Free proline accumulation in rice plants under different leaf water potential

Seedlings of drought-tolerance rice varieties Han 501and Han A03,and the drought sensitive varietiesNanjing 11 and Yanjing 2 were raised in a paddyfield and transplanted into pots at the age of 8leaves.Water stress started at the tillering stage byholding water from 0 MPa of the soil water potentialin pots till the leaves showed seriously wilting.

Responses of Native Tree Species to Soil Water Stress in a Tropical Forest on Limestone,Vietnam

Forests over limestone in the tropics have received little attention and limestone forests in Vietnam have been overlooked to an even greater extent in terms of tree physiology. In Ba Be National Park, Vietnam, soil water availability in limestone forests seems to be the most limiting factor in the dry season. Therefore, in order to enhance the preliminary knowledge of choosing native tree species for enrichment planting in the restoration zone, characteristics of the 20 native tree species to soil water stress were investigated in a limestone forest. One-ha plot each consisting of twenty-five 20 m × 20 m plots was established in undisturbed forests. All trees ≥ 10 cm DBH were measured in 20 m × 20 m plots, while twenty-five 5 m × 5 m subplots were established in order to sample the regeneration of tree species with a DBH < 10 cm. The Scholander apparatus and freezing point osmometry were used in order to measure the leaf water potential (Ψw) and leaf osmotic potential (Ψπ) of the 20 native tree species, respectively in this study. 61 species belonging to 34 families of all trees with a DBH ≥ 10 cm were recorded in one ha, while 31 species representing 18 families of trees < 10 cm DBH were identified in 625 m2. The 20 species’ leaf water and osmotic potential values revealed significant differences among species. The maximum leaf water potential was not affected by any anticipated sources of variation, while the minimum water potential, however, showed significant variation to soil water stress. The results in the study area emphasized the importance of water factors in influencing tree species distribution;it could be concluded that native species with wide water potential ranges would be better able to withstand water changes and might be thus good candidates for reforestation (enrichment planting) in limestone areas.

Morphophysiological responses of forest seedling species subjected to different water regimes

Water availability is a limiting factor for the establishment and development of forest species.To understand the appropriate conditions for the initial post-transplanting phase,it is necessary to understand the specific morphophysiological characteristics of the species,such as the leaf water potential and the efficiency of photosystemⅡ.We aimed to identify the influence of different water regimes on the morphophysiological aspects of young plants of two forest species(Cedrela.fissilis Vellozo and Eucalyptus saligna Sm.).Two greenhouse experiments were conducted for 28 days;one for each species.The design was completely randomized,and the treatments consisted of six different water regimes.Leaf water potential(Ψw)and chlorophyll a fluorescence were evaluated every 7 days.At the end of the experiment,morphological attributes(height,collection diameter,root volume,and dry matter)were measured and histological blades were made.The water demand of E.saligna was higher than that of C.fissilis and required greater replacement within a shorter period.The rehydration fromΨw=-2 Mpa allowed for a fast recovery of the young C.fissilis plants(Ψw=-1.5,Fv/Fm=0.796),which indicated good physiological plasticity of this species when submitted to water stress at a level that is not severe.The total dry matter allocation was different among species.Seedlings of E.saligna presented the best responses when submitted to a continuous water supply regime,while C.fissilis seedlings presented the best response under intermittent irrigation conditions.

Water adaptive traits of deep-rooted C_3 halophyte(Karelinia caspica(Pall.) Less.) and shallow-rooted C_4 halophyte(Atriplex tatarica L.) in an arid region,Northwest China

This paper focused on the water relations of two halophytes differing in photosynthetic pathway, phe- notype, and life cycle： Karelinia caspica （Pall.） Less. （C3, deep-rooted perennial Asteraceae grass） and Atriplex tatarica L. （C4, shallow-rooted annual Chenopodiaceae grass）. Gas exchange, leaf water potential, and growth characteristics were investigated in two growing seasons in an arid area of Xinjiang to explore the physiological adaptability of the two halophytes. Both K. caspica and A. tatarica showed midday depression of transpiration, in- dicating that they were strong xerophytes and weak midday depression types. The roots of A. tatarica were con- centrated mainly in the 0-60 cm soil layer, and the leaf water potential （~L） increased sharply in the 0-20 cm layer due to high soil water content, suggesting that the upper soil was the main water source. On the other hand, K. caspica had a rooting depth of about 1.5 m and a larger root/shoot ratio, which confirmed that this species uptakes water mainly from deeper soil layer. Although A. tatarica had lower transpiration water consumption, higher water use efficiency （WUE）, and less water demand at the same leaf water potential, it showed larger water stress impact than K. caspica, indicating that the growth of A. tatarica was restricted more than that of K. caspica when there was no rainfall recharge. As a shallow-rooted C4 species, A. tatarica displayed lower stomatal conductance, which could to some extent reduce transpiration water loss and maintain leaf water potential steadily. In contrast, the deep-rooted C3 species K. caspica had a larger root/shoot ratio that was in favor of exploiting groundwater. We concluded that C3 species （K. caspica） tapes water and C4 species （A. tatarica） reduces water loss to survive in the arid and saline conditions. The results provided a case for the phenotype theory of Schwinning and Ehleringer on halophytic plants.

