Response of wheat canopy CO2 and water gas-exchange to soil water content under ambient and elevated CO2

The nature of the interaction between drought and elevated CO₂ partial pressure (pC_a) is critically important for the effects of global change on crops. Some crop models assume that the relative responses of transpiration and photosynthesis to soil water deficit are unaltered by elevated pC_a, while others predict decreased sensitivity to drought at elevated pC_a. These assumptions were tested by measuring canopy photosynthesis and transpiration in spring wheat (cv. Minaret) stands grown in boxes with 100 L rooting volume. Plants were grown under controlled environments with constant light (300 µmol m^?2 s^?1) at ambient (36 Pa) or elevated (68 Pa) pC_a and were well watered throughout growth or had a controlled decline in soil water starting at ear emergence. Drought decreased final aboveground biomass (?15%) and grain yield (?19%) while elevated pC_a increased biomass (+24%) and grain yield (+29%) and there was no significant interaction. Elevated pC_a increased canopy photosynthesis by 15% on average for both water regimes and increased dark respiration per unit ground area in well‐watered plants, but not drought‐grown ones. Canopy transpiration and photosynthesis were decreased in drought‐grown plants relative to well‐watered plants after about 20–25 days from the start of the drought. Elevated pC_a decreased transpiration only slightly during drought, but canopy photosynthesis continued to be stimulated so that net growth per unit water transpired increased by 21%. The effect of drought on canopy photosynthesis was not the consequence of a loss of photosynthetic capacity initially, as photosynthesis continued to be stimulated proportionately by a fixed increase in irradiance. Drought began to decrease canopy transpiration below a relative plant‐available soil water content of 0.6 and canopy photosynthesis and growth below 0.4. The shape of these responses were unaffected by pC_a, supporting the simple assumption used in some models that they are independent of pC_a.     

Contrasting physiological effects of partial root zone drying in field-grown grapevine (Vitis vinifera L. cv. Monastrell) according to total soil water availability

Different spatial distributions of soil moisture were imposed on field-grown grapevines by applying the same irrigation volumes to the entire (DI; deficit irrigation) or part of the (PRD; partial root zone drying) root zone. Five treatments were applied: controls irrigated at 60% ETc (crop evapotranspiration) for the whole season (308 mm year(-1)); DI-1 and PRD-1 that received the same irrigation as controls before fruit set, 30% ETc from fruit set to harvest and 45% ETc post-harvest (192 mm year(-1)); and DI-2 and PRD-2 that were the same, except that 15% ETc was applied from fruit set to harvest (142 mm year(-1)). Compared with DI-1, PRD-1 maintained higher leaf area post-veraison and increased root water uptake, whole-plant hydraulic conductance, leaf transpiration, stomatal conductance, and photosynthesis, but decreased intrinsic gas exchange efficiency without causing differences in leaf xylem abscisic acid (ABA) concentration. Compared with DI-2, PRD-2 increased leaf xylem ABA concentration and decreased root water uptake, whole-plant hydraulic conductance, leaf transpiration, stomatal conductance, and photosynthesis, mainly at the beginning of PRD cycles. Distinctive PRD effects (e.g. greater stomatal closure) depended on the volumetric soil water content of the wet root zone, as predicted from a model of root-to-shoot ABA signalling.     

The responses of stomata and leaf gas exchange to vapour pressure deficits and soil water content

