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Original title:
Sources of Carbon and Nitrogen for Leaf Growth in Grasses 
Translated title:
Quellen von C- und N-Substraten für das Blattwachstum von Gräsern 
Document type:
Fakultät Wissenschaftszentrum Weihenstephan 
Schnyder, J. (Univ. Prof. Dr.) 
Matyssek, Rainer (Prof. Dr.); Schmidhalter, Urs (Prof. Dr.) 
Subject group:
BIO Biowissenschaften 
carbon; nitrogen; leaf growth; fluxes; sources; storage; reserves; defoliation 
TUM classification:
BIO 485d; BIO 628d 
Aims: The subject of the present study was the use of carbon and nitrogen substrates for leaf growth in a C3 (Lolium perenne L.) and C4 (Paspalum dilatatum Poir.) grass. Specifically, the interests were, first, to explore how carbon and nitrogen substrates are used to produce leaf area, and second, to determine which sources supply them. In order to do this, a novel methodological approach to estimate C and N import into leaf growth zones was developed and coupled with steady-state labelling of photosynthesis (13CO2/12CO2) and N uptake (15NO3-/14NO3-). Time-courses of tracer incorporation into leaf growth zones were analyzed with compartmental models thus to resolve the number and kinetics of distinct pools supplying leaf growth. Materials & Methods: Plants of L. perenne and P. dilatatum were grown in mixed stands at 15°C (leading to C3 dominance) and 23°C (C4 dominance). Thus manipulated, individual plants grew in different environments and attained contrasting status, largely associated with their hierarchical positions within the stand. Compared to subordinate –shaded– plants (the C3 grass at 23°C, the C4 grass at 15°C), dominant –well-lit– plants (the C3 grass at 15°C, the C4 grass at 23°C) were bigger, taller, intercepted a greater proportion of incoming light, and had higher photosynthesis and N uptake rates. Results & Discussion: In response to severe defoliation, leaf area production was buffered from C shortage by an increased efficiency of substrates use in leaf area expansion. This was based on two mechanisms: mobilisation of C and N stores located within the growth zone, and decreases in the density of produced tissue. This response was evident in all plants, but its magnitude varied greatly between treatments, being directly related to the plant C status at the moment of defoliation. Thus, dominant L. perenne plants were able to maintain unaltered leaf area expansion rates for up to 2 d after defoliation, while leaf expansion rate decreased abruptly in subordinate P. dilatatum plants. In a second step, the sources of C and N supplying leaf growth were explored in undisturbed plants. Leaf growth relied largely on photoassimilates delivered either directly after fixation or short-term storage. Short-term C stores were equally important in dominant and subordinate plants. Hence, no link was found between the importance of stores and C acquisition rate. Conversely, compared to dominant plants, leaf growth in subordinate plants relied more on mobilized N from long-term stores, being largely independent of external N. These differences correlated well with the ratio of C to N in growth-substrates, and were associated with responses in N uptake. Conclusions: the present study demonstrates that (i) refoliation of these C3 and C4 species is sustained by identical mechanisms: short-term mobilisation of reserves within the growth zone, and reduced costs of produced leaf area, however (ii) the expression of these mechanisms depend strongly on the growth zone C status prior to defoliation. The second part of the study showed that (iii) the importance of C stores is not influence by photosynthesis capacity but largely associated to buffering light/dark cycles in both L. perenne and P. dilatatum. However, (iv) it revealed a negative association between the ability of these grasses to acquire external N and the relative importance of long-term internal stores in supplying N for leaf growth suggesting a common control mechanism may be operating. 
Translated abstract:
Zielsetzung: Die vorliegende Arbeit befasst sich mit der Nutzung von C- und N-Substraten im Blattwachstum einer C3 (Lolium perenne L.) und einer C4 Grasart (Paspalum dilatatum Poir.). Es soll insbesondere geklärt werden wie C- und N-Substrate in Blattflächenwachstum umgesetzt werden, und aus welchen Quellen diese Substrate stammen. Diese Fragestellungen wurden mit neuen methodischen Ansätzen in Kombination mit ‚steady-state’ Markierung der Photosyntheseprodukte (13CO2/12CO2) und des aufgenommene...    »
Publication :
Universitätsbibliothek der TU München 
Oral examination:
Controlled terms:
Deutsches Weidelgras C3-Pflanzen Spreite Wachstum Kohlenstoffstoffwechsel Stickstoffstoffwechsel Paspalum C4-Pflanzen 
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