Para-nitrophenyl Phosphate as a Substrate for Some Acid Phosphatases in Roots of Vicia faba

A cytochemical and biochemical study of acid phosphatases inroots of Vicia faba using p-nitrophenylphosphate(p-NPP) as substratehas shown the lack of specificity of the substrate which canbe acted upon by a K⁺-activated acyl phosphatase, nucleotidepyrophosphatase, glucox-6-phosphatase, 5' (3')-ribonucleotidephosphohydrolase, nucleotide phosph-transferase and those acidphosphatases demonstrable with ß-glycerophosphate.It is suggested that care should be taken in the interpretationof both biochemical and cytochemical studies employing sucha non-specific substrate as P-NPP. Vicia faba, broad bean, root, acid phosphatases     

Scale and uncertainty in modeled soil organic carbon stock changes for US croplands using a process‐based model

Process‐based model analyses are often used to estimate changes in soil organic carbon (SOC), particularly at regional to continental scales. However, uncertainties are rarely evaluated, and so it is difficult to determine how much confidence can be placed in the results. Our objective was to quantify uncertainties across multiple scales in a process‐based model analysis, and provide 95% confidence intervals for the estimates. Specifically, we used the Century ecosystem model to estimate changes in SOC stocks for US croplands during the 1990s, addressing uncertainties in model inputs, structure and scaling of results from point locations to regions and the entire country. Overall, SOC stocks increased in US croplands by 14.6 Tg C yr^?1 from 1990 to 1995 and 17.5 Tg C yr^?1 during 1995 to 2000, and uncertainties were ±22% and ±16% for the two time periods, respectively. Uncertainties were inversely related to spatial scale, with median uncertainties at the regional scale estimated at ±118% and ±114% during the early and latter part of 1990s, and even higher at the site scale with estimates at ±739% and ±674% for the time periods, respectively. This relationship appeared to be driven by the amount of the SOC stock change; changes in stocks that exceeded 200 Gg C yr^?1 represented a threshold where uncertainties were always lower than ±100%. Consequently, the amount of uncertainty in estimates derived from process‐based models will partly depend on the level of SOC accumulation or loss. In general, the majority of uncertainty was associated with model structure in this application, and so attaining higher levels of precision in the estimates will largely depend on improving the model algorithms and parameterization, as well as increasing the number of measurement sites used to evaluate the structural uncertainty.     

Causes of vertical stratification in the density of Cameraria hamadryadella

1. The density of Cameraria hamadryadella, a leaf-mining moth, is vertically stratified within the crown of oak trees. It occurs at higher densities on foliage in the lower crown. 2. Oviposition preference tests indicate that females display no preference to oviposit on foliage from the lower tree crown over foliage from the upper tree crown. 3. Experiments in which potted trees were placed at various heights indicate that foliage nearest ground level receives more oviposition, and that the higher rates of oviposition on foliage near the ground is not caused by differences in quality between foliage from low or high in the tree crown. 4. Host-plant- and natural-enemy-mediated juvenile mortality and the abundance of parasitoids did not differ between the upper and lower crown. 5. Vertical differences in the timing of leaf production within the tree crown are unlikely to account for the observed gradient in the abundance of C. hamadryadella. Furthermore, the mean date of leaf fall does not differ among heights within the tree crown. 6. It is argued that microclimatic gradients and interspecific competition are also unlikely to account for the observed gradients in the density of C. hamadryadella within the tree crown. 7. Because of the absence of effects of other potentially causal factors, the most likely explanation for the gradient in density of C. hamadryadella is a lack of movement by females into the upper tree crown from overwintering, emergence, or resting sites located in the lower tree crown, combined with egg depletion by females as they move from the lower to the upper tree crown. 8. It is suggested that the lack of movement and egg depletion hypothesis should serve as the null hypothesis in studies of vertical stratification of tree-feeding insects. In the absence of evidence of an effect of foliage quality, natural enemies, plant phenology, interspecific competition, or microclimate, the movement and egg depletion hypothesis is the most reasonable.     

Alliance and Conflict: The World System of the Iñupiaq Eskimos

Alliance and Conflict: The World System of the Iñupiaq Eskimos. Ernest S. Burch Jr. Lincoln: University of Nebraska Press, 2005.     

Effects of tree height on branch hydraulics, leaf structure and gas exchange in California redwoods

We examined changes in branch hydraulic, leaf structure and gas exchange properties in coast redwood ( Sequoia sempervirens ) and giant sequoia ( Sequoiadendron giganteum ) trees of different sizes. Leaf-specific hydraulic conductivity ( k _L) increased with height in S. sempervirens but not in S. giganteum , while xylem cavitation resistance increased with height in both species. Despite hydraulic adjustments, leaf mass per unit area (LMA) and leaf carbon isotope ratios ( δ ¹³C) increased, and maximum mass-based stomatal conductance ( g _mass) and photosynthesis ( A _mass) decreased with height in both species. As a result, both A _mass and g _mass were negatively correlated with branch hydraulic properties in S. sempervirens and uncorrelated in S. giganteum . In addition, A _mass and g _mass were negatively correlated with LMA in both species, which we attributed to the effects of decreasing leaf internal CO₂ conductance ( g _i). Species-level differences in wood density, LMA and area-based gas exchange capacity constrained other structural and physiological properties, with S. sempervirens exhibiting increased branch water transport efficiency and S. giganteum exhibiting increased leaf-level water-use efficiency with increasing height. Our results reveal different adaptive strategies for the two redwoods that help them compensate for constraints associated with growing taller, and reflect contrasting environmental conditions each species faces in its native habitat.