# Litter C:N Ratio and Soil Water Retention Drive Early CO and NO Emissions from Recycled Litter on Urban Lawns

Tom Künnemann, Guillaume Humbert, Hugues Clivot, Gonzague Alavoine, Patrice Cannavo, R Guenon, Gwenaëlle Lashermes

► To cite this version:

Tom Künnemann, Guillaume Humbert, Hugues Clivot, Gonzague Alavoine, Patrice Cannavo, et al. Litter C:N Ratio and Soil Water Retention Drive Early CO and NO Emissions from Recycled Litter on Urban Lawns. VII EuroSoil, Sep 2025, Seville (Spain), Spain. hal-05304452

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# Litter C:N Ratio and Soil Water Retention Drive Early CO₂ and N₂O Fluxes from Recycled Litter on Urban Lawns

T. Künnemann¹,², G. Humbert², G. Alavoine², P. Cannavo¹, H. Clivot², R. Guénon¹, G. Lashermes²

(1) L'Institut Agro Rennes-Angers, UP EPHor; (2) INRAE, URCA, UMR FARE

September 11th, 2025, Sevilla, EUROSOIL

<figure><img src="image_2.png" /></figure>
Plants and soils are key contributors to most **ecosystem services** in cities

<figure><img src="image_3.png" /></figure>

Decomposition

<figure><img src="image_4.png" /></figure>

C storage
Fertility
Infiltration
Biodiversity...

(Sadeghian 2013;
Wang et al. 2022)
Plants and soils are key contributors to most **ecosystem services** in cities

**Lawns** cover up to 50-70% of urban green spaces (UGSs) worldwide (Ignatieva et al. 2020)

**Ecosystem services provided by UGS soils could be enhanced by recycling litter on lawn soil** (Kotze et al. 2021; Ferlauto et al., 2024)

Litter generally exported and
composted (Templer et al., 2015)

Litter recycling on soil

Contrasted
litter

Decomposition

C storage
Fertility
Infiltration
Biodiversity...

(Sadeghian 2013;
Wang et al. 2022)
Returning litter to the surface of urban soils can result in **GHG emissions**

Locally regulated by **litter biochemistry** and **soil properties** (Chaves et al., 2021; Abalos et al., 2022)

On the long term, **management intensity** modify soil properties (Shen et al., 2025)

<figure><img src="image_5.png" /></figure>

Litter recycling on soil

Contrasted litter

Biochemistry

C:N, soluble, lignin ...

Management intensity

CO₂ and N₂O fluxes

(Xia et al., 2018)

Soil properties

[C and N], water retention capacity...
**Knowledge Gaps**

CO₂ and N₂O fluxes in urban ecosystems during decomposition

* Impact of tree, shrub, and grass litter decomposition

* Soils with contrasted management intensities

CO₂ and N₂O

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

**Objective**

Assess how **potential CO₂ and N₂O fluxes** are influenced by **urban litter biochemistry** under **two management intensities** of lawns during decomposition.
CO₂ and N₂O fluxes depend on the biochemical
properties of litter and soil properties.

H1

Litter with high N and soluble contents
increases CO₂ and N₂O fluxes.

H2

**Organic matter rich lawn soil** can promote
CO₂ and N₂O fluxes by providing a greater ...

- C and N availability,

- water retention capacity.

<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

CO₂ and N₂O

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

CO₂ and N₂O
Experimental approach

1 Characterize a wide range of
**contrasting litter types**

28 litters

<figure><img src="image_13.png" /></figure>

Total C and N
Water soluble C and N
Van Soest fractions

<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /></figure>

2 Characterize the CO₂ and N₂O flux potentials of 5 litters for 2 lawn soils

5 litters

<figure><img src="image_16.png" /></figure>

<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /></figure>

<figure><img src="image_19.png" /></figure>

<figure><img src="image_20.png" /></figure>

<figure><img src="image_21.png" /></figure>

Low-intensity
management soil

<figure><img src="image_22.png" /></figure>

High-intensity
management soil
<figure><img src="image_23.png" /><figcaption>LOW-intensity management</figcaption></figure>

<figure><img src="image_24.png" /><figcaption>HIGH-intensity management</figcaption></figure>

<table><tr><td>Org. C</td><td>1.8</td><td>5.9</td><td>%</td></tr><tr><td>MB-C</td><td>0.35</td><td>1.60</td><td>g kg<sup>-1</sup></td></tr><tr><td>Tot. N</td><td>0.2</td><td>0.5</td><td>%</td></tr><tr><td>C:N</td><td>10</td><td>12</td><td></td></tr><tr><td>NO<sub>3</sub><sup>-</sup></td><td>9.0</td><td>20</td><td>mg kg<sup>-1</sup></td></tr><tr><td>NH<sub>4</sub><sup>+</sup></td><td>0.2</td><td>0.2</td><td>mg kg<sup>-1</sup></td></tr><tr><td>Olsen P</td><td>12</td><td>73</td><td>mg kg<sup>-1</sup></td></tr><tr><td>pH</td><td>5.8</td><td>6.7</td><td></td></tr><tr><td>Bulk density</td><td>1.4</td><td>0.8</td><td>g cm<sup>-3</sup></td></tr><tr><td>Water retention at FC</td><td>22</td><td>71</td><td>g H<sub>2</sub>O g<sup>-1</sup></td></tr><tr><td>WFPS at FC</td><td>70</td><td>95</td><td>%</td></tr><tr><td>Sandy loam</td><td></td><td></td><td>Sandy loam</td></tr></table>

