Surface mining for coal alters the original soil profile characteristics and the associated physical, chemical, and biological conditions. Our objectives were to compare soil characteristics and the distribution of nutrients to 1 m depth over a chronosequence of 40 years to determine when a reclaimed mine soil (RMS) returned to premined conditions. We sampled 5 sites aged 0 to 20 years reclaimed by the crosspit spreader technique (CP) and 3 sites aged 20 to 40 years reclaimed by the mixed overburden technique (MO). An unmined site (UM) served as a control. Changes in soil texture (sand to clay loam) after mining corresponded with increased macroaggregation (>2 mm) and enhanced C sequestration up to ~250 Mg C ha-1 at the MO20 site. Soil chemical [pH, electrical conductivity (EC), and sodium adsorption ratio (SAR)] and physical properties [bulk density (BD) and texture] met or exceeded reclamation and revegetation standards. Most soil C was associated with organic matter, but a small amount of lignitic C was detected in some samples. Soil organic C and N reached or exceeded premined concentrations after 0 and 10 years, respectively. Soil NO3--N and P did not reach premined conditions, but soil K, Ca, Mg and S exceeded premined conditions and stratified after 10-15 years. Micronutrients exceeded premined concentrations. Soil microbial biomass and mineralization rates recovered after 16 years of reclamation. Bacteria and fungi recovered to premined levels after 20 years. The CP20 site was most closely related to the UM site, but sites 10 years and older were comparable. Dominant phyla (Actinobacteria, Acidobacteria and Proteobacteria; 70% of all sequences) returned to premined levels after 10 years, which correlated with soil quality indicators, suggesting the importance of these phyla in soil health. Community-level physiological profiles did not differ between sites and metabolic diversity peaked at CP15 and CP20. GeoChip showed separation between the UM sites and reclamation sites. Soil microbial functionality appeared to recover faster than taxonomic composition of the soil microbial community. Further analysis of functional genes will expand upon this research so that we may better quantify soil quality in RMS.

No description available.

No description available.

Canada’s Boreal Plains peatlands comprise 2.1% of the world’s terrestrial carbon store and are vital water supplies for adjacent upland ecosystems in this sub-humid climate. Projections indicate that future drought and wildfire events will be more frequent and severe, enhancing moisture deficits and threatening the functional role of peatlands as net carbon sinks. Peatland margins existing at the peatland-upland interface have been identified as deep smouldering hotspots on the landscape, where margin carbon loss accounts for 50 to 90% of total peatland carbon loss, dependent on hydrogeological setting. Previous chronosequence analysis of peatland bog recovery from wildfire disturbance has chronicled a return to carbon sink status within 20 years, but has not included margins nor peatlands located in coarse or heterogeneous-textured hydrogeological settings with varying degrees of groundwater connectivity. This analysis identifies and describes margin vegetation communities and recovery trajectories with time since fire and across hydrogeological settings. No significant differences were identified in margin area over time or margin peat depths across hydrogeological settings. Margin canopy composition consists of mixed coniferous and broadleaf deciduous species, with enhanced litterfall characterizing the dominant early to mid successional ground layer composition. Both peatland bog middle and margin vegetation communities were found to be dominated by feathermoss growth ~60 years following wildfire, which represents an accelerated trajectory from previous chronosequence analyses. Increased peatland and margin fuel loads with time since fire are also demonstrated using aboveground biomass calculations. Restoration practitioners can use this study to identify recovery milestones and altered trajectories, with their associated feedbacks, that perpetuate a broadleaf canopy and limited Sphagnum moss paludification. Fire managers should include confined peatlands in coarse-textured hydrogeological settings with deep smouldering margins in their management considerations and consider intervention (forest treatments) to open the canopy and prevent legacy carbon losses by severe wildfires. / Thesis / Master of Science (MSc)

Over the last 30 years, Crab Orchard National Wildlife Refuge in Southern Illinois has made a strong and well-documented effort to convert agricultural lands to forest to further their mission of wildlife and habitat conservation. Our research seeks to assess the influence that this land use conversion has on ecological function and to establish ecological indicators of successful restoration. We examined five potential soil-based indicators of ecological function across a chronosequence of afforested sites at the refuge and compared them to nearby row crop agricultural sites and mature forest sites with similar soils and landscape positions. Collected soil samples were analyzed for total carbon, total nitrogen, labile carbon, aggregate stability, and bulk density. Soil texture analysis was also conducted to validate comparisons among sites. The data were analyzed using a multivariate analysis of variance comparing land uses as well as linear regression analyses looking at the influence of age since restoration on an index value created by subtracting the soil indicator value of the nearby agricultural site from that of the forested site. The index value was used as the dependent variable in order to control for variation among sites and isolate the influence of age. Aggregate stability and labile carbon were positively correlated with age since restoration and bulk density was negatively correlated with age since restoration. These three soil parameters were promising indicators of restored ecological function in afforested sites. Target values for these indicators were proposed. Our results help to determine the timeframe in which these ecological functions return following restoration and can be used to assess the success of current and future afforestation projects.

