The utilization of nitrogen from insect capture by different growth forms of Drosera from Southwest Australia

Summary Plants of Drosera species, neighbouring noncarnivorous plants, and arthropods on or near each Drosera sp. were collected at 11 contrasting habitat locations in SW Australia. At three of the sites clones of the rare glandless mutant form of D. erythrorhiza were collected alongside fully glandular counterparts. The ¹⁵N value (¹⁵N/¹⁴N natural isotope composition) of insect-free leaf and stem fractions was measured, and the data then used to estimate proportional dependence on insect N (%N_dI) for the respective species and growth forms of Drosera. The data indicated lower %N_dI values for rosette than for self-supporting erect or for climbing vine species. The latter two groups showed an average %N_dI value close to 50%. The %N_dI increased with length and biomass of climbing but not erect forms of Drosera. ¹⁵N values of stems were positively correlated with corresponding values for leaves of Drosera. Leaf material was on average significantly more ¹⁵N enriched than stems, possibly due to delayed transport of recent insect-derived N, or to discrimination against ¹⁵N in transfer from leaf to the rest of the plant. The comparison of ¹⁵N values of insects and arthropod prey, glandless and glandular plants of D. erythrorhiza indicated %N_dI values of 14.3, 12.2 and 32.2 at the respective sites, while matching comparisons based on ¹⁵N of insect, reference plants and glandular plants proved less definitive, with only one site recording a positive %N_dI (value of 10.4%) despite evidence at all sites of feeding on insects by the glandular plants. The use of the ¹⁵N technique for studying nutrition of carnivorous species and the ecological significance of insect feeding of different growth forms of Drosera growing in a large range of habitats is discussed.     

Carbon isotope composition of CH4 from rice paddies in Japan

Carbon isotope ratios (¹³C) for bubble CH₄ in a submerged paddy soil were studied in Yokohama, Japan, throughout a growing period, and its variation was found. Bubble CH₄ collected from other 33 paddy fields in Japan was also measured for its ¹³C and the results agreed with Yokohama. Furthermore, the variation occurred irrespective of the amount and the type of supplied organic substances to the fields (whole rice straw, rice stubble, or compost). The ¹³C value (average value of -55.9 ± 4.24) from these paddy fields was higher than those of the CH₄ emitted from African and North American paddies. The higher value was little affected by their difference in the supplied organic substances. CH₄ oxidation likely occurs for bubble CH₄ in the shallow paddy fields. A rough estimate of the total CH₄ production, using isotope mass balance, showed that 17 to 22% of organic carbon supplied to Japanese paddies transforms to CH₄.     

The origin of ovarian neuropeptide Y (NPY)-immunoreactive nerve fibres from the inferior mesenteric ganglion in the pig

Summary Applying a double-immunofluorescence technique, the porcine ovary is demonstrated to receive two populations of NPY-immunoreactive nerve fibres originating from the inferior mesenteric ganglion: one with colocalized tyrosine hydroxylase and supplying predominantly the ovarian vasculature, and a second, solely NPY-immunoreactive and almost exclusively associated with growing follicles. A third group of tyrosine hydroxylase-and dopamine--hydroxylase-positive, but NPY-negative nerve fibres is associated with ovarian blood vessels and, to a minor extent, with ovarian follicles. As revealed by retrograde tracing, the vast majority of postganglionic neurons projecting to the ovary is located in a discrete area of the ganglion, suggesting a somatotopic organization of the porcine inferior mesenteric ganglion. Moreover, the finding indicate that three subpopulations of postganglionic sympathetic neurons with different chemical codes supply different target components of the porcine ovary. The physiological relevance of the described neurons in the nervous control of ovarian functions remains to be elucidated.A portion of these results has been presented in abstract form (Majewski et al. 1991)     

Sensory projections to the nucleus basalis prosencephali of the pigeon

Summary The afferent pathways to the nucleus basalis prosencephali of the pigeon were studied by use of the horseradish peroxidase (HRP) technique. It was confirmed that this nucleus receives a direct pathway from the nucleus sensorius principalis nervi trigemini and that, as in the starling, it receives a direct input from the nucleus lemnisci lateralis, pars ventralis, an auditory relay. Totally novel is the finding that the nucleus basalis prosencephali is the target of a direct pathway originating in the medullary nucleus vestibularis superior. All three pathways bypass the thalamus. From within the telencephalon the nucleus basalis prosencephali also receives fibres from the tuberculum olfactorium and the peri-ectostriatal belt, suggestive of olfactory and visual input. Marked cell bodies were also found in the neostriatum frontolaterale. It is assumed that these arose from HRP uptake by axons of the tractus fronto-archistriatalis that course through the nucleus basalis prosencephali to the anterodorsal archistriatum. Marked fibres and bouton-like formations were observed in the latter structure. The afferents to the nucleus basalis prosencephali are discussed in conjunction with the probable role of the nucleus as a sensorimotor coordinator of the pecking/feeding behaviour of the pigeon.     

