Reduced N cycling in response to elevated CO2, warming,and drought in a Danish heathland: Synthesizing results of the CLIMAITE project after two years of treatments

Field‐scale experiments simulating realistic future climate scenarios are important tools for investigating the effects of current and future climate changes on ecosystem functioning and biogeochemical cycling. We exposed a seminatural Danish heathland ecosystem to elevated atmospheric carbon dioxide (CO₂), warming, and extended summer drought in all combinations. Here, we report on the short‐term responses of the nitrogen (N) cycle after 2 years of treatments. Elevated CO₂ significantly affected aboveground stoichiometry by increasing the carbon to nitrogen (C/N) ratios in the leaves of both co‐dominant species (Calluna vulgaris and Deschampsia flexuosa), as well as the C/N ratios of Calluna flowers and by reducing the N concentration of Deschampsia litter. Belowground, elevated CO₂ had only minor effects, whereas warming increased N turnover, as indicated by increased rates of microbial NH₄⁺ consumption, gross mineralization, potential nitrification, denitrification and N₂O emissions. Drought reduced belowground gross N mineralization and decreased fauna N mass and fauna N mineralization. Leaching was unaffected by treatments but was significantly higher across all treatments in the second year than in the much drier first year indicating that ecosystem N loss is highly sensitive to changes and variability in amount and timing of precipitation. Interactions between treatments were common and although some synergistic effects were observed, antagonism dominated the interactive responses in treatment combinations, i.e. responses were smaller in combinations than in single treatments. Nonetheless, increased C/N ratios of photosynthetic tissue in response to elevated CO₂, as well as drought‐induced decreases in litter N production and fauna N mineralization prevailed in the full treatment combination. Overall, the simulated future climate scenario therefore lead to reduced N turnover, which could act to reduce the potential growth response of plants to elevated atmospheric CO₂ concentration.     

Cranial and appendicular ontogeny of Bactrosaurus johnsoni,a hadrosauroid dinosaur from the Late Cretaceous of northern China

Abstract: The juvenile anatomy of various cranial and appendicular elements of the hadrosauroid dinosaur Bactrosaurus johnsoni is described in detail. Growth changes are documented from juvenile to adult stages for each skeletal element available. In the studied skull, ontogenetic trends consist of: development of features on the ventral surface of the frontal; reduction in the slope of the posteromedial process of the premaxilla; a posterior shift of the dorsal process of the maxilla; development of concavities on the medial surface of the prefrontal; increased robustness and development of the ventral flange of the jugal; decreased curvature of the long axis of the quadrate; increased ventral deflection of the dentary; and changes in the length/width proportions and depth of the anterior surface of the predentary. In the appendicular skeleton, the majority of ontogenetic variation from juvenile to adult occurs in the limb bones, including increased robustness of the deltopectoral crest of the humerus; relative shortening of the ulna; increased development of the fourth trochanter and mediolateral widening of the distal end of the femur; increased expansion of the cnemial crest of the tibia; and the increased prominence of articular protuberances and flanges of the metatarsals. A survey of the phylogenetically informative characters present in B. johnsoni indicates that several characters concerning the frontal, maxilla, jugal, quadrate, predentary, dentary, scapula, humerus and ilium are affected by ontogeny. Nevertheless, the majority of phylogenetic characters are not ontogenetically variable, suggesting that a substantial amount of the information provided by juvenile and subadult specimens for phylogenetic inference is reliable in basal hadrosauroids.     

The Germination of Vavraia culicis Spores1

Buffered solutions of KCl and NaCl were tested for their stimulatory effect on the germination of variously-aged spores of Vavraia culicis. Germination was optimal in 0.2 M KCl, pH 6.5 for one isolate, and, for another isolate, peaks of germination occurred at pH 7.0 and 9.5. Spores incubated for several hours in suboptimal solutions became unable to germinate under optimal conditions. After being returned to water, they regained their ability to germinate. Calcium chloride, magnesium chloride, and ammonium chloride inhibited germination. After ingestion by mosquito larvae, spores germinated near the posterior end of the midgut.     

