Plant population ecology

This paper is aimed to elucidate the ecological scenario in Italy in the Early to Middle Pleistocene, when species of the genus Homo are known to spread across Europe in two distinct waves: earlier than 1.2 Ma and at about 600 ka, respectively. This topic represents both (1) a fundamental aspect for a better understanding of the factors that allowed humans to colonize the middle latitudes of Eurasia, and (2) a reasonable frontier for current Quaternary palaeobiology, thanks to increasing knowledge of regional and local patterns. As for Italy, a combination of palaeobotanical and palaeontological data sets shows on the one hand a general complexity in both space and time, and on the other hand changes of considerable importance within and among the biological communities. These changes had a major importance during the worldwide change in the Earth climatic system known as “Middle Pleistocene Revolution”, which according to our data culminates with crucial effects of the extreme conditions of MIS 16. Subsequently, during great part of the Middle Pleistocene, the peculiar features of the Italian territory may have favoured isolation and a local persistence of plant populations and possibly mammal taxa, humans included, as for instance suggested by the corrected chronology of the Ceprano calvarium.

This study was conducted to investigate the effect of sowing date and plant population on biomass, grain yield and components of yield. The early sowing (10 Nov.) gave higher grain yield over late sowing (10 Dec.) by 60.6%. Differences in grain yield between 10 Nov. and ...

A field study was carried out with the potato (Solanum tuberosum L.) variety BP1 to determine the influence of plant population density and seed tuber size on the crop’s physiological growth components and yield performance under optimal field conditions. Two factors considered were seed tuber size and population density. The first factor involved four seed sizes; S1 (small), 200-350 mm in diameter; S2 (medium), 350-450 mm in diameter; S3 (large), 450-550 mm in diameter and S4 (very large), greater than 550 mm in diameter. The second factor was population density (E) and it was at three levels; level 1 (E1) at 90 by 15 cm, level 2 (E2) at 90 by 30 cm, level 3 (E3) at 90 by 45 cm spacing. Parameters measured included shoot emergence (germination), haulm growth and yield. There were significant differences in mean percentage germination at 9, 10, 11 and 12 days after planting across the four seed sizes. Plants from larger seed potato tubers exhibited greater
physiological growth and yield (kg/ha) compared to smaller seed tubers when the experiment was terminated at 95 days after
emergence. Large and very large seed potato tubers exhibited greater overall resource use efficiency of allocation of metabolites as measured by growth components and yield at all plant density levels compared to small and medium sized seed tubers. This had implications on the duration of the bulking, physiological growth and consequently on yields obtained at harvest. At the same time, plant population density had no significant (p>0.05) effect on the number of days to emergence. From the results obtained in this study, it can be concluded that the optimum plant population density for good yield was 90 by 30 cm and that large and very large seed sets gave the best yield. © 2012 Friends Science Publishers

Striga hermonthica is a major constraint to smallholder subsistence agriculture production in the sub-Saharan African region. Low soil fertility and overall environmental degradation has contributed to the build-up of the parasitic weed infestation. Improved cropping systems have to be introduced to address the interrelated problems of S. hermonthica and soil fertility decline. Thus, the effects of improved fallow with leguminous shrub Sesbania sesban on maize yields and levels of S. hermonthica infestation on farm land in the bimodal highlands of western Kenya were investigated. The experimental treatments were arranged in a phased entry, and randomized complete block scheme were six months Sesbania fallow, 18 months Sesbania fallow, six months natural fallow consisting of regrowth of natural vegetation without cultivation, 18 months natural fallow, continuous maize cropping without fertilizer application, and continuous maize cropping with P and N fertilization. Results show that Sesbania fallows significantly (p<0.05) increase maize yield relative to continuous unfertilized maize. S. hermonthica plant populations decrease in continuous maize between the first season (mean = 428 000 ± 63 000 ha−1) and second season (mean=51 000 ± 15 000 ha−1), presumably in response to good weed management. S. hermonthica seed populations in the soil decrease throughout the duration of the experiment in the continuous maize treatments. Short-duration Sesbania fallows can provide modest yield improvements relative to continuous unfertilized maize, but short-duration weedy fallows are ineffective. Continuous maize cultivation with good weed control may provide more effective S. hermonthica control than fallowing.

