林冠截持降雨模型的初步研究

通过对林冠截持过程的研究,将单场降雨划分成很多个小的时段,顺序计算各小时段内降雨在林冠内的分配,建立了一个林冠降雨截持模型.模型考虑了冠层和树干干燥度对冠层雨期蒸发的影响,并在计算雨期蒸发时引入冠层叶面积指数、单位林地面积上树干表面积.运用模型对华北落叶松林的降雨截持进行模拟,结果表明,模拟穿透雨与实测穿透雨基本吻合,误差在±1 mm范围内,但在小降雨(＜6 mm)时模拟值偏低;树干茎流量模拟值偏低,茎流模拟相对误差随着降雨量增大而减小.同时模拟了穿透降雨的过程,结果与林内自动气象站实测穿透降雨的过程基本吻合,模拟效果较好.     

Plant competitive ability and the transitivity of competitive hierarchies change with plant age

Plant competitive effect and response ability are known to change with plant age, however it remains unclear how competitive hierarchies among plant species change as plants age and transition between life stages. We examined the competitive interactions among seven species in all pairwise combinations in a greenhouse experiment. Competitive effect and response were measured as the relative yield (RY) for each target-neighbor species combination for both seedling and adult plants. Competitive hierarchies were constructed based on competitive effect and response scores, and we examined the degree of transitivity in the seedling and adult competitive hierarchies. The competitive effect hierarchy did not vary substantially with plant age, while the competitive response hierarchy was highly variable between juvenile and adult plants. Competitive effect and response ability were positively correlated at both plant stages. The seedling relative yield matrix was predominantly transitive, while there were far fewer transitive competitive relationships among the adult plants. The breakdown of the clear competitive hierarchy among seedlings as plants aged may explain why competition does not appear to be an active mechanism structuring some late-successional plant communities. In early-successional communities, interactions among seedlings with a clear competitive hierarchy may establish competitive ability—abundance relationships that persist as a legacy effect even though the breakdown of the competitive hierarchy among adult plants removes competition as an active mechanism structuring some late-successional plant communities.     

A competitive selection model

A multi-locus model for complete positive assortative mating is discussed. For a two-locus model, if the gene frequencies for the two loci are different, as they are likely to be, it is shown that in equilibrium the population is not composed of only two homozygous types, as is usually thought. The limiting distribution will have three homozygous genotypes depending upon the initial gene frequencies. If there are m-loci such that gene frequencies at all loci are different, there will be (m+1) such homozygous genotypes present in the equilibrium population, one in each phenotypic group.     

A comparative study of competitive ability between two cactophilic species in their natural hosts

Abstract Competition is a major aspect of the ecology of insect communities exploiting ephemeral and fragmented resources. We analysed the effect of intraspecific (single species culture) and interspecific (mixed species culture) competition on larval viability, developmental time and wing length in the cactophilic Drosophila buzzatii and Drosophila koepferae (Diptera: Drosophilidae) reared in cultured media prepared with fermenting tissues of three common natural cactus hosts in nature at different densities. Our results show that all traits measured were affected by both intra‐ and interspecifc competition, although the effect of competition depended on the Drosophila species and the rearing cactus. In fact, flies tended to have a lower viability, shorter wing size and longer developmental time as a function of increasing density in single species culture in both D. buzzatii and D. koepferae (intraespecific competition). Besides, the performance of both species was seriously affected (shorter body size, slower developmental times, lower viability) by the presence of heterospecific competitors except in the case of D. koepferae reared in its primary host plant, Trichocereus terschekii. We also show that D. koepferae successfully utilized Opuntia quimilo, which is absent in most parts of its distribution range. We discuss the roles of intra‐ and interspecific competition as determinants of the relative abundance of these two species in the arid zones of Southern South America.     

