避雨环境下苹果幼树水分状态指标对干旱胁迫的响应

在避雨环境下进行土壤水势渐进式下降处理,研究了苹果树体水分状态指标对土壤干旱胁迫响应的敏感性,分析了不同水分状态指标与树体水分平衡之间的关系.结果表明: 树干直径日较差(MDS)及中午树干水势(Ψ_stem)对干旱胁迫最敏感.MDS对参考蒸散(ET₀)有明显的响应,且对干旱胁迫比较敏感,与ET₀呈显著正相关,相对树干直径日较差(MDS_r)与相对土壤水势(Ψ_{r soil})呈显著负相关,树干直径可实现连续性测量及自动化记录.Ψ_stem对土壤干旱胁迫较敏感,且与ET₀呈显著负相关,相对中午树干水势(Ψ_{r stem})与Ψ_{r soil}呈显著相关,目前叶水势和树干水势难以实现自动化连续性观测.其他树体水分状态指标,如黎明前叶水势(Ψ_pd)、树干直径日生长量(DG)和气孔导度(g_s)等对中度或重度干旱胁迫也有不同程度的响应,但总体上对土壤水势变化的响应不敏感.     

Do tree-ring traits reflect different water deficit responses in young poplar clones (Populus × canadensis Mönch ‘I-214’ and P. deltoides ‘Dvina’)?

Poplar clones are known to display a wide range of tolerance to drought and water-use efficiency, but the effects of water deficit on stem growth and tree-ring characteristics are rarely taken into account. This study was conducted in order to investigate whether the main tree-ring traits correlate with irrigation regimes during the growing season in ‘I-214’ and ‘Dvina’ 4-year-old poplar clone saplings grown in concrete tanks, during three consecutive years. Total carbon, stable carbon isotope, Klason lignin and α-cellulose contents were analyzed to characterize wood biochemistry; ring width, wood density, mean vessel density and mean vessel lumen area were analyzed to characterize wood anatomy to assess the influence of irrigation regime. In both clones, wood formed in 2005 was more enriched in ¹³C, suggesting drought-induced stomatal closure. Wood formed in 2006 was less variable in δ¹³C in relation to irrigation regimes. ‘Dvina’ showed higher Klason lignin content and wood density than ‘I-214’, whatever the irrigation regime, despite the larger ring widths. ‘Dvina’ has the potential to recover promptly after drought stress, but at the expense of poor wood technological properties, while ‘I-214’ could continue to grow more uniformly under limited water availability, though at a lower rate.     

Responses of Papaya Seedlings (Carica papaya L.) to Water Stress and Re-Hydration: Growth, Photosynthesis and Mineral Nutrient Imbalance

The effects of water stress and subsequent re-hydration on growth, leaf abscission, photosynthetic activity, leaf water potential and ion content were investigated in papaya seedlings (Carica papaya L.) cv. “Baixinho de Santa Amalia”. Water stress was imposed by suspending irrigation during 34 days. Thereafter, plants were regularly re-watered. Drought arrested plant growth, induced leaf abscission and drastically decreased photosynthetic rate. However, leaf water potential was hardly reduced. Water deficit also induced sodium, potassium and chloride accumulation in leaves and roots, and did not modify nitrogen levels in both organs. Re-hydration stimulated growth, promoted emergence of new leaves, reactivated photosynthetic machinery function and reduced ion content to control levels. The results indicated that the ability of papaya plants to improve drought tolerance is not mediated through the reduction of leaf abscission, the detention of growth or the decrease of net CO₂ assimilation. In contrast, the data suggested that under water stress conditions these plants appear to posses a certain capacity to increase ion content, which might contribute to osmotic adjustment.     

