Do elevation of CO2 concentration and nitrogen fertilization alter storage and remobilization of carbon and nitrogen in pedunculate oak saplings? (original) (raw)
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Tree Physiology, 2001
Pedunculate oak (Quercus robur L.) seedlings were grown for 3 or 4 months (second-and third-flush stages) in greenhouses at two atmospheric CO 2 concentrations ([CO 2 ]) (350 or 700 µmol mol -1 ) and two nitrogen fertilization regimes (6.1 or 0.61 mmol N l -1 nutrient solution). Combined effects of [CO 2 ] and nitrogen fertilization on partitioning of newly acquired carbon (C) and nitrogen (N) were assessed by dual 13 C and 15 N short-term labeling of seedlings at the second-or third-flush stage of development. In the low-N treatment, root growth, but not shoot growth, was stimulated by elevated [CO 2 ], with the result that shoot/root biomass ratio declined. At the second-flush stage, overall seedling biomass growth was increased (13%) by elevated [CO 2 ] regardless of N fertilization. At the third-flush stage, elevated [CO 2 ] increased growth sharply (139%) in the high-N but not the low-N treatment. Root/shoot biomass ratios were threefold higher in the low-N treatment relative to the high-N treatment. At the second-flush stage, leaf area was 45-51% greater in the high-N treatment than in the low-N treatment. At the-third flush stage, there was a positive interaction between the effects of N fertilization and [CO 2 ] on leaf area, which was 93% greater in the high-N/elevated [CO 2 ] treatment than in the low-N/ambient [CO 2 ] treatment. Specific leaf area was reduced (17-25%) by elevated [CO 2 ], whereas C and N concentrations of seedlings increased significantly in response to either elevated [CO 2 ] or high-N fertilization. At the third-flush stage, acquisition of C and N per unit dry mass of leaf and fine root was 51 and 77% greater, respectively, in the elevated [CO 2 ]/high-N fertilization treatment than in the ambient [CO 2 ]/low-N fertilization treatment. However, there was dilution of leaf N in response to elevated [CO 2 ]. Partitioning of newly acquired C and N between shoot and roots was altered by N fertilization but not [CO 2 ]. More newly acquired C and N were partitioned to roots in the low-N treatment than in the high-N treatment.
Global Change Biology, 2003
Nitrogen-fixing plant species growing in elevated atmospheric carbon dioxide concentration ([CO 2 ]) should be able to maintain a high nutrient supply and thus grow better than other species. This could in turn engender changes in internal storage of nitrogen (N) and remobilisation during periods of growth. In order to investigate this one-yearold-seedlings of Alnus glutinosa (L.) Gaertn and Pinus sylvestris (L.) were exposed to ambient [CO 2 ] (350 mmol mol 21) and elevated [CO 2 ] (700 mmol mol 21) in open top chambers (OTCs). This constituted a main comparison between a nitrogen-fixing tree and a nonfixer, but also between an evergreen and a deciduous species. The trees were supplied with a full nutrient solution and in July 1994, the trees were given a pulse of 15 N-labelled fertiliser. The allocation of labelled N to different tissues (root, leaves, shoots) was followed from September 1994 to June 1995. While N allocation in P. sylvestris (Scots pine) showed no response to elevated [CO 2 ], A. glutinosa (common alder) responded in several ways. During the main nutrient uptake period of June±August, trees grown in elevated [CO 2 ] had a higher percentage of N derived from labelled fertiliser than trees grown in ambient [CO 2 ]. Remobilisation of labelled N for spring growth was significantly higher in A. glutinosa grown in elevated [CO 2 ] (9.09% contribution in ambient vs. 29.93% in elevated [CO 2 ] leaves). Exposure to elevated [CO 2 ] increased N allocation to shoots in the winter of 1994±1995 (12.66 mg in ambient vs. 43.42 mg in elevated 1993 shoots; 4.81 mg in ambient vs. 40.00 mg in elevated 1994 shoots). Subsequently significantly more labelled N was found in new leaves in April 1995. These significant increases in movement of labelled N between tissues could not be explained by associated increases in tissue biomass, and there was a significant shift in C-biomass allocation away from the leaves towards the shoots (all above-ground material except leaves) in A. glutinosa. This experiment provides the first evidence that not only are shifts in C allocation affected by elevated [CO 2 ], but also internal N resource utilisation in an N 2-fixing tree.
