不同密度樟树(Cinnamomum camphora)幼苗生长和叶片性状对氮磷添加的响应

人类活动改变了氮素从大气向陆地生态系统输入的方式和速率,进而导致森林生态系统养分变化和失衡。研究氮磷添加对不同密度樟树(Cinnamomum camphora)幼苗生长和叶片性状的影响,可以为全球氮磷沉降背景下亚热带地区樟树人工林的经营管理提供依据。本试验以1年生樟树幼苗为试验材料,选择氯化铵(NH_4Cl)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,种植密度设置10、20、40和80株·m~(-2 )4个水平。实验数据表明:N、P和N+P处理对樟树幼苗的苗高和地径均有促进作用,且N+P处理对幼苗生长的促进效果最好。N、P和N+P处理在整体上均能增加幼苗叶片的SPAD值,N和N+P处理均增加了幼苗叶片的比叶面积(SLA),而P处理减少了幼苗的SLA。随着种植密度的增大,N、P和N+P处理下樟树平均单株幼苗的苗高、地径、SPAD值呈现下降的趋势,各施肥处理下叶片的SLA变化规律不明显。密度和氮磷添加对叶片的SPAD值产生显著的交互作用。

Responses of Cinnamomum camphora seedling growth and leaf traits to additions of nitrogen and phosphorous under different planting densities

Human activities have changed the rate at, and the way in which nitrogen (N) is input from the atmosphere to terrestrial ecosystems, leading to changes in nutrients, and elemental imbalances in forest ecosystems. Many terrestrial ecosystems are currently experiencing increasing inputs of N and P from human activities. In recent years, increased N deposition in forests has occurred due to fossil fuel combustion, N-based fertilizer use, and other activities. It is predicted that N deposition will continue to increase worldwide. On the other hand, forest soils in southern China are more P-limited, because they are highly weathered and leached, and little P is released even from the weathering of primary P-bearing minerals. As a result, P fertilization is widely used in the subtropical forests of southern China. However, relatively little information is available about the effect of P addition on forest growth. Planting density is an important area of research in tree competition, which affects the utilization of plant resources and the acquisition of occupied space. Understanding the relationship between plant density and tree growth would help to estimate and quantify stand development patterns over time. As individual trees in a stand grow in size, individual competition for resources in high-density stands is more intense than in low-density stands. Although there are some studies about the effects of density or N and P additions on tree growth, no studies have systematically examined the effects of N and P additions on plant growth under different planting densities. In this study, the effects of N and P additions on growth and leaf traits of Cinnamomum camphora seedlings under different planting densities were studied, in order to provide a basis for plantation ecosystem management in the subtropical region under global N and P deposition. In this study, NH₄Cl and NaH₂PO₄·2H₂O were selected to simulate atmospheric N and P additions with 4 treatments (CK, N, P and N+P) and seedling density was set at 4 levels (10, 20, 40, and 80 seedings/m²). The results showed that N, P and N+P treatments all increased seedling height and ground diameter of C. camphora seedlings, and that the N+P treatment had the largest effect on seedling growth. N, P and N+P treatments increased the soil and plant analyzer development (SPAD), N and N+P treatments also increased the specific leaf area (SLA), whereas P treatment decreased the SLA. In seedlings treated with N, P, and N+P, seedling height, ground diameter, and SPAD decreased with increasing density, whereas the SLA of seedlings treated with different treatments changed irregularly. The interactive effect of density and N+P addition on SPAD of seedlings was significant.