种子大小和干旱胁迫对辽东栎幼苗生长和生理特性的影响

在温室内遮阴条件下,设置80%、60%、40%和20%田间持水量(对照、轻度、中度和重度干旱)4个处理,研究种子大小和干旱胁迫对盆栽辽东栎幼苗生长和生理特性的影响。结果表明:大种子(3.05±0.38 g)幼苗的单株叶面积、总干质量和根冠比在所有处理均显著大于小种子(1.46±0.27 g)幼苗,前者的株高、基径、叶片数、比叶面积、相对生长率和净同化率等生长参数在轻度、中度和重度干旱处理均不同程度大于后者。大种子幼苗叶片过氧化物酶(POD)、过氧化氢酶(CAT)和超氧化物歧化酶(SOD)活性均高于小种子幼苗,前者叶片丙二醛(MDA)、可溶性蛋白、游离脯氨酸含量和叶绿素总量在部分干旱处理显著大于后者。除根冠比外,其他生长参数均随干旱胁迫增强逐渐减小,重度干旱处理大、小种子幼苗总干质量分别比对照降低19.4%和20.0%。POD、CAT和SOD活性均随干旱胁迫增强先升后降,在中度干旱处理,大、小种子幼苗POD活性分别显著高于对照126.7%和142.1%,CAT活性分别显著高于对照170.0%和151.9%。在重度干旱处理,大、小种子幼苗MDA含量分别显著高于对照86.5%和68.9%。可...     

梨枣在果实生长期对土壤水势的响应

以4年生梨枣为试验材料,在果实生长期设置了4个土壤水势水平,研究不同处理梨枣茎秆直径生长、光合速率、蒸腾速率、叶片相对含水量以及果实数量对土壤水势的响应,探讨了梨枣果实生长期适宜的土壤水势范围。结果表明:1)在果实缓慢生长期,茎秆直径生长缓慢;土壤水势高于-84 kPa时能显著地降低落果率。2)果实快速生长期,茎秆直径日最大值和叶片相对含水量能反映梨枣的水分状况;适当的控制土壤水势能显著的提高叶片的水分利用效率;土壤水势高于-84 kPa时果实快速生长期出现坐果现象。3)果实生长期前期的土壤水势低至-461 kPa会影响果实生长期叶片的功能和后期的坐果。因此,梨枣果实生长期的适宜的土壤水势范围为-41—-84 kPa,提高了叶片水分利用效率,提高了单果重,不影响产量。     

Stomatal factors and vulnerability of stem xylem to cavitation in poplars

The relationships between the vulnerability of stem xylem to cavitation, stomatal conductance, stomatal density, and leaf and stem water potential were examined in six hybrid poplar (P38P38, Walker, Okanese, Northwest, Assiniboine and Berlin) and balsam poplar (Populus balsamifera) clones. Stem xylem cavitation resistance was examined with the Cavitron technique in well-watered plants grown in the greenhouse. To investigate stomatal responses to drought, plants were subjected to drought stress by withholding watering for 5 (mild drought) and 7 (severe drought) days and to stress recovery by rewatering severely stressed plants for 30 min and 2 days. The clones varied in stomatal sensitivity to drought and vulnerability to stem xylem cavitation. P38P38 reduced stomatal conductance in response to mild stress while the balsam poplar clone maintained high leaf stomatal conductance under more severe drought stress conditions. Differences between the severely stressed clones were also observed in leaf water potentials with no or relatively small decreases in Assiniboine, P38P38, Okanese and Walker. Vulnerability to drought-induced stem xylem embolism revealed that balsam poplar and Northwest clones reached loss of conductivity at lower stem water potentials compared with the remaining clones. There was a strong link between stem xylem resistance to cavitation and stomatal responsiveness to drought stress in balsam poplar and P38P38. However, the differences in stomatal responsiveness to mild drought suggest that other drought-resistant strategies may also play a key role in some clones of poplars exposed to drought stress.     

沙柳和柠条茎水力学特性对模拟降雨改变的响应

利用模拟降雨控制试验(对照、降雨增加45%和减少50%),研究了黄土高原水蚀风蚀交错带典型灌木沙柳和柠条茎水力学特性对模拟降雨改变的响应,以揭示两种灌木对未来降雨改变的适应性.结果表明: 沙柳茎比导水率(K_s)、比叶导水率(K_l)和Huber值对增水有显著响应,而对干旱无显著响应;柠条黎明前和正午叶水势、水分传输效率(K_s及K_l)对干旱有显著响应,但对增水无响应.两种灌木不同处理间抵抗栓塞能力无显著差异,沙柳不同处理间正午原位栓塞程度亦无显著差异,而柠条干旱处理正午原位栓塞程度显著增大.沙柳增水处理导管直径和导管面积占边材面积的比例显著增加,干旱导致沙柳导管密度显著增大,水力直径变小;柠条增水处理的木质部结构无明显改变,干旱导致其导管密度和木材密度显著增加.说明增水提升了沙柳的水力功能,而长期干旱显著降低了柠条水力功能,预测在未来气候旱化条件下,柠条的水力适应性可能不如沙柳.     

