Estimation of rhizodeposition at field scale: upscaling of a 14C labeling study

Abstract

Background and aims Rhizodeposition of plants is the most uncertain component of the carbon (C) cycle. By existing approaches the amount of rhizodeposition can only roughly be estimated since its persistence in soil is very short compared to other organic C pools. We suggest an approach to quantify rhizodeposition at the field scale by assuming a constant ratio between rhizodeposited-C to root-C. Methods Maize plants were pulse-labeled with 14 CO 2 under controlled conditions and the soil 14 CO 2 efflux was separated into root and rhizomicrobial respiration. The latter and the 14 C activity remaining in the soil corresponded to total rhizodeposition. By relating rhizodeposited-14 C to root-14 C a rhizodeposition-toroot ratio of 0.56 was calculated. This ratio was applied to the root biomass C measured in the field to estimate rhizodeposition under field conditions. Results Maize allocated 298 kg C ha −1 as root-C and 166 kg C ha −1 as rhizodeposited-C belowground, 50 % of which were recovered in the upper 10 cm. The fate of rhizodeposits was estimated based on the 14 C data, which showed that 62 % of total rhizodeposition was mineralized within 16 days, 7 % and 0.3 % was incorporated into microbial biomass and DOC, respectively, and 31 % was recovered in the soil.Conclusions We conclude that the present approach allows for an improved estimation of total rhizodeposition, since it accounts not only for the fraction of rhizodeposits remaining in soil, but also for that decomposed by microorganisms and released from the soil as CO 2 .

Rhizodeposition of organic carbon by plants with contrasting traits for resource acquisition: responses to different fertility regimes

“…In contrast, strong correlations between total rhizodeposited 13 C and leaf or root biomass were observed supporting previous studies which assume that exudation patterns were affected by species identity and particularly root biomass (Van der Krift et al 2001;Blagodatskaya et al 2014). All together, these results suggest that changes of rhizodeposition rate following fertilization were not dependent of soil microbial community but rather support a substantial influence of plant features (Farrar et al, 2003;Warembourg et al, 2003;Kuzyakov and Cheng, 2004;Badri and Vivanco, 2009) on rhizodeposition processes as already demonstrated by previous studies on grassland (Van der Krift et al, 2001;Pausch et al, 2013) and forest species (Bowden et al, 2004). …”

Variation in soil C and microbial functions across tree canopy projection and open grassland microenvironments

“…No variation in soil organic C associated with grapevine trees was observed within the vineyards. The high TOC observed in soil under oak canopies might be the result of the long-term transfer to the soil of high amounts of organic C deriving from the aboveground tree biomass (Moreno et al, 2007) and tree rhizodeposition (Pausch et al, 2013), as well as from dejections of grazing sheep that, particularly in the summer, rest in the shade under the tree canopies. According to what was observed by Gómez-Rey et al (2012), PAU showed a content of C 0 , MR basal , and MR higher than that in PAO, indicating a larger soil microbial activity and a positive trend for C stock potential.…”

Investigation of photosynthate-C allocation 27 days after 13C-pulse labeling of Zea mays L. at different growth stages

“…This translates to 4.6 t C ha −1 translocated belowground annually, which is partitioned into 2.1 t C ha −1 lost as CO 2 by rhizosphere respiration, 2.2 t C ha −1 allocated to root biomass and 0.3 t C ha −1 incorporated into SOC. However, the longevity of the latter maize-C pool in soil post-27 days remains to be determined, including the potential positive priming effect of maize rhizoexudation on extant SOC (Pausch et al 2012).…”