Water Statuses Research Articles

Confined water redistribution governs nanomechanical property changes of cement pastes curing at different air pressures

The water status within concrete under low air pressure (AP) condition has been reported to affect the long-term properties of concrete in plateau regions, however, the underlying mechanism for the microstructural changes is not fully understood yet. In this paper, the confined water statuses within cement pastes curing at 98% RH and different APs (i.e. 101 kPa, 60 kPa, and 20 kPa) were first demonstrated and then correlated to the nanomechanical property changes of calcium-silicate-hydrates (C-S-H) phase by means of the 1H NMR relaxometry and nanoindentation techniques. The results show that low AP conditions increase the evaporable water content and drive the water movement from interlayer spaces to gel pores during wetting at 98% RH. According to the nanoindentation investigations, low AP conditions increase the volume fraction of high-density (HD) C-S-H and improve the nanomechanical and creep characteristics and bending strength of hardened cement pastes, which is attributed to the water redistribution within C-S-H phase.

Water partitioning and migration in unsaturated bentonites by low‐field NMR characterization

AbstractWater behavior in bentonite clay pores is influenced by soil–water interaction mechanisms such as capillary and adsorptive forces. Quantitative measurement of these water statuses remains challenging, leading to the adoption of advanced techniques. This study uses low‐field nuclear magnetic resonance (NMR) technique to investigate water partitioning dynamics and changes in the water state in sodium‐rich Wyoming bentonite and calcium‐rich Denver bentonite under various humidity conditions. NMR T2 relaxation and T1–T2 mapping techniques, along with a multi‐Gaussian decomposition method, enable a quantitative analysis of capillary and adsorptive water in both bentonites. A conceptual water partitioning model is derived to explain water molecule trajectories of water molecules under unsaturated conditions. Our findings indicate distinct transitions in hydrated layers for Na+‐smectite and Ca2+‐smectite at different relative humidity (RH) ranges. Characteristic T2 ranges are identified for capillary and adsorptive water in both clays and provide valuable insights into their water behavior. This study advances our understanding of soil properties at different RH environments and highlights the potential of low‐field NMR techniques in characterizing capillary and adsorptive water in bentonite clays.

Differentiating nutritional and water statuses in Hass avocado plantations through a temporal analysis of vegetation indices computed from aerial RGB images

Maximizing crop production efficiently and sustainably through plant health monitoring is key for global food security. Monitoring large areas with remote sensing technologies such as unmanned aerial vehicles (UAVs) with sensors deals with time and money issues; however, the usage of advanced sensors such as hyperspectral, multispectral and thermal cameras limit their usage among all the stakeholders. In this study we explore different vegetation indices (VIs) extracted from aerial RGB images acquired in different flights to differentiate the nutritional and water statuses of Hass avocado plantations. We used an image processing workflow consisting of image selection through a convolutional neural network (CNN) model, tree crown segmentation, color correction and feature extraction to automate the computation of VIs from RGB images. To compare the performance of VIs in the differentiation of nutritional and water statuses, we proposed a comparison metric called Mean Distance between Vegetation Indices (MDVI), analyzed the evolution of the extracted features, and studied their relationships with gold standard Normalized Difference Vegetation Index (NDVI) measurements. Since the extracted features from each group vary from flight to flight due to multiple factors such as the light intensity of each season and the phenological stage of the plant, the proposed comparison metric leverages the differences between the features extracted from each group, thus reducing these temporal effects. We found that Modified Green Red Vegetation Index (MGRVI) allows a better differentiation of nutritional and water statuses. Furthermore, the correlation coefficients of this VI in the three statuses and NDVI for nitrogen group range between 0.63 and 0.85, indicating a positive strong relationship. The results of this work show that MGRVI has a potential to be used as a correlation variable in studies that only use RGB sensors in order to monitor the nutritional and water status of crops.