Protective mechanism of desiccation tolerance in Reaumuria soongorica: Leaf abscission and sucrose accumulation in the stem

Reaumuria soongorica (Pall.) Maxim., a perennial semi-shrub, is widely found in semi-arid areas in northwestern China and can survive severe desiccation of its vegetative organs. In order to study the protective mechanism of desiccation tolerance in R. soongorica, diurnal patterns of net photosynthetic rate (Pn), water use efficiency (WUE) and chlorophyll fluorescence parameters of Photosystem II (PSII), and sugar content in the source leaf and stem were investigated in 6-year-old plants during progressive soil drought imposed by the cessation of watering. The results showed that R. soongorica was characterized by very low leaf water potential, high WUE, photosynthesis and high accumulation of sucrose in the stem and leaf abscission under desiccation. The maximum Pn increased at first and then declined during drought, but intrinsic WUE increased remarkably in the morning with increasing drought stress. The maximal photochemical efficiency of PSII (Fv/Fm) and the quantum efficiency of noncyclic electric transport of PSII(Φ_PSII) decreased significantly under water stress and exhibited an obvious phenomenon of photoinhibition at noon. Drought stressed plants maintained a higher capacity of dissipation of the excitation energy (measured as NPQ) with the increasing intensity of stress. Conditions of progressive drought promoted sucrose and starch accumulation in the stems but not in the leaves. However, when leaf water potential was less than −21.3 MPa, the plant leaves died and then abscised. But the stem photosynthesis remained and, afterward the plants entered the dormant state. Upon rewatering, the shoots reactivated and the plants developed new leaves. Therefore, R. soongorica has the ability to reduce water loss through leaf abscission and maintain the vigor of the stem cells to survive desiccation. Supported by the Program of the Research of Vegetation Restoration in Arid Areas of Lanzhou (Grant No. 03-2-27) and the National Natural Science Foundation of China (Grant No. 30270243)     

Protective mechanism of desiccation tolerance in <Emphasis Type="Italic">Reaumuria soongorica</Emphasis>: Leaf abscission and sucrose accumulation in the stem

Reaumuria soongorica (Pall.) Maxim., a perennial semi-shrub, is widely found in semi-arid areas in northwestern China and can survive severe desiccation of its vegetative organs. In order to study the protective mechanism of desiccation tolerance in R. soongorica, diurnal patterns of net photosynthetic rate (Pn), water use efficiency (WUE) and chlorophyll fluorescence parameters of Photosystem II (PSII), and sugar content in the source leaf and stem were investigated in 6-year-old plants during progressive soil drought imposed by the cessation of watering. The results showed that R. soongorica was characterized by very low leaf water potential, high WUE, photosynthesis and high accumulation of sucrose in the stem and leaf abscission under desiccation. The maximum Pn increased at first and then declined during drought, but intrinsic WUE increased remarkably in the morning with increasing drought stress. The maximal photochemical efficiency of PSII (Fv/Fm) and the quantum efficiency of noncyclic electric transport of PSII(Φ_PSII) decreased significantly under water stress and exhibited an obvious phenomenon of photoinhibition at noon. Drought stressed plants maintained a higher capacity of dissipation of the excitation energy (measured as NPQ) with the increasing intensity of stress. Conditions of progressive drought promoted sucrose and starch accumulation in the stems but not in the leaves. However, when leaf water potential was less than −21.3 MPa, the plant leaves died and then abscised. But the stem photosynthesis remained and, afterward the plants entered the dormant state. Upon rewatering, the shoots reactivated and the plants developed new leaves. Therefore, R. soongorica has the ability to reduce water loss through leaf abscission and maintain the vigor of the stem cells to survive desiccation.     

