Effects Of Soil Water Deficit Research Articles

Evaluación de parámetros relacionados con el crecimiento de plantas de café (Coffea arabica L.) en respuesta al déficit hídrico del suelo

Contextualization: Water is indispensable for plant development, and its response to water deficit varies according to the species and their growth stages. Knowledge gap: The magnitude of the effect of soil water deficit on the growth of young coffee (Coffea arabica L.) plants evaluated over time is unknown. Purpose: Research was carried out to identify the effect of soil water deficit and, therefore, the sensitivity to drought in young coffee plants. Methodology: The deficit irrigation method was used. Coffee plants of the Cenicafé 1 variety were planted at three months old in cylindrical pots and conditioned for four months in mesh houses at Cenicafé - Planalto. After conditioning, the effect on plants' growth and dry matter subjected to five ranges of soil matric potential was evaluated over 140 days. Potentials ranged from -20±10 kPa (control) to -1600±100 kPa. Results and conclusions: The results showed that soil water deficit affects the growth of young coffee (C. arabica) plants, which could define C. arabica at this stage as drought sensitive. Plants subjected to the least stress and the extreme drought showed a 30% and 57% decrease in dry matter, respectively. For growth variables, the effect of water deficit was evident in the evaluations at 77, 113, and 140 days of treatment application. In all cases, the results showed differences between the extreme drought and the control of up to 30cm in height and equatorial diameter, 0.9 m2 of leaf area, 132 leaves, 3 branches, and 66 nodes. The mathematical models that explained the effect of drought on dry mass were of the logarithmic type. It was identified that for weather and soil conditions similar to those in the study, young coffee plants begin to deteriorate after 40 days of drought. With a soil matric potential close to -40 kPa, for a time of 120 days, coffee plants can lose 10% of dry mass, and when the potential exceeds -90 kPa there can be further losses in dry matter and decreases in the number of branches between the 77 and 113 days.

The Interactive Effects of Deficit Irrigation and Bacillus pumilus Inoculation on Growth and Physiology of Tomato Plant.

The effects of inoculating plant growth promoting rhizobacteria (PGPR) and soil water deficits on crop growth and physiology remain largely unknown. Here, the responses of leaf gas exchange, growth, and water use efficiency (WUE) of tomato plants to Bacillus pumilus (B.p.) inoculation under four irrigation strategies (I1-I4) were investigated in a greenhouse. Results showed that soil water deficits, especially at I4 (20%, v/v), significantly decreased leaf stomatal conductance (gs), transpiration rate (Tr), and photosynthetic rate (An), and the decrease of gs and Tr were more pronounced than An. Reduced irrigation regimes significantly lowered dry matter and plant water use both in the non-B.p. control and the B.p. plants, while reduced irrigation significantly increased plant WUE, and B.p. inoculation had little effect on this parameter. Synergistic effects of PGPR and deficit irrigation on leaf gas exchange, leaf abscisic acid content, and stomatal density were found in this study, and specifically, B.p. treated plants at I4 possessed the highest WUE at stomatal and leaf scales, suggesting that B.p. inoculation could optimize water use and partly alleviate the negative effects of soil water deficit. These findings provide useful information for effective irrigation management and the application of PGPR in agriculture in the future.

Water deficit responses of field-grown Pinot noir mediated by rootstock genotypes in a cool climate region

Under the global warming scenario, water scarcity is expected to intensify in most grape-growing regions. The use of drought-tolerant rootstocks is considered a useful tool to mitigate the negative effects of soil water deficit on vine functioning. Differences in leaf gas exchange, plant water status, specific hydraulic conductivity in petioles (Kpetiole), xylem vessel size and vegetative vigour of field-grown Pinot noir grafted onto five rootstocks (3309C, 101-14 MGt, Kober 5BB, Riparia Gloire de Montpellier, 41B MGt) were investigated during one season under water deficit in Switzerland. The water deficit was imposed by installing waterproof and non-reflecting plastic sheets on the soil from March to harvest (September) to avoid rainfall infiltration. Rootstocks had stronger effects on vine water status than on gas exchanges. During the grape ripening stage, vines grafted onto 41B MGt and 101-14 MGt were characterised by more severe water stress as shown by the lowest values of pre-dawn leaf (Ψpd), stem water potential (Ψstem) and water stress integral (SΨ), whereas 3309C and Kober 5BB rootstocks induced milder effects. Significant differences in photosynthesis (A), stomatal conductance (gs) and transpiration (E) were only observed between vines grafted onto 41B MGt and 3309C at later stages of ripening. Changes induced by rootstocks in shoot vigour, Kpetiole and the number and size of xylem vessels in petioles and stems were correlated to differential responses of Pinot noir to water deficit. The increased vegetative vigour induced by 3309C and Kober 5BB was associated with the highest Kpetiole, xylem vessel size and a good plant water status of Pinot noir under low soil water availability. Kober 5BB induced the highest yield, probably due to the better vine water status, whereas vines grafted onto 41B MGt showed the lowest malic acid content and yeast assimilable nitrogen in berries.

