Water deficit in field-grown Gossypium hirsutum primarily limits net photosynthesis by decreasing stomatal conductance,increasing photorespiration,and increasing the ratio of dark respiration to gross photosynthesis

Much effort has been expended to improve irrigation efficiency and drought tolerance of agronomic crops; however, a clear understanding of the physiological mechanisms that interact to decrease source strength and drive yield loss has not been attained. To elucidate the underlying mechanisms contributing to inhibition of net carbon assimilation under drought stress, three cultivars of Gossypium hirsutum were grown in the field under contrasting irrigation regimes during the 2012 and 2013 growing season near Camilla, Georgia, USA. Physiological measurements were conducted on three sample dates during each growing season (providing a broad range of plant water status) and included, predawn and midday leaf water potential (Ψ_PD and Ψ_MD), gross and net photosynthesis, dark respiration, photorespiration, and chlorophyll a fluorescence. End-of-season lint yield was also determined. Ψ_PD ranged from −0.31 to −0.95 MPa, and Ψ_MD ranged from −1.02 to −2.67 MPa, depending upon irrigation regime and sample date. G. hirsutum responded to water deficit by decreasing stomatal conductance, increasing photorespiration, and increasing the ratio of dark respiration to gross photosynthesis, thereby limiting P_N and decreasing lint yield (lint yield declines observed during the 2012 growing season only). Conversely, even extreme water deficit, causing a 54% decline in P_N, did not negatively affect actual quantum yield, maximum quantum yield, or photosynthetic electron transport. It is concluded that P_N is primarily limited in drought-stressed G. hirsutum by decreased stomatal conductance, along with increases in respiratory and photorespiratory carbon losses, not inhibition or down-regulation of electron transport through photosystem II. It is further concluded that Ψ_PD is a reliable indicator of drought stress and the need for irrigation in field-grown cotton.     

Soil organic carbon and nitrogen stocks in an age-sequence of poplar stands planted on marginal agricultural land in Northeast China

The capacity of a ground-based canopy sensor to detect stress-related parameters of cotton (Grossypium hirsutum) was investigated in a split-plot field experiment for two consecutive growing seasons in central Greece. Three levels of irrigation (22, 31 and 40 cm water) were the whole-plot factor and three rates of fertilizer (60, 110 or 160 kg N ha^?1) were the split-plot factor with three replications. Irrigation level was the major factor that explained variations in leaf isotopic composition (δ¹⁵N and δ¹³C) within growing seasons and cotton yield at harvest. The rate of fertilizer application did not have a significant effect on cotton yield because there was sufficient residual soil N to meet crop needs. Canopy NDVI was highly correlated to yield when cotton response to differential irrigation was detected. The obtained correlations between canopy reflectance and stress-related parameters (leaf N, δ¹⁵N and δ¹³C) and the stability of the relationship between NDVI and yield over two consecutive seasons indicated that ground-based remote sensing can be used to assess the level of water stress that occurred during the growing season. The application of this technology for in-field monitoring of water stress may prove valuable in semiarid regions where water is often the most limiting factor in crop production.     

Aerated subsurface irrigation water gives growth and yield benefits to zucchini, vegetable soybean and cotton in heavy clay soils