Drought Stress Induced the Flavonoid Content in Moringa (Moringa oleifera Lam.) Leaves

Flavonoid is one of the most widely available bioactive compounds presence in the Moringa (Moringa oleifera Lam.) leaves. Osmotic stress is known to induce flavonoid production, however, the water level varies among plant species. This study aimed to examined the effects of water stress levels on the flavonoid content of Moringa leaves. The plants were treated withholding watering at three intervals (I): i.e.,: 1 (as control), 3 and 7 days based on the evaporated water during the treatments. The drought treatments were given within 4 different periods (D) before the plants were harvested, i.e.,: 8, 16, 24 and 32 days, and measured for the growth and biomass, proline (Pro) and chlorophyll (Chl) content, leaf water potential (WP), leaf relative water content (RWC), quercetin (Q) and kaempferol (K) content, and water use efficiency of flavonoid (WUEf). The results showed that the drought treatments induced different water statuses in the plants by decreases the leaf relative water content (RWC) and leaf water potential (WP) and increases of proline content significantly (up to 3 fold). Growth and biomass production decreased with the increase of water stress, whereas flavonoid content increased when the drought was mild and decreased again under severe drought. The highest content of flavonoids (1314.53 mg/kg leave biomass for Q and 2984.15 mg/kg leave biomass for K) and WUEf were shown when the plants were treated with 3 days drought for 16 days periods before the plants were harvested (I2D2) with no significant reduction in leaf biomass. This result suggests that the treatment of I2D2 is the best for bioactive production in Moringa.

Combinational Variation Temperature and Soil Water Response of Stomata and Biomass Production in Maize, Millet, Sorghum and Rice

Environmental responses of stomatal conductance (gs) as basic information for a photosynthesis-transpiration-coupled model have been increasing under global warming. This study identified the impact of gs behavior under different soil water statuses and temperatures in rice, maize, millet, and sorghum. The experiments consisted of various soil moisture statuses from flooding to drying and combination of soil moisture status and temperature. There was a reduction in shoot biomass of maize and sorghum caused by decreasing of gs, photosynthesis (A), and transpiration (E) in early imposed waterlogging without dependent temperature, whereas millet and rice were dependent on temperature variation. The effect of gradual soil drying, gs, A, and E of maize, millet, and sorghum were caused by low temperature, except rice. The impact of the combination of various soil water statuses and temperatures on gs is important for the trade-off between A and E, and consequently shoot biomass. However, we discovered that an ability to sustain gs is essential for photo assimilation and maintaining leaf temperature through evapotranspiration for biomass production, a mechanism of crop avoidance in variable soil water status and temperature.

N2O Emission and Nitrification/Denitrification Bacterial Communities in Upland Black Soil under Combined Effects of Early and Immediate Moisture

Soil moisture is the major factor influencing microbial properties and nitrous oxide (N2O) production. Agricultural soils can be probed under wetting, wet/dry alternating, and constant moisture conditions to evaluate the combined effects of early (previous) and immediate (current) moisture on N2O emission and nitrification/denitrification. In view of the water history of upland black soil, five moisture regimes comprising different antecedent and present water holding capacity (WHC) levels were set up in the microcosm study. The 20% WHC was adopted as the initial legacy moisture, while three immediate water statuses include constant WHC, dry-wet cycle, and incremental moisture. Quantitative PCR and 16S rRNA amplicon sequencing were used to assess the impact of current and previous moisture on the bacterial community composition and abundance of nitrification/denitrification genes (amoA, nirS, and nosZ); the soil physicochemical properties, and N2O emission were monitored. The N2O production and nitrifying-denitrifying microbial communities were influenced by the antecedent moisture and pattern of the dry-wet cycle. The nitrifying-denitrifying microbial communities, especially members of β-/γ-Proteobacteria, Bacteroidetes and Gemmatimonadetes, in black soil were important in explaining the variation of N2O production. The key taxonomic groups in response to the moisture alteration, e.g., Acidobacteria, Sphingobacteriia, Deltaproteobacteria, Methylobacterium, Gemmatimonas and Pseudarthrobacter, etc., were also highlighted. The soil nitrate, ammonium nitrogen, N2O emission, nitrification/denitrification and mineralization were profoundly impacted by water regimes and showed statistically significant correlation with specific bacterial genera; the nitrite/nitrate reduction to ammonium could be boosted by high moisture. Both nitrifier denitrification and heterotrophic denitrification could be enhanced substantially when the black soil moisture was increased to above 60% WHC. These findings help evaluate the effects of the water mode on the N2O emission from black soil, as well as the associated impacts on both soil fertility and the global environment.