Annals of Forest Science, 2004
A dual long-term 13 C and 15 N labeling was used to assess the contribution of winter assimilated carbon (C) and nitrogen (N) for the spring growth flush of two-year-old cork oak plants. Changes in concentrations and partitioning of winter assimilated C and N, total C and N, and total-non-structural carbohydrates were followed from January to August in the various plant parts (first year and second year leaves, stem, branches, coarse and fine roots). No loss of winter C and N was observed with time suggesting that winter assimilates are retained within the plant and contribute to storage. A strong mobilisation of C and N was demonstrated from first year leaves and fine roots during the spring growth flush. Leaves from the second year and, to lesser extent, branches acted as sinks for winter C and N. At the beginning of the new leaf growth, a significant decrease in starch concentration occurred in first year leaves. In August, before leaf fall we observed also a mobilisation from first year to second year leaves, of N assimilated after labeling. We conclude that under these experimental conditions, both winter and current C and N were used for the spring growth flush of the cork oak plants. The foliage grown during the previous year was a source of winter and recently assimilated N and a source of C from recent assimilates for the new growth in the spring. Quercus suber / 13C labeling / 15N labeling / remobilisation / carbohydrates Résumé-Mise en réserve hivernale du carbone et de l'azote et remobilisation lors de la croissance saisonnière de chênes-lièges (Quercus suber L.) âgés de deux ans. Un double marquage 13 C et 15 N à long terme a été réalisé afin d'évaluer la contribution du carbone (C) et de l'azote (N) assimilés durant l'hiver, à la croissance printanière de chênes-lièges âgés de deux ans. Les évolutions concomitantes des concentrations et de la répartition du C, du N, ainsi que la concentration en glucides totaux non structuraux, ont été suivies de janvier à août dans les différents organes (feuilles préexistantes et printanières, tige principale, rameaux axillaires, grosses et fine racines) des jeunes arbres. Le C et le N assimilés durant l'hiver ne sont pas perdus par les plants. Une forte mobilisation de C et de N est observée au printemps, pendant la période de croissance aérienne, au niveau des feuilles préexistantes et des racines fines. Les feuilles développées au printemps et, dans une moindre mesure les rameaux axillaires, importent le C et le N assimilés durant l'hiver. Lorsque la croissance des nouvelles feuilles démarre, une diminution significative de la concentration en amidon est observée dans les feuilles préexistantes. En août, lors de leur sénescence, une exportation d'azote nouvellement assimilé est aussi observée au niveau des feuilles préexistantes. Nous concluons que, dans nos conditions expérimentales, il existe une coopération entre le C et le N assimilés en hiver et au printemps pour assurer la croissance printanière des plants de chêne-liège. Il est démontré en outre que feuilles préexistantes sont une source de N hivernal et de C et de N nouvellement assimilés pour cette nouvelle croissance. Quercus suber / marquage 13 C / marquage 15 N / remobilisation / carbohydrates
Oecologia, 1991
Seeds of Gliricidia sepium (Jacq.) Walp., a tree native to seasonal tropical forests of Central America, were inoculated with N-fixing Rhizobium bacteria and grown in growth chambers for 71 days to investigate interactive effects of atmospheric CO2 and plant N status on early seedling growth, nodulation, and N accretion. Seedlings were grown with CO2 partial pressures of 350 and 650 gbar (current ambient and a predicted partial pressure of the mid-21st century) and with plus N or minus N nutrient solutions to control soil N status. Of particular interest was seedling response to CO2 when grown without available soil N, a condition in which seedlings initially experienced severe N deficiency because bacterial N-fixation was the sole source of N. Biomass of leaves, stems, and roots increased significantly with CO2 enrichment (by 32%, 15% and 26%, respectively) provided seedlings were supplied with N fertilizer. Leaf biomass of N-deficient seedlings was increased 50% by CO z enrichment but there was little indication that photosynthate translocation from leaves to roots or that plant N (fixed by Rhizobium) was altered by elevated CO2. In seedlings supplied with soil N, elevated CO2 increased average nodule weight, total nodule weight per plant, and the amount of leaf nitrogen provided by N-fixation (as indicated by leaf 615N). While COz enrichment reduced the N concentration of some plant tissues, whole plant N accretion increased. Results support the contention that increasing atmospheric CO2 partial pressures will enhance productivity and N-fixing activity of N-fixing tree seedlings, but that the magnitude of early seedling response to CO2 will depend greatly on plant and soil nutrient status.
