Differential modulation of crown allometry and stem growth at gap edges in five European tree species by drought conditions

Background In Central Europe,forests are increasingly affected by various disturbances,resulting in an increasing gap formation in the canopy.In order to support goal-oriented management,more knowledge is required about the acclimation of the crown and its effects on the basal area growth of trees at the edge of a gap.Methods This work compared trees'growth and crown structure at the edge of a transient gap,with a gap size of more than 80m^(2),with trees in the stand that were at least 30m away from the gap.A total of 249 European beeches(Fagus sylvatica L.),Norway spruces(Picea abies L.Karst),Scots pines(Pinus sylvestris L.),oaks(Quercus spp.;Quercus petraea(Matt.)Liebl.,Quercus robur L.),and silver firs(Abies alba Mill.)were examined on long-term experimental plots in southern Germany.Various crown measures were developed and calculated using high-resolution terrestrial laser scanning(TLiDAR)to capture the three-dimensional crown structures.Growth responses to edge conditions were measured based on tree rings.Using linear mixed models,we predict the basal area increment of edge trees relative to trees in the stand under wet and dry soil moisture conditions after the gap formation.Results We identified i)species-specific acclimation of the crown of edge trees after the gap formation,ii)under wet soil moisture conditions a growth increase of 25%–45%for beech,pine,and oak edge trees and growth losses of 5%–60%for spruce and fir and iii)coniferous tree species benefited from the edge position regarding their basal area increment under dry soil moisture conditions and deciduous tree species grew regardless of the soil moisture conditions at the edge of a gap.Conclusion Gaps have a species-specific effect on the habitus and growth of edge trees and can have both positive and negative impacts on silviculture.

The BEL1-like transcription factor GhBLH5-A05 participates in cotton response to drought stress

Drought stress impairs crop growth and development.BEL1-like family transcription factors may be involved in plant response to drought stress,but little is known of the molecular mechanism by which these proteins regulate plant response and defense to drought stress.Here we show that the BEL1-like transcription factor GhBLH5-A05 functions in cotton(Gossypium hirsutum)response and defense to drought stress.Expression of GhBLH5-A05 in cotton was induced by drought stress.Overexpression of GhBLH5-A05 in both Arabidopsis and cotton increased drought tolerance,whereas silencing GhBLH5-A05 in cotton resulted in elevated sensitivity to drought stress.GhBLH5-A05 binds to cis elements in the promoters of GhRD20-A09 and GhDREB2C-D05 to activate the expression of these genes.GhBLH5-A05 interacted with the KNOX transcription factor GhKNAT6-A03.Co-expression of GhBLH5-A05 and GhKNAT6-A03 increased the transcription of GhRD20-A09 and GhDREB2C-D05.We conclude that GhBLH5-A05 acts as a regulatory factor with GhKNAT6-A03 functioning in cotton response to drought stress by activating the expression of the drought-responsive genes GhRD20-A09 and GhDREB2C-D05.

Effects of Different Exogenous Substances on Seed Germination of Isatis indigotica Under Drought Stress and Chemical Composition of Isatis indigotica leaves

This study was to investigate the effects of three exogenous substances on chemical constituents of Isatis indigotica leavesand their efficacy in alleviating drought stress, and explore the methods of applying exogenous substances to efficient cultivationof Isatis indigotica. Polyethylene glycol (PEG) was used to simulate drought stress to deal with seeds of Isatis indigotica at thegermination stage (concentration: 0, 10%, 15%, and 20%). Simultaneous operation of exogenous growth regulators [microbialinoculum (MI), γ-aminobutyric acid (GABA) and salicylic acid (SA)] and PEG were implemented in seeds of Isatis indigotica.The effects of drought stress and the mitigation of exogenous substances were observed by statistics of seed germination potential,germination rate, hypocotyl length, and radicle length of each treatment. The effects of exogenous substances on the content ofalkaloids, crude protein and free amino acids in the leaves of Isatis indigotica grown in a greenhouse were determined after sprayingexogenous substances on the plants. The differences of germination potential, germination rate, hypocotyl length, and radicle lengthamong 15% PEG stress treatment, 10% PEG stress treatment and the control were significant (P<0.05). According to the predesignedgermination standard, the seeds did not germinate under 20% PEG stress treatment. When the PEG concentration was 15%, the resultsof seed germination potential and germination rate after adding MI were significantly different from those under stress alone (P<0.05).When exposed to 10% PEG stress, the supplementation of GABA led to a notable increase in radicle length of Isatis indigotica seeds,showing significant differences compared to other three treatments. The application of MI and GABA under 15% PEG stress resultedin a significant increase in the radicle and hypocotyl length of Isatis indigotica seeds compared to other two treatments. The contentof the total alkaloids in leaves of Isatis indigotica was significantly increased after spraying GABA. Meanwhile, the contents of crudeprotein and the total free amino acids were kept constant after spraying exogenous substances. Application of MI and GABA couldalleviate drought stress of Isatis indigotica. The content of the total alkaloids in leaves of Isatis indigotica could significantly increaseafter spraying GABA.