Ecophysiological responses of Caragana korshinskii Kom. under extreme drought stress: Leaf abscission and stem survives

Caragana korshinskii Kom. is a perennial xerophytic shrub, well known for its ability to resist drought. In order to study ecophysiological responses of C. korshinskii under extreme drought stress and subsequent rehydration, diurnal patterns of gas exchange and chlorophyll (Chl) fluorescence parameters of photosystem II as well as Chl content were analyzed. Plant responses to extreme drought included (1) leaf abscission and using stem for photosynthesis, (2) improved instantaneous water-use efficiency, (3) decreased photosynthetic rate and partly closed stomata owing to leaf abscission and low water status, (4) decreased maximum photochemical efficiency of photosystem II (PSII) (variable to maximum fluorescence ratio, F_v/F_m), quantum efficiency of noncyclic electron transport of PSII, and Chl a and Chl b. Four days after rehydration, new leaves budded from stems. In the rewatered plants, the chloroplast function was restored, the gas exchange and Chl fluorescence returned to a similar level as control plant. The above result indicated that maintaining an active stem system after leaf abscission during extreme drought stress may be the foundation which engenders these mechanisms rapid regrowth for C. korshinskii in arid environment.     

不同灌水量对2个蓝浆果品种幼苗生长和耗水规律的影响及相关性分析

以兔眼蓝浆果(Vaccinium ashei Reade)品种'Brightwell'和南方高丛蓝浆果(V.corymbosum hybrids)品种'Misty'为研究对象,研究不同灌水量〔50%WC、75%WC、100%WC(CK)和125%WC〕(WC为单株日耗水量)对幼苗生长、单株耗水量的日变化和月变化、单株净增干质量、总耗水量和水分利用效率的影响,并采用回归分析法对单株月耗水量与月均温和月均空气相对湿度的相关性进行分析.结果显示:随灌水量提高,2个品种幼苗的地径、单株枝长和单株总叶面积的增量总体上均不断增大,但单株枝长增量略有波动;单株根、茎、叶和总干质量总体上均逐渐增大,根冠比则逐渐减小;单株净增干质量和总耗水量均随灌水量提高而增大,而水分利用效率则在50%WC条件下最低、在75%WC条件下最高.在相同灌水量条件下,品种'Misty'幼苗的地径和单株枝长的增量,单株茎、叶和总干质量及水分利用效率基本上均高于品种'Brightwell',而其单株总叶面积增量、单株根干质量、根冠比和总耗水量却基本上低于后者.在7月份至9月份,2个品种幼苗单株耗水量的日变化基本上呈单峰曲线,但其单株耗水量峰值出现的时间段则因品种和灌水量不同而异;在全天不同时间段和不同月份,2个品种幼苗的单株耗水量均随灌水量提高而增大;在相同灌水量条件下,品种'Misty'幼苗的单株耗水量总体上低于品种'Brightwell'.回归分析结果表明:2个品种幼苗的单株月耗水量与月均温呈显著或极显著正相关,与月均空气相对湿度呈显著或极显著负相关.综合分析结果表明:蓝浆果幼苗的耗水量不但与品种特性有关,而且还受到土壤水分含量、气温和空气湿度的影响;在相同灌水量条件下,品种'Brightwell'幼苗的耗水量高于品种'Misty',但其水分利用效率却低于后者.在中国南方地区,品种'Brightwell'和'Misty'的适宜灌水量分别为100%WC和75%WC.     

Contribution of arbuscular mycorrhizal fungi (AMF) to the adaptations exhibited by the deciduous shrub Anthyllis cytisoides L. under water deficit

