冻融引起的土壤NO3-~NH4+波动对高寒草原植物吸收偏好的影响

Differentiation of the preferential absorption of NO3- and NH4+ by plants has been regarded as an important way to understand interspecific competition and niche differentiation. Soil N form availability plays a critical role in controlling the plant absorption for NO3- and NH4+. Phase transformation caused by strong freezing and thawing cycles changes the soil redox environment on the Qinghai-Tibet Plateau, and then affects the soil nitrification and denitrification processes, leading to rhizosphere soil NO3- and NH4+ concentrations in fluctuating states. However, how this process affects the N fixation and the efficiency of nutrient uptake by plants from soil is unclear. The applicant has been engaged in the study of soil-plant nutrition adaptation mechanism, and found that different plant functional groups were differentiated in the N uptake on the northern Tibetan steppe. Based on the existing and experimental data from Xianza ecological station, we plan to conduct controlled experiments and adopt isotope tracer technique, minirhizotron technique and freeze-thaw simulation to investigate changes of NO3- and NH4+ concentrations in soil profiles under different freezing-thawing rates, frequency and intensity, as well as to clarify the effects of root configuration on N absorption efficiency and organic/interspecific distribution. The successful completion of this project will reveal the adjustment strategy and absorption preference adaptation mechanism of alpine plants in response to NO3- and NH4+ fluctuation. It will be of great scientific value to understand the biogeochemical cycle in alpine region and the adaptability of species to extreme environment.

植物对NO3-和NH4+吸收偏好是理解种间竞争和生态位分化的重要途径，土壤N素赋存形态是影响植物吸收偏好的关键所在。青藏高原强烈冻融作用引起的相态转化改变土壤氧化还原环境，继而影响土壤硝化、反硝化过程，导致根际土壤NO3-与NH4+浓度处于波动状态。然而，这一过程如何影响高寒植物对N素同化固定作用，以及土壤-植物养分传递效率尚不明确。申请者硕博期间一直从事土壤-植物营养适应机制研究，发现了高寒草原不同物种对土壤N素吸收偏好存在差异。本项目拟依托申扎生态站已有的实验基础，进一步通过野外稳定同位素示踪、微根窗和室内冻融模拟等方法，弄清冻-融速率、频次及强度变化下土壤不同形态N素释放量及其剖面分布，阐明不同形态N素的吸收效率、器官/种间分配特征与根系生长参数的关系，回答土壤相态改变引起的NO3-~NH4+波动下高寒植物的应对调整策略与吸收偏好适应机制，对认知极端环境下物种适应性有重要科学价值。

N素是高寒和极地生态系统重要的限制性因子。本项目以西藏高寒草原为研究对象，以土壤-植物N素传递和调节过程为主线，通过同位素示踪和微根窗等方法，定位监测融化期和冻结期土壤中不同形态N素释放和波动规律，探讨不同形态N素的吸收效率、器官/种间分配特征与根系生长参数的关系，阐明土壤相态改变引起的NO3-~NH4+波动下高寒植物的应对调整策略与吸收偏好适应机制。研究发现高寒草原土壤主导N素随季节存在波动，完全融化期表现为硝态N含量高，而冻融循环期表现为铵态N含量高。植物N素吸收偏好随土壤主导N素形态会发生相应的变化。根系系统大小（根重、表面积、体积和直径）对植物N素吸收速率没有显著性影响，而根系构型特征（比表面积和比根长）是决定N素吸收速率的关键参数。研究结果对认知高山生态系统植物养分获取策略以及适应机制具有重要意义。