施氮及不同根系分隔模式对尾叶桉和降香黄檀幼苗生长及叶片生理特性的影响

豆科与非豆科树种混交作为一种人工林培育可持续发展模式,在保证木材产量和维持氮素平衡中发挥了重要作用。该研究通过大棚盆栽试验,设计3个施氮水平(0、3、6g·株-1)及3种根系分隔方式(不隔、网隔、膜隔),分析了不同氮素水平及根系分隔模式对尾叶桉(Eucalyptus urophylla)与降香黄檀(Dalbergia odorifera)植株幼苗生长、叶片生理特性、根系形态及生物量的影响。结果表明:(1)随施氮量的增加,尾叶桉与降香黄檀的苗高、地径均呈递增趋势;不同根系分隔模式下,尾叶桉苗高、地径均在不隔模式下生长最好,降香黄檀则在膜隔模式下生长最好。(2)与不施氮处理相比,施氮3、6g·株-1水平下尾叶桉与降香黄檀叶片的超氧化物歧化酶(SOD)活性、过氧化物酶(POD)活性及可溶性蛋白含量均显著升高,而丙二醛(MDA)含量则呈降低趋势。(3)尾叶桉与降香黄檀根系的总长度、总表面积、总体积、平均直径、根尖数和比根长均随氮素水平的增加而增加,且各氮素水平间的差异显著;同一氮素水平下,尾叶桉的根系生长总体表现为不隔网隔膜隔,而降香黄檀根系生长则表现为膜隔不隔网隔,且两树种不同分隔模式间差异显著。(4)尾叶桉与降香黄檀各器官生物量及总生物量均随施氮量的增加而增加,并在6g·株-1施氮水平下生物量最大;各器官生物量分配中,尾叶桉各器官生物量所占比例大小依次为:茎(40.59%)叶(32.37%)根(27.04%),降香黄檀各器官生物量所占比例大小依次为:根(47.67%)茎(40.08%)叶(12.25%)。研究表明,尾叶桉与降香黄檀混交一定程度上扩展了根系横向和纵向水平的养分生态位,扩大了根系吸收土壤养分的空间,同时根系互作提高了降香黄檀的固氮能力,对土壤有效氮的产生有较大影响。

Effect of Nitrogen Application on the Growth and Leaf Physiological Traits of Eucalyptus urophylla and Dalbergia odorifera Seedlings under Different Root Partitioning Patterns

Leguminous and non legume tree mixed system, as a sustainable development model for artificial forest cultivation, which plays an important role in ensuring timber yield and maintaining nitrogen balance. A pot experiment in greenhouse was conducted to investigate effects of different N fertilizer and root barriers on the seedling growth, leaf physiological, root morphology and biomass of E. urophylla and D. odorifera intercropping system. The experimental designs included three nitrogen fertilization levels of 0, 3 and 6·g N per tree and three root barrier patterns including no barrier, nylon barrier and plastic barrier. The results showed as follows: (1) seedling height and ground diameter of E. urophylla and D. odorifera presented an increasing trend with the increase of nitrogen application. Under different root barrier patterns, the seedling height of E. urophylla and ground diameter were the best without barrier, while D. odorifera grew much better under the model of the plastic barrier. (2) When compared to the non N treatment, the content of leaf superoxide dismutase (SOD) activity, peroxidase (POD) activity and soluble protein content for each species relatively increased, but the content of malonaldehyde (MDA) declined. (3) The total root length, total root surface area, total root volume, mean diameter, root tip and specific root length of E. urophylla and D. odorifera increased by applying nitrogenous fertilizers, and differed from each other significantly. Under the same nitrogen level, the root growth of E. urophylla was no barrier > nylon barrier > plastic barrier, while root growth of D. odorifera exhibited plastic barrier > no barrier > nylon barrier, and under different root barrier patterns the growth between both species was significant different. (4) The level of nitrogen, was resposible to the biomass of various organs and total biomass of E. urophylla and D. odorifera. and reached its maximum when the nitrogen level was 6 g N per plant. Among the biomass allocation of various organs, the proportion of biomass of each organ for E. urophylla was stem (40.59%) > leaf (32.37%) > root (27.04%), for D. odorifera was root (47.67%) > stem (40.08%) > leaf (12.25%). These results showed that E. urophylla and D. odorifera mixed system expanded the root horizontal and longitudinal level of nutrient ecological niche, and enlarged the space for root absorption of soil nutrients. At the same time, the root interaction enhanced the nitrogen fixation ability of D. odorifera, and it had a great impact on the production of soil available nitrogen.