生物土壤结皮对荒漠土壤种子库和种子萌发的影响

研究了腾格里沙漠东南缘在不同自然条件（风、温度、水分）下,人工固沙植被区（24龄、41龄、50龄）和相邻天然植被区的两种生物土壤结皮对荒漠土壤种子库和种子萌发的影响。结果表明,荒漠土壤种子库在苔藓结皮上的储量显著高于藻类结皮。随着生物土壤结皮的发育,种子萌发量在苔藓结皮上增加,在藻类结皮上减少。生物土壤结皮层的含水量对种子萌发有显著的影响（p〈0.05）,植物种子在湿润处理的生物土壤结皮上的萌发量高于干燥处理的生物土壤结皮上的种子萌发量。生物土壤结皮表层温度和亚表层温度对荒漠植物种子萌发无显著影响（p〉0.05）,但总体而言,对于苔藓结皮,植物种子在较高温度下的萌发量略高于在较低温度下的萌发量,而对于藻类结皮,植物种子在较低温度下的萌发量略高。     

COMMUNITY STRUCTURE DYNAMICS OF EPILITHIC AND EPIPHYTIC DIATOMS IN A MISSISSIPPI STREAM1

Epilithic and epiphytic diatoms were collected monthly from 18 June 1979 through 19 May 1980 from both shaded and unshaded sites of Sessums Creek, a shallow, oligotrophic and strongly alkaline stream in northeastern Mississippi. The dominant macroalgae were filamentous green algae belonging to the non-mucilage producing genera Cladophora and Rhizoclonium. Ninety taxa were identified with Navicula minima Grun. and Nitzschia dissipata (Kütz.) Grun. accounting for 50% of all valves counted. Other important taxa were Navicula menisculus var. upsaliensis (Grun.) Grun., N. cryptocephala var. veneta (Kütz.) Rabh., Achnanthes minutissima Kütz. and Cymbella turgida (Greg.) Cl. With few exceptions, the more dominant taxa were equally abundant in the shaded and unshaded sites and also in the epilithon and epiphyton. Species diversity (H') and the number of taxa in a sample in all four habitats showed an identical pattern, being lowest in winter and highest in fall. No one pair of habitats was more structurally similar than any-other pair when compared by a similarity index (SIMI). Apparently, differences in light intensity and substrate type had little effect on diatom distribution in Sessums Creek and it was concluded that the locality sampled supported a single, nearly homogeneous diatom community.     

Membrane lipids in Ceratodon purpureus protonemata grown at high and low temperatures

Ceratodon purpureus (Hedw.) Brid. was grown at two temperatures, 20 and 4°C. The protonemata grown at 4°C fixed more CO₂ at low temperatures; but their frost tolerance, tested as the recovery of photosynthesis after frost treatment, was not better than in the protonemata grown at 20°C. The effects of the growth temperature were studied on the membrane lipids of intact protonemata and on the lipid and protein contents of isolated thylakoid membranes. A large proportion, 70 to 90%, of the thylakoid membrane lipids was lost unless precautions were taken to inhibit the lipid-degrading enzyme activities. The lipid content of the thylakoid membranes of protonemata grown at 20 and 4°C was 3.9 and 4.8 mol (mol chlorophyll)⁻¹, respectively. Only minor differences were found in the lipid class composition. Monogalactosyldi-acylglycerol constituted more than 50 mol-% of the thylakoid membrane lipids at both 20 and 4°C. However, each lipid class had a higher average number of double bonds per lipid molecule in cold growth conditions. The protein content of the thylakoid membranes was low at both 20 and 4°C. These characteristics of the thylakoid membranes may be a prerequisite for the observed ability of protonemata to photosynthesize even at subzero temperatures.     

Structural characteristics of a diatom community epiphytic on Ruppia maritima

Epiphytic diatoms were collected from both the leaves and internodes of Ruppia maritima in a New Jersey salt marsh during the growing season of the host plant. Community diversity (H and the number of diatom taxa) values were initially high as Ruppia began its growth, but quickly dropped to sustained low levels as vegetative growth of the host ceased and new attachment sites were no longer available. A critical examination of all structural characteristics indicated that the leaves and internodes of Ruppia support a single, nearly homogeneous epiphytic diatom community. An analysis of variance indicated that differences between leaves and internodes were minimal, as did a comparison of the assemblages present on these two sites by a selected similarity index. A total of 57 taxa were encountered and the single dominant taxon was Navicula pavillardi, which accounted for one out of every three individuals counted. A comparison of the epiphytic diatom community with those inhabiting the sediments on the marsh proper revealed that the marsh sediments were the major source of individuals for Ruppia colonization.     