Advances in Research of Drought Stress in Major Pinus spp.: A Bibliometric Analysis and Narrative Review

Climate change has caused fluctuations in the frequency and severity of droughts,favoring extended periods of drought associated with anthropic actions and triggering other stressful abiotic effects that threaten terrestrial ecosystems.As climate warming intensifies,drought is a major challenge for forest growth.Pine(Pinus Linn.)is an important genus of forest in the Northern Hemisphere and has a certain tolerance to drought.This article analyzes and reviews the advances in research about drought stress of major Pinus spp.plants in recent years and discusses understanding and future core problems.To adapt to water-deficient environments,pine plants adapt to drought by changing growth traits,closing some stomata on leaves,changing the growth and structure of roots,and adjusting their physiological activities.Moreover,the expression of specific genes is altered,causing changes in the expression of several signaling molecules and metabolites to counteract drought stress.

Comparative genomic analysis of N6-methyladenosine regulators in nine rosaceae species and functional characterization in response to drought stress in pear

N 6-methylated adenine(m6 A)is an emerging epigenetic marker in eukaryotic organisms that plays an important role in biological functions and in enriching genetic information.m6 A exerts these functions via the dynamic interplay among m6 A writers,erasers,and readers.However,little is known about the underlying mechanisms of m6 A in plant growth and stress responses.Here,we identified 276 masked m6 A regulators from nine Rosaceae species(Pyrus bretschneideri,Pyrus betulifolia,Pyrus communis,Malus domestica,Fragaria vesca,Prunus avium,Prunus mume,Prunus persica,and Rubus occidentalis).We classified and named these genes in more detail based on phylogenetic and synteny analysis.The expansion of m6 A regulators in Maloideae was dated back to the recent whole-genome duplication(WGD)in Rosaceae.Based on the expression pattern analysis and gene structure analysis of m6 A regulators,m6 A was shown to be a significant factor in regulating plant development and resistance.In addition,PbrMTA1-silenced pear plants displayed significantly reduced drought tolerance and chlorophyll content,as well as increased electrolyte leakage and concentrations of malondialdehyde and H2 O2.

Salicylic Acid Application Mitigates Oxidative Damage and Improves the Growth Performance of Barley under Drought Stress

Drought is a severe environmental constraint,causing a significant reduction in crop productivity across the world.Salicylic acid(SA)is an important plant growth regulator that helps plants cope with the adverse effects induced by various abiotic stresses.The current study investigated the potential effects of SA on drought tolerance efficacy in two barley(Hordeum vulgare)genotypes,namely BARI barley 5 and BARI barley 7.Ten-day-old barley seedlings were exposed to drought stress by maintaining 7.5%soil moisture content in the absence or presence of 0.5,1.0 and 1.5 mM SA.Drought exposure led to severe damage to both genotypes,as indicated by phenotypic aberrations and reduction of dry biomass.On the other hand,the application of SA to drought-stressed plants protected both barley genotypes from the adverse effects of drought,which was reflected in the improvement of phenotypes and biomass production.SA supplementation improved relative water content and proline levels in drought-stressed barley genotypes,indicating the osmotic adjustment functions of SA under water-deficit conditions.Drought stress induced the accumulation of reactive oxygen species(ROS),such as hydrogen peroxide(H2O2)and superoxide(O_(2)•^(−)),and the lipid peroxidation product malondialdehyde(MDA)in the leaves of barley plants.Exogenous supply of SA reduced oxidative damage by restricting the accumulation of ROS through the stimulation of the activities of key antioxidant enzymes,including superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),ascorbate peroxidase(APX)and glutathione peroxidase(GPX).Among the three-applied concentrations of SA,0.5 mM SA exhibited better mitigating effects against drought stress considering the phenotypic performance and biochemical data.Furthermore,BARI barley 5 showed better performance under drought stress than BARI barley 7 in the presence of SA application.Collectively,our results suggest that SA played a crucial role in improving water status and antioxidant defense strategy to protect barley plants from the deleterious effects of water deficiency.

