Factors affecting the nodulation and growth of tropical woody legume seedlings

This study surveys the occurrence of nodulation in woody legume species in Panamá and Costa Rica, describes nodule and root characteristics, and researches host-bacteria specificity, nodulation potential of soils, and the effects of light, added nitrogen, and rhizobia and VA mycorrhizal fungi inoculation on seedling growth. I examined 83 species in 37 genera and found 80% to be nodulated. Percent nodulated species in the Caesalpinioideae, Mimosoideae, and Papilionoideae was 17, 95, and 86, respectively, with no correlation between nodule morphology and tribal classification. Nodules formed mainly at root branch points which supports epidermal breaks as an important rhizobia infection route. More non-nodulated than nodulated species had root hairs. Several species emitted volatile sulfur-containing compounds, including the toxic compound ethylmercaptan, from roots, germinating seeds, and other tissues. These emissions may have an allelopathic action against pathogens, predators, or other plants. In contrast to the general non-specificity of most legumes for rhizobia, Mimosa pigra L. was highly specific and only nodulated in flooded soils. This species' specificity, combined with a limited occurrence of its root nodule bacteria may limit its natural distribution, but its spread as an invasive weed is facilitated when fill material from rivers is deposited in other areas. ^ An experimental light level of 1.5% of full sun completely inhibited seedling nodulation, as do similar naturally low levels in forest understory. In the forest, trees and seedlings were not nodulated. in some soils with suspected high N content. For six experimental species, added N progressively increased seedling growth while decreasing nodule biomass; at the highest level of added N nodulation was completely suppressed. Species and individuals showed variation in nodule biomass at high N applications which may indicate an opportunity for genetic selection for optimal N acquisition. Rhizobia inoculation had a small positive effect on seedling shoot growth, but VA mycorrhiza inoculation overwhelmingly increased seedling size, biomass, and leaf mineral concentration. In lowland tropical forest, VA mycorrhizal colonization appears indispensable for legume nodulation because of the fungus' ability to supply P in deficient soils. This requirement makes the legume-rhizobia-mycorrhiza association obligately tripartite. ^

From foster care to college: Young adults' perceptions of factors that impacted their academic achievement

Despite increased Federal, state, and local efforts in the United States to improve outcomes among young adults who emancipate from foster care, low educational achievement and attainment continue to characterize this vulnerable subpopulation. Approximately 50% of foster children do not obtain a high school diploma or a general equivalency diploma (GED). Only about 20% of former foster children enroll in college, compared to 60% of youth not in foster care. The purpose of this study was to explore, describe and explain the perceptions of college students who had lived in foster care regarding the external and internal influences that impacted their academic achievement and attainment. Interviews with a purposefully selected sample of 24 Florida college students were conducted; transcripts were coded and analyzed thematically. Findings included that participants experienced a particular set of external and internal influences at school, in foster care settings, and in the community. External influences include interactions with (a) multiple non-relative guardians and case workers, (b) relatives, especially siblings, (c) mentors, (d) teachers and school administrators, and (e) school counselors. Internal influences include the barriers of anger and bad behavior and a newly identified set of internal characteristics, called success strengths by the researcher, that promote academic achievement and college attainment. Implications are as follows: (a) Future theory on academic achievement concerning foster youth should reflect the importance of the affective aspect of school interactions. (b) Policy should mandate awareness training for educators, social workers, and other adults who work with former foster youth to increase professionals' awareness of the barriers, supports and success strengths that impact the academic lives of children and youth in foster care. (c) Adult educators and human resource development professionals should develop and implement appropriate new education and training materials and interventions. Future research may include a similar interview with former foster youth who graduated from college and with foster youth who leave school before graduating. Finally, a study with a nationally representative sample of college enrolled former foster children should be conducted to determine the relative importance of the barriers, supports and success strengths identified in this study.