气候变暖背景下，中亚热带天然林和人工林吸收根有机碳基团分解研究

Absorptive roots is the non-lignified fine roots in plants, which are the major source of soil organic carbon (SOC) because of their short lifespan and rapid turnover rate. As global warming progresses, a quantified information on the contribution of absorptive roots to SOC and its’ fractions is of great importance to get a better understanding of how climate change will affect SOC dynamic and associated terrestrial ecosystem carbon source/sink. However, such information is hampered by several factors: 1) sampling of absorptive roots is difficulty, and therefore the decomposition of absorptive roots among different forest types is lacking; 2) the mechanisms control absorptive roots decomposition is different from that of fine roots; 3) the decomposition of organic carbon functional groups in absorb roots is rarely been quantified. Therefore, this study is aimed to comprehensively examine the effects of experimental warming using open top chamber (OTC) on the decomposition of absorb roots in three forests including natural broadleaf forest (Betula luminifera), coniferous (Cryptomeria fortunei) and broadleaf (Alnus cremastogyne Burk ) plantations at Emei mountain to identify general mechanism. Furthermore, the content of seven organic carbon functional groups at different decomposition stages during two years will be quantified by using the nuclear magnetic resonance technique. This novel approach will allow to elucidate on the total C input of different organic C functional groups through decomposition and consequences for ecosystem function under global warming. This study will also be complimented with the investigation of the microbial composition and soil properties during decomposition. Our results will produce significant beneficial impacts that will help in improving the theory of absorptive roots decomposition, clarifying the relationship between absorptive roots and the stability of SOC, and understanding the soil carbon cycle in the context of global change.

吸收根是植物中非木质化的细根，寿命短、周转快，是土壤有机碳（SOC）的主要来源。气候变暖背景下，精确区分和量化不同森林类型吸收根对SOC组分的贡献，有助于更好地认识土壤碳动态，阐明未来陆地生态系统碳源/汇功能对气候变化的响应机制。然而，吸收根对SOC组分贡献的研究面临诸多难题：1）吸收根取样困难，缺乏不同森林类型吸收根分解的比较研究；2）吸收根分解机制与细根存在较大差异；3）难以量化吸收根有机碳基团的分解。基于此，本项目以峨眉山广泛分布的亮叶桦天然林，柳杉人工针叶林，桤木人工阔叶林为研究对象，通过原位OTC增温试验，从吸收根的初始化学质量、土壤微生物群落结构和土壤理化性质3个方面揭示吸收根分解的控制因素；同时，利用核磁共振技术，量化吸收根7类有机碳基团的分解动态。研究结果对于进一步完善吸收根分解理论、阐明吸收根与土壤碳稳定性之间的联系、了解全球变化背景下的土壤碳循环具有重要的学术价值。

吸收根数量大、寿命短，分解慢，是土壤有机碳的重要来源。精确区分和量化吸收根有机碳基团的分解，对于进一步揭示吸收根在维持土壤有机碳稳定性方面的关键作用具有重要意义。目前，全球气候变化,尤其是两个因子的交互作用，如何影响不同森林类型的吸收根有机碳基团分解仍有待阐明。根据项目任务书、结合野外样地的实际情况，本课题以润楠天然林和柳杉人工林吸收根为研究对象，采用有机玻璃增温箱和减雨槽（30%）模拟增温和减雨，结合13C核磁共振和微生物高通量测序技术，研究了增温、减雨及增温&减雨对吸收根7类有机碳基团分解及其微生物学机制。经过一年半的分解实验，我们发现：（1）增温、减雨及增温&减雨对润楠幼嫩型1级根和成熟型1级根、柳杉1-2级和3-4级细根的分解速率和碳氮释放均无显著影响；（2）分解12个月后，增温、减雨及二者的交互作用显著增加了柳杉1-2级根的Methoxyl C 和O-alkyl C 基团的相对丰度，但降低了O2-alkyl C，O-aromatic C 和Carboxylic C的相对丰度，而对不同分解阶段（3，5，8和12个月）润楠两类1级根和柳杉3-4级根有机碳基团组成的影响较小；（3）增温、减雨和增温&减雨并未显著影响表层土壤（0-10cm）各类有机碳基团的相对丰度、碳氮循环相关的酶活性（β-1,4-葡萄糖苷酶，β-1,4-N-乙酰氨基葡萄糖苷酶和亮氨酸氨基肽酶），细菌和真菌多样性及其群落组成。研究结果表明短期的增温和减雨并不能显著影响天然林和人工林土壤微生物群落结构、土壤碳氮循环相关的酶活性，从而不能影响吸收根分解及其碳氮释放。其次，以增温和减雨为主要特征的全球气候变化很可能通过降低人工林低级根分解后期的Alkyl C:O-alkyl C，从而使人工林土壤具有更多的易分解碳输入，降低土壤的腐殖化程度，在一定程度上很可能会加速人工林土壤碳的流失。