A model of canopy photosynthesis incorporating protein distribution through the canopy and its acclimation to light, temperature and CO2

Background and Aims

The distribution of photosynthetic enzymes, or nitrogen, through the canopy affects canopy photosynthesis, as well as plant quality and nitrogen demand. Most canopy photosynthesis models assume an exponential distribution of nitrogen, or protein, through the canopy, although this is rarely consistent with experimental observation. Previous optimization schemes to derive the nitrogen distribution through the canopy generally focus on the distribution of a fixed amount of total nitrogen, which fails to account for the variation in both the actual quantity of nitrogen in response to environmental conditions and the interaction of photosynthesis and respiration at similar levels of complexity.

Model

A model of canopy photosynthesis is presented for C₃ and C₄ canopies that considers a balanced approach between photosynthesis and respiration as well as plant carbon partitioning. Protein distribution is related to irradiance in the canopy by a flexible equation for which the exponential distribution is a special case. The model is designed to be simple to parameterize for crop, pasture and ecosystem studies. The amount and distribution of protein that maximizes canopy net photosynthesis is calculated.

Key Results

The optimum protein distribution is not exponential, but is quite linear near the top of the canopy, which is consistent with experimental observations. The overall concentration within the canopy is dependent on environmental conditions, including the distribution of direct and diffuse components of irradiance.

Conclusions

The widely used exponential distribution of nitrogen or protein through the canopy is generally inappropriate. The model derives the optimum distribution with characteristics that are consistent with observation, so overcoming limitations of using the exponential distribution. Although canopies may not always operate at an optimum, optimization analysis provides valuable insight into plant acclimation to environmental conditions. Protein distribution has implications for the prediction of carbon assimilation, plant quality and nitrogen demand.     

两春小麦品种竞争能力、水分利用效率及产量关系的研究

用盆栽方法测定了2个春小麦品种－地方品种和尚头与现代品种陇春－8275在5个土壤水分梯度下,单、混播时的水分消耗、水分利用效率、竞争能力和籽实产量。单播条件下,在极低水分条件下（12％）,和尚头有相对较高的产量,在水分条件较好时陇春－8275有较高的产量;在保持各水分处理条件下,地方品种和尚头较之现代品种陇春－8275消耗更多的水分,水分利用效率较低。混播条件下,各尚头有较高生物量、籽实产量及较强的竞争能力,竞争优势不受土壤水分的影响,其表现为高个体生物量品种较之低个体生物量品种消耗更多的水分,陇春－8275受到强烈的抑制,消耗较少的水分及较低的籽实产量。表明进化选择的是竞争能力,而非单播下的产量表现。可以预见,在小麦育种中选育具小根系的对水分弱竞争能力的品种将成为半干旱区今后育种的一个重要方法。     

A model for the competitive growth of two diatoms

A parallel between an experimental situation in marine microecology and its analytical model is presented. Two diatoms are cultured in a continuous flow apparatus and are studied for their competitive performance. A differential equations model is proposed to represent their growth behavior. The parameters of the model are evaluated from the experimental data and it is then identified from additional data.     

A study of age-related architectural changes that are most damaging to bones

Osteoporosis-related bone damage causes major socioeconomic problems. For efficient use of therapeutic agents, it is necessary to be able to reliably identify patients with high propensity for nontraumatic fracture. Age-related bone loss imposes several architectural changes in bone; one of the few ways to estimate damage due to individual changes, and hence determine the most serious types of damage, is via the analysis of suitable mathematical models. Anatomical sites such as the vertebral body, proximal femur, and distal radius are locations where most age-related fractures occur. The inner porous (or trabecular) bone from these sites, which resemble disordered cubic networks, play a significant role in load transmission at these sites. Analysis of a mathematical model of porous bone is used to show that perforation of elements of the network is the most damaging architectural change to a bone. We also show that an expression for bone strength, derived on this basis, can capture changes in strength caused by the inclusion of other features like thinning of trabecular bone and the anisotropy of the network. We finally argue that bone density, which is currently the most routinely used diagnostic, cannot be a reliable surrogate for bone strength.     

