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With a view toward understanding species-specific differences in juvenile tree mortality and the community-level implications of these differences, we characterized juvenile survivorship of 10 dominant tree species of oak transition-northern hardwood forests using species-specific mathematical models. The mortality models predict a sapling's probability of dying as a function of its recent growth history. These models and species-specific growth functions (published elsewhere), characterize a species' shade tolerance. Combined growth and mortality models express a sapling's probability of mortality as a function of light availability. We describe the statistical bases and the field methods used to calibrate the mortality models. We examined inter- and intraspecific variation in juvenile mortality across three sites: Great Mountain Forest (low pH, nutrient poor soils) in northwestern Connecticut, a calcareous bedrock region (neutral pH, nutrient rich soils) also in northwestern Connecticut, and a site in central-western Michigan (low pH, nutrient poor soils). Interspecific differences in juvenile mortality have profound effects on community dynamics and composition; the importance of these effects is demonstrated through a spatially explicit simulator of forest dynamics (SORTIE). The 10 species we examined occupy a continuum of survivorship levels at 1% of full sun. There was surprisingly little intraspecific variation in mortality functions for sugar maple, American beech, eastern hemlock, and white ash between the Great Mountain and Michigan sites. However, there was a striking increase in survivorship for sugar maple in the calcareous site. Differences in survivorship among the sites are correlated with soil pH and presumably nutrient availability. Growth rates in high-light and low-light survivorship are inversely correlated across species; as level of shade tolerance increases, a species grows more slowly in high light and exhibits increased survivorship under low light. Our results indicate that interspecific differences in sapling mortality are critical components of forest community dynamics.

We describe two recessive alleles of a rice heterochronic gene, plastochron1-1 (pla1-1) and pla1-2, that reduce the length of the plastochron to approximately half that of the wild type. Because the onset of the reproductive phase in pla1 was not temporally affected, the number of leaves produced in the vegetative phase was nearly twice that produced in the wild type. Panicle development was severely disturbed in pla1 mutants. In pla1-1, many primordia of primary rachis branches were converted into vegetative shoots. These ectopic shoots repeated the initiation of panicle development and the conversion of primary rachis branches into shoots. In the weak allele pla1-2, however, only the basal one or two primordia developed as vegetative shoots, and the remaining primordia developed to produce a truncated panicle. These results indicate that both vegetative and reproductive programs are expressed simultaneously during the reproductive phase of pla1; however, the degree varied depending on the strength of the allele. Accordingly, pla1 is a heterochronic mutation that extends the vegetative period. The shoot apical meristem of pla1 was larger than that of the wild type, although the shape was not modified. An in situ hybridization experiment using the histone H4 gene as a probe revealed that cell divisions are accelerated in the pla1 meristem. The PLA1 gene is considered to regulate the duration of the vegetative phase by controlling the rate of leaf production in the meristem