Hydraulic role in differential stomatal behaviors at two contrasting elevations in three dominant tree species of a mixed coniferous and broad-leaved forest in low subtropical China

Quantifying the variation in stomatal behavior and functional traits of trees with elevation can provide a better understanding of the adaptative strategies to a changing climate. In this study, six water-and carbon-related functional traits were examined for three dominant tree species, Schima superba, Pinus massoniana and Castanopsis chinensis, in a mixed coniferous and broad-leaved forest at two elevations(70 and 360 m above sea level,respectively) in low subtropical China. We hypothesized that trees at higher elevations would develop more efficient strategies of stomatal regulations and greater water transport capacity to cope with more variable hydrothermal conditions than those at lower elevations. Results show that the hydraulic conductivity did not differ between trees at the two elevations, contrary to our expectation. The C. chinensis trees had greater values of leaf mass per unit area(LMA), and the S. superba and C. chinensis trees had greater values of wood density(WD),relative stem water content(RWC), and ratio of sapwood area to leaf area(Hv) at the 360-m elevation than at 70-m elevation. The mean canopy stomatal conductance was greater and more sensitive to vapor deficit pressure at360 m than at 70 m for both S. superba and C. chinensis, while stomatal sensitivity did not differ between the two contrasting elevations for P. massoniana. The midday leaf water potential(ψL) in P. massoniana was significantly more negative at 360 m than at 70 m, but did not vary with increasing elevation in both S. superba and C. chinensis.Variations in Hvcan be related to the differential stomatal behaviors between the two elevations. The variations of stomatal behavior and ψLwith elevation suggested the isohydric strategy for the two broad-leaved species and the anisohydric strategy for the conifer species. The species-specific differences in LMA, WD, RWC, and Hvbetween the two elevations may reflect conservative resource use strategies at the higher elevation. Our findings revealed a close relationship between hydraulic and stomatal behavior and may help better understand the functional responses of forests to changing environmental conditions.

Morphological and physiological responses to drought stress of carob trees in Mediterranean ecosystems

The greatest failure rate of reforestation programs is basically related to water deficit,especially at the seedling stage.Therefore,the main objective of this work is to investigate the responses of three accessions of carob trees(Ceratonia siliqua L.)with 2-year-old from different climate regions to drought generated by four water treatments:Tc(250 mm),T1(180 mm),T2(100 mm),and T3(50 mm).The first accession(A1)comes from the protected national park of Ichkeul in northern Tunisia.This zone belongs to the bioclimatic sub-humid stage.The second accession(A2)comes from Melloulech,located in the center-east of Tunisia,belonging to the bioclimatic semi-arid stage.The third accession(A3)comes from the mountain of Matmata,located in the south of Tunisia,belonging to the bioclimatic hyper-arid stage.The experiment was undertaken in a greenhouse.Gaz exchange indices(net photosynthesis(A),stomatal conductance(gs),transpiration rate(E),and internal CO_(2) concentration(Ci))were determined.Predawn(Ψpd)and midday(Ψmd)leaf water potentials,relative soil water content(SWC),and morphological parameters(plant height(H),number of leaves(NL),number of leaflets(Nl),and number of branches(NB))were estimated.The results showed that significant differences(P<0.001)were found between physiological and morphological parameters of each accession.The highest growth potential was recorded for Tc treatment in both accessions A1 and A2.Significant decreases in gs,E,Ci,and SWC were recorded with the increases in water stress applied from treatment T1 to T3.Positive and significant correlations were found between SWC andΨpd for all studied accessions.Ψpd andΨmd decreased as water stress increased,ranging from–0.96 to–1.50 MPa at sunrise and from–1.94 to–2.83 MPa at midday,respectively,under control and T3 treatments.C.siliqua accessions responded to drought through exhibiting significant changes in their physiological and morphological behavior.Both accessions A1 and A2 showed greater drought tolerance than accession A3.These seedlings exhibit different adaptive mechanisms such as stress avoidance,which are aimed at reducing transpiration,limiting leaf growth,and increasing root growth to exploit more soil water.Therefore,C.siliqua can be recommended for the ecological restoration in Mediterranean ecosystems.

