Response of needle photosynthetic and anatomical characteristics of naturally regenerated Pinus koraiensis seedlings to different canopy densities.

We took 5-year-old Pinus koraiensis seedlings under natural secondary forests with canopy densities of 0.2-0.3, 0.4-0.6, and 0.7-0.9 at Laoshan Plantation Experimental Station in Maoershan Experimental Forest Farm of Northeast Forestry University as monitor object, and P. koraiensis seedlings under full-light environment as control (CK), to investigate the photosynthetic characteristics and the anatomical structure of P. koraiensis needles in response to the changes of canopy densities. The results showed that the height and diameter of P. koraiensis seedlings tended to decrease while specific leaf area increased with the increases of canopy densities. The total biomass of P. koraiensis seedlings under different canopy densities ranked in an order of 0.4-0.6＞CK＞0.7-0.9＞0.2-0.3. Photosynthetically active radiation (PAR) was significantly and positively correlated with leaf biomass, stem biomass, and root biomass. The net photosynthetic rate, transpiration rate, and intercellular CO2 concentration of P. koraiensis seedlings showed a decreasing trend with the increases of canopy densities, while the stomatal conductance showed an increasing trend. Net photosynthetic rate and chlorophyll a/b showed a significant positive correlation with PAR. Stomatal density showed a gradual decreasing trend with the increases of canopy densities, and the needle cross-sectional area, mesophyll tissue area, xylem area, and phloem area of P. koraiensis seedlings under canopy density 0.4-0.6 were significantly higher than those in other treatments. P. koraiensis seedlings with stronger photosynthetic abilities and higher needle anatomy parameters under canopy density 0.4-0.6, and were able to maintain strong competitiveness in this habitat. Those results indicated that 5-year-old P. koraiensis seedlings need certain shading environment.本研究以帽儿山实验林场老山人工林实验站郁闭度为0.2～0.3、0.4～0.6和0.7～0.9的天然次生林下5年生红松苗为对象,以全光环境(CK)下红松苗为对照,研究其针叶光合特性以及解剖结构对郁闭度变化的响应,探讨林下红松苗生长发育与林分光环境之间的关系,揭示红松苗耐荫性特征。结果表明: 红松苗高和地径均随着郁闭度的增大而呈下降趋势,比叶面积随郁闭度的增大而显著增加,不同郁闭度下红松苗总生物量由大到小排序为:郁闭度0.4～0.6＞CK＞郁闭度0.7～0.9＞郁闭度0.2～0.3。针叶光合有效辐射与红松的叶生物量、茎生物量、根生物量呈显著正相关。红松苗的净光合速率、蒸腾速率和胞间CO2浓度均随着郁闭度的增大呈逐渐下降的趋势,气孔导度随郁闭度的增大呈上升趋势,且净光合速率、叶绿素a/b与光合有效辐射呈显著正相关。红松苗的气孔密度随着郁闭度的增大呈逐渐下降的趋势,郁闭度为0.4～0.6时,红松苗的针叶横截面积、叶肉组织面积、木质部面积、韧皮部面积均显著高于其他处理。红松苗在郁闭度0.4～0.6下光合作用较强,针叶解剖结构中各参数数值较高,红松苗能在此生境中保持较强的竞争力,也说明红松5年生苗需要一定的避荫环境。.