Light induced transpiration in a chlorophyll deficient mutant of Hordeum vulgare

A chlorophyll deficient mutant of Hordeum vulgare L. was investigated with respect to its transpiration response to light pulses. Broad band blue light. 380–500 nm, caused a significant transpiration response, while broad band red light did not. The transpiration response to changes in the ambient CO₂-concentration was the same in the chlorophyll deficient mutant as in green plants. The absence of a transpiration response to red light in the mutant was therefore not the result of a defective CO₂-response. It is concluded that the specific blue light response is not mediated via photosynthetic CO₂-fixation. The nature of the blue light response is discussed.     

Winds at departure shape seasonal patterns of nocturnal bird migration over the North Sea

On their migratory journeys, terrestrial birds can come across large inhospitable areas with limited opportunities to rest and refuel. Flight over these areas poses a risk especially when wind conditions en route are adverse, in which case inhospitable areas can act as an ecological barrier for terrestrial migrants. Thus, within the east-Atlantic flyway, the North Sea can function as an ecological barrier. The main aim of this study was to shed light on seasonal patterns of bird migration in the southern North Sea and determine whether departure decisions on nights of intense migration were related to increased wind assistance. We measured migration characteristics with a radar that was located 18 km off the NW Dutch coast and used simulation models to infer potential departure locations of birds on nights with intense nocturnal bird migration. We calculated headings, track directions, airspeeds, groundspeeds on weak and intense migration nights in both seasons and compared speeds between seasons. Moreover, we tested if departure decisions on intense migration nights were associated with supportive winds. Our results reveal that on the intense migration nights in spring, the mean heading was towards E, and birds departed predominantly from the UK. On intense migration nights in autumn, the majority of birds departed from Denmark, Germany and north of the Netherlands with the mean heading towards SW. Prevailing winds from WSW at departure were supportive of a direct crossing of the North Sea in spring. However, in autumn winds were generally not supportive, which is why many birds exploited positive wind assistance which occurred on intense migration nights. This implies that the seasonal wind regimes over the North Sea alter its migratory dynamics which is reflected in headings, timing and intensity of migration.     

Daytime noise predicts nocturnal singing in urban robins

Ambient noise interferes with the propagation of acoustic signals through the environment from sender to receiver. Over the past few centuries, urbanization and the development of busy transport networks have led to dramatic increases in the levels of ambient noise with which animal acoustic communications must compete. Here we show that urban European robins Erithacus rubecula, highly territorial birds reliant on vocal communication, reduce acoustic interference by singing during the night in areas that are noisy during the day. The effect of ambient light pollution, to which nocturnal singing in urban birds is frequently attributed, is much weaker than that of daytime noise.     

Photosynthesis and Chlorophyll Fluorescence in Two Hybrids of Sorghum under Different Nitrogen and Water Regimes

In two hybrids of sorghum (Sorghum bicolor Moench.), C51 and C42, high nitrogen concentration (HN) increased net photosynthetic rate (PN), stomatal conductance (gs), and transpiration rate (E) of well watered (HW) plants. Water stressing (LW plants) resulted in low PN, gs, and E in both hybrids, but the values were still higher in HN plants as compared to low nitrogen-grown (LN) plants. Intercellular CO2 concentration (Ci) increased in droughted plants. This increase was much higher in LN plants as compared to HN plants. Instantaneous water use efficiency was lower in LN plants as a consequence of a greater effect of water stress on photosynthesis. Leaf water potential was reduced by water stress in all treatments. Analysis of chlorophyll a fluorescence at room temperature showed that photosystem 2 (PS2) was rather tolerant to the water stress imposed. Water stress caused a slight decrease in the efficiency of excitation capture by open PS2 reaction centres (Fv/Fm). The in vivo quantum yield of PS2 photochemistry (PS2) and the photochemical quenching coefficient (qP) were slightly reduced, while the nonphotochemical quenching coefficient (qN) was increased under the water stress. However, in hybrid C42 these characters were little or not affected by the water stress.     

Gas Exchange and Emission of Chlorophyll Fluorescence during the Monocycle of Rust, Angular Leaf Spot and Anthracnose on Bean Leaves as a Function of their Trophic Characteristics

Measurements related to gas exchange and chlorophyll fluorescence emission were taken from healthy and diseased bean leaves with rust, angular leaf spot, and anthracnose during lesion development for each disease. The experiments were performed at different temperatures of plant incubation, and using two bean cultivars. The main effect of temperature of plant incubation was in disease development. There was no significant difference between cultivars in relation to disease development and in magnitude of physiological alterations when disease severity was the same for each cultivar. These diseases reduced the net photosynthetic rate and increased the dark respiration of infected leaves after the appearance of visible symptoms and the differences between healthy and diseased leaves increased with disease development. The transpiration rate and stomatal conductance were stable during the monocycle of rust, however, these two variables decreased in leaves with angular leaf spot and anthracnose beginning with symptom appearance and continuing until lesion development was complete. Carboxylation resistance was probably the main factor related to reduction of photosynthetic rate of the apparently healthy area of leaves with rust and angular leaf spot. Reduction of the intercellular concentration of CO₂, due to higher stomatal resistance, was probably the main factor for leaves with anthracnose. Chlorophyll fluorescence assessments suggested that there was no change in electron transport capacity and generation of ATP and NADPH in apparently healthy areas of diseased leaves, but decreases in chlorophyll fluorescence emission occurred on visibly lesioned areas for all diseases. Minimal fluorescence was remarkably reduced in leaves with angular leaf spot. Maximal fluorescence and optimal quantum yield of photosystem II of leaves were reduced for all three diseases. Bean rust, caused by a biotrophic pathogen, induced less damage to the regulation mechanisms of the physiological processes of the remaining green area of diseased leaves than did bean angular leaf spot or anthracnose, caused by hemibiotrophic pathogens. The magnitude of photosynthesis reduction can be related to the host–pathogen trophic relationships.     