The responses of leaf conductance, leaf water potential and rates of transpiration and net photosynthesis at different vapour pressure deficits ranging from 10 to 30 Pa kPa^-1 were followed in the sclerophyllous woody shrub Nerium oleander L. as the extractable soil water content decreased. When the vapour pressure deficit around a plant was kept constant at 25 Pa kPa^-1 as the soil water content decreased, the leaf conductance and transpiration rate showed a marked closing response to leaf water potential at-1.1 to-1.2 MPa, whereas when the vapour pressure deficit around the plant was kept constant at 10 Pa kPa^-1, leaf conductance decreased almost linearly from-0.4 to-1.1 MPa. Increasing the vapour pressure deficit from 10 to 30 Pa kPa^-1 in 5 Pa kPa^-1 steps, decreased leaf conductance at all exchangeable soil water contents. Changing the leaf water potential in a single leaf by exposing the remainder of the plant to a high rate of transpiration decreased the water potential of that leaf, but did not influence leaf conductance when the soil water content was high. As the soil water content was decreased, leaf conductances and photosynthetic rates were higher at equal levels of water potential when the decrease in potential was caused by short-term increases in transpiration than when the potential was decreased by soil drying.As the soil dried and the stomata closed, the rate of photosynthesis decreased with a decrease in the internal carbon dioxide partial pressure, but neither the net photosynthetic rate nor the internal CO₂ partial pressure were affected by low water potentials resulting from short-term increases in the rate of transpiration. Leaf conductance, transpiration rate and net photosynthetic rate showed no unique relationship to leaf water potential, but in all experiments the leaf gas exchange decreased when about one half of the extractable soil water had been utilized. We conclude that soil water status rather than leaf water status controls leaf gas exchange in N. oleander.     

干旱、CO2和温度升高对春小麦光合、蒸发蒸腾及水分利用效率的影响

研究了干旱、CO2 浓度和温度升高对春小麦生育期、光合速率 (Pn)、蒸发蒸腾 (ET)及水分利用效率 (WUE)的影响 .结果表明 ,大气CO2 浓度升高 (5 5 0、70 0 μmol·mol-1)虽可延长抽穗 成熟期 ,但高温 (日平均温度高于正常日平均温度约 4 .8℃ )对生育期的影响远大于高CO2 影响 ,使得高CO2 、高温下抽穗 成熟期缩短 ,且种子提前萌发 ;CO2 浓度升高和高温共同作用使各水分处理的小麦光合增强、气孔阻力增加、叶片水平的水分利用效率 (WUEl)和群体水平的水分利用效率 (WUE)增大 ,但对蒸腾速率影响不显著 .对蒸发蒸腾的影响因不同的土壤水分而不同 ,在高 (田间持水量的 75 %～ 85 % )、中 (田间持水量的 5 5 %～6 5 % )水分条件下 ,高温和高CO2 使蒸发蒸腾增加 ,而在低水分条件 (田间持水量的 35 %～ 4 5 % )下 ,高温和高CO2 使蒸发蒸腾减少     

Water-use efficiency and transpiration efficiency of wheat under rain-fed conditions and supplemental irrigation in a Mediterranean-type environment

Growth and water use were measured in wheat (Triticum aestivum L.) grown in northern Syria in a typical Mediterranean climate over five seasons 1991/92–1995/96. Water use was partitioned into transpiration (T) and soil evaporation (E_s) using Ritchie's model, and water-use efficiency (WUE) and transpiration efficiency (TE) were calculated. The aim of the study was to examine the influence of irrigation and nitrogen on water use, WUE and TE. By addition of 100 kg N ha^-1, E_s was reduced from 120 mm to 101 mm under rain-fed conditions and from 143 mm to 110 mm under irrigated conditions, and T was increased from 153 mm to 193 mm under rain-fed conditions and from 215 mm to 310 mm under irrigated conditions. Under rain-fed conditions, about 35% of evapotranspiration (ET) may be lost from the soil surface for the fertilized crops and 44% of ET for the unfertilized crops. Transpiration accounted for 65% of ET for the fertilized crops and 56% for the unfertilized crops under rain-fed. As a result of this, WUE was increased by 44% for dry matter and 29% for grain yield under rain-fed conditions, and by 60% for dry matter and 57% for grain yield under irrigated conditions. Transpiration efficiency for the fertilized crops was 43.8 kg ha^-1 mm^-1 for dry matter and 15 kg ha^-1 mm^-1 for grain yield, while TE for the unfertilized crops was 33.6 kg ha^-1 mm^-1 and 12.2 kg ha^-1 mm^-1 for dry matter and grain yield, respectively. Supplemental irrigation significantly increased post-anthesis water use, transpiration, dry matter and grain yield. Water-use efficiency for grain yield was increased from 9.7 to 11.0 kg ha^-1 mm^-1 by supplemental irrigation, although WUE for dry matter was not affected by it. Irrigation did not affect transpiration efficiency for grain yield, but decreased transpiration efficiency for dry matter by 16%. This was associated with higher harvest index as a result of good water supply in the post-anthesis period and increased transpiration under irrigated conditions.     

