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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 371 (1994), S. 60-62 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Plant water use (transpiration, E) is regulated by the available energy (Rn) and air saturation deficit (D) above the canopy (Fig. \a}. The relative importance of these two factors in regulating plant or ecosystem water use is theoretically summarized in a decoupling coefficient, Q, (OQ 1) derived ...
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  • 2
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We have investigated the interactions between resource assimilation and storage in rosette leaves, and their impact on the growth and reproduction of the annual species Arabidopsis thaliana. The resource balance was experimentally perturbed by changing (i) the external nutrition, by varying the nitrogen supply; (ii) the assimilation and reallocation of resources from rosette leaves to reproductive organs, by cutting or covering rosette leaves at the time of early flower bud formation, and (iii) the internal carbon and nitrogen balance of the plants, by using isogenic mutants either lacking starch formation (PGM mutant) or with reduced nitrate uptake (NU mutant).When plants were grown on high nitrogen, they had higher concentrations of carbohydrates and nitrate in their leaves during the rosette phase than during flowering. However, these storage pools did not significantly contribute to the bulk flow of resources to seeds. The pool size of stored resources in rosette leaves at the onset of seed filling was very low compared to the total amount of carbon and nitrogen needed for seed formation. Instead, the rosette leaves had an important function in the continued assimilation of resources during seed ripening, as shown by the low seed yield of plants whose leaves were covered or cut off. When a key resource became limiting, such as nitrogen in the NU mutants and in plants grown on a low nitrogen supply, stored resources in the rosette leaves (e.g. nitrogen) were remobilized, and made a larger contribution to seed biomass. A change in nutrition resulted in a complete reversal of the plant response: plants shifted from high to low nutrition exhibited a seed yield similar to that of plants grown continuously on a low nitrogen supply, and vice versa. This demonstrates that resource assimilation during the reproductive phase determines seed production.The PGM mutant had a reduced growth rate and a smaller biomass during the rosette phase as a result of changes in respiration caused by a high turnover of soluble sugars (Caspar et al. 1986; W. Schulze et al. 1991). During flowering, however, the vegetative growth rate in the PGM mutant increased, and exceeded that of the wild-type. By the end of the flowering stage, the biomass of the PGM mutant did not differ from that of the wild-type. However, in contrast to the wild-type, the PGM mutant maintained a high vegetative growth rate during seed formation, but had a low rate of seed production. These differences in allocation in the PGM mutant result in a significantly lower seed yield in the starchless mutants. This indicates that starch formation is not only an important factor during growth in the rosette phase, but is also important for whole plant allocation during seed formation. The NU mutant resembled the wild-type grown on a low nitrogen supply, except that it unexpectedly showed symptoms of carbohydrate shortage as well as nitrogen deficiency.In all genotypes and treatments, there was a striking correlation between the concentrations of nitrate and organic nitrogen and shoot growth on the one hand, and sucrose concentration and root growth on the other. In addition, nitrate reductase activity (NRA) was correlated with the total carbohydrate concentration: low carbohydrate levels in starchless mutants led to low NRA even at high nitrate supply. Thus the concentrations of stored carbohydrates and nitrate are directly or indirectly involved in regulating allocation.
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  • 3
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Sunflower plants (Helianthus annuus L.) were subjected to soil drying with their shoots either kept fully turgid using a Passioura-type pressure chamber or allowed to decrease in water potential. Whether the shoots were kept turgid or not, leaf conductance decreased below a certain soil water content. During the soil drying, xylem sap samples were taken from individual intact and transpiring plants. Xylem sap concentrations of nitrate and phosphate decreased with soil water content, whereas the concentrations of the other anions (SO42 and Cl−) remained unaltered. Calcium concentrations also decreased. Potassium, magnesium, manganese and sodium concentrations stayed constant during soil drying. In contrast, the pH, the buffering capacity at a pH below 5 and the cation/anion ratio increased after soil water content was lowered below a certain threshold. Amino acid concentration of the xylem sap increased with decreasing soil water content. The effect of changes in ion concentrations in the xylem sap on leaf conductance is discussed.
