Theme 01: Ecophysiology of Grasslands
Description
The influence of the hierarchical position on the relationship between C gains and C losses (respiration) of individuals was investigated in a alfalfa (Medicago sativa) stand. The hierarchical position that an individual occupied was defined by its height relative to the stand height. Stands were established by arranging potted individual plants at a density of 400 plants m-2. Stands were grown in growth cabinets. 13C steady-state labelling was used to assess C fixation (Cnew) by individuals during a photoperiod of 16 h. Respiration of shoots was measured during the following 8 h dark period. The amount of Cnew used in shoot respiration (Cnew,R) was calculated from the rate of respiration and the isotopic composition of respiratory CO2. The rate of Cnew,R of each individual was proportional to the product of Cnew and the hierarchical position of the individual. For individuals in high hierarchical positions, Cnew,R was about 10 % of Cnew. This proportion decreased with decreasing hierarchical position. Conversely, the amount of C respired by the consumption of other substrates (Cold,R) was about 0.5 % of the shoot C mass. This was true for all plants, independent of their hierarchical position. It was concluded that plants getting into low hierarchical positions had to invest increasingly more carbohydrates from reserves to sustain maintenance needs.
Citation
Lötscher, M. and Schnyder, Hans, "Effect of the Hierarchical Position of Individuals in a Medicago sativa Stand on Shoot Respiration" (2021). IGC Proceedings (1993-2023). 8.
https://uknowledge.uky.edu/igc/19/1/8
Included in
Effect of the Hierarchical Position of Individuals in a Medicago sativa Stand on Shoot Respiration
The influence of the hierarchical position on the relationship between C gains and C losses (respiration) of individuals was investigated in a alfalfa (Medicago sativa) stand. The hierarchical position that an individual occupied was defined by its height relative to the stand height. Stands were established by arranging potted individual plants at a density of 400 plants m-2. Stands were grown in growth cabinets. 13C steady-state labelling was used to assess C fixation (Cnew) by individuals during a photoperiod of 16 h. Respiration of shoots was measured during the following 8 h dark period. The amount of Cnew used in shoot respiration (Cnew,R) was calculated from the rate of respiration and the isotopic composition of respiratory CO2. The rate of Cnew,R of each individual was proportional to the product of Cnew and the hierarchical position of the individual. For individuals in high hierarchical positions, Cnew,R was about 10 % of Cnew. This proportion decreased with decreasing hierarchical position. Conversely, the amount of C respired by the consumption of other substrates (Cold,R) was about 0.5 % of the shoot C mass. This was true for all plants, independent of their hierarchical position. It was concluded that plants getting into low hierarchical positions had to invest increasingly more carbohydrates from reserves to sustain maintenance needs.