Inadequate oxygen concentration in the root zone is a constraint to plant performance particularly in heavy, compacted and/or saline soils. Sub-surface drip irrigation (SDI) offers a means of increasing oxygen to plant roots in such soils, provided irrigation water can be hyper-aerated or oxygenated. Hydrogen peroxide (HP) at the rate of 5 litre ha⁻¹ at the end of each irrigation cycle was injected through SDI tape to a field-grown zucchini (courgette) crop (Cucurbita pepo) on a saturated heavy clay soil in Queensland, Australia. Fruit yield, number and shoot weight increased by 25%, 29% and 24% respectively due to HP treatment compared to the control. Two pot experiments with vegetable soybean (Glycine max) and cotton (Gossypium hirsutum) compared the effectiveness of HP and air injection using a Mazzei air injector (a venturi), throughout the irrigation cycle in raising crop yield in a heavy clay soil kept at saturation or just under field capacity. Fresh pod yield of vegetable soybean increased by 82–96% in aeration treatments compared with the control. The yield increase was associated with more pods per plant and greater mean pod weight. Significantly higher above ground biomass and light interception were evident with aeration, irrespective of soil water treatment. Similarly cotton lint yield increased by 14–28% in aeration treatments compared with the control. The higher lint yield was associated with more squares and bolls per plant which accompanied greater above ground biomass and an increase in root mass, root length and soil respiration. Air injection and HP effected greater water use, but also brought about an enhancement of water use efficiency (WUE) for pod and lint yield, and increased leaf photosynthetic rate in both species but had no effect on transpiration rate and stomatal conductance per unit leaf area. Aeration-induced enhanced root function was arguably responsible for greater fruit set and yield in all three crops, while in vegetable soybean greater canopy cover, radiation interception and total vegetative biomass were responsible for additional yield benefit. Increased aeration of the root zone in heavy clay soils employing either air injection or HP proved beneficial to SDI irrigated crops, irrespective of the soil water conditions, and can add value to grower investments in SDI.     

Effect of Simultaneous Water Deficit Stress and Meloidogyne incognita Infection on Cotton Yield and Fiber Quality

Both water deficit stress and Meloidogyne incognita infection can reduce cotton growth and yield, and drought can affect fiber quality, but the effect of nematodes on fiber quality is not well documented. To determine whether nematode parasitism affects fiber quality and whether the combined effects of nematode and drought stress on yield and quality are additive (independent effects), synergistic, or antagonistic, we conducted a study for 7 yr in a field infested with M. incognita. A split-plot design was used with the main plot factor as one of three irrigation treatments (low [nonirrigated], moderate irrigation, and high irrigation [water-replete]) and the subplot factor as 0 or 56 l/ha 1,3-dichloropropene. We prevented water deficit stress in plots designated as water-replete by supplementing rainfall with irrigation. Plots receiving moderate irrigation received half the water applied to the water-replete treatment. The severity of root galling was greater in nonfumigated plots and in plots receiving the least irrigation, but the amount of irrigation did not influence the effect of fumigation on root galling (no irrigation × fumigation interaction). The weights of lint and seed harvested were reduced in nonfumigated plots and also decreased as the level of irrigation decreased, but fumigation did not influence the effect of irrigation. Nematodes affected fiber quality by increasing micronaire readings but typically had little or no effect on percent lint, fiber length (measured by HVI), uniformity, strength, elongation, length (based on weight or number measured by AFIS), upper quartile length, or short fiber content (based on weight or number). Micronaire also was increased by water deficit stress, but the effects from nematodes and water stress were independent. We conclude that the detrimental effects caused to cotton yield and quality by nematode parasitism and water deficit stress are independent and therefore additive.     

Additional Fertilizer and Nematicide Combinations on Upland Cotton to Manage Rotylenchulus Reniformis and Meloidogyne Incognita in Alabama

Plant parasitic nematodes are major pests on upland cotton worldwide and in the United States. The reniform nematode, Rotylenchulus reniformis and the southern root-knot nematode Meloidogyne incognita are some of the most damaging nematodes on cotton in the United States. Current management strategies focus on reducing nematode populations with nematicides. The objective of this research was to integrate additional fertilizer and nematicide combinations into current practices to establish economical nematode management strategies while promoting cotton yield and profit. Microplot and field trials were run to evaluate fertilizer and nematicide combinations applied at the pinhead square (PHS) and first bloom (FB) plant growth stages to reduce nematode population density and promote plant growth and yield. Cost efficiency was evaluated based on profit from lint yields and chemical input costs. Data combined from 2019 and 2020 suggested a nematicide seed treatment (ST) ST + (NH₄)₂SO₄ + Vydate^® C-LV + Max-In^® Sulfur was the most effective in increasing seed cotton yields in the R. reniformis microplot trials. In R. reniformis field trials, a nematicide ST + (NH₄)₂SO₄ + Vydate^® C-LV at PHS supported the largest lint yield and profit per hectare at $1176. In M. incognita field trials, a nematicide ST + 28-0-0-5 + Vydate^® C-LV + Max-In^® Sulfur at PHS and FB supported the largest lint yields and profit per hectare at $784. These results suggest that combinations utilizing fertilizers and nematicides applied together across the season in addition to current fertility management show potential to promote yield and profit in R. reniformis and M. incognita infested cotton fields.     