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  • 4
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Sunflower plants [Helianthus annuus L.) were subjected to soil drought. Leaf conductance declined with soil water content even when the shoot was kept turgid throughout the drying period. The concentration of abscisic acid in the xylem sap increased with decreasing soil water content. No general relation could be established between abscisic acid concentration in the xylem sap and leaf conductance due to marked differences in the sensitivity of leaf conductance of individual plants to abscisic acid from the xylem sap. The combination of these results with data from Gollan, Schurr & Schulze (1992, see pp. 551–559, this issue) reveals close connection of the effectiveness of abscisic acid as a root to shoot signal to the nutritional status of the plant.
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  • 5
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The cost of nitrogen storage to current growth was examined in relation to N availability in the biennial Cirsium vulgare. Plants were grown outdoors, in sand culture, with continuous diel drip irrigation of fertilization medium containing one of five different N concentrations. Plants grown at the highest N concentration stored twice as much N in their tap roots as did plants grown at the lowest N concentration. In high-N-grown plants, the storage of N reserves occurred during the period of maximum growth, at the same time as tap-root production. At the time of maximum biomass, stored N was also at a maximum. During the period following maximum biomass, no additional storage of N occurred. This pattern was observed despite frequent late-season leaf senescence which resulted in a large pool of potentially mobile N which could have been stored at no cost to growth. In low-N-grown plants, the production of tap-root storage tissue and the filling of that tissue with stored N were staggered. Tap-root production and growth occurred during the period of maximum growth, as in the high-N-grown plants. However, filling of the storage tissue with N occurred late in the growing season, when the pool of mobile N from senescent leaves was large. The utilization of this late-season N source occurred with little or no cost to growth, and this N is labelled, according to previous definitions, as ‘accumulated’. The costs of storing N in plants of the different N treatments were calculated using two models based on different growth constraints. In one model, the cost of N storage was represented as lost growth due to allocation of N to storage, rather than to the photosynthetic shoot (i.e. growth was assumed to be limited by carbon acquisition). In the second model, the storage cost was calculated as lost growth due to allocation of N to storage, rather than to the nitrogen-acquiring fine-root system (i.e. growth was assumed to be limited by nitrogen acquisition). In both models, the total cost of N storage was predicted to decrease as N availability decreased due to smaller storage pool sizes in plants of the low-N treatments. The cost of filling the tap root with stored N as a percentage of the total storage cost was also reduced as N availability decreased due to the occurrence of late-season accumulation. By relying, at least in part, on late-season accumulation, plants grown at the lowest three levels of N availability reduced total storage costs by 15 to 22%. The results demonstrate that plants are capable of adjusting their storage patterns in response to low nitrogen availability such that the costs of storage are reduced.
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  • 6
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Plants of Cirsium vulgare (Savi) Ten. were cultivated under five different nitrogen regimes in order to investigate the effects of nitrogen supply on the storage processes in a biennial species during its first year of growth.External N supply increased total biomass production without changing the relationship between ‘productive plant compartments’ (i.e. shoot plus fine roots) and ‘storage plant compartments’ (i.e. structural root dry weight, which is defined as the difference between tap root biomass and the amount of stored carbohydrates and N compounds). The amount of carbohydrates and N compounds stored per unit of structural tap root dry weight was not affected by external N availability during the season, because high rates of N supply increased the concentration of N compounds whilst decreasing the carbohydrate concentration, and low rates of N supply had the opposite effect. Mobilization of N from senescing leaves was not related to the N status of the plants. The relationship between nitrogen compounds stored in the tap root and the maximum amount of nitrogen in leaves was an increasing function with increasing nitrogen supply. We conclude that the allocation between vegetative plant growth and the growth of storage structures over a wide range of N availability seems to follow predictions from optimum allocation theory, whereas N storage responds in a rather plastic way to N availability.
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  • 7
    ISSN: 1432-2048
    Keywords: Humidity response ; Stomata ; Transpiration ; Water potential ; Water stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Short-term (hours) changes in plant water status were induced in hazel (Corylus avellana L.) by changing the evaporative demand on a major portion of the shoot while maintaining a branch in a constant environment. Stomatal conductance of leaves on the branch was influenced little by these short-term changes in water status even with changes in leaf water potential as great as 8 bars. Long-term (days) changes in plant water status were imposed by soil drying cycles. Stomatal conductance progessively decreased with increases in long-term water stress. Stomata still responded to humidity with long-term water stress but the range of the conductance response decreased. Threshold responses of stomata to leaf water potential were not observed with either short-term or long-term changes in plant water status even when leaves wilted. It is suggested that concurrent measurements of plant water status may not be sufficient for explaining stomatal and other plant responses to drought.