Detecting tree water stress using a trunk relative water content measurement sensor

Irrigation water management in tree crops requires timely and accurate determination of crop water status for making irrigation scheduling decisions. However, commonly used techniques for measuring tree water statuses, such as stem water potential measured with pressure chambers or leaf stomatal conductance measured with porometers, are manually operated and lack the timeliness for making irrigation decisions in real-time. The objective of this research was to develop and field test a new electronic sensor system capable of continuously monitoring tree trunk relative water content. Replicated sensors were installed in experimental orchards planted with pomegranate and nectarine trees. Data collected from the sensor readings were compared with periodic trunk diameter, stem water potential, and leaf stomatal conductance measurements. Strong linear correlations were observed between sensor readings and tree trunk diameter variations but with a 3–4-hour phase lag. Sensor readings were also strongly correlated to stem water potential (R2 = 0.58-0.85) and leaf stomatal conductance (R2 = 0.60-0.84) for both pomegranate and nectarine trees. The next step is to further validate the sensors in commercial orchards and apply the sensors for making real-time irrigation water management decisions.

Responsiveness of Early Response to Dehydration Six-Like Transporter Genes to Water Deficit in Arabidopsis thaliana Leaves.

Drought is one of the main abiotic stresses, which affects plant growth, development, and crop yield. Plant response to drought implies carbon allocation to sink organs and sugar partitioning between different cell compartments, and thereby requires the involvement of sugar transporters (SUTs). Among them, the early response to dehydration six-like (ESL), with 19 members in Arabidopsis thaliana, form the largest subfamily of monosaccharide transporters (MSTs) still poorly characterized. A common feature of these genes is their involvement in plant response to abiotic stresses, including water deficit. In this context, we carried out morphological and physiological phenotyping of A. thaliana plants grown under well-watered (WW) and water-deprived (WD) conditions, together with the expression profiling of 17 AtESL genes in rosette leaves. The drought responsiveness of 12 ESL genes, 4 upregulated and 8 downregulated, was correlated to different water statuses of rosette leaves. The differential expression of each of the tandem duplicated AtESL genes in response to water stress is in favor of their plausible functional diversity. Furthermore, transfer DNA (T-DNA) insertional mutants for each of the four upregulated ESLs in response to water deprivation were identified and characterized under WW and WD conditions. To gain insights into global sugar exchanges between vacuole and cytosol under water deficit, the gene expression of other vacuolar SUTs and invertases (AtTMT, AtSUC, AtSWEET, and AtβFRUCT) was analyzed and discussed.

Response of leaf water potential, stomatal conductance and chlorophyll content under different levels of soil water, air vapor pressure deficit and solar radiation in chili pepper (Capsicum chinense)

Flood and drought have been increasing due to global climate changes and these extreme water-related events often affect crop productions globally. This study aims to develop a growth simulation model that correspond to sequential soil water status by revealing morph-physiological related responses on the chili pepper (Capsicum spp.). Two experiments were conducted in a greenhouse and nine treatments were established between dry and waterlogged soil conditions by using a slope field with sand. Results showed leaf water potential and stomatal conductance decreased with increasing soil water stress level. On the other hand, chili pepper increased total chlorophyll content and decreased chlorophyll a/b ratio to compensate the redaction of the leaf area as a response to soil water stress. Moreover, high air vapor pressure deficit and solar radiation condition influenced their morph-physiological traits as environmental stress coupled with soil water stress. A multiple regression model for estimating shoot dry weight (SDW) using plant height (PH) and soil plant analysis development (SPAD) was developed (SDW = 0.131 PH + 0.047SPAD − 2.408). It showed a high coefficient of determination (R2adj = 0.836). This model is certainly useful for estimating SDW under wide range soil water statuses and vapor pressure deficit conditions.

