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Nitrogen Response of Panicum Species Differing in CO 2 Fixation Pathways. I. Growth Analysis and Carbohydrate Accumulation 1
Author(s) -
Wilson J. R.,
Brown R. H.
Publication year - 1983
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1983.0011183x002300060029x
Subject(s) - panicum , biology , botany , nutrient , nitrogen fixation , relative growth rate , dry matter , temperate climate , horticulture , growth rate , ecology , bacteria , genetics , geometry , mathematics
The apparent higher N use efficiency (NUE) of tropical than temperate grasses could be associated with the more efficient C 4 cycle of CO 2 fixation possessed by tropical grasses. This possible association between NUE and the CO 2 fixation pathway was tested on five Panicum species with different pathways. P. maximum Jacq. (C 4 ), P. prionitis Griseb. (C 4 ), P. hylaeicum Mez (C 3 ), P. laxum Sw. (C 3 ), and also the intermediate (C 3 /C 4 ) species, P. schenckii Hack. were grown at day/night temperatures of 35/30 and 24/ 19°C. Plants were grown initially in complete nutrient solutions and then in N‐free solutions. Measurements of relative growth rate (R w ), leaf expansion, and leaf CO 2 exchange rate (CER) made just before and during the N withholding period. Panicum maximum maintained a higher R w , than the other species over a wide range of plant N status and had the highest maximum NUE of 6.1 kg of dry matter kg −l N day −1 . Panicum prionitis did not show the same absolute advantage in R w nor NUE over the C 3 species. However, both C 4 species generally showed a smaller relative decline in growth and CER at low N status than the C 3 and C 3 /C 4 species. Leaf area expansion was more sensitive to N stress than CER and there was some evidence that the C 4 species were able to continue leaf development at lower leaf N concentrations than the C 3 species. Growth temperature did not cause qualitative differences in the response to N, but NUE (kg kg −1 N day −1 ) was higher at 35/30°C than 24/19°C, except for P. schenckii . Morphological differences between species such as stem development also appeared to contribute to changes in R w with development of N deficiency. It is concluded that the inherently higher efficiency of the C 4 photosynthetic pathway does not necessarily lead to higher NUE of dry matter production of tropical grasses.