The competitive ability of stem cells from mice with Hertwig's anemia

Mice homozygous for the gene, an, have a macrocytic, normochromic anemia. In this report, attempts have been made to cure Hertwig's anemia (an/an) by injecting genetically normal (+/+) stem cells. The anemia of unirradiated an/an mice was alleviated but not completely cured by injection of as many as 3 X 10(7) +/+ bone marrow cells. Lethal irradiation of the an/an recipients was necessary before injections of 10(7) +/+ marrow cells were effective in normalizing the blood parameters. The inability to achieve normal blood values without first destroying the host's own stem cells suggested that the indigenous an/an cells compete effectively with injected +/+ cells. This hypothesis was tested by injecting varying numbers of stem cells from C57BL/6J-+/+ mice, together with stem cells from either WBB6F1-an/an or, as controls, from their WBB6F1-+/+ littermates, into lethally irradiated hosts. The C57BL/6J and WBB6F1 mice have electrophoretically distinguishable hemoglobins. The an/an cells are able to compete in the repopulation of the host hematopoietic tissue as shown by the presence of WBB6F1 hemoglobin in the recipients. The cells from mice with Hertwig's anemia, however, do not compete as effectively as do the same number of cells from the +/+ littermates. These results indicate that the pluripotent hematopoietic stem cells of an/an mice are reduced in number, seeding capacity, or proliferative potential.     

Reduced competitive ability due to Wolbachia infection in the parasitoid wasp Trichogramma kaykai

Several hymenopteran parasitoids are infected with parthenogenesis‐inducing (PI) Wolbachia. Infected wasps produce daughters instead of sons from unfertilized eggs. Thus far, little is known about the direct effects of PI Wolbachia on their host's fitness. Here, we report reduced competitive ability due to Wolbachia infection in a minute parasitoid wasp, Trichogramma kaykai Pinto and Stouthamer (Hymenoptera: Trichogrammatidae). Immature survival of infected individuals in a host parasitized by a single infected female, laying a normal clutch of eggs, was lower than those parasitized by a single uninfected individual. When the offspring of infected and uninfected females shared the same host, the infected immatures had significantly lower survival rates than their uninfected counterparts. The survival rate of infected immatures was higher when they competed with other infected immatures from a different infected parent than in competition with uninfected immatures of conspecific wasps. Thus, the host Trichogramma can suffer a substantial reduction in fitness when it is infected with the PI Wolbachia. We discuss why such a reduction is to be expected when populations of infected and uninfected individuals co‐occur, and how the reduced competitive ability of PI Wolbachia influences the spread of the bacteria in the field.     

Contrasting community responses to fertilization and the role of the competitive ability of dominant species

Question: Do contrasting biotic contexts in nutrient‐poor grasslands affect the predictability of invasion by exploitative species following fertilization? Location: French Alps. Methods: We examined community responses after 2 years of nutrient addition for two nutrient‐poor European calcareous grasslands, a mesoxeric community dominated by the short bunchgrass Bromus erectus and a mesic community dominated by the tall rhizomatous grass Brachypodium rupestre. We also performed reciprocal transplantations of these two dominant slow‐growing species and Arrhenatherum elatius, a tall fast‐growing grass that dominates nutrient‐rich communities and is likely to invade nutrient‐poor communities after fertilization. Transplants were grown with or without neighbors, in order to measure their individual responses (without neighbors) and competition intensity (by comparing performances with and without neighbors using the Relative Neighbor Effect index – RNE) during one growing season in all three communities. Results: In the Bromus community, fertilization induced a strong increase in fast‐growing grasses (including A. elatius). Competition intensity was low for the three transplanted grasses, but strongly increased with resource addition, to reach values observed in the Arrhenatherum community. In the Brachypodium community, no change in competition intensity with fertilization was detected, because of the high mortality of the two “non‐resident” species, irrespective of the presence of neighbors. Conclusions: Community responses to nutrient improvement are context‐dependent and vary as a function of the biotic environment. Soil processes are proposed as the main drivers of community resistance to the invasion of fast‐growing species in the mesic, nutrient‐poor grassland dominated by the large conservative competitor B. rupestre.     