Panicle Water Potential,a Physiological Trait to Identify Drought Tolerance in Rice

Two upland rice varieties （IRAT109, IAPAR9） and one lowland rice variety （Zhenshan 97B） were planted in summer and treated with both normal （full water） and drought stress in the reproductive stage. Panicle water potential （PWP） and leaf water potential （LWP） were measured every 1.0-1.5 h over 24 h on sunny days. Both PWP and LWP of upland varieties started to decrease later, maintained a higher level and recovered more quickly than that of the lowland variety. The results show that PWP can be used as an indicator of plant water status based on the parallel daily changes, and the high correlation between PWP and LWP. Similar correlations were also observed between PWP, LWP and eight traits related to plant growth and grain yield formation. PWP seemed to be more effective for distinguishing the upland rice varieties with different drought-tolerant ability. Differences in PWP and LWP between upland and lowland rice varieties were also observed at noon even under normal water conditions, implying the incorporation of the drought-tolerant mechanism to improve the photosynthesis and yield of traditional paddy rice.

Effect of Pre-Anthesis Drought Hardening on Post-Anthesis Physiological Characteristics,Yield and WUE in Winter Wheat

A drought event can cause yield loss or entire crops to fail.In order to study the effects of continuous drought on physiological characteristics,yield,and water use efficiency(WUE)of winter wheat(Triticum aestivum L.),the variety“Zhoumai 22”was grown in controlled water conditions of the pot-planted winter wheat under a mobile rainout shelter.Foot planting and safe wintering were used to evaluate,winter wheat under different drought conditions,including light,moderate and severe drought at the jointing,heading,and filling stages.The soil water content was controlled at 60–70%,50–60%,or 40–50%of field capacity.Experimental trials included 3 pre-anthesis drought hardening,3 three-stage continuous drought,and 1 test control conditions.Under drought stress conditions,winter wheat leaf water potential,soil plant analysis development(SPAD),photosynthesis parameters,and yield declined due to pre-anthesis drought hardening.And the degree of decline:continuous drought>pre-anthesis drought hardening.Changes in the post-anthesis photosynthetic capacity of winter wheat were mainly related to the pre-anthesis drought level,rather than post-anthesis rehydration.The threshold of non-stomata limiting factors caused by photosynthesis at the filling stage is 40–50%FC,while comprehensive yield and WUE affected,the yield in severe drought treatments was the most significant,B3C3 and B3C3G3 decreased by 55.68%and 55.88%,respectively.Pre-anthesis drought was the main reason for the decreased crop yield.Thus,severe drought should be avoided during planting,while pre-anthesis light drought is a suitable choice for watersaving and crop production,as proper pre-anthesis drought hardening(60–70%FC)is feasible and effective.

Short-term responses to salinity of seabuckthorn (Hippophae rhamnoides L.) seedlings in the extremely cold and saline Qinghai region of China

The investigation of the mechanisms of plant adaptation to stressor action is one of the leading directions of current biological studies. To understand the mechanism of salt tolerance of seabuckthom （Hippophae rhamnoides L.） and identify its ability to cope with the salinity effect in the saline and extremely cold region of Qinghai, China, a test was conducted with two-year-old seedlings subjected to 0, 200, 400 and 600 mmol·L^-1 NaClsolutions for 30 d. The results show that with an increase in salinity, the biomass of H. rhamnoides seedlings clearly decreased. Leaf water potential （ψw） and relative water content （RWC） were significantly reduced under salinity, with severe water shortages appearing in leaves. At the same time, the total chlorophyll content declined markedly. When salinity increased and stress time prolonged, the net CO2 assimilation rate （A） significantly declined. Intercellular CO2 concentration （Ci） declined at first and was then followed by an increase over the stress time. We conclude that H. rhamnoides grown in the extremely cold and saline region of Qinghai has a certain resistance to salt, which can be planted at appropriate salinity levels.

Responses of nighttime sap flow to atmospheric and soil dryness and its potential roles for shrubs on the Loess Plateau of China