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  • 8
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Net photosynthesis of Picea abies was measured in a spruce forest in northern Germany with temperature- and humidity-controlled cuvettes in 4 different crown layers on shoots of different ages. These measurments were performed such that temperature and humidity either followed ambient conditions or were kept constant. Annual courses of light-, temperature-, and humidity-related net photosynthesis were determined. Spruce had a remarkably constant rate of CO2 uptake from April to September for 1-year and older needles. Light saturation was achieved at 25 klx. Current year needles had the highest rates of CO2 uptake in early summer, but these rates decreased by autumn. Photosynthetic capacity decreased with needle age and, on a dry weight basis, it was higher in the shade than in the sun crown. The temperature optimum was between 13 and 23° C. Photosynthesis in spruce decreased when air humidity was low. The effect of the natural weather conditions on photosynthetic capacity was determined. The habitat is characterized by a high frequency of low light intensities (75% of total daytime below 20 klx) and cool temperatures (80% of daytime between 9 and 21° C). Low air humidity was only present when light intensities were high. The major limiting factor for production was low light intensities, which reduced photosynthetic capacity in the sun crown to 42% below maximum possible rates. Adverse temperatures reduced CO2 uptake by 28% and large water vapor pressure deficits reduced rates by only 2% compared with maximum possible rates. The limited adaptation to light is discussed.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 82 (1990), S. 427-429 
    ISSN: 1432-1939
    Keywords: Insectivorous plants ; Insect capture ; Leaf growth ; Nitrogen storage ; Drosera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Rates of insect capture increased with leaf area in the insectivorous plant Drosera rotundifolia, and growth of new leaves was related to insect capture. However, increased leaf growth was counterbalanced by leaf abscission which was in turn related to insect capture and leaf growth. Leaf loss equaled leaf growth in plants having natural rate of insect capture. A large proportion of the nitrogen gain from prey was stored in the hypocotyl; it was estimated from feeding experiments that about 24% to 30% of the nitrogen stored in the hypocotyl after winter originated from insect capture in the previous season. The effect of insect capture is discussed in relation to the life cycle of Drosera.
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  • 10
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The photosynthesizing branches of Hammada scoparia, one of the typical dwarf shrubs of the Negev desert, undergo a seasonal change from succulent to xeromorphic anatomy. This trend is accompanied by a marked decrease of water content and of total water Ψ plant and osmotic Ψ π plant potential. Irrigated plants do not show such transitions. The daily courses of Ψ plant and Ψ π plant showed minima around noon and a tendency for maxima before sunrise. Turgor pressure Ψ p plant reached minima around noon and became negative (until ca.-10 bars). Generally, Ψ plant decreases with increasing water vapour concentration difference between plant and air (WD) in the first half of the day, and in the second half the reversal of this trend occurs. Mostly smaller increments of Ψ plant were correlated with larger increases in WD which lead to the conclusion that stomates closed enough to maintain transpiration at a constant value. Non-irrigated and irrigated plants showed different hysteresis loops of relation between Ψ plant and WD. Regulatory reduction of transpiration appears largely independently of Ψ plant which is in spring and with irrigated plants on a high level, with non-irrigated plants in summer on a low level. In summer the continous but decreasing drop of Ψ plant with increasing WD was interpreted as caused by a change in soil or root resistance. Independent of the seasonal state and of the Ψ plant level, H. scoparia regulates its water status within limited ranges of Ψ p plant changes: the irrigated plants on a higher level, the non-irrigated on a lower level of Ψ p plant . The water contents of the tissues of H. scoparia are linearily related to Ψ plant as well as Ψ p plant . Steeper slopes with non-irrigated plants in summer than with spring palnts and with irrigated plants during the whole season signify that in the latter a certain increment in turgor pressure corresponds to a large gain in water content while in the non-irrigated summer plants it varies only little for an identical change in Ψ p plant . This behaviour of non-irrigated wild plants apparently is due to the change of the elastic properties of the tissues in the assimilating branches.
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