Leaf Water Potential Values Research Articles

Scheduling deficit subsurface drip irrigation of apple trees for optimizing water use

The impact of four different irrigation strategies on soil and plant water status and fluxes of photosynthesis (A) and chamber transpiration (E) has been studied under continental climate on field-grown apple trees (Malus domestica ‘Gala’) in 2010 and 2011. The non-irrigated treatment resulted in a decrease in soil water content (SWC) throughout the season in comparison with irrigated treatments. Non-irrigated trees showed more negative values of predawn leaf water potential (ΨP), which decreased to − 0.2 MPa, reflecting a moderate water stress during the fruit ripening period. A decrease (15 to 25%) of stomatal conductance (gs), leaf photosynthesis (A), and transpiration (E) were observed in these water-stressed trees (T1). Well-irrigated trees during the whole season (T2) showed the highest rates of gs, A, E, as well as of ΨP values, which were around − 0.1 MPa. Trees irrigated only during the fruit cell division period (stage I) and the ripening period (stage III) (T3) showed a small decrease (10%) in leaf gas exchanges. A regulated deficit irrigation (RDI) applied only during the fruit cell growth (stage II) on trees and well-irrigated during the fruit cell division period and the ripening period (T4) seems to have little effects on gas exchanges and no effects on yield and fruit quality before and after storage. Therefore, the results showed that with the exception of RDI treatment, increasing water stress reduced the physiological parameters due to stomatal and non-stomatal limiting factors. However, such regulated deficit irrigation saved 45% of water compared to the comfort irrigation. Considering these results, regulated deficit subsurface drip irrigation applied during the fruit growth II is a sustainable strategy for saving water, increasing water use efficiencies, and preserving the physicochemical quality of the apple fruits before and after storage.

Water Deficit Synchronizes Berry Color Development in Crimson Seedless Table Grapes

Crimson Seedless is one of the most important table grape cultivars in the world, but often exhibits uneven berry color when grown in warm climates. Deficit irrigation is used extensively by growers during the ripening phase to advance fruit maturity and color, but there is a lack of information about the relationship between irrigation practices and fruit ripening variability. We imposed deficit irrigation in a commercial Crimson Seedless vineyard in the Maipo Valley, Chile, from veraison to harvest in two consecutive seasons. The fruit was tested for uniformity of Brix, firmness, and the color parameters “L”, “a”, “b”, and the Color Index of Red Grapes using analysis of variance on absolute residuals (Levene’s test). Postveraison water stress increased water productivity, Brix, and slightly improved berry coloration, but did not affect berry weight, size, or firmness. Moderate levels of water stress improved color uniformity at harvest, as lower values of leaf water potential were associated with a lower percentage of green berries that never matured. These results confirmed the role of deficit irrigation in the table grape ripening process. In contrast, extending the fruit ripening period by delaying harvest beyond 18 Brix did not increase color accumulation, but did increase berry shatter.

Primary productivity and physiological responses of Vitis vinifera L. cvs. under Free Air Carbon dioxide Enrichment (FACE)

Abstract Two Vitis vinifera L. cultivars, Riesling and Cabernet Sauvignon, were grown in the Geisenheim VineyardFACE (Free Air Carbon dioxide Enrichment) system under rain-fed conditions to investigate the effects of elevated CO2 on the productivity of grapevines for three consecutive years (2014–2016) following planting in 2012. The FACE system consisted of six 12 m diameter rings, with three at ambient CO2 (aCO2, 400 ppm), and three rings at elevated CO2 (eCO2, + 20% of aCO2 level). Vegetative growth, single leaf gas exchange and yield parameters were monitored for the three growing seasons. Vegetative growth parameters responded differently to CO2 treatments depending on biomass components. Trunk cross section area, as an indicator of perennial growth, showed a significant increase for Riesling under eCO2 but not for Cabernet Sauvignon. Fresh biomass as lateral leaf area and fresh weight of summer pruning were stimulated by elevated CO2 for both cultivars. Leaf gas exchange measurements for both cultivars showed a significant increase in net assimilation rate and an improved intrinsic water use efficiency for all three years under eCO2 conditions. However, contrary to expected stomatal behaviour of grapevines, transpiration rate and stomatal conductance were higher under elevated CO2 for Riesling and Cabernet Sauvignon in all three seasons. Higher values of pre-dawn leaf water potential recorded under eCO2 point towards an interaction with soil water availability and root system development. Elevated CO2 resulted in higher yield in terms of higher bunch weight, but did not affect average number of bunches per vine or sugar content of must at harvest date. Accordingly, bunch architecture was altered under elevated CO2 levels. The increase in primary productivity of grapevines under eCO2 indicates yield gains that can be expected under even modest near-future CO2 scenarios. However, higher water use, particularly if maintained as grapevines transition to maturity, may have critical implications for the future adaptation of non-irrigated viticulture to increasing temperature and periods of rainfall deficit.

