Effects of elevated atmospheric CO2 on fine root length and distribution in an oak-palmetto scrub ecosystem in central Florida

Atmospheric CO₂ concentration is rising and it has been suggested that a portion of the additional carbon is being sequestered in terrestrial vegetation and much of that in below-ground structures. The objective of the present study was to quantify the effects of elevated atmospheric CO₂ on fine root length and distribution with depth with minirhizotrons in an open-top chamber experiment in an oak-palmetto scrub ecosystem at Kennedy Space Centre, Florida, USA. Observations were made five times over a period of one and a half years in three ambient chambers (350 p.p.m. CO₂), three CO₂ enriched chambers (700 p.p.m. CO₂), and three unchambered plots. Greater root length densities were produced in the elevated CO₂ chambers (14.2 mm cm^?2) compared to the ambient chambers (8.7 mm cm^?2). More roots may presumably lead to more efficient acquisition of resources. Fine root abundance varied significantly with soil depth, and there appeared to be enhanced proliferation of fine roots near the surface (0–12 cm) and at greater depth (49–61 cm) in the elevated CO₂ chambers. The vertical root distribution pattern may be a response to availability of nutrients and water. More studies are needed to determine if increased root length under CO₂ enriched conditions actually results in greater sequestering of carbon below ground.     

The influence of diet on growth and secretion behaviour of myrmecophilous Polyommatus icarus caterpillars (Lepidoptera: Lycaenidae)

Abstract.

• 1 Caterpillars of the facultatively myrmecophilous butterfly Polyommatus icarus were reared on inflorescences, or foliage, of four natural hostplant species and on an artificial diet to study dietary effects on larval growth and secretory capacity.
• 2 Caterpillars achieved highest weights and relative growth rates when fed flowers of Medicago sativa, Lotus corniculatus or Melilotus officinalis. Larvae reared on Coroniüa varia (flowers and leaves), foliage of M.sativa and on the artificial diet pupated at lower weights and achieved lower growth rates.
• 3 In standardized experiments with the ant species Lasius flavus, secretion rates from the dorsal nectar organ (DNO) were 2 times higher among flower-fed caterpillars than among foliage-fed siblings or caterpillars on the artificial diet. Larvae reared on C.varia flowers were superior to all other food treatments with respect to secretion rates.
• 4 High water content of larval diet, as in flowers, appears to be important for lycaenid caterpillars to achieve high secretion rates, whereas the correlation between myrmecophily and nutrient availability, as evidenced by growth rates, was less pronounced.
• 5 Using experimental data on larval growth and secretion rates, the lifetime volume of secretions from the DNO is estimated to range from 2 to 5 μl in most food treatments. Only on C.varia flowers (5.5–8.7 μl) and on M.sativa leaves (0.9–1.1 μl) did the caterpillars deviate in their absolute investment in myrmecophily.
• 6 The estimated lifetime investment accounted for 1.6–5.5% of prepupal fresh weight in all food treatments except on C.varia flowers (7.8–12.3%).

     

Specificity of the Glucose Transport System in Leishmania tropica Promastigotes*

SYNOPSIS. The glucose transport system in Leishmania tropica promastigotes was characterized by the use of labeled 2-deoxy-D-glucose (2-DOG), a nonmetabolizable glucose analog. The uptake system has a Q₁₀ of 2 and a heat of activation of 10.2 kcal/mole. The glucose transport system is subject to competitive inhibition by 2-DOG, glucosamine, N-acetyl glucosamine, mannose, galactose, and fructose which suggests that substitutions in the hexose chain at carbons 2 and 4 do not affect carrier specificity. In contrast, changes at carbon 1 (α-methyl-D-glucoside, 1,5-anhydroglucitol) and carbon 3 (3–0-methyl glucose) lead to loss of carrier affinity since these sugars do not compete for the glucose carrier. Sugars that compete with the glucose carrier have one common feature—they all exist in the pyranose form in solution. The carrier for D-glucose does not interact with L-glucose or any of the pentose sugars tested. Uptake of 2-DOG is inhibited by glycerol. This inhibition, however, is noncompetitive; it is evident, therefore, that glucose and glycerol do not compete for the same carrier. Glycerol does not repress the glucose carrier since cells grown in presence of glycerol transport the sugar normally.     

