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氮添加对混栽杉木-楠木叶性状的影响

Effects of Nitrogen Addition on Leaf Traits of Cunninghamia lanceolata and Phoebe chekiangensis Mixed Plantation

  • 摘要:
    目的 氮沉降是全球性的环境问题,对植物生长有着重要影响。叶经济谱是植物在叶片水平上一系列连续变化的、有规律的权衡策略谱,是目前植物生态领域的一个重要概念。为探讨氮添加对植物幼苗叶片的影响,本研究分析了氮添加条件下单栽杉木幼苗、单栽楠木幼苗和混栽杉木-楠木幼苗的叶性状。
    方法 本试验通过人工氮添加的方法,设置2个施氮水平,分别为0 kg·hm−2·a−1 N(对照)和30 kg·hm−2·a−1 N(氮添加),每个施氮水平又分别包括杉木幼苗,楠木幼苗以及杉木-楠木幼苗(杉木幼苗与楠木幼苗1:1行状混栽)3个处理。该试验分别测定和计算了杉木幼苗和楠木幼苗的株高、地径、冠幅、荧光参数、比叶质量、净光合速率、单位质量最大净光合速率和呼吸速率等8个指标。
    结果 杉木幼苗的呼吸速率和光合能力显著高于楠木幼苗,但比叶质量显著低于楠木幼苗。混栽显著升高了杉木幼苗的呼吸速率和楠木幼苗的光合能力,但显著降低了杉木幼苗和楠木幼苗的比叶质量以及杉木幼苗的净光合速率。这可能是因为混栽导致了两种幼苗之间的种间竞争,两者都把更多的能量分配到了竞争之中,但楠木幼苗的竞争能力比杉木幼苗更强。氮添加显著增加了杉木幼苗的比叶质量和光合能力,也显著增加了楠木幼苗的呼吸速率和光合能力,但显著降低了两种幼苗的比叶质量。另外,施氮显著降低了混栽杉木幼苗的光合能力及楠木幼苗的呼吸速率,也显著降低了两种幼苗的比叶质量。这些结果说明氮添加在一定程度上改变了混栽状态下的杉木幼苗和楠木幼苗的叶性状。在竞争状态下,杉木幼苗和楠木幼苗对氮添加不同的响应可能与自身因素有关,杉木对环境的敏感性强于楠木,试验设计中添加的氮量对楠木幼苗生长产生的影响相对较小,并且可能也与楠木幼苗较强的耐酸性及其较高的与光合相关的酶含量和酶活性有关。
    结论 本研究说明杉木幼苗更靠近叶经济谱回报快的一端,而楠木幼苗更靠近回报慢的一端,单纯的混栽不会改变两者在叶经济谱中的相对位置,但是氮添加使杉木幼苗向叶经济谱回报慢的一端发展,而楠木幼苗向叶经济谱回报快的一端发展。

     

    Abstract:
    Objective To analyze the leaf traits of Chinese fir (Cunninghamia lanceolata) and nanmu (Phoebe chekiangensis) in pure and mixed plantations and to study the effect of nitrogen deposition on leaf economic characters.
    Method In this experiment, two nitrogen application levels were set by artificial nitrogen addition: 0 kg·ha-1yr-1N (contrast) and 30 kg·ha-1yr-1N (nitrogen addition). Every level consisted of three treatments: pure Chinese fir seedlings, pure nanmu seedlings and mixed Chinese fir and nanmu seedlings (1∶1 row mixing of Chinese fir seedlings and nanmu seedlings). During the experiment, eight indicators, including height of plants, diameter, crown width, fluorescence parameters, specific leaf mass, net photosynthetic rate, maximum net photosynthetic rate per unit mass and respiration rate of both Chinese fir seedlings and nanmu seedlings were measured. SPSS was used to analyze the significance of their differences among different treatments.
    Result The results showed that the respiration rate and photosynthetic capacity of pure Chinese fir seedlings were significantly higher than that of pure nanmu seedlings, and the specific leaf weight was significantly lower than that of nanmu seedlings. Mixed planting significantly increased the respiration rate of Chinese fir seedlings and the photosynthetic capacity of nanmu seedlings, but significantly reduced the specific leaf mass of Chinese fir seedlings and nanmu seedlings and the net photosynthetic rate of Chinese fir seedlings. This may be due to the mixing led to interspecific competition between the seedlings of the two species, both of which allocated more energy to competition, but the nanmu seedlings dominated in competition. Nitrogen addition significantly increased the specific leaf mass and photosynthetic capacity of pure Chinese fir seedlings, and also significantly increased the respiration rate and photosynthetic capacity of nanmu seedlings, but significantly decreased the specific leaf mass of two seedlings. In addition, in mixture, nitrogen application significantly reduced the photosynthetic capacity of Chinese fir seedlings and the respiration rate of nanmu seedlings, and the specific leaf quality of two seedlings also decreased significantly. This indicated that the addition of nitrogen changed the leaf economic characters of Chinese fir seedlings and nanmu seedlings under mixed state to some extent. In the condition of competition, the different responses of Chinese fir seedlings and nanmu seedlings to nitrogen adding may be associated with their own factors. Chinese fir is more sensitive to the environment than nanmu. The content of nitrogen addition in this experiment had relatively little effect on the growth of nanmu seedlings. It might also be related to the stronger acid resistance of nanmu seedlings and its higher photosynthetic-related enzymes content and enzymes activity.
    Conclusion Chinese fir seedlings are closer to the fast end of leaf economic spectrum, while nanmu seedlings were closer to the slow end, and the simple mixing will not change the relative position of the two seedlings in leaf economic spectrum. However, nitrogen addition can make Chinese fir seedlings develop towards the slow end of leaf economic spectrum, while nanmu seedlings develop towards the fast end of leaf economic spectrum.

     

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