Effects of warming and nutrients on sediment community respiration in shallow lakes: an outdoor mesocosm experiment

1. Climate warming is expected to change respiration in shallow lakes but to an extent that depends on nutrient state. 2. We measured sediment respiration (SR) over the season in the dark on intact sediment cores taken from a series of flow‐through, heated and unheated, nutrient‐enriched and unenriched mesocosms. The natural seasonal temperature cycle ranged from 2 to 20 °C in the unheated mesocosms. In the heated mesocosms, the temperature was raised 4–6 °C above ambient temperatures, depending on season, following the A2 climate change scenario downscaled to the local position of the mesocosms, but enlarged by 50%. We further measured ecosystem respiration (ER) in the mesocosms based on semi‐continuous oxygen measurements. 3. SR changed over the season and was approximately ten times higher in summer than in winter. SR showed no clear response to warming in the nutrient‐enriched treatment, while it increased with warming in the unenriched mesocosms which also had lower fish densities. 4. ER was not affected by artificial warming or nutrient enrichment, but it was ten times higher in summer than in winter. 5. SR contributed 24–32% to ER. The SR:ER ratio was generally stimulated by warming and was higher in winter than in summer, especially in the nutrient‐enriched mesocosms. 6. Our results indicate that climate warming may lead to higher SR, especially in clear, macrophyte‐dominated systems. Moreover, the contribution of SR to ER will increase with higher temperatures, but decrease as the winters get shorter.     

The Starch Statolith Hypothesis and the Optimum Angle of Geotropic Stimulation

When roots of cress seedlings (Lepidium sativum L.) are stimulated for 10 min at an angle of 135° (i.e. the root tips are pointing obliquely upward), the resulting geotropic curvatures become larger than after 10 min stimulation at 45°. This well-known behavior has been explained by the better conditions for statoliths, initially located in the floor end of the statocytes, to slide along the cell walls when root tips are pointing upward at 135° than when pointing downward at 45°. Accepting this explanation, one would predict the optimum angle of stimulation to be near 45° when roots had first been kept inverted long enough for their statoliths to accumulate in the opposite end of each functional statocyte. This prediction has been verified in experiments with cress seedlings which were first kept inverted for 16 min, then stimulated for 10 min at given angles, and subsequently rotated parallel to the horizontal axis of the klinostat at 2 rpm. Under these conditions, roots stimulated at 45° curve faster during a 20 to 30 min period on the klinostat than roots stimulated at 135°, but thereafter they stop curving. Roots stimulated at 135°, on the other hand, although initially curving slower than those at 45°, continue curving for at least a whole hour, and attain larger curvatures than the others after 40 min. The optimum shifts from near 45° to near 135° during the course of the klinostat rotation. The behavior of normal and pre-invertcd roots is interpreted as the result of at least two effects: (1) a stimulation due to the movement of amyloplasts, which is enhanced if these are allowed to slide along the cell walls, and (2) a modification of the development of the resulting curvatures by tonic effects, which are inhibitory between stimulation angles 0° and 90°, and absent or enhancing between 90° and 180°.     

Production of alloantibodies against caprine lymphocyte antigens

In all, 217 primiparous goats were each injected with blood cells from their own newborn kid. Eighty-five goats were given mononuclear cells, 61 were given leucocytes and 71 received whole blood. The goats were injected one, two or three times before collection of sera. Sera were also collected from 42 non-injected, primiparous goats. The sera were compared with regard to their potential value in class I histocompatibility typing. The percentage of potentially valuable sera was highest in the group of animals injected twice with whole blood (66 X 7%). However, this percentage was not significantly higher than the percentage in the group of animals injected once with whole blood (54 X 7%). It is concluded that injecting primiparous goats once with whole blood from their own newborn kid, is a rapid and easy method, which gives a high yield of alloantisera with potential value in class I histocompatibility typing.     