Journal of Integrative Plant Biology, 2008
Plants grown under elevated atmospheric [CO 2 ] typically have decreased tissue concentrations of N compared with plants grown under current ambient [CO 2 ]. The physiological mechanisms responsible for this phenomenon have not been definitely established, although a considerable number of hypotheses have been advanced to account for it. In this review we discuss and critically evaluate these hypotheses. One contributing factor to the decreases in tissue N concentrations clearly is dilution of N by increased photosynthetic assimilation of C. In addition, studies on intact plants show strong evidence for a general decrease in the specific uptake rates (uptake per unit mass or length of root) of N by roots under elevated CO 2. This decreased root uptake appears likely to be the result both of decreased N demand by shoots and of decreased ability of the soil-root system to supply N. The best-supported mechanism for decreased N supply is a decrease in transpiration-driven mass flow of N in soils due to decreased stomatal conductance at elevated CO 2 , although some evidence suggests that altered root system architecture may also play a role. There is also limited evidence suggesting that under elevated CO 2 , plants may exhibit increased rates of N loss through volatilization and/or root exudation, further contributing to lowering tissue N concentrations.
Elevated CO 2 and plant nitrogen-use: is reduced tissue nitrogen concentration size-depend
Oecologia, 1993
Plants often respond to elevated atmospheric CO2 levels with reduced tissue nitrogen concentrations relative to ambient CO2-grown plants when comparisons are made at a common time. Another common response to enriched COz atmospheres is an acceleration in plant growth rates. Because plant nitrogen concentrations are often highest in seedlings and subsequently decrease during growth, comparisons between ambient and elevated CO2-grown plants made at a common time may not demonstrate CO2-induced reductions in plant nitrogen concentration per se. Rather, this comparison may be highlighting differences in nitrogen concentration between bigger, more developed plants and smaller, less developed plants. In this study, we directly examined whether elevated CO2 environments reduce plant nitrogen concentrations independent of changes in plant growth rates. We grew two annual plant species, Abutilon theophrasti (C3 photosynthetic pathway) and Amaranthus retroflexus (C4 photosynthetic pathway), from seed in glass-sided growth chambers with atmospheric CO2 levels of 350 gmol-mol-1 or 700 gmol 9 mol-1 and with high or low fertilizer applications. Individual plants were harvested every 2 days starting 3 days after germination to determine plant biomass and nitrogen concentration. We found: 1. High CO2-grown plants had reduced nitrogen concentrations and increased biomass relative to ambient CO2-grown plants when compared at a common time; 2. Tissue nitrogen concentrations did not vary as a function of CO2 level when plants were compared at a common size; and 3. The rate of biomass accumulation per rate of increase in plant nitrogen was unaffected by CO2 availability, but was altered by nutrient availability. These results indicate that a CO2-induced reduction in plant nitrogen concentration may not be due to physiological changes in plant nitrogen use efficiency, but is probably a size-dependent phenomenon resulting from accelerated plant growth.
1999
N-fixing trees facilitate the growth of neighboring trees of other species. These neighboring species benefit from the simple presence of the N fixation symbiosis in their surroundings. Because of this phenomenon, it has been hypothesized that a change in atmospheric CO 2 concentration may alter the role of N-fixing trees in their environment. It is thought that the role of N-fixing trees in ecosystems of the future may be more important since they may help sustain growth increases due to increased CO 2 concentration in nitrogen limited forests. We examined: (1) whether symbiotically fixed N was exuded from roots, (2) whether a doubled atmospheric CO 2 concentration would result in increased organic N exudation from roots, and (3) whether increased temperature or N availability affected N exudation from roots. This study analyzed exudation of dissolved organic N from the roots of seedlings of the N-fixing tree Robinia pseudoacacia L. in a full factorial design with 2 CO 2 (35.0 and 70.0 Pa) × 2 temperature (26 or 30 • C during the day) × 2 N fertilizer (0 and 10.0 mM N concentration) levels. Trees with no other source of N except N fixation exuded about 1% to 2% of the fixed N through their roots as dissolved organic N. Increased atmospheric CO 2 concentrations did not, however, increase N exudation rates on a per gram belowground biomass basis. A 4 • C increase in temperature and N fertilization did, however, significantly increase N exudation rates. These results suggest that exudation of dissolved organic N from roots or nodules of N-fixing trees could be a significant, but minor, pathway of transferring N to neighboring plants in a much more rapid and direct way than cycling through death, decomposition and mineralization of plant residues. And, while exudation rates of dissolved organic N from roots were not significantly affected by atmospheric CO 2 concentration, the previously observed 'CO 2 fertilization effect' on N-fixing trees suggests that N exudation from roots could play a significant but minor role in sustaining increases in forest growth, and thus C storage, in a CO 2 enriched atmosphere.
