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We imposed two different global changes, climate warming and declining species richness, to synthesized grassland ecosystems, in order to determine both their single-factor effect as well as their possible interactions on plant phenology. Twelve climate-controlled chambers were therefore exposed to two temperature treatments (0 °C and 3 °C above ambient air temperature) and three species richness treatments (1,3 and 9 species). Measurements consisted of visual phenological observations of the appearance of flower buds until flowering and of autumn senescence stages, as well as of readings of the leaf chlorophyll content. In spring, chlorophyll concentrations increased under warming (9.7%) and decreasing species richness (39.4%). Warming also induced an earlier spring start (4 days) and enhanced flower production, whereas decreasing species richness likewise enhanced flower production but delayed the start of spring (16 days). In autumn, leaf senescence started simultaneously at the two temperature treatments and three species richness levels, but the end of the senescence was delayed in the heated chambers, as well as in the monocultures. Although warming and species richness interacted with species identity, no warming×species richness interactions were found. In conclusion, although warming and species richness influenced the duration of the growing season, none of these effects were reflected in the above-ground biomass of the individual plants. Under the projected climatic changes, warming will therefore not necessarily enhance the productivity of the individual plants.
Abstract
This paper examines the following questions: (1) Do early pioneer species have a greater impact on the survival and growth of different successional native trees compared to the shrub Rhodomyrtus tomentosa? (2) Do canopy treatments affect soil nutrients and light availability? (3) What is the mechanism underlying the interaction between nurse species and target species? Degraded shrubland sites (Heshan, Guangdong, China), under moist subtropical conditions were studied. About 1-year-old seedlings of Pinus massoniana, Schima wallichii, Schefflera heptaphylla, Castanopsis hystrix, Cryptocarya chinensis and Castanea chinensis were transplanted under the canopy of R. tomentosa, Dicranopteris dichotoma and in open interspaces without vegetation. Survival and growth were recorded from the first growing season after planting. Leaf gas exchange, water potential, soil physicochemical characters and irradiation were then measured. Canonical redundancy analyses (RDA) were used to evaluate the relationships between environmental factors and seedling survival and growth conditions. Both R. tomentosa and D. dichotoma canopy treatment facilitated seedling survival and growth either directly or indirectly. Irradiance/radiation was considered the most important resource (factor) for seedling growth in subtropical regions, however, soil nutrients and species are yet to be examined simultaneously with irradiance/radiation under field conditions. We conclude that early successional species facilitates the survival and growth of late successional species in subtropical shrublands. However, further predictions of successional trajectories remain elusive and are influenced by stochastic processes, including arrival order, shade tolerance, physiological character of the colonizing species and their competitive interactions.
Fifteen onion genotypes (one standard check and 14 exotic cultivars) were evaluated in RCBD with 3 replications at Melkassa Research Center during the 1999/2000 growing season (Aug.–Feb.). The objective of the study was to understand the association of characters with seed yield. The genotypic correlation coefficients were greater in magnitude than the phenotypic ones. Seed yield/plant had a high, significant correlation with number of flower stalks/plant, number of seeds and flowers/umbel and umbel size. Bolting and flowering period had a significant negative correlation with seed yield/plant. From the path analysis results, the number of flower stalks/plant, bolting period, thousand seed weight, flower stalk diameter and umbel size had a high direct positive effect on seed yield/plant. Since the direct and indirect effects through these components on seed yield are high and positive, selection should concentrate on these traits for high seed yield in onion cultivars. Since these components were found to affect seed yield they could be used for developing varieties for the growing onion industry in the country.
A two-year pot experiment was carried out in a green-house to investigate the dry matter (DM) accumulation, distribution and redistribution in maize, the transpiration intensity/leaf area and the dry leaf weight. The uptake, distribution and redistribution of phosphorus was also studied. The total dry matter weight (DMW) of aerial plant parts increased up to 108 days after emergence (DAE) and then, with the exception of the grain, decreased to the final harvest. Averaged over two years, the most DM was transported to the grain from the stalk (69.41%) and the least from the leaf-sheath (1.69%). The lowest transpiration intensity calculated per dm 2 hour -1 was 0.41 g and the highest 1.35 g. The transpiration intensity calculated per unit weight of dry leaf blades was 0.62 and 2.80 g. In both years the total phosphorus uptake increased in all aboveground plant parts up to the 80 th day after emergence and then, with the exception of the grain, decreased to the final harvest. At the end of the growing season the grain stored most (84.85%) of the absorbed phosphorus, averaged over two years.
Eight cultivars of dry-land wheat (Triticum aestivum L.) historically planted in Shaanxi Province, China, were grown in plots with irrigation and drought treatments during the growing seasons of 2011–2014, so as to characterize the differences in the rate and duration of the grain-filling stage among cultivars. The experimental results showed no obvious change among cultivars with respect to the duration of the grain-filling stage and no significant correlation between duration and grain weight. The filling rates of all three phases (lag, linear, and mature periods) showed significant differences among cultivars and had a greater effect on the grain weight than the duration of the filling stage, even though drought decreased the filling rate in the linear and mature periods. A lower filling rate led to a lighter grain weight in inferior grains than in superior grains. For the superior and inferior grains in the central spikelets, modern cultivars possess faster filling rates, especially in the lag and linear periods, whereas for the whole spike, no significant trend with cultivar replacement was observed. Faster filling rates with stable filling durations will be beneficial in obtaining additional yield increases.