A reduced protein model with accurate native-structure identification ability

A protein model that is simple enough to be used in protein-folding simulations but accurate enough to identify a protein native fold is described. Its geometry consists of describing the residues by one, two, or three pseudoatoms, depending on the residue size. Its energy is given by a pairwise, knowledge-based potential obtained for all the pseudoatoms as a function of their relative distance. The pseudoatomic potential is also a function of the primary chain separation and residue order. The model is tested by gapless threading on a large, representative set of known protein and decoy structures obtained from the "Decoys 'R' Us" database. It is also tested by threading on gapped decoys generated for proteins with many homologs. The gapless threading tests show near 98% native-structure recognition as the lowest energy structure and almost 100% as one of the three lowest energy structures for over 2200 test proteins. In decoy threading tests, the model recognized the majority of the native structures. It is also able to recognize native structures among gapped decoys, in spite of close structural similarities. The results indicate that the pseudoatomic model has native recognition ability similar to comparable atomic-based models but much better than equivalent residue-based models.     

Trade-offs between dispersal and competitive ability: a comparative study of wind-dispersed Asteraceae forbs

An underlying assumption in many models of coexistence and species response to fragmentation is the trade-off between dispersal and competitive abilities among species. Despite a well-founded theoretical ground for this assumption, the mechanism itself has not been as thoroughly explored. Empirical studies of the dispersal/competition trade-off have so far mainly concerned the dispersal distance of single offspring, whereas most models where the trade-off is assumed concern dispersal rate, i.e. the number of offspring that is dispersed outside a local patch per time unit. When species differ in fecundity this should also affect the dispersal rate. We therefore investigated different aspects of dispersal ability and competitive ability in the recruitment phase for 15 wind-dispersed Asteraceae species. A trade-off was found between dispersal ability at the offspring level, i.e. distance travelled by single seeds, and competitive ability in the recruitment phase, but no trade-off was found between dispersal ability at the brood level, i.e. the dispersal ability of single seeds in combination with fecundity, and competitive ability in the recruitment phase. The results were supported both by cross-species analysis and analyses by phylogenetically independent contrast. If this is a general pattern then it is troublesome for models making the assumption that there is a trade-off between dispersal rate and competitive ability.     

A dynamic, architectural plant model simulating resource-dependent growth

BACKGROUND AND AIMS: Physiological and architectural plant models have originally been developed for different purposes and therefore have little in common, thus making combined applications difficult. There is, however, an increasing demand for crop models that simulate the genetic and resource-dependent variability of plant geometry and architecture, because man is increasingly able to transform plant production systems through combined genetic and environmental engineering. MODEL: GREENLAB is presented, a mathematical plant model that simulates interactions between plant structure and function. Dual-scale automaton is used to simulate plant organogenesis from germination to maturity on the basis of organogenetic growth cycles that have constant thermal time. Plant fresh biomass production is computed from transpiration, assuming transpiration efficiency to be constant and atmospheric demand to be the driving force, under non-limiting water supply. The fresh biomass is then distributed among expanding organs according to their relative demand. Demand for organ growth is estimated from allometric relationships (e.g. leaf surface to weight ratios) and kinetics of potential growth rate for each organ type. These are obtained through parameter optimization against empirical, morphological data sets by running the model in inverted mode. Potential growth rates are then used as estimates of relative sink strength in the model. These and other 'hidden' plant parameters are calibrated using the non-linear, least-square method. KEY RESULTS AND CONCLUSIONS: The model reproduced accurately the dynamics of plant growth, architecture and geometry of various annual and woody plants, enabling 3D visualization. It was also able to simulate the variability of leaf size on the plant and compensatory growth following pruning, as a result of internal competition for resources. The potential of the model's underlying concepts to predict the plant's phenotypic plasticity is discussed.     

