Edaphic limitations to growth and photosynthesis in Sierran and Great Basin vegetation

Summary Soils derived from hydrothermally altered andesite support unique communities of Sierran conifers (Pinus ponderosa Laws. and P. jeffreyi Grev. and Balf.) amongst sagebrush (Artemisia tridentata Nutt.) vegetation in the western Great Basin. Plants grown in soil derived from hydrothermally altered bedrock had lower growth rates, total biomass, and net photosynthetic rates than plants grown in soil derived from unaltered andesite of the same formation. Total dry mass was 10 to 28% lower for conifers grown in altered soil whereas dry mass of Artemisia tridentata and Bromus tectorum L. was reduced by over 90%. Results from a nutrient amendment experiment indicated that low phosphorus was the dominant limitation in altered soil, and phosphorus-deficiency affected growth primarily by limiting leaf area development rather than direct inhibition of photosynthesis. The proportionately greater reduction of biomass for Artemisia and Bromus grown in altered soil supports our hypothesis that Great Basin vegetation is excluded from altered soil by intolerance to nutrient deficiency. The Sierran conifers growing on this rock type are therefore free of competition for water with Great Basin vegetation and are able to persist in an exceptionally dry climate.     

Nitrogen fixation by subclover associations fertilized with sulfur

Summary The effect of S fertilization on symbiotic N₂ fixation was measured with the¹⁵N technique and the N difference method in a lysimeter study using Josephine loam (Typic Haploxurults). Nitrogen fixation by subclover (Trifolium subterraneum L.) was strongly enhanced by added S. The association of soft chess (Bromus mollis L.) or filaree (Erodium botrys (Cav.) Bertol.) with subclover increased the percentage of N in subclover that was fixed, with the results that N₂ fixation was increased beyond that due to the mere increase in subclover biomass. Nitrogen fixation estimates by¹⁵N dilution and N difference methods were highly correlated (r²=0.97), and S fertilizer did not result in any significant differences in N₂-fixation estimation by the two methods. Both methods were useful in distinguishing between soil N uptake and N₂ fixation where S applications produced highly significant increases in both uptake and fixation. Application of sulfur fertilizers to much annual rangeland has the potential to increase pasture productivity through enhanced N₂ fixation. Contribution of the University of California Hopland Field Station and Department of Agronomy and Range Science, Univ. of California, Davis, CA 95616.     

Biological activity and chemical isolation of root saponins of six cultivars of alfalfa (Medicago sativa L.)

Wheat, cheat and Trichoderma viride bioassays were used to establish the relationship between the content of biologically active saponins in the roots and the degree of winter dormancy and/or time of six cultivars of alfalfa over the period January to August, 1988. Wheat and cheat bioassay results indicated no significant difforences among cultivars, whereas T. viride was inhibited most by extracts of roots collected during months with high rainfall and rapid growth. Cheast seedling roots were inhibited 8–10% more than those of wheat seedling roots indicating that alfalfa root saponins were more effective as allelopathic compounds in preventing growth of cheat than that of wheat alone. An average of 14 different saponins per cultivar were separated by thin-layer chromatograms. Saponins, and the aglycones produced by acid hydrolysis of the May samples, were separated by thin-layer chromatography. The conclusion is that the amount, structure, and type of saponins present in alfalfa roots vary with time.     

Responses to fertility and disturbance in a low-diversity grassland

We examined variation in species composition in a low-diversity, anthropogenic grassland in response to 11 years of nitrogen (N) manipulation and disturbance. The species-poor grassland (2–3 species/0.5 m²) represents a wide spread vegetation type (>10 million ha in North America) dominated by the introduced perennial grasses Bromus inermis and Agropyron cristatum. Four levels of N and three of soil disturbance were applied in all combinations to plots (5 × 15 m, N = 120) in a completely randomized design each year. Seeds or transplants of 47 species were added to ensure that dispersal was not a barrier to changes in species composition. After 11 years of treatment, all but the most disturbed plots continued to be dominated by B. inermis. The cover of the second-most abundant species, A. cristatum, decreased with disturbance but did not vary significantly with N. Despite the lack of changes in the identity of the dominant species, our environmental manipulations strongly influenced ecosystem characteristics. Added N increased soil available N, and decreased the cover of bare ground and light availability. Soil disturbance decreased aboveground biomass, and increased the cover of bare ground and light availability. Sawdust application, designed to decrease N availability, significantly reduced community biomass, and increased light availability and the cover of bare ground, but did not alter nutrient availability or species composition. The results highlight the difficulty of restoring diversity in species-poor, anthropogenic communities dominated by introduced species, and thus the importance of conserving remnants of diverse natural grasslands.     