Physiological response of onion (Allium cepa L.) seedlings to shungite application under two soil water regimes

The application of carbon-rich substrates to agricultural soils is discussed as a strategy to improve soil properties and fertility, which can affect plant physiological traits and enhance agricultural crop yield. The aim of this study was to evaluate if shungite, carbon-rich sedimentary-volcanic rock, may improve plant ecophysiological traits under sufficient water supply as well as soil water deficit. A pot culture experiment was conducted with onion (Allium cepa L.) seedlings, using four shungite concentrations (0, 5, 10 and 20 g kg−1) in an Umbric Podzols and two water regimes: well-watered and drying-wetting cycles. Soil water deficit decreased root nutrient content, depressed seedlings growth, net CO2 assimilation rate (An), stomatal conductance (gs) and the respiration rates in both darkness (Rd) and the light (Rl), but increased water use efficiency (WUE) at leaf level. Shungite application decreased the leaf necrosis under both water regimes and increased total leaf length of DW seedlings. Compared with the well-watered conditions, under drying-wetting cycle shungite stimulated the increase of the An rate and WUE at low measurement temperature. No significant effect of shungite was found for Rd, Rl, Rl/Rd, Rd/Ag (Ag = An + Rl) and Rl/Ag regardless soil water regimes. Shungite application was not so successful to eliminate the negative effects of soil water deficit on growth and physiological processes of A. cepa. The observed positive effects of shungite on the physiological traits of onion seedlings were more likely associated with the increase in the content of nutrients than with the improvement in soil water properties.

Root system plays an important role in responses of plant to drought in the steppe of China

AbstractIn the temperate grasslands of northern China, there exists a large range of soil texture. However, previous studies have mainly focused on the effect of climate water deficit on plant traits and have paid little attention to the effect of soil water deficit because grasses tend to use rainfall water directly. We measured eight drought‐related plant traits of 12 widely distributed perennial species in the temperate grassland in northern China and examined drought‐related plant traits under different aridity index ([ET0 − P]/ET0) and soil sand/clay ratio. The 12 species were categorized into three functional groups: fibrous‐rooted C4 species, fibrous‐rooted C3 species, and tap‐rooted C3 species. Our results showed that increasing climate drought had influence on all selected functional groups, and the influence on aboveground biomass and height was especially large on fibrous‐rooted C3 species. Coarse soil led to increased root length of fibrous‐rooted C3 and tap‐rooted C3 species. Our results imply that root system can be important to plant responses under drought, and soil texture can have influence on plant, though most of the traits show resistance to coarser soil.

Effects of Soil Water Deficit on Three Tree Species of the Arid Environment: Variations in Growth, Physiology, and Antioxidant Enzyme Activities

Low water availability predicted under climate change is a major abiotic factor limiting plants growth and productivity. In this study a greenhouse experiment was conducted on three important tree species of arid environment: Conocarpus erectus (CE), Acacia modesta (AM), and Salix tetrasperma (ST). Young saplings were subjected to control (C), medium (MWD) and severe soil water deficit (SWD) treatments and response was evaluated. Results showed that in all the three species leaf, stem and root dry weight production remained similar to C under MWD treatment but decreased significantly under SWD. The highest decrease in total dry weight was noticed in ST and the lowest was evidenced in AM under SWD. Root:shoot ratio increased significantly in both CE and AM under MWD and SWD. Furthermore, chlorophyll content decreased while proline content increased significantly in both MWD and SWD treatments. The production of oxidants (hydrogen peroxide and superoxide anions) and antioxidants (superoxide dismutase, catalase, peroxidase and ascorbate peroxidase) increased significantly under both MWD and SWD treatments and were the highest in AM in both MWD and SWD treatments. Therefore, we may conclude that all the three species can tolerate medium water stress due to increased root production and an effective antioxidant defense mechanism.

