Photosynthetic Response to Soil Water Contents of an Annual Pioneer C4 Grass (Agriophyllum squarrosum) in Hunshandak Sandland,China

Net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and leaf water potential (Ψ_l) of an annual pioneer C₄ grass (Agriophyllum squarrosum) were compared under different simulated precipitation events in a field of Hunshandak Sandland, China. The increase of soil water content (SWC) had significant effect on these physiological traits (p<0.001). In the vegetative stage, the values of P _N, E, and g _s went up sharply when SWC increased at the beginning, while they went down with continuous increase of SWC. P _N, E, and g _s increased 1.4, 1.7, and 1.7 fold, respectively, with SWC range from 6.7 to 11.6 %. In the reproductive stage, similar trends were found, except for the climate with a higher SWC. This indicated that A. squarrosum was very sensitive to the small increment of SWC which might have a large photosynthetic potential. Ψ_l increased by about 8 % as the SWC changed from 6.7 to 8.8 %, and then maintained a steady level when the SWC was higher than 8.8 %, while the values of P _N, E, and g _s kept increasing even after this SWC. This might indicate that the adjustment of Ψ_l response to the changes of SWC lagged that of the photosynthetic parameters. This revised version was published online in August 2006 with corrections to the Cover Date.     

Age-dependent changes of the ion content and the circadian leaf movement period in thePhaseolus pulvinus

The circadian movement of the lamina of primary leaves ofPhaseolus coccineus L. depends on circadian changes of the K⁺, Cl^- and (depending on the Cl^- availability) malate content in the swelling and shrinking motor cells of the laminar pulvinus. After sowing in soil, the laminar pulvinus develops within about 26 days. When the leaves emerge from the soil (about 6 days after sowing) and the pulvinus starts with the diurnal movement (about 9 days after sowing) the pulvinar dimensions are about half of those of the mature pulvinus. The anatomical structure, however, is basically the same as in the developed pulvinus. In soil-grown plants, the K⁺, Cl^- and malate content as well as the period length of the circadian leaf movement rhythm change in the developing pulvinus. In the embryo of the dry seed, the Cl^- content is low (0.03 mmol g^-1 DW), the K⁺ content, however, 22-fold higher than the Cl^- content. When the leaves emerge from the soil, the pulvinar K⁺ and Cl^- content is the same as in the whole embryo of the dry seed. In the developing pulvinus the K⁺ content increases by a factor of 2 and the Cl^- content by a factor of 41 in the mature pulvinus. The pulvinar malate content increases between the 6th and 10th day from about 40 to 180Μmol g^-1 DW, then decreases until the 17th day and remains thereafter on a low level (around 80 Μmol g^-1 DW). These results indicate that the Cl^- availability increases in the developing pulvinus with age. It explains furthermore why in young leaves malate was found as counterion to K⁺ in the osmotic leaf movement motor, in older ones, however, Cl^-. The circadian leaf movement starts 9 days after sowing. The period length decreases during the development of the pulvinus from 31.3 to 28.6 h in leaves of intact soil-grown plants. In leaves which were cut from the plants and immersed with their petioles in distilled water, the age dependent decrease of the period length is also found. However, the period lengths are shorter by more than 1 h than in the leaves of intact plants. The increasing Cl^- availability in the developing pulvinus does not seem to be the cause for the age dependent shortening of the period length, because the period length in 22 days old Cl^- deprived pulvini is the same as in 22 days old pulvini with a high Cl^- content.     

Crown development in a pioneer tree, Rhus trichocarpa, in relation to the structure and growth of individual branches

Based on an allometric reconstruction, the structure and biomass-allocation patterns of branches and current-year shoots were investigated in branches of various heights in the pioneer tree Rhus trichocarpa, to evaluate how crown development is achieved and limited in association with height. Path analysis was conducted to explore the effects of light availability, basal height and size of individual branches on branch structure and growth. Branch angle was affected by basal height, whereas branch mass was influenced primarily by light availability. This result suggests that branch structure is strongly constrained by basal height, and that trees mediate such constraints under different light environments. Previous-year leaf area and light availability showed positive effects on current-year stem mass. In contrast, branch basal height and mass negatively affected current-year stem mass. Moreover, the length of stems of a given diameter decreased with increasing branch height. Therefore the cost of biomass investment for a unit growth in length is greater for branches of larger size and at upper positions. Vertical growth rate in length decreased with increasing height. Height-dependent changes in stem allometry and angle influenced the reduction in vertical growth rate to a similar degree.     

