Biology ETDs

Publication Date

5-13-2017

Abstract

In the northwestern part of South America, seasonally dry forests have undergone extensive conversion to savannas to support ranching and agriculture. The combination of fire and vegetation removal employed for clearing, together with extensive agricultural practices, often lead to loss of soil fertility. This results in land that is no longer useful for agriculture and on which historical forests are unable to regenerate. This study examined the effects of common agricultural practices on soil fungal communities by simulating the effects of fire followed by plant removal. The goal was to determine whether common practices have rapid effects on soil communities, which in turn could signal a decline in soil quality. To provide a climatological context for this study, I first performed an analysis (presented in Chapter 1) that employed a 40-year database of daily precipitation totals, from a rain-gauge station located in the central portion of the Caribbean savannas of Colombia. The goal was to assess intra- and inter-annual variability in precipitation. I found that overall there is a tendency toward dryer years starting in the mid 1990´s. In addition, despite the documented relationship between El Niño and decreased precipitation, correlation between El Niño occurrence and total monthly precipitation was not statistically significant. Such results can be explained in part by local fluctuations in temperature and precipitation. Finally, results from this study highlight the importance of studying the distribution of precipitation at different time scales, which can provide insights into the pulse-driven nature of seasonally dry Tropical systems. A second study (Chapter 2) examined changes in the composition of fungal communities in a Colombian seasonally dry savanna over a three-month period, under conditions simulating the local agricultural practices of vegetation burning and removal. Fungal community composition was estimated using next-generation pyrosequencing targeting the ribosomal RNA internal transcribed spacer (ITS) regions. The general fungal community was dominated by species of Ascomycota and Basidiomycota, many of which had been described previously from culture studies of tropical soils. Significant community changes occurred over time, but there were not dramatic differences between removal and non-removal experimental plots. The community at three months after vegetation cutting or removal differed in overall diversity from that observed at zero and thirty days. Several fungal taxa were identified as potential indicator species of either early or late sampling periods. Overall, it appears that the decline in soil health observed for sites subjected to long-term agricultural practices are not reflected in dramatic fungal community changes observed for a single season, even in the case of complete above- ground vegetation removal. Additional studies will be required to document the time-course for changes in microbial community composition that accompany such decline.

Project Sponsors

The Colombian Government, the Administrative Department of Science, Technology and Information COLCIENCIAS (COLCIENCIAS-COLFUTURO 617)

Language

English

Keywords

soil fungi, dry savannas, soil ecology

Document Type

Dissertation

Degree Name

Biology

Level of Degree

Doctoral

Department Name

UNM Biology Department

First Committee Member (Chair)

Donald O. Natvig

Second Committee Member

Diana E. Northup

Third Committee Member

Scott L. Collins

Fourth Committee Member

Andrea Porras-Alfaro

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