Using mathematical models to evaluate germination rate and seedlings length of chickpea seed (Cicer arietinum L.) to osmotic stress at cardinal temperatures

Cicer arietinum is the 3rd most important cool season legume crop growing in vast arid and semi-arid regions of the world. A lab experiment was designed using hydrothermal time model (HTT) to investigate the chickpea seed germination (SG) behavior, cardinal temperatures and germination responses across fluctuating temperatures (Ts) and water potentials (Ψs). Seeds of chickpea var. NIFA 1995 were germinated at six constant Ts (7, 14, 21, 28, 35 and 42°C) each having the following five water potentials: 0, -0.2, -0.4–0.6 and -0.8 MPa. Germination percentage (G%) decreased significantly at (*P ≤ 0.05) from 86.7% at 28°C in -0.2 MPa to 10% in -0.2 MPa at 7°C. The germination rate (GR = 1/t50) against different T percentiles exhibited that linear increase was observed in the GR pattern above and below the To. Based on the confidence intervals of the model coefficients and (R2: 0.96), the average cardinal temperatures were 4.7, 23 and 44.2°C for the base (Tb), optimal (To) and ceiling (Tc) temperatures respectively. θT1 value was observed maximum at 28°C in -0.2 MPa and decreases with decreasing Ψ (-0.8 MPa). In comparison with control, the θT2 value was also highest in -0.2 MPa at 28°C. The thermal time (TT) concept is well fitted to germination fraction data in distilled water with an R2 value increasing 0.972. The hydro time constant (θH) increased with an increase in T to To and then decreased when T>To. The ѱb(50) irregularly varied with increasing T, σΨb was also recorded lowest (0.166 MPa) at 28°C and highest (0.457 MPa) at 7°C. Based on the statistical analysis, cardinal temperatures, hydrothermal time constant (θHTT) and germination findings the HTT gives an insight into the interactive effect of T and Ψ on seed germination time courses under varying environmental conditions.

Temperate tree seedlings have similar drought vulnerability despite having different hydraulic drought responses in adults

Climate change is projected result in higher frequencies of drought events across the world and lead to reduced performance in many temperate tree species. However, many studies in this area focus specifically on adult tree drought responses and overlook how trees in other age classes might differ in their vulnerability. Evidence shows that seedling drought response can differ from that of adults and furthermore that demographic performance in the seedling age class will have disproportionately strong effects on the assembly dynamics of future forests, together suggesting that understanding seedling drought responses will be critical to our ability to predict how forests will respond to climate change. In this study, we measured four indices of hydraulic response to drought (leaf water potential, photosynthetic capacity, non-structural carbohydrate concentration, and hydraulic conductivity), as well as interaction effects with shade treatments, for seedlings of two temperate tree species that differ in their adult drought response: isohydric Acer saccharum and anisohydric Quercus rubra . We found a strong isohydric response in A. saccharum seedlings that included conservation of leaf water potentials (> -1.8 MPa) and reductions in non-structural carbohydrate concentrations consistent with reduction of stomatal conductance. Quercus rubra seedlings were able to survive to more negative water potentials, but only rarely, and they showed a similar reduction in photosynthetic capacity as was found for A. saccharum . Our results suggest that, although Q. rubra seedlings display some anisohydric responses to drought, they are more isohydric than adults. Both species seem to be relatively similar in their vulnerability to drought despite the differences predicted from adult drought response, and our results suggest that seedlings of both species will be similarly vulnerable to future drought events.

Physiological alterations and enzymatic evaluation of soybean cultivars under water deficit

Drought is one of the main abiotic factors limiting agricultural productivity, capable of having a major impact on the yield of most crops. The knowledge of the physiological and biochemical mechanisms that differentiate resistance and susceptibility to water deficit among soybean strains can be used in the generation of more tolerant cultivars. In this sense, the objective of this study was to characterize physiologically, two soybean cultivars with different patterns of tolerance to drought in the field, by determining photosynthetic rates, lipid peroxidation levels and antioxidant enzyme activity under three levels of water potential. Upon reaching the V4 development stage, the irrigation of the plants was suspended and three data collection were performed: full irrigation (control); moderate water deficit (Ψ = -1.5 ± 0.2 MPa) and severe deficit (Ψ = -3.0 MPa ± 0.2 MPa). Variations in perspiration rate, stomatal conductance, as well as decrease in photosynthetic rate were significant between the two cultivars, where the water potentials in cultivar BR 16 anticipated on average two days achieving the same water potentials in Embrapa 48 cultivar, thus presenting better efficiency in water use. In addition, the increased activity of enzymes and lipid peroxidation were more significant in the cultivar BR 16, demonstrating that this cultivar is less tolerant to drought than Embrapa 48 cultivar, corroborating to agronomic data previously found in the field.