Factors Affecting Shedding of Flowers in Soybean (Glycine max (L.) Merrill)

Flower shedding in soybean, Glycine max (L.) Merrill, was studiedusing cultivar ‘Clark’, isoline E₁t, which has relativelylong racemes for convenient identification and observation ofindividual flowers. On each raceme studied, pod set was greatestat the proximal (basal) positions, whereas shedding was greatestat the most distal positions. When proximal flowers were removedas they reached anthesis, pod set increased at the more distalpositions. Pod set was increased in some instances by applicationof water directly to the ovaries as a drop in the calyx cup.Peroxidase activity changed in parallel with ovary development,increasing rapidly in growing pods but not in shedding flowers.Increases in flower peroxidase was mainly in ovary walls. Flowerstaken at or near anthesis from positions with high percent podset could be grown in vitro with especially good ovary enlargement,whereas ovaries in flowers taken from positions of low pod setdid not enlarge in culture. Unidentified substances were extracted from young pods which,when incorporated into lanolin and tested in an in situ bioassay,could mimic the effect of proximal flowers in inducing sheddingof distal flowers. Indole-3-acetic acid resembled the extractedmaterials in inducing shedding, but differed by eliciting side-effectsthat extracts did not. The growth substances abscisic acid,gibberellic acid, and benzyladenine did not promote sheddingin the in situ test. The evidence was taken to indicate that soybean flower sheddingis induced in distal flowers by substances from the more proximal,fertilized ovaries, and that this is possibly due to interferencewith some of the intense metabolic changes that follow pollinationand fertilization.     

SOME OBSERVATION ON AIR-ION-ENHANCED IRON CHLOROSIS IN BARLEY (HORDEUM VULGARIS) SEEDLINGS

The air ion effects on "active" and "residual" iron distributionin barley seedlings were studied in the course of the developmentof ironchlorosis in an iron-free culture medium. "Active" or"acid soluble" iron plays an important role for chlorophyllbiosynthesis and is extractable with 1.0 N HCl from dried tissues,and "residual" or "acid insoluble" iron does not participatein this chlorophyll formation process and is not extracted with1.0 N HCl. Ions of either charge induced a significant decrease in activeiron content which was associated with a decrease in chlorophyllcontent. Concomitantly, there occurred an increase in both theresidual iron and the cytochrome c fractions. The increase inresidual iron content may involve not only cytochrome c butalso other cytochromes and ironcontaining enzymes as well. Theauthors have proposed a hypothesis that the site of air ionaction in the experiments reported may be the regulatory systemscontrolling iron metabolism in the seed and young seedling.Through this action air ions apparently divert more endogenousfree-state iron to residual iron (consisting of cytochromesand Fe-containing enzymes) than to active iron. Tracer experiments showed that air ions enhanced the uptakeof exogenous iron by early germinating barley seeds. The increasedincorporation of iron was not influenced by light. (Received December 10, 1964; )     

The influence of fish on leaf breakdown in a Virginia pond

1. To find if fish affect leaf breakdown, sugar maple leaves ( Acer sacchrum March) were placed in a soft-water, farm pond at a depth of 1 m for up to 3 months in four treatment groups: (1) enclosure with sunfish (Lepomis macrochirus Rafinesque) (SUNFISH treatment); (2) enclosure with catfish ( Ictalurus punctatus Rafinesque) (CATFISH treatment); (3) enclosure without fish (NO FISH treatment); and (4) no enclosure (OPEN treatment). The study was conducted in spring and autumn.
2. The leaf breakdown rates, k ±95% CL, for SUNFISH (0.0082± 0.00059 and 0.0111±0.00162 d⁻¹) and CATFISH (0.0072±0.00096 and 0.0103±0.00077 d⁻¹) were greater in spring and summer, respectively, than in the OPEN treatments (0.0065 ±0.00048 and 0.0105± 0.00141 d⁻¹) and NO FISH (0.0067±0.00039 and 0.0088±0.00099 d⁻¹). However, only k for SUNFISH was significantly different from NO FISH and OPEN treatments.
3. Fish in the pond did not appear to affect breakdown rates of OPEN leaf packs in the first replicate but k approached that of the fish treatments in the second replicate.
4. Fish may have promoted leaf breakdown directly by fragmentation of leaves while foraging for food and, indirectly, by agitation of leaves, leading to increased microbial activity.