Physiological drought responses improve predictions of live fuel moisture dynamics in a Mediterranean forest

The moisture content of live fuels is an important determinant of forest flammability. Current approaches for modelling live fuel moisture content typically focus on the use of drought indices. However, these have mixed success partly because of species-specific differences in drought responses. Here we seek to understand the physiological mechanisms driving changes in live fuel moisture content, and to investigate the potential for incorporating plant physiological traits into live fuel moisture models. We measured the dynamics of leaf moisture content, access to water resources (through stable isotope analyses) and physiological traits (including leaf water potential, stomatal conductance, and cellular osmotic and elastic adjustments) across a fire season in a Mediterranean mixed forest in Catalonia, NE Spain. We found that differences in both seasonal variation and minimum values of live fuel moisture content were a function of access to water resources and plant physiological traits. Specifically, those species with the lowest minimum moisture content and largest seasonal variation in moisture (Cistus albidus: 49–137% and Rosmarinus officinalis: 47–144%) were most reliant on shallow soil water and had the lowest values of predawn leaf water potential. Species with the smallest variation in live fuel moisture content (Pinus nigra: 96–116% and Quercus ilex: 56–91%) exhibited isohydric behaviour (little variation in midday leaf water potential, and relatively tight regulation of stomata in response to soil drying). Of the traits measured, predawn leaf water potential provided the strongest predictor of live fuel moisture content (R2 = 0.63, AIC = 249), outperforming two commonly used drought indices (both with R2 = 0.49, AIC = 258). This is the first study to explicitly link fuel moisture with plant physiology and our findings demonstrate the potential and importance of incorporating ecophysiological plant traits to investigating seasonal changes in fuel moisture and, more broadly, forest flammability.

Fostering sustainable water use in almond (Prunus dulcis Mill.) orchards in a semiarid Mediterranean environment

ABSTRACTThis work examines the long-term effects of deficit-irrigation (DI) practices in almond crop (Prunus dulcis Mill.) in agronomical and physiological terms. The trial was conducted during four-year monitoring period (2014–2017), in an experimental orchard (SW Spain), subjected to three irrigation regimes; i) a full-irrigation treatment (FI), which received 100% of crop evapotranspiration (ETC); ii) a regulated-deficit irrigation (RDI50), which received 50% of ETC during the kernel-filling period; and iii) a low-frequency deficit irrigation (LFDI), that was subjected to continuous periods of irrigation-restriction defined in terms of threshold values of leaf-water potential (Ψleaf) during the kernel-filling period. During the water stress period, there were monitored Ψleaf, stomatal conductance (gs) and canopy temperature (TC). Significant improvements in terms of water-use efficiency were found, as no differences in terms of yield between FI and LFDI were found, leading to the conclusion that significant water savings (between 27 and 40%) can be achieved without compromising the yield. Moreover, threshold values of Ψleaf and thermal indicators were defined which will allow establishing future irrigation scheduling without compromising almond yield, especially when DI strategies are being applied.

