School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
Tree Physiol. 2012 Apr;32(4):389-400. doi: 10.1093/treephys/tps027. Epub 2012 Apr 5.
Urbanization is accelerating across the globe, elevating the importance of studying urban ecology. Urban environments exhibit several factors affecting plant growth and function, including high temperatures (particularly at night), CO(2) concentrations and atmospheric nitrogen deposition. We investigated the effects of urban environments on growth in Quercus rubra L. seedlings. We grew seedlings from acorns for one season at four sites along an urban-rural transect from Central Park in New York City to the Catskill Mountains in upstate New York (difference in average maximum temperatures of 2.4 °C; difference in minimum temperatures of 4.6 °C). In addition, we grew Q. rubra seedlings in growth cabinets (GCs) mimicking the seasonal differential between the city and rural sites (based on a 5-year average). In the field experiment, we found an eightfold increase in biomass in urban-grown seedlings relative to those grown at rural sites. This difference was primarily related to changes in growth allocation. Urban-grown seedlings and seedlings grown at urban temperatures in the GCs exhibited a lower root: shoot ratio (urban ~0.8, rural/remote ~1.5), reducing below-ground carbon costs associated with construction and maintenance. These urban seedlings instead allocated more growth to leaves than did rural-grown seedlings, resulting in 10-fold greater photosynthetic area but no difference in photosynthetic capacity of foliage per unit area. Seedlings grown at urban temperatures in both the field and GC experiments had higher leaf nitrogen concentrations per unit area than those grown at cooler temperatures (increases of 23% in field, 32% in GC). Lastly, we measured threefold greater (13)C enrichment of respired CO(2) (relative to substrate) in urban-grown leaves than at other sites, which may suggest greater allocation of respiratory function to growth over maintenance. It also shows that lack of differences in total R flux in response to environmental conditions may mask dramatic shifts in respiratory functioning. Overall, our findings indicating greater seedling growth and establishment at a critical regeneration phase of forest development may have important implications for the ecology of urban forests as well as the predicted growth of the terrestrial biosphere in temperate regions in response to climate change.
城市化在全球范围内加速，这使得研究城市生态学变得尤为重要。城市环境存在多种影响植物生长和功能的因素，包括高温（尤其是夜间）、二氧化碳浓度和大气氮沉降。我们研究了城市环境对红栎幼苗生长的影响。我们从橡子中培育了一个季节的幼苗，在纽约市中央公园到纽约州北部卡茨基尔山脉的城乡梯度的四个地点种植（平均最高温度差异为 2.4°C；最低温度差异为 4.6°C）。此外，我们在生长箱（GC）中种植了红栎幼苗，模拟城市和农村站点之间的季节性差异（基于 5 年的平均值）。在田间实验中，我们发现城市生长的幼苗的生物量比农村生长的幼苗增加了 8 倍。这种差异主要与生长分配的变化有关。城市生长的幼苗和在 GC 中以城市温度生长的幼苗的根：茎比例较低（城市约为 0.8，农村/偏远约为 1.5），降低了与构建和维护相关的地下碳成本。这些城市幼苗与农村生长的幼苗相比，将更多的生长分配给了叶子，从而使叶片的光合面积增加了 10 倍，但单位面积叶片的光合能力没有差异。在田间和 GC 实验中，在城市温度下生长的幼苗单位面积的叶片氮浓度高于在较凉爽温度下生长的幼苗（田间增加 23%，GC 增加 32%）。最后，我们测量到城市生长的叶片呼吸 CO2（相对于基质）的（13）C 富集程度是其他地点的三倍，这可能表明呼吸功能向生长的分配大于维持。这也表明，对环境条件的总 R 通量没有差异可能掩盖了呼吸功能的巨大变化。总的来说，我们的研究结果表明，在森林发育的关键再生阶段，幼苗的生长和建立更为旺盛，这可能对城市森林的生态学以及预测在气候变化下温带地区陆地生物群落在响应环境条件时发生的剧烈变化具有重要意义。
