Showing papers by "Ernst Detlef Schulze published in 1993"

Evaporation and canopy characteristics of coniferous forests and grasslands.

Abstract: Canopy-scale evaporation rate (E) and derived surface and aerodynamic conductances for the transfer of water vapour (gs and ga, respectively) are reviewed for coniferous forests and grasslands. Despite the extremes of canopy structure, the two vegetation types have similar maximum hourly evaporation rates (Emax) and maximum surface conductances (gsmax) (medians = 0.46 mm h-1 and 22 mm s-1). However, on a daily basis, median Emax of coniferous forest (4.0 mm d-1) is significantly lower than that of grassland (4.6 mm d-1). Additionally, a representative value of ga for coniferous forest (200 mm s-1) is an order of magnitude more than the corresponding value for grassland (25 mm s-1). The proportional sensitivity of E, calculated by the Penman-Monteith equation, to changes in gs is >0.7 for coniferous forest, but as low as 0.3 for grassland. The proportional sensitivity of E to changes in ga is generally ±0.15 or less.

Decreased Ribulose-1,5-Bisphosphate Carboxylase-Oxygenase in Transgenic Tobacco Transformed with Antisense Rbcs .6. Effect on Photosynthesis in Plants Grown at Different Irradiance

Abstract: Tobacco (Nicotiana tabacum L) plants transformed with ‘antisense’ rbcS to decrease the expression of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) have been used to investigate the contribution of Rubisco to the control of photosynthesis in plants growing at different irradiances Tobacco plants were grown in controlled-climate chambers under ambient CO2 at 20°C at 100, 300 and 750 μmol·m−2·s−1 irradiance, and at 28°C at 100, 300 and 1000 μmol·m−2·s−1 irradiance (i) Measurement of photosynthesis under ambient conditions showed that the flux control coefficient of Rubisco (C infRubisco supA ) was very low (001–003) at low growth irradiance, and still fairly low (024–027) at higher irradiance (ii) Short-term changes in the irradiance used to measure photosynthesis showed that C infRubisco supA increases as incident irradiance rises, (iii) When low-light (100 μmol·m−2·s−1)-grown plants are exposed to high (750–1000 μmol·m−2·s−1) irradiance, Rubisco is almost totally limiting for photosynthesis in wild types However, when high-light-grown leaves (750–1000 μmol·m−2·s−1) are suddenly exposed to high and saturating irradiance (1500–2000 μmol·m−2·s−1), C infRubisco supA remained relatively low (023–033), showing that in saturating light Rubisco only exerts partial control over the light-saturated rate of photosynthesis in “sun” leaves; apparently additional factors are co-limiting photosynthetic performance, (iv) Growth of plants at high irradiance led to a small decrease in the percentage of total protein found in the insoluble (thylakoid fraction), and a decrease of chlorophyll, relative to protein or structural leaf dry weight As a consequence of this change, high-irradiance-grown leaves illuminated at growth irradiance avoided an inbalance between the “light” reactions and Rubisco; this was shown by the low value of C infRubisco supA (see above) and by measurements showing that non-photochemical quenching was low, photochemical quenching high, and NADP-malate dehydrogenase activation was low at the growth irradiance In contrast, when a leaf adapted to low irradiance was illuminated at a higher irradiance, Rubisco exerted more control, non-photochemical quenching was higher, photochemical quenching was lower, and NADP-malate dehydrogenase activation was higher than in a leaf which had grown at that irradiance We conclude that changes in leaf composition allow the leaf to avoid a one-sided limitation by Rubisco and, hence, overexcitation and overreduction of the thylakoids in high-irradiance growth conditions, (v) ‘Antisense’ plants with less Rubisco contained a higher content of insoluble (thylakoid) protein and chlorophyll, compared to total protein or structural leaf dry weight They also showed a higher rate of photosynthesis than the wild type, when measured at an irradiance below that at which the plant had grown We propose that N-allocation in low light is not optimal in tobacco and that genetic manipulation to decrease Rubisco may, in some circumstances, increase photosynthetic performance in low light

Decreased Ribulose-1,5-Bisphosphate Carboxylase-Oxygenase in Transgenic Tobacco Transformed with Antisense Rbcs .5. Relationship between Photosynthetic Rate, Storage Strategy, Biomass Allocation and Vegetative Plant-Growth at 3 Different Nitrogen Supplies