Fatty acid composition of mutants of the moss Physcomitrella patens

The fatty acid composition of various mutant strains of the moss Physcomitrella patens has been compared to the wild-type. These included strains defective in their responses to auxins and/or cytokinins, one which releases much more cytokinin into the medium than the wild-type, and two aphototropic strains. The lipids of the aphototropic mutants were also studied after culture in different light regimes. Although some differences in fatty acid composition have been found between strains, these alone are probably not responsible for their physiological differences. Considerable changes occur in many fatty acids in senescent or dark-grown material, including changes in the proportion of C₂₀ polyenoic fatty acids.     

Localization of membrane-associated calcium following cytokinin treatment in Funaria using chlorotetracycline

We have investigated the changes in membrane-associated calcium that occur during cytokinin induced bud formation in Funaria hygrometrica Hedw. using the fluorescent Ca²⁺-chelate probe chlorotetracycline (CTC). In the target caulonema cells a localization of CTC fluorescent material becomes evident at the presumptive bud site 12 h after cytokinin treatment. By the time of the initial asymmetric division this region is four times as fluorescent as the entire caulonema cell. Bright CTC fluorescence remains localized in the dividing cells of the bud. To relate the changes in CTC fluorescence to changes in Ca²⁺ as opposed to membrane-density changes we employed the general membrane marker N-phenyl-1-naphthylamine (NPN). NPN fluorescence increases only 1.5 times in the initial bud cell. We conclude that the relative amount of Ca²⁺ per quantity of membrane increases in this localized area and is maintained throughout bud formation. We suggest that these increases in membrane-associated Ca²⁺ indicate a localized rise in intracellular free Ca²⁺ concentration brought about by cytokinin action.Abbreviations BA 6-benzyladenine - CTC chlorotetracycline - ER endoplasmic reticulum - NPN N-phenyl-1-naphthylamine     

The potential effects of energy related activities on the seasonal trajectories of epiphytic marine diatoms

Seasonal successional trajectories of transplanted and experimental diatom communities were studied during the summer of 1973. Manipulation of these diatom assemblages was accomplished through the development of an in situ experimental apparatus capable of incubating these organisms without doing violence to the community itself.In one set of experiments the effects of water quality were tested on the development of inocula from grossly similar but fairly distant locations. In another set the native inoculum was incubated in the continual presence of Fe, Cu, Cr, Pb, Zn and crude oil. Seasonal succession took place in all of the control and experimental communities. During the course of succession the trajectories of assemblages under some conditions converged while others diverged. Since the random fluctuations in the environment were constant for all assemblages, the abundances of individual species were due to niche packing and interspecific restraints on the biotic potential of selected diatom species as well as the changes in water quality. The most diverse community was an experimentally mixed one. The high diversity of this community was probably due to niche packing a phenomenon which restricted the realized niches of many species and hindered their blooming. Paradoxically twice as many species (40%) had their greatest niche breadth in the mixed community as did species in the transplanted (20%) or native controls (17%). Enrichment of the incubation medium with heavy metals and oil altered the community structure and diversity of most experimental vessels. Growth of some species was depressed while that of others was enhanced. The trajectories of the communities enriched with oil and Pb were quite similar throughout the summer. The Cu and Cr assemblages initially followed the trajectory of oil and Pb but later diverged. Greatest species diversity was consistantly found in the community incubated in the presence of Cu. The Fe enriched community generally diverged from all the others. Recurrent group analysis identified distinctive groups of species for each of the experimental assemblages as well as controls.The response of these diatom communities incubated under natural conditions were characteristic of resilient communities in which populations with different structures were quickly established.Supported by ERDA Contract E (11-1) 3254, Reference Number (COO) 3254-28. The authors would like to acknowledge Dr. Howard Rubin for his assistance in writing the many computer programs used in this investigation.This paper represents a revised expansion of a thesis project accepted by the CCNY Biology Faculty in partial fulfillment of the requirements of the M.A. degree in September 1976.     

Isopentenyladenine from mutants of the moss, Physcomitrella patens

The culture media from gametophore over-producing mutants of the moss Physcomitrella patens have been examined for their cytokinin content. Two cytokinins have been detected, one of which has been identified as N⁶-(Δ²-isopentenyl) adenine (2iP).