Monitoring fruit daily growth indicates the onset of mild drought stress in apple

This work tests the possibility to monitor fruit growth as a potential physiological indicator for tree water status and productive performance in apple, for potential implementation in decision support systems for irrigation scheduling. Starting from 10 weeks after full bloom (WAFB), a wide range of plant water statuses was induced in a “Gala” apple orchard by applying different shading (with red-50%, white-50%, and black-20% nets) and irrigation levels (severe-SS, moderate-MS and no-NS stress). For each net*irrigation treatment combination, midday stem water potential (mSWP) was assessed weekly, while fruit diameter variations were continuously monitored using automatic fruit gauges, from 10 WAFB until harvest. Leaf gas exchanges were also monitored at 14 and 16 WAFB. As expected, the different net*irrigation treatment combinations widely affected mSWP, leaf gas exchanges and fruit growth. On all dates of measurement, leaf gas exchanges were tightly correlated with mSWP, while daily fruit growth showed significant but weaker correlations with mSWP. In all cases, these relationships indicated the onset of drought stress below the threshold of about 1.2 g fruit−1 day−1, which corresponded to mSWP below -1 MPa. Almost no correlation was found between mSWP and the other parameters derived from the fruit daily growth pattern (midday, maximum and minimum absolute growth rates (AGR) and fruit shrinkage). Based on these results, we can conclude that, although fruit daily growth rate is not related to mSWP as tightly as leaf gas exchanges, it represents a promising physiological indicator to be implemented in a decision support system for irrigation scheduling. Specific fruit growth thresholds indicating the onset of drought should be defined, depending on the orchard conditions and productive target.

Imaging analysis of chlorophyll fluorescence induction for monitoring plant water and nitrogen treatments

The objective of this study was to check whether different water and nitrogen treatments and, even the water-nitrogen coupling effect of plants could be correctly differentiated via chlorophyll a fluorescence image. We developed a classification method using the imaging analysis of chlorophyll a fluorescence induction based on Artificial Neural Network. The measurements were carried out on scheffera octophylla (Lour.) Harms, and the images were recorded at 690 nm with a high-resolution imaging device consisting of LEDs for an excitation at 460 nm and an Electron-Multiplying CCD camera. The effect of three different water and three different nitrogen treatments on the fluorescence parameters were obtained by hundreds of time-resolved fluorescence images. We used a Radial Basis Function neural network to model and test the sample data. The results showed that the different water and nitrogen statuses of plants were identified by the chlorophyll a fluorescence images and showed a high recognition accuracy. Compared with nitrogen, water had more of an influence on chlorophyll a fluorescence and was easier to identify. However, because the water and nitrogen restrict and promote each other, studying the coupling effect of water and nitrogen is necessary. Nine levels of water-nitrogen coupling plants were tested and classified. We discovered that a significant decrease on the classified accuracy was observed for the high nitrogen and low nitrogen treatments, while under a medium N-supply, the recognition rate was high. The method in this paper allowed plants to be classified under different water and nitrogen treatments, and has the potential to monitor the water and nitrogen coupling effect of plants in situ.

Sequence of Changes in Maize Responding to Soil Water Deficit and Related Critical Thresholds.

The sequence of changes in crop responding to soil water deficit and related critical thresholds are essential for better drought damage classification and drought monitoring indicators. This study was aimed to investigate the critical thresholds of maize growth and physiological characteristics responding to changing soil water and to reveal the sequence of changes in maize responding to soil water deficit both in seedling and jointing stages based on 2-year’s maize field experiment responding to six initial soil water statuses conducted in 2013 and 2014. Normal distribution tolerance limits were newly adopted to identify critical thresholds of maize growth and physiological characteristics to a wide range of soil water status. The results showed that in both stages maize growth characteristics related to plant water status [stem moisture content (SMC) and leaf moisture content (LMC)], leaf gas exchange [net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs)], and leaf area were sensitive to soil water deficit, while biomass-related characteristics were less sensitive. Under the concurrent weather conditions and agronomic managements, the critical soil water thresholds in terms of relative soil moisture of 0–30 cm depth (RSM) of maize SMC, LMC, net Pn, Tr, Gs, and leaf area were 72, 65, 62, 60, 58, and 46%, respectively, in seedling stage, and 64, 64, 51, 53, 48, and 46%, respectively, in jointing stage. It indicated that there is a sequence of changes in maize responding to soil water deficit, i.e., their response sequences as soil water deficit intensified: SMC ≥ LMC > leaf gas exchange > leaf area in both stages. This sequence of changes in maize responding to soil water deficit and related critical thresholds may be better indicators of damage classification and drought monitoring.

