Global warming accelerates shrub expansion in high-latitude and high-elevation ecosystems. Over the last several decades, alpine dwarf-pine Pinus pumila has expanded its range in northern Japan because of enhanced shoot growth under warm climatic conditions. In alpine regions, local environmental conditions and the length of the growing season, vary depending on the topography, elevation, and snowmelt time. This leads to spatially varying shoot performances that are co-affected by climatic change. We applied a warming, shading, and defoliation treatment to assess how temperature and carbon relations in interaction with habitat type (elevation and snowmelt time) affect shoot growth and photochemical efficiency of needles in this species. Photochemical efficiency (Fv/Fm) was maximized during peak growth in the middle of growing season (mid-July–mid-August), and it increased in the shading and warming treatments especially in the early and late season. Shoot growth increased only in the warming treatment, and was not affected by shading and defoliation. These results indicate that shoot growth of alpine dwarf-pine is limited by low temperature, but not by carbon assimilation, i.e., growth is sink- rather than source-limited. Furthermore, the seasonal trend of photochemical efficiency shifted to the late season at higher elevations, and the recovery time of photochemical efficiency took longer in the late-snowmelt habitat, where the growing season was short. Therefore, warmer summers and longer snow-free periods are likely to enhance the growth and areal expansion of alpine dwarf-pine at the expense of the adjacent, species-rich, low-stature alpine plant communities.

中文翻译：

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日本高山矮松Pumila的光化学效率和枝条生长对实验性变暖，遮光和脱叶的响应

全球变暖加速了高纬度和高海拔生态系统中灌木的扩张。在过去的几十年中，由于在温暖的气候条件下增加了枝条的生长，高山矮松松树松在日本北部的范围有所扩大。在高山地区，当地的环境条件和生长期的长短取决于地形，海拔和融雪时间。这导致了受气候变化共同影响的拍摄表现在空间上的变化。我们进行了加温，遮光和脱叶处理，以评估温度和碳素关系与栖息地类型（海拔和融雪时间）的相互作用如何影响该物种的新梢生长和针的光化学效率。光化学效率（Fv / Fm）在生长季节中期（7月中旬至8月中旬）达到峰值增长时达到最大值，而在遮光和暖化处理中（尤其是在季节的早期和晚期）则有所增加。芽的生长仅在加温处理中增加，而不受阴影和脱叶的影响。这些结果表明，高山矮松的枝条生长受到低温的限制，但不受碳同化的限制，即生长受汇的限制而不是受源的限制。此外，在高海拔地区，光化学效率的季节性趋势已转移到后期，而在融雪后期，生长季节较短的栖息地，光化学效率的恢复时间则更长。因此，