金叶银杏半同胞子代无性系的叶色和色素含量变化及呈色机制分析

对4月份至11月份金叶银杏‘万年金'( Ginkgo biloba ‘Wannianjin')32个半同胞子代无性系与亲本的叶色差异进行比较;比较了不同色系叶片的色素含量和比值及叶色参数(L*、a*和b*)的变化,分析了叶色参数与叶片色素含量的相关性;并观察了不同色系的叶绿体超微结构。结果表明：32个半同胞子代无性系可被分为金黄、浅黄、草绿和蓝绿4个色系。随时间推移,草绿和蓝绿色系叶片的总叶绿素( Chl)、叶绿素a( Chla)、叶绿素b( Chlb)和类胡萝卜素( Car)含量均呈“双峰型”变化趋势,Car/Chl和Car/Chla比值的变幅均较小;而金黄和浅黄色系叶片的上述色素含量呈“升高—降低—升高”变化趋势,Car/Chl和Car/Chla比值总体呈“迅速下降—相对稳定—缓慢升高”的变化趋势。各色系叶片的上述色素含量在夏季均不同程度下降,Car/Chlb比值变化差异较大,且金黄和浅黄色系的各色素含量均低于草绿和蓝绿色系。随时间推移,金黄和浅黄色系叶片的L*、a*和b*值以及草绿和蓝绿色系叶片的L*和b*值均先降低后升高,后2个色系的a*值则先升高后下降;并且,前2个色系的L*和b*值总体上显著高于后2个色系,而a*值则总体上低于后2个色系。金黄色系的Chla和Chl含量与L*和a*值显著负相关,而其Car/Chl和Car/Chla比值则与L*、a*和b*值显著或极显著正相关;浅黄色系的Chlb含量与a*值显著负相关,其Car/Chla比值与L*和b*值以及Car/Chlb比值与a*值均显著正相关;草绿色系的Chla含量与L*值显著负相关,其Car/Chla比值与L*和b*值以及Car/Chlb比值与a*值均显著正相关;这3个色系叶片的其余指标间以及蓝绿色系叶片的各指标间均无显著相关性。观察结果显示：金黄和浅黄色系的叶绿体基粒片层发育不健全,基粒片层可见但排列较疏松,且无明显垛叠,分布范围小而稀疏;蓝绿和草绿色系叶绿体的基粒类囊体垛叠层数均较多,基粒片层发达且排列紧致、整齐,分布范围大而稠密。综合分析结果表明：‘万年金'4个色系半同胞子代无性系叶片的呈色差异和叶色变化由多种因素控制,其中,Car/Chl和Car/Chla比值高且叶绿体基粒片层发育不健全是叶片呈黄色的主要原因。     

Epidermal Features of Leaves and Their Taxonomic Significance in Subfamily Ophiopogonoideae (Liliaceae)

This paper reports epidermal features of leaves in Ophiopogonoideae. Thirty-nine species and one variety (29 species, 1 variety in Ophiopogon, 6 species in Liriope, 4 species in Peliosanthes)were examined under scanning electron microscope. In addition, transections of stomatal apparatuses of six species (Ophiopogon: 3 species; Liriope: 2 species; Peliosanthes: 1 species) were made and examined under light microscope. The stomatal apparatus in Liriope, Ophiopogon and Peliosanthes is of the anomocytic type. These types of epidermal features of leaves in these genera are recognized: Cuticular processes type, No cuticular processes type and No stomatal band type. The cuticular processes type can be further divided into three patterns: Fibrillose, Massive and Wrinkled-massive. The taxonomic value of the epidermal features of leaves in Ophiopogonoideae is rather evident. (1)These epidermal features can be used to distinguish among those species of Ophiopogon, Liriope and Peliosanthes, even in their vegetative state; (2) The different patterns of cuticular processes are helpful to reasonable classification of some species in Ophiopogon, (3)They are of great value for recognizing some sections, (4) These epidermal features of leaves also provide evidence for further discussion on relationships among Ophiopogon, Liriope, and Peliosanthes. The evolutionary trend of the epidermal features of leaves in Ophiopogonoideae is No stomatal band type→No cuticular process type(stomatal band)→Cuticular process type (stomatal band). According to the epidermal features of leaves, flowers and fruits, Ophiopogon, Liriope and Peliosanthes are closely related, forming a subfamily Ophiopogonoideae. Ophiopogon is more close to Liriope than to Peliosanthes, and they should be grouped into the same tribe-Ophiopogoneae. Liriope seems to be more primitive than Ophiopogon. Peliosanthes, which constitutes another tribe of its ownPeliosantheae, is more advanced than Ophiopogon and Liriope, and it might have beenderived from its ancestor early.     

