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Hawkes CV (2004) Effects of Biological Soil Crusts on Seed Germination of Four Endangered Herbs in a Xeric Florida Shrubland During Drought

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Hawkes CV (2004) Effects of Biological Soil Crusts on Seed Germination of Four Endangered Herbs in a Xeric Florida Shrubland During Drought Hawkes CV (2004) Effects of biological soil crusts on seed germination of four endangered herbs in a xeric Florida shrubland during drought. Plant Ecol 170:121- 134 In a south-central Florida rosemary shrubland, the effects of biological soil crusts on the germination of four small-seeded herbs (Eryngium cuneifolium, Hypericum cumulicola, Paronychia chartacea, and Polygonella basiramia) were studied using a series of greenhouse and field experiments. This study sought to determine propitious environmental conditions for the continued survival of these four federally endangered species and further develop our limited understanding of the effects of biological soil crusts on the germination of vascular plants. In the greenhouse experiment, three of the four species (Eryngium cuneifolium, Hypericum cumulicola, and Paronychia chartacea) showed significantly greater germination in pots with crust left intact than in pots with destroyed, or autoclaved crust. The other species (Polygonella basiramia) showed no significant difference in germination between the two treatments. In the field experiment, plots were established in which resident soil crusts were either left intact, flamed, or mechanically disturbed. To investigate the effects of time since fire and distance to dominant shrub (Florida rosemary, Ceratiola ericoides), plots were set-up in three ages of postfire and two distances from the dominant shrub (away and near). Seeds of all four species were disseminated in field plots and checked monthly for germination. One species, Hypericum cumulicola, showed significant levels of increased germination in plots with crust as opposed to burned or disturbed plots. Germination was low for all four herbs and each species showed a unique response to effects of soil crust disturbance, time since fire, and distance to C. ericoides. In general, germination was highest among all species in recently burned plots away from C. ericoides. Lastly, the pot study showed that intact soil crust collected from Floridian rosemary shrubland had significantly higher gravimetric soil moisture than soils with destroyed crusts. This paper gave no suggestions for future studies. This study is relevant to my meta-analysis project because it involves various treatments of cryptobiotic crusts and the effects of these treatments on the germination of plants in a shrubland ecosystem. I will undoubtedly use this study as a citation in my introduction as an example of crust presence enhancing germination. Although it is important to note that this study found positive effects of the crust on the native plants. I am curious to know how these treatments of the crust would affect the non-native species. Prasse R, Bornkamm R (2000) Effect of microbiotic soil surface crusts on emergence of vascular plants. Plant Ecol 150: 65-75 In the north-western Negev desert of Isreal, the effects of cyanobacteria-dominated microbiotic soil crusts on the germination of vascular plants was examined across three ecotypes: plinth, interdune, and hard crust. This study seeks to expand upon the limited, and equivocal studies examining the effects of crust on germination. Specifically, the scientists note that most experiments have taken place within rangelands in the United States and therefore studies taking place elsewhere or in other ecosystems are much needed. The authors hypothesized that 1) the presence of microbiotic crusts would reduce emergence densities of vascular plants, and 2) the mechanism by which this reduction occurs is by limiting lodgement probabilities for seeds. In each ecotype, 12 groups of 6 20 x 20 cm subplots were set-up. Treatment included two disturbance subplots, two crust removal subplots, and two left as control. One of each treatment type was subsequently covered with a sheet to determine if the removal of the crust prevented the seeds from being deposited or if the crust prevents seeds from contact with the mineral soil. For all ecotypes, vascular plant germination occurred only in plots that had been covered and disturbed. Therefore, uncovered disturbed plots had significantly higher densities of germination than the uncovered control plots. In addition, the uncovered disturbed plots had significantly higher densities of germination than the covered disturbed plots. The authors conclude that this study supports the hypothesis that intact soil crust of the north-western Negev desert have inhibitory effects on the germination of vascular plants. They propose an explanation; that intact soil crust prevents the seeds from becoming lodged while the disturbed crust acts as a seed trap. As the soil crust in this ecosystem is dominated by cyanobacteria, a seed landing on the smooth surface of undisturbed crust would be in sharp contrast to seed landing on a disturbed microsite with considerable roughness. The former situation would likely enhance germination. The authors conclude that more studies are needed to ultimately determine the positive and negative effects of microbiotic crusts on vascular plants. This is a study that directly supports the hypothesis in my own meta-analysis study. I will be able to apply this study to a greater extent by determining what microorganisms dominate soil in coastal sage scrub. Some scientists have noted that the many variations in crust composition and morphology may be the reason for both the inhibiting and encouraging effects of the presence of microbiotic soil crusts. Zaady E, Gutterman Y, Boeken B (1997) The germination of mucilaginous seeds of Plantago coronopus, Reboudia pinnata, and Carrichtera annua on cyanobacterial soil crust from the Negev Desert. Plant Soil 190: 247-252 This study examined the effects of intact, crushed, and sterilized microphytic soil crusts on three native annual plants in a shrubby desert ecosystem of the Negev Desert. These microphytic soil crusts range in development from 2-3mm to 15mm in thickness along an increasing rainfall gradient. Microcoleus vaginatus and N-fixing Nostoc punctiforme are the most abundant cyanobacteria found in the Negev. All three annuals (Plantago coronopus, Reboudia pinnata, and Carrichtera annua) are profuse in the landscape and synthesize mucilaginous seeds that adhere to the soil surface (known as myxospermy). In previous studies, myxospermy protects against ants and other seed predators by adhering to the wet, crusted soil surface. Our current understanding of the effects of microphytic soil crust on the germination of vascular plants is limited and equivocal; many studies have reported both inhibition and enhancement of germination by soil crusts. In addition, our knowledge of how mucilaginous seeds interact with microphytic soil crust is further limited. Speculating that each species has developed a unique relationship with the soil crust, the authors hypothesized that germination results would be varied for each annual species. Fifty seeds of each annual were placed in a petri dish of microphytic soil crust collected from the field with one of the following treatments: intact crust, crushed crust, sterile intact crust, sterile crushed crust, and No.1 Whatman filter paper (5 replicates). Results showed that each species has a unique response to the presence and manipulation of soil crust. For example, P. coronopus showed significantly decreased rates of germination when the crust was crushed or removed. In this case, germination was inhibited because of biological and abiotic factors. Germination in the other species, Reboudia pinnata, and Carrichtera annua, were inhibited in crushed and sterilized soil crust. Therefore, substrates of live, crushed soil crusts will increase the germination of Reboudia pinnata, and Carrichtera annua compared to crushed soil crusts that have been sterilized. This study shows that myxospermy does not enhance germination when such seeds are exposed to microphytic soil crusts. The authors conclude that further studies are needed to distinguish the biotic and abiotic effects of microphytic soil crust and germination and why inhibition or enhancement occurs. This study is relevant to my meta-analysis topic because it is examining the effects of cryptobiotic crust on the germination of plants. In addition, I like how the authors were able to separate the biotic and abiotic effects of the crust. However, they do not speculate or go into any detail about what these biotic effects actually are. .
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