贵州茂兰喀斯特森林两树种叶片气孔形态特征及其对蒸腾的影响

【目的】 石漠化是中国西南喀斯特地区严重的环境问题, 探讨在喀斯特生境下树种气孔对蒸腾需求的响应及环境因子的影响,了解类似气候条件下相似物种对外界环境条件的基本调节策略,为喀斯特地区森林的保护和石漠化治理提供参考。【方法】 在贵州茂兰喀斯特地区,以常绿树种胀果树参(Dendropanax inflatus)和落叶树种瓜木(Alangium platanifolium)为对象,利用热扩散探针(TDP)对树干液流进行了野外监测,同步记录小气候数据,采集两树种叶片样本带回实验室进行干燥处理,然后在电子显微镜下做气孔结构分析。【结果】 ①常绿和落叶树种树干的液流速率(F_S)日变化规律相似,整体来看,观察期落叶树种瓜木的F_S(585.25±53.46) g/h]高于常绿树种胀果树参的(384.83±39.12) g/h],说明落叶树种比常绿树种的蒸腾作用强。②落叶树种瓜木的气孔密度(SD)(1 005.08±80.99) 个/mm²]显著大于常绿树种胀果树参的(237.16±21.67) 个/mm²](P<0.05,df=48,F=7.08),但两树种的气孔开度(SO)、气孔长度(SC)以及气孔器大小(SAS)均无显著差异(P>0.05,df=48,F=2.65);同时SD与SO、SC之间均存在显著负相关(P<0.05,df=9,F=14.00;P<0.05,df=9,F=17.12),相比较低气孔密度的常绿树种胀果树参气孔较长,开度较大。③两树种的SD与F_s均呈极显著正相关(P<0.01,df=48,F=16.03;P<0.01,df=48,F=32.10),说明两树种蒸腾与气孔密度小有关;同时两树种气孔密度与太阳辐射强度(R_n)均呈显著正相关(P<0.05,df=48,F=7.66;P<0.01,df=48,F=47.18),落叶树种瓜木的SC与R_n呈显著正相关(P<0.05,df=48,F=13.06),常绿树种胀果树参的SD还与大气温度(T_a)呈显著正相关(P<0.05,df=48,F=5.02), SC与T_a呈显著正相关(P<0.05,df=48,F=6.32),SO与T_a、R_n呈极显著正相关(P<0.01,df=48,F=17.20;P<0.01,df=48,F=14.81),说明R_n是影响两树种气孔形态的主要环境因子。【结论】 环境因子和气孔形态变化均在调节树木蒸腾中起作用,以气孔密度较低的常绿树种胀果树参对环境条件的响应更强,从蒸腾调节的角度来看,气孔密度大小以及环境因子影响叶片气孔形态的差异是导致树木蒸腾强弱差异的关键所在,类似落叶树种瓜木有高气孔密度的物种更适合在复杂的喀斯特生境下生长。

Leaf stomatal morphological characteristics and their effects on transpiration for two tree species in Maolan Karst area,Guizhou Province

【Objective】 Rocky desertification is a serious environmental problem in southwest China. Research on tree transpiration and its stomatal regulation should benefit vegetation restoration and forest management in the Karst area.【Method】 We synchronously performed field measurements of sap flow by using a thermal diffusion probe and collected microclimate data. The leaf samples were collected and taken to the laboratory for drying treatment, and subsequently, stomatal structure analysis was performed under an electron microscope, including that of the evergreen Dendropanax inflatus and deciduous Alangium platanifolium.【Result】 ① There were similar sap flow (F_S) diurnal patterns for the deciduous and evergreen species; overall, the sap flow rate was higher in the deciduous species A. platanifolium (585.25±53.46) g/h] than in the evergreen species D. inflatus (384.83±39.12) g/h] during the observation period, indicating that the transpiration of the evergreen tree species was stronger than that of the deciduous tree species. ② Stomata density was higher in the deciduous species (1 005.08±80.99) individual/mm ²] than in the evergreen species (237.16±21.67) individual/mm²] (P < 0.05, df=48, F=7.08). However, there were no significant differences in stomatal openness, stomatal conductance, and stomatal apparatus size between the two species (P > 0.05, df=48, F=2.65). Additionally, there was a significant negative relationship between stomata density and stomata openness and conductance (P < 0.05, df=9, F=14.00; P < 0.05, df=9, F=17.12); low stomata density evergreen trees have longer stomata and openness compared to that of high stomata density deciduous trees.③ The stem sap flow of the two tree species was significantly positively related to stomatal density (P < 0.01, df=48, F=16.03; P < 0.01, df=48, F=32.10), showed that the transpiration was related to low the stomatal density. Meanwhile, the stomatal density was significantly positively correlated with solar radiation intensity (R_n) (P < 0.05, df=48, F=7.66; P < 0.01, df=48, F=47.18). The stomatal conductance of the deciduous A. platanifolium was significantly positively correlated with R_n (P < 0.05, df=48, F=13.06). The stomatal density of the evergreen D. inflatus was significantly negatively correlated with air temperature (T_a) (P < 0.05, df=48, F=5.02). A significant positive relationship between stomatal conductance and T_a (P < 0.05, df=48, F=6.32) was significantly positively correlated with T_a and R_n (P < 0.01, df=48, F=17.20; P < 0.01, df=48, F=14.81), indicated that R_n was the main environmental factor affects the stomatal morphology of the two tree species.【Conclusion】 Both environmental variables and changes in stomatal morphology play a role in regulating tree transpiration. Environmental conditions were more responsive in the evergreen tree D. inflatus, lowering stomatal density. The difference in stomatal density and stomatal morphology, which is affected by environmental factors, is the reason behind the transpiration difference. Species with high stomatal density are more suitable for growth in complex Karst habitats.