Antecedentes y Objetivos: Agave angustifolia, o chelem, es el único maguey silvestre de la Península de Yucatán y es el ancestro de especies domesticadas de gran valor económico y cultural. Presta importantes servicios ambientales como recurso alimenticio para la fauna, fijación de suelos arenosos y captura de carbono en ambientes áridos con suelos pobres. Es un cultivo potencial de cara al aumento de las sequías predichas para la región y del empobrecimiento genético del henequén. El objetivo de este trabajo es recabar datos sobre la densidad de sus poblaciones, su patrón espacial, estructura poblacional y la relación entre su abundancia y los factores ambientales en el matorral costero de Yucatán, con el fin de evaluar su uso en la restauración ecológica.Métodos: Se muestrearon tres localidades costeras: Chuburná (Ch), San Benito (SB) y Río Lagartos (RL). En SB y RL se trazaron 36 cuadrantes de 4 m2; dentro de cada uno se estimó el porcentaje de cobertura de Agave angustifolia, el...

Fertile, green, di-haploid plants were obtained at high frequencies from several indica × Basmati rice F1 hybrids and/or F2 plant populations using an improved anther culture procedure. Anthers from cold-pretreated (10 °C for 10 d) panicles of six indica (HKR120, HKR86-3, HKR86-217, PR106, Gobind andCH2 double dwarf) and two Basmati rice (Basmati 370,Taraori Basmati) varieties and 14 heterotic indica ×Basmati F1/F2 hybrids were cultured in modified agarose-solidified N6M, Heh5M and RZM media. Best callus induction frequencies (2.6–78%) were obtained in RZM medium containing 4% (w/v) maltose,2,4-D, NAA and kinetin. F2 plants compared to F1 hybrids and parental rice varieties, were more responsive to anther culture. Androgenesis frequencies of 31–78% were obtained for indica × Basmati F2 plants in RZM medium in just 30 d which are comparable to or higher than that reported for japonica rice varieties and hybrids involving japonica rice parent(s). Agarose (1.0% w/v)-solidified MS medium containing 3.0% maltose, kinetin, BAP, and NAA, induced green shoot regeneration in 0–51% of the anther-derived callide pending upon the genotype. High plant regeneration frequencies (67–337 green plants per 1000 anthers)were obtained from anther calli of several F1hybrids (Gobind × Basmati 370 and HKR120 ×Taraori Basmati) and F2 plants (Gobind × Basmati370, Gobind × Taraori Basmati, HKR86-3 × TaraoriBasmati). A sample of 498 plants obtained from the above hybrids, were transferred to pots with>90% survival; 8–78% of these plants had >5%spikelet fertility and were diploid. In addition,18% of the haploid plants could be diploidized by submerging in 0.1% colchicine solution for 16–18 h. The improved anther culture procedure reported here, resulted in several fold increase in the recovery of green plants from recalcitrant indica × Basmati rice hybrids compared to previous published procedures. The study may accelerate the introgression of desirable genes from indica into Basmati rice using anther culture as a breeding tool.

The article represents a link between the concept of discrete description of the ontogenesis of plants and the cellular automata approach for the spatial-temporal modelling of plant population dynamics. The continuous process of individual plant development may be subdivided into several stages on the basis of morphological indicators reflecting functional importance of plants at different stages. The number and duration of age stages may vary from species to species, among life-forms within species, and under different environment conditions. The duration of age stages and the probability of transition from one stage to another for a given plant depend on the plant’s neighbourhood pattern, the type of ontogenesis and the site conditions. Such data are available from numerous field studies.
The presented approach allows simulation of a plant population as a set of cellular automata located on a plane. The age stages of these automata can be changed according to simple rules, which reflect the types of plant ontogenesis, different life spans of age states, and different sizes of plants in the neighbourhood. This approach is different from matrix models, which are usually used for this purpose, in that here we can directly simulate the role of space interactions in the population dynamics. We constructed some cellular automata models based on experimental data, which reflect the ontogenesis types and life-forms of plants. The models demonstrate that simple rules of plant development with simply defined local interactions lead to complicated dynamics. The results show new possibilities of applications of discrete simulation modelling for analysis of plant populations and community dynamics.