干旱、CO2和温度升高对春小麦光合、蒸发蒸腾及水分利用效率的影响

研究了干旱、CO₂浓度和温度升高对春小麦生育期、光合速率(P_n)、蒸发蒸腾(ET)及水分利用效率(WUE)的影响.结果表明,大气CO₂浓度升高(550、700μmol·mol^-1)虽可延长抽穗成熟期,但高温(日平均温度高于正常日平均温度约4.8℃)对生育期的影响远大于高CO₂影响,使得高CO₂、高温下抽穗成熟期缩短,且种子提前萌发;CO₂浓度升高和高温共同作用使各水分处理的小麦光合增强、气孔阻力增加、叶片水平的水分利用效率(WUEl)和群体水平的水分利用效率(WUE)增大,但对蒸腾速率影响不显著.对蒸发蒸腾的影响因不同的土壤水分而不同,在高(田间持水量的75%～85%)、中(田间持水量的55%～65%)水分条件下,高温和高CO₂使蒸发蒸腾增加,而在低水分条件(田间持水量的35%～45%)下,高温和高CO₂使蒸发蒸腾减少.     

Physiological mechanisms contributing to the increased water-use efficiency in winter wheat under deficit irrigation

Deficit irrigation in winter wheat has been practiced in the areas with limited irrigation water resources. The objectives of this study were to (i) understand the physiological basis for determinations of grain yield and water-use efficiency in grain yield (WUE) under deficit irrigation; and (ii) investigate the effect of deficit irrigation on dry matter accumulation and remobilization of pre-anthesis carbon reserves during grain filling. A field experiment was conducted in the Southern High Plains of the USA and winter wheat (cv. TAM 202) was grown on Pullman clay loam soil (fine mixed thermic Torretic Paleustoll). Treatments consisted of rain-fed, deficit irrigation from jointing to the middle of grain filling, and full irrigation. The physiological measurements included leaf water potential, net photosynthetic rate (Pn), stomatal conductance (Gs), and leaf area index. The rain-fed treatment had the lowest seasonal evapotranspiration (ET), biomass, grain yield, harvest index (HI) and WUE as a result of moderate to severe water stress from jointing to grain filling. Irrigation application increased seasonal ET, and ET increased as irrigation frequency increased. The seasonal ET increased 20% in one-irrigation treatments between jointing and anthesis, 32-46% in two-irrigation treatments, and 67% in three- and full irrigation treatments. Plant biomass, grain yield, HI and WUE increased as the result of increased ET. The increased yield under irrigation was mainly contributed by the increased number of spikes, and seeds per square meter and per spike. Among the irrigation treatments, grain yield increased significantly but the WUE increased slightly as irrigation frequency increased. The increased WUE under deficit irrigation was contributed by increased HI. Water stress during grain filling reduced Pn and Gs, and accelerated leaf senescence. However, the water stress during grain filling induced remobilization of pre-anthesis carbon reserves to grains, and the remobilization of pre-anthesis carbon reserves significantly contributed to the increased grain yield and HI. The results of this study showed that deficit irrigation between jointing and anthesis significantly increased wheat yield and WUE through increasing both current photosynthesis and the remobilization of pre-anthesis carbon reserves.     

Effects of tussock size and soil water content on whole plant gas exchange in Stipa tenacissima L.: Extrapolating from the leaf versus modelling crown architecture

