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Photosynthetic gas exchange and the stable isotope composition of leaf water: comparison of a xylem-tapping mistletoe and its host 总被引:4,自引:2,他引:2
Photosynthetic gas exchange and the stable isotopic composition of foliage water were measured for a xylem tapping mistletoe, Phoradendron juniperinum, and its host tree, Juniperus osteosperma, growing in southern Utah. The observed isotopic composition of water extracted from foliage was compared to predictions of the Craig-Gordon model of isotopic enrichment at evaporative sites within leaves. Assimilation rates of juniper were higher and stomatal conductance was lower than the values observed for the mistletoe. This resulted in lower intercellular/ ambient CO2 values in the juniper tree relative to its mistletoe parasite. For mistletoe, the observed foliage water hydrogen and oxygen isotopic enrichment was less than that predicted by the model. In juniper, foliage water hydrogen isotopic enrichment was also lower than that predicted by the evaporative enrichment model. In contrast, the oxygen isotopic enrichment in juniper foliage water was slightly greater than that predicted for the evaporative sites within leaves. Hydrogen isotopic enrichment in mistletoe foliage shows systematic variation with stem segment, being highest near the tips of the youngest stems and decreasing toward the base of the mistletoe, where isotopic composition is close to that of stem water in the host tree. In a correlated pattern, mid-day stomatal conductance declined abruptly in mistletoe foliage of increasing age. 相似文献
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ABSTRACT. The cicadelloid leaf-hoppers, Eurymela distincta (Signoret) and Eurymela fenestrata (Le Pelletier & Serville), feed on the phloem sap of Eucalyptus spp. The osmotic pressure profile of haemolymph and gut fluids is consistent with a filtration mechanism based on passive osmosis. This is responsible for shunting water rapidly from foregut to hindgut in the relatively simple filter chamber. The osmotic gradient which drives the system is probably produced by active secretion of sodium and potassium into the Malpighian tubules and posterior midgut. Although the osmotic pressures in all parts of the system are higher, the mechanism is probably similar to that previously described for xylem-feeding cicadas.
The major haemolymph cations are sodium and magnesium and the concentrations of sodium and magnesium in the urine are higher than potassium. A variety of storage granules in the midgut contain calcium, phosphorus (as phosphate), ferric iron, zinc, magnesium, manganese and copper. 相似文献
The major haemolymph cations are sodium and magnesium and the concentrations of sodium and magnesium in the urine are higher than potassium. A variety of storage granules in the midgut contain calcium, phosphorus (as phosphate), ferric iron, zinc, magnesium, manganese and copper. 相似文献
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Kirk, W W., Davies, H. V. and Marshall, B. 1985. The effectof temperature on the initiation of leaf primordia in developingpotato sprouts.J. exp. Bot. 36: 16341643. Initiation of leaf primordia in potato sprouted out of soilin light was an asymptotic function of thermal time and thebase temperature for the process was 3.6 °C. The parametervalues of the asymptotic function were universal for cv. MarisPiper. The estimated rate of leaf primordium initiation decreasedlinearly from 0.033 leaf pnmordia (K day)1 when abouteight leaf primordia were present to zero after a maximum numberof 24 leaf primordia had been initiated. The decrease in rateof development with increasing number of primordia may be dueto depletion of mother tuber resources. The transition of theapex from a vegetative to a reproductive state was not the factorlimiting the initiation of additional leaf primordia. Key words: Potato, Solanum tuberosum L., leaf primordia initiation, temperature, thermal time, development 相似文献
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Plants of white clover ( Trifolium repens L.) cv. Olwen were grown in an open glasshouse maintained at a mean temperature of 20o C and ovule growth and seed production measured. Differences in the rate of growth of ovules within ovaries were observed as early as 2 days after pollination. Ovules reached a maximum size after 8 days with the smallest only half the size of the largest. After 8 days, the smallest ovules became flaccid and shrivelled. Ovule position within the ovary had little effect on the frequency of seed set and although there was an apparently higher probability that central ovules produced a seed than those nearer the peduncle or style this was not statistically significant. Inflorescence position and floret position on the inflorescence had a significant effect on the number of seeds per floret and seed weight; the first formed inflorescences and the first florets to be pollinated on each inflorescence had more seeds per floret and heavier seeds and fewer florets with no seed than later pollinated florets. There were also differences between florets within the same whorl. The role of a number of factors which may influence floret site utilisation are discussed. 相似文献
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Growth rates in vitro of Pseudomonas syringae and Xanthomonas pruni were measured over the temperature range 0–36 °C. The estimated temperature optimum for X. pruni was 31 °C, with a doubling time of 1.53 h. The estimated temperature optimum for P. syringae was 28 °C with a doubling time of 1.27 h, although analysis showed no significant difference in the doubling times over the range 23–33 °C, indicating an unusual plateau at the maximum rate of growth of this organism. P. syringae and related plant pathogenic Pseudomonas spp. grew well at low temperatures, but X. pruni did not. Cultures of P. syringae and X. pruni had a very short lag phase after their incubation temperature was changed from 4 °C to a temperature close to their optimum (29 °C). When the incubation temperature of these organisms was changed from 11.5–29 °C, X. pruni grew without a lag phase at the rate expected for the higher temperature. However, the initial growth rate of P. syringae at the higher temperature was significantly greater than that at which the organism subsequently developed. The ecological significance of these points is discussed. The usefulness of the Arrhenius coefficients as characteristics of these organisms is discussed. 相似文献
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Non-resistant but tolerant cv. Cara and non-resistant but relatively intolerant cv. Pentland Dell were grown in split plots encompassing a range of population densities of potato cyst nematode, Globodera pallida. Light interception and its efficiency of conversion were estimated by regular ground cover measurements and plant harvests. It was concluded that increasing levels of infestation with G. pallida only slightly decreased the efficiency of utilisation of intercepted radiation. Heavy infestation of G. pallida initially decreased the top growth and light interception of both cultivars by similar proportions, but in later harvests, this adverse effect markedly decreased for Cara whereas it slightly increased for Pentland Dell. This difference was due to the heavily infested Cara eventually achieving and maintaining 100% ground cover whereas the equivalent Pentland Dell never exceeded 75% ground cover. Consequently, final tuber yields were decreased much more for Pentland Dell than for Cara though the decreases in tuber yield were less than those for top growth. The importance of nematode effects on top growth, and hence on light interception, with regard to both yield losses and tolerance differences, were clearly demonstrated. Both linear and logarithmic models were used to describe the relationship between the initial population density of G. pallida and yield, and the implications of differences in tolerance on the parameters in the logarithmic model are discussed. 相似文献