Sensitivity of Northern Highbush Blueberry Cultivars to Soil Water Deficits during Various Stages of Fruit Development

In many regions, water limitations are increasing because of frequent and persistent droughts and competition for water resources. As a result, growers in these regions, including those producing blueberries, must limit irrigation during drier years. To identify the most critical periods for irrigation, we evaluated the effects of soil water deficits during various stages of fruit development on different cultivars of northern highbush blueberry (Vaccinium corymbosum L.). The study was conducted for 2 years in western Oregon and included two early season cultivars, ‘Earliblue’ and ‘Duke’, a midseason cultivar, ‘Bluecrop’, and two late-season cultivars, ‘Elliott’ and ‘Aurora’. Volumetric soil water content and stem water potentials declined within 1 to 2 weeks with no rain or irrigation in each cultivar and were lowest during the later stages of fruit development. Water deficits reduced berry weight by 10% to 15% in ‘Earliblue’ and ‘Elliott’ when irrigation was withheld in the second year during early or late stages of fruit development and by 6% to 9% in ‘Aurora’ when irrigation was withheld in either year during the final stages of fruit development. However, water deficits only reduced yield significantly in ‘Aurora’, which produced 0.8 to 0.9 kg/plant fewer fruit per year when irrigation was withheld during fruit coloring. In many cases, water deficits also reduced fruit firmness and increased the concentration of soluble solids in the berries, but they had inconsistent effects on titratable acidity and sugar-to-acid ratios. As a rule, water deficits were most detrimental during later stages of fruit development, particularly in midseason and late-season cultivars, which ripened in July and August during the warmest and driest months of the year.

Effects of Soil Water Deficit at Different Growth Stages on Maize Growth, Yield, and Water Use Efficiency under Alternate Partial Root-Zone Irrigation

To investigate the effects of alternate partial root-zone irrigation (APRI) and water deficit at different growth stages on maize growth, physiological characteristics, the grain yield, and the water use efficiency (WUE), a pot experiment was conducted under a mobile automatic rain shelter. There were two irrigation methods, i.e., conventional irrigation (CI) and APRI; two irrigation levels, i.e., mild deficit irrigation (W1, 55%~70% FC, where FC is the field capacity) and serious deficit irrigation (W2, 40%~55% FC); and two deficit stages, i.e., the seedling (S) and milking stage (M). Sufficient irrigation (W0: 70%~85% FC) was applied throughout the growing season of maize as the control treatment (CK). The results indicated that APRI and CI decreased the total water consumption (ET) by 34.7% and 23.8% compared to CK, respectively. In comparison to CK, APRI and CI increased the yield-based water use efficiency (WUEY) by 41% and 7.7%, respectively. APRI increased the irrigation water efficiency (IWUE) and biomass-based water use efficiency (WUEB) by 8.8% and 25.5% compared to CK, respectively. Additionally, ASW1 had a similar grain yield to CK and the largest harvest index (HI). However, the chlorophyll and carotenoid contents were significantly reduced by 13.7% and 23.1% under CI, and by 11.3% and 20.3% under APRI, compared to CK, respectively. Deficit irrigation at the milking stage produced a longer tip length, resulting in a lower grain yield. Based on the entropy weight method and the technique for order preference by similarity to an ideal solution (TOPSIS) method, multi-objective optimization was obtained when mild deficit irrigation (55%~70% FC) occurred at the seedling stage under APRI.

Photosynthesis product allocation and yield in sweetpotato with different irrigation levels at mid-season