Effect of irrigation suspension on the growth, water state and production of spinach (Spinacia olerácea L.) plants

Spinach is susceptible to drought conditions, and, because of climate change, it is necessary to optimize water application to crops. Therefore, a test was carried out in a completely randomized design (CRD) with four treatments consisting of the following irrigation suspension durations: T1: 0 d, T2: 4 d, T3: 7 d and T4: 10, with six replicates for a total of 24 experiment units (EU). Each EU consisted of 6 plants, for a total of 120 plants that were transplanted to 2 L pots with a mixture of peat and soil (2:1). The upper part of the substrate was maintained with a higher moisture content in the treatment without irrigation suspension and in the one with irrigation suspended for 4 d. An inversely proportional relationship was observed between the moisture content and the leaf water potential. The treatment without irrigation suspension recorded the highest leaf water potential value during the measurement period. There were no significant differences between the chlorophyll content in the SPAD units or for the leaf area, stomatal conductance and dry mass. The fresh mass presented significant differences and had the highest value in the treatment without suspension of irrigation.

Component crop physiology and water use efficiency in response to intercropping

Abstract Interspecies specific interactions are generally regarded as drivers of plant productivity in multispecies agroecosystems. Complementary use of resource in diverse communities can enhance community productivity through optimal use of plant-available resources and positive interactions such as facilitation can ameliorate high abiotic stress conditions. We studied the effects on physiological response, leaf traits and water use efficiency of a multifunctional species intercropping system consisting of peanut (Arachis hypogaea L.), watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai], okra [Abelmoschus esculentus (L.) Moench], cowpea [Vigna unguiculata (L.) Walp.], and pepper (Capsicum annuum L.) planted alone or in various intercropping combinations in a low fertilizer input system in the peak of summer heat in Texas. Differences in gas exchange measurements were detected only in watermelon in year 2 of the study when okra was the dominant crop. This same year watermelon specific leaf area (SLA) was significantly higher when okra was present in a treatment and particularly in the three and four species combinations, Wpwo and Wpwoc, 27.5 and 31.0 m2 kg−1, respectively, as compared to watermelon grown in monoculture, strip intercropped with peanut (Spw) and within row intercropped with peanut (Wpw), 20.4, 20.1, and 19.8 m2 kg−1, respectively. This corresponds with an increase watermelon leaf N concentration and a decrease in leaf C:N ratio in Wpwo and Wpwoc treatments. No differences in d13C composition, a measure of water use efficiency over the leaf lifespan, were detected across cropping system for each species. Water use efficiency based on per plant production (WUEyield) indicated an increase in water use efficiency in dominant crops such as watermelon in 2011 and okra in 2012, but a reduction in WUEyield subordinate crops such as cowpea and pepper both years of the study. Peanut grown in monoculture and strip intercropped with watermelon had significantly lower leaf water potential values in 2012, −2.2 and −2.1 MPa, respectively, as compared to intercropping systems increasing in level of integration (Wpw = − 1.1, Wpwo = − 0.6, Wpwoc = − 1.3, Wall = −1.1 MPa), indicating peanut benefited from alterations to microclimate and facilitative interactions with companion crops in some intercropping systems through a reduction in plant water stress. The results from this study suggest there may be a benefit to a multifunctional intercropping system in the form of increased food production per unit of water input in dominant crops and reduced water stress for some component species. This is important to producers; showing a method to increase overall crop production without increasing water inputs.

Responses of Hazelnut Trees to Organic and Conventional Managements in the Dryland

Hazelnut trees (Corylus avellana L.) give yields without any more reduction under dryland. However, it is not known how plant water status and gas exchanges response to organic management under the dryland. In an attempt to answer this question, such responses, which are leaf water potential (LWP), stomatal conductance (gs) and photosynthetically active radiation (PAR) of hazelnut trees, were studied under organic and conventional managements in the dryland conditions. It was also investigated possible effects of those parameters on organic and conventional hazelnut trees vs. SWC and atmospheric stress (i. e., air vapour pressure deficit-VPD). Organic hazelnut trees had slightly higher ET and yield, and lower SWC than conventional hazelnut trees. However, generally, slightly higher LWP and gs values were obtained for conventional hazelnut trees while the value of VPD was higher in organic hazelnut orchards. LWP, PAR, gs response to SWC and VPD and relationships between each others were generally imperceptibly higher in organic hazelnut trees than conventional hazelnut trees but no stronger responses and relationships. Plant canopy measurements were mostly parallel with the results obtained values of ET, yield, SWC and VPD. Precipitation during the year influenced both hazelnut orchards managements to have higher yield and keep life alive. However, it could be emphasized that hazelnut trees under organic and conventional hazelnut managements required supplement irrigation to avoid summer water stress, and for providing fruit fulling and accumulation of reserves for the following year. Finally, it can be conclude that organic farming is a good alternative for hazelnut orchards in dryland.

