摘要:

Using field and greenhouse studies, we examined the relationships among pinyon pines (Pinus edulis), their ectomycorrhizal mutualists, and their moth herbivores as a function of soil fertility. We studied two soil types—the ash and cinder soils of the San Francisco volcanic field and nearby sandy loam soils. In the field, pinyons growing in cinders suffered from reduced moisture, negative nitrogen mineralization rates, low phosphate levels, reduced growth, and high moth herbivory relative to pinyons growing in sandy loam. Pinyons growing in cinders also had twofold higher levels of ectomycorrhizal colonization than their noncinder counterparts. Similarly, in the greenhouse, seedlings grown in cinders had higher levels of ectomycorrhizal colonization and greater numbers of ectomycorrhizae than seedlings grown in sandy loam. Seedling shoot growth was significantly enhanced by ectomycorrhizae in both soils. These patterns support three conclusions. First, field and greenhouse studies demonstrated that trees growing in nutrient‐poor soils had higher levels of ectomycorrhizal colonization than trees growing in better soils. Second, across soil types, variation in ectomycorrhizal colonization was better predicted by soil fertility than by herbivory. However, herbivory negatively affected ectomycorrhizae in the stressful cinder environment. Third, although mycorrhizae can be parasitic under some conditions, ectomycorrhizae had mutualistic impacts on pinyon seedlings across the environmental extremes we studied.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11461.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

As pollination biology undergoes unprecedented growth as a discipline, confusion in the use of terms has become increasingly common. The need for a flexible yet unambiguous terminology has become urgent. As an example we discuss how the term “pollination efficiency” is used differently by 18 studies, and “pollinator effectiveness” by seven others. Here we present flowcharts of two general models of pollination systems (biotic and abiotic) that trace all the events from pollen production to development of seed or fruit, and we develop a lexicon for the quantities of pollen, processes of transfers (to a vector, to a stigma), and ratios of quantities that are of interest in studies of pollination and mating systems. An appendix includes a glossary of the definitions we suggest.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11462.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Prior studies of crop/weed gene flow inCucurbita pepohave demonstrated that pollinators can deposit mixed pollen loads. The fate of microgametophytes emerging from these pollen mixtures is unknown. In an effort to define the relationship between pollen mixture composition and progeny composition, experimental plants representing a zucchini cultivar and a cross‐compatible free‐living type were genotyped with an isozyme marker and grown under greenhouse conditions. Weighed mixtures of weed/crop pollen were applied to stigmas of both types in differing ratios. Subsequent fertilizations were tracked by an electrophoretic screen of over 1,600 progeny from 39 fruits. Equal mixtures of weed/crop pollen do not produce a corresponding suite of progeny. Pollen of the pistillate parent is favored, and this advantage increases as the proportion of pollen from the pistillate parent increases. However, increasing the proportion of zucchini pollen does not produce a corresponding increase in fertilization success when the free‐living type is used as pistillate parent. These results indicate that microgametophyte competition in both domesticated and free‐livingCucurbitagynoecia could be a significant component of gene flow dynamics. The nature of this competition can only be defined by experiments that control numerous variables, both paternal and maternal, that might be involved. The tendency for crop/weed hybrids to occur at different portions of the ovary suggests that interactions involving two factors—microgametophyte growth rate and gynoecium structure—might play a significant role.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11463.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

The consequences of inbreeding for reproductive traits were investigated for two closely related annual lupines that differ in their mating system.Lupinus bicolor (Leguminosae) is a primarily selling species whileLupinus nanusoutcrosses at intermediate rates. A controlled crossing program was used for each species to produce selfed and outcrossed progeny. These progeny were then grown in a greenhouse and scored for the date of first flower, flower morphology, and autofertility. Selfed progeny ofL. bicolorproduced significantly smaller flowers but did not differ from outcrossed progeny for the remaining traits. Selfed progeny ofL. nanusproduced flowers that significantly differed in shape and had fewer ovules than the flowers of outcrossed progeny. Selfed progeny ofL. nanusalso had significantly lower rates of autofertility in comparison to outcrossed progeny. The significant effects of inbreeding on these mating system traits may indicate the presence of directional dominance at the loci underlying these characters. The consequences of these direct effects of inbreeding on reproductive traits for plants growing in natural populations may include nonadaptive changes in the outcrossing rate between generations.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11464.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Janzen proposed that foliage of herbaceous plants may serve as the attractant for large herbivore dispersal of seeds. Such herbivore dispersal was envisioned to select for traits enhancing ingestion and passage of viable seeds through the animal. We tested this “Foliage is the Fruit” (FF) hypothesis by collecting and collating appropriate data fromBuchloe dactyloides (buffalograss), one of the two dominant grasses of the shortgrass prairie. Passage of buffalograss diaspores through cattle had a positive effect on germination and seedling growth from intact diaspores, damage other than that due to mastication (15%) was minimal, and retention time was 1–5 days. This combination of retention time and migratory herbivores during the northward expansion of shortgrass prairie should have enhanced migration of buffalograss northward to Montana from its area of origin in central Mexico, and our comparisons with its five close dioecious relatives (the “Buchloe group”) showed that buffalograss does possess a suite of distinctive FF traits. Lab analyses of foliage quality and digestibility also confirmed the high quality of its foliage. After reviewing comparable data forBouteloua gracilis (blue grama), we conclude that buffalograss and blue grama, which dominate major portions of the largest North American steppe Province, provide strong support for the FF hypothesis.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11465.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