In this study we evaluated daily whole plant transpiration and net photosynthetic rates in Stipa tenacissima L. (Poaceae) tussocks of different sizes subjected to three levels of soil moisture. The crown architecture of 12 tussocks was reconstructed with the 3D computer model Yplant taking into account the morphology and physiology of the leaves determined at different soil moisture levels. We also calculated whole plant transpiration by extrapolating leaf transpiration in different senescence conditions measured with a diffusion porometer. This extrapolated transpiration overestimated transpiration, particularly when the soil moisture level was high (>15% of volumetric soil water content). At this high level of soil moisture, large tussocks (>60 cm in diameter), which were sexually mature and had a large leaf surface area, were the most efficient with regard to daily water use efficiency (whole plant net photosynthesis/whole plant transpiration). Whole plant water use efficiency decreased with tussock size primarily because small tussocks exhibited high transpiration rates. Small tussocks were more sensitive to soil drying than large and intermediate ones, presenting a faster rate of leaf senescence as water deficit increased. Leaf acclimation to irradiance, which was significantly influenced by the degree of mutual shading among neighbouring leaves, along with the ontogeny of the tussock and its effect upon leaf senescence were found to be the main mechanisms involved in the different responses to water limitations found in whole plant gas exchange variables. Our results show that the size of each individual plant must be taken into account in processes of scaling-up of carbon gain and transpiration from leaf to stand, as this is a particularly relevant aspect in estimating water use by semiarid vegetation.     

不同土壤水分处理对水稻光合特性及产量的影响

为探明土壤水分对水稻生长发育的影响机理,以武香粳14和两优培九为试验材料,分析了不同土壤水分处理下(W1、W2、W3和CK分别表示土壤体积含水量为20%、30%、40%和5cm水层灌溉)的水稻光合特性、产量及水分生产率等。结果表明,轻度水分胁迫(W3)具有处理间最大的叶片气孔导度、蒸腾速率和净光合速率,其他处理规律不显著。灌浆初期各水分处理下叶位间光合指标均表现为:剑叶＞顶2叶＞顶3叶>顶4叶,其他生育期规律不显著。与对照处理(CK)相比,武香粳14的W1、W2和W3处理的产量分别减少61.14%和29.13%、增加0.96%,水分生产率分别减少10.69%、增加1.53%和20.61%;两优培九的产量分别减少64.11%和28.76%,增加2.08%,水分生产率分别减少16.39%,增加2.46%和22.13%。研究结果为水稻精确灌溉和节水生产提供了技术支撑。     

The exclusion of ambient aerosols changes the water relations of sunflower (Helianthus annuus) and bean (Vicia faba) plants

Aerosols are an ubiquitous component of the atmospheric environment of plants but their ecophysiological role is largely unknown. Here we address this role by comparing the water relations of plants grown in ventilated greenhouses with ambient air (AA), and filtered air (FA) where particle concentrations had been reduced by more than 99%. Beans and sunflowers were grown in well watered soil or hydroponics. Humidity response curves of gas exchange were recorded along with sap flow, water potentials, and osmotic potentials.Hydroponically grown FA sunflowers and FA beans showed 20–40% lower stomatal conductance and lower transpiration compared to the respective AA plants under identical conditions. In sap flow measurements, the leaf-area related transpiration of soil-grown FA sunflowers was about 20–30% lower than for AA plants, partially due to lower night time values. Midday water potentials as well as osmotic potentials of FA plants were higher compared to the respective AA plants, while pre-dawn water potentials did not differ.Reduced transpiration of FA plants with stable photosynthesis was observed for beans and can be explained by the “hydraulic activation of stomata”, where deposited hygroscopic aerosols form liquid water connections along the stomatal walls, thereby forming a second, liquid-water type of stomatal transpiration. Simultaneously decreased transpiration and photosynthesis were observed for sunflower and point to a smaller stomatal aperture of FA plants. To our knowledge, this is the first study allocating an important functional role to natural aerosol concentrations. It further supports the idea that particulate air pollution may decrease the water use efficiency and the drought tolerance of plants.     

