模拟氮沉降对入侵植物薇甘菊光合特性的影响

该文将探讨氮沉降对外来植物薇甘菊（Mikania micrantha）光合特性的影响。在广州东北郊薇甘菊生长的木荷（Schima superba）人工幼林地进行模拟氮沉降处理，以NH4NO3作为氮源，设置3个氮沉降水平，分别为N0（N：0 g·m-2·a-1）、N5（N：5 g·m-2·a-1）以及N10（N：10 g·m-2·a-1）。在模拟氮沉降的26个月后，采用LI-6400便携式光合仪对不同氮沉降处理下薇甘菊（Mikania micrantha）光合特性进行了测定，分析了不同氮沉降处理之间薇甘菊光合生理指标的差异。结果表明：在试验时间内，不同氮沉降处理之间的薇甘菊净光合速率（Pn）、气孔导度（Gs）、蒸腾速率（Tr）和水分利用效率（WUE）日均值的差异不显著（p〉0.05），但这些光合生理指标的大小均表现为N10？N5？N0，氮沉降一定程度提高了薇甘菊的光合作用，可能加速薇甘菊的生物入侵。光合有效辐射（PAR）是影响薇甘菊净光合速率（Pn）的主导因子，其次为叶片温度（Tl）和大气温度（Ta），它们均与Pn呈极显著正相关（p〈0.01），而与空气相对湿度（RH）呈不显著的负相关（p？0.05）。氮处理对薇甘菊最大净光合速率（P′max）、表观量子效率（a）、暗呼吸速率（Rd）、光饱和点（LSP）和光补偿点（LCP）的影响不明显（p？0.05）。P′max、a、LSP和LCP分别介于21.21~22.07、0.058~0.059、1546.0~1653.3和8.0~9.3μmol·m-2·s-1之间，在氮沉降下薇甘菊表现出高光合潜力及强阳性植物的特征。该文可为研究氮沉降下薇甘菊入侵林地的机制提供有价值的参考。

Effects of simulated nitrogen deposition on photosynthetic characteristics of the invasive plant Mikania micrantha

In order to evaluate the effects of nitrogen deposition on the invasiveness of Mikania micrantha, the authors examined the effects of simulated nitrogen deposition （N0 treatment, N： 0 g·m-2·a-1. N5 treatment, N： 5 g·m-2·a-1. And N10 treatment, N： 10 g·m-2·a-1） which had been conducted for 26 months on photosynthetic characteristics of Mikania micrantha using the LI-6400 gas exchange and fluorescence system in young Schima superb plantation with Mikania micrantha in Zengcheng, Guangdong province,＆amp;nbsp;China. The results showed that the daily average of either the net photosynthetic rate （Pn）, stomatal conductance （Gs）, transpiration rate （Tr）, or the water use efficiency （WUE） for Mikania micrantha among the three levels of simulated N deposition treatments was not significant （p？0.05）, although N10？N5？N0 for each of these photosynthetic characteristics. But the nitrogen deposition improved the photosynthesis of Mikania micrantha. The photosynthetic active radiation （PAR） was a dominant factor influencing Pn and it was followed by the leaf temperature （Tl） and atmospheric temperature （Ta）, and they each were significantly positively correlated with net photosynthetic rate （Pn） （p＆lt;0.01）. The air relative humidity had no significant negative correlation with Pn （p？0.05）. The responses of the maximum net photosynthetic rate （P′max）, apparent quantum efficiency （a）, dark respiration rate （Rd）, light saturation point （LSP） and the light compensation point （LCP）for Mikania micrantha to the simulated nitrogen deposition treatments were not significant （p？0.05）. P′max, a, LSP and LCP of Mikania micrantha ranged from 21.21 to 22.07 t·hm-2, 0.058 to 0.059 μmol·m-2·s-1, 1 546.0 to 1 653.3 μmol·m-2·s-1 and 8.0 to 9.3 μmol·m-2·s-1, respectively, and thus the species showed high photosynthetic potential and strong positive plants under nitrogen deposition. The study aimed to understand the physiological and ecological characteristics of Mikania micrantha, and provide valuable reference to explore the mechanism of invasion in young plantation. Mikania micrantha could be further investigated in light of increasing nitrogen deposition.