Introduction. The use of mycorrhizal fungi as biofertilizers can reduce chemical inputs during the nursery phase, allowing the production of high quality plant material with reduced fertilizer inputs. The lack of complete knowledge of each crop’s responsiveness to mycorrhizal symbiosis, however, is still a handicap to the routine application of this biotechnology for commercial purposes. In our work, the influence of early mycorrhization as an alternative to standard P fertilization programs for two tropical crops, papaya and pineapple, was assessed in a greenhouse experiment. Materials and methods. Papaya seedlings and pineapple planting material were inoculated with the arbuscular mycorrhizal fungus (AMF) Glomus mosseae and cultured on substrates with increasing amounts of soluble P. Data concerning plant development and nutritional status were determined 5 months (papaya) and 7 months (pineapple) after inoculation. Results. For both crops, benefits derived from mycorrhization, expressed in terms of plant development and nutritional status, were significantly higher than those derived from P application. Overall, mycorrhizal papaya plants exhibited significantly higher biomass and macroelement contents in shoots than plants without mycorrhizas at any P level. Mycorrhizal effects on pineapple at the lowest P level were significant in terms of plant development and P shoot contents. Conclusions. Differential benefits derived from mycorrhization seem to be correlated to each crop’s internal P requirements. Our work highlights the potential benefits of integrating early mycorrhization at the nursery stage in order to reduce P fertilizer inputs in sustainable plant production systems. Introduction. L’utilisation de champignons mycorhiziens comme biofertilisants peut réduire les intrants chimiques en pépinière, ce qui permet de produire des plants de haute qualité avec moindre apport d’engrais. Le manque de connaissances approfondies sur la réactivité de chaque culture à la symbiose mycorhizienne est cependant encore un handicap pour l’application systématique de cette biotechnologie à des fins commerciales. Dans nos travaux, l’influence de la mycorhization précoce utilisée en remplacement de programmes usuels de fertilisation en phosphore a été évaluée pour deux cultures tropicales, le papayer et l’ananas, dans une expérimentation en serre. Matériel et méthodes. Des plants de papayers et des rejets d’ananas ont été inoculés avec le champignon mycorhizien à arbuscules (AMF) Glomus mosseae et cultivés sur substrats enrichis de quantités croissantes de P soluble. Des données sur le développement de la plante et son état nutritionnel ont été déterminées 5 mois (papayer) et 7 mois (ananas) après l’inoculation. Résultats. Pour les deux cultures étudiées, les bénéfices tirés de la mycorhization, exprimés en termes de développement de la plante et de son état nutritionnel, ont été significativement plus élevés que ceux découlant de l’application de P. Dans l’ensemble, quelle que soit la quantité de P ajoutée au substrat, les papayers mycorhizés ont présenté significativement des teneurs plus élevées en biomasse et en macroélément dans les tiges que les plantes sans mycorhizes. L’effet des mycorhizes sur l’ananas au plus bas niveau de P a été important vis-à-vis du développement de la plante et de la teneur en P de la tige. Conclusions. Les avantages différentiés provenant de la mycorhization semblent être corrélées aux exigences spécifiques en P de chaque culture. Notre travail met en évidence les avantages potentiels de la mycorhization précoce au stade de pépinière pour réduire les intrants en engrais phosphorés dans des systèmes durables de production végétale. Introducción. El uso de hongos formadores de micorrizas como biofertilizantes puede reducir los insumos químicos en vivero, permitiendo obtener plantas de alta calidad con un menor aporte de abonos. Sin embargo, una de las mayores dificultades para la aplicación sistemática de esta biotecnología reside en la ausencia de un conocimiento profundo de la respuesta a la simbiosis micorrícica de muchos cultivos. En nuestro trabajo, se evalúa el efecto de la micorrización temprana en papaya y piña, como alternativa a los programas rutinarios de fertilización fosforada durante la fase de vivero. Material y métodos. Las plántulas de papaya y los brotes de piña se inocularon con el aislado micorrícico Glomus mosseae y se cultivaron sobre sustratos enriquecidos con cantidades crecientes de P soluble. A los 5 y 7 meses después de la inoculación (papaya y piña, respectivamente), se registraron los valores correspondientes a desarrollo y estado nutricional. Resultados. Para ambos cultivos, los beneficios derivados de la micorrización tanto en desarrollo como en estado nutricional fueron significativamente superiores a los derivados de la aplicación de P soluble. Así, independientemente de la cantidad de P aplicado, las papayas micorrizadas presentaron valores de biomasa y de contenido foliar en macronutrientes significativamente mayores que las no micorrizadas. En el caso de la piña, el efecto observado al nivel más bajo de P, resultó ser de gran importancia en términos de desarrollo y contenido foliar de fósforo. Conclusión. La diferencia en magnitud de los beneficios observados parecen estar correlacionados con las exigencias específicas de P para cada cultivo. Nuestro trabajo pone de relieve las ventajas potenciales de la micorrización temprana durante la fase de vivero como alternativa sostenible para reducir el uso de abonos fosforados en los sistemas de producción vegetal.

Loss-of-function mutations at the maize Glossy15 (Gl15) locus alter the normal transition from juvenile-to-adult growth by conditioning the abbreviated expression of juvenile epidermal cell traits and the coordinate precocious expression of adult epidermal cell features. These include epicuticular wax composition, cell wall characteristics, and the presence or absence of differentiated epidermal cell types (e.g., epidermal macrohairs and bulliform cells). A transposon-induced mutable allele of Glossy15 (gl15-m1) was isolated and employed in both phenotypic and genetic analyses to characterize the role of Gl15 in the maize juvenile-to-adult phase transition. Comparisons between Gl15-active and Gl15-inactive somatic sectors in the leaves of variegated plants demonstrated that the Gl15 gene product acts in a cell-autonomous manner to direct juvenile epidermal differentiation but does not affect factors that regulate the overall process of phase change. Examination of the gl15-m1 phenotype in the Corngrass1, Teopod1, and Teopod2 mutant backgrounds showed that the prolonged expression of juvenile epidermal traits associated with these mutations also required Gl15 activity. These results support a model whereby the cell-autonomous Gl15 gene product responds to a juvenility proqram that operates throughout the vegetative shoot to condition the juvenile differentiation of maize leaf epidermal cells

