Seedling growth, root development and nutrient use efficiency of Cypress clones in response to calcium fertilizer

Background: Cypress (Cupressus funebris Endl.) is an important tree species in the subtropics of China, it is also a major tree species for afforestation and forest land restoration under infertile site conditions. Cypress is considered to be a calcicolous tree, whose there are growth and development can be promoted significantly by exchangeable Calcium (Ca2+) in the soil. However, most of the subtropical regions have infertile acidic soils, in which Ca2+ gradually becomes a limiting element for cypress growth. Results: In this study, different concentrations of Ca2+ fertilizer were added under fertile and infertile soil conditions. Cypress clones responded differently to Ca2+ addition in different soil conditions. In the infertile soil, the addition of 3 g•kg− 1 Ca2+ advanced and prolonged the fast-growing period of seedling height growth, increased plant height and dry biomass, promoted the development of fine roots ≤ 1.5 mm in diameter, and improved accumulation efficiencies of nitrogen (N), phosphorous (P) and Ca by the roots in cypress clones; however, the addition of 6 g•kg− 1 Ca2+ inhibited height growth and root development of cypress. In the fertile soil, Ca2+ addition delayed and shortened the fast-growing period for cypress height growth, but plant height and dry biomass did not differ significantly between treatments; Ca2+ addition also inhibited the development of fine roots. The clone with fast height growth had a larger proportion of roots with a diameter ≤ 1.5 mm and achieved higher N accumulation efficiency, while Ca accumulation efficiency showed genotypic differences only in the fertile soil. Conclusions: An appropriate level of Ca2+ can be added to infertile soil to promote cypress seedling growth, and clones with fast height growth and developed fine roots can be selected for cultivation and promotion in the fertile soil without Ca2+ application.