Soil water deficit is one of the important factors affecting the source–sink balance of sweetpotato at mid-season growth (storage root initiation period). However, water regulation at mid-season sweetpotato growth is often ignored. In this study, field trials were conducted to diagnose leaves in the middle of sweetpotato growth, and then three mid-season irrigation levels (CK: 0 m3/hm2; W1: 150 m3/hm2; W2: 300 m3/hm2) were established. The effects of different irrigation levels on photosynthetic physiological indexes, 13C transfer allocation, and yield of sweetpotato were studied. The results revealed that mid-season irrigation significantly increased the relative moisture content of sweetpotato leaves, maximum photochemical efficiency (Fv/Fm), and net photosynthetic rate (Pn) (P < 0.05), which effectively alleviated the effects of soil water deficit. The Pn values with irrigation treatments W1 and W2 were significantly higher than those with control (CK) treatment in all three study periods. Among these, the W2 treatment had the highest Pn at 70 d, an increase of 113.4% compared with CK in 2019 test, and W1 had the highest Pn at 110 d and 150 d (P < 0.05). The trend of stomatal conductance (Gs) was basically consistent with Pn. The transpiration rate (Tr) of W2 was the highest at 70 d, an increase of 59.8–69.7% compared with CK, but the Tr of W1 was the highest at 110 d and 150 d. The 13C total accumulation in the W1 treatment was the highest at 70 d, 110 d, and 150 d, when it was 21.9%, 20.4%, and 33.1% higher than that of the W2 treatment in 2019 test (P < 0.05), respectively. The 13C allocation rate of storage roots treated with W1 was the highest in all periods, reaching as high as 73.1–76.1% at 150 d (P < 0.05). At 70 d, the 13C allocation rate of fiber roots and stems was highest in the CK treatment, whereas the 13C allocation rate of leaves was highest in W2 (P < 0.05). At 110 d and 150 d, the 13C allocation rate of stems and leaves in CK was the highest (P < 0.05). The biomass of W2 was the highest at 70 d, but the root-to-shoot ratio and the dry weight of root became gradually lower than those of the CK and W1 treatments at the late season, when they were reduced by 28.4% and 32.2% compared to W1 at 150 d in 2019 test (P < 0.05). The yield of W1 was increased significantly by 33.3–34.9% compared with CK (P < 0.05), but W2 only had an increased production of 14.5–20.7% (P < 0.05) compared to CK (P < 0.05). The irrigation water utilization efficiency of W2 was 59.4–61.8% and 39.1–43.5% lower than those of the CK and W1 treatments (P < 0.05), respectively. Together, these results validate the field sweetpotato mid-season water management model, which is of great significance for guiding actual production of sweetpotato and increasing the potential of sweetpotato.

Water Deficit Effects on Soybean Root Morphology and Early-Season Vigor

This study was conducted to determine if root, shoot, and gas exchange traits of determinate and indeterminate soybean cultivars respond differently to soil water deficit. The effect of soil water deficit imposed 4 and 10 days after sowing on growth and development parameters of determinate and indeterminate soybeans was evaluated for 18 and 30 days in experiment I and II, respectively. At both 18 and 30 days after seeding, nearly all root, shoot, and physiological parameters were inversely correlated with the soil moisture level, and the adverse effects of drought stress were more evident in Progeny P5333RY than in Asgrow AG5332. For both cultivars, the effect of soil water deficit on net photosynthesis was mainly due to stomatal limitations. The developed algorithms for the plant processes based on the environmental productivity index were not different between the cultivars, suggesting that soybean plants respond in a similar way irrespective of their growth habits, probably due to the shorter period of water stress.

Changes in growth and soil microbial communities in reciprocal grafting clones between Populus deltoides males and females exposed to water deficit conditions

Our findings highlight that male-rooted clones (M/M and F/M) of Populus deltoides are more water-deficit tolerant than female-rooted clones (F/F and M/F), as shown by a smaller decrease in total biomass and net photosynthetic rate in the male-rooted clones. It has been reported that graft clones (female scion and male rootstock) in poplars may be an option to mitigate the effects of water deficit on plants. However, the extent to which grafting mitigates the effect of soil water deficit on soil microorganisms remains poorly understood. The research was designed to investigate the effects of soil water deficit on plant growth, soil microbial communities, and soil enzymatic activities of the reciprocal graft clones of P. deltoides. Four different graft clones (female shoot scion and female rootstock, F/F; male shoot scion and female rootstock, M/F; male shoot scion and male rootstock scion, M/M; and female shoot scion and male rootstock, F/M) in P. deltoides were used. Two watering regimes, irrigation and soil water deficit (i.e., non-irrigation conditions, natural levels of precipitation) were included in the experiments. The microbial community structure was quantified using phospholipid fatty acid. Under water deficit, the decreases in total biomass, net photosynthetic rates, and leaf nitrogen content were more evident in M/M and F/M than in F/F and M/F. Bacterial phospholipid fatty acids (PLFAs) and actinomycetal PLFAs remained unaffected in the four graft clones. In contrast, during soil water deficit, fungal PLFAs were higher in M/M and F/M soil coincided with higher extracellular activities of β-1,4-N-acetyl-glucosaminidase and leucine aminopeptidase. Male-rooted clones (M/M and F/M) are more tolerant to water deficit than female-rooted clones (F/F and M/F). It is possible that the better performance of M/M and F/M, when exposed to water deficit, is associated mainly with higher fine root activity, greater specific root length and root/shoot ratio as well as increased fungal PLFAs.