Contribution of high-resolution remotely sensed thermal-infrared imagery to high-throughput field phenotyping of an apple progeny submitted to water constraints

The genetic variability of fruit trees in response to drought stress is scarcely studied. As adaptation of scion cultivars to abiotic constraints constitutes a new challenge for fruit production, in particular where water scarcity is likely to occur, development of high-throughput phenotyping strategies applicable in the field to assess the tree response to soil drought among large populations is needed, overcoming the limitations of usual in-planta measurements. In this research, remotely sensed images were acquired by ultra-light aircraft (ULA) and an unmanned aerial vehicle (UAV) during 4 years in a field trial where an apple progeny (122 hybrids) was studied under contrasted summer irrigation regimes. Ortho-images were simultaneously acquired in visible (RGB), near-infrared (NIR) and thermalinfrared (TIR) bands. After rthorectification, georeferencing and mosaicking, RGB and NIR images were used to compute different vegetation indices over the field trial, while TIR imaging allowed extraction of the vegetation surface temperature (Ts), which was calibrated at ground level by using hot and cold reference targets. The Morans'f water deficit index (WDI), which combines the surface minus air temperature (Ts-Ta) and the normalized difference vegetation index (NDVI), was used as a stress phenotypic variable. WDI estimates the ratio of actual to maximal evapotranspiration (WDI=1.ETact/ETmax) in discontinuous plant covers. Like the Ts-Ta variable, it significantly discriminated the tree water statuses and genotypes. On the basis of different plant- and image-based indices, individual tree behaviour trends (isohydric vs. anisohydric) can be distinguished among the progeny, irrespective of tree vigour. This opens potential applications for plant breeding, and genetic bases of apple tree response to water stress are currently investigated through quantitative trait locus (QTL) detection. Making use of ULA with flights performed at 40-60 m altitude made it possible to strongly improve the TIR image resolution ('10 cm) and to limit the number of vegetation/soil mixed pixels. However, it will require careful image posttreatment, possibly including classification and/or segmentation.

Water resources management: traditional technology and communities as part of the solution

Abstract. Rajasthan, the largest State in India, has one of the most critical water statuses. Rajasthan, with more than 10.4 % of the country’s geographical area, supports more than 5.5 % of the human population and 18.70 % of the livestock, but only has 1.16 % of the total surface water available in the country. More than 60 % of the state is a part of the Great Thar Desert, and of the total 142 desert blocks in the country, 85 blocks are in the state of Rajasthan. The per capita annual water availability in the state is about 780 m3, compared with the minimum requirement of 1000 m3. It is feared that the availability would fall below 450 m3 by the year 2050. Thus, increasing population coupled with erratic rainfall further aggravates the water crisis. It is possible to harvest and augment water resources through the construction of small water harvesting structures called johads and the implementation of local water governance. This has been amply demonstrated by the successful experience of local communities in Alwar District in Rajasthan. Since 1985, 8600 johads have been built in 1086 villages. This has resulted in the rise in water levels in the shallow aquifer, increase in the area under single and double crops, increase in forest cover and drinking water supply security. The water collected in a johad during the monsoon penetrates into the sub-soil. This recharges the groundwater and improves the soil moisture in vast areas. The water in the johad can be used directly for irrigation, drinking water by animals, and other domestic purposes. The other advantage of this structure is that it checks soil erosion, mitigates floods, and ensures water availability in wells or boreholes used for drinking water supply, even for several successive drought years. Also, during the dry season when the water gradually recedes in the johad, the land inside the johad itself becomes available for cultivation.

