Effects of throughfall manipulation on soil nutrient status: results of 12 years of sustained wet and dry treatments

To investigate the potential effects of changing precipitation on forest ecosystems, the Throughfall Displacement Experiment (TDE) was established on Walker Branch Watershed, Tennessee, in 1993. Three different throughfall amounts were tested: ?33% (DRY); ambient (no change, AMB); and +33% (WET). Throughfall manipulations had no statistically significant effects on total C, N, exchangeable Ca²⁺, Mg²⁺, bicarbonate‐extractable P, or extractable SO₄^2? in soils after 12 years of sustained treatments. Increased K⁺ inputs in the WET treatment resulted in relative increases in exchangeable K⁺compared with the AMB and DRY treatments. Soil C, N, and extractable P declined in all treatments over the 12‐year study, and the declines in N were inexplicably large. Field observations contrasted with earlier simulations from the Nutrient Cycling Model (NuCM), which predicted greater decreases in exchangeable K⁺, Ca²⁺, Mg²⁺, and extractable P in the order WET>AMB>DRY, and no change in C, N, and extractable SO₄^2?. The failure of the NuCM model to accurately predict observed changes is attributed to the lack of mechanisms for deep rooting and the transfer of throughfall K⁺ from one plot to another in the model. Measurements of element availability using resin membranes during the final years showed higher values in wet and lower values in dry treatments compared with ambient conditions for mineral N, K, Mn, Zn, and Al, but the opposite for B, Ca, and Mg. In the cases of Ca and Mg, the patterns in resin values were similar to those at the soil exchange sites (greatest in the dry treatment) and appeared to reflect pretreatment differences. This study showed that while longer term changes in soil nutrients are likely to occur with changes in precipitation, potential changes over this 12‐year interval were buffered by ecosystem processes such as deep rooting.     

A Dynamic Model for Plant Growth: Validation Study Under Changing Temperatures

A dynamic simulation model to describe vegetative growth ofplants, for which some functions and parameter values have beenestimated previously by optimization search techniques and numericalexperimentation based on data from constant temperature experiments,is validated under conditions of changing temperatures. To testthe predictive capacity of the model, dry matter accumulationin the leaves, stems, and roots of tobacco plants (Nicotianatabacum L.) was measured at 2- or 3-day intervals during a 5-weekperiod when temperatures in controlled-environment rooms wereprogrammed for changes at weekly and daily intervals and inascending or descending sequences within a range of 14 to 34°C. Simulations of dry matter accumulation and distributionwere carried out using the programmed changes for experimentaltemperatures and compared with the measured values. The agreementbetween measured and predicted values was close and indicatesthat the temperature-dependent functional forms derived fromconstant-temperature experiments are adequate for modellingplant growth responses to conditions of changing temperatureswith switching intervals as short as 1 day. Nicotiana tabacum, tobacco, translocation, partitioning, root growth, shoot growth     

Unusual growth in a rugose coral

A small, solitary rugose coral, probably belonging to Aulacophyllum hemicrassatum Sloss, from the Middle Devonian of Iowa, U.S.A., grew normally (conically) for three-fourths of its length, then, in an apparent reversal of pattern, decreased in diameter so that the uppermost part of the corallum is an inverted cone. The reversal of normal growth is attributed to polyp injury or disease that gradually, rather than suddenly, decreased the polyp's ability for normal growth and skeleton building.     

Dynamics of Content and Authorship Patterns in The Wildlife Society Journals (1937–2007)

Abstract: A previous analysis of the content of articles published in The Wildlife Society (TWS) journals from 1937 to 1989 concluded that TWS should strive to publish more articles on nongame and endangered species, ecosystems, habitat fragmentation, and human dimensions. We revisited this analysis and included the years 1990–2007 to determine whether, and how, TWS journals have addressed previous concerns. We also analyzed changes in subject content for TWS journals from 1937 to 2007 using selected terms that we considered indicative of emerging trends within the wildlife profession and society by documenting patterns of use of these terms as key words. Additionally, we evaluated authorship patterns for all TWS journals during 1937–2007 to determine trends in both numbers of authors per article and author affiliations. Our analysis demonstrated that the content of TWS journals has changed over time, and the changes reflected emerging themes in TWS, the wildlife profession, and society. We documented increases in published studies of nongame species and multiple species and articles with multiple authorships representing diverse affiliations. We argue that these patterns reflect a TWS response to shifts in public opinion, policy developments, advances in technology, and changes in university curricula. Although the number of studies published on human dimensions and conservation education has increased over time, these disciplines remained underrepresented.     