Anthyllis cytisoides L. is highly colonized by arbuscular mycorrhizal fungi (AMF) and behaves as a drought-avoider species in the field. Our objectives were: (1) to study the response of A. cytisoides when exposed to moderate (acclimation) or severe (peak) drought and subsequent rewatering under nursery conditions; and (2) to verify if AMF improved the adaptation of A. cytisoides to stress. The soil compactness in drought-acclimated treatments increased four times compared with that of well-watered controls, which could reinforce the effects of water deficit on plant physiology. Photosynthetic rates decreased by around 50% and 70% and leaf conductance decreased by 40% and 50% in drought-acclimated non-mycorrhizal and mycorrhizal plants, respectively. Peak drought limited plant growth, accelerated leaf senescence and induced the conversion of starch into soluble sugars in the leaves of stressed plants. The accumulation of sugars could contribute to a decrease in water potential in order to achieve the required tension to let water move from soil to shoot. Mycorrhizal plants showed a two-fold higher chlorotic leaf biomass than non-mycorrhizal plants under severe drought. Moreover, mycorrhizal A. cytisoides showed enhanced epicuticular waxes on the surfaces of the remaining green leaves. Increased leaf senescence, together with wax deposition, could reduce whole plant transpiration, thus allowing mycorrhizal plants to maintain a higher leaf relative water content (50%) than non-mycorrhizal plants (35%). After drought recovery, leaf abscission in stressed mycorrhizal plants was 10 times greater than that in non-mycorrhizal plants. The results suggest that AMF conferred greater responsiveness of A. cytisoides to drought. Enhanced wax deposition and leaf senescence could be an ecological adaptation to cope with severe water deficit.     

Drought tolerance is associated with rooting depth and stomatal control of water use in clones of Coffea canephora

* BACKGROUND AND AIMS: Drought is a major environmental constraint affecting growth and production of Coffea canephora. Selection of C. canephora clones has been largely empirical as little is known about how clones respond physiologically to drought. Using clones previously shown to differ in drought tolerance, this study aimed to identify the extent of variation of water use and the mechanisms responsible, particularly those associated morphological traits. * METHODS: Clones (14 and 120, drought-tolerant; 46 and 109A, drought-sensitive, based on their abilities to yield under drought) were grown in 120-L pots until they were 12-months old, when an irrigation and a drought treatment were applied; plants were droughted until the pressure potential (psi(x)) before dawn (pre-dawn) reached -3.0 MPa. Throughout the drought period, psi(x) and stomatal conductance (g(s)) were measured. At the end of the experiment, carbon isotope ratio and parameters from pressure-volume curves were estimated. Morphological traits were also assessed. * KEY RESULTS AND CONCLUSIONS: With irrigation, plant hydraulic conductance (K(L)), midday psi(x) and total biomass were all greater in clones 109A and 120 than in the other clones. Root mass to leaf area ratio was larger in clone 109A than in the others, whereas rooting depth was greater in drought-tolerant than in drought-sensitive clones. Predawn psi(x) of -3.0 MPa was reached fastest by 109A, followed progressively by clones 46, 120 and 14. Decreases in g(s) with declining psi(x), or increasing evaporative demand, were similar for clones 14, 46, and 120, but lower in 109A. Carbon isotope ratio increased under drought; however, it was lower in 109A than in other clones. For all clones, psi(x), g(s) and K(L) recovered rapidly following re-watering. Differences in root depth, K(L) and stomatal control of water use, but not osmotic or elastic adjustments, largely explained the differences in relative tolerance to drought stress of clones 14 and 120 compared with clones 46 and 109A.     

Modification of Vegetative Phenology in a Tropical Semi‐deciduous Forest by Abnormal Drought and Rain1

The control of vegetative phenology in tropical trees is not well understood. In dry forest trees, leaf abscission may be enhanced by advanced leaf age, increasing water stress, or declining photoperiod. Normally, it is impossible to dissect the effects of each of these variables because most leaves are shed during the early dry season when day length is near its minimum and leaves are relatively old. The 1997 El‐Niño Southern Oscillation caused a ten‐week long, severe abnormal drought from June to August in the semi‐deciduous forests of Guanacaste, Costa Rica. We monitored the effect of this drought on phenology and water status of trees with young leaves and compared modifications of phenology in trees of different functional types with the pattern observed during the regular dry season. Although deciduous trees at dry sites were severely water stressed (Ψstem < ‐7MPa) and their mesic leaves remained wilted for more than two months, these and all other trees retained all leaves during the abnormal drought. Many trees exchanged leaves three to four months earlier than normal during the wet period after the abnormal drought and shed leaves again during the regular dry season. Irrigation and an exceptional 70 mm rainfall during the mid‐dry season 1998/1999 caused bud break and flushing in all leafless trees except dormant stem succulents. The complex interactions between leaf age and water stress, the principal determinants of leaf abscission, were found to vary widely among trees of different functional types.     

