模拟氮沉降条件下木荷幼苗光合特性、生物量与C、N、P分配格局

设置模拟氮沉降的控制试验,以NH4NO3作为外加氮源,设计CK(0kg N hm-2·a-1)、LN(50 kg N hm-2·a-1)、MN(100 kg N hm-2·a-1)、HN(150 kg N hm-2· a-1)4个处理,历时9个月,测定木荷(Schima superba)幼苗的光合特性、生物量和C、N、P含量及其分配格局对氮沉降的响应.结果表明:(1)木荷幼苗的最大净光合速率和光饱和点随着氮处理水平增加呈先增加后减小的特点,在中氮处理下极显著增加(P＜0.01).氮处理降低了幼苗的光补偿点和暗呼吸速率,光补偿点在低氮处理下显著降低(P＜0.05),暗呼吸速率在低中氮处理下极显著降低(P＜0.01),高氮处理下显著降低(P＜0.05).未见氮处理对表观量子效率产生显著影响.(2)氮处理促进了木荷的全株生物量以及各部分生物量的增长.随着氮处理水平的增加,叶重比呈升高的趋势,而根重比和根冠比呈降低的趋势,在高氮处理下叶重比的增加和根重比、根冠比的降低都达到了显著水平(P＜0.05).(3)氮沉降促进各器官N含量的增加,在高氮处理下根和茎中N含量极显著增加(P＜0.01),叶中N含量显著增加(P＜0.05).而各器官C含量随着氮沉降程度的增加呈先增加后降低的趋势,在中氮处理下根和茎中C含量极显著增加(P＜0.01),叶中C含量显著增加(P＜0.05).但各器官P含量变化趋势各不相同,随着氮的增加,根中P含量是呈先增加后降低的趋势,而茎和叶中P含量是呈降低的趋势.氮沉降一定程度上降低了木荷各器官的C/N比值而增加了N/P比值.

Photosynthetic characteristics, biomass allocation, C,N and P distribution of Schima superba seedlings in response to simulated nitrogen deposition

Human activities have caused increased nitrogen (N) input to forest ecosystems through fertilizer production and fossil fuel combustion in recent decades and this input is likely to continue in the near future. Therefore, studying the effects of N deposition on morphological and physiological characteristics of plants increasingly becomes a major focus in the field of ecological and environmental sciences. To explore physiological response of sub-tropical forest to N deposition, Schima superba was selected as an important constructive species of sub-tropical forest. Four treatments including Control (CK, 0 kg N hm^-2·a^-1), Low N (LN, 50 kg N hm^-2·a^-1), Medium N (MN, 100 kg N hm^-2·a^-1) and High N (HN, 150 kg N hm^-2·a^-1) were conducted in the present study. At the beginning and in the middle of each month, N-treated plots were sprayed with NH₄NO₃ solution with concentrations of 0 mol N/L (CK), 0.12 mol N/L (LN), 0.24 mol N/L (MN) and 0.36 mol N/L (HM) respectively. The photosynthetic characteristics, biomass allocation, C, N and P distribution in response to different N deposition were investigated in one-year-old S. superba seedlings after nine months. The results showed that:(1) The trend of maximum net photosynthetic rate (Pn_max) of S. superba was increased firstly, and then decreased with the increase of nitrogen supply. With the treatment of MN and HN, Pn_max increased by 21.1% (P<0.01) and 16% (P<0.01), respectively. The change of light saturation point (LSP) was similar as the Pn_max. LN and MN caused the increase of LSP by 10.6% (P<0.01) and 13.1% (P<0.01), respectively. But the LSP in the HN was significantly lower than that in the CK (P<0.01). The LCP reduced significantly in LN (P<0.05), and Rd reduced significantly under different N treatments (P<0.01 for LN and MN; P<0.05 for HN).The apparent quantum yield (AQY) were of no significant difference under the different N treatments. (2) N deposition enhanced total biomass, leaf biomass, stem biomass and root biomass of S. superba seedlings significantly. The treatments of MN and HN induced the increase of total biomass by 168.5% (MN, P<0.01) and 130.5% (HN, P<0.05), respectively. Root biomass increased by 145.6% with MN treatments (P<0.01). N treatments caused significant increase of leaf biomass by 247.4% (MN, P<0.01) and 228.5% (HN, P<0.01). Leaf weight ratio increased while root weight ratio and root to shoot ratio reduced with different concentration of N treatments. (3) N concentrations increased, but P concentrations decreased in soil upon N deposition. Under HN, the N concentrations increased by 44.65% (P<0.01), 35.06% (P<0.01) and 24.78% (P<0.05) in roots, stems and leaves respectively. The C concentrations inclined firstly, and then declined with the increase of nitrogen supply in the roots, stems and leaves. Furthermore, C concentrations of different organs increased significantly under MN in comparison with CK (P<0.01 for roots and stems, P<0.05 for leaves).The change of P concentrations in the roots appeared positively to LN and MN, but negatively to HN. However, P concentrations in the stems and leaves appeared negatively to N deposition (P<0.01).To a certain extent, N deposition induced the decrease of C/N ratio and the increase of N/P ratio in the roots, stem and leave of S. superba seedlings.