Evaluating the Effects of Environmental Conditions on Sensed Parameters for Green Areas Monitoring and Smart Irrigation Systems.

The irrigation of green areas in cities should be managed appropriately to ensure its sustainability. In large cities, not all green areas might be monitored simultaneously, and the data acquisition time can skew the gathered value. Our purpose is to evaluate which parameter has a lower hourly variation. We included soil parameters (soil temperature and moisture) and plant parameters (canopy temperature and vegetation indexes). Data were gathered at 5 different hours in 11 different experimental plots with variable irrigation and with different grass composition. The results indicate that soil moisture and Normalized Difference Vegetation Index are the sole parameters not affected by the data acquisition time. For soil moisture, the maximum difference was in experimental plot 4, with values of 21% at 10:45 AM and 27% at 8:45 AM. On the other hand, canopy temperature is the most affected parameter with a mean variation of 15 °C in the morning. The maximum variation was in experimental plot 8 with a 19 °C at 8:45 AM and 39 °C at 12:45 PM. Data acquisition time affected the correlation between soil moisture and canopy temperature. We can affirm that data acquisition time has to be included as a variability source. Finally, our conclusion indicates that it is vital to consider data acquisition time to ensure water distribution for irrigation in cities.

Interactive Effects of CO2 Concentration and Water Regime on Stable Isotope Signatures, Nitrogen Assimilation and Growth in Sweet Pepper.

Sweet pepper is among the most widely cultivated horticultural crops in the Mediterranean basin, being frequently grown hydroponically under cover in combination with CO2 fertilization and water conditions ranging from optimal to suboptimal. The aim of this study is to develop a simple model, based on the analysis of plant stable isotopes in their natural abundance, gas exchange traits and N concentration, to assess sweet pepper growth. Plants were grown in a growth chamber for near 6 weeks. Two [CO2] (400 and 800 µmol mol-1), three water regimes (control and mild and moderate water stress) and four genotypes were assayed. For each combination of genotype, [CO2] and water regime five plants were evaluated. Water stress applied caused significant decreases in water potential, net assimilation, stomatal conductance, intercellular to atmospheric [CO2], and significant increases in water use efficiency, leaf chlorophyll content and carbon isotope composition, while the relative water content, the osmotic potential and the content of anthocyanins did change not under stress compared to control conditions support this statement. Nevertheless, water regime affects plant growth via nitrogen assimilation, which is associated with the transpiration stream, particularly at high [CO2], while the lower N concentration caused by rising [CO2] is not associated with stomatal closure. The stable isotope composition of carbon, oxygen, and nitrogen (δ13C, δ18O, and δ15N) in plant matter are affected not only by water regime but also by rising [CO2]. Thus, δ18O increased probably as response to decreases in transpiration, while the increase in δ15N may reflect not only a lower stomatal conductance but a higher nitrogen demand in leaves or shifts in nitrogen metabolism associated with decreases in photorespiration. The way that δ13C explains differences in plant growth across water regimes within a given [CO2], seems to be mediated through its direct relationship with N accumulation in leaves. The changes in the profile and amount of amino acids caused by water stress and high [CO2] support this conclusion. However, the results do not support the use of δ18O as an indicator of the effect of water regime on plant growth.

Comparative effect of salinity on growth, grain yield, water use efficiency, δ(13)C and δ(15)N of landraces and improved durum wheat varieties.

Supplemental irrigation with low-quality water will be paramount in Mediterranean agriculture in the future, where durum wheat is a major crop. Breeding for salinity tolerance may contribute towards improving resilience to irrigation with brackish water. However, identification of appropriate phenotyping traits remains a bottleneck in breeding. A set of 25 genotypes, including 19 landraces and 6 improved varieties most cultivated in Tunisia, were grown in the field and irrigated with brackish water (6, 13 and 18dSm(-1)). Improved genotypes exhibited higher grain yield (GY) and water use efficiency at the crop level (WUEyield or 'water productivity'), shorter days to flowering (DTF), lower N concentration (N) and carbon isotope composition (δ(13)C) in mature kernels and lower nitrogen isotope composition (δ(15)N) in the flag leaf compared with landraces. GY was negatively correlated with DTF and the δ(13)C and N of mature kernels and was positively correlated with the δ(15)N of the flag leaf. Moreover, δ(13)C of mature kernels was negatively correlated with WUEyield. The results highlight the importance of shorter phenology together with photosynthetic resilience to salt-induced water stress (lower δ(13)C) and nitrogen metabolism (higher N and δ(15)N) for assessing genotypic performance to salinity.