Abstract: Wild-type tobacco (Nicotiana tabacum L.) plants and transgenic tobacco transformed with antisense rbcS to decrease expression of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco; EC 4.1.1.39) were grown at 300 mol.m -2 .s -1 irradiance and 20 o C at either 0.1, 0.7 or 5 mM NH 4 NO 3 . In high nitrogen (N), growth was reduced in parallel with the inhibition of photosynthesis when Rubisco was decreased by genetic manipulation. In limiting N, photosynthesis was reduced strongly when Rubisco was decreased by genetic manipulation, but growth was hardly affected. At all N levels, decreased expression of Rubisco led to a decrease in the amount of starch accumulated in the leaves

The Influence of Ammonium on Nitrate Uptake and Assimilation in 2-Year-Old Ash and Oak Trees - A Tracer-Study with 15N

Abstract: Interactions between ammonium and nitrate as competitive N sources depend on various biotic and abiotic factors. The preference for one of these N sources and the influence of ammonium on nitrate uptake and nitrate reductase activity was investigated in a 15N labelling experiment using 2-year-old potted plants of ash (Fraxinus excelsior L.) and oak (Quercus robur L.) under greenhouse conditions. Seedlings of both tree species use ammonium and nitrate in equal amounts when both N forms are supplied in a 1:1 ratio (1.5 mM NH4 + + 1.5 mM NO3 −), although there is a slight tendency that ammonium is preferred. In both species total N uptake is higher if ammonium and nitrate are supplied simultaneously when compared with uptake of nitrate alone (3 mM nitrate). If nitrate is the sole N source N uptake is only half as high as if ammonium and nitrate are supplied in a ratio of 1:1. The distribution of nitrate reductase between shoot and roots is not influenced by the N-form: nitrate reductase activity is ...

Nitrogen and carbohydrate storage in biennials originating from habitats of different resource availability

Abstract: Four biennial species (Arctium tomentosum, Cirsium vulgare, Dipsacus sylvester and Daucus carota) which originate from habitats of different nutrient availability were investigated in a 2-year experiment in a twofactorial structured block design varying light (natural daylight versus shading) and fertilizer addition. The experiment was designed to study storage as reserve formation (competing with growth) or as accumulation (see Chapin et al. 1990). We show that (i) the previous definitions of storage excluded an important process, namely the formation of storage tissue. Depending on species, storage tissue and the filling process can be either a process of reserve formation, or a process of accumulation. (ii) In species representing low-resource habitats, the formation of a storage structure competes with other growth processes. Growth of storage tissue and filling with storage products is an accumulation process only in the high-resource plant Arctium tomentosum. We interpret the structural growth of low-resource plants in terms of the evolutionary history of these species, which have closely related woody species in the Mediterranean area. (iii) The use of storage products for early leaf growth determines the biomass development in the second season and the competitive ability of this species during growth with perennial species. (iv) The high-resource plant Arctium has higher biomass development under all conditions, i.e. plants of low-resource habitats are not superior under low-resource conditions. The main difference between high- and low-resource plants is that low-resource plants initiate flowering at a lower total plant internal pool size of available resources.

Uptake of 15NH3 by Picea abies in Closed Chamber Experiments

Abstract: Above-ground deposition of anthropogenic trace gases like NH3 and NOx is considered as a main factor for nitrogen (N) loading of Picea abies ecosystems. In order to quantify NH3 deposition, tracer experiments with 15N labelled NH3 were carried out in fumigation chambers (GSF Munchen). NH3 uptake is linearly related to the gas concentration in the air, but the relation differs between organs and depends on N-nutrition of the organs. Plants well supplied with N have a lower NH3 uptake per g dry weight then plants deprived of N. Only a small amount of the offered gas deposits to the external plant surfaces. The NH3 uptake rates of spruce indicate that NH3 may be regarded as being just as or even more important as environmental pollutant than NOx with respect to N loading of spruce ecosystems.

15N-Labelled Ammonium and Nitrate Uptake by the Grass Calamagrostis villosa

Abstract: Calamagrostis villosa dominates the understory vegetation in declining spruce forests at higher elevations of the Central European mountain areas which show symptoms of needle yellowing and associated magnesium (Mg) deficiency. It was hypothesized that grasses would preferentially take up nitrate-nitrogen (NO3-N) over ammonium-nitrogen (NH4-N) which would support the cation balance in Mg deficient soils. In order to test this hypothesis, growth experiments were carried out in the greenhouse using plants which were cultivated in sand for nine weeks with full nutrient solution containing 0.2 or 2 mmol of N with different NH4 + to NO3 − ratios (1:0, 0.5:0.5, 0:1). In a short term experiment with labelled 15NH4 + and 15NO3 −, uptake of NH4 + and NO3 − was measured. When NO3 − was the only N source it was taken up at similar rate per g dry mass as in the experiment in which NH4 + was the only N source. However, at high supply pure NO3 − nutrition resulted in higher biomass. In contrast, supply of only...