大兴安岭火烧迹地土壤氮营养生境特征及其对植被恢复的影响机制

Fire represents a major interference factor of forest ecosystem in the Great Xing’an Mountains, and fire-induced changes in “soil nitrogen habitat” are thought to be a potential obstacle to native vegetation recovery. This project will, firstly, focus on the changes in soil nitrogen availability in burned sites as opposed to virgin coniferous forests, including amounts and ratio of NH4+ and NO3-, ammonification and nitrification process, microbial mechanism, and controlling factors of soil nitrogen transformation(e.g. temperature, humidity, pH, C/N ratio and characteristic organic compounds). Then, the eco-physiological responses of saplings of four native coniferous species (Larix gmelini, Pinus sylvestris var. mongolica, Picea koraiensis, and Picea jezeonsis var. microsperma) to different “nitrogen habitat” will be examined to identify the species-preferred nitrogen source (nitrate or ammonium), by in situ NH4+/NO3- fertilizer test, and solution culture approches, respectively. The objectives of this project are: (1) to quantify the original “soil nitrogen habitat” in virgin coniferous forests and the successive changes in burned sites; (2) to characterize the adapted or specilized nitrogen habitat for saplings of each native coniferous species, and to ascertain whether the “nitrogen habitat” in burned areas be suitable to native vegetation recovery; (3) to probe into reasonable techniques regulating the “soil nitrogen habitat” in post-fire sites. This project would have important significance in native vegetation recovery.

在我国大兴安岭寒温带针叶林区，火是森林生态系统的首要干扰因素。由此产生的立地氮营养生境变化，可能是原生植物群落恢复的障碍因子。本项目将系统研究原始针叶林与火烧迹地土壤矿质氮供应数量、形态格局(NH4+/NO3-)、动态特征、微生物机理及转化过程的控制因素（温度、湿度、pH值、C/N、特征有机物等）；研究兴安落叶松、樟子松、红皮云杉、鱼鳞云杉等针叶树种幼苗、幼树在不同氮营养生境中的生理生态响应与生长表现。通过上述研究，旨在揭示并量化大兴安岭寒温带针叶林土壤原始氮营养生境特征及其在火烧迹地植被恢复过程中的变化规律，确定各针叶树种在早期生长过程中最适于怎样的个性化氮营养生境以及火烧迹地植被恢复过程中氮营养生境特征是否适于其原生植被类型恢复，并探讨合理调控火烧迹地土壤氮营养生境的技术途径。该项研究对寒温带针叶林区火烧迹地原生植物群落恢复有理论和现实意义。

火是大兴安岭寒温带针叶林区的首要干扰因素，土壤氮营养生境对火干扰的响应迅速而强烈。本项目系统研究原始针叶林地与火烧迹地土壤矿质氮供应数量、形态格局、转化过程的动态特征，分析生境控制因素；并在此基础上，深入研究该区主要针叶树种早期在不同氮营养生境中的生理生态响应。研究对于准确认识寒温带针叶林区原生土壤氮营养生境特征、火烧迹地土壤氮营养生境变化规律、针叶树种早期氮适应性均有重要意义，可为寒温带针叶林区火烧迹地原生植被类型恢复提供科学参考。主要研究结论如下：（1）大兴安岭原始林地土壤矿质氮总量在几mg/kg至十几mg/kg范围波动，呈明显的NH4+-N优势土壤氮营养生境特征。（2）火烧后，土壤矿质氮总量与土壤NH4+-N优势度激增，并以月为时间尺度锐减，而后随植被恢复逐步回落甚至低于原始林地；相对表层土壤，下层土壤供氮水平受火干扰影响降低。大兴安岭火烧迹地恢复初期土壤净氮矿化速率波动区间扩大；相对表层土壤，下层土壤净氮矿化速率受火干扰影响降低。（3）土壤湿度限制排水不良区域土壤氮矿化，有利于排水较好区域土壤氮矿化或土壤氮有效性；火烧导致的土壤pH值变化对土壤氮矿化未产生显著影响；重度火烧迹地土壤微生物群落物种多样性响应迅速，并随火后次生演替阶段逐步变化，而后随植被恢复火烧效应消失；火烧未导致土层间微生物群落物种多样性差异。（4）大兴安岭主要针叶树种早期在NH4+-N优势营养生境中适应性较好。