Elevated CO 2 and plant nitrogen-use: is reduced tissue nitrogen concentration size-dependent
Oecologia, 1993
Plants often respond to elevated atmospheric CO2 levels with reduced tissue nitrogen concentrations relative to ambient CO2-grown plants when comparisons are made at a common time. Another common response to enriched CO2 atmospheres is an acceleration in plant growth rates. Because plant nitrogen concentrations are often highest in seedlings and subsequently decrease during growth, comparisons between ambient and elevated CO2-grown plants made at a common time may not demonstrate CO2-induced reductions in plant nitrogen concentration per se. Rather, this comparison may be highlighting differences in nitrogen concentration between bigger, more developed plants and smaller, less developed plants. In this study, we directly examined whether elevated CO2 environments reduce plant nitrogen concentrations independent of changes in plant growth rates. We grew two annual plant species. Abutilon theophrasti (C3 photosynthetic pathway) and Amaranthus retroflexus (C4 photosynthetic pathway), from seed in glass-sided growth chambers with atmospheric CO2 levels of 350 μmol·mol−1 or 700 μmol·mol−1 and with high or low fertilizer applications. Individual plants were harvested every 2 days starting 3 days after germination to determine plant biomass and nitrogen concentration. We found: 1. High CO2-grown plants had reduced nitrogen concentrations and increased biomass relative to ambient CO2-grown plants when compared at a common time; 2. Tissue nitrogen concentrations did not vary as a function of CO2 level when plants were compared at a common size; and 3. The rate of biomass accumulation per rate of increase in plant nitrogen was unaffected by CO2 availability, but was altered by nutrient availability. These results indicate that a CO2-induced reduction in plant nitrogen concentration may not be due to physiological changes in plant nitrogen use efficiency, but is probably a size-dependent phenomenon resulting from accelerated plant growth.
PLANT PHYSIOLOGY, 2005
Patterns of synthesis and breakdown of carbon (C) and nitrogen (N) stores are relatively well known. But the role of mobilized stores as substrates for growth remains less clear. In this article, a novel approach to estimate C and N import into leaf growth zones was coupled with steady-state labeling of photosynthesis ( 13 CO 2 / 12 CO 2 ) and N uptake ( 15 NO 3 2 / 14 NO 3 2 ) and compartmental modeling of tracer fluxes. The contributions of current C assimilation/N uptake and mobilization from stores to the substrate pool supplying leaf growth were then quantified in plants of a C 3 (Lolium perenne) and C 4 grass (Paspalum dilatatum Poir.) manipulated thus to have contrasting C assimilation and N uptake rates. In all cases, leaf growth relied largely on photoassimilates delivered either directly after fixation or short-term storage (turnover rate 5 1.6-3.3 d 21 ). Long-term C stores (turnover rate , 0.09 d 21 ) were generally of limited relevance. Hence, no link was found between the role of stores and C acquisition rate. Short-term (turnover rate 5 0.29-0.90 d 21 ) and long-term (turnover rate , 0.04 d 21 ) stores supplied most N used in leaf growth. Compared to dominant (well-lit) plants, subordinate (shaded) plants relied more on mobilization from long-term N stores to support leaf growth. These differences correlated well with the C-to-N ratio of growth substrates and were associated with responses in N uptake. Based on this, we argue that internal regulation of N uptake acts as a main determinant of the importance of mobilized long-term stores as a source of N for leaf growth.
Scientific Reports, 2015
The influence of carbon dioxide (CO2) and soil fertility on the physiological performance of plants has been extensively studied, but their combined effect is notoriously difficult to predict. Using Coffea arabica as a model tree species, we observed an additive effect on growth, by which aboveground productivity was highest under elevated CO2 and ammonium fertilization, while nitrate fertilization favored greater belowground biomass allocation regardless of CO2 concentration. A pulse of labelled gases (13CO2 and 15NH3) was administered to these trees as a means to determine the legacy effect of CO2 level and soil nitrogen form on foliar gas uptake and translocation. Surprisingly, trees with the largest aboveground biomass assimilated significantly less NH3 than the smaller trees. This was partly explained by declines in stomatal conductance in plants grown under elevated CO2. However, unlike the 13CO2 pulse, assimilation and transport of the 15NH3 pulse to shoots and roots varied a...