Mowing reshapes the multielement stoichiometry of aboveground plant matter: A lesson from two cities for urban lawn management

Le résumé fourni par la source

Lawns are among the most widespread forms of urban green infrastructure, yet the ecological consequences of mowing are usually assessed through biodiversity or biomass alone. Using ecological stoichiometry, we tested whether mowing frequency directly alters not only plant biomass and taxonomic composition but also the multielement composition of biomass entering urban food webs. We studied roadside lawns across two cities, under three mowing intensities: low (one cut annually), moderate (three), and frequent (six). We quantified shoot and root biomass across 14 sites, and multielement stoichiometry and plant community structure in a representative subset of 6 sites. Mowing directly affected plant multielement stoichiometry, regardless of changes in biomass production and community structure. Compared to once-per-year mowing, frequent mowing increased median shoot concentrations of P (∼1.3-fold), K (∼1.1-fold), Na (∼9.4-fold), and Mg (∼1.3-fold) but decreased the Fe (∼0.5-fold), Mn (∼0.8-fold), Ni (∼0.5-fold), Cr (∼0.4-fold), and Pb (∼0.7-fold) concentrations and the C:P (∼0.8-fold), N:P (∼0.9-fold), and K:Na (∼0.1-fold) ratios. Root chemistry was considerably less responsive. The stoichiometric shifts were driven primarily by the direct effects of mowing; community composition contributed less. Therefore, mowing affects biogeochemical processes primarily by altering the stoichiometry of plant biomass, and only secondarily by changing the structure and productivity of vegetation. By changing the shoot elemental composition, mowing may affect the nutritional quality and contamination load of matter entering food webs, potentially cascading through trophic networks and nutrient cycles, although broader ecological consequences remain to be tested directly. We recommend integrating stoichiometric perspectives into sustainable urban green space management.

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