Shoot

About: Shoot is a research topic. Over the lifetime, 32188 publications have been published within this topic receiving 693348 citations.

Nutrition and growth of coniferous seedlings at varied relative nitrogen addition rate

Abstract: The growth of two provenances of Pinus sylvestris L. were compared with two provenances of Picea abies (L.) Karst. and with Pinus contorta Dougl. when grown in solution cultures with low nutrient concentrations. Nitrogen was added at different exponentially increasing rates, and the other nutrients were added at a rate high enough to ensure free access of them to the seedlings. During an initial period of the culture (a lag phase), when the internal nutrient status was changing from optimum to the level of the treatment, deficiency symptoms appeared. The needles yellowed and the root/shoot ratio increased. The initial phase was followed by a period of exponential growth and steady-state nutrition. The needles turned green again, and the root/shoot ratio stabilized at a level characteristic of the treatment. These patterns were the same as previously reported for other tree species. The relative growth rate during exponential growth was numerically closely equal to the relative nitrogen addition rate. The maximum relative growth rates were about 6 to 7.5% dry weight increase day-1. This is a much lower maximum than for broad-leaved species (about 20 to 30% day-1) under similar growth conditions. The internal nitrogen concentrations of the seedlings and the relative growth rates were stable during the exponential period. Close linear relationships were found between these parameters and the relative addition rate up to maximum growth. During steady state the relative growth rates of the different plant parts were equal. However, there were large differences between genotypes in absolute root growth rate at the same seedling size because of differences in root/shoot ratio. Lodgepole pine had the highest root growth rate, whereas that of Norway spruce, especially the southern provenance, was remarkably low. Yet, Norway spruce had a high ability to utilize available nutrients. In treatments with free nutrient access, growth allocation to the shoot had a high priority in all genotypes, but there was still a marked tendency for luxury uptake of nutrients. Nitrogen productivity (growth rate per unit of nitrogen) was lower than in broadleaved species and highest in lodgepole pine. The relevance of the dynamic factors, i.e. maximum relative growth rate, nutrient uptake rate, nitrogen productivity, growth allocation and root growth rate, are discussed with regard to conifer characteristics and selection value.

Effects of CO2 Enrichment and Nitrogen Stress on Growth, and Partitioning of Dry Matter and Nitrogen in Wheat and Maize

Abstract: Atmospheric CO2 levels are increasing, but little is known about how this will affect tissue concentrations and the partitioning of agriculturally important nutrients such as nitrogen (N) within crop plants. To investigate this, a glasshouse experiment was conducted in which wheat, a C3 species, and maize, a C4 species, were grown for 8 weeks at high CO2 (1500 cm3 m-3) on N supplies ranging from deficient (0.5 mol m-3) to more than adequate for maximum growth (25 mol m-3). Wheat responded to both CO2 enrichment and N supply; maize responded only to N supply. CO2-enriched wheat produced about twice the dry matter of control plants at all levels of N supply. Tiller and ear numbers were increased by CO2 enrichment irrespective of N supply. Enriched wheat plants had a lower Leaf Area Ratio but higher Net Assimilation Rate and Relative Growth Rate than control plants. There was no effect of CO2 enrichment on specific leaf weight. The enriched plants had lower shoot to root dry matter ratios than the controls at 6 mol m-3 N and higher. Shoot to root dry matter ratios of both wheat and maize increased with increasing N supply. CO2-enriched wheat plants accumulated more N than the controls but the proportional increase in N content was not as great as that in dry matter, with the result that concentrations of total-N and nitrate-N were lower in all organs of enriched plants, including ears. Nitrate reductase activity was lower in enriched than in control wheat plants. N-use efficiency by wheat was increased by CO2 enrichment. From a practical point of view, the study indicates that critical total-N and NO3-N concentrations used to diagnose the N status of wheat will need to be reassessed as global CO2 levels increase. Elevated CO2 may also reduce the protein content of grain and thus the baking quality of hard wheats.

Nitrogen isotope composition of tomato (Lycopersicon esculentum Mill. cv. T‐5) grown under ammonium or nitrate nutrition

Abstract: Studies that quantify plant δ15N often assume that fractionation during nitrogen uptake and intra-plant variation in δ15N are minimal. We tested both assumptions by growing tomato (Lycopersicon esculetum Mill. cv. T-5) at NH4+ or NO−3 concentrations typical of those found in the soil. Fractionation did not occur with uptake; whole-plant δ15N was not significantly different from source δ15 N for plants grown on either nitrogen form. No intra-plant variation in δ15N was observed for plants grown with NH+4. In contrast. δ15N of leaves was as much as 5.8% greater than that of roots for plants grown with NO−3. The contrasting patterns of intra-plant variation are probably caused by different assimilation patterns. NH+4 is assimilated immediately in the root, so organic nitrogen in the shoot and root is the product of a single assimilation event. NO−3 assimilation can occur in shoots and roots. Fractionation during assimilation caused the δ15N of NO−3 to become enriched relative to organic nitrogen; the δ15N of NO−3 was 11.1 and 12.9% greater than the δ15N of organic nitrogen in leaves and roots, respectively. Leaf δ15N may therefore be greater than that of roots because the NO−3 available for assimilation in leaves originates from a NO−3 pool that was previously exposed to nitrate assimilation in the root.