Impact of drought on assimilates partitioning associated fruiting physiognomies and yield quality attributes of desert grown cotton

Deficit irrigation has great significance for sustainable cultivation of cotton in water scarce arid regions, but this technique creates drought situation that induces stress adaptive changes in cotton plants due to indeterminate growth habit. In the present experiment, the impact of drought stress on assimilates partitioning associated vegetative and reproductive development, and yield quality attributes of cotton were examined under desert conditions. Four levels of drip irrigation including 100, 80, 60, and 40% replenishment of depleted water from field capacity were applied to develop drought stress regimes during two growing seasons (2015 and 2016). Results revealed that under limited water supplies, plant’s preference for allocation of photo-assimilates was roots?>?leaves?>?fruits that substantially increased root–shoot ratio and hampered reproductive growth. Consequently, boll density (m^?2), fresh boll weight and lint yield (kg ha^?1) were significantly reduced. An obvious change in partitioning of assimilates inside stressed bolls was observed that indicated relatively more accumulation in seeds than fiber, thus reducing the fiber quality. In addition, decreased starch, oil, and protein contents in seeds of stressed plants markedly reduced 100 seeds weight and also the vigor. Later, seed quality confirmatory tests of subsequent years (2016 and 2017) showed significant reduction in emergence counts (m^?2) and seedling biomasses of seeds harvested from deficit drip irrigated cotton. These results suggest that deficit irrigation could necessarily be an appropriate yield optimization and water saving technique for cotton in desert environment but, for the best quality fiber and cottonseeds, full irrigation should be preferred.     

膜下滴灌水氮调控对南疆棉花产量及水氮利用率的影响

为探明水氮调控对膜下滴灌棉花的生长特性、产量构成因素以及水氮利用效率的影响,设置了3个灌溉水量和5个氮素水平进行大田棉花膜下滴灌试验.结果表明: 随着灌溉水量的增加,棉花的株高、主茎叶数、果枝数和叶面积指数显著增加,棉花叶、茎干物质积累增加,但抑制了根系生长,与低(4950 mm·hm^-2)和高(6750 mm·hm^-2)灌水量处理相比,中灌水量(5850 mm·hm^-2)处理平均单株有效铃数和单铃质量分别增加0.96、0.4个和0.22、0.11 g.与其他施氮处理相比,施氮量为300 kg·hm^-2时棉花茎直径显著增加,促进了棉花蕾、铃和根系的发育,而且在灌水量为5850 mm·hm^-2条件下,棉花干物质由营养器官向生殖器官的分配比灌水量为4950和6750 mm·hm^-2处理分别增加5.1%和29.6%.灌溉水量对棉花产量有显著影响,对衣分率影响不显著,而施氮量对棉花产量和衣分率都有一定的影响,但灌溉水量过低会抑制氮肥增产效应的发挥.在本试验条件下,灌水量为5850 mm·hm^-2、施氮量为300 kg·hm^-2时,棉花生长健壮,株型结构优化,显著促进了干物质向生殖器官的运转,有效铃数、单铃质量和衣分增加,产量达到最高(6992 kg·hm^-2),水分利用效率和氮肥利用率分别达1.45 kg·m^-3和45.9%.     