Comparing canopy temperature and leaf water potential as irrigation scheduling criteria of potato in water-saving irrigation strategies

Irrigation scheduling is important in irrigation water management. In this study, full (FI),deficit (DI) and partial root drying (PRD) irrigation strategies were applied in Agria and Ramospotato cultivars. Canopy temperature (CT) and leaf water potential (LWP) were assessed as thepotential tools for irrigation scheduling during the vegetative and productive growth stages.LWP varied between ca. -1.4 and -1.6 MPa and was not significantly different between FI, DIand PRD irrigation treatments. The LWP and CT values were not significant between the twopotato cultivars during the measurements, but CT was frequently significant between theirrigation treatments such that the PRD treatments were significantly 5 and 2 oC warmer than FIand DI treatments, respectively. Higher CT in PRD caused significant yield penalty such that DIand FI produced almost two times higher fresh tuber yield. Analysis revealed that CT hadsignificantly higher correlation (r=0.66) with water productivity (weight of fresh tuber yielddivided by volume of applied irrigation water) than LWP, which its correlation was notsignificant (r=0.40). This showed that crop water productivity could be better controlled by CT.Moreover, it was realized that the seven-day irrigation interval was far longer than required andpotatoes in all irrigation treatments were under water stress, especially in PRD, that mightpartially explain the 50% yield penalty of PRD compared to DI. The reason was that due to highatmospheric demand, soil water in the wet part of the root system would be completely depletedearlier by the time of next irrigation event. Conclusively, the CT is recommended as a morereliable crop water status and irrigation scheduling indicator than LWP in response to differentwater-saving irrigation managements.

Alterations in growth, photosynthetic activity and tissue-water relations of tea clones in response to different soil moisture content

Significant effect of water stress conditions were observed on morphological and physiological growth parameters of tea (Camellia sinensis). Water stress tolerant tea clones suitable for hilly areas have been identified in this study. The influence of different levels of water deficit on physiological and morphological parameters in tea [Camellia sinensis (L.) O. Kuntze] clones was investigated. Tea clones (BSS-449, BSS-379, P-312, UPASI-9, T-383, RR-17, AV-2 and T-78) growing under controlled condition (under shade, potted condition) were subjected to three irrigation treatment, a control (70.0% soil moisture content), moderate water deficit (38.3% soil moisture content) and sever water deficit (6.9% soil moisture content). Plants submitted to severe water deficit showed significant reduced leaf numbers, leaf areas, and plant heights while reduction in plant height and leaf area and leaf numbers was not significant in moderate water deficit. A significant change in chlorophyll content was observed during the water stress condition. Photosynthesis decreased in both water deficit treatments and was related to stomatal factors and photochemical efficiency of photosystem II. Water relation parameters, e.g. leaf water potential, osmotic potential, turgor potential, relative water content and cellular elasticity were also measured to evaluate plant adaptation to water stress. The highest leaf water potential values were found in the control condition, for all the clones. Cell wall rigidity, measured as elastic modulus, increased under severe water stress, resulting in a loss of turgor at lower leaf water potential. Results of the study suggest that the degree of drought tolerance depends on the interactions between the tea clones and the levels of water stress. The available data also indicates that UPASI-9 is capable of tolerating water stress, and should be suitable for dry areas.