Stress indicators based on airborne thermal imagery for field phenotyping a heterogeneous tree population for response to water constraints.

As field phenotyping of plant response to water constraints constitutes a bottleneck for breeding programmes, airborne thermal imagery can contribute to assessing the water status of a wide range of individuals simultaneously. However, the presence of mixed soil-plant pixels in heterogeneous plant cover complicates the interpretation of canopy temperature. Moran's Water Deficit Index (WDI = 1-ETact/ETmax), which was designed to overcome this difficulty, was compared with surface minus air temperature (T s-T a) as a water stress indicator. As parameterization of the theoretical equations for WDI computation is difficult, particularly when applied to genotypes with large architectural variability, a simplified procedure based on quantile regression was proposed to delineate the Vegetation Index-Temperature (VIT) scatterplot. The sensitivity of WDI to variations in wet and dry references was assessed by applying more or less stringent quantile levels. The different stress indicators tested on a series of airborne multispectral images (RGB, near-infrared, and thermal infrared) of a population of 122 apple hybrids, under two irrigation regimes, significantly discriminated the tree water statuses. For each acquisition date, the statistical method efficiently delineated the VIT scatterplot, while the limits obtained using the theoretical approach overlapped it, leading to inconsistent WDI values. Once water constraint was established, the different stress indicators were linearly correlated to the stem water potential among a tree subset. T s-T a showed a strong sensitivity to evaporative demand, which limited its relevancy for temporal comparisons. Finally, the statistical approach of WDI appeared the most suitable for high-throughput phenotyping.

Validation of thermal indices for water status identification in grapevine

The use of thermal imaging represents a substantial progress in monitoring plant water status and therefore drought stress in field conditions. However, the effective use of thermal imaging requires consistent methods for data acquisition and image analysis. We determined the temperature variation of grapevine canopies by the use of thermal imaging in a proximal manner, and calculated stomatal conductance index (IG) and crop water stress index (CWSI), aiming to assess the plant water status that was measured as variations in stomatal conductance. The study was conducted in a hillside commercial vineyard with Graciano (Vitis vinifera L.) vines grown under two different water statuses. Leaf stomatal conductance was measured to determine plant water status and indices derived from individual grapevine leaves, clusters and canopies were assessed by thermal imaging. Measurements were carried out under different light conditions (sunlit and shaded part of the canopy) and at different times of the day (morning, midday and afternoon) to analyze the robustness and sensitivity of thermal imaging for detecting changes in a range of plant water status and experimental conditions.Highly significant correlations were found between the calculated indices (IG and CWSI) and the measured stomatal conductance. The strongest relationships between IG and CWSI and the measured stomatal conductance were obtained at midday, on the shaded side of the grapevine canopy. Therefore, those sampling conditions were the most appropriate to estimate variation in stomatal conductance in a non-contact manner through the use of thermal imaging.Furthermore, the sensitivity of berry temperature to changes in grapevine water status was quantified. The acquired thermal images for vine clusters were corrected for berry emissivity, which was estimated to be 0.96. For water stressed grapevines, berry temperature was increased as much as 1–2°C above clusters from non-water stressed grapevines, thus potentially affecting berry composition.

Sap flow and trunk maximum daily shrinkage (MDS) measurements for diagnosing water status of Populus euphratica in an inland river basin of Northwest China

ABSTRACTUsing sap flow flux density and trunk maximum daily shrinkage (MDS) as the main plant‐based water stress indicators and combined with soil salinity parameters and plant population characteristics, water statuses of Populus euphratica were diagnosed. Based on these parameters, optimal groundwater depth for maintaining the development of natural P. euphratica were explored in middle and lower reaches of the Tarim River. When excluding the impact of soil salinity and climatic factors, our results demonstrated that sap flow flux density in P. euphratica decreases with increase groundwater depth and that such a negative correlation is significant. It also showed that MDS has a significant positive correlation with groundwater depth. When the water table depth reached 4.5–5.0 m, our study showed a significant reduction in sap flow flux density changes of P. euphratica apparent and increasing MDS, indicating that the growth of P. euphratica is under drying stress, and the plant adapts to the environment through reducing transpirational water consumption by self‐regulation. When water table is in the range of 4–6 m, the populations characteristics (coverage, density and frequency) of P. euphratica under different groundwater depth reached the maximums. We conclude that groundwater depth between 4.5 and 5.0 m is the optimum restoring P. euphratica and its ecosystem in the middle and lower reaches of the Tarim River. Copyright © 2013 John Wiley & Sons, Ltd.

