Carbon dioxide dynamics in a residential lawn of a tropical city.

Turfgrass is an important component of the urban landscape frequently considered as an alternative land cover to offset anthropogenic CO2 emissions. However, quantitative information of the potential to directly remove CO2 from the atmosphere by turfgrass systems is lacking, especially in the tropics. Most assessments have considered the carbon accumulated by grass shoots and soil, but not the release of CO2 to the atmosphere by soil respiration (i.e., soil CO2 efflux). Here, we measured at high-temporal resolution (30-min) soil CO2 efflux, production, and storage rate for nearly three years in a residential lawn of Singapore. Furthermore, we quantified the carbon capture related to biomass production and CO2 emissions from fossil fuel consumption associated with maintenance activities (e.g., mowing equipment). Warm and humid conditions resulted in relatively constant rates of soil CO2 efflux, CO2 storage in soil, and aboveground biomass production (3370, 652, 1671 Mg CO2 km-2 yr-1; respectively), while the systematic use of mowing machinery emitted 27 Mg CO2 km-2 yr-1. Soil CO2 efflux and CO2 mowing emissions represent carbon losses to the atmosphere, while CO2 storage in soil and biomass productivity represent gains of carbon into the ecosystem. Under a steady state in which soil CO2 losses are only compensated by atmospheric CO2 uptake by photosynthesis, an ideal clipping waste disposal management, in which no CO2 molecule returns to the atmosphere (i.e., clippings are not burnt), and a 3-week mowing regime, this site can act as a sink of 2296 Mg CO2 km-2 yr-1. In the scenario of incinerating all clippings, the lawn acts as an emission source of 1046 Mg CO2 km-2 yr-1. Thus, management practices that reduce mowing frequency together with clipping disposal practices that minimize greenhouse gas emissions are needed to make urban lawns a potential natural solution to mitigate global environmental change.

Global patterns of leaf mechanical properties.

Leaf mechanical properties strongly influence leaf lifespan, plant-herbivore interactions, litter decomposition and nutrient cycling, but global patterns in their interspecific variation and underlying mechanisms remain poorly understood. We synthesize data across the three major measurement methods, permitting the first global analyses of leaf mechanics and associated traits, for 2819 species from 90 sites worldwide. Key measures of leaf mechanical resistance varied c. 500-800-fold among species. Contrary to a long-standing hypothesis, tropical leaves were not mechanically more resistant than temperate leaves. Leaf mechanical resistance was modestly related to rainfall and local light environment. By partitioning leaf mechanical resistance into three different components we discovered that toughness per density contributed a surprisingly large fraction to variation in mechanical resistance, larger than the fractions contributed by lamina thickness and tissue density. Higher toughness per density was associated with long leaf lifespan especially in forest understory. Seldom appreciated in the past, toughness per density is a key factor in leaf mechanical resistance, which itself influences plant-animal interactions and ecosystem functions across the globe.