Effect of Deficit Irrigation and Planting Method on Maize Plants under Middle Delta Conditions of Egypt

Two field experiments were carried out at El-Gemmeiza Agricultural Research Station Farm, Egypt, during 2017 and 2018 summer seasons to study the effect of soil water deficit and the planting method on maize plant under Middle Delta conditions of Egypt. Irrigation at 65% available soil moisture depletion (AVSMD) did not significantly decrease chlorophyll content, dry matter (DM), leaf area index (LAI), crop growth rate (CGR), relative water content (RWC), osmotic potential (OP), ear length, ear diameter, rows per ear, kernels per row,100-kernel weight and grain yield. 50 % irrigation treatment decreased crop water productivity (CWP) by 9.93 % across the two seasons compared to irrigation at 80 % AVSMD. Irrigation at 80 % of AVSMD increased drought sensitivity (YR/ SD) and the drought susceptibility index (S) and CWP in both seasons. The reduction in WCU due to irrigation at 65 % of AVSMD reached 19.34 to 20.30 % and the improvement in CWP was 15.42 to 14.37 % compared to the irrigation at 50 % (control) in both seasons, respectively. Sowing maize plants on beds140 cm apart on both sides of beds and the distance between the hills was 25 cm (24000 plants per feddan) resulted in the highest chlorophyll content, DM, LAI, CGR, RWC, ear height, ear length, 100-kernel weight and grain yield in the two seasons, This treatment decreased YR/SD and S. Decreasing YR/SD and S. such decreases were accompanied with increasing CWP. It can be recommend that sowing maize plants on beds140 cm apart on both sides of beds, and the distance between hills 25 cm and irrigation at 65 % of AVSMD decreased WCU and improved CWP, in addition this treatment did not significantly decrease yield and its components and attained the lowest YR/S and S values.

Effects of soil moisture on water transport, photosynthetic carbon gain and water use efficiency in tomato are influenced by evaporative demand

Although deficit irrigation has long been recognized as a water-saving practice, the beneficial effects on crop production and on water use efficiency under varying atmospheric evaporative demands has rarely been examined. In the present study, the coordinated effects of soil moisture and atmospheric vapor pressure deficit (VPD) on photosynthetic carbon gain versus water transport and water use efficiency in tomato were addressed. Experiments were designed with factorial combinations of two levels of VPD and two gradients of soil moisture. Low VPD (VPD < 1.0 kPa) compensated for the negative effect of soil water deficit on plant photosynthesis and productivity by reducing the resistance for CO2 transport. Moreover, low VPD moderated water stress by reducing the force driving passive water movement and preventing turgor loss, which sustained stomatal openness and reduced the resistance to CO2 uptake. In addition to stomatal conductance, the mesophyll conductance for CO2 transport from the substomatal cavities to the chloroplasts was increased synchronously in low-VPD-grown plants. The effect of water-use efficiency on the yields and plant biomass was substantially increased in the low-VPD treatment for both deficit irrigation and well-irrigated conditions. Water use efficiency was maximized in the combinatory treatment of deficit irrigation and low VPD. The present study demonstrated that the beneficial effect of deficit irrigation on tomato was amplified by decreasing VPD to the range of 0.5–1 kPa by decreasing the resistance for CO2 uptake from the atmosphere to the carboxylation site. Moreover, the adverse effects of deficit irrigation were pronounced with increased VPD when exceeding 1 kPa. Therefore, VPD plays significant roles in mediating the magnitudes of the beneficial or negative effects of deficit irrigation. The present study highlights the significance of the integrative regulation of soil and atmospheric moisture conditions, which provides novel insight for water-saving tomato production.

