黄土丘陵区辽东栎群落优势种和主要伴生种树干液流动态特征

Characteristics of sap flow dynamics in dominant and companion trees in a natural secondary oak forest in the loess hilly region

运用Granier热扩散探针法(TDP),于2011年5月对黄土丘陵区延安市南郊公路山辽东栎群落优势种(辽东栎)和3个伴生种(山杏、细裂槭、桃叶卫矛)树干液流进行连续测定,并同步监测气象环境因子(太阳辐射、空气温度和相对湿度)和土壤水分动态,比较分析辽东栎、山杏、细裂槭、桃叶卫矛的树干液流通量密度日变化动态及其对环境因子的响应特征。结果表明,辽东栎、山杏、细裂槭和桃叶卫矛液流通量密度日变化动态特征总体上反映了气象环境因子变化的昼夜规律性,呈单峰或双峰型曲线,但辽东栎与山杏、细裂槭、桃叶卫矛液流通量密度日变化规律存在一定的差异。辽东栎液流启动时间较早,通常在5:00左右,而山杏、细裂槭和桃叶卫矛液流启动时间均晚于辽东栎一个小时以上。辽东栎液流达到峰值的时间也较其它树种早,通常出现在9:00前后;细裂槭、桃叶卫矛和山杏液流通量密度达到峰值的时间分别在10:00、11:00和13:00前后。细裂槭和桃叶卫矛液流通量密度日变化曲线峰值较窄。除此之外,土壤水分状况对伴生种的影响程度要比优势种的大。相关分析表明,树干液流通量密度与太阳辐射和空气水汽压亏缺均呈极显著正相关。优势种与伴生种的液流动态差异可能与树木本身特性以及群落对光能的限制性再分配有关。

This study was performed to gain an understanding of the time cumulative effects of grazing intensity on the diversity of species, life forms, functional groups, and biomass and their relationships on an alpine meadow. From 2012 to 2015, we conducted a controlled grazing trial with six grazing intensities on an alpine meadow located in the northeastern Qinghai-Tibet Plateau. We investigated the diversity and life form of species, functional group diversity （richness, evenness, and dominance were used as diversity indices）, and aboveground biomass in four years. We used repeated measures and linear regression methods to analyze the effect of grazing intensities and grazing years on plant species diversity, life forms, and functional groups, as well as on the relationship between the diversities and biomass. The following results were obtained. （1） Grazing intensity and grazing year had significant effects on biomass, with the biomass significantly decreasing with an increase in grazing intensity. There was irregularity in biomass changes in different grazing intensity plots with progression of the grazing year. （2） There were significant effects of grazing year on abundance, evenness, and dominance in term of the plant species, life forms, and functional groups. However, the grazing intensity and grazing year had an interactive influence on the richness of plant species, and grazing intensity had a time cumulative effect on the richness of plant species. （3） In the plant diversities with different organizational levels under grazing disturbance, only the richness of plant species was significantly correlated with all diversity indices. The richness of plant species can be used as a representative index for measuring plant species diversity. （4） In the study of the relationship between diversity and biomass, the richness of plant species in the lighter grazing intensity plot （Plot 2） was significantly decreased with increasing biomass, whereas the richness of plant species, life forms, and functional groups showed no relationship with biomass in other grazing intensity plots. The evenness of life forms in the high intensity grazing plots （Plots 4, 5, and 6） significantly decreased with an increase in biomass. The dominance of life forms in the high intensity grazing plots （Plots 4, 5, and 6） significantly increased with an increase in biomass. In conclusion, the diversity of life forms can be used as an effective index for rapidly predicting plant biomass under grazing disturbance because this diversity is the most sensitive to biomass variation.