Photosynthesis in an Australian rainforest tree,Argyrodendron peralatum,during the rapid development and relief of water deficits in the dry season

Summary Rates of apparent photosynthesis were measured in situ at five positions between the upper crown and a lower branch of a 34 m tall Argyrodendron peralatum (F.M. Bailey) H.L. Edlin ex I.H. Boas tree, and on an understorey sapling of the same species growing in a northern Australian rainforest. At the end of the dry season, rapid reductions in photosynthetic rates occurred in the upper crown within three days after a rain event, but changes in the lower crown and the sapling were less marked. Complete recovery of photosynthesis followed a second rain event. At high photon flux densities, stomatal conductance to water vapour decreased in a curvilinear fashion as the vapour pressure difference between leaf and air increased. Apparent photosynthesis was linearly related to stomatal conductance on the first clear day after each rain event, but there was no relationship between these parameters at the end of a brief natural drying cycle. Under conditions of adequate water supply, stomatal conductances of both upper crown and understorey leaves increased linearly with increasing photon flux density up to about 300 mol m^-2 s^-1. During water deficits, stomatal conductances in leaves from the understorey increased much more rapidly at very low photon flux densities than did conductances in leaves from the upper canopy.     

Regulation of mesophyll photosynthesis in intact wheat leaves by cytoplasmic phosphate concentrations

The effect of D-(+)-mannose, inorganic phosphate (Pi) and mannose-6-phosphate on net mesophyll CO₂ assimilation rate (A) and stomatal conductance (g_s) of wheat (Triticum aestivum L.) leaves was studied. The compounds were supplied through the transpiration stream of detached leaves from plants grown in sand in growth cabinets or glasshouses, with different concentrations of Pi (0.25, 1.0 and 4.0 mM) supplied during growth. In all cases, 10 mM D-(+)mannose caused 40–60% reduction of A within 30 min, though the time courses differed for flag leaves and the sixth leaf on the mainstem of glasshouse- and cabinet-grown plants. D-(+)Mannose had a similar effect on A in leaves having a fourfold range in total phosphate content. Effects of D-(+)mannose in reducing g_s were always slower than on A. When the CO₂ concentration in the leaf chamber was adjusted to maintain intercellular CO₂ concentration (C_i) constant as A declined after mannose supply, g_s still declined indicating that stomatal closure was not caused by changing C_i. Supplying mannose-6-phosphate at 10 and 1 mM and Pi at 5 and 10 mM concentrations caused rapid reductions in g_s and also direct reductions in A. The observed effects of mannose and Pi on assimilation are consistent with the proposed regulatory role of cytoplasmic Pi in determining mesophyll carbon assimilation that has been derived previously using leaf discs, protoplasts and chloroplasts.Abbreviations and symbols A net mesophyll CO₂-assimilation rate - C_a, C_i external (assimilation-chamber) and intercellular CO₂ concentration, respectively - g_s stomatal conductance - Man6P mannose-6-phosphate - Pi orthophosphate     

Sensitivity to far-red radiation in stomata of Phaseolus vulgaris L.: Rhythmic effects on conductance and photosynthesis

The influence of far-red (FR; 700–800 nm) radiation on steady-state stomatal conductance and net photosynthesis in P. vulgaris has been studied. Whereas FR radiation alone was relatively ineffective, addition of FR to a background of white light (WL; predominantly 400–700 nm) resulted in increased stomatal conductance. Stomata exhibited a marked diurnal sensitivity to FR. The action maximum for enhancing stomatal conductance was near 714 nm. A combination of FR and infra-red (IR; >800 nm) enhanced net photosynthesis when added to a background of WL. When IR alone was added to WL, there was a net decrease in photosynthesis, indicating that it is the FR waveband which is responsible for the observed photosynthetic effects. Naturally occurring levels of FR radiation (235 mol·m^-2·s^-1) in vegetation-canopy shade enhanced net photosynthetic CO₂ gain by 28% when added to a background of 55 mol·m^-2·s^-1 WL.Abbreviations BL blue - FR far-red - IR infra-red - PAR photosynthetically active radiation - R red - WL white light     

