Morphological and Physiological Resource Trade-Offs Affect the Response of Poa pratensis to Urban Shading

The shading of urban buildings and understory space has a severe impact on cold-season turfgrass urban greening. To explore the effect of shading stress on the typical cold-season turfgrass of Poa pratensis, the six shading gradients of 0% (full light, CK, 6 × 104 lux), 20% (1-layer shade net, 4.8 × 104 lux), 43% (2-layer shade net, 3.42 × 104 lux), 64% (3-layer shade net, 1.92 × 104 lux), 81% (4-layer shade net, 1.14 × 104 lux) and 96% (5-layer shade net, 0.24 × 104 lux) were set up for simulating tree shading, and the morphological and physiological indices were measured. The results showed that in the early growth stage of P. pratensis, it mainly adapted to shading stress through morphological changes, while in the late growth stage it mainly adapted to shading stress through physiological changes. The aboveground height and root length of P. pratensis in the late growth stage showed that the low shading (20% and 43%) was higher than that of the CK and the high shading (64%, 81% and 96%) was lower than that of the CK. The tiller number decreased with an increase in shading degree, and it was lower than that in the CK in the late growth stage. The highest biomass occurred under 64% shading, reaching 171.43% above CK. Chlorophyll and soluble sugar first increased and then decreased with shading intensity, and both were significantly lower than CK under all the shading treatments in the late growth stage. Therefore, 20% to 40% was the optimal growth shading range for the P. pratensis seedlings’ short-term growth and physiological homeostasis. These findings offer a theoretical and practical reference for establishing, maintaining, and rationally allocating P. pratensis in urban shaded environments.