14C-assimilate partitioning within white clover plant - soil system: effects of photoperiod/temperature treatments and defoliation.

摘要

Pot-grown shoots of white clover (Trifolium repens) were pulse-labelled with 14CO2 in order to establish the partitioning of recently assimilated carbon among the different parts of the plant-soil system with special interest in belowground compartments. 14C-partitioning did not change significantly after a 24-h chase period. Leaves and stolons contained more than half of the total radioactivity recovered (TRR). Soil residues (microbial biomass and non-metabolized rhizodeposits) accounted for 7% TRR and rhizosphere CO2 was 25% TRR. In order to investigate seasonal effects on assimilate partitioning below ground, low photoperiod and dayight temperature conditions were examined. (10 h - 20deg C/18deg C, PTL treatment) with high photoperiod and dayighttemperature conditions (16 h-25deg C/20deg C, PTH treatment). Plants under PTH conditions favoured 14C-assimilate partitioning to leaves at the expense of storage organs such as stolons and roots. This was supported by distribution of the relative specific activity (RSA) which indicated a significant higher activity of leaves than of roots. The reduction of 14C allocated to roots (from 11% TRR in PTL treatment to 7% TRR in PTH conditions) was accompanied by a reduction of 14C found in rhizosphere CO2 (from 25% TRR to 12% TRR) and in soil residues (from 7% TRR to 3% TRR). This indicated that rhizodeposition of recently fixed carbon is correlated to C allocation to roots. A moderate defoliation (27% of leaf biomass removed) did not modify 14C-partitioning within the plant-soil system. A severe defoliation (51% of leaf biomass removed) increased 14C allocated to remaining leaves from 28% TRR to 37% TRR at the expense of stolons. Partitioning of labelled assimilates to belowground remained unchanged. It is suggested that the age of a plant strongly influences its response to leaf removal.