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

Cypress (Cupressus funebris Endl.) is an important tree species in the subtropical regions of China; it is also a major tree species for afforestation and forest land restoration under low-fertility soil conditions. Cypress is considered a calcicolous tree, and its growth and development can be promoted significantly by exchangeable calcium (Ca2+) in the soil. However, most of the subtropical regions have low-fertility acidic soils, in which Ca2+ gradually becomes a limiting element for Cypress growth. In this study, different concentrations of Ca2+ fertilizer were added under fertile soil (3 g kg(-1) NPK fertilizer added) and low-fertility soil (0 g kg(-1) NPK fertilizer added) conditions. Cypress clones responded differently to Ca2+ addition in different soil conditions. The seedling height and dry matter quality of Cypress in fertile soil were significantly greater than those in low-fertility soil, but plant height and dry biomass did not differ significantly among Ca2+ treatments. The accumulation efficiencies of nitrogen (N), phosphorous (P) and Ca all differed significantly among the Ca2+ treatments. In low-fertility soil, the addition of 3 g kg(-1) Ca2+ significantly promoted development of roots 0.5-2 mm in diameter, and both the C1 and C2 clones achieved their highest N, P and Ca accumulation efficiencies. When the Ca2+ concentration increased to 6 g kg(-1), the seedling height, dry matter quality and root development were lower than those of the 3 g kg(-1) Ca2+ treatment. In the fertile soil, the addition of Ca2+ significantly inhibited development of roots 0.5-1 mm in diameter. The highest N accumulation efficiency was achieved under the 0 g kg(-1) Ca2+ treatment, and the highest Ca accumulation efficiency was achieved under the 6 g kg(-1) Ca2+ treatment. Seedling height, root dry weight, roots 0-1.5 mm in diameter and Ca accumulation showed a significant interaction effect between NPK fertilizer and Ca2+. Therefore, Ca accumulation was more efficient in low-fertility soils. Under low-fertility soil conditions, the addition of CaSO4 can promote the root development of seedlings and advance and prolong the fast growth period of seedling height. Cypress clones can be used as an important tree species for afforestation under low-fertility soil conditions, especially under calcareous soil conditions.