Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China.
Glob Chang Biol. 2014 Jul;20(7):2230-9. doi: 10.1111/gcb.12501. Epub 2014 May 2.
Carbon dioxide (CO2 ) enhancement (eCO2 ) and N addition (aN) have been shown to increase net primary production (NPP) and to affect water-use efficiency (WUE) for many temperate ecosystems, but few studies have been made on subtropical tree species. This study compared the responses of NPP and WUE from a mesocosm composing five subtropical tree species to eCO2 (700 ppm), aN (10 g N m(-2) yr(-1) ) and eCO2 × aN using open-top chambers. Our results showed that mean annual ecosystem NPP did not changed significantly under eCO2 , increased by 56% under aN and 64% under eCO2 × aN. Ecosystem WUE increased by 14%, 55%, and 61% under eCO2 , aN and eCO2 × aN, respectively. We found that the observed responses of ecosystem WUE were largely driven by the responses of ecosystem NPP. Statistical analysis showed that there was no significant interactions between eCO2 and aN on ecosystem NPP (P = 0.731) or WUE (P = 0.442). Our results showed that increasing N deposition was likely to have much stronger effects on ecosystem NPP and WUE than increasing CO2 concentration for the subtropical forests. However, different tree species responded quite differently. aN significantly increased annual NPP of the fast-growing species (Schima superba). Nitrogen-fixing species (Ormosia pinnata) grew significantly faster only under eCO2 × aN. eCO2 had no effects on annual NPP of those two species but significantly increased annual NPP of other two species (Castanopsis hystrix and Acmena acuminatissima). Differential responses of the NPP among different tree species to eCO2 and aN will likely have significant implications on the species composition of subtropical forests under future global change.
二氧化碳（CO2）增强（eCO2）和氮添加（aN）已被证明会增加许多温带生态系统的净初级生产力（NPP），并影响水分利用效率（WUE），但对亚热带树种的研究较少。本研究利用开顶式气室比较了由五种亚热带树种组成的中尺度群落对 eCO2（700 ppm）、aN（10 g N m-2 yr-1）和 eCO2×aN 的 NPP 和 WUE 的响应。我们的结果表明，在 eCO2 条件下，年平均生态系统 NPP 没有显著变化，在 aN 条件下增加了 56%，在 eCO2×aN 条件下增加了 64%。生态系统 WUE 在 eCO2、aN 和 eCO2×aN 条件下分别增加了 14%、55%和 61%。我们发现，生态系统 WUE 的观测响应主要是由生态系统 NPP 的响应驱动的。统计分析表明，在生态系统 NPP（P = 0.731）或 WUE（P = 0.442）方面，eCO2 和 aN 之间没有显著的相互作用。我们的结果表明，与增加 CO2 浓度相比，增加氮沉降可能对亚热带森林的生态系统 NPP 和 WUE 产生更大的影响。然而，不同的树种反应非常不同。aN 显著增加了速生树种（荷木）的年 NPP。固氮树种（红豆树）仅在 eCO2×aN 条件下生长速度显著加快。eCO2 对这两个树种的年 NPP 没有影响，但显著增加了另外两个树种（厚壳桂和尖叶杜英）的年 NPP。不同树种对 eCO2 和 aN 的 NPP 响应的差异可能对未来全球变化下亚热带森林的物种组成产生重大影响。