The processes by which plant spatial patterns are formed, and the effects of those patterns on plant community dynamics, remain important areas of research in plant ecology. Plant spatial pattern formation has been linked to many ecological processes that act to structure plant communities at different spatiotemporal scales. Past studies of pattern formation are common, but recent methodological advances in data collection and analysis have permitted researchers to conduct more advanced observational studies of pattern formation in space and time. While studies of the effects of plant spatial patterns were formally rare, they have increased in the last decade as new types of experiments and analysis have been developed to better understand the myriad effects of plant patterns on community dynamics. My dissertation research examined both the causes and consequences of plant spatial patterns in the context of natural and experimental Great Basin semi-arid plant communities. In both cases, I implemented novel methodologies for data collection, experimental design, and data analysis in an attempt to address current gaps in knowledge related to the processes by which plant spatial patterns are formed, as well as the effect of plant spatial patterns on community dynamics. The results inform both basic and applied plant ecology, and set the stage for further research on the causes and consequences of plant spatial patterns in semi-arid plant communities.

RATIONALE: Recent studies indicate that plants can partition electron transport through alternative oxidase (AOX) and cytochrome c oxidase (COX) in response to environmental cues, thus modulating respiratory efficiency. The ¹⁸O discrimination method necessary for measuring electron partitioning in vivo, however, has been restricted to laboratory settings due to equipment constraints. Since plants grown in more natural and variable environments may not respond as predicted by laboratory experiments, I developed a new field-compatible analytical method and then applied it to three ecophysiological studies. METHODS: To address these needs, I developed a field-compatible method in which plant tissue was incubated in 12 mL septum-capped vials for 0.5 – 3 h, after which the incubation air was transferred to 3.7 mL storage vials for subsequent measurement by mass spectrometry. I also developed mathematical tools to correct for unavoidable contamination, and to detect and address curvature in the data – whether intrinsic to the respiration or due to contamination, – and to extend the usable dynamic range of the mass spectrometer. These methods were used to investigate respiratory responses (1) in canopy trees growing across a soil nutrient gradient at the Franz Josef chronosequence, New Zealand; (2) in a nutrient manipulation experiment of Griselinea littoralis; and (3) in a long-term nutrient-, temperature-, and light manipulation at Toolik, Alaska, USA. Leaf dry matter content, specific leaf area, nitrogen (N), phosphorus (P), sugars, starch, and AOX/COX protein concentrations were also measured as explanatory variables. (Leaf Cu and Fe were measured at the Franz Josef chronosequence.) RESULTS: Discrimination values computed using my methods replicated previously reported results over a range of 10 – 31‰, with precision generally better than ±0.5‰, thus demonstrating its validity as tool for measuring respiratory electron partitioning. Foliar respiration declined with site age across the soil chronosequence, increasing with leaf N levels, r² = 0.8, but electron partitioning declined with increasing N/P, r² = 0.23. AP activity was positively correlated with leaf P, Cu, and starch, r² = 0.71. In younger soils, however, declines in respiration were attributed to declines in cytochrome pathway (CP) activity, whereas across the older sites respiration declined due to a reduction in AOX pathway (AP) activity. The Griselinia nutrient-manipulation experiment partially confirmed these results: AOX protein levels were highest in N-deficient plants rather than in plants deficient in both N and P. AP activity was very low in all leaves, however, possibly due to low illumination. In support of this claim, leaves that had developed in the sun had higher AOX/COX protein ratios than those that had developed in the greenhouse. In Griselinia roots, CP activity declined by more than half in response to nutrient deficiency, whereas AP activity was unchanged. At the Arctic site, only one species changed electron partitioning in response to nutrient addition. Betula nana, the most successful adapter to improved mineral nutrition, doubled leaf CP activity without changing AP activity. Species grown in full sun at that site also had higher AOX/COX protein ratios than those that grew in enclosures. CONCLUSIONS: This is the first study of how engagement of terminal respiratory oxidases in plants responds to multiple nutrient deficiencies, both in nature and in a controlled environment. I have uncovered some intriguing relationships, including the possible importance of N/P to electron partitioning, as well as a role for Cu. The results also suggest that electron partitioning is sensitive to plant energy balance, as suggested by the low AP activities and low AOX/COX protein ratios in shaded plants. Perhaps most significantly, the AP and CP appeared to act independently of each other, rather than through a concerted “partitioning” process. In addition to their own scientific merit, these results illustrate the value of using the new field-compatible method to conduct ecophysiological investigations of plant respiratory electron partitioning on a much large scale, and under more realistic conditions, than has been previously possible.