不同灌溉方式对水稻生物学特性与水分利用效率的影响

以杂交水稻两优培九为试验材料,利用测坑栽培条件,比较了4种灌溉方式下的水稻生物学特性与水分利用效率.结果表明,与淹水灌溉相比,间歇灌溉叶面积指数大,叶片光合速率高,蒸腾速率较低,叶片水分利用效率高;半干旱栽培叶片水分利用效率相对较高;干旱栽培叶面积指数小,叶片净光合速率和水分利用效率降低,且后期叶片早衰.间歇灌溉、半干旱栽培和干旱栽培比淹水灌溉分别节水8.75%、17.96%和29.69%;产量分别增产24.02%、减产5.07%和减产38.93%;水分利用效率以间歇灌溉最高,半干旱栽培次之,淹水灌溉和干旱栽培较低.间歇灌溉下稻粒的整精米率、精米率、粒长均高于其它处理,但垩白粒率和垩白度低于其它处理;随着稻田耗水量的减少,水稻的直链淀粉含量降低,而胶稠度和蛋白质含量提高.试验结果表明间歇灌溉为南方稻区较适宜的灌溉方式.     

Influence of mulching on the pattern of growth and water use by spring wheat and moisture storage on a fine textured soil

Eight tonnes ha^–1 of stubble were used to mulch spring wheat (Triticum aestivum) on a fine textured soil with the aim of controlling both transpiration and soil evaporation during the wet pre-anthesis phase to increase moisture supply during grain filling in the eastern wheatbelt of Western Australia. Mulching reduced leaf area per plant by reducing the culm number; consequently the green area index was reduced. Reduced culm number was associated with low soil temperature which at 50 mm depth averaged 7°C lower under the mulched crop relative to the control crop in mid-season. The smaller canopies of the mulched crop used 15 mm less water than those of the control before anthesis; this difference in water-use was due equally to reduced transpiration and soil evaporation. However, the mulched crop was unable to increase ET during grain filling, a response associated with the persistence of low soil temperature for most of the growth period. Hence, total ET for the season was significantly lower (18 mm) under the mulched crop than the control crop. At harvest, mulching did not have significant effects on total above-ground dry matter and grain yields, but it increased water use efficiency for grain yield by 18%, grain weight by almost 17% and available moisture in both uncropped and cropped plots by an average of 43 mm.To determine whether there was any residual effects of soil treatment on moisture storage during the summer fallow period, soil moisture was monitored both in cropped plots and uncropped plots, that were either mulched or unmulched during the growing season, from harvest in October 1988 until next planting in June 1989. Available moisture at next planting was correlated with moisture storage at harvest despite the differences in run-off, soil evaporation and fallowing efficiency (increase in moisture storage as a percentage of rainfall) between treatments during fallowing. Therefore, the mulched treatments had more moisture available (30 mm), mostly as a result of less water use during cropping in the previous growing season, than the unmulched treatment.The study shows that mulching may be used to restrain both transpiration and soil evaporation early in the season to increase availability of soil moisture during grain filling. Secondly, mulching during the previous growing season had little effect on soil moisture during the summer fallow period, however, the moisture saved by mulching during cropping was conserved for the following season. These results indicate the importance of evaluating mulching of winter crops in terms of crop yield in the subsequent growing season as well as in the current season in which the soil was treated.Abbreviations D through drainage - DAS days after sowing of the crop on 31 May 1988 - DM dry matter produced in the above-ground portion of the crop (kg ha^–1) - E₀ evaporation from Class A pan (mm) - E_s evaporation from uncropped soil (mm) - E_sc evaporation from soil beneath the wheat canopy (mm) - ET evapotranspiration (mm) - FE fallowing efficiency (gain in soil moisture storage/rainfall) - GAI green area index (area of green vegetation per unit land area) - GWUE water-use efficiency for grain production (grain yield/total ET, kg ha^–1mm^–1) - K extinction coefficient (see equation 1) - RO run-off of moisture from soil surface during/following rainfall (mm) - SM available soil moisture (mm) at harvest (SMh) or at planting (SMp) - WUE water-use efficiency for total above-ground dry matter yield (see GWUE)     

不同施肥水平对旱地冬小麦水分利用效率的影响

1987—1988年,研究了旱地施肥对冬小麦(Triticum aestivum cv．Shanhe No．6)水分利用效率的影响,初步探讨了“以肥调水”的生理机制。施肥不仅提高了旱地土壤含水量,更重要的是提高了土壤水势和土壤水的有效性,从而增加了有效水分利用。施肥增大旱地冬小麦绿叶面积,延缓叶片衰老,从而降低土壤蒸发,增加蒸腾用水潜势和光合潜势,但净同化率不一定提高。施肥增加旱地冬小麦总的水分利用(ET,即蒸散量)和蒸腾(T)用水,增加地上部生物产量,提高了经济产量和水分利用效率。施肥使冬小麦同时具有耗水和节水以抵御干旱的能力,对植株具有调节作用,使之更好地适应干旱环境。     

