Song Liang, Zhang Yong-Jiang, Chen Xi, Li Su, Lu Hua-Zheng, Wu Chuan-Sheng, Tan Zheng-Hong, Liu Wen-Yao, Shi Xian-Meng
Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, No. 88 Xuefu Road, Kunming, 650223, Yunnan, China,
J Plant Res. 2015 Jul;128(4):573-84. doi: 10.1007/s10265-015-0721-z. Epub 2015 Mar 27.
Fan life forms are bryophytes with shoots rising from vertical substratum that branch repeatedly in the horizontal plane to form flattened photosynthetic surfaces, which are well suited for intercepting water from moving air. However, detailed water relations, gas exchange characteristics of fan bryophytes and their adaptations to particular microhabitats remain poorly understood. In this study, we measured and analyzed microclimatic data, as well as water release curves, pressure-volume relationships and photosynthetic water and light response curves for three common fan bryophytes in an Asian subtropical montane cloud forest (SMCF). Results demonstrate high relative humidity but low light levels and temperatures in the understory, and a strong effect of fog on water availability for bryophytes in the SMCF. The facts that fan bryophytes in dry air lose most of their free water within 1 h, and a strong dependence of net photosynthesis rates on water content, imply that the transition from a hydrated, photosynthetically active state to a dry, inactive state is rapid. In addition, fan bryophytes developed relatively high cell wall elasticity and the osmoregulatory capacity to tolerate desiccation. These fan bryophytes had low light saturation and compensation point of photosynthesis, indicating shade tolerance. It is likely that fan bryophytes can flourish on tree trunks in the SMCF because of substantial annual precipitation, average relative humidity, and frequent and persistent fog, which can provide continual water sources for them to intercept. Nevertheless, the low water retention capacity and strong dependence of net photosynthesis on water content of fan bryophytes indicate a high risk of unbalanced carbon budget if the frequency and severity of drought increase in the future as predicted.
扇状生物是苔藓植物，其茎从垂直基质上长出，在水平面上反复分支，形成扁平的光合表面，非常适合从流动的空气中截留水分。然而，关于扇状苔藓植物的详细水分关系、气体交换特征及其对特定微生境的适应性仍知之甚少。在本研究中，我们测量并分析了亚洲亚热带山地云雾森林（SMCF）中三种常见扇状苔藓植物的微气候数据，以及水分释放曲线、压力-体积关系和光合水分与光响应曲线。结果表明，林下相对湿度高，但光照水平和温度低，雾对SMCF中苔藓植物的水分可利用性有很大影响。扇状苔藓植物在干燥空气中1小时内就会失去大部分自由水，以及净光合速率对含水量的强烈依赖性，这意味着从水合、光合活跃状态到干燥、不活跃状态的转变很快。此外，扇状苔藓植物具有相对较高的细胞壁弹性和耐干燥的渗透调节能力。这些扇状苔藓植物的光合作用光饱和点和补偿点较低，表明它们耐阴。由于年降水量大、平均相对湿度高以及频繁且持续的雾，扇状苔藓植物很可能能够在SMCF的树干上繁茂生长，这些条件可以为它们提供持续的水源以供截留。然而，如果未来干旱的频率和严重程度如预测的那样增加，扇状苔藓植物的低保水能力和净光合作用对含水量的强烈依赖性表明碳收支失衡的风险很高。