Leaf age and salinity influence water relations of pepper leaves

Plant growth is reduced under saline conditions even when turgor in mature leaves is maintained by osmotic adjustment. The objective of this study was to determine if young leaves from salt-affected plants were also osmotically adjusted. Pepper plants (Capsicum annuum L. cv. California Wonder) were grown in several levels of solution osmotic potential and various components of the plants' water relations were measured to determine if young, rapidly growing leaves could accumulate solutes rapidly enough to maintain turgor for normal cell enlargement. Psychrometric measurements indicated that osmotic adjustment is similar for both young and mature leaves although osmotic potential is slightly lower for young leaves. Total water potential is also lower for young leaves, particularly at dawn for the saline treatments. The result is reduced turgor under saline conditions at dawn for young but not mature leaves. This reduced turgor at dawn, and presumably low night value, is possibly a cause of reduced growth under saline conditions. No differences in leaf turgor occur at midday. Porometer measurements indicated that young leaves at a given salinity level have a higher stomatal conductance than mature leaves, regardless of the time of day. The result of stomatal closure is a linear reduction of transpiration.     

Sulphate deprivation depresses the transport of nitrogen to the xylem and the hydraulic conductivity of barley (Hordeum vulgare L.) roots

During the first 4 d after the removal of SO ₄ ^2- from cultures of young barley plants, the net uptake of ¹⁵N-nitrate and the transport of labelled N to the shoot both decline. This occurred during a period in which there was no measurable change in plant growth rate and where the incorporation of [³H]leucine into membrane and soluble proteins was unaffected. Reduced N translocation was associated with six- to eightfold increases in the level of asparagine and two- to fourfold increases in glutamine in root tissue; during the first 4 d of SO ₄ ^2- deprivation there were no corresponding increases in amides in leaf tissue. The provision of 1 mol · m^–3 methionine halted, and to some extent reversed the decline in NO ₃ ^- uptake and N translocation which occurred during continued SO ₄ ^2- deprivation. This treatment had relatively little effect in lowering amide levels in roots. Experiments with excised root systems indicated that SO ₄ ^2- deprivation progressively lowered the hydraulic conductivity, Lp, of roots; after 4 d the Lp of SO ₄ ^2- -deprived excised roots was only 20% of that of +S controls. In the expanding leaves of intact plants, SO ₄ ^2- deprivation for 5 d was found to lower stomatal conductance, transpiration and photosynthesis, in the order given, to 33%, 37% and 18% of control values. The accumulation of amides in roots is probably explained by a failure to export either the products of root nitrate assimilation or phloem-delivered amino-N. This may be correlated with the lowered hydraulic conductivity. Enhanced glutamine and-or asparagine levels probably repressed net uptake of NO ₃ ^- and ¹³NO ₃ ^- influx reported earlier (Clarkson et al. 1989, J. Exp. Bot. 40, 953–963). Attention is drawn to the similar hydraulic signals occurring in the early stages of several different types of mineral-nutrient stresses.Abbreviations Asn asparagine - Gln glutamine - Lp hydraulic conductivity J.L.K. is extremely grateful to the British Council for supporting his working visit to Long Ashton. We thank John Radin for helpful discussion and encouragement.     