Different hydraulic strategies under drought stress between Fraxinus mandshurica and Larix gmelinii seedlings

Persistent and severe drought induced by global climate change causes tree mortality mainly due to the hydraulic imbalance of conduit systems,but the magnitude of injury may be species dependent.A water-exclusion experiment was carried out on seedlings of two tree species with distinct characteristics,i.e.,Fraxinus mandshurica and Larix gmelinii to examine hydraulic responses of leaf,stem,and root to drought stress.The two species displayed different hydraulic strategies and related traits in response to drought stress.L.gmelinii reduced its leaf hydraulic conductance by quick stomatal closure and a slow decline in leaf water potential,with a more isohydric stomatal regulation to maintain its water status.In contrast,F.mandshurica was more anisohydric with a negative stomatal safety margin,exhibiting strong resistance to embolism in stem and leafstem segmentation of hydraulic vulnerability to preserve the hydraulic integrity of stem.These differences in hydraulic behaviors and traits between the two species in response to drought stress provide a potential mechanism for their coexistence in temperate forests,including which in the forest modeling would improve our prediction of tree growth and distribution under future climate change.

Inoculation with Pseudomonas spp. Containing ACC-Deaminase Partially Eliminates the Effects of Drought Stress on Growth,Yield,and Ripening of Pea (Pisum sativum L.)

Two preselected plant growth promoting rhizobacteria(PGPR) containing 1-aminocyclopropane-1-carboxylate(ACC) -deaminase(EC 4.1.99.4) were used to investigate their potential to ameliorate the effects of drought stress on growth,yield,and ripening of pea(Pisum sativum L.) . Inoculated and uninoculated(control) seeds of pea cultivar 2000 were sown in pots(four seeds pot-1) and placed in a wire house. The plants were exposed to drought stress at different stages of growth(vegetative,flowering,and pod formation) by skipping the respective irrigation. Results revealed that inoculation of peas with PGPR containing ACC-deaminase significantly decreased the "drought stress imposed effects" on the growth and yield of peas. Exposure of plants to drought stress at vegetative growth stage significantly decreased shoot growth by 41% in the case of uninoculated plants,whereas,by only 18% in the case of inoculated plants compared to nonstressed uninoculated control. Grain yield was decreased when plants were exposed to drought stress at the flowering and pod formation stage,but inoculation resulted in better grain yield(up to 62% and 40% higher,respectively) than the respective uninoculated nonstressed control. Ripening of pods was also delayed in plants inoculated with PGPR,which may imply decreased endogenous ethylene production in inoculated plants. This premise is further supported by the observation that inoculation with PGPR reduced the intensity of classical "triple" response in etiolated pea seedlings,caused by externally applied ACC. It is very probable that the drought stress induced inhibitory effects of ethylene could be partially or completely eliminated by inoculation with PGPR containing ACC-deaminase.

Effects of Drought Stress Simulated by Polyethylene Glycol on Seed Germination, Root and Seedling Growth, and Seedling Antioxidant Characteristics in Job’s Tears

Two Job’s tears cultivars, yy18-1 (high resistance to drought stress) and yy12-7 (susceptible to drought stress) were used to investigate the responses of seed germination, root and seedling growth, and seedling antioxidant characteristics to drought stress simulated by polyethylene glycol (PEG) 6000 solutions with 0, -0.05, -0.1, -0.15, and -0.2 MPa osmotic potentials. The results showed that the germination energy, germination rate, germination index, root and seedling lengths, root and seedling diameters, root and seedling fresh masses, root and seedling dry masses, and seedling relative water content (RWC) decreased with the decrease of the osmotic potential of PEG 6000 solution. The contents of hydrogen peroxide (H2O2), malondialdehyde (MDA), and proline in seedling increased with the decrease of the osmotic potential of PEG 6000 solution. The activities of peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) in seedling increased and then decreased with the decrease of osmotic potential of PEG 6000 solution. -0.1 MPa was the optimal osmotic potential of PEG 6000 solution simulated drought stress at germination stage for Job’s tears. The proline content and activities of POD and CAT were important mechanisms for the maintenance of drought resistance in Job’s tears seedling.

