Early snowmelt by an extreme warm event affects understory more than overstory trees in Japanese temperate forests

We conducted a warming experiment (four 20 m by 20 m plots) in temperate forests of Japan to determine the effects of earlier snowmelt on both understory dwarf bamboo plants and overstory birch trees. Our experimental treatment advanced snowmelt by about 10 days and increased soil temperatures that were associated with increased rates of soil nitrogen (N) mineralization and nitrification. Furthermore, these changes led to lower C:N ratios of leaves together with the greater growth of understory bamboo vegetation, with no changes in leaf C:N or growth rates of overstory birch trees. Together, our results demonstrate that advancing snowmelt by an extreme warm event in temperate forests is likely to affect N cycling and will benefit understory vegetation without a commensurate change in overstory vegetation, likely due to the increase in available soil N. This is the dataset of plant growth, soil N properties, and plamnt leaf traits obtained by the field snowmelt manipulation experiment.本研究在日本温带森林中开展了增温实验（设置4块20 m×20 m的样地），旨在探究融雪提前对林下矮生竹类植物以及上层白桦林的影响。本实验通过调控使融雪提前约10天，并提升了土壤温度，该变化与土壤氮（N）矿化速率及硝化速率的提升密切相关。此外，上述变化使得林下竹类植被的叶片碳氮比（C:N）降低，同时其生长量显著提升；而上层白桦林的叶片碳氮比与生长速率均未发生改变。综合来看，本研究结果表明，温带森林中极端暖事件引发的融雪提前，可能会影响土壤氮循环，并使林下植被获益，而上层植被则未出现相应变化，这一现象大概率源于有效态土壤氮的增加。本数据集即为本野外融雪调控实验所获取的植物生长、土壤氮素属性以及植物叶片性状相关数据。