University of Pennsylvania, Department of Biology, Philadelphia, Pennsylvania 19104, USA.
Ecology. 2012 Apr;93(4):815-24. doi: 10.1890/11-1003.1.
The semiarid, northern Mongolian steppe, which still supports pastoral nomads who have used the steppe for millennia, has experienced an average 1.7 degrees C temperature rise over the past 40 years. Continuing climate change is likely to affect flowering phenology and flower numbers with potentially important consequences for plant community composition, ecosystem services, and herder livelihoods. Over the growing seasons of 2009 and 2010, we examined flowering responses to climate manipulation using open-top passive warming chambers (OTCs) at two locations on a south-facing slope: one on the moister, cooler lower slope and the other on the drier, warmer upper slope, where a watering treatment was added in a factorial design with warming. Canonical analysis of principal coordinates (CAP) revealed that OTCs reduced flower production and delayed peak flowering in graminoids as a whole but only affected forbs on the upper slope, where peak flowering was also delayed. OTCs affected flowering phenology in seven of eight species, which were examined individually, either by altering the time of peak flowering and/or the onset and/or cessation of flowering, as revealed by survival analysis. In 2010, which was the drier year, OTCs reduced flower production in two grasses but increased production in an annual forb found only on the upper slope. The particular effects of OTCs on phenology, and whether they caused an extension or contraction of the flowering season, differed among species, and often depended on year, or slope, or watering treatment; however, a relatively strong pattern emerged for 2010 when four species showed a contraction of the flowering season in OTCs. Watering increased flower production in two species in 2010, but slope location more often affected flowering phenology than did watering. Our results show the importance of taking landscape-scale variation into account in climate change studies and also contrasted with those of several studies set in cold, but wetter systems, where warming often causes greater or accelerated flower production. In cold, water-limited systems like the Mongolian steppe, warming may reduce flower numbers or the length of the flowering season by adding to water stress more than it relieves cold stress.
半干旱的蒙古北部草原仍然支持着千年来一直使用这片草原的游牧民族，在过去的 40 年中，该地区的平均气温上升了 1.7 摄氏度。持续的气候变化可能会影响开花物候和花的数量，这可能对植物群落组成、生态系统服务和牧民的生计产生重要影响。在 2009 年和 2010 年的生长季节，我们在一个朝南的斜坡上的两个位置使用开顶式被动加热室（OTCs）来检查对气候的开花响应：一个在较潮湿、较凉爽的下部斜坡上，另一个在较干燥、较温暖的上部斜坡上，在那里，我们以一个因子设计添加了浇水处理。主坐标典范分析（CAP）显示，OTCs 整体上减少了禾本科植物的花产量并延迟了它们的开花高峰期，但仅影响了上部斜坡上的草本植物，那里的开花高峰期也被延迟。OTCs 影响了 8 个单独检查的物种中的 7 个的开花物候，这是通过改变开花高峰期的时间以及通过生存分析揭示的开花的开始和停止来实现的。在 2010 年，这是一个较干旱的年份，OTCs 减少了两种禾本科植物的花产量，但增加了仅在上部斜坡上发现的一年生草本植物的产量。OTCs 对物候的特定影响，以及它们是否导致开花季节的延长或缩短，因物种而异，并且通常取决于年份、斜坡或浇水处理；然而，在 2010 年，当四个物种在 OTCs 中显示出开花季节缩短时，出现了一个相对较强的模式。在 2010 年，浇水增加了两个物种的花产量，但与浇水相比，斜坡位置更经常影响开花物候。我们的结果表明，在气候变化研究中考虑景观尺度的变异性很重要，这与在寒冷但较湿润的系统中进行的几项研究形成对比，在这些系统中，变暖通常会导致花产量增加或加速。在像蒙古草原这样寒冷、水分受限的系统中，变暖可能会通过增加水分胁迫而不是缓解寒冷胁迫，从而减少花的数量或开花季节的长度。
