The functional categories of these proteins include the regulation of transcription and translation, photosynthesis, cytoskeleton, secondary metabolism, HSPs/chaperones, redox homeostasis and defense response. The results suggest that poplars' tolerance to drought stress relates to the control of reactive oxygen species (ROS) and to osmoprotective capacity. The differential regulation of some drought-responsive proteins, such as HSPs and the enzymes related to redox homeostasis and regulation of secondary metabolism, plays an important role in poplars' tolerance and acclimation to drought stress. In conclusion, acclimation to water deficit involves changes in cellular metabolism and the regulation of gene networks. The present study not only provides new insights into the mechanisms of acclimation and tolerance to drought stress in different poplar populations but also provides clues for improving poplars' drought tolerance through breeding or genetic engineering.

Adaptive responses to progressive drought stress in two Populus cathayana populations

The young, vegetatively propagated cuttings of Populus cathayana Rehder were exposed to a progressive drought stress for 12 weeks in a greenhouse to characterize the physiological and biochemical basis of drought adaptation in woody plants. Two contrasting populations were employed in our study, which were from the wet and dry climate regions in western China, respectively. The results showed that the adaptive responses of P. cathayana to drought were affected by drought intensity and poplar genotype (population). The progressive drought stress significantly inhibited plant growth, increased carotenoid contents and, at the same time, accumulated soluble sugars and free proline in the plants of both populations tested. On the other hand, the gradually increasing drought also induced antioxidative systems including the increase of the activities of superoxide dismutase (SOD) and guaiacol peroxidase (POD). Moreover, there were different responses to progressive drought stress between the two contrasting populations. Compared with the wet climate population, the dry climate population had lower shoot height and growth rate, higher free proline content, and more efficient photoprotective system (such as higher carotenoid content and Car/Chl) and antioxidant system (such as higher POD activity), as a result of drought stress. These results suggest that the dry climate population possesses better drought tolerance than the wet climate population. The differences in drought tolerance may be closely related with efficient photoprotective system, accumulation of the osmoprotectant proline as well as the increased capacity of the antioxidative system to scavenge reactive oxygen species, and the consequent suppressed level of lipid peroxidation under drought conditions.

Effect of Mn toxicity on morphological and physiological changes in two Populus cathayana populations originating from different habitats

The cuttings of Populus cathayana were exposed to four different manganese (Mn) concentrations (0, 0.1, 0.5 and 1 mM) in a greenhouse to investigate the toxicity of Mn and the detoxifying responses of woody plants. Two contrasting populations of P. cathayana, which were from wet and dry climate regions in western China, respectively, were examined in our study. The results showed that high concentration of Mn caused significant decrease in shoot height, biomass accumulation, and leaf number and leaf areas. Injuries to the anatomical features of leaves were also found as the reduced thickness of palisade and spongy parenchyma, the decreased density in the conducting tissue and the collapse and split in the meristematic tissue in the central vein. Moreover, Mn treatments caused the accumulation of hydrogen peroxide (H2O2), and then resulted in oxidative stress indicated by the oxidation of proteins and DNA. Many physiological responses were employed to cope with the toxicity of Mn, including the increase in the contents of non-protein thiol (NP-SH), phytochelatins (PCs) and phenolics compounds and the stimulated activities of guaiacol peroxidase (GPX) and polyphenol oxidase (PPO) for the chelation of Mn and for the antioxidation of reactive oxygen species. The population from dry climate habitat showed a lower leaf concentration of Mn, higher contents of the chelators, and higher activities of GPX and PPO than did the wet climate population at the same Mn treatment, thereby possessing a superior Mn tolerance. In both populations, most of the Mn was accumulated in the shoot, which is favorable regarding phytoremediation.

Interactions between water deficit, ABA, and provenances in Picea asperata

The effects of exogenous abscisic acid (ABA) on the acclimation of Picea asperata to water deficit were investigated in two populations originating from wet and dry climate regions of China. Exogenous ABA was sprayed onto the leaves, and changes in plant growth and structure, gas exchange, water use efficiency (WUE), endogenous ABA content, and antioxidant enzyme levels were monitored. The results demonstrated that ABA application affected the two P. asperata populations in different ways during the water deficit. ABA application resulted in significantly lower CO(2) assimilation rates (A) under water deficit in plants from the wet climate population, whereas there were no significant changes in this parameter in the dry climate population. On the other hand, ABA application significantly decreased the dry shoot biomass, stomatal conductance (g(s)), transpiration rate (E), and malondialdehyde (MDA) content, and it significantly increased the leaf mass per area (LMA), root/shoot ratio (Rs), fine root/total root ratio (Ft), WUE, ABA content, and the superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) activities under water-deficit conditions in the dry climate population, whereas ABA application did not significantly affect these parameters in the wet climate population. The results clearly demonstrated that sensitivity to an exogenous ABA application is population-dependent in P. asperata. Direct evidence is presented that variation in physiological mechanisms rather than different rates of ABA absorption explain the population differentiation in the sensitivity to exogenous ABA, and that the physiological basis for the amplified response to water deficit caused by exogenous ABA, present mainly in the dry climate population, is related to internal ABA accumulation. These results provide evidence for adaptive differentiation between populations of P. asperata, and they support the expected relationship between environmental heterogeneity and the magnitude of plastic responses in plant populations.