Kaolin and Jasmonic acid improved cotton productivity under water stress conditions

Drought is one of the most emerging threat that causes a severe reduction in cotton plant growth and development. Being cotton is a major cash crop has great threat to prevailing drought events in Pakistan. A field experiment was conducted in Kharif season 2018 at Research Area of MNS-University of Agriculture, Multan, Pakistan to assess the role of foliar applied kaolin and jasmonic acid on vegetative growth, gas exchange and reproductive traits of cotton under normal irrigated and artificial water deficit conditions. The experiment was laid -out in a factorial randomized complete block design with split – split plot arrangement. Main plots were allocated for irrigation levels, sub-plots for two -cotton genotypes viz. NIAB − 878 and SLH − 19 while sub – sub plots for treatments of kaolin and Jasmonic acid. Water deficit stress was created by skipping irrigation at flowering for 21 days. Foliar sprays of Kaolin (5%, w/v) and Jasmonic acid (100 μM) were applied alone or in combination at 60 days after planntinon both to normal irrigated and water-stresse skip irrigation while irrigation water alone was sprayed in control plots. Both cotton genotypes responded variably to normal irrigated and skip conditions. Skipping irrigation for up to 21 days at flowering caused a significant decrease in leaf relative water content, SPAD values, net photosynthetic rate and seed cotton yield in both the genotypes. Seed cotton yield showed an overall decline of 24.7% in skip over Normal irrigated crop. The genotype NIAB − 878 produced maximum seed cotton yield of 3.304 Mg ha⁻¹ in normal that dropped to 2.579 Mg ha⁻¹ in skip, thus showing an average decline of 21.9 %. Similarly, SLH − 19 produced 2.537 Mg ha⁻¹ seed cotton under normal that dropped to 1.822 Mg ha⁻¹ in skip, showing an average decline of 28.2%. The Application of Kaolin and JA Jasmonic acid, either applied individually or in combination, improved vegetative and reproductive development of both cotton varieties in normal and skip regimes. However, combined kaolin and Jasmonic Acid application proved to be more beneficial in terms of seed cotton production and other parameters studied.     

Impact of melatonin and tryptophan on water stress tolerance in white lupine (Lupinus termis L.)

Melatonin  has been identified as a signal molecule that regulates plant responses to different abiotic and biotic stresses. Melatonin (MT) and its precursor tryptophan (Try) have a major role in improving plant stress tolerance to different environmental stresses such as water deficiency. The rapid increase in the Egyptian population caused insufficient protein sources, especially those of animal origin, in their diet. The possible solution is to augment the diet with legumes such as white lupine which are relatively rich in protein. Thus, the current experimental work was carried out to find changes in growth, biochemical aspects and yield quantity and quality of white lupine plant with spraying of both MT and Try at different concentrations on plant shoot under water deficit stress conditions. Results showed that water deficit (75 or 50% of water irrigation requirements; WIR) caused significant reduction in growth, photosynthetic pigments, indole acetic acid and yield compared with those received 100% WIR. Seed yield significantly decreased (p < 0.05) by 26.98 and 41.64% by decreasing WIR to 75 and 50%. The decrease was accompanied by significant increase in phenolic contents, hydrogen peroxide, lipid peroxidation and some antioxidant enzymes, while nitrate reductase enzyme was decreased. However, external application of either MT or Try significantly alleviated the adverse effects of water deficit (growth suppression), since MT or Try-treated plants recovered more quickly than untreated plants. Moreover, MT or Try—treated plants had higher photosynthetic pigments, indole acetic acid, phenolic, as well as yield quantity and quality under the three WIR as compared with untreated plants. Melatonin treatment at 100 µM and Tryptophan at 200 µM increased weight of seeds/plant by 78.29 and 52.19%, 71.49 and 43.78% and 41.21 and 13.07% in plants irrigated with 100, 75 and 50% WIR, respectively. Exogenous MT and Try significantly reduced hydrogen peroxide and malondialdehyde content, while markedly increased the activities of antioxidant enzymes and nitrate reductase under different WIR. Finally, the current study concluded that MT and Try treatments alleviated the detrimental effects of water deficiency and accelerated the recovery mainly via improving white lupine plants tolerance in forms of enhancing photosynthetic pigments, indole acetic acid, phenolic and antioxidant capacity.     

