C and N allocation in soil under ryegrass and alfalfa estimated by 13C and 15N labelling

Abstract

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 15 N before the plants were clipped or shaded, and labelled twice with 13 CO 2 thereafter. Ten days after clipping and shading, the 15 N and 13 C in shoots, roots, soil, dissolved organic nitrogen (DON) and carbon (DOC) and in microbial biomass, as well as the 13 C in soil CO 2 were analyzed. Results After clipping, about 50 % more 13 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 2 efflux under both species and the 13 C recovery of soil CO 2 under L. perenne. The 15 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 13 C was preferentially retained in the shoots of both species. This caused a decreased 13 C recovery in the roots of M. sativa. Similarly, the total soil CO 2 efflux under M. sativa decreased more than 50 % after shading. The 15 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 15 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.

Successive Harvests Affect Yield, Quality and Metabolic Profile of Sweet Basil (Ocimum basilicum L.)

“…These procedures typically result in a biomass reduction, although compensatory positive effects on the growth rate following defoliation have been also reported [58,59]. Defoliation also enhances the above-ground N yield of grasses [60], because of an increase uptake and preferential allocation of nitrogen to the shoots [61]. In the same way as our results, single clipping reduced leaf biomass in ryegrass and increased cytokinin concentration in leaves [62].…”

Fungal nutrient allocation in common mycorrhizal networks is regulated by the carbon source strength of individual host plants

“…This suggests that the shading treatment reduced the C supply for the CMN and that the AM fungus was unable to maintain its high colonization rate. Medicago sativa for example has been shown to respond very sensitively to shading, and even short-term shading can reduce the C allocation to the root system, and lead to a higher C allocation, particularly to the shoot meristems, to compensate for the decrease in the photosynthetic activity (Schmitt et al, 2013). Shading for 1-2 wk has been shown to reduce the mycorrhizal colonization of plants, but not to lower the C costs relative to nutrient benefit for the host plant (Heinemeyer et al, 2004;Olsson et al, 2010).…”

Host plant quality mediates competition between arbuscular mycorrhizal fungi

“…One possible explanation for why light conditions affect fungal competition is that shaded plants have a 'tighter' carbon budget than non-shaded plants and are more likely to control their root colonization (Schmitt et al 2013a). Given a tighter carbon budget, we would predict plants to allocate more carbon to R. irregularis compared to G. aggregatum because previous tests in root organ cultures demonstrated that R. irregularis generally transfers more P per unit of C compared to G. aggregatum .…”