Response Mechanism of Plants to Drought Stress

Drought stress is an important factor affecting plant growth and development.It will provide a theoretical basis for cultivating new stress-resistant varieties and improving water utilization rate of plants by studying the regulation mechanism of osmotic adjustment and water transportation under drought stress,and understanding the physiological and biochemical characteristics and stress resistance mechanism.

The Response of Different Drought-resistance of Wheat Varieties under Drought Stress and the Regulating Role of Nitric Oxygen

[Objective]The aim was to study the response mechanism of drought stress of wheat varieties in different drought-resistance species,and protect the effect of exogenous NO on oxidative damage and photosynthetic apparatus of wheat leaves under drought stress.[Method]Using low-resistance Yumai 949 and high-resistance Xiamai 5 as test materials,drought stress was carried out to seedlings in five-leaf stage with 15% PEG-6000,and then NO（0.75 mmol/L SNP,sodium nitroprusside,exogenous NO donor） was used for regulation in drought condition,and antioxidant and photosynthetic activities was determined.Three treatments were set in the experiment.[Result]SOD,CAT and APX activities of high resistance Xiamai 5 were much higher than low resistance Yumai 949,so were MDA and chlorophyll content.And the change range of these physiological indexes of high resistance species was smaller than high-yielding and low resistance species under drought stress.NO increased the adaptation to drought stress of these physiological indexes significantly.[Conclusion]Exogenous NO could increase the activity of antioxidant enzymes of wheat leaves under drought stress,and enhance the drought resistance of wheat.

Effects of Drought Stress on Osmotic Regulation Substances of Five Catalpa bungei Clones

[Objective] This study aimed to investigate the effects of drought stress on osmotic regulation substances of Catalpa bungei clones. [Method] Potting experimental was carried out with plastic film sealing method, to differentiate the degrees of drought stress based on changes in soil water content and leaf water potential and investigate variations in contents of osmotic regulation substances（free proline,soluble sugar and soluble protein） in leaves of five Catalpa bungei clones under different degrees of drought stresses. [Result] According to changes in soil water content and leaf water potential, the whole process of drought stress was divided into normal level（CK, with soil water content of 97.49% and leaf water potential of-0.54MPa）, light drought（LD with soil water content of 59.96% and leaf water potential of-1.28 MPa）, mediate drought（MD with soil water content of 34.19% and leaf water potential of-2.32 MPa） and severe drought（SD with soil water content of 14.52%and leaf water potential of-2.99 MPa）. The soil water content and leaf water potential of five Catalpa bungei clones reached the highest correlation in exponential fitting, with an average R2of 0.989 3（P0.001）. The free proline content in leaves of five Catalpa bungei clones increased rapidly with the increasing degree of drought stress（P 0.001）. To be specific, free proline contents of Catalpa bungei clones015-1 and 7080 were 34.39 and 33.41 times of the normal level under severe drought conditions, which reached an extremely significant level（P0.001）; the free proline content of Catalpa bungei clone 1-3 rapidly increased to（855.46±227.52） μg/g Fw under light drought conditions. The soluble protein content in leaves showed different variation trends. To be specific, the soluble protein content of Catalpa bungei clone 7080 was the lowest at various drought stages and reached（1.644 ±0.137）mg/g Fw under normal conditions; the soluble protein content of Catalpa bungei clone 1-3 was relatively high under normal conditions and was reduced rapidly under light drought conditions, showing different response patterns. [Conclusion] Osmotic regulation substances in leaves of five Catalpa bungei clones all have certain response to drought stress. Free proline is the most important osmotic regulation substance, followed by soluble protein, while soluble sugar makes no significant contribution. According to changes in content of osmotic regulation substances, Catalpa bungei clone 7080 has relatively high capacity and good drought resistance, while Catalpa bungei clone 1-3 has the rapidest response to drought stress.

