阔叶红松林生态系统土壤碳循环对增氮和减水交互作用的响应

The Changbai mountains is an important eco-function areas in our country, which shows the trend of nitrogen deposition increase and rainfall decrease for about 30 years, which may cause significant change of the carbon sink function. The research will take the temperate zonal climax vegetation ( broad-leaved Korean pine forest ) as the research object, through field experiment simulated climate change scenario such as nitrogen addition and rainfall decrease, CIA600 Minirhizotron technique, LGR continuous online monitoring technology, microbial high-throughput sequencing technologies and a linear discriminant analysis effect size (LEfSe) method, and the objective of this research is to quantify the carbon sink-source relationship between the soil carbon cycle input component (root system and litter) and output component (soil carbon flux, including autotrophic respiration, heterotrophic respiration and methane flux) in order to reveal the soil carbon dynamics under the interaction between nitrogen addition and precipitation decrease. At the same time, we will check or rebuild zonal soil flux model that provide accurate estimates about the regional soil carbon flux method using the actual data of soil carbon flux by continuous observation. The research will provide data support and model estimation method which could be used to accurately estimate the change of soil carbon storage under the global change in temperate forest in northeastern china.

长白山区是我国重要的生态功能区，近30年连续观测表现出了氮沉降增加和降水减少的趋势，进而可能会引起该区域碳汇功能的显著变化。本研究将以长白山原始阔叶红松林（我国温带地带性顶极植被）为研究对象，通过野外控制试验、微根管技术、LGR连续在线监测技术、微生物高通量测序技术和线性判别效应量分析等方法，定量探讨土壤碳输入（根系和凋落物）和输出（自养呼吸、异养呼吸和甲烷通量）之间的收支关系，揭示土壤碳循环对氮沉降和降水变化交互作用的响应。同时，利用实际连续观测的土壤碳通量数据，校验或重建该区域土壤碳通量模型，为准确估测该区域土壤碳通量提供方法支持。该研究可为科学评估全球变化背景下我国温带森林生态系统碳收支变化趋势提供科学依据。

本研究以长白山阔叶红松林为研究对象，利用自2009年开始模拟增氮和减水的野外控制试验，通过增氮（50 kg•hm-2•yr-1）、减水（-30%穿透雨）对生长季土壤呼吸、细根形态、菌丝长度、微生物群落结构的影响，探究长期增氮、减水对生长季阔叶红松林土壤呼吸的影响，为更加准确的测定生态系统在生长季对气候变化的响应提供科学依据。主要研究结果如下：（1）增氮、减水及其交互作用普遍增加了生长季的土壤呼吸及其组分速率。在增氮处理下，平均每年总土壤呼吸速率（Rs）、异养呼吸速率（Rh）和自养呼吸速率（Ra）分别平均提高了47%、94%和38%；在减水处理下平均增加18%、53%和24%（2）增氮、减水通过增加生长季根系生物量增强了土壤呼吸，并且细根生长指标的变化可以解释自养呼吸量的生长季动态。在生长季，增氮处理使0-10 cm 土层的根系总长度和总表面积平均每月分别降低2%和1%，而细根直径平均增加6%；减水处理使其平均降低12%、13%和9%；增氮和减水交互作用使其平均降低4%、11%和4%。（3）增氮、减水及其交互作用显著改变了不同土层深度的菌丝总长度，进而直接影响菌根真菌自身的呼吸作用，间接影响根系呼吸和非根际区的土壤呼吸，增氮减水交互作用对菌丝总长度表现出拮抗的非叠加性效应。（4）土壤微生物量不是影响土壤呼吸的主要因素，微生物多样性和群落结构是土壤呼吸的主要影响因素。增氮和减水作用下细菌、真菌群落均向抗干扰能力强的种类转变。综上所述，增氮减水可以通过影响细根形态、菌丝总长度以及微生物群落结构而改变土壤呼吸，进而影响生长季的土壤碳循环。此外，土层深度也可以间接调节土壤呼吸对气候因子（比如增氮和减水）的响应。