根鞘微生境对羽毛针禾沙生适应性的生态调节

羽毛针禾(Stipagrostis pennata)是古尔班通古特沙漠流动沙丘的先锋禾草和优良固沙植物,本研究从形态结构、理化特性、生物学特性等方面对其复杂的根区生境进行了分析。结果表明:①野生羽毛针禾能够形成特殊的根鞘结构(即由土壤颗粒与根表分泌物及根毛、菌丝体相互胶结、缠绕形成的特殊结构),使根区环境相对稳定;②根鞘的存在可有效扩大根系与土壤的接触面积,有利于根系-土壤信息交流及水分和养分的交换,对植物忍耐干旱逆境胁迫尤为重要;③根鞘的形成明显改善了其所在微生境的土壤条件,根鞘含水量可达外围土壤的5倍,成为潜在的水库;根鞘的形成明显改善了养分尤其是氮素累积状况,其全氮含量显著高于外围土壤,速效氮、微生物量氮含量极显著(P<0.01),高于外围土壤;根鞘微生境呈碱性,pH值略低于外围土壤;④根鞘中碱性磷酸酶、脲酶、多酚氧化酶、蔗糖酶等各类水解酶、氧化酶均极显著(P<0.01)高于根外围土壤,反映出根鞘微生物学过程较强、土壤肥力较高,可有效增加土壤有机碳氮的转化,促进根鞘微生境养分循环;⑤可培养微生物分析结果显示,细菌在根鞘微生境中占绝对优势(99.72%±0.09%);可培养微生物优势类群为芽胞杆菌属(Bacillus)、链霉菌属(Streptomyces)、青霉属(Penicillium)。上述微生物具有固沙、固氮、解磷、产抗生素等生态潜能,有助于改善羽毛针禾根区营养吸收,促进植株生长。因此,作为对高温、缺水恶劣环境的一种应答结构,根鞘的形成促进了植物根土界面的信息交流及水分和养分的交换,有利于植物、土壤、微生物建立互惠互利的关系,对植物忍耐干旱逆境胁迫尤为重要。

Ecological Regulation of Stipagrostis pennata by Rhizosheath Microhabitat

Stipagrostis pennata is a typical pioneer psammophyte species in Gurbantunggut Desert of the Junggar Basin in Northern Xinjiang. It is resistant to high temperature, drought, and sandstorms. It is also an excellent forage for livestock. This psammophyte resists drought through several mechanisms. This study expands our knowledge of its ecological effect on sand surface stability due to the presence of a rhizosheath. Results showed that: (1) Rhizosheaths differ markedly from typical soil grains for their physical and chemical properties, and are important biological factors in the formation, stability, and fertility of soil. (2) The space between rhizosheaths and roots may store water to help the plant resist drought. Rhizosheath soil was significantly (P<0.01) wetter than surrounding sand soil. The most likely explanation of this difference is that the presence of mucigel within the rhizosheath increases the water-holding capacity of that soil. There were also abundant organic nutrients in the rhizosheath soil. The available nitrogen (such as NH+4) and microbial biomass nitrogen in the rhizosheath were both significantly (P<0.01) higher than those in non-rhizosheath soil. (4) The significantly higher activity of soil enzymes (ployphenol oxidase, peroxidase, invertase, urease, alkaline phosphatase) found in the rhizosheath suggested increased C and N cycling. (5) Rhizosheath microhabitats were found to be a favorable environment for the growth and development of microorganisms, especially fungi. The quantities of bacteria, fungi, actinomycetes and oligotrophic bacteria cultured from rhizosheath soil were significantly higher than those in non-rhizosheath soil. Based on the primary identification, the dominant genera were Bacillus, Streptomyces and Penicillium. These organisms might play important roles in forming the rhizosheath, inhibiting the growth of plant pathogens, and increasing plant-available nutrients, thereby promoting plant growth. Thus, the rhizosheath of Stipagrostis pennata is an important adaptation to arid environments, and an integral part of soil microbe ecology.