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Phosphorus and nitrogen uptake capacities were assessed during 36–58 d drying cycles to determine whether the ability of sagebrush (Artemisia tridentata Nutt.) to absorb these nutrients changed as the roots were subjected to increasing levels of water stress. Water was withheld from mature plants in large (6 I) containers and the uptake capacity of excised roots in solution was determined as soil water potentials decreased from −0.03 MPa to −5.0 MPa. Phosphorus uptake rates of excised roots at given substrate concentrations increased as preharvest soil water potentials decreased to −5.0 MPa. Vmax and Km also increased as soil water potentials declined. Declining soil water potentials depressed nitrogen uptake...
Cyanobacteria have evolved a significant environmental adaptation, known as a CO(2)-concentrating-mechanism (CCM), that vastly improves photosynthetic performance and survival under limiting CO(2) concentrations. The CCM functions to transport and accumulate inorganic carbon actively (Ci; HCO(3)(-), and CO(2)) within the cell where the Ci pool is utilized to provide elevated CO(2) concentrations around the primary CO(2)-fixing enzyme, ribulose bisphosphate carboxylase-oxygenase (Rubisco). In cyanobacteria, Rubisco is encapsulated in unique micro-compartments known as carboxysomes. Cyanobacteria can possess up to five distinct transport systems for Ci uptake. Through database analysis of some 33 complete genomic...
Seasonal differences have been observed in the ability of desiccated mosses to dissipate absorbed light energy harmlessly into heat. During the dry summer season desiccation-tolerant mosses were more protected against photo-oxidative damage in the dry state than during the more humid winter season. Investigation of the differences revealed that phototolerance could be acquired or lost even under laboratory conditions. When a desiccated poikilohydric moss such as Rhytidiadelphus squarrosus is in the photosensitive state, the primary quinone, Q(A), in the reaction centre of photosystem II is readily reduced even by low intensity illumination as indicated by reversibly increased chlorophyll fluorescence. No such reduction...
For grass seeds that lose dormancy through after ripening in dry storage, the probability of germination following a particular wetting event can be predicted only if the relationship between storage temperature and change in after-ripening status is known. This study examined patterns of seed dormancy loss in Bromus tectorum L., quantifying changes in germination percentage, speed, and uniformity through time. Seed collections from three semi-arid habitats were stored at temperatures from 10–40 °C. At monthly intervals, subsamples were incubated at 5/15, 10/20, 15/25, and 20/30 °C. For recently harvested seeds, germination percentage, mean germination time, and days between 10% and 90% of total germination...
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Predawn plant water potential (Ψw) is used to estimate soil moisture available to plants because plants are expected to equilibrate with the root-zone Ψw. Although this equilibrium assumption provides the basis for interpreting many physiological and ecological parameters, much work suggests predawn plant Ψw is often more negative than root-zone soil Ψw. For many halophytes even when soils are well-watered and night-time shoot and root water loss eliminated, predawn disequilibrium (PDD) between leaf and soil Ψw can exceed 0.5 MPa. A model halophyte, Sarcobatus vermiculatus, was used to test the predictions that low predawn solute potential (Ψs) in the leaf apoplast is a major mechanism driving PDD and that...
Mechanisms of protection against photo-oxidation in selected desiccation-tolerant lichens and mosses have been investigated by measuring loss of light absorption during desiccation and chlorophyll fluorescence as indicators of photoprotection. Apparent absorption (1-T) spectra measured in the reflectance mode revealed stronger absorption of photosynthetic pigments in hydrated than in desiccated organisms, but differences were pronounced only in a cyanolichen, less so in some chlorolichens, and even less in mosses. Since the amplitude of chlorophyll fluorescence is a product of (1-T) light absorption by chlorophyll and quantum yield of fluorescence, and since fluorescence is inversely related to thermal energy dissipation,...
The relationship between photosynthetic energy conservation and thermal dissipation of light energy is considered, with emphasis on organisms which tolerate full desiccation without suffering photo-oxidative damage in strong light. As soon as water becomes available to dry poikilohydric organisms, they resume photosynthetic water oxidation. Only excess light is then thermally dissipated in mosses and chlorolichens by a mechanism depending on the protonation of a thylakoid protein and availability of zeaxanthin. Upon desiccation, another mechanism is activated which requires neither protonation nor zeaxanthin although the zeaxanthin-dependent mechanism of energy dissipation remains active, provided desiccation occurs...
An hypothesis was formulated that phosphorus (P) partitioning in tissues of C4 leaves would permit C4 plants to resist P deficiency better than C3 plants. To test this hypothesis, 12 C3, C4, and C3-C4 intermediate species were grown at adequate, deficient, and severely deficient P supply in a solid-phase-buffered sand culture system to characterize photosynthetic and growth responses. Species differed considerably in response to P stress. The growth of C3 species was more sensitive to P supply than C4 species, but C3 and C4 species had similar photosynthetic P use efficiency, and C4 species did not have low leaf P content, contrary to our hypothesis. In fact, leaf photosynthetic rates were not correlated with growth...
    map background search result map search result map High apoplastic solute concentrations in leaves alter water relations of the halophytic shrub, Sarcobatus vermiculatus High apoplastic solute concentrations in leaves alter water relations of the halophytic shrub, Sarcobatus vermiculatus