Hormonal factors controlling the initiation and development of lateral roots

The decapitated primary root of 3-day-old Alaska pea seedlings has been used as a test system to determine the activities on lateral root formation of six auxins, six cytokinins and several other naturally-occurring compounds. Their effects were assessed on (1) the initiation of lateral root primordia, (2) the emergence of visible lateral roots, and (3) the elongation of these laterals. All the auxins, at the optimum concentration of 10^-4M, promoted the initiation of lateral root primordia, and all except 3-indolylpropionic acid inhibited the elongation of the resulting lateral roots. Their effects on the emergence of laterals were small and varied. All the cytokinins, at 10^-6M and above, inhibited both the initiation and the emergence of lateral roots, zeatin being the most powerful inhibitor. The emergence process was about twice as sensitive as the initiation of primordia to the presence of cytokinins. The cytokinin ribosides were generally less active than the free bases. Abscisic acid and xanthoxin inhibited both emergence and elongation, the concentration for 50% decrease of emergence being about 10^-4M. Gibberellic acid had little clear effect on any of the three criteria. Nicotinic acid and thiamine at 10^-3M promoted both the initiation of primordia and their emergence: pyridoxal phosphate stimulated both emergence and elongation but did not influence the initiation of primordia. Adenine and guanine had little effect but decreased root elongation some 25%. The strong inhibiting effect of the cytokinins may well be the basis for the marked inhibition exerted by the root-tip on lateral root formation, while the promoting effects of auxins may explain the previously observed promotion of lateral root formation by the young shoot and cotyledons.     

Structure of Labyrinthula sp. Zoospores*

SYNOPSIS. A species of Labyrinthula closely resembling L. algeriensis was isolated from marsh grass, Spartina alterniflora. Zoosporulation was obtained in ～50% of the cultures, which were grown on a modified Vishniac medium, when yeasts were used as food organisms; when the temperature was ～22 C; when thiamine (0.2 mg/l, biotin (1 μg/l, Ba (1 μg/l, and cholesterol (5 mg/l) were present; and when the cells were grown on a semisolid medium (0.6% agar) rather than higher concentrations of agar. The motile cells were similar to biflagellated fungal zoospores in that they were pyriform and laterally biflagellated. The anterior flagellum (13-15 μ long) possessed what appeared to be 2 rows of mastigonemes and was uniform in diameter while the posterior flagellum (6-10 μ) lacked mastigonemes and was tapered distally into a whiplash. The planonts are apparently not isogametes since planogametic copulation could not be induced and since synaptinemal complexes were not observed in sectioned presporangia.     

Two‐step vegetation response to enhanced precipitation in Northeast Brazil during Heinrich event 1

High resolution palynological and geochemical data of sediment core GeoB 3910‐2 (located offshore Northeast Brazil) spanning the period between 19 600 and 14 500 calibrated year bp (19.6–14.5 ka) show a land‐cover change in the catchment area of local rivers in two steps related to changes in precipitation associated with Heinrich Event 1 (H1 stadial). At the end of the last glacial maximum, the landscape in semi‐arid Northeast Brazil was dominated by a very dry type of caatinga vegetation, mainly composed of grasslands with some herbs and shrubs. After 18 ka, considerably more humid conditions are suggested by changes in the vegetation and by C_org and C/N data indicative of fluvial erosion. The caatinga became wetter and along lakes and rivers, sedges and gallery forest expanded. The most humid period was recorded between 16.5 and 15 ka, when humid gallery (and floodplain) forest and even small patches of mountainous Atlantic rain forest occurred together with dry forest, the latter being considered as a rather lush type of caatinga vegetation. During this humid phase erosion decreased as less lithogenic material and more organic terrestrial material were deposited on the continental slope of northern Brazil. After 15 ka arid conditions returned. During the humid second phase of the H1 stadial, a rich variety of landscapes existed in Northeast Brazil and during the drier periods small pockets of forest could probably survive in favorable spots, which would have increased the resilience of the forest to climate change.