Sorghum is an important grain crop in many parts of the world, especially in dry regions. It is an important crop for food and feed, and its role in energy production is currently growing. In Ethiopia, sorghum is a multi-purpose crop used for many different functions such as fuel, housing and animal feed. Information on genetic diversity levels among and within sorghum accessions will increase the efficiency of the sorghum improvement programmes. Field experiments were conducted in Potchefstroom, South Africa, during the summer growing seasons of 2009 and 2010, to estimate the level of phenotypic diversity among 22 sorghum accessions. The experiment was laid out in a randomised complete block design with three replications. Nine qualitative and 20 quantitative morphological traits were recorded. Analysis of variance for the quantitative traits revealed that differences among accessions were highly significant for all traits. Qualitative traits diversity index values varied from 31% (panicle compactness and shape) to 84% (glume colour). The pair-wise genetic distances based on phenotypic traits showed varying genetic distances. Cluster analysis of the phenotypic traits resulted in four distinct groups of accessions with genetic distances ranging from 0.40 to 1.59. Therefore, the phenotypic markers provide a useful measure of genetic distances among sorghum accessions to identify potential donors or parental material for future breeding efforts.
Wheat (Triticum aestivum L.) production in the warm areas of South Asia is severely affected by spot blotch caused by Cochliobolus sativus. There are several inoculum sources suspected to harbor C. sativus during the off season. This study was conducted to determine survival and potential sources of C. sativus inoculum from rice stubble, wheat seed, soil and weeds in three cropping systems (wheat-rice, wheat-fallow and wheat-green manure) during the 2004 and 2005 wheat growing seasons at Rampur, Nepal. Wheat seed, soil and rice stubble in the field, and weed plants in and around research plots were examined for the presence of the pathogen. Koch’s postulates were applied to verify representative strains. The pathogen was found in the wheat seed at moderate to high levels, but was absent in soil samples and rice stubble collected from the field before wheat was sown after rice. Weeds such as Blumea sp., Dichanthium annulatum, Digitaria ciliaris, Phalaris minor, Saccharum officinarum, Axonopus compressus, Brachiaria mutica, Eleusine coracana, Panicum sp., Paspalum scrobiculatum, Pennisetum purpureum, Setaria italica, Zea mays and Zizania aquatica harbored C. sativus. The C. sativus strains isolated from these weeds infected wheat by producing typical spot blotch symptoms. It is concluded that the weeds prevalent in different cropping sequences and on adjacent uncultivated land can serve as secondary hosts for C. sativus. This study presents important new information that could assist in better understanding spot blotch epidemiology and in developing integrated management strategies for spot blotch of wheat in the warmer growing regions of South Asia.
The objectives of the study were to determine the extent of nitrate leaching and maize yields in four drainpipe spacing variants (15 m, 20 m, 25 m and 30 m). The study was carried out at an experimental reclamation field during a period of five years (growing seasons). Maize was grown as the trial crop and the same agricultural practices were applied in all drainpipe spacing variants in all trial years. Nitrogen fertilization rates varied in different trial years (from 145 kg/ha/year to 175 kg/ha/year). The results indicate that nitrate concentrations in drainage water exceeded the allowable values in a larger part of the year (four to seven months) in all drainpipe spacing variants and maximum values were from 18.15 mg.dm−3 (drainpipe spacing of 15 m in 1999/00) up to 34.71 mg.dm−3 (drainpipe spacing of 25 m in 2002/03). Quantity of nitrogen leached differed from year to year and corresponded to the total nitrogen added with fertilization and annual precipitation. Statistically significant higher maize yields were achieved in most years with the drainpipe spacing of 15 m compared to other drainpipe spacing variants.
Wheat is the second most important crop after rice in India and occupies approximately 28.5 million hectare area. Salinity is one of the major factors reducing plant growth and productivity worldwide, and affects about 7% of world’s total land area. In India about 6.73 million hectare land area is salt affected. The aim of this study was to investigate the morpho- physiological and biochemical response of wheat to temporal salinity (ECiw = 10.0 dSm–1) exposures. Ten wheat genotypes were evaluated in two successive growing seasons (2012–2014), with complete randomized design with three replications under both salinity stress and non-stress conditions. The morpho-physiological and biochemical character measured in this investigation, inhibited under both salt stresses (S1 & S2) conditions but much more significantly inhibited under long-term salinity exposure (S2) than S1 because interrupting the metabolic process of plant, resulting in reduced growth and productivity. According to correlation result, selection of high yield genotypes can be done based on plant height (0.649*), tiller plant–1 (0.808**) and leaf area (0.687*). The multivariate morphophysiological and biochemical parameters should be further used to develop salinity tolerance in wheat breeding improvement programmes.
The grouping of locations from local-scale multi-environmental trials (METs) into megaenvironments has been criticized. Some European countries, e.g. the Czech Republic, Poland and Germany, have been characterized as possessing homogeneous environmental conditions. For aligned environmental conditions, it has been assumed that cultivar rankings will be similar and consequently cannot be used to designate mega-environments. An example of METs at the local scale is the Polish Post Registration Variety Testing System. The objective of this study was to determine groups of test sites within 16 Polish regions which are characterized by similar yield ranking of 50 winter wheat cultivars over three growing seasons (2011–2013). The compatibility of these cultivar yield rankings across regions was evaluated using Pearson correlation coefficients. Thereby, the 16 regions were divided into six groups (mega-environments) of locations. Regions within each group have similar cultivar rankings, whereas between groups, we observed different cultivar rankings, indicating crossover interactions. Besides similar cultivar yield responses the regions within megaenvironments were characterized also by similar environmental (soil and/or climate) conditions.