1-Aminocyclopropane-1-Carboxylic Acid Transported from Roots to Shoots Promotes Leaf Abscission in Cleopatra Mandarin (Citrus reshni Hort. ex Tan.) Seedlings Rehydrated after Water Stress

The effect of water stress and subsequent rehydration on 1-aminocyclopropane-1-carboxylic acid (ACC) content, ACC synthase activity, ethylene production, and leaf abscission was studied in Cleopatra mandarin (Citrus reshni Hort. ex Tan.) seedlings. Leaf abscission occurred when drought-stressed plants were allowed to rehydrate, whereas no abscission was observed in plants under water stress conditions. In roots of water-stressed plants, a high ACC accumulation and an increase in ACC synthase activity were observed. Neither increase in ACC content nor significant ethylene production were detected in leaves of water-stressed plants. After rehydration, a sharp rise in ACC content and ethylene production was observed in leaves of water-stressed plants. Content of ACC in xylem fluid was 10-fold higher in plants rehydrated for 2 h after water stress than in nonstressed plants. Leaf abscission induced by rehydration after drought stress was inhibited when roots or shoots were treated before water stress with aminooxyacetic acid (AOA, inhibitor of ACC synthase) or cobalt ion (inhibitor of ethylene-forming enzyme), respectively. However, AOA treatments to shoots did not suppress leaf abscission. The data indicate that water stress promotes ACC synthesis in roots of Cleopatra mandarin seedlings. Rehydration of plants results in ACC transport to the shoots, where it is oxidized to ethylene. Subsequently, this ethylene induces leaf abscission.     

干旱胁迫对宁夏枸杞生长及果实糖分积累的影响

文章研究不同干旱胁迫下宁夏枸杞生长及果实糖分积累的变化规律,为宁夏枸杞在干旱地区高产栽培提供参考依据。采用盆栽控水试验,设置正常灌水、轻度干旱、中度干旱和重度干旱处理,研究了干旱胁迫对宁夏枸杞植株生长、生物量分配以及果实糖分积累的影响。结果表明：干旱抑制宁夏枸杞新稍、果实、株高和地径的生长：随着干旱程度加剧,根和茎中干物质分配率逐渐升高,而枝条、叶和果实中干物质分配率大幅降低;轻度干旱有利于果实发育过程中果糖的积累,中度和重度干旱胁迫则不利于成熟期果糖和蔗糖积累;干旱胁迫明显降低成熟期转化酶、蔗糖磷酸合成酶（SPS）和蔗糖合成酶（SS）的活性;果实发育过程中果糖的含量与SPS和转化酶活性存在极显著相关。可见,在果实发育期,土壤含水量为田间持水量55％以上,能促进宁夏枸杞果实中糖分积累,有效提高果实品质。     

亚低温与干旱胁迫对番茄植株水分传输和形态解剖结构的影响

为探讨亚低温和干旱对植株水分传输的影响机制,以番茄幼苗为试材,利用人工气候室设置常温(昼25 ℃/夜18 ℃)和亚低温(昼15 ℃/夜8 ℃)环境,采用盆栽进行正常灌水(75%～85%田间持水量)和干旱处理(55%～65%田间持水量),分析了温度和土壤水分对番茄植株水分传输、气孔和木质部导管形态解剖结构的影响。结果表明: 与常温正常灌水处理相比,干旱处理使番茄叶水势、蒸腾速率、气孔导度、水力导度、茎流速率、气孔长度和叶、茎、根导管直径显著减小,而使叶、茎、根导管细胞壁厚度和抗栓塞能力增强;亚低温处理下番茄叶水势、蒸腾速率、气孔导度、水力导度和叶、茎、根导管直径显著降低,但气孔变大,叶、根导管细胞壁厚度和叶、茎、根抗栓塞能力显著升高。亚低温条件下土壤水分状况对番茄叶水势、蒸腾速率、气孔导度、水力导度、气孔形态、叶、根导管结构均无显著影响。总之,干旱处理下番茄通过协同调控叶、茎、根结构使植株水分关系重新达到稳态;亚低温处理下番茄植株水分关系的调控主要通过改变叶和根导管结构实现,且受土壤水分状况的影响较小。     

