Laboratory of Forestry, Ghent University, Geraardsbergsesteenweg 267, Melle-Gontrode, Belgium.
Ann Bot. 2012 Apr;109(5):1037-46. doi: 10.1093/aob/mcs015. Epub 2012 Feb 16.
The response of forest herb regeneration from seed to temperature variations across latitudes was experimentally assessed in order to forecast the likely response of understorey community dynamics to climate warming.
Seeds of two characteristic forest plants (Anemone nemorosa and Milium effusum) were collected in natural populations along a latitudinal gradient from northern France to northern Sweden and exposed to three temperature regimes in growth chambers (first experiment). To test the importance of local adaptation, reciprocal transplants were also made of adult individuals that originated from the same populations in three common gardens located in southern, central and northern sites along the same gradient, and the resulting seeds were germinated (second experiment). Seedling establishment was quantified by measuring the timing and percentage of seedling emergence, and seedling biomass in both experiments.
Spring warming increased emergence rates and seedling growth in the early-flowering forb A. nemorosa. Seedlings of the summer-flowering grass M. effusum originating from northern populations responded more strongly in terms of biomass growth to temperature than southern populations. The above-ground biomass of the seedlings of both species decreased with increasing latitude of origin, irrespective of whether seeds were collected from natural populations or from the common gardens. The emergence percentage decreased with increasing home-away distance in seeds from the transplant experiment, suggesting that the maternal plants were locally adapted.
Decreasing seedling emergence and growth were found from the centre to the northern edge of the distribution range for both species. Stronger responses to temperature variation in seedling growth of the grass M. effusum in the north may offer a way to cope with environmental change. The results further suggest that climate warming might differentially affect seedling establishment of understorey plants across their distribution range and thus alter future understorey plant dynamics.
为了预测气候变化对林下群落动态的可能影响，本研究通过实验评估了森林草本植物种子对不同纬度温度变化的响应，以预测气候变化对林下植物动态的可能影响。
从法国北部到瑞典北部的自然种群中采集了两种典型森林植物（银莲花和小米草）的种子，并在生长室中暴露于三种温度条件下（第一个实验）。为了检验本地适应的重要性，还进行了来自同一种群的成年个体的反向移植实验，将其移植到位于相同纬度的南部、中部和北部的三个普通花园中，并对产生的种子进行发芽实验（第二个实验）。通过测量种子的萌发时间和比例以及幼苗的生物量，对幼苗的建立进行了量化。
春季变暖增加了早花植物银莲花的萌发率和幼苗生长速度。来自北部种群的夏季开花草小米草的种子在生物量生长方面对温度的反应比南部种群更强烈。来自不同种群的种子在生长室中都表现出幼苗生物量随着起源纬度的增加而减少，而不管种子是来自自然种群还是普通花园。来自移植实验的种子的萌发比例随着离家距离的增加而降低，这表明母株具有本地适应性。
本研究发现，两种植物的幼苗萌发和生长都随着分布范围的中心向北部边缘减少。北部小米草幼苗对温度变化的更强反应可能为适应环境变化提供了一种途径。研究结果进一步表明，气候变化可能会对林下植物在其分布范围内的幼苗建立产生不同的影响，从而改变未来林下植物的动态。
