Effect of shading and clipping of ryegrass and alfalfa on C allocation and fluxes as estimated by 14C labeling
P 1.12 in Ecosystem Function
The photosynthetic rate is a driving force for carbon (C) allocation within different pools in the plant-soil-microorganism system. Thus, factors controlling photosynthesis, such as light availability or defoliation, alter the substrate supply. Two plant species, ryegrass (Lolium perenne, L.) and alfalfa (Medicago sativa, L.), were grown under controlled laboratory conditions. To analyze the redistribution of stored C, repeated 14CO2 pulse labeling was used, followed by shading and clipping of the plants 5 days after the last pulse. Subsequently, for each treatment the 14CO2 efflux from the soil was measured. The 14C content in above- and below-ground plant biomass, soil, rhizosphere and their microorganisms was determined 10 days after shading and clipping. Applied 14C was detected in the newly grown shoots of clipped plants, tending to originate from roots and less from remaining shoots. A trend to a 14C increase in rhizosphere soil and its microorganisms after clipping was found. Compared to non-shaded plants, a higher 14C activity was detected in shoots and roots after the shading. Plants not limited in their photosynthetic ability gain more new unlabeled C leading to dilution of earlier assimilated 14C. As expected, there was no significant difference in 14CO2-efflux between the different treatments. This study demonstrates that 14C labeling coupled with clipping or shading of plants is a suitable approach to determine the translocation of stored C in plant and soil pools.