The impact of rising temperatures on water balance and phenology of European beech (Fagus sylvatica L.) stands

In this article, we outline the set-up and the application of an eco-hydrological box model, with the aim to describe the water balance of deciduous (Fagus Sylvatica L.) forest stands. The water balance model (WBM) uses standard meteorological parameters as input variables and runs on a daily time step. It consists of two modules. The aboveground module (1) comprises routines for fog precipitation generation, precipitation interception and snowfall/snowmelt dynamics. Covered belowground processes (2) are bypass flow, percolation, soil evaporation and transpiration, where the latter two processes are considered separately. Preceding to the WBM, a routine is introduced, specifying the intra-annual foliage dynamics of beech. Emphasis is also laid on the inter-annual variation of beech phenology. Leaf sprouting and leaf senescence are calculated as functions of day-length and air temperature. The WBM was applied to four European beech dominated forest stands in the northeastern part of Austria. They are located on a gradient of declining annual precipitation (from west to east). The two easterly sites are located close to the (dry) limit of the natural distribution of beech. Records of soil moisture were used for the adjustment of 26 parameters. On all sites the calibration process (simulated annealing) delivered good predictions of soil moisture (Nash–Sutcliffe efficiency ≥ 0.925). Then, the obtained parameterization was used to apply different scenarios of global warming. The temperature was increased step-wisely up to 4 °C. All scenarios were run (1) with present phenological conditions and (2) with phenology responding to higher temperatures. This way, we wanted to assign the effect of higher temperatures and longer growing seasons on the water dynamics of the forest stands. A warming of 1 °C corresponded roughly to an elongation of the growing season of 4.5 days, where the start of the growing season was affected more strongly than the end. Apparently, higher temperatures led to drier soils. The strongest change was observed in early summer, also amplified by an earlier start of the growing season. Rising temperatures led to lower export fluxes of liquid water, simultaneously increasing evapotranspiration (ET). The gain in ET was almost entirely assignable to increased soil evaporation. Drier soils led to a sharp depression of transpiration during summer months. This decline was compensated by the effect of elongated growing seasons. The risk of severe drought was increased by higher temperatures, but here the contribution of growing season length was negligible. Drier soils seem to hamper the stands’ productivity. For all warming scenarios, the estimated increase of the gross primary production, caused by longer periods of assimilation, is nullified by the effect of soil water deficit in mid-summer.

Monitoring the Effects of Water Stress in Cotton Using the Green Red Vegetation Index and Red Edge Ratio

The main objective of this work was to study the feasibility of using the green red vegetation index (GRVI) and the red edge ratio (RE/R) obtained from UAS imagery for monitoring the effects of soil water deficit and for predicting fibre quality in a surface-irrigated cotton crop. The performance of these indices to track the effects of water stress on cotton was compared to that of the normalised difference vegetation index (NDVI) and crop water stress index (CWSI). The study was conducted during two consecutive seasons on a commercial farm where three irrigation frequencies and two nitrogen rates were being tested. High-resolution multispectral images of the site were acquired on four dates in 2017 and six dates in 2018, encompassing a range of matric potential values. Leaf stomatal conductance was also measured at the image acquisition times. At harvest, lint yield and fibre quality (micronaire) were determined for each treatment. Results showed that within each year, the N rates tested (&gt; 180 kg N ha−1) did not have a statistically significant effect on the spectral indices. Larger intervals between irrigations in the less frequently irrigated treatments led to an increase (p &lt; 0.05) in the CWSI and a reduction (p &lt; 0.05) in the GRVI, RE/R, and to a lesser extent in the NDVI. A statistically significant and good correlation was observed between the GRVI and RE/R with soil matric potential and stomatal conductance at specific dates. The GRVI and RE/R were in accordance with the soil and plant water status when plants experienced a mild level of water stress. In most of the cases, the GRVI and RE/R displayed long-term effects of the water stress on plants, thus hampering their use for determinations of the actual soil and plant water status. The NDVI was a better predictor of lint yield than the GRVI and RE/R. However, both GRVI and RE/R correlated well (p &lt; 0.01) with micronaire in both years of study and were better predictors of micronaire than the NDVI. This research presents the GRVI and RE/R as good predictors of fibre quality with potential to be used from satellite platforms. This would provide cotton producers the possibility of designing specific harvesting plans in the case that large fibre quality variability was expected to avoid discount prices. Further research is needed to evaluate the capability of these indices obtained from satellite platforms and to study whether these results obtained for cotton can be extrapolated to other crops.

