Photosynthetic responses to soil water stress in summer in two Japanese urban landscape tree species (Ginkgo biloba and Prunus yedoensis): effects of pruning mulch and irrigation management

Key message: Stomatal regulation involves beneficial effects of pruning mulch and irrigation on leaf photosynthesis inPrunus yedoensisandGinkgo bilobaunder moderate drought.G. bilobashowed conservative water use under drought. Abstract: Leaf photosynthesis is highly sensitive to soil water stress via stomatal and/or biochemical responses, which markedly suppress the growth of landscape trees. Effective irrigation management to maintain leaf photosynthesis and information on species-specific photosynthetic responses to soil water stress are essential for the sustainable management of landscape trees in Japan, in which summer drought often occurs. In order to investigate effective irrigation management, we used plants with moderate soil water stress as controls, and examined the effects of daily irrigation and pruning mulch on leaf photosynthesis in container-grown Ginkgo biloba and Prunus yedoensis, which are the first and second main tall roadside trees in Japan. Stomatal conductance was significantly increased by pruning mulch and daily irrigation, with similar increases in leaf photosynthesis being observed in P. yedoensis and G. biloba. In order to obtain information on species-specific photosynthetic responses to soil water stress, we compared the responses of leaf photosynthesis and leaf water status to reductions in soil water content (SWC) between the two species. G. biloba maintained a constant leaf water potential, leaf water content, maximum carboxylation rate, and electron transport rate with reductions in SWC, whereas reductions were observed in P. yedoensis. We concluded that pruning mulch and irrigation effectively offset the negative impact of moderate water stress on leaf photosynthesis in summer in P. yedoensis and G. biloba via stomatal regulation, and also that G. biloba maintained its photosynthetic biochemistry and leaf water status better than P. yedoensis under severe water stress.