만개기 단근처리를 통한 수분스트레스가 '후지'/M.9 사과나무의 수체반응 및 과실특성에 미치는 영향

본 시험은 5~6월 수분스트레스가 사과나무의 광합성, 신초생장 및 과실품질에 미치는 영향을 구명하고자 실시하였다. 단근은 만개기(4월 30일)에 원줄기에서 30cm와 60cm 떨어진 곳에서 열 방향에 따라 양쪽 혹은 한쪽으로 처리 하였다. 무처리구의 5~6월 오후 평균 잎수분포텐셜은 -1.80MPa 이상을 유지하였지만, 단근 처리구들은 -1.80MPa 이하였다. 단근 처리 정도에 따른 5~6월경 오후 평균 잎 수분포텐셜은 양쪽 30cm 단근구(-2.06MPa), 양쪽 60cm 단근구(-2.02MPa), 한쪽 30cm 단근구(-1.91MPa) 순으로 낮았다. 한쪽 30cm 단근 처리와 양쪽 30cm 단근 처리는 5~6월 광합성속도를 각각 무처리구의 80% 및 65% 수준으로 감소시켰다. 또한, 한쪽 30cm 단근구의 무처리구 대비 총 신초장과 평균 과중의 감소 정도는 각각 25% 및 11% 정도였던 반면에 양쪽 30cm 단근구는 각각 45% 및 15% 정도였다. 그러나 가용성 고형물 함량 및 착색 정도는 단근 처리구들이 무처리구보다 높았으며, 양쪽 단근구들이 한쪽 단근구보다 더 높았다. 결론적으로, 5~6월 오후 평균 잎 수분포텐셜이 -1.80MPa 이하이면 과실비대가 감소되었고, -2.00MPa 이하이면 신초생장이 감소되었다. This study was conducted to find out the influence of water stress from May to June on photosynthesis, shoot growth and fruit quality of apple trees. Fuji'/M.9 apple trees were root pruned at full bloom (30th April), parallel to the row of 30 cm or 60 cm from the trunk, to one side or both sides of trunk. The average value of afternoon leaf water potential from May to June of the no root pruning was maintained over -1.80 MPa, but that of root-pruning treatments was maintained under -1.80 MPa. In the comparison of average value of leaf water potential from May to June by root-pruning degree, the root pruning both sides at 30 cm from trunk was lowest (-2.06 MPa), followed by the root pruning both sides at 60 cm (-2.02 MPa) and the root pruning one side at 30 cm (-1.91 MPa). Root pruning one side at 30 cm or both sides at 60 cm reduced photosynthetic rate from May to June by 80% or 65%, respectively, compared with no root pruning. So, the degree of decreasing total shoot length or average fruit weight compare to the no root pruning of the root pruning one side at 30 cm was 25% or 11%, respectively, and those of the root pruning both sides at 30 cm was 45% or 15%, respectively. However, the soluble solid content and fruit color of the root pruning was higher than those of the no root pruning, and those of the root pruning both sides was higher than root pruning one side. These results indicate that the fruit enlargement was decreased when the average value of average leaf water potential from May to June was under -1.80 MPa, and the shoot growth was decreased when that was under -2.00 MPa.

Linking the transpirable soil water content of a vineyard to predawn leaf water potential measurements

A new expression of the time derivative of predawn leaf water potential was proposed by equalizing two expressions of the grapevine transpiration. This expression was established when transpiration is the only driver of the vineyard water balance. Under Mediterranean climate, this condition is met for long periods of drought i.e. most of the summer time under the hypothesis that there is no water movement (capillary rise) from the deep layers of the soil. The proposed approach showed that changes in predawn leaf water potential (Ψpd) values are in inverse relation with the Total Transpirable Soil Water (TTSW) which characterizes the maximal water stock of the soil and in direct relation with reference evapotranspiration (ETo) and the basal crop coefficient (kcb) of the vine. The relation between Ψpd changes and cumulated ETo is linear with a slope related to the ratio of “kcb to TTSW”. This ratio can be therefore estimated from field measurements and climatic data.This approach was tested on two year observations performed by Acevedo-Opazo et al. (2010) in vineyards cultivated with cv. Shiraz and Mourvedre, without any irrigation. Analysis of the data obtained in 49 sites per vineyard for several dates in the very dry summers of 2003 (Shiraz) and 2005 (Mourvedre) showed strong and significant adjustments of the model. These results proved the linear relationship between the sum of ETo and Ψpd. For each site of the vineyard, the approach demonstrated the possibility to provide site-specific estimates of the ratio of kcb to TTSW. This theoretical and practical development could have applications for water management and soil studies in Mediterranean vineyards.