Physiological responses to drought and enhanced UV-B radiation in two contrastingPicea asperatapopulations

The responses of two Picea asperata Mast. populations to enhanced ultraviolet B (UV-B) radiation under well-watered and drought conditions were investigated to further elucidate the effect of UV-B radiation on drought tolerance. Two P. asperata populations originating from wet- and dry-climate regions in China were employed. Drought significantly decreased the CO2assimilation rate, stomatal conductance, and effective photosystem II quantum yield, while it significantly increased nonphotochemical quenching and the activity of superoxide dismutase in both populations. Compared with the wet-climate population, the dry-climate population was more acclimated to drought stress and showed much higher superoxide dismutase and ascorbate peroxidase activities and much lower levels of malondialdehyde and electrolyte leakage. Enhanced UV-B radiation also induced a significant decrease in chlorophyll content in both populations under well-watered conditions and a significant increase in UV-absorbing compounds in the wet-climate population. After exposure to different UV-B radiation levels and watering regimes over one growing season, the increases in malondialdehyde and electrolyte leakage, which are indicators of damage to the cellular membrane induced by drought, were less pronounced under the combination of enhanced UV-B radiation and drought than they were under well-watered conditions without enhanced UV-B radiation. In addition, an additive effect of drought and UV-B radiation on the CO2assimilation rate and stomatal conductance was observed in the wet-climate population and on the activity of ascorbate peroxidase and nonphotochemical quenching in the dry-climate population. These results suggest that the UV-B exposure may have alleviated some of the damage induced by drought.

Physiological and biochemical responses to high Mn concentrations in two contrasting Populus cathayana populations

We exposed the cuttings of Populus cathayana to Hoagland's solution containing four different manganese (Mn) concentrations (0, 0.1, 0.5 and 1mM) in a greenhouse to characterize the physiological and biochemical basis of Mn resistance in woody plants. Two contrasting populations of P. cathayana were used in our study, which were from the wet and dry climate regions in western China, respectively. The results showed that Mn treatments significantly decreased chlorophyll content and growth characteristics, including shoot height, basal diameter, biomass accumulation and total leaf area in the two populations. Mn treatments also significantly increased the levels of abscisic acid (ABA), polyamines and free amino acids especially proline (Pro), histidine (His) and phenylalanine (Phe) available for cellular signaling and heavy metal chelation. In addition, high Mn concentrations also caused oxidative stress indicated as the accumulation of hydrogen peroxide (H(2)O(2)) and malondialdehyde (MDA) contents. On the other hand, there were different responses to Mn stress between the two contrasting populations. Compared with the dry climate population, the wet climate population accumulated more Mn in plant tissues especially in leaves; it showed lower tolerance index and more pronounced decrease in growth and chlorophyll contents. The wet climate population not only accumulated less ABA, putrescine and free amino acids, but also exhibited lower activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX), thus suffering from more serious oxidative damage. Therefore, our results showed that the wet climate population was more susceptible to Mn stress than the dry climate population.

Differences in some morphological, physiological, and biochemical responses to drought stress in two contrasting populations of Populus przewalskii

The cuttings of Populus przewalskii Maximowicz were exposed to three different watering regimes (100, 50, and 25% of the field capacity) in a greenhouse to characterize the morphological, physiological, and biochemical basis of drought tolerance in woody plants. Two contrasting populations of P. przewalskii were used in our study, which were from the wet and dry climate regions in western China, respectively. The results showed that there were significant differences in responses to three different watering regimes in both populations tested; drought not only significantly affected dry mass accumulation and partitioning but also significantly decreased chlorophyll pigment contents and accumulated free proline and total amino acids. On the other hand, drought also significantly increased the levels of abscisic acid, hydrogen peroxide, and superoxide radical as secondary messengers to induce the entire set of antioxidative systems including the increase of reduced ascorbic acid (ASA) content and the activities of superoxide dismutase, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase (GR). Moreover, there were different responses to drought stress between the two contrasting populations of P. przewalskii. Compared to the wet climate population, the dry climate population showed lower dry matter accumulation and partitioned more biomass to root systems, and accumulated more free proline and total amino acids for osmotic adjustment. The dry climate population also showed more efficient antioxidant systems with higher content of ASA and higher activities of ascorbate peroxidase and GR than the wet climate population.