土壤深松和补灌对小麦干物质生产及水分利用率的影响

研究一次深松耕作后土壤水分对冬小麦籽粒产量和水分利用率的影响,为小麦节水高产栽培提供理论依据.于2008-2009和2009-2010两个小麦生长季,选用高产小麦品种济麦22,采取测墒补灌的方法,研究了深松+旋耕和旋耕2种耕作方式下土壤水分对小麦0-200 cm土层土壤含水量、干物质积累与分配、籽粒产量及水分利用率的影响.结果表明,(1)深松+旋耕40-180 cm土层土壤含水量低于旋耕处理;旗叶光合速率和水分利用率,开花后干物质积累量及其对籽粒的贡献率显著高于旋耕处理.(2)W3(补灌至0-140 cm土层土壤相对含水量播种期为85％,越冬期80％,拔节和开花期75％)成熟期0-200cm土层土壤含水量与W1(播种期80％,越冬期80％,拔节和开花期75％)和W2处理(播种期80％,越冬期85％,拔节和开花期75％)无显著差异;W3和W'3(播种期85％,越冬期85％,拔节和开花期75％)60-140 cm土层土壤含水量分别低于W4(播种期85％,越冬期85％,拔节和开花期75％)和W'4(播种期90％,越冬期85％,拔节和开花期75％)处理;W3和W'3灌浆中后期旗叶光合速率较高,开花后干物质积累量及其对籽粒的贡献率显著高于其他处理,获得高的籽粒产量和水分利用率.综合考虑籽粒产量、水分利用率和灌溉效益,在深松+旋耕条件下,两年度分别以W3和W'3为节水高产的最佳处理.     

Using trunk diameter sensors for regulated deficit irrigation scheduling in early maturing peach trees

The aim of this paper was to test the possibility of scheduling regulated deficit irrigation (RDI) using exclusively maximum daily trunk shrinkage (MDS) measurements, and that RDI strategies can be applied in early maturing peach trees reducing significantly the seasonal water use. During three growing seasons, 6-year-old peach trees (Prunus persica (L.) Batsch cv. Flordastar) grafted on P. persica × P. amygdalus GF-677 peach rootstock were submitted to different drip irrigation treatments. Control (T0) plants were irrigated above the estimated crop evapotranspiration level (≈130% ET_C) and T1 plants were submitted to RDI, which were irrigated in order to maintain MDS signal intensity (SI) values close to unity (no irrigation-related stress) from the fruit thinning stage to 2 weeks after harvest, at MDS SI values close to 1.3 during the early postharvest period, and at MDS SI values of 1.6 during the late postharvest period. The RDI strategy assayed reduced the seasonal water applied by 35-42% with respect to estimated ET_C without affecting yield efficiency components or the distribution of different peach fruit categories, while improving water productivity. The only vegetative growth component affected by RDI was pruning weight, indicating that vigor regulation as a result of RDI may decrease the competition for assimilates between vegetative apexes and reserve tissues. Also, the absence of any significant effect of RDI on the ratio between yield and the increase in trunk cross sectional area suggested similar carbon partitioning schemes during fruit growth. To improve the precision of MDS SI-driven schedule in RDI strategies changes in the irrigation protocol should be considered so that the scheduled water deficit levels are attained more rapidly. For this, when it is necessary to change from a MDS SI threshold value to a higher one, the daily irrigation rate should be decreased by more than 3%.     

Physiological Effects of Plant Hormones in Cotton Under Drought

Effects of plant hormones indole-3-yl-acetic acid (IAA), gibberellic acid (GA), benzylaminopurine (BAP), abscisic acid (ABA) and ethrel (ETH) in 5 M concentration on gas exchange, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO, EC 4.1.1.39) activity, pigment content and yield in cotton (Gossypium hirsutum L. cv. H-777) under drought were studied. At reproductive stage (55 – 60 d after sowing) these hormones were sprayed on shoots one day prior to stress imposition by withholding irrigation. The soil moisture of control plants was kept at field capacity. Net photosynthetic rate (P_N), stomatal conductance (g_s), transpiration rate (E), carboxylation efficiency (CE), water use efficiency (WUE), RuBPCO activity, boll number per plant, seed number per plant and lint mass per plant significantly decreased at drought while chlorophyll (Chl) b content and flower number per plant increased. ABA and ETH significantly reduced gas exchange parameters, Chl a and Chl b content. Detrimental drought effect on P_N, g_s, E, CE, RuBPCO and lint mass per plant was significantly alleviated by BAP and also its effect on seed number and lint mass per plant was significantly alleviated with the ABA treatment.     