Relationship between photochemical reflectance index and leaf ecophysiological and biochemical parameters under two different water statuses: towards a rapid and efficient correction method using real‐time measurements

The use of the photochemical reflectance index (PRI) as a promising proxy of light use efficiency (LUE) has been extensively studied, and some issues have been identified, notably the sensitivity of PRI to leaf pigment composition and the variability in PRI response to LUE because of stress. In this study, we introduce a method that enables us to track the short-term PRI response to LUE changes because of photosynthetically active radiation (PAR) changes. The analysis of these short-term relationships between PRI and LUE throughout the growing season in two species (Quercus robur L. and Fagus sylvatica L.) under two different soil water statuses showed a clear change in PRI response to LUE, which is related to leaf pigment content. The use of an estimated or approximated PRI0, defined as the PRI of perfectly dark-adapted leaves, allowed us to separate the PRI variability due to leaf pigment content changes and the physiologically related PRI variability over both daily (PAR-related) and seasonal (soil water content-related) scales. The corrected PRI obtained by subtracting PRI0 from the PRI measurements showed a good correlation with the LUE over both of the species, soil water statuses and over the entire growing season.

Phosphoproteome Dynamics Upon Changes in Plant Water Status Reveal Early Events Associated With Rapid Growth Adjustment in Maize Leaves

Plant growth adjustment during water deficit is a crucial adaptive response. The rapid fine-tuned control achieved at the post-translational level is believed to be of considerable importance for regulating early changes in plant growth reprogramming. Aiming at a better understanding of early responses to contrasting plant water statuses, we carried out a survey of the protein phosphorylation events in the growing zone of maize leaves upon a range of water regimes. In this study, the impact of mild and severe water deficits were evaluated in comparison with constant optimal watering and with recovery periods lasting 5, 10, 20, 30, 45, and 60 min. Using four biological replicates per treatment and a robust quantitative phosphoproteomic methodology based on stable-isotope labeling, we identified 3664 unique phosphorylation sites on 2496 proteins. The abundance of nearly 1250 phosphorylated peptides was reproducibly quantified and profiled with high confidence among treatments. A total of 138 phosphopeptides displayed highly significant changes according to water regimes and enabled to identify specific patterns of response to changing plant water statuses. Further quantification of protein amounts emphasized that most phosphorylation changes did not reflect protein abundance variation. During water deficit and recovery, extensive changes in phosphorylation status occurred in critical regulators directly or indirectly involved in plant growth and development. These included proteins influencing epigenetic control, gene expression, cell cycle-dependent processes and phytohormone-mediated responses. Some of the changes depended on stress intensity whereas others depended on rehydration duration, including rapid recoveries that occurred as early as 5 or 10 mins after rewatering. By combining a physiological approach and a quantitative phosphoproteomic analysis, this work provides new insights into the in vivo early phosphorylation events triggered by rapid changes in plant water status, and their possible involvement in plant growth-related processes.

Study of Air Anion Concentration in Various Water Statuses

Atmospheric ions are produced by many natural and anthropogenic sources and their concentrations vary widely between different environments. In this study, we conducted in a southern coastal province of China, where we chose some typical sites to observe. The observations included negative air ion concentration, positive air icon concentration, wind speed, temperature and relative humidity, and negative air icon concentration in materials and plants. The results showed that negative air icon concentration changed more obviously in different water statuses, and showed a certain degree of mutual relations. In order to improve the urban ecological environment, the authors proposed the use of water and wind actively to increase the distribution of negative air anion concentration in urban planning and construction.