Collected in **Angers**, the greenest city of France (102 m² of UGS per inhabitant)

<figure><img src="image_25.png" /></figure>

**Representative of global UGS management practices** (Ignatieva et al. 2020; Watson et al., 2020)
Microcosm

3 T DM ha⁻¹
of litter

<figure><img src="image_26.png" /></figure>

Fixed at **in situ**
densities

Temperature : 15°C

Moisture at
100% field capacity

Water retention effect :
70% field capacity

<figure><img src="image_27.png" /></figure>

Incubation of 5 litters with 2 soils
Microcosm

3 T DM ha⁻¹
of litter

<figure><img src="image_28.png" /></figure>

Fixed at *in situ*
densities

Temperature : 15°C

Moisture at
**100% field capacity**

Water retention effect :
**70% field capacity**

Incubation of 5 litters with 2 soils

Net CO₂ and N₂O and
fluxes

IR analyzer

Frequent measurements

<figure><img src="image_29.png" /></figure>

Mineral N dynamic

NH₄⁺, NO₃⁻ extractions
with KCl

5 measurements

<figure><img src="image_30.png" /></figure>

<figure><img src="image_31.png" /></figure>
# Contrasted biochemical properties across the 28 urban litter types

<figure><img src="image_32.png" /></figure>

## Selection of 5 litters

<figure><img src="image_33.png" /><figcaption>Tilia
(Til)</figcaption></figure>

<figure><img src="image_34.png" /><figcaption>Cornus
(Cor)</figcaption></figure>

<figure><img src="image_35.png" /><figcaption>Meadow
mix (Pr2)</figcaption></figure>

<figure><img src="image_36.png" /><figcaption>Lolium
(LoA)</figcaption></figure>

<figure><img src="image_37.png" /></figure>

## N and soluble compounds gradient

- Rarely studied

- Representative
<figure><img src="image_38.png" /></figure>

LOW-intensity soil

<figure><img src="image_39.png" /></figure>

HIGH-intensity soil

<figure><img src="image_40.png" /></figure>

H1 CO₂ and N₂O fluxes varied significantly between litter types, with limited fluxes from litter with low N content.
<figure><img src="image_41.png" /></figure>

<figure><img src="image_42.png" /></figure>

H1

CO₂ and N₂O fluxes were strongly correlated with **C:N ratios** of litter, which influenced **N availability** in soil.

<figure><img src="image_43.png" /></figure>
<figure><img src="image_44.png" /></figure>

<figure><img src="image_45.png" /></figure>

H1

CO₂ and N₂O fluxes were strongly correlated with **C:N ratios** of litter, which influenced **N availability** in soil.

<figure><img src="image_46.png" /></figure>

The 25 senescent litter types would present a **low N₂O emission potential**.

Minor role of soluble compounds content.
<figure><img src="image_47.png" /></figure>

LOW-intensity soil

<figure><img src="image_48.png" /></figure>

HIGH-intensity soil

<figure><img src="image_49.png" /></figure>

H2 N₂O fluxes were more important in the high-intensity management soil.

Similarly, CO₂ fluxes were slightly increased in this soil.
<figure><img src="image_50.png" /></figure>

H2

The **greater water retention capacity** (i.e., WFPS) of the high-intensity management soil **increased N₂O fluxes.**
Low-intensity
soil

<figure><img src="image_51.png" /></figure>

High-intensity
soil

<figure><img src="image_52.png" /></figure>

Recycling of senescent
**litter** have a **low N₂O**
**emission potential**

<figure><img src="image_53.png" /></figure>

Enhance **ecosystem services**

<figure><img src="image_54.png" /></figure>

Infiltration
(Fung et al. 2022)

<figure><img src="image_55.png" /></figure>

Fertility
(Ferlauto et al., 2024)

<figure><img src="image_56.png" /></figure>

Biodiversity
(Mills et al. 2020)

Minimizing the **overall C footprint** compared to litter **exportation and composting**

<figure><img src="image_57.png" /></figure>

<figure><img src="image_58.png" /></figure>

N₂O and CH₄

<figure><img src="image_59.png" /></figure>

Windrow
compost

(Zhu-Barker et al., 2017)
<figure><img src="image_60.png" /></figure>

Thank you for your attention

<figure><img src="image_61.png" /></figure>

<figure><img src="image_62.png" /></figure>

INRAO
FARE

<figure><img src="image_63.png" /></figure>

<figure><img src="image_64.png" /></figure>

UNIVERSITE
DE REIMS
CHAMPAGNE-ARDENNE

<figure><img src="image_65.png" /></figure>

L'INSTITUT
agro Rennes-Angers

Unite propre de recherche EPHor

ADEME

<figure><img src="image_66.png" /></figure>

AGENCE DE LA
TRANSITION
ECOLOGIQUE

<figure><img src="image_67.png" /></figure>

Région
PAYS
de la
LOIRE
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