林隙大小和隙内位置对小兴安岭蒙古栎林内红松光合能力的影响

【目的】确定红松(Pinus koraiensis)幼树在次生林生境中生长的最适林隙面积及林隙内位置,为恢复温带地带性顶极植被阔叶红松林提供科学依据,同时为优化抚育经营措施提供支持。【方法】以黑龙江小兴安岭红松幼树(15 a)为试验材料,采用CIRAS-2光合仪分别测定蒙古栎(Quercus mongolica)次生林4种林隙大(206.1 m²)、中(116.9 m²)、小(52.4 m²)、林内(对照,12.6 m²)]内3种位置(中心区、过渡区与边缘区)生长的红松幼树光合参数(最大净光合速率、光饱和点、光补偿点和蒸腾速率等)、叶绿素含量和微环境因子(透光率、气温),采用带有180°鱼眼镜头的Nikon CoolPix 4500数码相机采集林隙照片并计算出各样地透光率。通过比较不同大小林隙及隙内不同位置红松幼树光合能力之间的差异,分析林隙大小及隙内不同位置对红松幼树光合能力的影响。【结果】①红松幼树的光合能力在中、小林隙内显著提高,中、小林隙使其最大净光合速率较在林内(对照)显著提高20.0%~60.7%,且中林隙又显著高于小林隙9.2%~15.1%,而大林隙对其无显著影响;②在各大小林隙内红松幼树最大净光合速率沿林隙中心区至边缘区微环境梯度均呈规律性递减(92.7%~22.5%);③在中、小林隙内红松幼树的光饱和点高于林内,但光补偿点却低于林内;在中林隙内其蒸腾速率、气孔导度和胞间CO₂浓度高于林内,而叶绿素含量低于林内;在各林隙内沿中心区至边缘区微环境梯度,红松幼树的光饱和点降低而光补偿点提高,蒸腾速率和气孔导度呈递减趋势,而叶绿素含量呈递增趋势。【结论】红松幼树在蒙古栎林中林隙(116.9 m²)内的中心区光合能力较强。建议在阔叶红松林恢复实践中创建适宜大小的林隙,充分利用林隙内的中心位置来加速其恢复进程。

Effects of gap sizes and within-gap positions on the photosynthetic capacity of Pinus koraiensis in Quercus mongolica forests in Xiaoxing’an Mountains

【Objective】 The objective of this study was to determine the suitable forest gap area and position in the gaps for the growth of Pinus koraiensis saplings in secondary forests and provide a scientific basis for the restoration of temperate zonal climate vegetation and broad-leaved P. koraiensis forests. Simultaneously, the findings could provide a theoretical support for optimizing management practices. 【Method】P. koraiensis saplings (15 a) from Xiaoxing’an Mountains were used as the test material. Photosynthetic parameters (maximum net photosynthesis rate, light saturation point, light compensation point, and transpiration rate), chlorophyll content, and micro-environmental factors (light transmittance, temperature) of P. koraiensis saplings grown in three locations (central area, transition area, and edge area) in four gapslarge gap (206.1 m²), medium gap (116.9 m²), small gap (52.4 m²), understory (control, 12.6 m²)]in secondary Quercus mongolica forests were measured using a CIRAS-2 photosynthesis instrument. A Nikon CoolPix 4500 digital camera with a 180° fisheye lens was used to collect photographs of the gaps and obtain the light transmittance at various plots. By comparing the differences in the photosynthetic capacity of P. koraiensis saplings in different gap sizes and within-gap positions, we explored the effects of gap sizes and within-gap positions on the photosynthetic capacity of P. koraiensis saplings.【Result】(1) The photosynthetic capacity of the P. koraiensis saplings was significantly higher in medium and small gaps. Specifically, the medium and small gaps increased the maximum net photosynthetic rate by 20.0%-60.7% compared with that in understory, and the rate within the medium gap was higher than that of the small gap by 9.2%-15.1%. However, the large gap had no significant effect on the photosynthetic rate. (2) The maximum net photosynthetic rate of P. koraiensis saplings in various gaps decreased along the micro-habitat gradient of the center, transition and edge areas of the gaps (92.7%-22.5%). (3) In the medium and small gaps, the light saturation point of P. koraiensis saplings was higher than that for the forest understory, and the light compensation point was lower than that in the forest understory. However, the transpiration rate, stomatal conductance, and intercellular CO₂ concentration in the medium gap were higher than those in the forest understory, and the chlorophyll content was lower than that in the forest understory. The micro-habitat gradient from the central area to the edge area of the gaps reduced the light saturation point of the P. koraiensis saplings, and increased the light compensation point, and decreased the transpiration rate and stomatal conductance, and increased the chlorophyll content.【Conclusion】P. koraiensis saplings in the secondary Q. mongolica forest had a strong photosynthetic capacity in the central area of the medium gaps (116.9 m²). Therefore, to restore P. koraiensis forests rapidly, suitable gaps should be created, and full use of the central position in the gaps should be made.