Respiration and reproductive effort in Xanthium canadense.

Abstract

The proportion of resources devoted to reproduction in the plant is called the reproductive effort (RE), which is most commonly expressed as the proportion of reproductive biomass to total plant biomass production (RE(W)). Reproductive yield is the outcome of photosynthates allocated to reproductive structures minus subsequent respiratory consumption for construction and maintenance of reproductive structures. Thus, RE(W) can differ from RE in terms of photosynthates allocated to reproductive structures (RE(P)). * Dry mass growth and respiration of vegetative and reproductive organs were measured in Xanthium canadense and the amount of photosynthates and its partitioning to dry mass growth and respiratory consumption were determined. Differences between RE(W) and RE(P) were analysed in terms of growth and maintenance respiration. * The fraction of allocated photosynthates that was consumed by respiration was smaller in the reproductive organ than in the vegetative organs. Consequently, RE(P) was smaller than RE(W). The smaller respiratory consumption in the reproductive organ resulted from its shorter period of existence and a seasonal decline in temperature, as well as a slower rate of maintenance respiration, although the fraction of photosynthates consumed by growth respiration was larger than in the vegetative organs. * Reproductive effort in terms of photosynthates (RE(P)) was smaller than that in terms of biomass (RE(W)). This difference resulted from respiratory consumption for maintenance, which was far smaller in the reproductive organ than in vegetative organs.