Differences in vital demographic rates in three populations of the epiphytic bromeliad, Werauhia sanguinolenta

Since the response to differences in resource availability is most pronounced in smaller individuals of vascular epiphytes such as Werauhia sanguinolenta Cogn. et Marchal (Bromeliaceae), I expected variation in growth and survival of small individuals to play an important role in the dynamics of entire populations. Four annual censuses (2002–2005) of three study populations, which were located across the isthmus of Panama, allowed me to construct stage transition matrices, and to conduct growth analysis and elasticity analysis. Differences between populations were highly consistent through time, but, contrary to expectations, hardly related to the comportment of smaller plants. For example, although average mortality rates were highest at the driest site, close to the Pacific, small plants were not predominantly affected. Similarly, although the highest relative growth rates (RGR) of individuals and the highest population growth rates (λ) were found in the population with the highest moisture input, which was located close to the Atlantic coast, this was not due to a particularly strong stimulation of RGR in small plants. Elasticity analysis indicated rather small differences in the importance of the three demographic processes growth, survival, and reproduction for population growth in the three populations, but invariably identified the survival of large tanks as the single most important process determining λ.     

Population dynamics of Mammillaria magnimamma Haworth. (Cactaceae) in a lava-field in central Mexico

One of the habitats occupied by Mammillaria magnimamma is a 2000-year old lava-field, in Mexico City. The great ecological interest on this lava-field and the little knowledge there is regarding cacti population ecology have compelled us to analyse the demography of this species to evaluate its present conservation status at this site. We studied two populations of this species within the lava-field: one in a disturbed site (i.e., recently burned) and another one in a well preserved site. For each population we built two size-based population projection matrices (1996/97 and 1997/98). Demographic data were gathered directly from observations of plant fates from one year to the next. Additionally, seed germination and seedling establishment experiments were carried out in the field to estimate fecundity values and seedling survival probabilities. The four matrices built were used to perform numerical analyses simulating yearly stochastic demographic variation to project the overall population's long-term behaviour under these changing conditions. Three of the four matrices showed λ values slightly below unity. In these cases elasticity values were highest for matrix entries corresponding to plants remaining in their same category. The matrix that showed a λ value above unity (well preserved site, 1997/98) had higher elasticity values for entries referring to seedling survival and growth. The numerical simulations of demographic stochasticity showed that the population appears to be growing at a slow rate. According to the simulation results, the variation in overall population size over time may be accounted for by yearly variation in seed germination and seedling survival. Population persistence probability might decrease significantly if fire frequency increases. This revised version was published online in August 2006 with corrections to the Cover Date.     

The plant cell pressure probe

The pressure probe is a micro manometer for the simultaneous direct recording and manipulation of plant cell hydrostatic pressure. It is used to map in space and time the turgor pressures of individual cells within tissues and organs of intact plants. This is used to study the hydraulic architecture of tissues, tissue movement and the responses of tissues to water stress. The approach can be augmented by simultaneous measurement of individual cell osmotic pressure. This permits the hydraulic driving forces across selectively permeable membranes and walls to be assessed fully. By manipulating manually the pressure, cell wall elasticity and its properties can also be mapped. Under some conditions this can be extended to plastic behaviour.     

气象因子对农田设计排涝模数的影响

设计排涝模数的计算对农田安全和有效降低涝灾损失意义重大.本文选取天津市宁河区封闭农田小区为研究对象,分析了主要气象因子对农田设计排涝模数的影响.为解决观测样本有限的问题,在现场观测试验的基础上,以总径流深为目标,使用互信息、偏秩相关方法分析了参数敏感性,结合土壤含水量、地下水位相对变化量得到了合理的模型参数,建立了三水源超渗-蓄满耦合产流模型,进行了产流量和设计排涝模数估算,并分析了降雨和蒸发等气象因子对设计排涝模数的影响.结果表明:1960—2015年,研究区夏季降水量显著减少,蒸发量变化不明显.排涝模数随降水量减少而减少,且随着设计重现期的增大,降水和设计排涝模数的减少量均有所增大,但总体来讲,气象因子对设计排涝模数的影响并不大,现行设计排涝模数可不进行修订.     

