外来入侵植物和共生本地植物对无机氮形态的偏好及机制

The percentages of ammonium nitrogen (NH4+) and nitrate nitrogen (NO3-) are different in the nitrogen deposited from atmosphere, and the abilities to use different forms of nitrogen are different between plant species. Many studies found that nitrogen deposition facilitates invasion success of introduced plants. However, very few studies considered the effects of nitrogen forms on biological invasions, and nearly no studies considered the mechanisms underlying the preferences for nitrogen forms by exotic invasive plants. We hypothesize that nitrogen form preference by plants may be associated with their long term adaptation to the main nitrogen form in soils. Plants could alter nitrogen forms in soils by altering soil microbes, which in turn influences nitrogen preference by plants. In order to test the hypothesis, we plan to grow the invasive plant Xanthium strumarium and its native congeneric X. Sibiricum in pots, which prefer NO3- and NH4+ respectively based on our previous studies. We will measure NO3- and NH4+ contents in rhizosphere soils and community structures and functions of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB), and analyze the relationships among plant N form preference, N forms in soils, and those functional soil microbes. In order to evaluate the generality of the mechanisms underlying N form preference among different plants, we plan to determine NO3- and NH4+ contents in soils and N form preferences by 15 invasive plants and 15 co-occurring natives using 15N stable isotope technique, analyzing the differences in the relationships between N form preference and main soil N forms among plants. In addition, we plan to further explore the mechanisms underlying N form preference using three plants preferring NO3-and three plants preferring NH4+, in terms of N form preference, main soil N forms, AOB and NOB. The results are important for understanding the possible changes and related mechanisms in the impacts of exotic plants under climate change (N deposition) in the future, and the effects of exotic plant invasions on nitrogen cycling and related soil microbes, and adaptive evolution of invasive plants.

大气沉降氮中氨氮、硝氮%不同，不同植物对不同形态氮的利用不同。大量研究表明，氮沉降可促进外来植物入侵，但相关研究很少考虑氮形态的效应，对植物氮形态偏好机制的研究更少。项目假设，植物氮形态偏好与其对土壤主要形态氮的长期适应有关，植物可影响土壤微生物，进而影响土壤氮形态，反过来影响植物的氮偏好。为验证假设，项目以前期发现的偏好硝氮的外来入侵植物瘤突苍耳和偏好铵氮的本地植物苍耳为材料，测定根围土铵氮和硝氮含量及氨氧化菌和亚硝酸氧化菌的群落结构与功能，分析植物氮形态偏好、土壤主要氮形态和硝化细菌间的关系。为评估氮偏好机制的普适性，项目用15N技术研究15对入侵植物和本地植物对氮形态的偏好及其与根围土氮转化的关系；选择偏好铵氮和硝氮的入侵植物各3种，进一步研究氮形态偏好的机制。这对认识环境变化下外来植物入侵性的演化及机制，外来植物入侵对土壤氮循环和相关微生物的影响，以及植物的适应进化等均有重要意义。

氮是影响外来植物入侵的重要因素之一，但有关氮形态对外来入侵入侵的影响研究较少，还不清楚外来植物氮形态利用策略、成因、分子机制及其与入侵性的关系。1）为确定外来入侵植物瘤突苍耳和共生本地近缘植物苍耳氮形态利用策略的差异，项目在不同氮形态及比例下，研究了两种苍耳生长、生物量分配、光合、叶氮含量、氮同化酶活性等的差异，对不同形态氮的吸收动力学相关参数的差异，对不同形态氮偏好吸收的差异。2）为确定两种苍耳氮形态利用策略形成的进化生态学机制，项目在不同土壤环境下，研究了两种苍耳对土壤氮转化、氮形态和硝化细菌的影响，以及全株浸提物对土壤硝化作用的影响。3）为初步确定两种苍耳氮形态偏好的分子机制，项目研究了两种苍耳硝转运蛋白、铵转运蛋白基因及其在不同氮形态和水平下表达的差异。4）为评估外来入侵植物和共生本地植物氮形态利用的差异普遍性，项目通过15N标记法，比较了29种外来入侵植物和54种本地植物氮形态利用的差异。结果表明，1）瘤突苍耳吸收硝态氮的能力更强，偏好吸收硝态氮，在硝态氮下生长更好；苍耳吸收硝态氮和铵态氮是能力相似，氮形态偏好不明显，但在铵态氮下生长更好；种间竞争影响氮形态偏好，以及两种苍耳生长的差异。2）瘤突苍耳能改变土壤氨氧化细菌、氨氧化古菌、亚硝酸氧化菌Nitrobacter-like NOB和Nitrospira-like NOB的群落结构、提高土壤硝化速率和硝态氮含量，与其偏好的氮形态一致；苍耳不能提高土壤硝化速率。3）瘤突苍耳有更多的硝转运蛋白，潜在的参与硝氮吸收的转运蛋白基因的表达量更高、且受硝氮诱导，硝酸还原酶活性更高；苍耳有更多的铵转运蛋白，潜在的参与铵氮吸收的转运蛋白基因的表达量更高。4）83种外来入侵植物和共生本地植物的氮形态偏好差异不显著，除个别少数植物外，都偏好硝态氮。项目明确了两种苍耳氮形态偏好，初步揭示了两种苍耳氮形态偏好的进化生态学和分子生物学机制，这对理解全球变化背景下瘤突苍耳入侵性的表达具有重要的意义。