Tomato yield and water use efficiency change with various soil moisture and potassium levels during different growth stages.

Faced with the scarcity of water resource and irrational fertilizer use, it is highly important to supply plants with water and fertilizer at desiderated stages to improve yield with high water use efficiency (WUE). A pot experiment was conducted to investigate the effects of growth stage-specific water deficiency and potassium (K) fertilization on tomato yield and WUE. The entire growing season of tomato was divided into 5 stages: vegetative growth stage (VG), flowering and fruit setting stage (FS), early fruit growth stage (FG), fruit development stage (FD) and fruit maturity stage (FM). Three soil moisture (W) and three K fertilization levels were set up. W levels included W1, W2 and W3, indicating that soil water was maintained at 60–70% field capacity, 70–80% field capacity, and 80–90% field capacity, respectively. K levels included K1, K2 and K3, indicating that 0 g K2O per kg soil, 0.46 g K2O per kg soil and 0.92 g K2O per kg soil was applied. All combinations of the three W and three K levels were solely imposed at each of the five growth stages, for other four stages, plants were watered to 80–90% field capacity without K fertilizer (W3K1). The permanent W3K1 over the entire growth stage was taken as control (CK). The results showed that W deficiency imposed at all stages significantly affected tomato yield (P<0.01), except for VG stage in which W deficiency did not cause yield loss. K fertilization level during FS or FM stage had a significant effect on yield (P<0.01). A significant interaction effect of W and K on yield was only observed during FM stage. For WUE, significant effect of W deficiency at FS, FD and FM stages were observed, and a significant effect of K levels at FS, FD and FM stages was observed. Specifically, K fertilization was necessary during specific growth stage of tomato (i.e. FS and FM). During FS stage, even if a sufficient water supply seems necessary, a deficit irrigation with K fertilization could be applied as K fertilization could alleviate the negative effect of soil water deficit, however, excess of K fertilization during FM stage should be avoided to maintain tomato yield and WUE.

Warming and water deficit impact leaf photosynthesis and decrease forage quality and digestibility of a C4 tropical grass.

Global warming is predicted to cause more intense extreme events such as heat waves, flooding and severe droughts, producing significant effects on agriculture. In tropics, climate change will severely impact livestock production affecting water availability, forage quality and food for cattle. We investigated the isolated and combined effects of soil water deficit (wS) and + 2°C increase in canopy temperature (eT) on leaf gas exchange, chlorophyll fluorescence, carbohydrate content, forage quality and in vitro dry matter digestibility (IVDMD) of a field-grown C4 tropical forage grass Panicum maximum Jacq. using a temperature-free air-controlled enhancement (T-FACE) system. The wS and eT treatments showed no effects on photosystem II photochemistry. However, wS under ambient temperature decreased net photosynthesis rate (A), stomatal conductance (gs ) and maximum rate of carboxylation of Rubisco (Vcmax ), leading to a reduced starch content in leaves. A 16% reduction in leaf dry mass (LDM) and reduction in forage quality by increasing fibers, reducing crude protein (CP) and decreasing the IVDMD was also observed by effect of wS. Warming under adequate soil moisture (eT) significantly increased LDM by 25% but reduced the forage quality, increasing the lignin content and reducing starch, CP and digestibility. The combined wSeT treatment reduced A, gs , Vcmax and the forage quality. When compared to control, the lignin content in leaves increased by 43, 28 and 17% in wS, eT and wSeT, respectively, causing a significant reduction in IVDMD. We concluded that despite physiological mechanisms to acclimate to warming, both warming and water deficit will impair the quality and digestibility of C4 tropical pastures.

Is a reduction in stomatal conductance the main strategy of Garcinia brasiliensis (Clusiaceae) to deal with water stress?