Effects of Drought Stress on Morphological and Physiological Indices of New Coix Varieties in Yunnan

In order to study the effects of drought stress on the morphological and physiological indexes of Yunnan Coix at different growth stages, two new varieties of Yunnan Coix Wenyi 4 and Wenyi 5 were used as experimental materials, potted and compared with CK by normal irrigation. Morphological indices such as plant height, stem diameter and physiological indices such as protein, soluble sugar, chlorophyll content and relative conductivity (REC) of the two varieties under drought stress at seedling stage, tillering stage and jointing stage were determined, and data statistics and variance analysis were performed for each index. The results showed that the morphological indices, plant height of Wenyi 4 and Wenyi 5 were significantly affected by drought stress at seedling stage, while the stem diameter was significantly affected by drought stress at seedling and jointing stage. In terms of physiological indices, the relative conductivity, protein and soluble sugar contents of Wenyi 5 increased at a higher degree, whereas chlorophyll content decreased at a higher degree, indicating that Wenyi 5 was greatly affected by drought stress. Through the analysis of drought resistance of the tested materials at different stages by polar ordination method, the results were as follows: jointing stage of Wenyi 5>jointing stage of Wenyi 4>seedling stage of Wenyi 4>seedling stage of Wenyi 5>tillering Stage of Wenyi 4>Tillering Stage of Wenyi 5. For the growth period, the drought resistance was as follows: jointing stage>seedling stage>tillering stage. In conclusion, Wenyi 4 has strong drought resistance and is suitable for droughtresistant cultivation.

RNAi Mediated Drought and Salinity Stress Tolerance in Plants

RNAi mediated gene silencing demonstrated to serve as a defence mechanism against abiotic stress. Some endogenous small RNAs (microRNA and siRNA) have emerged as important players in plant abiotic stress response. Drought and salinity are the major environmental stresses that limit the agricultural food production. miRNA involved in drought and salinity stress response, including ABA response, auxin signalling, osmoprotection and antioxidant defence by downregulating the response target gene. It is observed that some of the microRNAs are upregulated or downregulated in response to drought and salt stress. We reviewed that miR167, miR393, mir474, miR169g are upregulated whereas miR168, miR396, miR397 are downregulated in rice plant during drought stress. Moreover, our detail categorical analysis on the basis of mechanism of action found that miRNA involved in drought stress was 28% in ABA signalling and response, 14.2% in auxin signalling, 9.52% in miRNA processing, 14.2% in cell growth, 9.52% in antioxidant defence, 4.76% in CO2 fixation and 9.52% in osmotic adjustment. Similarly, miRNA involved in salinity stress was 5.8% in auxin signalling, 23.5% in vegetative phase change and root, shoot, leaf and vascular development, 11.76% in gynoecium and stamens development, 8.82% in metabolic adaptation, 2.74% in early embryogenesis and 41.17% not known. Importantly, some common miRNAs such as miR159, miR167, miR169, miR393 and miR397 play an important role in both drought and salinity stress conditions. Here, in this review, we mainly focused on the current status of miRNAs, mechanism of action and their regulatory network during drought and salinity stress in plants.

Physiological Response of Paspalum notatum’s Leaf and Root under Persistent Drought Stress

To investigate the correlation and difference between Paspalum notatum’s leaf and root under drought adversity,this study tested the physiological responses of wild Paspalum notatum’s leaf and root under 0(CK),1,3,5,7,14,21,and 28 d drought stress treatment.These physiological responses include osmotic regulating substance,antioxidant enzyme activity,malonaldehyde content,cell membrane permeability,and chlorophyll content.According to the results,the soluble protein content,proline concentration,malonaldehyde content,cell membrane permeability and CAT activity in Paspalum notatum’s leaf and root tended to increase with the prolongation of drought stress;the soluble sugar content and SOD activity first increased and then decreased;POD dropped gradually;the contents of chlorophyll a,b and total chlorophyll first declined,then mounted,and lastly dropped again.During the early stage of drought stress,SOD and CAT acted as the main antioxidant enzymes in Paspalum notatum’s leaf and root.However,with the aggravation of drought stress the predominant antioxidant enzymes became SOD in the root system whereas CAT and POD in the leaf.It implicates drought has a strong influence on root’s CAT and leaf’s SOD and POD.Leaf is the major organ regulating the osmosis and photosynthesis of Paspalum notatum.The findings can provide a useful theoretical basis for improving Paspalum notatum’s drought tolerance.