Acclimation of thermal physiology in natural populations of Drosophila melanogaster : a test of an optimality model

Many organisms modify their physiological functions by acclimating to changes in their environment. Recent studies of thermal physiology have been influenced by verbal models that fail to consider the selective advantage of acclimation and thus make no predictions about variation in acclimation capacity. We used a quantitative model of optimal plasticity to generate predictions about the capacity of Drosophila melanogaster to acclimate to developmental temperature. This model predicts that the ability to acclimate thermal sensitivity should evolve when temperature varies greatly among generations. Based on the model, we expected that flies from the highly seasonal environment of New Jersey would acclimate thermal sensitivity more than would flies from the less seasonal environment of Florida. When raised at constant and fluctuating temperatures, flies from these populations failed to adjust their thermal optima in the way predicted by the model, suggesting that current assumptions about functional and genetic constraints should be reconsidered.     

Evidence of a Minimum Patch Size Threshold of Reproductive Success in an Endangered Songbird

ABSTRACT That area-sensitive songbirds breed only in relatively large patches suggests that there may be a minimum patch size threshold in which they will breed, even when controlling for the total amount of habitat in the landscape. We searched for minimum patch size thresholds of presence, territory establishment by males, pairing success, and reproductive success for 2 migratory songbirds that differed in sensitivity to patch size: golden-cheeked warblers (Dendroica chrysoparia) and white-eyed vireos (Vireo griseus). We assessed 2 potential limiting factors: brown-headed cowbird (Molothrus ater) parasitism and arthropod biomass (food resource). We determined whether either factor was related to patch size and compared measurements of each above and below the observed thresholds. We monitored 24 golden-cheeked warbler and 47 white-eyed vireo territories in 12 patches. We found evidence of a minimum patch size threshold (between 15.0 ha and 20.1 ha) of reproductive success for golden-cheeked warblers, but not for white-eyed vireos. We found no minimum patch size thresholds for presence, territory establishment by males, or pair formation for either species. Conservation practices based on thresholds of presence, territory establishment, or pair formation might not address issues of reproduction for golden-cheeked warblers. We failed to find evidence that cowbird parasitism or arthropod biomass were limiting factors. The ability to identify patch size thresholds of reproductive success for target species could be useful in conservation and management for setting goals for retention and restoration of target species’ habitat patch size.     

14CO2 Fixation, Translocation, and Carbon Metabolism in Rapidly Expanding Leaves ofPopulus deltoides

To examine ¹⁴CO₂ fixation, potential translocation, and carbonflow among leaf chemical fractions of young developing leaves,the shoot tip of 24-leaf cottonwood (Populus deltoides Bartr.ex. Marsh) plants were cut off under water, placed in artificialxylem sap, and treated with ¹⁴CO₂ in continuous and pulse-chaseexperiments. Additional leaves on whole plants were spot treatedon the lamina tip to follow export from the tip only. The analysedleaves ranged in age from leaf plastochron index(LPI) –5to 3, the spot treated leaves from LPI 2 to 5. After 30 minfixation, the specific activity in the lamina tip increasedlinearly with leaf age from LPI –5 to 1 (0.5 to 4.5 kBqmg^–1). Specific activity in the lower lamina increasedslowly with leaf age and did not reach 500 kBq mg^–1 untilLPI –1. Total ¹⁴CO₂ fixed in the lower lamina exceededthat fixed in the tip by LPI –2 because of the large amountof tissue present in the lower lamina. Although the lamina tipfixed high levels of ¹⁴CO₂, pulse-chase studies coupled withautoradiography indicated no vein loading or translocation fromthe tip until about LPI 4 or 5. The ¹⁴C fixed in both tip andlower lamina was incorporated at the site of fixation and wasnot distributed to younger tissue or translocated from the lamina.Although the percentage distribution (¹⁴C in each chemical fractioncompared with the total in all fractions) of ¹⁴C among certainchemical fractions, e.g. sugars, amino acids and proteins, indicatedthat the mesophyll of the tip was more mature than the lowerlamina, physiologically both leaf sectors were immature basedon the expected ¹⁴C distribution in mature tissue. Informationfrom this and other studies indicates that the extreme tip ofa developing cottonwood leaf first begins to export photosynthateabout LPI 4 or 5 on a 24-leaf plant. The first photosynthatetranslocated may be incorporated into the vascular tissues andmesophyll directly below the tip. However, as the tip continuesto mature photosynthate is translocated past the immature lowerlamina into the petiole and out of the leaf. Populus deltoides Bartr. ex. Marsh, eastern cottonwood, translocation, leaf development, ¹⁴C fixation, carbon metabolism