Effects of varying air and soil moisture on the water relations and growth of sugar beet

Sugar beet were grown for short periods with different amounts of moisture in the soil and air. Growing plants in wet soil (23 % moisture on dry weight) compared with dry soil (15% moisture) increased growth of the shoots and roots and plant dry weights by 15% in young plants and 10% in mature plants. Growing plants in wet air containing 10.9 g m^-3 of water (equivalent to a saturation deficit of 2.5 mb) compared with dry air containing 6.4 g m^-3 of water (saturation deficit = 8.5 mb) increased the dry weights of both young and mature plants by 8%, mostly by increasing the sizes of their storage roots. Wet air and wet soil increased the net assimilation rates of both young and mature plants. Wet soil, but not wet air, increased leaf areas of young plants by accelerating leaf expansion, and both increased the leaf area of mature plants by slowing senescence of the older leaves. Wet soil increased the water potential of the leaves of both young and mature plants and, by doing so, increased their stomatal conductances and rates of photosynthesis. Wet air also increased stomatal conductances and rates of photosynthesis of leaves of plants of both ages, but without changing their water potentials. Stomatal conductances and photosynthetic rates were greater for young leaves than mature on the same plant and at the same water potential. It is suggested that at certain stages in the crops growth photosynthetic efficiency could be increased by applying additional water as a mist to increase the moisture content of the air around the crop.     

The effect of water stress on photosynthesis and related parameters in Pinus halepensis

Net photosynthesis, transpiration, dark respiration rates and stomatal and mesophyll resistances were studied in young potted seedlings of Pinus halepensis Mill. under gradually decreasing soil and leaf water potentials. Stomatal resistance under non-limiting xylem water potentials was 6–7 times higher than mesophyll resistance. Stomata started to close at threshold xylem water potentials of −0.8 MPa, whereas mesophyll resistance started to increase at about −1.4 MPa. Decreasing xylem water potentials increased the CO₂ compensation point and decreased the water use efficiency (expressed by the photosynthesis to transpiration ratio) and dark respiration rate. It is concluded that at least part of the drought resistance characteristics of P. halepensis are associated with a sensitive stomatal mechanism which enables an efficient control of water loss.     

分根区施保水剂对玉米气孔导度和单叶WUE的影响

盆栽条件下,研究了陕单9号玉米(zea mays L．)在根区不施保水剂(对照)、分根区施保水剂和根区全施保水剂3种处理下,叶片气孔导度、CO2吸收和H2O蒸腾的变化。结果表明,在75％土壤饱和持水量下,各指标在3种处理之间没有明显差别;在50％土壤饱和持水量下,分根区施保水剂显著降低了叶片气孔导度,叶片CO2吸收量和H2O蒸腾量也同时降低,但H2O蒸腾量下降幅度更大;在两种水分条件下,分根区施保水剂均能提高玉米单叶水分利用效率(water use efficiency,WUE)。     

土壤水分状况及环境条件对水稻蒸腾的影响

在南方红壤区用田间测坑试验,研究了高、中、低3种土壤水分条件下的早、晚稻蒸腾速率和水分利用效率的变化,蒸腾日变化结果表明,蒸腾速率受许多田间小气候因子的影响,相关分析及多元逐步回归分析表明,叶片与空气相对湿度差和叶面温度对水稻叶片蒸腾影响最大,处理B（中等土壤水分条件）可以明显提高叶片水利用率和产是,处理C提高了叶片水分利用效率,却导致晚稻减产,早稻中、低土壤水分条件可以减小叶片蒸腾速率,而晚稻上并不能明显减少叶片蒸腾。     

