Abstract: Biochar is a carbonrich solid material produced by heating biomass in an oxygenlimited environment, which has been widely concerned as a soil conditioner, fertilizer release carrier and carbon (C) storage agent in recent years. In this study, a pot experiment was conducted to investigate the effects of three kinds of biochar (rice husk biochar, RHB; cotton straw biochar, CSB; woodchip biochar, WCB) amended with 1%, 2.5%, 5%, 10% (dry mass basis) on pH, capillary capacity, organic matter and available nutrient concentrations of limestone soil, and the growth traits, root characteristics of Robinia pseudoacacia L. seedlings (45 days old) at a karst site. The results showed that biochar application improved root characteristics and promoted the growth of R. pseudoacacia. Compared with CK, RHB_2.5 significantly accelerated total root length, total root surface area and the root length of 0-0.6, 0.6-1.2, 1.2-1.8 mm in diameter of R. pseudoacacia by 198%, 125%, 287%, 209% and 146%, respectively. RHB₅ and WCB_2.5 significantly increased the root activity by 36% and 32%, respectively. CSB₁₀ increased seedling height, basal diameter, aboveground biomass, and total biomass by Symbol`@@30%, 6%, 147% and 118%, respectively. Root/shoot ratio was decreased significantly by 57% after CSB₅ application. Moreover, biochar application remarkably improved soil water and nutrient availability, and the effects increased with the increase of application rate. Compared with the CK, RHB₁₀, CSB₁₀ and WCB₁₀ increased soil organic matter by 25%, 195% and 68%, available N by 49%, 105% and 45%, available P by 114%, 766% and 115%, and available K by 170%, 27% and 89%, respectively. RHB₁ and WCB_10 increased soil pH by 1.22% and 1.48%, respectively. Therefore, biochar application can improve quality of limestone soil in karst area, and promote root development and growth of R. pseudoacacia seedlings, which is of importance to the improvement of limestone soil and revegetation in karst area.

Key words: Chinese bulbul (Pycnonotus sinensis), temperature, body mass, energy budget, photoperiod, digestive tract morphology.