Genetic research as the valid base of strategies for breeding rust resistant wheats

It is known that few wheat cultivars maintain their resistance to rust diseases for a long period of time, particularly when crop populations become genetically more uniform. A number of genetically diverse, so far unexploited, sources of rust resistance in the natural as well as mutagenized population of wheat cultivars were identified. Several of these genes were placed in agronomically superior well-adapted backgrounds so that they could be used as pre-breeding stocks for introducing genetic diversity for resistance in a crop population. Some of these stocks when employed as parents in several cross combinations in a breeding programme have generated a number of promising cultivars with diversity for resistance.Many presently grown wheats in India, near-isogenic lines each with Lr14b, Lr14ab, Lr30 and certain international cultivars were identified as possessing diverse sources of adult plant resistance (APR) to leaf rust. Prolonged leaf rust resistance in some of the Indian cultivars was attributed to the likely presence of Lr34 either alone or in combination with other APR components. Tests of allelism carried out in certain cultivars that continue to show adequate levels of field resistance confirm the presence of Lr34, which explains the role that this gene has played in imparting durability for resistance to leaf rust. Also, Lr34 in combination with other APR components increases the levels of resistance, which suggests that combination of certain APR components should be another important strategy for breeding cultivars conferring durable and adequate levels of resistance. A new adult plant leaf rust resistance source that seems to be associated with durability in Arjun has been postulated. Likewise, cultivars possessing Sr2 in combination with certain other specific genes have maintained resistance to stem rust.Further, non-specific resistances that were transferred across widely different genotypes into two of the popular Indian wheats provided easily usable materials to the national breeding programmes for imparting durable resistance to stripe rust.     

CO2 enrichment predisposes foliage of a eucalypt to freezing injury and reduces spring growth

Seedlings of Eucalyptus pauciflora, were grown in open-top chambers fumigated with ambient and elevated [CO₂], and were divided into two populations using 10% light transmittance screens. The aim was to separate the effects of timing of light interception, temperature and [CO₂] on plant growth. The orientation of the screens exposed plants to a similar total irradiance, but incident during either cold mornings (east-facing) or warm afternoons (west-facing). Following the first autumn freezing event elevated CO₂-grown plants had 10 times more necrotic leaf area than ambient CO₂ plants. West-facing plants had significantly greater (25% more) leaf damage and lower photochemical efficiency (F_v/F_m) in comparison with east-facing plants. Following a late spring freezing event east-facing elevated CO₂ plants suffered a greater sustained loss in F_v/F_m than west-facing elevated CO₂- and ambient CO₂-grown plants. Stomatal conductance was lower under elevated CO₂ than ambient CO₂ except during late spring, with the highest leaf temperatures occurring in west-facing plants under elevated CO₂. These higher leaf temperatures apparently interfered with cold acclimation thereby enhancing frost damage and reducing the ability to take advantage of optimal growing conditions under elevated CO₂.     

International research on cassava photosynthesis, productivity, eco-physiology, and responses to environmental stresses in the tropics

The review sums up research conducted at CIAT within a multidiscipline effort revolving around a strategy for developing improved technologies to increase and sustain cassava productivity, as well as conserving natural resources in the various eco-edaphic zones where the crop is grown, with emphasis on stressful environments. Field research has elucidated several physiological plant mechanisms underlying potentially high productivity under favourable hot-humid environments in the tropics. Most notable is cassava inherent high capacity to assimilate carbon in near optimum environments that correlates with both biological productivity and root yield across a wide range of germplasm grown in diverse environments. Cassava leaves possess elevated activities of the C₄ phosphoenolpyruvate carboxylase (PEPC) that also correlate with leaf net photosynthetic rate (P _N) in field-grown plants, indicating the importance of selection for high P _N. Under certain conditions such leaves exhibit an interesting photosynthetic C₃-C₄ intermediate behaviour which may have important implications in future selection efforts. In addition to leaf P _N, yield is correlated with seasonal mean leaf area index (i.e. leaf area duration, LAD). Under prolonged water shortages in seasonally dry and semiarid zones, the crop, once established, tolerates stress and produces reasonably well compared to other food crops (e.g. in semiarid environments with less than 700 mm of annual rain, improved cultivars can yield over 3 t ha⁻¹ oven-dried storage roots). The underlying mechanisms for such tolerance include stomatal sensitivity to atmospheric and edaphic water deficits, coupled with deep rooting capacities that prevent severe leaf dehydration, i.e. stress avoidance mechanisms, and reduced leaf canopy with reasonable photosynthesis over the leaf life span. Another stress-mitigating plant trait is the capacity to recover from stress, once water is available, by forming new leaves with even higher P _N, compared to those in nonstressed crops. Under extended stress, reductions are larger in shoot biomass than in storage root, resulting in higher harvest indices. Cassava conserves water by slowly depleting available water from deep soil layers, leading to higher seasonal crop water-use and nutrient-use efficiencies. In dry environments LAD and resistance to pests and diseases are critical for sustainable yields. In semiarid zones the crop survives but requires a second wet cycle to achieve high yields and high dry matter contents in storage roots. Selection and breeding for early bulking and for medium/short-stemmed cultivars is advantageous under semiarid conditions. When grown in cooler zones such as in tropical high altitudes and in low-land sub-tropics, leaf P _N is greatly reduced and growth is slower. Thus, the crop requires longer period for a reasonable productivity. There is a need to select and breed for more cold-tolerant genotypes. Selection of parental materials for tolerance to water stress and infertile soils has resulted in breeding improved germplasm adapted to both favourable and stressful environments. An erratum to this article is available at .