Heteroblastic features of leaf anatomy in maize were identified by conducting a quantitative analysis of leaf anatomy. Heteroblastic variation in cuticle thickness and epidermal cell shape paralleled changes in previously defined juvenile- and adult-specific traits. The other traits examined in this study (thickness of the leaf blade, epidermal and bundle sheath cell size, vascular area, interveinal distance, mesophyll area : bundle sheath area ratio) varied in a more complex fashion. To determine which of these traits are regulated by genes involved in shoot maturation, we examined the effect of the Teopod2 (Tp2) mutation on their expression. Tp2 increases the number of leaves that express the juvenile form of cuticle thickness, epidermal cell shape, and vascular area and causes all other leaves to produce intermediate (juvenile/adult) forms of these traits. It has little or no effect on any of the other traits we examined. Thus, much of the heteroblastic variation in the internal anatomy of the maize leaf appears to be regulated by factors that are unrelated to the developmental phenomenon of phase change. The effect of Tp2 on leaf anatomy is interesting not only because it provides a criterion for distinguishing between different types of heteroblastic traits, but also because it provides some insight into the nature of the developmental processes involved in shoot maturation. In particular, the observation that Tp2 leaves are quantitatively intermediate between juvenile and adult leaves supports the hypothesis that some phase-specific aspects of leaf identity are regulated in a combinatorial fashion rather than by mutually exclusive patterns of gene expression.

Variable spatial and temporal environments are known to affect the population dynamics of plants, but studies of local-scale variability and its relationship to demographic change within a population remain limited. Using mapped plants, we examined the population dynamics of a coastal grassland endemic, Silene douglasii var. oraria, in two habitats over 10 yr. We hypothesized that ecological differences between rocky and grassy habitats might influence demographic parameters, including adult survival, growth, and density. Soil pH, soil moisture, and other abiotic variables differed little between habitats, but microsite differences in light, soil depth, and vegetation height were related to variation in Silene density and plant circumference. We also found significantly higher population densities, lower adult mortality, and more juvenile recruitment in rocky areas. Finite rates of population growth varied across years and habitats (X = 0.82-1.12), with different patterns evident in the two habitats. In both, observed population sizes in 1992 were similar to matrix projections using 1982-1985 data. Populations declined in size in some years despite high adult survivorship and variable recruitment. More intensive study of seedlings is needed, including experimental evaluation of the role of light and competition. However, the habitat-specific differences we observed imply that ecological studies and conservation plans developed for rare plants should consider the effect of local scale variability on demography

Two naturally occurring, sympatric, northern Georgia populations of Pinus taeda L. (loblolly pine) and P. echinata Mill. (shortleaf pine) were examined with respect to genetic diversity within populations and the frequency, spatial distribution, and morphology of putative hybrids. Shortleaf pine predominated at the \"road\" site while loblolly pine predominated at the \"granite outcrop\" site. Hybrid individuals were identified by their IDH allozyme genotype, the only such locus known to be fixed for different alleles in the two species. All allozymatically detectable hybrids (34 at the road site and two at the granite outcrop site) were juveniles that were distributed in open, sunny patches. A similar pattern of recruitment was seen for juveniles of the parental species. Hybrids were spatially distant from mature shortleaf pine, suggesting that shortleaf pine was not the seed parent. Discriminant analysis on needle characteristics indicated that loblolly pine was easily distinguished from shortleaf pine and the hybrids, but that shortleaf pine and the hybrids were barely distinguishable from each other. A diagnostic cpDNA restriction site marker indicated that shortleaf pine sired all the hybrids at both sites. No evidence of later generation hybridization was found

