Abstract
The objective of this work was to determine if the impact of nitrogen (N) on the release of organic carbon (C) into the soil by roots (rhizodeposition) correlated with the effect of this nutrient on some variables of plant growth. Lolium multiflorum Lam. was grown at two levels of N supply, either in sterile sand percolated with nutrient solution or in non-sterile soil. The axenic sand systems allowed continuous quantification of rhizodeposition and accurate analysis of root morphology whilst the soil microcosms allowed the study of 14 C labelled C flows in physico-chemical and biological conditions relevant to natural soils. In the axenic sand cultures, enhanced N supply strongly increased the plant biomass, the plant N content and the shoot to root ratio. N supply altered the root morphology by increasing the root surface area and the density of apices, both being significantly positively correlated with the rate of organic C release by plant roots before sampling. This observation is consistent with the production of mucilage by root tips and with mechanisms of root exudation reported previously in the literature, i.e. the passive diffusion of roots solutes along the root with increased rate behind the root apex. We proposed a model of root net exudation, based on the number of root apices and on root soluble C that explained 60% of the variability in the rate of C release from roots at harvest. The effects of N on plant growth were less marked in soil, probably related to the relatively high supply of N from non-fertiliser soil-sources. N fertilization increased the shoot N concentration of the plants and the shoot to root ratio. Increased N supply decreased the partitioning of 14 C to roots. In parallel, N fertilisation increased the root soluble 14 C and the 14 C recovered in the soil per unit of root biomass, suggesting a stimulation of root exudation by N supply. However, due to the high concentration of N in our unfertilised plants, this stimulation was assumed to be very weak because no significant effect of N was observed on the microbial C and on the bacterial abundance in the rhizosphere. Considering the difficulties in evaluating rhizodeposition in non sterile soil, it is suggested that the root soluble C, the root surface area and the root apex density are additional relevant variables that should be useful to measure along with the variables that are commonly determined when investigating how plant functioning impacts on the release of C by roots (i.e soil C, C of the microbial biomass, rhizosphere respiration).
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Claims 10
Claim · model-written summary
Enhanced N supply strongly increased plant biomass, plant N content and the shoot to root ratio in axenic sand cultures.
- Taxon
- Lolium multiflorum
Lolium multiflorume0 - Treatment
- enhanced N supplye1
- Outcome
- plant biomass, the plant N content and the shoot to root ratioe1
- Direction
- increasede1
- Setting
- axenic sand culturese1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Lolium multiflorum Lam. was grown at two levels of N supply”
e1“In the axenic sand cultures, enhanced N supply strongly increased the plant biomass, the plant N content and the shoot to root ratio”
Claim · model-written summary
N supply increased root surface area and the density of root apices.
- Taxon
- Lolium multiflorumLolium multiflorume0
- Organ / stage
- roote2
- Treatment
- N supplye2
- Outcome
- root surface area and the density of apicese2
- Direction
- increasinge2
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Lolium multiflorum Lam. was grown at two levels of N supply”
e2“N supply altered the root morphology by increasing the root surface area and the density of apices”
Claim · model-written summary
Root surface area and density of root apices were significantly positively correlated with the rate of organic C release by roots.
- Taxon
- Lolium multiflorumLolium multiflorume0
- Organ / stage
- apicese2
- Outcome
- rate of organic C release by plant rootse3
- Direction
- positively correlatede3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Lolium multiflorum Lam. was grown at two levels of N supply”
e2“N supply altered the root morphology by increasing the root surface area and the density of apices”
e3“both being significantly positively correlated with the rate of organic C release by plant roots”
Claim · model-written summary
A model of root net exudation based on root apex number and root soluble C explained 60% of the variability in the rate of C release from roots.
- Taxon
- Lolium multiflorumLolium multiflorume0
- Outcome
- variability in the rate of C release from rootse4
- Value
- 60%e4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Lolium multiflorum Lam. was grown at two levels of N supply”
e4“that explained 60% of the variability in the rate of C release from roots at harvest”
Claim · model-written summary
N fertilization increased the shoot N concentration and the shoot to root ratio of the plants.
- Taxon
- Lolium multiflorumLolium multiflorume0
- Treatment
- N fertilizatione5
- Outcome
- shoot N concentration of the plants and the shoot to root ratioe5
- Direction
- increasede5
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Lolium multiflorum Lam. was grown at two levels of N supply”
e5“N fertilization increased the shoot N concentration of the plants and the shoot to root ratio”
Claim · model-written summary
The effects of N on plant growth were less marked in soil than in sand.
- Taxon
- Lolium multiflorumLolium multiflorume0
- Outcome
- effects of N on plant growthe6
- Direction
- less markede6
- Setting
- soile6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Lolium multiflorum Lam. was grown at two levels of N supply”
e6“The effects of N on plant growth were less marked in soil”
Claim · model-written summary
Increased N supply decreased the partitioning of 14C to roots.
- Taxon
- Lolium multiflorumLolium multiflorume0
- Treatment
- Increased N supplye7
- Outcome
- partitioning of 14 C to rootse7
- Direction
- decreasede7
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Lolium multiflorum Lam. was grown at two levels of N supply”
e7“Increased N supply decreased the partitioning of 14 C to roots”
Claim · model-written summary
N fertilisation increased root soluble 14C and the 14C recovered in soil per unit of root biomass.
- Taxon
- Lolium multiflorumLolium multiflorume0
- Treatment
- N fertilisatione1
- Outcome
- root soluble 14 C and the 14 C recovered in the soil per unit of root biomasse1
- Direction
- increasede1
- Setting
- soile1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Lolium multiflorum Lam. was grown at two levels of N supply”
e1“N fertilisation increased the root soluble 14 C and the 14 C recovered in the soil per unit of root biomass”
Claim · model-written summary
N supply had no significant effect on rhizosphere bacterial abundance.
- Taxon
- Lolium multiflorumLolium multiflorume0
- Treatment
- Ne1
- Outcome
- bacterial abundance in the rhizospheree1
- Direction
- no_changeinferrede1
- Qualifier
- microbial Ce1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Lolium multiflorum Lam. was grown at two levels of N supply”
e1“no significant effect of N was observed on the microbial C and on the bacterial abundance in the rhizosphere”
Claim · model-written summary
The authors suggest that root soluble C, root surface area and root apex density should be measured alongside the usual rhizodeposition variables.
- Taxon
- Lolium multiflorumLolium multiflorume0
- Outcome
- root soluble C, the root surface area and the root apex densitye1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Lolium multiflorum Lam. was grown at two levels of N supply”
e1“the root soluble C, the root surface area and the root apex density are additional relevant variables that should be useful to measure”
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See all 11 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.