Physiological responses to drought and shade in two contrasting Picea asperata populations

The responses of photosynthetic gas exchange, chlorophyll fluorescence, activities of antioxidant enzymes and lipid membrane peroxidation of two contrasting Picea asperata Mast. populations to 30% of full sunlight (shade) and full sunlight (sun) were investigated under well‐watered and drought conditions. Two contrasting populations were from the wet and dry climate regions in China, respectively. For both populations tested, drought resulted in lower needle relative water content (RWC), CO2 assimilation rate (A), stomatal conductance (gs) and effective PSII quantum yield (Y), and higher non‐photochemical quenching (qN), superoxide dismutase (SOD), ascorbate peroxidase (APX) activities as well as malondialdehyde (MDA) levels and electrolyte leakage in sun plants, whereas these changes were not significant in shade plants. For the wet climate population, shade plants showed higher chlorophyll contents (Chla, Chlb and Chla + b) than sun plants under both well‐watered and drought conditions. Our study results implied that shade, applied together with drought, ameliorated the detrimental effects of drought. On the other hand, compared with the wet climate population, the dry climate population was more tolerant to drought in the sun treatment, as indicated by less decreases in A and mass‐based leaf nitrogen content (Nmass), more responsive stomata, greater capacity for non‐radiative dissipation of excitation energy as heat (analysed by qN), and higher level of antioxidant enzyme activities as well as lower MDA content and electrolyte leakage. These results demonstrated that the different physiological strategies were employed by the P. asperata populations from contrasting climate regions when the plants were exposed to drought and shade.

Sex-specific physiological and growth responses to water stress in Hippophae rhamnoides L. populations

Dioecious plant species and those occupying diverse habitats may present special analytical problems to determine effects of environmental stress. Here, sex-specific physiological and growth responses of two contrasting sea buckthorn (Hippophae rhamnoides L.) populations were recorded after exposure to different watering regimes. The populations used were from wet and dry climate regions in China, respectively. In the semi-controlled environmental study, the well-watered and water-deficiency plants which were watered to 100 % and 50 % field capacity were used, respectively. Sexual differences in height growth (HT), dry matter accumulation (DMA), root/shoot ratio (RS), specific leaf area (SLA), net photosynthesis (A), transpiration (E), instantaneous water use efficiency (WUEi) and carbon isotope composition (δ13C) between the male and female individuals were detected under water-deficiency treatment in both populations tested. However, these sexual differences were not detected under well-watered treatment. On the other hand, compared with the wet climate population, the dry climate population showed lower HT, DMA, SLA, A and E, and higher RS under both watering regimes. The dry climate population also showed higher WUEi and δ13C as affected by water deficit than the wet climate population. These morphological and physiological responses to drought showed that the different populations and the different sexual individuals may employ different survival strategies under environmental stress. The male individuals and the dry climate population would have a conservative water-use strategy in response to drought stress.

Different responses of two contrasting Populus davidiana populations to exogenous abscisic acid application

Purpose of this study was to investigate different responses of two contrasting Populus davidiana populations to exogenous abscisic acid (ABA) application under well-watered and water-stressed conditions, and to further elucidate the role of ABA in drought tolerance. Two contrasting populations were from the wet and dry climate regions in China, respectively. Exogenous ABA was applied to the leaves by spraying and changes in plant growth and structure, gas exchange, endogenous ABA concentration and water use efficiency were monitored. The results demonstrated that exogenous ABA application significantly decreased height growth (Ht), total biomass (Tb), total leaf area (La), specific leaf area (Sla), net photosynthesis (A) and transpiration (E), and significantly increased root/shoot ratio (Rs), transpiration efficiency (WUE T), instantaneous water use efficiency (WUE i) and carbon isotope composition ( δ 13C) under well-watered and water-stressed conditions. These morphological and physiological responses to exogenous ABA application showed that ABA could play an important role to control drought tolerance in P. davidiana populations. However, distinct population differences were found in ABA-induced growth reduction, gas exchange decrease and water use efficiency increase. Compared with the wet climate population, the dry climate population was more responsive to exogenous ABA application, resulting in lower Ht, Tb, La, Sla, A and E, and higher Rs, WUE T, WUE i and δ 13C under all experimental treatments. Our results provide strong evidence for adaptive differentiation between populations of P. davidiana.

Population differences in physiological and morphological adaptations of Populus davidiana seedlings in response to progressive drought stress

Population differences in dry matter accumulation and allocation, gas exchange, abscisic acid content and water use efficiency of Populus davidiana seedlings were measured after exposure to well-watered and progressive drought stress treatments. Three populations used were form dry, middle and wet climate regions, respectively. Significant differences in height growth (Ht), total biomass (Tb), total leaf area (La), root/shoot ratio (Rs), specific leaf area (Sla), net photosynthesis ( A), transpiration ( E) and instantaneous water use efficiency (WUE i) between the populations were detected under two watering regimes; population differences in abscisic acid content (ABA) and carbon isotope composition ( δ 13 C ) were also detected under progressive drought stress treatment, but these differences were not significant under well-watered treatment. Compared with the wet climate population, the dry climate population had lower Ht, Tb, La, Sla, A and E, and higher Rs and WUE i. On the other hand, the dry climate population also exhibited higher ABA and δ 13 C as effected by drought stress than the wet climate population. These morphological and physiological adaptations to water availability showed that the different populations may employ different survival strategies under drought stress at the initial phase of seedling growth and establishment. The wet climate population possesses a prodigal water use strategy and quick growth, while the dry climate population exhibits a conservative water use strategies and slow growth. These differences in drought responses may be used as criteria for genotype selection in different climate regions.