Effects of nitrogen supply and high temperature on the growth and physiology of the chickpea

Chickpeas were grown with or without nitrate nitrogen feeding, or nodulated with Rhizobium leguminosarum. High [40°C day, 25°C night (HT)] and moderate [25°C day, 177°C night (LT)] temperature regimes were employed during growth. Growth rates, photosynthetic capacity and enzymes of carbon and nitrogen metabolism were monitored to assess the acclimatory capacity of the chickpea. Initial growth rates were stimulated by high temperatures, particularly in nitrate-fed and nodulated plants. Older HT plants had fewer laterals, smaller leaves, and fewer flowers were produced than in LT plants. There was some indication of an acclimation of photosynthesis to high temperatures and this was independent of nitrogen supply. Rubisco activity was increased by high growth temperatures. However, HT plants also had higher transpiration rates and lower water use efficiency than LT plants both in respective growth conditions and when compared in a common condition. High temperatures reduced shoot nitrate reductase activity but had little effect on root activity, which was the same if not greater than activity in LT roots. The amino acid, asparagine, was found at high concentrations in all treatments. Concentrations were maintained throughout growth in HT plants but declined with age in LT plants.     

Phosphorus concentrations in the leaves of defoliated white clover affect abscisic acid formation and transpiration in drying soil

Increased leaf phosphorus (P) concentration improved the water-use efficiency (WUE) and drought tolerance of regularly defoliated white clover plants by decreasing the rate of daily transpiration per unit leaf area in dry soil. Night transpiration was around 17% of the total daily transpiration. The improved control of transpiration in the high-P plants was associated with an increased individual leaf area and WUE that apparently resulted from net photosynthetic assimilation rate being reduced less than the reductions in the transpiration (27% vs 58%). On the other hand, greater transpiration from low-P plants was associated with poor stomatal control of transpirational loss of water, less ABA in the leaves when exposed to dry soil, and thicker and smaller leaf size compared with high-P leaves. The leaf P concentration was positively related with leaf ABA, and negatively with transpiration rates, under dry conditions ( P < 0.001). However, leaf ABA was not closely related to the transpiration rate, suggesting that leaf P concentration has a greater influence than ABA on the transpiration rates.     

Diel water movement between parenchyma and chlorenchyma of two desert CAM plants under dry and wet conditions

Abstract. Electric-circuit analogue models of the water relations of crassulacean acid metabolism (CAM) succulents such as Agave deserti and Ferocactus acanthodes have predicted diel movement of water between the water-storage parenchyma and the photo-synthetic chlorenchyma. Injection of tritiated water into either tissue in the laboratory confirmed substantial and bidirectional water movements, especially under conditions of wet soil. For A. deserti , water movement from the water-storage parenchyma to the chlorenchyma increased at night as the chlorenchyma osmotic pressure increased. Although nocturnal osmotic pressure increases and transpiration for both species were minimal in the field under dry conditions, diel changes in the deuterium: hydrogen ratio (expressed as ΔD) were similar for the water-storage parenchyma and the chlorenchyma. Such indication of [substantial mixing of water between the tissues over a 24-h cycle was more evident under wet conditions in the field. For A. deserti , ΔD then increased by 32%o from the afternoon to midnight and was essentially identical in the water-storage parenchyma and the chlorenchyma. For F. acanthodes , the diel changes in ΔD were one-third those of A. deserti , and ΔD was always slightly higher for the chlorenchyma than for the water-storage parenchyma, apparently reflecting the lower surface-to-volume ratio of A. deserti. In summary, data obtained using radioactive and stable isotopes strongly supported model predictions concerning diel cycles of internal water distribution for these CAM species.     

松嫩草原碱化草地角碱蓬群落水分生态的研究

 本文采用自行设汁的蒸散仪和加拿大Campbe 11科学仪器公司生产的自动气象设备测定了松嫩草原碱化草地角碱蓬群落的蒸散、蒸腾量、太阳辐射及空气温度等环境因子。分析结果表明生长季的睛天条件下,角碱蓬群落的蒸散、蒸腾速率的日进程均为单峰曲线,且各月份间差异很大。群落蒸腾速率与太阳辐射强度、空气温度、相对湿度、风速等环境因子紧密相关,其中与太阳辐射强度呈极显著正相关关系。生长季降雨量和土壤含水量在角碱蓬群落水分循环与平衡的过程中起重要调节作用。1992年6～8月的生长季中,角碱蓬群落总的水分亏缺较少(6.3mm),但各月份间差异很大,其中6月份水分亏缺最高(30.1mm)。