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Background and Aims: Below-ground translocated carbon (C) released as rhizodeposits is an important driver for microbial mobilization of nitrogen (N) for plants. We investigated how a limited substrate supply due to reduced photoassimilation alters the allocation of recently assimilated C in plant and soil pools under legume and non-legume species. Methods: A non-legume ( Lolium perenne) and a legume ( Medicago sativa) were labelled with N before the plants were clipped or shaded, and labelled twice with CO thereafter. Ten days after clipping and shading, the N and C in shoots, roots, soil, dissolved organic nitrogen (DON) and carbon (DOC) and in microbial biomass, as well as the C in soil CO were analyzed. Results: After clipping, about 50 % more C was allocated to regrowing shoots, resulting in a lower translocation to roots compared to the unclipped control. Clipping also reduced the total soil CO efflux under both species and the C recovery of soil CO under L. perenne. The N recovery increased in the shoots of M. sativa after clipping, because storage compounds were remobilized from the roots and/or the N uptake from the soil increased. After shading, the assimilated C was preferentially retained in the shoots of both species. This caused a decreased C recovery in the roots of M. sativa. Similarly, the total soil CO efflux under M. sativa decreased more than 50 % after shading. The N recovery in plant and soil pools showed that shading has no effect on the N uptake and N remobilization for L. perenne, but, the N recovery increased in the shoot of M. sativa. Conclusions: The experiment showed that the dominating effect on C and N allocation after clipping is the need of C and N for shoot regrowth, whereas the dominating effect after shading is the reduced substrate supply for growth and respiration. Only slight differences could be observed between L. perenne and M. sativa in the C and N distribution after clipping or shading. [ABSTRACT FROM AUTHOR]

Aims: Although water conservation in rice production has become increasingly important, the effects of water management on the allocation and dynamics of carbon (C) within the rice-soil system remain unknown. Methods: We compared the allocation and dynamics of C assimilated by rice under continuously flooded, non-flooded and alternate water regimes. Rice ( Oryza sative L. cv. Luliangyou 996) was labeled with CO and harvested 7 times within 45 days. Results: More C was released from roots into the soil in non-flooded and alternate water regimes treatments. Microbial C decreased with time after the labeling and was lowest under flooded condition. Roots and rhizomicrobial respiration followed the order of non-flooded > alternate water regimes > flooded treatment. Water management affected C distribution in aggregates with more C in macroaggregates in the non-flooded treatment. Estimated amounts of C transferred remaining belowground by rice 45 days after labeling were 1,986, 2,827 and 2,472 kg C ha, of which rhizodeposition accounted for about 41 %, 16 % and 30 % of C transferred belowground under non-flooded, flooded and alternate water regimes, respectively. Conclusions: Water management affected the allocation and dynamics of recently assimilated C within the rice-soil system and also changed the relative contribution of rhizodeposition to C transferred belowground. This study suggests the differences in the driving mechanisms of C sequestration under flooded vs. non-flooded and alternate water regimes. [ABSTRACT FROM AUTHOR]