Land-Use History in Ecosystem Restoration: A 40-Year Study in the Prairie-Forest Ecotone

Land‐use history, recent management, and landscape position influence vegetation at the Rockefeller Experimental Tract (RET), a 40‐year‐old restoration experiment in northeast Kansas. RET is representative of the prairie‐forest ecotone, containing native tallgrass prairie and oak‐hickory forest, but unique in having tracts of replanted prairie, seeded in 1957, that have undergone long‐term restoration treatments: burned, grazed, mowed, or untreated. A land‐use history database for RET was compiled using a geographic information system to integrate historic and contemporary sources of information. Restoration management on the reseeded prairie has had a profound effect on forest development: mowing or burning precluded forest establishment (<3% forest cover), whereas portions of untreated or grazed areas became heavily forested (>97% forest cover). Forest colonization depends upon biotic and edaphic conditions at the time restoration was initiated: for areas replanted to prairie and managed by grazing, forestation was 6% on land in cultivation prior to replanting, 20% on former pastureland, and 98% on land deforested just before replanting. Patterns of forest colonization were also significantly associated with three landscape positions: near existing forest, along water courses, and along ridge tops. Additionally, land‐use history analyses showed that the presence of various prairie and forest species resulted from persistence and not from colonization following restoration. Because of the lasting imprint of historic land use on the landscape, our results indicate that it is essential that restoration studies be evaluated within a site‐specific historical context.     

Disturbance,drought and dynamics of desert dune grassland,South Africa

A seven-year study of marked plants and plots in Stipagrostis ciliata (Desf.) de Winter dune grassland, in the arid (<100 mm yr^–1) Bushmanland area of the Northern Cape province of South Africa, was designed to test the hypothesis that establishment of ephemeral plants, and recruitment of perennial grasses was dependent upon disturbances that reduced the density of living perennial grass tussocks. In 1989, eight 4 m² plots were cleared of perennial vegetation by uprooting and removing all plants so as to resemble small-scale disturbances made by burrowing mammals or territorial antelope. The vegetation on the cleared plots and surroundings was monitored until 1996. Initial results supported our hypothesis. In wet years, when ephemeral plants were abundant, their average fresh mass was 2–3 times greater per unit area on the cleared plots than in control plots in adjacent, undisturbed grassland. Many Stipagrostis seedlings established in the cleared plots over the two years following clearing but were rare in adjacent areas among established conspecifics. However, a drought in 1992 (11 mm of rain over 12 months) lead to widespread mortality of the perennial grass, killing 56% (range 22–79%) of established tufts. High densities of Stipagrostis seedlings appeared following the drought-breaking rains in January 1993, both in the disturbed plots and in the surrounding `undisturbed' dune grassland. Ephemeral plants established in large numbers throughout the area during the high rainfall year of 1996 and were generally more numerous in the old disturbances than in control plots. Seven years after clearing the biomass of grass on the cleared plots was approximately 34% of the mass removed from the plots in 1989 whereas in the undisturbed grassland biomass was 66% of 1989 levels. Drought had little long-term effect on community composition, and Stipagrostis ciliata constituted 94–98% of plant community before and after drought. Cleared plots were recolonised by S. ciliata, but the contribution of other grass species increased by 6–9%. Synchronous recruitment following occasional drought-induced mortality can generate even-aged populations of the dominant desert dune grasses.     

Leaf breakdown in a regulated desert river: Colorado River, Arizona, U.S.A.

We compared processing rates (k _d) for leaves of the native willow (Salix exigua Nutt.) and cottonwood (Populus fremontii Wats.) to those of the non-native salt cedar (Tamarix chinensis Lour.) in the regulated Colorado River, U.S.A. Leaf packs of each species were incubated at Lees Ferry, approximately 26 km below Glen Canyon Dam, Arizona. Leaf packs were processed at 2, 21, 46, 84 and 142-d intervals. Water temperatures remained relatively constant (10 °C, SE ± 1 °C) during the study. There were significant differences in processing rates between species, with P. fremontii showing the fastest breakdown. After 142 d, only 20% of the P. fremontii leaf mass remained, whereas 30% and 52% of leaf masses remained for T. chinensis and S. exigua, respectively. The k _d value for P. fremontii was 0.0062 compared to 0.0049 and 0.0038 for T. chinensis and S. exigua, respectively. Invertebrate colonization was not significantly different between native and non-native plant species with oligochaetes the most abundant animal colonizing the leaf packs. Dual stable isotope analysis showed that leaf material was not the primary food for invertebrates associated with leaf packs. Processing rates for all leaf types were slow in the regulated Colorado River compared to rates reported in many other systems. This is likely due to the lack of caddisfly and stonefly shredders and perhaps slow metabolic rates by microbes.     