Responses to the timing of damage in an annual herb: Fitness components versus population performance

The timing of damage plays an important role in plant fitness but its effect on population performance has received relatively little attention. I examined the effect of the timing of damage on nine components of fitness and population performance in four populations of the annual Melampyrum pratense by clipping plants at the vegetative stage (early clipping) or at the beginning of the flowering period (late clipping). I estimated population performance using a matrix population model that predicts the long-term population growth rate, λ. In early clipping, the plants were usually able to compensate for the damage during the growing season. In consequence, early clipping reduced λ in only one out of four populations, whereas late clipping reduced it in three populations. The elasticity analyses revealed that the relative importance of different demographic transitions to λ varied among the populations. This among-population variation in the sensitivities of λ to demographic transitions makes it difficult to use changes in specific fitness components as a measure of population performance for annual plants with a seed bank. The current study illustrates that although early-season damage may have a negligible impact on population dynamics in annual plants, the effect of the timing of damage often varies among populations.     

Potential impact of harvesting on the population dynamics of two epiphytic bromeliads

Large numbers of epiphytes are extracted from cloud forests for ornamental use and illegal trade in Latin America. We examined the potential effects of different harvesting regimes on the population dynamics of the epiphytic bromeliads Tillandsia multicaulis and Tillandsia punctulata. The population dynamics of these species were studied over a 2-year period in a tropical montane cloud forest in Veracruz, Mexico. Prospective and retrospective analyses were used to identify which demographic processes and life-cycle stages make the largest relative contribution to variation in population growth rate (λ). The effect of simulated harvesting levels on population growth rates was analysed for both species. λ of both populations was highly influenced by survival (stasis), to a lesser extent by growth, and only slightly by fecundity. Vegetative growth played a central role in the population dynamics of these organisms. The λ value of the studied populations did not differ significantly from unity: T. multicaulis λ (95% confidence interval) = 0.982 (0.897–1.060) and T. punctulata λ = 0.967 (0.815–1.051), suggesting population stability. However, numerical simulation of different levels of extraction showed that λ would drop substantially even under very low (2%) harvesting levels. Matrix analysis revealed that T. multicaulis and T. punctulata populations are likely to decline and therefore commercial harvesting would be unsustainable. Based on these findings, management recommendations are outlined.     

Effects of extraction parameters on gel properties of carrageenan from <Emphasis Type="Italic">Kappaphycus alvarezii</Emphasis> (Rhodophyta)

Carrageenan was isolated under different extraction conditions from Kappaphycus alvarezii collected in North Sulawesi, Indonesia. Its gel properties include very strong elasticity even at low concentrations. Molecular weight and rheological properties were obtained by gel permeation chromatography and dynamic viscoelasticity measurements in order to clarify the average molecular weight at various extraction temperatures (50, 70, 90°C) and times (1, 3, 5 h), as well as gel formation ability. The results showed that both the weight-average and the number-average molecular weight decreased with increasing extraction temperature. However, the gelation rate of the carrageenan was found to be constant at around 40°C, whereas the storage modulus, G′, and loss modulus, G″, of the gels differed from each other.     

Ridge crest versus swale: contrasting plant–water relations and performance indexes in two understory plant species in a coastal maritime forest

Coastal-ridge plains are progradational landforms composed of elevated ridges and low-lying swales. The transitions between ridges and swales are steep, promoting dynamic shifts between xeric and mesic systems. Two understory plants that co-occur in ridge plains of North American mid-Atlantic maritime forests are Sabal minor and Ilex vomitoria. As coastal-ridge plains foster varying amounts of surface and sub-surface water driven largely by topography, the purpose of this study was to evaluate plant–water relations and chlorophyll a fluorescence in these two species. Ridge plants had lower leaf- and xylem-water potentials, lower osmotic potential (I. vomitoria), and lower symplastic water content (S. minor). Although there were no differences in potential- and effective-quantum yields, there were decreases in fluorescence performance index for ridge I. vomitoria and swale S. minor. While the data support potential water-stress conditions in ridge plants of both species, the data also suggest that I. vomitoria and S. minor use different physiological processes to tolerate hydrologically dynamic ridge–swale maritime forests.