Soybean leaf photosynthesis in relation to maturity classification and stage of growth

Leaf photosynthetic rates were measured on field-grown soybeans during the 1980 season. Comparisons were made between different cultivars and isolines representative of maturity groups I–IV. Mature, fully expanded leaves at different nodes on the plant were measured in high light to determine which had the highest potential photosynthetic rates at any one time. Successive leaves during the growing season had maximum rates which increased from about 22 mol CO₂ m^-2 s^-1 on 25 June to a peak of 30–44 mol CO₂ m^-2 s^-1 in early August.The persistency and eventual decline in the maximum rate was associated with the maturity group and related dates of flowering, pod fill and onset of senescence. Early maturing cultivars (groups I and II) had higher peak rates (38–44 mol CO₂ m^-2 s^-1) than later maturing cultivars (30–35 mol CO₂ m^-2 s^-1, groups III and IV). However, the photosynthetic rates of early maturing cultivars declined rapidly after attaining their peak, whereas the leaves of later maturing cultivars maintained their photosynthetic activity for much longer.     

Drought tolerance processes in soybeans

Fifteen soybean cultivars were evaluated in two water supply conditions, inducing or not a drought stress. Main canopy traits were measured several times during the reproductive period and, at maturity date, the yield components were estimated. Using principal components analysis, the main physiological functions involved in soybean drought tolerance are described: leaf cells enlargement and assimilates transport. These processes could be a good basis on which to define new selection criteria for soybean drought tolerance.     

Some Ultrastructural Changes Induced in Resistant and Susceptible Soybean Roots Following Infection by Rotylenchulus reniformis

A developmental electron microscopic study of the parasitism of Rolylenchulus reniforrnis in resistant ''Peking'' and susceptible ''Lee'' soybeans was made during a 21-day period under controlled conditions. Within 2 days of inoculation, the nematode had penetrated the cortical cells to the endodermis where it inserted its stylet, secreted and initiated syncytial formation and cell hypertrophy. Syncytia primarily involved pericycle tissues and, to a lesser extent, xylem parenchyma and endodermis. When identifiable, the cell into which the nematode stylet was inserted to initiate syncytial development was endodermal. Susceptible tissues exhibited two basic phases of development during this infection period: (i) an initial phase represented by partial cell wail lysis and separation; and (ii) an anabolic phase, characterized by organelle proliferation and development accompanied by secondary wall deposits, which provided nutrition for sessile female development. The resistant or hypersensitive reaction (HR) lacked the anabolic phase found in the susceptible reaction, and was characterized by an extension and usually accelerated type of Iysis found in the first phase of the syncytial development. The HR was usually very evident 4 days after inoculation, and could be identified by an almost complete lysis of the cell walls and cytoplasm. The possibility that the initial cell of the developing syncytium or "prosyncyte" may influence a susceptible or resistant reaction is discussed. Successive stages of cell wall dissolution and the deposition of secondary cell walls are described.     

Aluminium Stress Affects Nitrogen Fixation and Assimilation in Soybean (Glycine max L.)

Nitrogen fixation and assimilation in nodules and roots were studied in soybean (Glycine max L.) exposed to different levels of aluminium (Al) stress (0, 50, 200 and 500 μM). Al at 500 μM induced oxidative stress, which became evident from an increase in lipid peroxidation accompanied by a concomitant decline in antioxidant enzyme activities and leghaemoglobin breakdown. Consequently, there was also a reduction in nitrogenase activity. However, the leghaemoglobin levels and nitrogenase activity were unexpectedly found to be higher in nodules when the plants were treated with 200 μM Al. Of the enzymes involved in nitrogen assimilation, the activity of glutamate dehydrogenase-NADH was reduced in nodules under Al stress, but it was significantly higher in roots at 500 μM Al as compared to that in the control. In nodules, the glutamine synthetase/glutamate synthase-NADH pathway, assayed in terms of activity and expression of both the enzymes, was inhibited at >50 μM Al; but in roots this inhibitory effect was apparent only at 500 μM Al. No significant changes in ammonium and protein contents were recorded in the nodules or roots when the plants were treated with 50 μM Al. However, Al at ≥200 μM significantly increased the ammonium levels and decreased the protein content in the nodules. But these contrasting effects on ammonium and protein contents due to Al stress were observed in the roots only at 500 μM Al. The results suggest that the effect of Al stress on nitrogen assimilation is more conspicuous in nodules than that in the roots of soybean plants.     

Effect of abscisic acid application on root isoflavonoid concentration and nodulation of wild-type and nodulation-mutant soybean plants

Isoflavonoids (daidzein, genistein, and coumestrol) are involved in induction of nod genes in Bradyrhizobium japonicum and may be involved in nodule development as well. Abscisic acid (ABA) may also impact nodulation since ABA is reportedly involved in isoflavonoid synthesis. The current study was conducted to evaluate whether ABA plays a role in differential nodulation of a hypernodulated soybean (Glycine max L. Merr.) mutant and the Williams parent. Exogenous ABA application resulted in a decrease in nodule number and weight in both lines. Isoflavonoid concentrations were also markedly decreased in response to ABA application in both inoculated and noninoculated soybean roots. The inoculation treatment itself resulted in a marked increase in isoflavonoid concentrations of NOD1-3, regardless of ABA levels, while only slight increases occurred in Williams. The nodule numbers of both soybean lines across several ABA concentration treatments were highly correlated with the concentration of all three isoflavonoids. However, differences in internal levels of ABA between lines were not detected when grown in the absence of external ABA additions. It is concluded that differential nodule expression between the wild type and the hypernodulated mutant is not likely due to differential ABA synthesis.     