Gene expression and physiological responses to salinity and water stress of contrasting durum wheat genotypes.

Elucidating the relationships between gene expression and the physiological mechanisms remains a bottleneck in breeding for resistance to salinity and drought. This study related the expression of key target genes with the physiological performance of durum wheat under different combinations of salinity and irrigation. The candidate genes assayed included two encoding for the DREB (dehydration responsive element binding) transcription factors TaDREB1A and TaDREB2B, another two for the cytosolic and plastidic glutamine synthetase (TaGS1 and TaGS2), and one for the specific Na(+) /H(+) vacuolar antiporter (TaNHX1). Expression of these genes was related to growth and different trait indicators of nitrogen metabolism (nitrogen content, stable nitrogen isotope composition, and glutamine synthetase and nitrate reductase activities), photosynthetic carbon metabolism (stable carbon isotope composition and different gas exchange traits) and ion accumulation. Significant interaction between genotype and growing conditions occurred for growth, nitrogen content, and the expression of most genes. In general terms, higher expression of TaGS1, TaGS2, TaDREB2B, and to a lesser extent of TaNHX1 were associated with a better genotypic performance in growth, nitrogen, and carbon photosynthetic metabolism under salinity and water stress. However, TaDREB1A was increased in expression under stress compared with control conditions, with tolerant genotypes exhibiting lower expression than susceptible ones.

Metabolite Profiles of Maize Leaves in Drought, Heat, and Combined Stress Field Trials Reveal the Relationship between Metabolism and Grain Yield.

The development of abiotic stress-resistant cultivars is of premium importance for the agriculture of developing countries. Further progress in maize (Zea mays) performance under stresses is expected by combining marker-assisted breeding with metabolite markers. In order to dissect metabolic responses and to identify promising metabolite marker candidates, metabolite profiles of maize leaves were analyzed and compared with grain yield in field trials. Plants were grown under well-watered conditions (control) or exposed to drought, heat, and both stresses simultaneously. Trials were conducted in 2010 and 2011 using 10 tropical hybrids selected to exhibit diverse abiotic stress tolerance. Drought stress evoked the accumulation of many amino acids, including isoleucine, valine, threonine, and 4-aminobutanoate, which has been commonly reported in both field and greenhouse experiments in many plant species. Two photorespiratory amino acids, glycine and serine, and myoinositol also accumulated under drought. The combination of drought and heat evoked relatively few specific responses, and most of the metabolic changes were predictable from the sum of the responses to individual stresses. Statistical analysis revealed significant correlation between levels of glycine and myoinositol and grain yield under drought. Levels of myoinositol in control conditions were also related to grain yield under drought. Furthermore, multiple linear regression models very well explained the variation of grain yield via the combination of several metabolites. These results indicate the importance of photorespiration and raffinose family oligosaccharide metabolism in grain yield under drought and suggest single or multiple metabolites as potential metabolic markers for the breeding of abiotic stress-tolerant maize.

Comparative response of δ13C, δ18O and δ15N in durum wheat exposed to salinity at the vegetative and reproductive stages.

This study compared the performance of the stable isotope composition of carbon (δ(13) C), oxygen (δ(18) O) and nitrogen (δ(15) N) by tracking plant response and genotypic variability of durum wheat to different salinity conditions. To that end, δ(13) C, δ(18) O and δ(15) N were analysed in dry matter (dm) and the water-soluble fraction (wsf) of leaves from plants exposed to salinity, either soon after plant emergence or at anthesis. The δ(13) C and δ(18) O of the wsf recorded the recent growing conditions, including changes in evaporative conditions. Regardless of the plant part (dm or wsf), δ(13) C and δ(18) O increased and δ(15) N decreased in response to stress. When the stress conditions were established just after emergence, δ(15) N and δ(13) C correlated positively with genotypic differences in biomass, whereas δ(18) O correlated negatively in the most severe treatment. When the stress conditions were imposed at anthesis, relationships between the three isotope signatures and biomass were only significant and positive within the most severe treatments. The results show that nitrogen metabolism, together with stomatal limitation, is involved in the genotypic response to salinity, with the relative importance of each factor depending on the severity and duration of the stress as well as the phenological stage that the stress occurs.