Effect of Abscisic Acid on the Transpiration of Zea mays

Intact plants of Zea mays L. were treated with foliar sprays of cis-trans-abscisic acid (ABA) at concentrations from 10⁻⁹ to 10⁻⁴M. Even the lowest concentration caused a reduction of the transpiration rate as measured between 1 and 33 h after spraying. With increasing ABA concentrations, there was a nearly linear relationship between the logarithm of the ABA concentration and the (decreasing) transpiration rate within that period. Subsequently a partial recovery of the transpiration rate set in, beginning progressively later as the ABA concentration was increased. After 5 1/2 days the transpiration rate of plants treated with 10⁻⁹ and 10⁻⁸M was nearly back to normal, whereas plants treated with 10⁻⁴M transpiration at only about 2/3 their normal rate. In experiments with detached maize leaves supplied with water or ABA solutions (10⁻⁸ to 10⁻⁵M) through their cut bases, the transpiration of control leaves decreased gradually to a low level in 24 h. ABA caused a marked and rapid reduction of the transpiration rate compared to that of the controls. After a few hours, the transpiration of the treated leaves decreased at a slower rate than that of the controls, thus approaching the control values. After 35 h, the transpiration of leaves treated with 10⁻⁵M ABA was nearly the same as in untreated leaves. Exchanging the ABA solution for distilled water after 24 h had little effect on the subsequent course of the transpiration rate.     

Differences in the Responses to Water Stress of Growing and Non-Growing Regions of Maize Mesocotyls: Protein Synthesis on Total, Free and Membrane-Bound Polyribosome Fractions

The growing and non-growing regions of the mesocotyl of youngmaize seedlings show different responses to water stress withrespect to their ability to retain polyribosomes. The growingregion shows a marked reduction in total polyribosomes, althoughsome are retained within the stressed tissue. In the non-growingregion there is little stress-induced change to the total polyribosomecontent. These results support the contention that physiologicallyyounger, growing tissues are more sensitive to water stressthan more mature tissues that have ceased to grow. The free(FP) and membrane-bound (MBP) polyribosome content of the growingmesocotyl region is considerably greater than that of the non-growingregion, which is indicative of their more active metabolism.Both the MBP and FP fractions decline when the cells of thegrowing region are subjected to stress: no differential sensitivityis evident. Hence any qualitative changes in protein synthesisinduced by stress must be expected to result from changes inactivity of both polyribosome fractions. In the stressed non-growingregion, FP decline slightly, but MBP exhibit no consistent changes.     

A field technique for the determination of zooplankton grazing on natural bacterioplankton

SUMMARY. 1. A method for the determination of zooplankton community grazing rates on natural populations of bacteria is described.
2. Undisturbed zooplankton samples were incubated with ³H-thymidine-labelled bac teriioplankton, and animals and their food subsequently separated by size.
3. Prehandling of zooplankton by concentration before incubation reduce the grazing rates by a factor ranging from three to four.
4. Time series experiments showed that appropriate incubation periods ranged from 40 min at 14°C to 60 min at 10°C.
5. Spatial variability in the zooplankton was the main source of the overall standard error. This was considerably reduced by using composite samples.     

Cessation of Protein Synthesis in Water-Stressed Pea Roots and Maize Mesocotyls without loss of Polyribosomes. Effects of Lethal and Non-Lethal Water Stress

Pea roots and maize mesocotyl segments retain polyribosomeswhen subjected to mild and moderate water stress. Even underwater-stress conditions that are lethal, i.e. where there isno recovery of protein synthesis upon return to full hydration,some polyribosomes are retained. Therefore cessation of proteinsynthesis under water stress conditions is not due to the inabilityof cells to retain their polyribosomes. This observation contradictsseveral previous reports. The polynbosome content of PEG-stressedroots is lower, at equivalent water potentials, than that ofair-dried roots. We suggest that the capacity of a higher planttissue to withstand water stress cannot easily be correlatedwith its capacity to retain polyribosomes.     

Lymphocyte antigens in Norwegian goats: serological and genetic studies

Altogether, 292 goat alloantisera were screened for antilymphocyte reactivity in a two-step dye exclusion microcytotoxicity test. Fifteen different lymphocyte antigen specificities were characterized by cluster analysis and absorption studies. The specificities were designated N1-N15 (N for Norwegian). Lymphocytes from 247 Norwegian dairy goats were tested. Each animal displayed from none to four of the characterized specificities. Lysostrip testing and family studies indicated that the specificities N1-N14 were coded for by multiple alleles belonging to at least two closely linked loci. It is suggested that these loci are part of the caprine major histocompatibility complex. Family studies gave strong evidence that the specificity N15 was not coded for by genes located in the same region as the other 14 specificities. Absorption studies showed that this specificity was located on both lymphocytes and erythrocytes.