Effects of carbon dioxide concentration on the interactive effects of temperature and water vapour on stomatal conductance in soybean

Soybeans were grown at three CO₂ concentrations in outdoor growth chambers and at two concentrations in controlled-environment growth chambers to investigate the interactive effects of CO₂, temperature and leaf-to-air vapour pressure difference (LAVPD) on stomatal conductance. The decline in stomatal conductance with CO₂ was a function of both leaf temperature and LAVPD. In the field measurements, stomatal conductance was more sensitive to LAVPD at low CO₂ at 30 °C but not at 35 °C. There was also a direct increase in conductance with temperature, which was greater at the two elevated carbon dioxide concentrations. Environmental growth chamber results showed that the relative stomatal sensitivity to LAVPD decreased with both leaf temperature and CO₂. Measurements in the environmental growth chamber were also performed at the opposing CO₂, and these experiments indicate that the stomatal sensitivity to LAVPD was determined more by growth CO₂ than by measurement CO₂. Two models that describe stomatal responses to LAVPD were compared with the outdoor data to evaluate whether these models described adequately the interactive effects of CO₂, LAVPD and temperature.     

Max试验验证症状限制心肺运动试验为最大极限运动进一步临床研究*

目的: 验证临床受试者所完成的心肺运动试验（CPET）为最大极限运动,进一步设计完善Max试验验证CPET结果客观定量功能评估的准确性及以某特定指标的特定数值作为停止运动的标准是否可行。方法: 选择2017年9月至2019年1月在阜外医院签署知情同意书后进行CPET和Max试验受试者216例。其中正常受试者41例,因CPET峰值呼吸交换率（RER）≤1.10,或运动中心率和血压不上升,对CPET极限运动结果存在质疑的临床患者175例进行研究。其中60例已初步报告,本研究进一步扩大研究。Max试验方法：完成CPET测试后,先蹬车≥60 r/min,再施加130%峰值功率的恒定功率,鼓励受试者运动至不能坚持的极限状态。计算分析Max试验30 s的最大心率和最大摄氧量、及其与峰值心率和峰值摄氧量之间的差值和百分差值。百分差值=（Max值-峰值值）/Max值× 100%。评测标准：①若心率和摄氧量任一指标的差值百分比≤-10%（Max测试的数值低于CPET峰值数据）则定义Max试验操作失败,否则为成功;2若心率和摄氧量的差值百分比均在-10%~10%,则Max试验操作成功,证明CPET数据为极限运动,CPET 峰值相关数据较为准确;③若心率和摄氧量差值任一指标差值百分比≥10%时,则Max试验操作成功,证明CPET结果为非极限运动。结果: 病例组峰值摄氧量（L/min、ml/（min·kg）、%pred）、无氧阈（L/min、ml/（min·kg）、%pred）、峰值氧脉搏（ml/beat、%pred）、峰值RER、峰值收缩压（mmHg）、峰值运动负荷（W/min）、峰值心率（bpm）、摄氧有效性峰值平台（OUEP）（比值、%pred）低于正常组,二氧化碳通气有效性平均90 s最低值（Lowest Ve/VCO₂）（比值、%pred）、二氧化碳通气效率斜率（Ve/VCO₂ Slope）（比值、%pred）高于正常组（P<0.05）。所有正常组与病例组均安全无任何事件完成CPET和Max试验。216例受试者中,Max试验成功198例（91.7%）,其中证明CPET为极限运动182例,为非极限运动16例;失败18例（8.3%）。结论: 在临床检查中,若对CPET结果是否为最大极限存在质疑,利用Max试验可验证CPET是否为极限运动。Max试验方法安全可行,值得进一步深入研究和临床推广应用。     

Soybean leaf hydraulic conductance does not acclimate to growth at elevated [CO2] or temperature in growth chambers or in the field

Background and Aims

Leaf hydraulic properties are strongly linked with transpiration and photosynthesis in many species. However, it is not known if gas exchange and hydraulics will have co-ordinated responses to climate change. The objective of this study was to investigate the responses of leaf hydraulic conductance (K_leaf) in Glycine max (soybean) to growth at elevated [CO₂] and increased temperature compared with the responses of leaf gas exchange and leaf water status.

Methods

Two controlled-environment growth chamber experiments were conducted with soybean to measure K_leaf, stomatal conductance (g_s) and photosynthesis (A) during growth at elevated [CO₂] and temperature relative to ambient levels. These results were validated with field experiments on soybean grown under free-air elevated [CO₂] (FACE) and canopy warming.

Key results

In chamber studies, K_leaf did not acclimate to growth at elevated [CO₂], even though stomatal conductance decreased and photosynthesis increased. Growth at elevated temperature also did not affect K_leaf, although g_s and A showed significant but inconsistent decreases. The lack of response of K_leaf to growth at increased [CO₂] and temperature in chamber-grown plants was confirmed with field-grown soybean at a FACE facility.

Conclusions

Leaf hydraulic and leaf gas exchange responses to these two climate change factors were not strongly linked in soybean, although g_s responded to [CO₂] and increased temperature as previously reported. This differential behaviour could lead to an imbalance between hydraulic supply and transpiration demand under extreme environmental conditions likely to become more common as global climate continues to change.