Response of photosynthesis,growth,and acorn mass of pedunculate oak to diff erent levels of nitrogen in wet and dry growing seasons

The objective was to examine the effects of optimal leaf nitrogen levels>2.0%and suboptimal levels<2.0%,nitrogen nutrition on net photo synthetic rate,stem diameter increment,height growth increment and acorn mass of pedunculate oak during 2010 in the absence of drought stress and during 2011 under the impact of moderate drought stress.According to the results,moderate drought stress significantly reduced net photo synthetic rate,stem diameter increment and height growth increment,while acorn mass was not affected.Suboptimal nitrogen nutrition significantly reduced the net photo synthetic rate and stem diameter increment only in the wet year,acorn mass in both wet and dry years,while height growth increment was not significantly reduced by suboptimal nitrogen nutrition in either year.The results indicate that optimal nitrogen levels can stimulate photo synthetic rate and stem diameter increment of pedunculate oak only in the absence of moderate drought stress.Moreover,the results show that moderate drought stress is a more dominant stressor for photosynthesis and growth of pedunculate oak than suboptimal nitrogen nutrition,while for acorn development,it is the more dominant stressor.

Larch growth across thermal and moisture gradients in the Siberian Mountains

Climate-driven changes in the thermal and moisture regimes may variously influence different tree species growth and ranges.We hypothesize that drought resistant Siberian larch(Larix sibirica Ledeb.)and precipitation-sensitive Siberian pine(Pinus sibirica Du Tour)responded differently to climate change along the elevational thermal and precipitation gradients.We studied the influence of air temperature,precipitation,soil moisture,and atmospheric drought(indicated by the drought index SPEI)on larch and pine growth along the southward megaslope of the West Sayan Ridge.We found that since 2000 climate change resulted in increasing larch and pine radial growth index(GI)(c.1.5–3times)within treeline(2000–2300 m)and timberline(1900–2000 m)ecotones,i.e.within high precipitation zones.Within the forest-steppe ecotone(1100–1200 m)in which L.sibirica is the only species,larch GI stagnated or even decreased.The total forested area increased since 2000 up to+50%in the high elevations,whereas in the low elevations(<1400 m)area changes were negligible.Within treeline and timberline,trees’GI was stimulated by summer temperature.Meanwhile,temperature increase in early spring reduces GI due to living tissue activation followed by tissue damage by desiccation.Within forest-steppe,larch radial growth was mostly dependent on soil moisture.Warming shifted dependence on moisture to the early dates of the growing period.Acute droughts decreased GI within forest-steppe as well as within treeline,whereas the drought influence on both species within highlands was insignificant.Within forest-steppe seedlings establishment was poor,whereas it was successful within treeline and timberline.Current climate change leads to stagnation or even decrease in Larix sibirica growth in the southern lowland habitat.In combination with poor seedlings establishment,reduced growth threatens the transformation of open lowland forests into forest-steppe and steppe communities.Meanwhile,in the highlands warming facilitated the growth of Siberian larch and pine and the increase of forested area.

干旱胁迫对紫叶紫薇容器苗生长及生理的影响

为探究干旱胁迫对紫叶紫薇容器苗的生长及生理影响,以紫叶紫薇优良新品种‘丹红紫叶’2年生容器苗为研究对象,设计了5个干旱胁迫强度处理,测定不同干旱胁迫处理对容器苗生长及生理相关指标的影响。结果表明:干旱胁迫对紫叶紫薇容器苗的生长及生理的影响显著。随着干旱胁迫强度增加,紫叶紫薇容器苗叶片相对含水量、过氧化物酶活性、超氧化物歧化酶活性、可溶性蛋白含量、净光合速率、气孔导度、蒸腾速率总体上呈现降低趋势,重度干旱时这些指标分别比正常供水显著下降了21.45%、40.45%、31.92%、3.30%、81.25%、89.29%、87.17%,极重度干旱时达到最低值。可溶性糖含量、脯氨酸含量、丙二醛含量随着干旱胁迫程度增强而一直上升,重度干旱时分别比正常供水显著增加了122.92%、74.98%、288.34%,极重度干旱时达到最大值。随着干旱胁迫强度加重,过氧化氢酶活性、叶绿素相对含量、水分利用效率呈现先升高后降低的趋势,中度干旱时过氧化氢酶活性最大,叶绿素相对含量和水分利用效率则是轻度干旱最高,极重度干旱时最低。胞间CO_(2)浓度随着干旱胁迫加强而先降后升,正常供水的胞间CO_(2)浓度最高,中度干旱最低。紫叶紫薇容器苗具有抵御中度干旱的能力,当土壤相对含水量下降至30%~35%时应及时给苗木浇水灌溉。

