叶片毛尖对齿肋赤藓结皮凝结水形成及蒸发的影响

凝结水(隐匿降水)和降水是荒漠地区两种不同形式的水分来源，对荒漠生态系统极为重要。叶片毛尖(leaf hair points, LHPs)是很多荒漠藓类的重要外部形态结构特征，但它在藓类植物利用凝结水和降水中的作用尚不清楚。齿肋赤藓(Syntrichia caninervis)是古尔班通古特沙漠藓类结皮的优势种，其叶片顶端具有较长的白色毛尖。本文采用自制微渗计(h=3.5 cm, d=5.7 cm)研究了正常有毛尖和人工去除毛尖的齿肋赤藓结皮的凝结水特征及其在3种模拟降水梯度(1 mm, 3 mm, 6 mm)下的短期蒸发特征，结果表明：(1) 在凝结阶段，有毛尖结皮每时段的凝结水量均大于无毛尖结皮，但日出后有毛尖结皮凝结水下降速度稍快；有毛尖结皮的日凝结水量均大于无毛尖结皮，且前者的总凝结水量比后者多10.26%，即毛尖能增加10.26%的凝结水量。(2) 3种模拟降水梯度下，有毛尖结皮在各时段的累积蒸发率始终小于无毛尖结皮，以蒸发前期阶段最为明显，表明毛尖能显著减少和延缓结皮内的水分蒸发、延长植株水合时间，而且降水量越大减缓效果越明显。毛尖对这2种不同形式水分利用的差异是因为利用方式不同：对凝结水的利用主要归因于毛尖增大了结皮表面粗糙度，而减少对降水的蒸发主要是毛尖能反射阳光、形成内部毛细管及减小植株间隙的缘故。因此，毛尖的存在有利于齿肋赤藓结皮对凝结水和降水的利用，增强了藓类结皮对干旱环境的适应能力。

Effects of leaf hair points on dew deposition and rainfall evaporation rates in moss crusts dominated by Syntrichia caninervis, Gurbantunggut Desert, northwestern China

In arid areas where rainfall is rare and solar radiation is strong, reducing water loss and efficient water use are extremely important for plant survival. Desiccation-tolerant mosses are the dominant components of biological soil crusts (BSCs) in desert ecosystems. These mosses play important roles in soil surface stability, fertility, and ecological restoration. Crust-forming mosses have presumably developed special morphological and anatomical features to cope with harsh desert conditions, but the nature of these remains largely unknown. Some special morphological features (such as convex or concave leaves, papilla, and thick marginal cell walls) have been observed; providing evidence of long-term adaptation to the desert environment. Leaf hair points (LHPs) are important morphological structures in many desiccation-tolerant mosses. These are elongations of leaf midribs; they are generally white, with many small spiny teeth on their surfaces. A few preliminary studies have indicated that LHPs in several kinds of cushion mosses can reflect sunshine, absorb moisture from the air, and reduce water loss. Precipitation is the main water source in desert areas. The rainfall in the center of the Gurbantunggut Desert is only 70 to 150 mm per annum, and most rainfall events (89.8% in 1998-2007 data) are less than 5 mm. Even so, these events still enable desert mosses to reach and to maintain hydration for a time. In addition, dew and fog (occult precipitation) provide small amounts of water; not enough to hydrate mosses, but with a greater frequency than rainfall. Occult precipitation is thus another important water source for desert biology, and has a crucial role in these ecosystems. Research into the role of the LHPs of drought-resistant mosses is timely. We collected a dominant desert moss, Syntrichia caninervis, from the Gurbantunggut Desert of Xinjiang, China, to investigate the effect of LHPs on water use. The LHPs of S. caninervis are often broken in nature. Our method involved comparison of moss patches with LHPs and moss patches with LHPs manually removed. Characteristics of dew deposition and short-term rainfall evaporation (1 mm, 3 mm, 6 mm) of S. caninervis crusts with and without LHPs were studied using purpose-built micro-lysimeters (PVC, h=3.5 cm, d=5.7 cm). Results indicated that (1) Dew amounts on crusts with LHPs were greater than on crusts without LHPs. After sunrise, the dew on crusts with LHPs dried slightly faster. Daily dew amounts on crusts with LHPs were greater than on crusts without LHPs. The total dew amount for seven days on crusts with LHPs was 10.26% greater than on crusts without LHPs. Thus LHPs can improve dew amounts on S. caninervis crusts by 10.26%. (2) Rainfall evaporation rates from crusts with LHPs were lower than from crusts without LHPs at every time of evaporation; this was most obvious during the early period. LHPs can significantly delay and reduce water evaporation, thus extending the hydration time of S. caninervis crusts. These differences in water utilization are a result of two aspects. More efficient dew use is attributable to LHPs increasing the surface roughness of the crusts. By reflecting light, forming internal capillaries, and reducing gaps between individuals, LHPs are able to reduce rainfall evaporation. In conclusion, the existence of LHPs is favorable for the utilization of dew and rainfall by S. caninervis crusts, and increases the ability of these moss crusts to adapt to arid conditions.