Prospects of partial root zone irrigation for increasing irrigation water use efficiency of major crops in the Mediterranean region

Field experiments were conducted for 3 years from 2000 to 2002 to assess proportional crop yield differences obtained under conventional deficit irrigation (CDI) and partial root zone irrigation (PRI) practices, compared with full irrigation (FULL) where plant water requirements were fully met. The experimental crops included vegetables (tomato and pepper), field crops (maize and cotton) and citrus. The fruit yield of greenhouse‐grown tomato with FULL irrigation was higher than with PRI (7–22% lower) but was not significantly different. The PRI treatments had 7–10% additional tomato yield over CDI receiving the same amount of water. The yield of pepper, however, decreased in proportion to the level of irrigation deficit with no increase of irrigation water use efficiency (IWUE). No seed yield decrease was evident for cotton with the deficit treatments (PRI and CDI) compared with FULL irrigation. Similarly, the PRI treatment did not give any yield benefit for maize compared with CDI. The ranking of fruit yields of mandarin, FULL > PRI > CDI, was the same as that of other crops; however, the differences were not significant. Although the deficit treatments (PRI and CDI) had as high as 39% increase in IWUE, compared with FULL treatment, some adverse effects on fruit quality were evident such as smaller size of fruits under the deficit treatments.     

Does Water Deficit Stress Promote Ethylene Synthesis by Intact Plants?

The effect of plant water deficit on ethylene production by intact plants was tested in three species, beans (Phaseolus vulgaris L.), cotton (Gossypium hirsutum L.) and miniature rose (Rosa hybrida L., cv Bluesette). Compressed air was passed through glass, plant-containing cuvettes, ethylene collected on chilled columns, and subsequently assayed by gas chromatography. The usual result was that low water potential did not promote ethylene production. When plants were subjected to cessation of irrigation, ethylene production decreased on a per plant or dry weight basis of calculation. No significant promotion of ethylene production above control levels was detected when water deficit-treated bean or cotton plants were rewatered. The one exception to this was for cotton subjected to a range of water deficits, plants subjected to deficits of −1.4 to −1.6 MPa exhibited a transient increase of ethylene production of 40 to 50% above control levels at 24 or 48 hours. Ethylene was collected from intact leaves while plants developed a water deficit stress of −2.9 megapascals after rewatering, and no significant promotion of ethylene production was detected. The shoots of fruited, flowering cotton plants produced less ethylene when subjected to cessation of irrigation. In contrast, the ability of bench drying of detached leaves to increase ethylene production several-fold was verified for both beans and cotton. The data indicate that detached leaves react differently to rapid drying than intact plants react to drying of the soil with regard to ethylene production. This result suggests the need for additional attention to ethylene as a complicating factor in experiments employing excised plant parts and the need to verify the relevance of shock stresses in model systems.     

喷灌条件下耕作方式和亏缺灌溉对麦后移栽棉产量和水分利用的影响

探明耕作方式和亏缺灌溉对麦后移栽棉产量和水分利用的效应,对于建立麦后移栽棉的适宜耕作方式及灌溉制度十分重要.在大田条件下设置了翻耕和免耕2种耕作方式(灌水定额均为45 mm)及相应减小50％灌水定额的亏缺灌溉,分析了不同耕作方式和亏缺灌溉对棉花耗水规律、籽棉产量、水分利用效率和纤维品质的影响.结果表明:与翻耕相比,免耕减少了棉田20.3％的棵间土壤蒸发;不论何种耕作方式,亏缺灌溉在不影响棉花产量和纤维品质的同时,有效降低了耗水量,提高了水分利用效率.在喷灌条件下,灌水定额为22.5 mm的免耕耕作方式,不仅可有效降低麦后移栽棉田间无效棵间土壤蒸发,还可实现节水、优质、高产的有效统一.     