Aims Nocturnal sap flow(E_(night))has been observed in a variety of plant species and environmental conditions.In water-limited environ-ments,E_(night) is important in the regulation of plant water’s physi-ology.This study was designed to evaluate the way in which E_(night)(defined as sap flow from 20:30 to 06:00)responded to changes in the atmospheric vapor pressure deficit(VPD)and the soil water con-tent(SWC),and explored its potential physiological significance for different plant species in a semi-arid area.Methods We selected three shrub species:Vitex negundo L.(VN),Hippophae rhamnoides L.(HR)and Spiraea pubescens Turcz(SP)in the semi-arid Loess Plateau of China.The plots of the three communities dominated by each of three species were on the same hill slope.Half-hourly sap flow density was measured in six to seven sample stems for each species during the main grow-ing season(June to August 2015).VPD,SWC,leaf water potential(Ψleaf)and stomatal conductance(G_(s))were measured at the same time.Regression analyses were conducted to determine the rela-tionships between E_(night),E_(day),E_(night)/E_(daily),VPD and SWC at half-hourly and daily time scales,as well as between E_(night),E_(day) andΨleaf.Important Findings The mean values of E_(night) and E_(day) were higher,but E_(night)/E_(daily) val-ues were lower for VN compared to HR and SP.The responses of sap flow density to VPD and SWC varied at different temporal scales.VPD was the dominant factor that affected E_(night) and E_(day) at the half-hourly scale for all three species.In contrast,SWC was the key factor that influenced E_(day) at the daily time scale.The values of E_(day) and E_(night)/E_(daily) correlated negatively with SWC because the effect of SWC was stronger on E_(day) than on E_(night).Although the low fraction of E_(night)/E_(daily)(4%-7%)may indicate a minor short-term effect of E_(night) on the standing water balance,E_(night) had eco-physiologically significance to the plants.The discrepancy inΨleaf between sunset and the following day’s predawn(ΔΨ)indicated that stem refilling occurred during this period.SP had the higher fraction of recharge water among the three species,as it had the relatively higher value ofΔΨ/E_(night).E_(night) had positive relation-ship with predawn Gs.The increased Gs facilitated rapid onset of photosynthesis in the early morning.In addition,the positive correlation between E_(night) and E_(day) from 06:00 to 10:30 suggested that E_(night) was beneficial for transpiration in the following morning.The responses of E_(night) to VPD and SWC indicated differences in plant adaptation to drought stress,which provides important infor-mation for our understanding of the reactions to climate changes among species in semi-arid areas.

Non-invasive water status detection in grapevine(Vitis vinifera L.)by thermography

Grapevines are preferentially grown under mild to moderate water stress conditions to achieve the best compromise between wine quality and quantity.Water status detection for advanced irrigation scheduling is frequently done by predawn leaf water potential(ΨPD)or leaf stomata conductance(gL)measurements.However,these measurements are time and labor consuming.Therefore,the use of infrared thermography(IRT)opens up the possibility to study large population of leaves and to give an overview on the stomatal variation and their dynamics.In the present study IRT was used to identify water stress of potted grapevines.In order to define the sensitivity of IRT measurements to water stress,the IRT-based water status information were compared with simultaneously measuredΨPD and gL data.Correlations between IRT-based CWSI data on the one hand and gL andΨPD on the other showed the potential of IRT for water stress detection.However,the CWSI calculation procedure is laborious and the sensitivity of CWSI for water stress detection still needs to be improved.Therefore,further improvements are necessary in order to apply remote IRT-based systems for irrigation scheduling in the field.

Mediterranean sea cliff plants:morphological and physiological responses to environmental conditions

Aims The plants of Mediterranean sea cliff ecosystems are resistant to several environmental challenges.In this study,six species typical of the coastal rocky cliffs have been analyzed in order to evaluate their diverse morphological and physiological responses to their environment across the seasons,and to examine the strategy of the ecological group to which each species belongs.Since these species are widespread across the Mediterranean region,our aim was also to highlight their ecophysiological features in habitats where the direct influence of the sea is stronger.Methods The selected species are characteristic of the sea cliffs of Elba island(Tyrrhenian sea,Italy):the halophyte Crithmum maritimum,the semideciduous Helichrysum italicum and Lavandula stoechas and the sclerophylls Myrtus communis,Quercus ilex and Rhamnus alaternus.Four morphological traits-canopy height,leaf area,specific leaf area and leaf dry matter content-and two physiological traits-leaf water potential(LWP)and photosynthetic efficiency(PE),measured before the dawn and at midday-were analyzed.Water potential was measured by a pressure chamber and photosynthetic efficiency was determined by the analysis of chlorophyll fluorescence.Plant performance was also evaluated by calculating chronic(PIchr)and dynamic photoinhibition(PIdyn).Important Findings Crithmum maritimum showed high resistance to the recurrent dry periods,because of the high water storage capacity of its leaves and its PE declined markedly only in July,under the harshest climatic conditions.Semideciduous taxa utilize primarily an avoidance strategy,which aims at reducing the overall leaf surface,while sclerophylls mostly show a tolerance strategy towards the prevailing stressors,as demonstrated by LWP and PE,that are lower in the sclerophylls than in the semideciduous taxa during summer,due to osmoregulation and photoinhibition,respectively.Furthermore,variability of physiological parameters was higher in the sclerophylls than in the semideciduous taxa,because the former had to withstand wider oscillations of their LWP and PE.The sclerophyllous taxa underwent a slight loss of PE also in winter,likely owing to the combined action of low temperature and high irradiance.In Mediterranean sea cliff ecosystems,the stressful combination of high irradiance,high temperatures and low rainfall typical of the summer season may have been intensified by the shallow soil which displays a poor water storage capacity.On the other hand,winter stress,caused by high solar radiation and low temperatures,does not seem to seriously affect the performance of the studied species.