UV-B增强对荒漠地区隐花植物多样性及其结皮生态功能的影响

Biological soil crusts (BSCs) are main components in desert ecosystems, they also play a vital role in desert areas “ecosystem engineers”, and these functions depends mainly on the cryptogam in crustal communities. Ultraviolet-B (UV-B) radiation is one of the most significant factors in desert areas, especially, the composition, structure, and distribution pattern of vascular plants communities in desert areas were profoundly affected under the background of global environmental change. However, we know little about what are the impacts of enhanced UV-B radiation on species diversity and composition of cryptogam in crustal communities, and then whether these influences would cause change in ecological function of BSCs? In this project, we regard cryptogam in crustal communities of different succession stage as the research objects, based on the research accumulation for past several years and through the combination of field control and laboratory simulation experiments, reveals the effects of enhanced UV-B radiation on species diversity of cryptogam by viewing the changes of cryptogam diversity, coverage, biomass, surface structure and cell ultrastructure; studies the changes of ecological function to enhanced UV-B radiation via analyzing the responses of photosynthesis, respiration, nitrogen-fixing rate, and water-retaining capacity of crustal communities. The research results will provide novel insights into understanding the effects of enhanced UV-B on function evolution of BSCs in desert ecosystems, and supply the theoretical basis for desert ecosystems management under the background of global change.

生物土壤结皮(结皮)是荒漠生态系统的主要组成成分，发挥着“生态系统工程师”的功能，而这些功能的发挥主要取决于结皮群落中的隐花植物。UV-B辐射是荒漠地区最为显著的环境胁迫之一，尤其在全球环境变化背景下，其对荒漠维管束植物群落组成、结构及分布格局有重要影响。其对结皮群落中隐花植物种类多样性及组成有何影响，进而是否会导致结皮生态功能的改变？我们知之甚少。本项目基于多年连续研究积累，以不同演替阶段结皮及其隐花植物为研究对象，利用野外控制和室内模拟的手段，通过对UV-B增强引起的隐花植物多样性、盖度、生物量、表面结构及细胞超微结构变化的观测，揭示UV-B增强对隐花植物多样性的影响；通过对结皮群落光合作用、呼吸作用、固氮速率及其持水力对UV-B增强的响应分析，研究结皮生态功能因之而发生的改变；进而为全面认知UV-B增强对结皮在荒漠系统中功能演变的影响，以及全球变化背景下荒漠生态系统管理提供理论依据。

本项目以中国腾格里沙漠广泛存在的生物土壤结皮及其隐花植物(藻类、藓类)为研究对象，通过室内模拟和室外控制实验，研究了增强紫外线-B(UV-B)辐射、干旱及其复合作用以及可见光修复对生物土壤结皮及其隐花植物生理特性和细胞超微结构的影响。结果表明，(1)随着UV-B辐射增加，真藓和土生对齿藓两种藓类植物丙二醛(MDA)含量显著升高，叶绿素含量、叶绿素荧光参数、可溶性蛋白含量及其抗氧化酶活性明显降低，细胞超微结构遭到破坏，表现为叶绿体结构变形，类囊体片层排列稀疏紊乱、膨胀甚至模糊不清，嗜锇颗粒增多，且UV-B辐射强度越大，损伤越大。当去除UV-B辐射后，培养在可见光下的生理特性及细胞超微结构均有所恢复，说明可见光可部分修复UV-B对两种藓类的损伤；(2)野外控制条件下，高强度的UV-B辐射显著降低了聚鞘微鞘藻和真藓光合色素叶绿素荧光参数、光合色素含量以及抗氧化酶活性；UV-B强度越高，聚鞘微鞘藻和真藓MDA含量越高。在短时间内增强UV-B辐射有利于聚鞘微鞘藻和真藓的生长，但高强度和长时间的UV-B辐射抑制了这两种生物的生长。响应指数显示，UV-B辐射对真藓的损伤更大，说明真藓对UV-B辐射的敏感性高于聚鞘微鞘藻；(3)干旱胁迫和增强UV-B单独作用下，真藓和土生对齿藓类胡萝卜素和类黄酮含量均有所降低，脯氨酸含量升高，可溶性糖和可溶性蛋白含量显著降低。复合胁迫下，两种藓类紫外吸收物质和渗透调节物质含量升高，抵御UV-B的能力增强，说明干旱胁迫在一定程度上缓解了增强UV-B辐射对两种藓类造成的伤害。研究结果也预示着在未来UV-B辐射增强的情况下，温带荒漠生物土壤结皮的组成和结构将会发生显著变化，如BSCs中优势藓类真藓将会减弱，或逐渐被其它种类所替代，这种变化将会深刻地影响BSCs在荒漠生态系统中的功能，进而影响荒漠生态系统的健康和稳定。