Simple and multivariate linear models were used to demonstrate the influence of mechanical design and climate on stem morphology and branching architecture in 25 species of North American columnar cacti. The effect of phyletic inertia was tested by the method of independent contrasts. Stem girth was found to increase significantly slower with increased height within taxa (cross-sectional stem area alpha [plant height]0.603), than across taxon (cross-sectional stem area alpha [plant height]1.451). Juveniles are shown to be mechanically overbuilt and subsequently grow into more slender adult forms determined in part by structural limitations and the optimization of other stems functions. We make a structural analogy of relatively rigid columnar cacti to concrete columns and compare plants and models with similar growth forms lacking woody skeletons (barrel cacti). Taxa with woody support achieved a surface-to-volume ratio six times greater than taxa without woody support. Across taxon, cooler winter temperatures were associated with larger stem girths, and greater annual precipitation was associated with less frequent branching. The relationship between total plant surface and volume approaches isometry within taxa, but across taxon average individuals are scaled replicates. We hypothesize that architecture and average plant height are adjusted, in an evolutionary sense, to maintain geometric similitude between surface and volume along a climate gradient

Recent research has demonstrated that juvenile-stage woody plants from Alaska and eastern Siberia (Beringia) are more defended against browsing by hares (Lepus) in winter than the juvenile-stage of congeners from other subarctic regions. Our objectives were (1) to determine if similar biogeographical variation in woody plant defense occurs in subarctic North America, and (2) to evaluate some possible causes of this variation. To achieve these objectives we (1) conducted feeding trials that compared snowshoe hare (L. americanus) preferences for winter-dormant twigs of juvenile-stage tree birch and aspen from Alaska with hare preferences for the juvenile-stage of congeners and conspecifics from eastern North America (Maine and Connecticut), and (2) in the case of birch related hare preferences to twig defensive chemistry. We found that hares preferred eastern North American plants, and preferences for birch were related to defensive chemistry. Two historical explanations for such biogeographical variation in the chemical defense of juvenile-stage subarctic woody plants against browsing by hares have been suggested by Bryant et al.: (1) It is a consequence of geographic variation in the intensity of browsing by Pleistocene megaherbivores; or (2) it is a consequence of very large-scale spatial variation in intensity of browsing by hares and associated extant fire-adapted mammals. Using the glacial history and fire history of subarctic North America, we developed scenarios that allowed us to evaluate these historical hypotheses. We also considered the possibility that biogeographical variation in defense of subarctic woody plants against browsing by mammals is a result of ecological responses of plants to the physical environment. While fully recognizing that all three processes may have contributed to the biogeographical pattern in plant defense we documented, we have concluded that browsing by hares and other extant fire-adapted mammals is likely to be the most important cause. This conclusion indicates that the climatic variation that developed across subarctic North America after the ice age has resulted in a geographical pattern in North American wildfire history, which through effects on vegetation has influenced the intensity of selective browsing by mammals in winter and thereby resulted in biogeographical variation in the chemical defense of woody plants against browsing.

This study examines the productivity, sustainability, and management of tagua nuts from the palm Phytelephas aequatorialis under three management regimes in northwestern Ecuador. Tagua nuts are used internationally as an ivory substitute and the palm fronds are used locally as roof thatch. Plots were established in a control site and in three local management regimes: pure tagua groves; stands with tagua and cacao in an agroforestry system; and tagua groves where the undergrowth is cleared and old fronds removed. Data were collected for one year and local extractors were interviewed about their tagua management. Palm demography indicates heavy management with few subadult individuals and many more adult females than males. Productivity analyses do not demonstrate the influence of any one environmental variable on leaf or infructescence productivity. The pure tagua grove is the management regime most conducive to tagua sustainability. The sustainability results are underscored by the extractive methodology, where local extractors maximize tagua collected while minimizing collection time. These results are incorporated into management recommendations to foster tagua extraction while ensuring its sustainability and future use. /// Nueces de tagua están usados internacionalmente como un sustituto para marfil y las frondas de la palms se usa localmente para techos. Se estableció cuadrantes en un sitio de testigo y en trés regimenes de manejo local: arboledas de tagua pura; arboledas con tagua y cacao en un sistema agroforestal; arboledas de tagua donde se limpia el suelo y remueve las malezas y las frondas viejas. Se recolectaron datos por un año y se entrevistó extractores locales sobre su manejo de tagua. La demografia de las palmas indicó que el manejo es intenso con pocos individuos de subadultos y mucho más hembras adultas que varones. La analísis de la productividad no demostró la influencia de un solo variable en la productividad de hojas o infructescencias. La arboleda de tagua pura es el regimen de manejo más conducible a sustentabilidad de tagua. Los resultados de sustentabilidad están subrayados por la metodología de extracción, en que extractores locales maximizan la recolecciónn de tagua mientras minimizan el tiempo de recolección. Estos resultados están incorporados en unas recomendaciones a fomentar la extracción de tagua mientras asegura su sustentabilidad y uso futuro.