Nitrogen fertilization effects on dinitrogen fixation as influenced by legume species and proportion in legume-grass mixtures in Uruguay

Grasses grown in mixture with nodulated legumes often are N-limited, but N fertilization may result in reductions of N₂ fixation and legume stands. We studied N-fertilizer effects on N₂ fixation for three binary legume-grass mixtures in Uruguay. Replicated swards of white clover (Trifolium repens L.) (WC), red clover (Trifolium pratense L.) (RC), or birdsfoot trefoil (Lotus corniculatus L.) (BT), each in combination with tall fescue (Festuca arundinacea Schreb) (TF) at two legume proportions were sown in 1983 (Exp. 1) and 1984 (Exp. 2). In the fall of 1984, N treatments at 100 kg ha⁻¹ and controls were randomly assigned to subplots in Exp. 1 (established swards) and in Exp. 2 (at seeding). The soil for both experiments was a fine, montmorillonitic, mesic, Typic Argiudolls. Herbage fixed-N was estimated by ¹⁵N isotope-dilution with pure stands of TF as reference. In both experiments, N fertilization reduced the proportion of legume N derived from air (% Ndfa) and increased herbage yield only during the first 18 to 20 weeks after application. Fertilizer-N reduced annual fixed-N yield from 178 to 148 kg ha⁻¹ in Exp. 1 and from 65 to 29 kg ha⁻¹ in Exp. 2 Fixed-N yield for BT was markedly reduced by N in both experiments (33 to 53%), whereas for the clovers reduction was lesser in Exp. 1 (9 to 13%) than in Exp. 2 (46 to 64%). Negative effects of N on % Ndfa were more evident for the high legume proportion. We conclude that fertilization with 100 kg N ha⁻¹ reduced % Ndfa only for the immediate 18 to 20 weeks after application. Fertilizer-induced reduction of fixed-N yields lasted longer because of a more prolonged depression of legume proportion, especially for BT and for newly seeded swards. Journal Paper no. J.-13327 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, U.S.A. (Project 2281). Supported in part by the Facultad de Agronomía, Montevideo, Uruguay; and the International Atomic Energy Agency, Vienna, Austria (Project URU/5/012). Journal Paper no. J.-13327 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, U.S.A. (Project 2281). Supported in part by the Facultad de Agronomía, Montevideo, Uruguay; and the International Atomic Energy Agency, Vienna, Austria (Project URU/5/012).     

15N estimates of nitrogen fixation by white clover (Trifolium repens L.) growing in a mixture with ryegrass (Lolium perenne L.)

The ¹⁵N isotope dilution technique and the N difference method were used to estimate N₂ fixation by clover growing in a mixture with ryegrass, in a field experiment and a controlled environment experiment. Values obtained using N difference were approximately 25% lower than those estimated using ¹⁵N isotope dilution. In the field experiment there was a measured N benefit to grass growing with clover, equivalent to 42.7 kgN ha^-1. The grass in the mixture had a lower atom %¹⁵N content and a higher N content than grass in a monoculture; therefore values for N₂ fixation were different depending on choice of control plant i.e. monoculture or mixture grass. In the controlled environment experiment there were no significant differences between either the atom %¹⁵N contents or the N contents of monoculture grass and grass growing in a mixture with clover. It is concluded that there is a long term indirect transfer of N from clover to associated grass which can lead to errors in estimates of N₂ fixation.     

Short-term changes in carbon-isotope discrimination identify transitions between C3 and C4 carboxylation during Crassulacean acid metabolism

Short-term measurements of instantaneous carbon-isotope discrimination have been determined from mass-spectrometric analyses of CO₂ collected online during gas exchange for the epiphytic bromeliad Tillandsia utriculata L. Using this technique, the isotopic signature of CO₂ exchange for each phase of Crassulacean acid metabolism (CAM) has been characterised. During night-time fixation of CO₂ (Phase I), discrimination () ranged from 4.4 to 6.6, equivalent to an effective carbon-isotope ratio (¹³C) of –12.3 to –14.5 versus Pee Dee Belemnite (PDB). These values reflected the gross photosynthetic balance between net CO₂ uptake and refixation of respiratory CO₂, characteristic of CAM in the Bromeliaceae. When for the relative proportion of external (p _a ) and internal (p _i) CO₂ is taken into account, calculated p _i/p _a decreased during the later part of the dark period from 0.68 to 0.48. Measurements of during Phase II, early in the light period, showed the transition between C₄ and C₃ pathways, with carboxylation being increasingly dominated by ribulose bisphosphate carboxylase (Rubisco) as increased from 10.5 to 21.2 During decarboxylation in the light period (Phase III), CO₂ leaked out of the leaf and the inherent discrimination of Rubisco was expressed. The value of calculated from on-line measurements (64.4) showed that the CO₂ lost was considerably enriched in ¹³C, and this was confirmed by direct analysis of the CO₂ diffusing out into a CO₂-free atmosphere ( ¹³C = + 51.6 versus PDB). Instantaneous discrimination was characteristic of the C₃ pathway during Phase IV (late in the light period), but a reduction in showed an increasing contribution from phosphoenolpyruvate carboxylase. The results from this non-invasive technique confirm the observations that double carboxylation involving both phosphoenolpyruvate carboxylase and Rubisco occurs during the transient phases of CAM (II and IV) in the light period.Abbreviations and Symbols CAM Crassulacean acid metabolism - H⁺ (dawn-dusk) variation in titratable acidity - ¹³C carbonisotope ratio of plant organic material, relative to Pee Dee Belemnite (vs. PDB) - discrimination against ¹³CO₂, - p _i, p _a internal, external partial pressures of CO₂ - Rubisco ribulose1,5-bisphosphate carboxylase - PAR photosynthetically active radiation - PEPCase phosphoenolpyruvate carboxylase We are grateful for financial support in respect of research grants (GR3/5360, GR3/6419) and a studentship awarded by the Natural Environment Research Council, UK.     

