氮磷添加与不同栽植密度交互对樟树幼苗土壤化学性质的短期影响

研究氮磷添加对不同密度樟树(Cinnamomum camphora)幼苗土壤化学性质的影响,以期为全球化背景下樟树人工林生态系统的土壤养分管理提供依据。以1年生樟树幼苗为试验材料,选择氯化铵(NH4Cl)作为氮肥模拟大气氮沉降,以二水合磷酸二氢钠(NaH_2PO_4·2H_2O)模拟磷添加。氮磷处理设置CK、施N、施P和施N+P 4个水平,其中N、P和N+P施肥量分别为40 g m~(-2)a~(-1)(NH_4Cl)、20 g m-2a-1(NaH_2PO_4·2H_2O)和40g m~(-2)a~(-1)(NH_4Cl)+20 g m~(-2)a~(-1)(NaH_2PO_4·2H_2O)。种植密度设置4个水平:10、20、40和80株/m~2,试验时间为2017年6月至9月。研究结果表明,在各密度幼苗土壤中,N和N+P处理引起pH值的显著下降,N、P和N+P处理的土壤有机质和碱解N含量的变化规律不明显,P处理的幼苗土壤全P含量上升,P和N+P处理的土壤有效P含量增加,N+P处理的土壤全K含量以及N、P和N+P处理的土壤速效K含量均下降。在10、20和40株/m~2幼苗的土壤中,P处理的土壤全N含量高于N和N+P处理的,而80株/m~2幼苗的土壤全N含量低于其他密度幼苗。随着种植密度的增加,各施肥处理的土壤pH、全P、有效P、全K和速效K含量均呈现上升趋势,而施N和施P处理的土壤有机质呈现下降趋势,各施肥处理的土壤碱解N含量变化规律不明显。施肥和密度处理对樟树幼苗土壤有机质、碱解氮和速效钾含量有显著的交互作用。

Short-term interactive effects of nitrogen and phosphorus additions and different planting densities on soil chemical properties of Cinnamomum camphora seedlings

The functions of terrestrial ecosystems can be influenced by anthropogenic disturbances and global climate change, such as nitrogen (N) deposition and application of phosphorus (P) fertilizer. Atmospheric N compounds have increased sharply due to fossil fuel combustion, fertilizer use, and livestock husbandry development, which caused the atmospheric N deposition to increase. China has become the third largest N deposition area in the world followed by the United States and Europe. With further development of the economy, N deposition will be increasingly serious in China, especially in the developed southern China. An excess of N deposition can cause forest ecosystem N saturation, soil acidification, phosphorus limitation in the forest ecosystems. The acidic soils suffer from severe phosphorus deficiency in southern China. Thus P fertilizer is often applied in forestry production. But there are few reports on the effect of P addition or N+P addition on forest soils. The soil chemical properties were also influenced by N deposition and P fertilizer in forest ecosystem. Planting density can affect soil fertility by tree growth, completion of soil resource, and nutrient return from litter and root secretion. However, the responses of soil chemical properties to the N and P additions and planting density remain unclear. To date, no studies focused on the interactive effects of N and P additions and planting density on soil chemical properties in the southern China. The effects of N and P additions on soil chemical property were investigated in different densities of Cinnamomum camphora seedlings in order to provide a basis for the forest soil nutrient management. The study was conducted from June to September in 2017 using one-year-old C. camphora seedlings as test materials. We selected NH₄Cl and NaH₂PO₄·2H₂O to simulate atmospheric N and P additions with four treatments including CK (without nutrient added), N (40 g NH₄Cl m^-2 a^-1), P (20 g NaH₂PO₄·2H₂O m^-2 a^-1), and N+P (40 g NH₄Cl m^-2 a^-1 + 20 g NaH₂PO₄·2H₂O m^-2 a^-1). The seedling density was set at 4 levels (10, 20, 40, and 80 seedlings/m²). The results showed that in all density seedlings, N and N+P treatments significantly decreased soil pH, whereas soil organic matter and alkaline N treated with N, P, and N+P treatments changed irregularly. At the same time, soil total P content treated with P and available P content treated with P and N+P increased, and soil total K treated with N+P and available K content treated with N, P, and N+P decreased. The soil total N content treated with P was higher than that of N and N+P treatments in the density 10, 20, and 40 seedings·m^-2, whereas it was lower than other density seedlings in the density 80 seedings/m². The soil pH and the contents of total P, available P, total K, and available K treated with different fertiliser treatments increased with increasing seedling density. The content of soil organic matter treated with N or P decreased with increasing seedling density. The soil alkaline N treated with different fertiliser treatments changed irregularly. The interactive effects of density and N and P additions on soil organic matter, alkaline N and available K of seedlings were significant.