不同生育时期干旱对冬小麦氮素吸收与利用的影响

以抗旱性强的‘石家庄8号’和抗旱性弱的‘偃麦20’冬小麦(Triticum aestivum)为材料, 在田间遮雨棚条件下, 研究返青-拔节期、拔节-开花期和灌浆后期3个生育期不同干旱程度对冬小麦产量、氮素吸收、分配和利用的影响。结果表明, 在干旱条件下, 抗旱性强的‘石家庄8号’产量高于抗旱性弱的‘偃麦20’, 并且其3个生育时期轻度干旱均可提高产量。拔节-开花期干旱对两个冬小麦品种氮素的吸收和运转影响均最大, 其次为返青-拔节期, 而灌浆后期影响较小。不同生育期中度和重度干旱均降低了花前贮藏氮素向籽粒中的转移, 并且氮肥利用效率和生产率也较低, 而在返青-拔节和灌浆后期轻度干旱有利于营养器官的氮素向籽粒中转移, 提高了氮肥利用效率和生产率。在干旱条件下, 抗旱性强的‘石家庄8号’籽粒氮素积累对花前贮藏氮素再运转的依赖程度高, 而‘偃麦20’对花后氮素的积累和转移依赖较高。综合产量和氮素的转移特点, 在生产实践中, 返青-拔节期和灌浆后期要注意对小麦进行适度的干旱处理, 在拔节-开花期要保证冬小麦的充分灌溉, 从而有利于氮素的积累和分配。     

Model-assisted evaluation of crop load effects on stem diameter variations and fruit growth in peach

Key message

The paper identifies and quantifies how crop load influences plant physiological variables that determine stem diameter variations to better understand the effect of crop load on drought stress indicators.

Abstract

Stem diameter (D ^stem) variations have extensively been applied in optimisation strategies for plant-based irrigation scheduling in fruit trees. Two D ^stem derived water status indicators, maximum daily shrinkage (MDS) and daily growth rate (DGR), are however influenced by other factors such as crop load, making it difficult to unambiguously use these indicators in practical irrigation applications. Furthermore, crop load influences the growth of individual fruits, because of competition for assimilates. This paper aims to explain the effect of crop load on DGR, MDS and individual fruit growth in peach using a water and carbon transport model that includes simulation of stem diameter variations. This modelling approach enabled to relate differences in crop load to differences in xylem and phloem water potential components. As such, crop load effects on DGR were attributed to effects on the stem phloem turgor pressure. The effect of crop load on MDS could be explained by the plant water status, the phloem carbon concentration and the elasticity of the tissue. The influence on fruit growth could predominantly be explained by the effect on the early fruit growth stages.     

Mechanism of Photothermal Energy on the Growth and Yield of Rice under Water Level Regulation

The flooding caused by heavy rainfall in rice irrigation area and the drought caused by the drop of groundwater level are the research focus in the field of irrigation and drainage. Based on the comparative experiment and farmland water level control technology, this paper studied the average soil temperature under different soil layers (TM), the daily temperature change (TDC), the photosynthetic accumulation of single leaf and canopy in rice, and response of photothermal energy to rice root characteristics and growth factors in the paddy field under drought conditions. The results showed that the peak soil temperature under drought treatment was basically synchronous with the conventional irrigation, and the it was delayed by 2–6 h under flooding treatment compared to the drought treatment. Under different water gradients, the temperature decreased according to T_L > T_CK > T_H (L, H and CK represented water flooding, drought and control treatments), and the TDC was opposite. In addition to milky stage, the daily photosynthetic (Pn) accumulation of single leaf and canopy in the flooding and drought treated paddy fields were lower than conventional irrigation, and had a negative impact on leaf area index (LAI) and yield (YR), but did not form fatal damage. The root characteristic factors, RL (root length), RW (root weight), R-CR (root-canopy ratio) were promoted with drought, and YR under light drought was slightly higher than that under heavy drought. There was a strong positive correlation between TM and R-CR in all rice growth stages, while TDC-5 was negatively correlated with effective panicle number, TDC and R-CR in 20 cm soil layer were positively correlated. The correlation between daily Pn accumulation and YR was low, and the correlation between Pn and YR factors was negative or weak positive or negative. The total Pn was positively correlated with yield factors, and the correlation coefficient was higher than that of daily Pn.