TCA cycle remodeling drives proinflammatory signaling in humans with pulmonary tuberculosis

The metabolic signaling pathways that drive pathologic tissue inflammation and damage in humans with pulmonary tuberculosis (TB) are not well understood. Using combined methods in plasma high-resolution metabolomics, lipidomics and cytokine profiling from a multicohort study of humans with pulmonary TB disease, we discovered that IL-1β-mediated inflammatory signaling was closely associated with TCA cycle remodeling, characterized by accumulation of the proinflammatory metabolite succinate and decreased concentrations of the anti-inflammatory metabolite itaconate. This inflammatory metabolic response was particularly active in persons with multidrug-resistant (MDR)-TB that received at least 2 months of ineffective treatment and was only reversed after 1 year of appropriate anti-TB chemotherapy. Both succinate and IL-1β were significantly associated with proinflammatory lipid signaling, including increases in the products of phospholipase A2, increased arachidonic acid formation, and metabolism of arachidonic acid to proinflammatory eicosanoids. Together, these results indicate that decreased itaconate and accumulation of succinate and other TCA cycle intermediates is associated with IL-1β-mediated proinflammatory eicosanoid signaling in pulmonary TB disease. These findings support host metabolic remodeling as a key driver of pathologic inflammation in human TB disease.     

Light as a key driver of freshwater biofouling surface roughness in an experimental hydrocanal pipe rig

Biofouling in canals and pipelines used for hydroelectric power generation decreases the flow capacity of conduits. A pipeline rig was designed consisting of test sections of varying substrata (PVC, painted steel) and light levels (transparent, frosted, opaque). Stalk-forming diatoms were abundant in both the frosted and transparent PVC pipes but negligible in the painted steel and opaque PVC pipes. Fungi were slightly more abundant in the painted steel pipe but equally present in all the other pipes while bacterial diversity was similar in all pipes. Photosynthetically functional biofouling (mainly diatoms) was able to develop in near darkness. Different biological fouling compositions generated differing friction factors. The highest friction factor was observed in the transparent pipe (densest diatom fouling), the lowest peak friction for the opaque PVC pipe (lowest fouling biomass), and with the painted steel pipe (high fouling biomass, but composed of fungal and bacterial crusts) being intermediate between the opaque and frosted PVC pipes.     

Hydrologic and geologic factors that influenced spatial variations in loess deposition in China during the last interglacial-glacial cycle: results from proxy climate and GCM analyses

Results from climate proxy and General Circulation Model (GCM) analyses suggest that variations in soil moisture and desert expansion are key hydrologic and geologic factors, respectively, influencing temporal and spatial variations in loess texture and distribution in the Loess Plateau of China. During the last glacial period a reduction in soil moisture led to dune destabilization and a southward expansion of the desert (the source of loess) toward the Loess Plateau. Changes in soil moisture in East Asia may have been influenced by the size and extent of the Fennoscandian ice sheet, and the atmospheric circulation pattern that it induced downstream. These results suggest that both regional factors (i.e. changes in soil moisture and the position of the desert margin) and hemispherical factors (i.e. changes in the size and extent of the Eurasian ice sheets) have influenced loess deposition on the Loess Plateau of China.     

Electrostatic components of drug-receptor recognition. II. The DNA-binding antibiotic actinomycin

The semiempirical molecular orbital method PCILO has been used to study the electronic charge distribution and conformation of the antibiotic actinomycin. Molecular electrostatic potential fields have been constructed in three-dimensional space round the molecule and displayed stereoscopically together with contour maps in the orthogonal planes relative to that of the chromophore. It was found that the drug has a considerable dipole moment and that the electrostatic fields can be separated into two large regions; an area of positive potential surrounds the chromophore and one of negative potential is directed away from the peptide rings. In this and the preceding paper these observations are discussed with respect to drug-receptor recognition phenomena. Pattern-matching of complementary electrostatic fields between the drug and polynucleotide receptor can be discerned.