不同生育期玉米叶片光合特性及水分利用效率对水分胁迫的响应

利用大型移动防雨棚开展了玉米水分胁迫及复水试验,通过分析玉米叶片光合数据,揭示了不同生育期水分胁迫及复水对玉米光合特性及水分利用效率的影响。结果表明:水分胁迫导致玉米叶片整体光合速率、蒸腾速率和气孔导度下降以及光合速率日变化的峰值提前;水分胁迫后的玉米叶片蒸腾速率、光合速率和气孔导度为适应干旱缺水均较对照显著下降,从而提高了水分利用效率,缩小了与水分充足条件下玉米叶片的水分利用效率差值;在中度和重度水分胁迫条件下,玉米叶片的水分利用效率降幅低于光合速率、蒸腾速率和气孔导度的降幅, 有时甚至高于正常供水条件下的水分利用效率;适度的水分胁迫能提高玉米叶片的水分利用效率,从而增强叶片对水分的利用能力,抵御干旱的逆境;水分亏缺对玉米光合速率、蒸腾速率及水分利用效率的影响具有较明显滞后效应,干旱后复水,光合作用受抑制仍然持续;水分胁迫时间越长、胁迫程度越重,叶片的光合作用越呈不可逆性;拔节-吐丝期水分胁迫对玉米叶片光合作用的逆制比三叶-拔节期更难恢复。     

Benefits of alternate partial root-zone irrigation on growth, water and nitrogen use efficiencies modified by fertilization and soil water status in maize

Alternate partial root-zone irrigation (APRI) is a new water-saving technique and may improve crop water use efficiency without much yield reduction. We investigated if the benefits of APRI on biomass accumulation, water and nitrogen use efficiencies could be modified by different soil fertilization and watering levels in pot-grown maize (Zea mays L. cv. super-sweet No 28, a local variety). Three irrigation methods, i.e. conventional irrigation (CI), alternate partial root-zone irrigation (APRI, alternate watering on both sides of the pot) and fixed partial root-zone irrigation (FPRI, fixed watering on one side of the pot), two watering levels, i.e. water deficit (W₁, 45–55% of field capacity) and well-watered (W₂, 70–80% of field capacity), and two N fertilization levels, i.e. no fertilization and fertilization, were designed. Results showed that APRI and FPRI methods led to more reduction in transpiration than in photosynthesis, and thus increased leaf water use efficiency (leaf WUE, i.e. the ratio of leaf net photosynthetic rate to transpiration rate). Compared to the CI treatment, APRI and FPRI increased leaf WUE by 7.7% and 8.1% before the jointing stage and 3.6% and 4.2% during the jointing stage, respectively. Under the fertilization and well-watered conditions, APRI treatment saved irrigation water by 38.4% and reduced shoot and total dry masses by 5.9% and 6.7%, respectively if compared to the CI treatment. APRI also enhanced canopy WUE (defined as the amount of total biomass per unit water used) and nitrogen (N) apparent recovery fraction (Nr, defined as the ratio of the increased N uptake to N applied) by 24.3% and 16.4%, respectively, indicating that effect of APRI can be better materialized under appropriate fertilization and water supply. Responsible Editor: Rana E. Munns     

Responses of leaf stomatal density to water status and its relationship with photosynthesis in a grass

Responses of plant leaf stomatal conductance and photosynthesis to water deficit have been extensively reported; however, little is known concerning the relationships of stomatal density with regard to water status and gas exchange. The responses of stomatal density to leaf water status were determined, and correlation with specific leaf area (SLA) in a photosynthetic study of a perennial grass, Leymus chinensis, subjected to different soil moisture contents. Moderate water deficits had positive effects on stomatal number, but more severe deficits led to a reduction, described in a quadratic parabolic curve. The stomatal size obviously decreased with water deficit, and stomatal density was positively correlated with stomatal conductance (g(s)), net CO(2) assimilation rate (A(n)), and water use efficiency (WUE). A significantly negative correlation of SLA with stomatal density was also observed, suggesting that the balance between leaf area and its matter may be associated with the guard cell number. The present results indicate that high flexibilities in stomatal density and guard cell size will change in response to water status, and this process may be closely associated with photosynthesis and water use efficiency.