亏缺灌溉对干旱区两种乡土植物种子生产性能及其水分利用效率的影响

科学灌溉对植物种子生产具有重要意义。本研究以荒漠草原优良乡土植物沙芦草和牛枝子为对象,以充分灌溉为对照,探究不同生育时期亏缺灌溉对两种牧草种子生产和水分利用效率的影响。结果表明: 与对照相比,亏缺灌溉下两种植物土壤含水率下降,其中沙芦草土壤含水率下降主要发生在0～60 cm土层,牛枝子土壤水分下降未出现明显的分层现象。亏缺灌溉下沙芦草种子产量各构成因子差异均显著,开花期亏缺灌溉种子产量最高;牛枝子仅生殖枝数、小花数和荚果数差异显著,种子产量各处理差异不显著。相关分析显示,沙芦草种子产量与生殖枝数(r=0.776)、小穗数(r=0.717)呈显著正相关;牛枝子花序数与生殖枝数呈极显著负相关(r=-0.685),与小花数呈显著正相关(r=0.412)。与充分灌溉相比,亏缺灌溉下两种乡土植物种子生产耗水量减少,水分利用效率提高,其中,沙芦草开花期亏缺灌溉水分利用效率提高最多(32.9%);牛枝子分枝期亏缺灌溉提高最多(27.4%)。因此,适当亏缺灌溉可以提高两种植物水分利用效率。从水分利用效率和种子产量来看,干旱区沙芦草和牛枝子种子人工繁育时可采取亏缺灌溉,适宜亏缺的生育期分别为开花期和分枝期。     

Water Deficit Enhanced Cotton Resistance to Spider Mite Herbivory

We investigated the responses of cotton (Gossypium hirsutumL.)to the combined effects of soil water deficit and two-spottedspider mite (Tetranychus urticaeKoch) infestation. Two mitetreatments (-M: uninfested, +M: artificially infested 83 d aftersowing), and two water regimes (+W: well watered, -W: waterstressed) were combined factorially in four treatments. Mitecolonies developed at similar rates in well-watered and water-stressedcrops. Despite the similar intensity of infestation, visualsymptoms of mite injury were more marked in well-watered hostplants (+M+W) than in their water-stressed counterparts (+M-W).Lint yield of unstressed controls (-M+W) was 175 g m^-2. In uninfestedcrops, water deficit reduced yield by 30%, mites reduced theyield of well-watered crops by 92%, and the combination of miteinfestation and water deficit reduced yield by 72% (water effect:P<0.01;mite and interaction effect:P<0.0001). Differences in yieldresponses to mites between well-watered and water-stressed cropswere mostly related to differences in reproductive partitioning.The interaction between mites and water deficit was also significantfor other crop variables including canopy temperature, leafwater potential, concentration of nitrogen in reproductive structuresand seed oil concentration. The magnitude and consistency ofthe interaction between both stresses indicates that, underour experimental conditions, mechanisms of adjustment to waterdeficit may have enhanced cotton resistance to mites. This isfurther supported by (a) an increase in specific leaf weightand a parallel increase in leaf penetration resistance due towater deficit; (b) a negative association between macroscopicsymptoms of mite injury and leaf penetration resistance; and(c) a choice test showing that adult female mites preferredto feed and oviposit on leaves from well-watered plants.Copyright1998 Annals of Botany Company Gossypium hirsutumL.;Tetranychus urticaeKoch; leaf water potential; leaf penetration resistance; canopy temperature; multiple stresses; specific leaf weight; radiation use efficiency; nitrogen concentration; reproductive allocation.     

