Effect of nitrogen fertilisation on below‐ground carbon allocation in lettuce

Abstract

The aims of this study were to investigate the effect of nitrogen (N) fertilisation on the belowground carbon (C) translocation by lettuce and the CO 2 efflux from its rhizosphere. Two N fertilisation levels (80 and 160 kg N ha À1) and two growth stages (43 and 60 days) were tested. 14 C pulse labelling of shoots followed by 14 C monitoring in the soil, roots, microbial biomass and CO 2 efflux from the soil was used to distinguish between root-derived and soil organic matter-derived C. The 14 C allocation in the below-ground plant parts was 1.5-4.6 times lower than in the leaves. The total quantity of C translocated into the soil was much lower than in the case of cereals and grasses, amounting to 120 and 160 kg C ha À1 for low and high N respectively. N fertilisation diminished the proportion of assimilated C translocated below ground. About 5-8% of the assimilated C was respired into the rhizosphere. Rootderived CO 2 (the sum of root respiration and rhizomicrobial respiration) represented about 15-60% of the total CO 2 efflux from the planted soil. Two peaks were measured in the 14 CO 2 efflux: the first peak (4-5 h after labelling) was attributed to root respiration, whilst the second peak (12 h after labelling) was attributed to microbial respiration of exudates. Twelve days after labelling, 0.15-0.25% of the assimilated C was found in the microbial biomass. The higher microbial activity in the lettuce rhizosphere doubled the soil organic matter decomposition rate compared with unplanted soil.

Labile carbon retention compensates for CO2released by priming in forest soils

“…Microbial growth and enzyme production are accompanied by increased microbial demand for nutrients. Subsequently, microorganisms scavenge N from SOM and cause priming (Kuzyakov et al, 2002;Fontaine et al, 2004a;Cheng, 2009;Dijkstra et al, 2013;Paterson & Sim, 2013). This is apparent in the subtropical soil but only for single additions in the tropical soil.…”

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

“…The surface of the soil was covered with a PVC board and sealed with silicon, including around the maize stems. A leak check was carried out to confirm air tightness (Kuzyakov et al 2002). A beaker containing Ba 13 CO 3 (98 at.% 13 C; 4.5, 8.5, 8.0 and 8.0 g each for the 4 labeling occasions, respectively) was placed into the chamber and an aliquot of 1 M HCl was injected into the beaker every 1.5 h for 7 h. CO 2 concentration within the chamber was semi-quantita tively detected by GXH305 infrared detector (Beijing Analytical Equipment Co.) because of the differing wavelengths for maximum absorption of 13 CO 2 and 12 CO 2 .…”

Fate of rice shoot and root residues, rhizodeposits, and microbe-assimilated carbon in paddy soil – Part 1: Decomposition and priming effect

“…Previous studies have also reported that the rhizodeposits of rice account for ∼ 17 % of the photoassimilates (Nguyen, 2003) that enter paddy soil and that rice rhizodeposits include soluble exudates, root border cells, dead debris, and insoluble mucilage (Lu et al, 2003). In cereal crops, 10-25 % of root exudates are incorporated into SOC, and rhizodeposits are thought to play a key role in C cycling and sequestration in plant-soil-microbe systems (Kuzyakov et al, 2002(Kuzyakov et al, , 2003. In addition to the photosynthesized C substrates of plants, soil microbes are also able to assimilate CO 2 via the Calvin-Benson-Bassham cycle, thus can significantly contribute to the net uptake and assimilation of atmospheric CO 2 as well (Ge et al, 2013;Yuan et al, 2012b).…”

“…So far, the effect of C input from different C sources on the balance and stability of SOC has received limited attention. For example, the C in roots and shoots occurs as particulate matter and must be first depolymerized before be-ing taken up by microorganisms, whereas rhizodeposits are immediately available for uptake and assimilation by microorganisms, which is an important step in the formation of stable organic matter (Kuzyakov et al, 2002(Kuzyakov et al, , 2003. As low molecular weight substances, rhizodeposits are also protected from mineralization via adsorption onto soil particles (Jones and Edwards, 1998;Saidy et al, 2012;Sodano et al, 2016), which contributes to the stability and sequestration of SOC (Ge et al, 2012).…”