Combined use of δ¹³C, δ18O and δ15N tracks nitrogen metabolism and genotypic adaptation of durum wheat to salinity and water deficit.

• Accurate phenotyping remains a bottleneck in breeding for salinity and drought resistance. Here the combined use of stable isotope compositions of carbon (δ¹³C), oxygen (δ¹8O) and nitrogen (δ¹5N) in dry matter is aimed at assessing genotypic responses of durum wheat under different combinations of these stresses. • Two tolerant and two susceptible genotypes to salinity were grown under five combinations of salinity and irrigation regimes. Plant biomass, δ¹³C, δ¹8O and δ¹5N, gas-exchange parameters, ion and N concentrations, and nitrate reductase (NR) and glutamine synthetase (GS) activities were measured. • Stresses significantly affected all traits studied. However, only δ¹³C, δ¹8O, δ¹5N, GS and NR activities, and N concentration allowed for clear differentiation between tolerant and susceptible genotypes. Further, a conceptual model explaining differences in biomass based on such traits was developed for each growing condition. • Differences in acclimation responses among durum wheat genotypes under different stress treatments were associated with δ¹³C. However, except for the most severe stress, δ¹³C did not have a direct (negative) relationship to biomass, being mediated through factors affecting δ¹8O or N metabolism. Based upon these results, the key role of N metabolism in durum wheat adaptation to salinity and water stress is highlighted.

Effect of salinity and water stress during the reproductive stage on growth, ion concentrations, Delta 13C, and delta 15N of durum wheat and related amphiploids.

The physiological performance of durum wheat and two related amphiploids was studied during the reproductive stage under different combinations of salinity and irrigation. One triticale, one tritordeum, and four durum wheat genotypes were grown in pots in the absence of stress until heading, when six different treatments were imposed progressively. Treatments resulted from the combination of two irrigation regimes (100% and 35% of container water capacity) with three levels of water salinity (1.8, 12, and 17 dS m(-1)), and were maintained for nearly 3 weeks. Gas exchange and chlorophyll fluorescence and content were measured prior to harvest; afterwards shoot biomass and height were recorded, and Delta(13)C, delta(15)N, and the concentration of nitrogen (N), phosphorus, and several ions (K(+), Na(+), Ca(2+), Mg(2+)) were analysed in shoot material. Compared with control conditions (full irrigation with Hoagland normal) all other treatments inhibited photosynthesis through stomatal closure, accelerated senescence, and decreased biomass. Full irrigation with 12 dS m(-1) outperformed other stress treatments in terms of biomass production and physiological performance. Biomass correlated positively with N and delta(15)N, and negatively with Na(+) across genotypes and fully irrigated treatments, while relationships across deficit irrigation conditions were weaker or absent. Delta(13)C did not correlate with biomass across treatments, but it was the best trait correlating with phenotypic differences in biomass within treatments. Tritordeum produced more biomass than durum wheat in all treatments. Its low Delta(13)C and high K(+)/Na(+) ratio, together with a high potential growth, may underlie this finding. Mechanisms relating delta(15)N and Delta(13)C to biomass are discussed.

Shoot δ15N gives a better indication than ion concentration or Δ13C of genotypic differences in the response of durum wheat to salinity.

We compared the performance of different physiological traits that reveal genotypic variations in tolerance to salinity in durum wheat. A set of 114 genotypes was grown in hydroponics for over 3 months. Three conditions: control, moderate (12 dS m-1) and severe (17 dS m-1) salinity, were maintained for nearly 8 weeks before harvest. The genotype biomass in control conditions correlated with the biomass at the two salinity levels. Subsequently, two subsets of 10 genotypes each were selected on the basis of extreme differences in biomass at the two salinity levels while showing relatively similar biomass in control conditions. Carbon isotope discrimination (Δ13C), nitrogen isotope composition (δ15N), and the concentration of nitrogen, phosphorus and several ions (K+, Na+, Ca2+, Mg2+) were analysed in the two subsets for the three treatments. At 12 dS m-1, K+ concentration, K+/Na+ ratio, Δ13C and δ15N correlated positively and Na+ correlated negatively with shoot biomass. Under control conditions and at 17 dS m-1 no correlation was observed. However, the trait that correlated best with genotypic differences in biomass was δ15N at 12 dS m-1. This trait was the first variable chosen at each of the two salinity levels in a stepwise analysis. We consider the possible mechanisms relating δ15N to biomass and the use of this isotopic signature as a selection trait.