半寄生植物檀香对其人工群落氮素摄取与归还的研究

Santalum album (sandalwood) is a precious hemiparasite, which partially rely on their host plants to take up nutrients through the haustorium (a outgrowth organ on roots), especially for nitrogenous compounds. The mixed plantation of sandalwood with N2-fixing species (e.g., Acacia confusa and Dalbergia odorifera) is popular in southern China due to their N2-fixation capacity of host plants to provide the sandalwood with abundant nitrogen (N). However, the community-level effects of sandalwood concerning N capture and feedback are often ignored. Under field conditions, the 15N natural abundance technique will be firstly used to monitor N2-fixation capacity of host N2-fixing plants, and the 15N enrichment labelling technique will be then used to track potential interplant N movement and effects of N2-fixation on such N transfers from N2-fixing hosts A. confusa and D. odorifera to its hemiparasite sandalwood, and verse visa. Finally, using the litterbag method 15N-labeled of sandalwood litter will be added to field plots for quantifying the uptake and translocation of N between plant species within a plant community. Our objectives are not only to improve our better understanding of the physiological interactions in resource facilitation between hemiparasite sandalwood and its hosts, but also to provide insights into promising mixed-plantation patterns for the production and restoration of precious tropical tree forests in south China.

檀香为半寄生乔木，主要依靠从寄主植物摄取氮(N)素等养分维持生长。为了满足檀香的N素需求，生产上采用降香黄檀、台湾相思等固氮树种作为檀香的寄主。以往学者大多通过盆栽试验开展檀香寄生体系下养分转移研究，而檀香人工林内林木、草、土壤关系更为复杂，对其研究更能揭示檀香及其寄主间养分转移的真实情况。因此，系统研究檀香人工群落N素摄取与归还规律，有助于揭示檀香在群落中的作用与地位。本项目以10年生檀香-降香黄檀-台湾相思混交林为对象，应用15N自然丰度法结合无N沙培试验，研究林内降香黄檀与台湾相思的固氮效率；运用15N示踪法研究群落内的檀香N素摄取与归还规律，揭示寄主植物的固氮效率对檀香寄生体系N素转移的影响；通过15N示踪檀香凋落物的分解过程，探明该归还途径对群落植物N素利用的影响。本项目为理解半寄生植物养分转移规律提供一个群落尺度上的系统研究案例，并为檀香人工林高效培育与经营管理提供理论依据。

檀香是一种半寄生乔木，其心材含有名贵的芳香精油，近年来已在华南地区广泛种植。但檀香具有半寄生特性，人工栽培需要为其配置适宜的寄主植物，才能保证其正常生长。因此，研究檀香与寄主植物之间的养分传递规律，是檀香人工栽培技术亟需解决的重要科学问题。本项目以10年生檀香人工林为研究对象，揭示了群落内檀香吸盘吸附规律，证实檀香偏好寄生降香黄檀、台湾相思、火炭母等高氮植物；利用13C-15N双标记揭示固氮寄主降香黄檀、台湾相思能持续为檀香提供C、N，并发现林下草本植物亦能从3种标记的木本植物上获得微量的C、N，证实檀香始终是群落内C、N库端植物；采用15N自然丰度法，阐明两固氮寄主传递至檀香的N源中分别有20%和52%来自于固氮作用；运用网袋法开展凋落物分解试验，明确檀香凋落物具有较高的分解速率与养分含量，能迅速为群落归还养分。本项目为探索檀香“以贵养贵”的混交模式，大力发展我国珍贵用材树种产业，化解木材供给市场结构性矛盾，具有重要的战略意义。