Oxygation Enhances Growth, Gas Exchange and Salt Tolerance of Vegetable Soybean and Cotton in a Saline Vertisol

Impacts of salinity become severe when the soil is deficient in oxygen. Oxygation (using aerated water for subsurface drip irrigation of crop) could minimize the impact of salinity on plants under oxygen-limiting soil environments. Pot experiments were conducted to evaluate the effects of oxygation (12% air volume/volume of water) on vegetable soybean (moderately salt tolerant) and cotton (salt tolerant) in a salinized vertisol at 2, 8, 14, 20 dS/m ECe. In vegetable soybean, oxygation increased above ground biomass yield and water use efficiency (WUE) by 13% and 22%, respectively, compared with the control. Higher yield with oxygation was accompanied by greater plant height and stem diameter and reduced specific leaf area and leaf Na+ and Cl-concentrations. In cotton, oxygation increased lint yield and WUE by 18% and 16%, respectively, compared with the control, and was accompanied by greater canopy light interception, plant height and stem diameter. Oxygation also led to a greater rate of photosynthesis, higher relative water content in the leaf, reduced crop water stress index and lower leaf water potential. It did not, however, affect leaf Na+ or Cl- concentration. Oxygation invariably increased, whereas salinity reduced the K+ : Na+ ratio in the leaves of both species. Oxygation improved yield and WUE performance of salt tolerant and moderately tolerant crops under saline soil environments, and this may have a significant impact for irrigated agriculture where saline soils pose constraints to crop production.     

Effects of desiccation on the photosynthetic activity of intertidal microphytobenthos biofilms as studied by optical methods

Due to the periodic exposure to air during periods of low tide, desiccation can be expected to cause important limiting effects on the photosynthetic activity of intertidal microphytobenthos biofilms. This work addresses the study of the short-term effects of desiccation on microphytobenthos using a new, simple methodological approach to non-destructively estimate the water content of muddy intertidal sediments. The method is based on the non-destructive measurement of the specular reflectance in the visible spectral region, shown to be linearly related to the water content of the uppermost 200 µm of the sediment. During air exposure, water loss by the surface sediment layers was shown to induce marked decreases in both the photosynthetic activity, as measured by the maximum quantum yield of photosystem II, F_v/F_m, and the surface microalgal biomass, as estimated from the diffusive reflectance biomass index NDVI. The effects of desiccation were largely dependent on the rate of sediment de-watering. For a same level of desiccation, samples under fast desiccation (exposed to wind of 4.2 m s^− 1) showed much larger effects on F_v/F_m and NDVI comparatively to samples under slow desiccation (maintained under still air). By showing the rapid and significant effects of desiccation on microphytobenthos biofilm functioning, the results of this study have potentially important implications for the modelling of primary productivity of estuarine intertidal areas, as desiccation and factors inducing it may result in previously unaccounted effects on photosynthetic performance and productive biomass.     

Chlorophyll fluorescence upper-to-lower-leaf ratio for determination of irrigation time for Pentas lanceolata

The objective of this study was to use nondestructive measurements as the precise irrigation indices for potted star cluster (Pentas lanceolata). Drought stress was imposed on plants for 0, 3, 5, 7, 12, and 16 d by withholding water. Measurements were conducted on the third leaf counted from the apex (upper leaves) and on the third leaf from the bottom (lower leaves). Within the range of soil water content (SWC) from 10 to 45%, leaf water potential (WP), SWC, and soil matric potential (SMP), chlorophyll fluorescence, photochemical reflectance index (PRI), adjusted normalized difference vegetation index (aNDVI), and the reflectance (R) at 1950 nm (R₁₉₅₀) were measured. The plants reached the temporary wilting point at ?3.87 MPa of leaf WP; the maximal fluorescence yield of the light-adapted state (F_m′) ratio of upper-to-lower leaves was 1.7. When the F_m′ ratio was 1.3, it corresponded to lower-leaf WP < ?2.27 MPa, SWC < 21%, SMP < ?20 kPa, PRI < 0.0443, aNDVI < 0.0301, and R₁₉₅₀ > 8.904; it was the time to irrigate. In conclusion, the F_m′ ratio of upper-to-lower leaves was shown to be a nondestructive predictor of leaf WP and can be used to estimate irrigation timing.