Successional trends in herbaceous plant production and diversity were studied in an age sequence of sites, i.e. chronosequence, inferred to represent a meadow to aspen to fir to spruce-fir sere. Primary production was observed to decrease in a linear fashion with successional development. Three components of diversity; richness, heterogeneity, and equitability or evenness, each had low early successional values, reaching maximum diversity in mid-succession, and declining to intermediate levels with maturity. The magnitude of these trends varied greatly, depending on the methods used to determine plant dominance. Characteristics of various dominance indices and their applicability to this study were examined. Mean daily photosynthetic biomass was found to be an especially appropriate index of dominance for studying these seasonally dynamic communities. A checklist of 141 vascular plant taxa encountered in the study is included. The flora was determined to be exceedingly species rich, with values of the calculated diversity indices among the highest reported in the literature reviewed. The limitations of diversity indices to sampled data is discussed.

The rehabilitation of degraded soils, such as those associated with post-mining sites, requires knowledge of the soil ecosystem and its physical, chemical, and biological composition in order for rehabilitation efforts to fulfil the long-term goal of reconstructing a stable ecosystem for rehabilitated mine soil. This study addresses the need for appropriate assessment criteria to determine the progress of rehabilitation and subsequently the success of management practices. Significant contributions made by this investigation included the establishment of minimum and maximum values for microbial community measurements from two case studies of rehabilitated coal discard sites. Furthermore, it was shown that there was no relationship between changes in microbial community function and structure and the rehabilitation age of the sites. Following this, the considerable impact of management practices on microbial communities was illustrated. The first part of the study investigated the temporal changes in microbial community function and structure in a chronosequence of rehabilitated coal discard sites aged 1 to 11 years. The most important observation made during the investigation of the microbial communities in the different aged soil covers of the rehabilitated coal discard sites, was that there was no relationship between rehabilitation age and microbial activity or abundance of certain microbial groups. What was responsible for a clear differentiation between sites and a shift in microbial community attributes was the management practices applied. A comparison of two chronosequences of rehabilitated coal discard sites was achieved by an application of the 'space-for-time' hypothesis. Sites of different ages and at separate locations ('space') were identified to obtain a chronosequence of ages ('time'). The two chronosequences included sites aged 1 to 11 years (chronosequence A) and 6 to 17 years (chronosequence B), respectively. Sites in the same chronosequence were managed identically, while there was a distinct difference in management practices applied to each chronosequence. The long-term effect of the different management regimes on the soil microbial community function and structure was investigated. Again, there was no relationship between rehabilitation age and microbial community measurements. Fluctuations of selected microbial properties occurred in both chronosequences and similar temporal trends existed over the rehabilitation periods. However, the less intensively managed chronosequence (8) seemed more stable (less fluctuation occurred) over the rehabilitation period than the more intensively managed chronosequence (A). It was therefore concluded that the microbial communities in the less managed sites maintained their functional and structural integrity within bounds in the absence of management inputs or disturbance. While there was similarity in the trends over time for individual microbial community measurements, the seemingly more stable conditions in chronosequence 6 are important in terms of the goal of rehabilitation. / Thesis (Ph.D. (Environmental Science)--North-West University, Potchefstroom Campus, 2007

1. A longstanding goal of ecology and conservation biology is to understand the environmental and biological controls of forest succession. However, the patterns and mechanisms that guide successional trajectories, especially within tropical forests, remain unclear. 2. We collected leaf functional trait and abiotic data across a 110-year chronosequence within a tropical dry forest in Costa Rica. Focusing on six key leaf functional traits related to resource acquisition and competition, along with measures of forest stand structure, we propose a mechanistic framework to link species composition, community trait distributions and forest structure. We quantified the community-weighted trait distributions for specific leaf area, leaf dry matter concentration, leaf phosphorus concentration, leaf carbon to nitrogen ratio and leaf stable isotopic carbon and nitrogen. We assessed several prominent hypotheses for how these functional measures shift in response to changing environmental variables (soil water content, bulk density and pH) across the chronosequence. 3. Increasingly, older forests differed significantly from younger forests in species composition, above-ground biomass and shifted trait distributions. Early stages of succession were uniformly characterized by lower values of community-weighted mean specific leaf area, leaf stable nitrogen isotope and leaf phosphorus concentration. Leaf dry matter concentration and leaf carbon to nitrogen ratio were lower during earlier stages of succession, and each trait reached an optimum during intermediate stages of succession. The leaf carbon isotope ratio was the only trait to decrease linearly with increasing stand age indicating reduced water use efficiency in older forests. However, in contrast with expectations, community-weighted trait variances did not generally change through succession, and when compared to null expectations were lower than expected. 4. The observed directional shift in community-weighted mean trait values is consistent with the 'productivity filtering' hypothesis where a directional shift in water and light availability shifts physiological strategies from 'slow' to 'fast'. In contrast with expectations arising from niche based ecology, none of the community trait distributions were over-dispersed. Instead, patterns of trait dispersion are consistent with the abiotic filtering and/or competitive hierarchy hypotheses.