Autor: |
Fishbeck, Kathleen A., Phillips, Donald A. |
Zdroj: |
Crop Science; March 1982, Vol. 22 Issue: 2 p251-254, 4p |
Abstrakt: |
The effects of host plant and Rhizobiumstrain variation on apparent N2fixation (C2H2reduction) and total nonstructural carbohydrate (TNC) of the root system during regrowth of alfalfa (Medicago sativaL.) were studied to determine the prevalence of the known decline in C2H2‐reduction activity following shoot harvest. Harvest at 10% bloom in ramets of a ‘Dohfari’ clone inoculated with Rhizobium melilotistrain 102F28 decreased shoot carbon exchange rate (CER) 99% immediately, but C2H2reduction declined only 75% in the following 3 days. Thereafter, CER and C2H2reduction increased in parallel during shoot regeneration. Those data provided circumstantial evidence that carbohydrates stored in roots or root nodules were used to maintain low rates of C2H2reduction during the intial period of regrowth. In experiments with seedlings of 10 alfalfa cultivars inoculated with R. meliloti102F28 and in trials with Dohfari and ‘Vernal’ clones inoculated with one of 10 different R. melilotistrains, shoot harvest produced a significant (p ≤0.001) decline in C2H2reduction within 3 days to values ranging from 4‐30% of the original rate. Root system TNC generally declined over the same period, but in only two of the 30 host‐symbiont combinations examined was that change significant (p ≤0.05). No significant correlation was observed between C2H2‐reduction rate and root system TNC in the same plants at harvest (day 0) or on day 3 in any host‐symbiont combination. Results from this study suggest that although nonstructural carbohydrates are consumed in alfalfa roots during defoliation, the), are not used to maintain maximum (day 0) rates of N2fixation during the early stages of regrowth in widely different host‐symbiont combinations. This evidence is consistent with the concept that the recovery of N2fixation following shoot harvest depends upon the regrowth of new shoots. |
Databáze: |
Supplemental Index |
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