Growth, photosynthetic performance and antioxidative response of 'Hass' and 'Fuerte' avocado (Persea americana Mill.) plants grown under high soil moisture

‘Hass’ and ‘Fuerte’ avocado plants were grown under well-watered or waterlogged conditions. Results indicated significant effects on the majority of the allometric parameters in waterlogged plants, with ‘Fuerte’ displaying a more pronounced growth inhibition. Waterlogged conditions caused a progressive and simultaneous decline in net photosynthetic rate and stomatal conductance, earlier in ‘Fuerte’ than in ‘Hass’. Maximal potential quantum yield of PSII was unaffected by the soil water regime and/or variety and leaf water potential values in waterlogged plants were not more negative compared with control plants. ‘Fuerte’ waterlogged plants exhibited increased contents of thiobarbituric acid reactive substances, whereas oxidative injury was not detected in ‘Hass’. Finally, none of the two cultivars displayed valuable antioxidant potential, as evidenced by the decreased activities of the antioxidant enzymes superoxide dismutase, guaiacol peroxidase, glutathione peroxidase, and ascorbate peroxidase.

Effects of truncation intensity on the biomass allocation and physiological characteristics of Dendrocalamus latiflorus

The effects of three different truncation treatments, i.e., light, medium and heavy truncation treatments on biomass allocation, current-year twig indexes, and quantity of commodity lea-ves, net photosynthetic rate (Pn), transpiration rate (Tr), water use efficiency (WUE), and leaf water potential (LWP) values of Dendrocalamus latiflorus were studied, and the adaptation mechanisms and survival strategy of D. latiflorus under these silvicultural truncation treatments were discussed. Results showed that the biomass of D. latiflorus and its allocation rates were significantly affected by truncation treatments, compared with the untruncated control. Leaf to branch, leaf to stem, and branch to stem biomass ratios under all truncation treatments were significantly higher than under the untruncated control. The diameter, number, and length of current-year twigs, and the quantity of commodity leaves in light truncation and medium truncation treatments were markedly higher than in the control, and were increased by 43.0%, 53.3%, 29.8% and 39.5%, respectively, in medium truncation treatment compared with the control. After truncation treatments, the overall trend of the physiological characteristics of D. latiflorus, including Pn, Tr, WUE, LWP values, were displayed in the order of the peak stage > the telophase stage > the initial stage. The Pn, Tr and WUE values of D. latiflorus were significantly improved in the truncation treatments. The Pn va-lues were greatest in the medium truncation treatment followed by the light truncation treatment, heavy truncation treatment, and were the lowest in the control at the peak and telophase stages. At the peak and telophase stage the Pn values in the medium truncation treatment were 1.4 and 1.3 times as much as the control. The Tr values at the initial, peak and telophase stages were the greatest in the heavy truncation treatment, followed by the middle truncation treatment and the light truncation treatment, and were the lowest in the control. In this study, the medium truncation treatment showed a significant advantage in improving plant biomass allocation, quantity of commodity leaves, and other physiological indices, and could effectively improve the ability of moisture acquisition for D. latiflorus.

Is Soil Water Potential a Reliable Variable for Irrigation Scheduling in the Case of Peach Orchards?

Monitoring the crop water status of high-value crops such as fruit trees is generally performed through periodic measurements of physiological indicators on leaves or fruits using sophisticated instruments and complex procedures. These measurements are very often difficult to translate into irrigation advice. Soil water potential (SWP), however, is a basic soil water status variable that is correlated with plant water uptake, and it can easily be measured using sensors. Soil water potential can provide useful support for irrigation scheduling at the field scale, thus enhancing water savings in agricultural areas. In this work, we present the results of an experimental study conducted in the 2014 agricultural season on a peach orchard located in Lodi (Northern Italy). The purpose of this study was to evaluate the effects of an irrigation scheduling based on continuous SWP measurements collected at two soil depths (−15 and −35 cm) on the crop water status and the peach production relative to the farmer’s commonly adopted irrigation practice. To answer the question in the title, periodic measurements of physiological parameters such as leaf water potential, stomatal resistance (rs), transpiration (E), and crop water stress index were performed, along with monitoring of fruit size evolution and fruit sugar content at harvest. All of these variables were measured to assess the crop physiological state of the trees subjected to the two different irrigation treatments, with the final objective of determining whether the irrigation scheduling based on SWP measurements compromised the quality and quantity of produced peaches. Although obtained for only one agricultural season, the results showed that no considerably crop water stress occurred, even for the irrigation treatment based on SWP measurements. In particular, the most extreme values of leaf water potential, rs, E, and crop water stress index measured at midday were −2 MPa, 45 s m−1, 1.4 mm h−1 and 0.5, respectively, which are in good agreement with those observed in many studies for well-watered orchards in Mediterranean areas. In conclusion, we can stress that SWP monitoring can be considered to be a reliable alternative to the more costly and time-consuming physiological measurements for the irrigation scheduling of fruit crops such as peach orchards. This approach provides continuous information about the soil water status, thereby preventing plant water stress and reducing irrigation water consumption at the farm scale.