3种玉兰幼苗生长和生理特性对干旱胁迫的响应

【目的】研究干旱胁迫下天女木兰、望春玉兰、红花玉兰‘娇红2号’的生长和生理变化,揭示3种玉兰幼苗对干旱胁迫的响应机理,评价3种玉兰的抗旱性,为干旱地区引种、推广提供参考。【方法】以3种玉兰的2年生盆栽播种苗为试验材料,设置4个处理水平(土壤相对含水量80%~90%(CK),60%~70%(T_(1)),40%~50%(T_(2)),20%~30%(T_(3))),干旱胁迫50 d后分析生长、生理等19个指标的变化。【结果】(1)中度和重度干旱胁迫(T_(2)、T_(3))显著降低了3种玉兰的地径和各器官生物量增长量,显著增大了望春玉兰和红花玉兰‘娇红2号’的根冠比(P<0.05);重度干旱胁迫下(T_(3)),红花玉兰‘娇红2号’的株高和各器官生物量增长量显著高于望春玉兰(P<0.05);(2)与CK相比,T_(1)处理时红花玉兰‘娇红2号’叶绿素含量增加,其他干旱水平3种玉兰叶绿素含量逐渐降低;3种玉兰丙二醛含量、可溶性糖含量、可溶性蛋白含量、超氧化物歧化酶和过氧化氢酶活性随干旱加剧逐渐增加,T_(3)与CK均存在显著差异;望春玉兰脯氨酸含量先降低后升高,天女木兰和红花玉兰‘娇红2号’脯氨酸含量随干旱加剧呈上升趋势;3种玉兰过氧化物酶活性随干旱加剧变化规律不同,天女木兰过氧化物酶活性T_(2)处理最高,望春玉兰和红花玉兰‘娇红2号’T_(3)处理最高。(3)红花玉兰‘娇红2号’T_(1)处理净光合速率、胞间CO_(2)浓度、蒸腾速率最高,较CK分别高出2.67%、1.94%、3.09%,气孔导度和水分利用效率随干旱加剧逐渐降低;重度干旱胁迫(T_(3))显著降低了天女木兰和望春玉兰的净光合速率、胞间CO_(2)浓度、蒸腾速率、气孔导度、水分利用效率(P<0.05)。(4)隶属函数分析表明,3种玉兰抗旱性强弱为天女木兰>红花玉兰‘娇红2号’>望春玉兰。【结论】干旱胁迫影响了3种玉兰幼苗的生长和生理活性,使叶片细胞结构受损,植株生长缓慢,但植物能通过调节渗透调节物质含量和自身保护酶活性来抵御干旱,维持自身的正常生理代谢功能。综合各指标可知,天女木兰抗旱性最强,望春玉兰最弱。

植物生长剂对高温胁迫后黑木耳菌丝生长的影响

以黑木耳品种‘89-1’为试材,在40℃高温胁条件下,测定添加FA、NAA、6-BA、GA和IAA植物生长剂不同培养基的黑木耳菌丝长势和生长速度,研究了5种植物生长剂对高温胁迫后黑木耳菌丝生长及显微结构的影响,以期为黑木耳品种选育和生产实践提供参考依据。结果表明:不同植物生长剂对黑木耳菌丝长势和生长速度均有一定的影响,其中添加了GA的培养基,在25℃和40℃高温培养环境下,对黑木耳菌丝生长均有促进作用,当浓度配比为15×10^(-7)mg·mL^(-1)时,对高温胁迫后的黑木耳菌丝修复效果最佳。