Seasonal water uptake and movement in root systems of Australian phraeatophytic plants of dimorphic root morphology: a stable isotope investigation

A natural abundance hydrogen stable isotope technique was used to study seasonal changes in source water utilization and water movement in the xylem of dimorphic root systems and stem bases of several woody shrubs or trees in mediterranean-type ecosystems of south Western Australia. Samples collected from the native treeBanksia prionotes over 18 months indicated that shallow lateral roots and deeply penetrating tap (sinker) roots obtained water of different origins over the course of a winter-wet/summer-dry annual cycle. During the wet season lateral roots acquired water mostly by uptake of recent precipitation (rain water) contained within the upper soil layers, and tap roots derived water from the underlying water table. The shoot obtained a mixture of these two water sources. As the dry season approached dependence on recent rain water decreased while that on ground water increased. In high summer, shallow lateral roots remained well-hydrated and shoots well supplied with ground water taken up by the tap root. This enabled plants to continue transpiration and carbon assimilation and thus complete their seasonal extension growth during the long (4–6 month) dry season. Parallel studies of other native species and two plantation-grown species ofEucalyptus all demonstrated behavior similar to that ofB. prionotes. ForB. prionotes, there was a strong negative correlation between the percentage of water in the stem base of a plant which was derived from the tap root (ground water) and the amount of precipitation which fell at the site. These data suggested that during the dry season plants derive the majority of the water they use from deeper sources while in the wet season most of the water they use is derived from shallower sources supplied by lateral roots in the upper soil layers. The data collected in this study supported the notion that the dimorphic rooting habit can be advantageous for large woody species of floristically-rich, open, woodlands and heathlands where the acquisition of seasonally limited water is at a premium.     

Ecophysiology and distribution of the endemic leafless spurgeEuphorbia aphylla and the introducedE. tirucalli (Euphorbiaceae,Euphorbia sect.Tirucalli) in the Canary Islands

The leafless spurgeEuphorbia aphylla (Euphorbiaceae), an endemic species restricted to several of the Canary Islands where it inhabits coastal and arid localities, expresses Crassulacean Acid Metabolism (CAM) when it is subjected to summer drought. A flexible CAM is consistent with the general ecology of the species. It is the only member of sect.Tirucalli native to the Canary Islands and is at the north-western edge of the section's biogeographical range. The other members of the section have a paleotropic distribution and are found throughout Africa. Many of them are regarded as obligate CAM plants, includingE. tirucalli which was used as a comparison in ecophysiological experiments examining the response ofE. aphylla to drought and temperature.     

A pyrenoid-based carbon-concentrating mechanism is present in terrestrial bryophytes of the class Anthocerotae

It has been widely accepted that carbon assimilation in bryophytes is exclusively based on the conventional C₃ photosynthetic pathway. The occurrence of biochemical CO₂-concentrating mechanisms (C₄ or Crassulacean acid metabolism), which have developed in plants in the last 20–100 million years, has been discounted for bryophytes from studies of the carbon isotope composition (¹³C) of organic material. In contrast cyanobacteria and many algae show active accumulation of dissolved inorganic carbon via biophysical CO₂-concentrating mechanisms which are also found in the photobiont partners in certain lichens. The presence of a pyrenoid, a granular particle within the chloroplast, has been linked with CO₂-concentrating mechanism activity in green algae and lichens and we now show that such a mechanism is categorically associated with the occurrence of a pyrenoid in bryophytes belonging to the class of Anthocerotae. These observations have significant evolutionary implications for the development of terrestrial photosynthesis during the colonisation of the land, raising the intriguing question of why the pyrenoid-based CO₂-concentrating mechanism did not persist in the terrestrial environment.Abbreviations and Symbols CCM carbon-concentrating mechanism - DIG dissolved inorganic carbon (CO₂+HCO ₃ ^- +CO ₂ ^- ) - DW dry weight - K_0.5 external concentration of CO₂ at which half-maximal rates of CO₂ assimilation are reached - Rubisco ribulose-l,5-bisphosphate carboxylase-oxygenase - carbon isotope discrimination (%) - ¹³C carbon isotope ratio (%) This work was supported by the Natural Environment Research Council (GR3/8813) and the Leverhulme Trust. We thank Prof. A. Roy Perry (National Museum of Wales, Cardiff), Dr. B. Coppins and Mr. D. Long (Royal Botanic Garden Edinburgh) for access to herbarium specimens and Mr. M. Fletcher for providing living bryophytes.