Dynamic aspects of plant water potential revealed by a microtensiometer

Water potential is a fundamental thermodynamic parameter that describes the activity of water. In this paper, we describe the continuous measurement of plant water potential, a reliable indicator of its water status, using a novel in situ sensor known as a microtensiometer in mature grapevines under field conditions. The microtensiometer operates on the principle of equilibration of water potentials of internal liquid water with an external vapour or liquid phase. We characterised the seasonal and diurnal dynamics of trunk water potentials (Ψtrunk) obtained from microtensiometers installed in two grapevine cultivars, Shiraz and Cabernet Sauvignon, and compared these values to pressure chamber-derived stem (Ψstem) and leaf (Ψleaf) water potentials as well as leaf stomatal conductance. Diurnal patterns of Ψtrunk matched those of Ψstem and Ψleaf under low vapour pressure deficit (VPD) conditions, but diverged under high VPD conditions. The highest diurnal values of Ψtrunk were observed shortly after dawn, while the lowest values were typically observed in the late afternoon. Differential responses of Ψtrunk to VPD were observed between cultivars, with Shiraz more sensitive than Cabernet to increasing VPD over long time scales, and both cultivars had a stronger VPD response than soil moisture response. On a diurnal basis, however, time cross correlation analysis revealed that Shiraz Ψtrunk lagged Cabernet Ψtrunk in response to changing VPD. Microtensiometers were shown to operate reliably under field conditions over several months. To be useful for irrigation scheduling of woody crops, new thresholds of Ψtrunk need to be developed.

Biochemical Response and Nutrient Uptake of Two Arbuscular Mycorrhiza-Inoculated Chamomile Varieties Under Different Water Potentials

BackgroundWater-deficit stress is one of the most important sources of damage to crop production worldwide. Adopting appropriate varieties using soil microorganisms such as arbuscular mycorrhiza(AM) can significantly reduce theadverseeffectsofwater deficiency.This study is aimed to evaluate the role of Funneliformismosseaeon nutrients uptake and some physiological traits of two chamomile varieties namely Bodgold (Bod) and Soroksári(Sor) under water-deficit stress. The pot experiment was performed in a hydroponic system within a completely randomized design considering four replications. Three levels of water-deficit stress (PEG 6000) were taken into account at water potentials of -0.4 and -0.8MPa. The second factor was AM inoculation.ResultsWater-deficit stress significantly reduced the uptake of macro-nutrients (N, P, and K) and micro-nutrients (Fe, Cu, Mn, and Zn) in the shoots and roots. Moreover, the level of osmolytes (total soluble sugars and proline) and the activity of antioxidant enzymes in the shoots of both varieties increased under water-deficit stress. In the case of Sor variety, the level of these compounds was more satisfactory. AM improved plant nutrition uptake and osmolyte contents while enhancing antioxidant enzymes and reducing theadverseeffectsofwater-deficit stress. Under water-deficit stress, the growth and total dry weight improved upon AM inoculation. ConclusionsIn general, inoculation of chamomile with AM balanced the uptake of nutrients increased the level of osmolytes, antioxidant enzymes, and hence improved plant characteristics under water-deficit stress in both varieties, however, it was more effective in reducing stress damages in Sor variety.

Deficit Irrigation as a Tool to Optimize Fruit Quality in Abbé Fetél Pear

Climate change is leading to higher plant water requirements and rootstock can play a role in tree adaptation, since the more vigorous ones are also likely to be more stress resistant. Pear trees of the cv. Abbé Fetél grafted on BA29 (more vigorous) and SYDO (more dwarfing) quince were irrigated according to three different treatments: 110 C, 80 DI and 60 DI, corresponding to 110%, 80% and 60% of the crop evapotranspiration rate (ETc), respectively. Shoot and fruit growth, water potentials, leaf gas exchanges and dry matter content were monitored during the season. Fruit quality was evaluated at harvest and after 6 months of storage at 1 °C. Results show how for both rootstocks, 60 DI significantly decreased their stem (Ψstem) and leaf (Ψleaf) water potentials as well as leaf gas exchanges. In SYDO, final fruit size was affected by irrigation, with lower values on 60 DI, but in BA29, no differences were found between treatments. After storage, BA29 60 DI fruit showed a higher soluble solid content, while in SYDO fruit, firmness was more affected by irrigation level. In conclusion, despite a slight decrease in fruit size, reduced irrigation led to fruit with higher quality features that were also maintained after a long period of storage.

Third Year Survival, Growth, and Water Relations of West Gulf Coastal Plain Pines in East Texas

West Gulf Coastal Plain provenance loblolly (Pinus taeda L.), longleaf (Pinus palustris Mill.), shortleaf (Pinus echinata Mill.), and slash pines (Pinus elliottii Engelm.) were planted in December 2015 on three east Texas sites to compare initial growth and survival. Three years after planting, survival ranged from 26.4% to 76.4%. Damage by Texas leafcutter ants (Atta texana) caused significant mortality on one site, and feral hog (Sus scrofa) herbivory and uprooting greatly affected survival at two other sites. Tree heights were greater in loblolly and slash pine than in shortleaf and longleaf pine, whereas diameters were greater in loblolly than in slash, shortleaf, and longleaf. Height and survival rates were greater in Shelby County and were lowest in Cherokee County. Midday leaf-level water potentials were most negative for shortleaf and loblolly pines and varied across the three sites. Tree heights were significantly but weakly (R = −0.23) correlated to leaf-level water potentials. Study Implications Based on these results, loblolly pine is recommended for planting on sites where soil moisture is adequate, if early growth and survival are a concern. Slash pine can outcompete other pines on sites where soils are poorly drained. On soils that are excessively drained with low moisture, shortleaf may be considered. Given longleaf pine’s ability to retain needle moisture and surface area during periods of low soil moisture, longleaf pine is suggested for planting on the same sites. Longleaf pine will require more active management on any soil type in order to decrease herbaceous plant competition. Continued measurements are required to determine whether these growth and survival trends will continue over a full rotation.