A reduction in rainfall is predicted by climate models for some parts of the Amazon, and a decline in stomatal conductance (gs) is often the main effect of drought. The physiological effect of soil water deficit on other physiological traits has been little investigated in Amazonian trees. In this work we assess the effect of soil water deficit on leaf pigment content, gas exchange, chlorophyll fluorescence, total leaf area (AL), consumptive use of water (CUW, total amount of water used for irrigation), and biomass accumulation. Plants of Garcinia brasiliensis were grown in pots under greenhouse conditions and submitted to soil water deficit for 90 days, when several physiological parameters were measured. Water deficit was induced by reducing soil water content (SWC) to 25, 50 and 75% of field capacity (FC). The control was soil at 100% FC. Midday leaf water potential varied from − 0.72 MPa (SWC at 25% FC) to − 0.29 MPa in well-irrigated plants. Subjecting the plants to soil water deficit did not affect light saturating photosynthesis, leaf pigment content, Ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco) activity or fluorescence parameters. Under moderate water stress Garcinia plants did not reduce stomatal conductance (gs) which remained rather unchanged. Instead, we found that mild water stress led to an increase in total non-structural carbohydrates, and as the stress progressed AL substantially declined, at a SWC of 25% FC. Drastic reduction of AL in plants exposed to SWC of 25% FC contributed to a reduction in total biomass accumulation, and a drop in AL resulted in a decline in CUW in this treatment. These results show that although there is no effect of moderated water stress on photosynthesis, gs or photochemical responses, there is a remarkable effect of moderate drought on biomass accumulation.

Simulation of Stomatal Conductance and Water Use Efficiency of Tomato Leaves Exposed to Different Irrigation Regimes and Air CO2 Concentrations by a Modified "Ball-Berry" Model.

Stomatal conductance (gs) and water use efficiency (WUE) of tomato leaves exposed to different irrigation regimes and at ambient CO2 (a[CO2], 400 ppm) and elevated CO2 (e[CO2], 800 ppm) environments were simulated using the “Ball-Berry” model (BB-model). Data obtained from a preliminary experiment (Exp. I) was used for model parameterization, where measurements of leaf gas exchange of potted tomatoes were done during progressive soil drying for 5 days. The measured photosynthetic rate (Pn) was used as an input for the model. Considering the effect of soil water deficits on gs, an equation modifying the slope (m) based on the mean soil water potential (Ψs) in the whole root zone was introduced. Compared to the original BB-model, the modified model showed greater predictability for both gs and WUE of tomato leaves at each [CO2] growth environment. The models were further validated with data obtained from an independent experiment (Exp. II) where plants were subjected to three irrigation regimes: full irrigation (FI), deficit irrigation (DI), and alternative partial root-zone irrigation (PRI) for 40 days at both a[CO2] and e[CO2] environment. The simulation results indicated that gs was independently acclimated to e[CO2] from Pn. The modified BB-model performed better in estimating gs and WUE, especially for PRI strategy at both [CO2] environments. A greater WUE could be seen in plants grown under e[CO2] associated with PRI regime. Conclusively, the modified BB-model was capable of predicting gs and WUE of tomato leaves in various irrigation regimes at both a[CO2] and e[CO2] environments. This study could provide valuable information for better predicting plant WUE adapted to the future water-limited and CO2 enriched environment.

Photosynthesis and water relations of peach palms (Bactris gasipaes Kunth) under soil water deficit

The Amazonian peach palm is presently the main species of heart-of- palm producer in many Brazilian regions. Here we evaluated the effects of soil water deficit and rewatering on leaf water potential (ψleaf), gas exchange and chlorophyll fluorescence emission in peach palms. Plants were grown in 80 L-plastic pots under greenhouse conditions. Water deficit was imposed by water withdrawing for 13 days, when irrigation was re-established for 8 days more. ψleaf was measured at 5:30 a.m. and 1:30 p.m. Gas exchange measurements were performed at 8:00 a.m. and at 2:00 p.m., after chlorophyll a fluorescence evaluations. The minimum ψleaf value observed at predawn was − 1.6 MPa, when net CO2 assimilation (PN) was zero on the 13th day of water deficit, thus showing mesophytes characteristics. The sharp PN decrease of 94%, 6 days after the beginning of treatments, demonstrated the drastic effect of the soil water deficit. After rewatering, a rapid recuperation of ψleaf was observed, whereas PN, transpiration rate (E) and stomatal conductance (gs) recovered more slowly, reaching values exhibited by the control plants only 7 days after rewatering. The lower maximal quantum yield of photosystem II (PSII) (FV/FM) values in the midday for plants under water deficit indicated dynamic photoinhibition of PS II to excessive PPFD. These results suggest a drought tolerance of peach palm plants, showing stomatal control of water losses and PN limitation, whereas the photosynthetic apparatus was maintained by photoprotection processes.