Maximizing daily canopy photosynthesis with respect to the leaf nitrogen allocation pattern in the canopy

Summary A model of daily canopy photosynthesis was constructed taking light and leaf nitrogen distribution in the canopy into consideration. It was applied to a canopy of Solidago altissima. Both irradiance and nitrogen concentration per unit leaf area decreased exponentially with increasing cumulative leaf area from the top of the canopy. The photosynthetic capacity of a single leaf was evaluated in relation to irradiance and nitrogen concentration. By integration, daily canopy photosynthesis was calculated for various canopy architectures and nitrogen allocation patterns. The optimal pattern of nitrogen distribution that maximizes the canopy photosynthesis was determined. Actual distribution of leaf nitrogen in the canopy was more uniform than the optimal one, but it realized over 20% more photosynthesis than that under uniform distribution and 4.7% less photosynthesis than that under the optimal distribution. Redeployment of leaf nitrogen to the top of the canopy with ageing should be more effective in increasing total canopy photosynthesis in a stand with a dense canopy than in a stand with an open canopy.     

The effect of spontaneous mutations on competitive ability

Understanding the impact of spontaneous mutations on fitness has many theoretical and practical applications in biology. Although mutational effects on individual morphological or life‐history characters have been measured in several classic genetic model systems, there are few estimates of the rate of decline due to mutation for complex fitness traits. Here, we estimate the effects of mutation on competitive ability, an important complex fitness trait, in a model system for ecological and evolutionary genomics, Daphnia. Competition assays were performed to compare fitness between mutation‐accumulation (MA) lines and control lines from eight different genotypes from two populations of Daphnia pulicaria after 30 and 65 generations of mutation accumulation. Our results show a fitness decline among MA lines relative to controls as expected, but highlight the influence of genomic background on this effect. In addition, in some assays, MA lines outperform controls providing insight into the frequency of beneficial mutations.     

A hybrid of the invasive plant Sphagneticola trilobata has similar competitive ability but different response to nitrogen deposition compared to parent

Hybridization between introduced and related native species has been suggested to be a key driving force of evolutionary processes in invasions that may be accelerated by increasing nitrogen (N) deposition. We carried out two experiments to compare the competitive ability of a newly-reported putative hybrid (Sphagneticola calendulacea × Sphagneticola trilobata) to that of its invasive paternal parent and investigate its response to different N additions. Growth of the hybrid increased by 39.62 ± 15.69 % when grown with the native parent but showed no significant changes when grown with the invasive parent. Growth of invasive S. trilobata showed no significant changes when grown with the other two taxa. The hybrid and invasive parent inhibited the growth of the native parent by 33.27 ± 15.26 % and 78.56 ± 3.13 %, respectively. Low level N addition (50 kg N ha^?1) enhanced the growth of both the hybrid and native parent, whereas medium and high levels of N additions (150, 300 kg N ha^?1) had no effects on hybrid growth but decreased native parent growth. However, all N treatments had no significant effects on the growth of the invasive parent. Our results suggest that the hybrid is an equal competitor to its invasive parent and is more susceptible to N deposition. Therefore, this hybrid could be a threat to native diversity but may decline more than the invasive parent under high N conditions.     

A model for the ability of drugs to induce enhanced DNase I cleavage

A common property of sequence-selective DNA-binding drugs lies in their ability to induce an enhanced DNase I cleavage in regions surrounding their binding sites. A hypothetical model to explain the enhancements induced by drug binding to the minor-groove of DNA is presented. It involves the participation of three different single models: a mass action effect produced by the enzyme redistribution after drug binding; changes in the minor groove width size; and interactions between the enzyme and the drug, so increasing the cleavage in places located close to the binding site. The model is tested by using statistical data analysis. The hypothetical model might explain the experimental results better than any of the single models alone, but these models also appear to render significant results.