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生物结皮的形成发育具有明显的时空分异性,荒漠地区的诸多研究结果不能直接推演至黄土高原地区。研究黄土高原生物结皮的形成过程与发育特征,是对全球生物结皮认知的重要补充,也是揭示其生态功能的基础。论文选择陕北黄土高原水蚀风蚀交错区的典型小流域,通过定位动态观察和全面调查测算,探讨生物结皮的发育过程。结果表明:①流域内生物结皮经历了由退耕裸地—物理结皮—生物结皮的发育阶段。退耕撂荒的第1年,物理结皮便迅速形成;第2年,土表颜色明显变深,藓结皮开始发育。流域内藓结皮占绝对优势,发育稳定后(15 a)覆盖度可达90%。②不同发育年限生物结皮的物种组成及种数差异很大。发育初期(<6 a)发现苔藓植物2科4属5种,其中芦荟藓(Aloina rigida(Hedw.)Limpr.)和短喙芦荟藓(A.brevirostris(Hook.&Grev.)Kindb.)为先锋优势种。发育稳定的生物结皮(15 a)鉴定出苔藓植物2科8属13种。其中,丛藓科占6属8种,以对齿藓属(Didymodon)的尖叶对齿藓(D.constrictus(Mitt.)Saito)、黑对齿藓(D.nigrescens(Mitt.)Saito)、硬叶对齿藓尖叶变种(D.rigidulus Headw.var.ditrichoides(Hedw.)Zand.)所占种数最多。不同阶段的藓结皮均有藻类伴生,发育初期(<6 a)的藓结皮中鉴定出藻类植物26科35属50种。③水热同期的雨季是生物结皮形成的关键时期。发育2 a的生物结皮厚度达到6.3 mm,超过稳定结皮厚度(9.8~11.8 mm)的50%,抗剪强度约30 kPa。发育初期(<6 a),容重无明显变化(1.40~1.43 g·cm-3),发育稳定(15 a)后容重下降到1.0~1.3 g·cm-3。该区生物结皮的形成过程同荒漠区类似,但表现出发育速度快、稳定周期短的特点;藻类、苔藓组成及其优势种[坑形细鞘丝藻(Leptolyngbya foveolara)、尖叶对齿藓]与荒漠区明显不同。
The formation and development of biological crusts have obvious spatiotemporal differentiation. The results of many desert regions can not be deduced directly to the Loess Plateau. Studying the formation process and development characteristics of the biological crusts on the Loess Plateau is an important supplement to the cognition of the global biological crust and the basis for revealing its ecological functions. The paper selected a typical small watershed in the erosion-wind erosion crisscross region of the Loess Plateau in northern Shaanxi Province. Through the dynamic observation and comprehensive investigation and calculation, the developmental process of the biological crust was discussed. The results showed that: (1) biological crusts in the watershed experienced the development stage from the bare land returning to cultivation - physical crust - biological crusts. In the first year of returning farmland to wasteland, physical crusts formed rapidly; in the second year, the color of soil surface became deeper and the moss crust began to develop. The moss crust in the drainage basin occupies an absolute advantage. After the stable development (15 a), the coverage is up to 90%. ② The species composition and species number of biological crusts vary greatly in different developmental stages. In the early stage of development (<6 a), 5 species of 2 genera, 4 genera, 2 families were found, among which Aloina rigida (Hedw.) Limpr. And A. brevirostris (Hook. & Grev.) Kindb. Dominant species. Stable and stable biological crusts (15 a) identified 13 species of 2 genera, 8 genera and 2 bryophytes. Among them, the family Culicidae occupies 6 genera and 8 species, and the dominant species of Didymodon are D.constrictus (Mitt.) Saito, D.nigrescens (Mitt.) Saito, And D.rigidulus Headw.var.ditrichoides (Hedw.) Zand. All stages of moss crusts were associated with algae. In the early stage of development (<6 years), 50 species of 26 genera, 35 genera, 26 families were identified in moss crusts. ③ the same period of the rainy season is the biological crusts formed a critical period. The bio-crust thickness of 2 a was 6.3 mm, which exceeded 50% of the stable crust thickness (9.8-11.8 mm) and the shear strength was about 30 kPa. The bulk density did not change significantly (1.40-1.43 g · cm-3) during the initial developmental period (<6 a), and decreased to 1.0-1.3 g · cm-3 after stable development (15 a). The formation process of the biological crust in this area is similar to that in the desert area, but it shows the characteristics of rapid development and short stabilization period. The composition of algae and moss and their dominant species [Leptolyngbya foveolara, Moss] and the desert area is obviously different.