广西野生蔗及其近缘植物营养器官内部结构的初步研究

广西野生蔗及其近缘植物营养器官内部结构基本相同。但割手密叶片下表皮具有明显的气孔窝斑茅等则无。斑茅茎节间的维管束分布较均匀,河八王茎中央没有维管束分布,割手密与蔗茅茎中维管束的分布。居于二者之间。     

杂交水稻及其三系剑叶表面结构的扫描电镜比较观察

应用扫描电子显微镜,对野败型杂交水稻汕优50及其三系的剑叶表面进行了比较观察。结果表明:保持系和恢复系的气孔长度和气孔复体的表面积极为相似;不育系的气孔大于其父本;而杂交水稻的气孔最大,一定程度上体现了杂种优势。     

The effects of propagation environment and foliar area on the rooting physiology of Cordia alliodora (Ruiz & Pavon) Oken cuttings

 The effects of propagation microclimate and foliar area on the rooting of Cordia alliodora (Ruiz & Pavon) Oken cuttings were investigated using non-mist propagators with and without shade. Photosynthetic rates (P _n ), stomatal conductance (g _s ) and chlorophyll fluorescence ratio (Fv/Fm) of the cuttings were assessed during propagation. Pronounced differences in microclimate were recorded between treatments, with lower temperatures and vapour pressure deficit (VPD) under shade. During the first 8 days after insertion, P _n varied between 2.21 and 4.96 and 0.47 – 2.54 μmol CO₂ m^{–  2}s^{–  1} in the shaded and unshaded propagators, respectively. In the unshaded propagator, Fv/Fm decreased to a minimum of 0.72 2 days after insertion, recovering thereafter. In two separate rooting experiments, rooting percentage was reduced by high irradiance in the 20 and 30 cm² leaf area treatments, but not in the 10 cm² treatment. P _n decreased with an increase in leaf area in both shaded and unshaded propagators. Fv/Fm also declined with increasing leaf area in the high irradiance treatment. PAR and P _n were positively correlated under shade (r ² = 0.51) but negatively correlated in the unshaded treatment (r ² = 0.49); maximum P _n values were recorded at a PAR of 400 μmol m^{–  2} s^{–  1}. No significant differences in g _s were found between treatments, values ranging between 130 and 194 mmol H₂O m^{–  2} s^{–  1}. Positive correlations were found between rooting percentage and mean Fv/Fm. These results indicate that rooting of C. alliodora cuttings is related to photosynthetic activity during propagation, which is itself influenced both by propagator microclimate and cutting leaf area. Received: 7 May 1996 / Accepted: 17 December 1996     

Ecophysiological traits of plant functional groups in forest and pasture ecosystems from eastern Amazônia,Brazil

The plant functional group approach has the potential to clarify ecological patterns and is of particular importance in simplifying the application of ecological models in high biodiversity ecosystems. Six functional groups (pasture grass, pasture sapling, top-canopy tree, top-canopy liana, mid canopy tree, and understory tree) were established a priori based on ecosystem inhabited, life form, and position within the forest canopy profile on eastern Amazonian region. Ecophysiological traits related to photosynthetic gas exchange were then used to characterize such groups. The ecophysiological traits evaluated showed considerable variations among groups. The pasture grass functional group (a C₄ photosynthetic pathway species) showed high instantaneous water use efficiency (A _max/g _s@A _max), high photosynthetic nitrogen use efficiency (A _max/N _area), and high ratio of A _max to dark respiration (A _max/R _d). Among the species with the C₃ photosynthetic pathway, the top-canopy liana group showed the highest mean of A _max/g _s@A _max, statistically distinct from the lowest average presented by the understory tree group. Furthermore, the pasture sapling group showed the lowest average of A _max/R _d, statistically distinct from the high average observed for the understory tree group. Welch-ANOVAs followed by Games–Howell post hoc tests applied to ecophysiological traits produced reasonable distinctions among functional groups, although no significant distinction was detected between the groups top-canopy tree and pasture sapling. Species distribution within the functional groups was accurately reproduced by discriminant analyses based on species averages of ecophysiological traits. The present work convincingly shows that the functional groups identified have distinct ecophysiological characteristics, with the potential to respond differently to environmental factors. Such information is of great importance in modeling efforts that evaluate the effects of dynamic changes in tropical plant communities over ecosystem primary productivity.