The effects of irrigation management on floral induction of ‘Tommy Atkins' mango in bahia semiarid

ABSTRACT This study aimed to evaluate reduction strategies of irrigation for proper management of floral induction and production of 'Tommy Atkins' mangoes, in the semiarid region of the Bahia state, Brazil. Five treatments with reduced irrigation levels based on crop evapotranspiration (ETc) were applied in two development stages, FI - flowering and FII – fruiting. Water depths were T1 - 0% of ETc in FI and 100% in FII; T2 - 25% of ETc in FI and 100% in FII; T3 - 50% of ETc in FI and 100% in FII; T4 - 75% of ETc in FI and 100% in FII; and T5 - 100% of ETc in FI and FII. The treatments were arranged in a randomized complete block design with six replications. Photosynthesis and transpiration rates in phases FI and FII were larger at 8 am than at 2 pm, regardless of the strategies used. These strategies lead to smaller values of photosynthesis, transpiration and leaf water potential within flowering stage. Productive characteristics were not affected by irrigation level reduction for flower induction process, only for the cycles evaluated. Strategies with 0% of ETc in FI and 100% in FII or 25% of ETc in FI and 100% in FII are appropriate to flower induction in 'Tommy Atkins' mango.

Photosynthesis impairments precede noticeable changes in leaf water status of mango plants infected by Ceratocystis fimbriata

Mango wilt, caused by Ceratocystis fimbriata, is a disease of great economic importance in mango production. Considering that the physiological effects of this vascular disease are not fully characterized, this study aimed to investigate some alterations in mango leaves from cultivars Uba and Tommy Atkins, respectively, resistant and moderately resistant to mango wilt. The relationships between relative lesion indices (upward relative lesion length (URLL), the downward relative lesion length (DRLL) and the radial fungal colonization (RFC)) and water relations and gas exchange and chlorophyll a fluorescence parameters were evaluated at 10, 20 and 30 days after inoculation. The foliar concentrations of lipid peroxidation, total pigments and total free amino acids and proline were also determined. The URLL, DRLL and RFC increased overtime in both Uba and Tommy Atkins cultivars, but reached the greatest values for cv. Tommy Atkins. Although cultivars did not present contrasting results for most of the evaluated parameters, the relative changes between inoculated and non-inoculated plants of each cultivar were more disparate in plants from cv. Tommy Atkins. There were decreases of 55, 73, 65 and 22 %, respectively, for net carbon assimilation rate (A), stomatal conductance to water vapor (g s), transpiration rate (E) and internal-to-ambient CO2 concentration ratio (C i/C a) for inoculated plants from cv. Tommy Atkins in comparison to the non-inoculated plants. For inoculated plants from cv. Uba, there were decreases of 25, 41 and 36 % for A, g s and E while C i/C a decreased by 17 % in relation to the non-inoculated plants. Inoculated plants of cvs. Tommy Atkins and Uba showed pronounced reductions for midday leaf water potential and apparent hydraulic conductance relative to the control. Inoculated plants from cv. Uba showed values of predawn leaf water potential that were 25 % higher in comparison to inoculated plants from cv. Tommy Atkins. In addition, decreases in total chlorophyll concentration as well as increases in free amino acids and lipid peroxidation occurred for inoculated plants from cv. Tommy Atkins.