InPrunus mahaleb (Rosaceae), only a small proportion of those flowers that initially develop give rise to fruits, and the probability of producing fruit differs between flowers. The results of this study indicate that the probability of producing fruit is about 60% for the first (i.e., most proximal) flower to develop in each inflorescence, but very low for the last (i.e., most distal). This pattern is maintained regardless of between‐inflorescence differences in flowering phenology, suggesting that each inflorescence can be viewed as an independent subunit with respect to allocation of resources for reproduction. These results are compatible with the ovary reserve and selective abortion hypotheses for the adaptive value of low fruit set inP. mahaleb.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11466.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Coralloid roots ofMacrozamiahave more apparent developmental stages than those of many other cycad genera, providing an ideal study vehicle for obtaining a better understanding of the growth and development of symbiotic cycad coralloid roots. InM. communisL. Johnson, the process begins with initiation of young apogeotropic, papillose roots called “precoralloids” and involves phases of maturation, cyanobacterial invasion, coralloid formation, senescence, and regeneration. Active precoralloid apices continue to produce papillose tissue, but during precoralloid maturation, the prominent papillose sheath is gradually replaced by a thin, dermal layer with scattered lenticels. Cyanobacterial invasion has been observed at different stages of precoralloid maturation and stimulates further, irreversible development of precoralloids into coralloids. Newly invaded precoralloids in the process of transition may be readily identified by their distinctive apical lenticels. Coralloid development involves transformation of the original, apogeotropic precoralloid tissue as well as production of new coralloid tissue by apical meristems. Although continuous, these two coralloid regions may be recognized by their external morphology. New coralloid growth involves cessation of papillose sheath production, change in gravitropic response, proliferation of lenticels, and early differentiation of a conspicuous cyanobacterial zone. Three mechanisms enabling continuity of the coralloid root system are: 1) production of new precoralloids and coralloids from bases of existing roots of the same kind; 2) initiation of atypical roots from within the internal tissues of degenerating coralloids; and 3) development of internal secondary periderm during decortication of aging coralloid tissue.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11467.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Tubercles are swollen, stalked, warty branches arising from the main elongated roots of species in the terrestrial orchid genusApostasia (subfamily Apostasioideae). Generalized anatomy resembles that of the main roots, except tubercles lack a velamen and conductive strands are few. There are multinucleate cortical cells, and stomata occur in the epidermis. Pores of stomata appear to be permanently open and thus may enhance the interchange of gases between root tissues and soil under the moist conditions in which apostasias grow. Multicellular warts seem to function as holdfasts and are points of entry for mycorrhizal fungi.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11468.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

The number of developing leaves was compared to the number of mature expanded leaves in the crowns of 42 species of palms representing 28 genera. One species had fewer developing vs. mature leaves. Ten species had approximately the same number of developing and mature leaves. Eighteen species had approximately 1.5 times the number of developing leaves vs. mature leaves. Eleven species had approximately twice as many developing leaves vs. mature leaves. Two species (Copernicia gigasandGastrococos crispa) had approximately three times the number of developing vs. mature leaves. Additional data from the literature and previously unpublished observations for 19 species are also presented. The 1:1 ratio between the number of developing leaves vs. mature leaves, as hypothesized by earlier authors, was not found in most species of palms.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11469.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

We characterized the leaf anatomical characteristics and maximum assimilation rates of five neotropical Moraceae of different genera and successional positions. Plants were grown under different light levels and transferred to high light, simulating canopy openings. Total blade thickness increased with irradiance among all species, and thicker blades were developed when plants were switched. However, blade thickness, and the extent to which it was modified, was independent of the species’ successional position and did not predict photosynthetic performance. Palisade thickness was a good predictor of maximum photosynthetic rate, but only on a species‐specific basis. Overall, leaf thickening with increasing irradiance was associated more with structural than with photosynthetic changes. The early successionalsCecropia obtusifoliaandFicus insipidaexhibited similarly high photosynthetic plasticity and acclimation values, but differed in their leaf anatomical traits. The late successionalPoulsenia armataproduced the most anatomically plastic leaves, but failed to acclimate either anatomically or photosynthetically when transferred to higher light levels.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb11470.x

出版商:Wiley    

年代:1994

数据来源: WILEY