Genetic Diversity of Chinese Water Deer (Hydropotes inermis inermis): Implications for Conservation

The Chinese water deer (Hydropotes inermis inermis) is endemic to China. Historically, the species was widely distributed, but now, habitat loss and poaching have reduced its range and number drastically. In order to provide useful information for its conservation, we have investigated the genetic diversity and population structure of the Chinese water deer by analyzing the 403 bp fragment of the mitochondrial DNA (mtDNA) control region (D-loop). Eighteen different haplotypes were detected in 40 samples. Overall, Chinese water deer have a relatively high-genetic diversity compared to other rare cervid species, with a haplotype diversity of 0.923±0.025 and nucleotide diversity of 1.318 ± 0.146%. No obvious phylogenetic structure among haplotypes was found for samples of different origin. An analysis of molecular variance (AMOVA) showed significant differentiation between the Zhoushan and the mainland population (F_ST= 0.088, P < 0.001; Φ _ST = 0.075, P = 0.043), which suggests that exchanges of individuals between Zhoushan and the mainland should be avoided. We also recommend that a breeding center be set up for the mainland population.     

When Invasive Plants Disappear: Transformative Restoration Possibilities in the Western United States Resulting from Climate Change

Most ecologists believe that climate change poses a significant threat to the persistence of native species. However, in some areas climate change may reduce or eliminate non-native invasive species, creating opportunities for restoration. If invasive species are no longer suited to novel climate conditions, the native communities that they replaced may not be viable either. If neither invasive nor native species are climatically viable, a type of "transformative" restoration will be required, involving the translocation of novel species that can survive and reproduce under new climate conditions. Here, we illustrate one approach for restoration planning by using bioclimatic envelope modeling to identify restoration opportunities in the western United States, where the invasive plant cheatgrass ( Bromus tectorum ) is no longer climatically viable under 2100 conditions projected by the Geophysical Fluid Dynamics Laboratory (GFDL2.1) coupled atmosphere-ocean general circulation model. We then select one example of a restoration target area and identify novel plant species that could become viable at the site in the wake of climate change. We do so by identifying the closest sites that currently have climate conditions similar to those projected at the restoration target area in 2100. This approach is a first step toward identifying appropriate species for transformative restoration.     

Does prescribed burning mean a threat to the rare satyrine butterfly Hipparchia fagi? Larval-habitat preferences give the answer

The ecological effects of fire management, especially regarding arthropods are poorly investigated. Burning in winter was assumed to pose a threat to butterfly species hibernating as larvae. To assess the impact of prescribed burning on population viability, we analysed larval-habitat preferences of the highly endangered, xero-thermophilous butterfly Hipparchia fagi in vineyards of the Kaiserstuhl region (southern Germany). Microhabitat preference analyses for mature larvae and egg-laying females revealed a preference of H. fagi for Bromus erectus-dominated communities with sparse vegetation coverage and a distinct tuft growth of the host plant B. erectus on microclimatically benefited slopes. We explain the preference of B. erectus by a preference of vegetation structure. The grass tufts offer a suitable climatically buffered living space for larvae. Egg deposition took place on dry substrate at positions of high solar radiation, thus adapted to hot and dry microclimate. As the larval habitat was sparsely vegetated as well as generally legally protected, fire management was not applicable and therefore not affecting the populations. We think it is conceivable that H. fagi, occurring here at its northern range limit, might expand its larval habitat into denser, combustible B. erectus stands in the course of global warming. A change in habitat preferences would necessitate a re-evaluation of management options.