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Nitrogen relations of the sorghum‐Sfriga hermonthica hostparasite association: growth and photosynthesis
Author(s) -
CECHIN I.,
PRESS M. C.
Publication year - 1993
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1993.tb00866.x
Subject(s) - striga hermonthica , sorghum , striga , biology , photosynthesis , nitrogen , agronomy , botany , zoology , horticulture , chemistry , organic chemistry
The extent to which the parasitic angiosperm Striga hermonthica reduces the growth of its sorghum host is dependent on the concentration of nitrogen (as NH 4 NO 3 in 40% Long Ashton Solution) supplied to the plants. The biomass of 0.5,1 and 2 mol m −3 N‐grown infected plants was 22,30 and 66%, respectively, of uninfected plants after 140d growth. The biomass of 3 and 4 mol m −3 N‐grown infected plants differed little from uninfected plants. No grain was set in 0.5 and 1 mol m −3 N‐grown infected plants, grain yield reached 42 and 73% of controls in 2 and 3 mol m −3 N‐grown plants, and was unaffected in 4 mol m −3 N‐grown plants. Striga hermonthica also altered the allometry and architecture of the host, at all but the highest N concentration. Higher N concentration (3 and 4 mol m −3 N) reduced the growth of S. hermonthica. Foliar N concentrations in sorghum ranged from 11 mg g −1 dwt. in 0.5 mol m −3 N‐grown plants, to 28 mg g −1 dwt. in 4 mol m −3 N‐grown plants, and were not affected by S. hermonthica. Higher N concentrations were measured in S. hermonthica , and ranged from 18 to 45 mg g −1 dwt. in 0.5 and 3 mol m −3 N‐grown plants, respectively. The relationship between photosynthesis (CO 2 flux) and N concentration differed between uninfected and infected sorghum. This was most apparent in 0.5 mol m −3 N‐grown plants, with rates of 16 and 11 μmol m −2 s −1 in uninfected and infected plants, respectively (at 1500–1800 μmol m −2 s −1 photosynthetic photon flux density). At higher N concentrations, this difference was smaller, with both sets of plants reaching 26 μmol m −2 s −1 at 4 mol m −3 N. Varying the level of S. hermonthica infection showed that the effect of N on host photosynthesis cannot be explained by differences in the mass or number of parasites supported by the host. At low levels of infection in 1 mol m −3 N‐grown plants, the negative effect of the parasite was reversed, and photosynthesis in infected plants exceeded that in uninfected plants by 20%. Photosynthesis in S. hermonthica at 3 mol m −3 N (8 μmol m −2 s −1 ) was double that in 0.5 mol m −3 N‐grown plants. Stable carbon isotope and gas exchange measurements data demonstrated that this higher level of autotrophic carbon fixation was accompanied by a lower dependency on hetero trophic carbon. The latter ranged from 27 to 6% in 0 5 mol m −3 and 3 mol m −3 N‐grown plants, respectively.