Biological response of pioneer plant Macleaya cordata to N and P stresses under different water conditions

【Objectives】On September 8, 2008, a catastrophic dam failure accident occurred in the tailing pond of the Xinta Mining Ltd. Co. Xiangfen County, Shanxi Province, China. Residual tailings from the 9.8Xiangfen tailings dam failure covered the land and mixed with surface soil, and formed immature soil. With the immature soil as culture medium, a pot experiment was conducted to investigate effect of nitrogen(N)and phosphorous(P)applications on growth and physiological indicators of Macleaya cordata as well as associated soil enzyme activities and rhizosphere microbial quantity under different water conditions, aiming to provide a reference for screening and management of local alternative cultivated plants in the disaster area of the “9.8” Xiangfen tailings dam failure.【Methods】 The experiment was conducted in the Experimental Farm of Shanxi Agricultural University from March to December, 2013. N and P fertilizer was applied at two levels: intermediate N(N 0.2 g/kg, N1)and low N(N 0 g/kg, N0); and intermediate P(P2O5 0.2 g/kg, P1)and low P(P2O5 0 g/kg, P0). Water conditions were set at three levels: low water(35%-40% of field capacity, W1), intermediate water(45%-50% of field capacity, W2), and high water(75%-80% of field capacity W3). Totally 12 treatments were included: W1N0P0, W2N0P0, W3N0P0, W1N0P1, W2N0P1, W3N0P1, W1N1P0, W2N1P0, W3N1P0, W1N1P1, W2N1P1, W3N1P1, and each treatment was repeated 10 times. At the middle growth stage of M. cordata (July 6), five replicates were used for determining plant height, stem diameter, aboveground biomass, total root length, root weight, root absorption area, root vigor, root superoxide dismutase(SOD)and peroxidase(POD)activities, and malondialdehyde(MDA)content, as well as rhizosphere soil enzyme activities and microbial biomass. The other 5 replicates were used for determining the biological yield of M. cordata after the harvest(November 2). 【Results】 Drought and low N/P stresses have significant inhibitory effects on the growth and physiological indicators of M. cordata, as well as rhizosphere microbial quantity and soil enzyme activities. However, M. cordata still yields a certain amount of biomass and exhibits a stronger stress resistance, while other experimental crops fail to yield. The fertilization of P(calcium superphosphate)and N(urea)or irrigation of the immature soil covered by residual tailings increases the plant height, stem diameter, aboveground biomass, root weight, total root length, total and active root absorbing areas of M. cordata at varying degrees. Additionally, the root SOD and POD activities are enhanced, while the MDA content is decreased by the fertilization or irrigation. The effect of fertilization alone on M. cordata growth is: P N, the effect of fertilization + irrigation is better than that of fertilization alone, and there are significant synergic effects among the irrigation, N fertilization and P fertilization. P was the primary limiting factor for biomass formation of M. cordata grown in the immature soil. The rhizosphere microbial quantity and soil enzyme activities are significantly positively correlated with the root vigor and growth conditions of M. cordata. Well-developed root system promotes the propagation of rhizosphere microorganisms, and thus enhances associated soil urease and phosphatase activities. This mechanism ultimately promotes the development of M. cordata towards maturation.【Conclusions】 Owing to its drought and barren resistance, M. cordata can adapt to local environmental conditions in the disaster area of the “9.8” Xiangfen tailings dam failure. Taking into consideration its medicinal value, M. cordata can serve as an important alternative cultivated plant in the study area.