Physiological characteristics, gas exchange, and plant ion relations of quinoa to different saline groundwater depths and water salinity

ABSTRACTThe objective of this study was to investigate the influence of saline groundwater depths (SGDs) (0.3, 0.55, and 0.80 m) with salinity equivalent to irrigation water salinity (WS) and irrigation WS (10, 20, 30, and 40 dS m−1) on physiological characteristics, gas exchange, and plant ion relations of quinoa in cylindrical lysimeters in greenhouse conditions. Root length density (RLD) in the soil layer close to the saline shallow groundwater decreased. Soil aeration was the key point for reduction in RLD by decreasing SGD that was intensified by the increase in WS. It is concluded that root of quinoa was sensitive to anaerobic soil conditions. Results showed that the mean value of leaf water potential (Ψ) dropped from −1.53 to −3.09 MPa by increasing WS from 10 to 40 dS m−1. Increasing WS from the lowest to the highest level resulted in 48% decrease in leaf photosynthesis rate (An). Results revealed that leaf stomatal conductance (gs) was more sensitive to salinity than An. Stomatal closure in quinoa started to occur when the Ψ value fell below approximately −1.0 MPa. In general, increasing WS from 10 to 40 dS m−1 resulted in about 4.6-fold, 2.1-fold, and 2.6-fold increase in plant Na+, Ca2+, and Cl− concentration, respectively.

Survival strategies of Centrosema molle and C. macrocarpum in response to drought

The response of a genotype each of C. moll e and C. macrocarpum to drought (low soil moisture availability) was studied in a seasonally dry tropical environment throughout 3 consecutive years. Changes in soil water content, leaf water relations and gas exchange, chlorophyll fluorescence, forage yield and leaf area index (LAI) were compared in well-watered and droughted plots. Soil water depletion during the study occurred mostly at 0‒20 cm depth. Minimum values of leaf relative water content, water potential (ψ l ) and net photosynthesis in unwatered plants were within the ranges: 68 ( C. molle ) to 70% ( C. macrocarpum ); -1.6 ( C. molle ) to -0.9 MPa ( C. macrocarpum ); and 8 ( C. molle ) to 10 µmol/m 2 /s ( C. macrocarpum ), respectively. Leaf movements helped to avoid excessive solar radiation incidence, yet efficiency of chloroplast Photosystem II in stressed leaves of C. molle was negatively affected. Above-ground biomass and LAI were reduced only in C. macrocarpum (45‒50% reduction) as a result of moisture stress. Leaves of both species behaved as isohydric, though larger declines in ψ l in C. molle may suggest a less effective control of water loss; this promoted more leaf senescence. Drought survival in these species depends on a combination of avoidance and tolerance strategies; the relative importance of both mechanisms depends on species and the duration and intensity of water deficit. Further studies with a higher number of accessions/ecotypes of each species are suggested in order to corroborate our findings. Keywords: Acclimation, physiological response, soil transpirable water, tropical forage legumes, water stress.

Combining leaf physiology, hyperspectral imaging and partial least squares-regression (PLS-R) for grapevine water status assessment

Physiological measurements are considered to be the most accurate way of assessing plant water status, but they might also be time-consuming, costly and intrusive. Since visible (VIS)-to-shortwave infrared (SWIR) imaging spectrometers are able to monitor various bio-chemical alterations in the leaf, such narrow-band instruments may offer a faster, less expensive and non-destructive alternative. This requires an intelligent downsizing of broad and noisy hyperspectra into the few most physiologically-sensitive wavelengths. In the current study, hyperspectral signatures of water-stressed grapevine leaves (Vitis vinifera L. cv. Cabernet Sauvignon) were correlated to values of midday leaf water potential (Ψl), stomatal conductance (gs) and non-photochemical quenching (NPQ) under controlled conditions, using the partial least squares-regression (PLS-R) technique. It was found that opposite reflectance trends at 530–550nm and around 1500nm – associated with independent changes in photoprotective pigment contents and water availability, respectively – were indicative of stress-induced alterations in Ψl, gs and NPQ. Furthermore, combining the spectral responses at these VIS and SWIR regions yielded three normalized water balance indices (WABIs), which were superior to various widely-used reflectance models in predicting physiological values at both the leaf and canopy levels. The potential of the novel WABI formulations also under field conditions demonstrates their applicability for water status monitoring and irrigation scheduling.