模拟氮沉降对一年生香椿幼苗生长和光合特性的影响

为研究氮沉降对一年生香椿(Toonasinensis)幼苗夏季生长以及光合特性的影响,通过在夏季模拟氮沉降控制试验,以尿素为氮源供体,设置0kg(N)×hm~(-2)×a~(-1)(CK)、20kg(N)×hm~(-2)×a~(-1)、40kg(N)×hm~(-2)×a~(-1)、80kg(N)×hm~(-2)×a~(-1)、120 kg(N)×hm~(-2)×a~(-1)、180 kg(N)×hm~(-2)×a~(-1)不同氮添加水平以模拟氮沉降,对香椿幼苗地径、苗高、生物量及其分配和光合作用等进行研究。结果表明:1)不同氮添加量均促进了香椿幼苗地径、苗高和生物量的增加,地径、苗高和生物量均以氮添加水平180kg(N)×hm~(-2)×a~(-1)下最高,分别较CK高42.5%、64.4%和304.9%,且生物量向根、叶分配较多; 2)香椿幼苗叶片相对叶绿素含量(SPAD)随氮添加水平的增加而增加,在180 kg(N)×hm~(-2)×a~(-1)下最高,较CK增加73.9%;3)香椿幼苗表观量子效率(AQY)、最大净光合速率(Pnmax)、光饱和点(LSP)、光补偿点(LCP)以及暗呼吸速率(Rd)随氮添加水平的增加均呈现先升高后降低的趋势,其中LCP以80 kg(N)×hm~(-2)×a~(-1)下最高, AQY、Pnmax、LSP和Rd均以120kg(N)×hm~(-2)×a~(-1)下最高。结果表明,适量氮沉降能够促进香椿幼苗生长和光合能力的提高,但更高水平的氮沉降可能对香椿幼苗产生一定抑制作用。

Effects of simulated nitrogen deposition on growth and photosynthetic characteristics of one-year-old Toona sinensis seedlings

With global industrial and agricultural modernization, the characteristics and processes of various ecosystems have been profoundly affected due to increasing nitrogen deposition. Toona sinensis is a unique, dual-use plant widely distributed in China. It is used for medicinal purposes and is also a fast-growing timber tree species. To determine the threshold value of nitrogen deposition that could be sustained at the seedling stage of T. sinensis and to provide some theoretical basis for the cultivation of T. sinensis, a preliminary study was performed to test the response of annual T. sinensis seedlings to nitrogen deposition in summer. Annual T. sinensis seedlings were grown under the simulated nitrogen deposition experiment in summer. Urea was used as the nitrogen source, with six levels of nitrogen addition:0 kg(N)·hm^-2·a^-1, 20 kg(N)·hm^-2·a^-1, 40 kg(N)·hm^-2·a^-1, 80 kg(N)·hm^-2·a^-1, 120 kg(N)·hm^-2·a^-1, and 180 kg(N)·hm^-2·a^-1. The ground diameter, seedling height, biomass, and photosynthesis of T. sinensis seedlings were then measured. The results showed that nitrogen addition contributed to an improvement in the diameter, height, and biomass of T. sinensis seedlings. Ground diameter, height, and biomass were the highest after the addition of 180 kg(N)×hm^-2·a^-1 nitrogen and were 42.5%, 64.4%, and 304.9% higher, respectively, than the control values. The biomass of T. sinensis seedlings was distributed more to the root and leaf. The SPAD of seedling leaves increased with increasing levels of nitrogen addition. At the highest nitrogen addition of 180 kg(N)·hm^-2·a^-1, SPAD values were 73.9% higher than the control. The apparent quantum yield (AQY), maximum net photosynthetic rate (P_nmax), light saturation point (LSP), light compensation point (LCP), and the dark respiration rate (R_d) increased at first and then decreased with increasing levels of nitrogen addition. Except for LCP, which was highest at 80 kg(N)·hm^-2·a^-1, AQY, P_nmax, LSP, and R_d were the highest at 120 kg(N)·hm^-2·a^-1. This study showed that a certain level of nitrogen addition could promote the growth and enhance the photosynthetic ability of T. sinensis seedlings. However, there is a limit to the nitrogen deposition level tolerance of T. sinensis seedlings and when the nitrogen level increases to a certain point, photosynthetic ability begins to decline.