Data from: Air humidity thresholds trigger active moss spore release to extend dispersal in space and time

1. Understanding the complete dispersal process is important for making realistic predictions of species distributions, but mechanisms for diaspore release in wind-dispersed species are often unknown. However, diaspore release under conditions that increase the probability of longer dispersal distances and mechanisms that extend dispersal events in time may have evolutionary advantages. 2. We quantified air humidity thresholds regulating spore release in the moss Brachythecium rutabulum. We also investigated the prevailing micrometeorological conditions when these thresholds occur in nature and how they affect dispersal distances up to 100 m, using a mechanistic dispersal model. 3. We show that moss spores were mainly released when the peristome teeth were opening, as relative air humidity (RH) decreased from high values to relatively low (mainly between 90% and 75% RH). This most often occurred in the morning, when wind speeds were relatively low. Surprisingly, the model predicted that an equally high proportion of the spores would travel distances beyond 100 m (horizontally) when released in the wind conditions prevailing during events of RH decrease in the morning, that lead to peristome opening, as in the highest wind speeds. Moreover, a higher proportion of the spores reached high altitudes when released at the lower wind speeds during the morning compared to the higher speeds later in the day, indicating a possibility for extended dispersal distances when released in the morning. Dispersal in the morning is enhanced by a combination of a more unstable atmospheric surface layer, that promotes vertical dispersal, and a lower wind speed that decreases the spore deposition probability onto the ground, compared to later in the day. 4. Our study demonstrates an active spore release mechanism in response to diurnally changing air humidity. The mechanism may promote longer dispersal distances, because of enhanced vertical dispersal and because spores being released in the morning have more time to travel before the wind calms down at night. The mechanism also leads to a prolonged dispersal period over the season, which may be viewed as a risk spreading in time that ultimately also leads to a higher diversity of establishment conditions, dispersal distances and directions.1. 完整理解传播过程对精准预测物种分布格局至关重要，但风媒传播物种的传播体释放机制仍鲜为人知。然而，在更易实现长距离传播的条件下触发传播体释放，以及能够延长传播时间窗口的机制，或许具有进化优势。 2. 本研究以藓类植物粗枝青藓（Brachythecium rutabulum）为研究对象，量化了调控其孢子释放的空气湿度阈值；同时借助机制性扩散模型，探究了自然环境中该阈值出现时的主流微气象条件，及其对100米范围内传播距离的影响。 3. 研究结果显示，藓类孢子主要在蒴齿张开时释放：当相对空气湿度（Relative Air Humidity, RH）从高值降至相对低值（主要介于90%~75% RH区间）时，蒴齿便会开启，这一过程多发生在风速较低的清晨。令人意外的是，模型预测：若在清晨相对湿度下降、蒴齿开启的气象条件下释放孢子，尽管此时风速较低，但能达到100米以上水平传播距离的孢子占比，与高风速条件下释放的孢子占比相当。此外，相较于当日晚些时候的高风速环境，清晨低风速条件下释放的孢子能够抵达更高海拔的比例更高，这表明清晨释放的孢子或可实现更长距离的传播。与当日晚些时候相比，清晨时段的近地面大气层更不稳定，能够促进垂直传播，且风速更低会降低孢子沉降至地面的概率，二者共同作用提升了清晨时段的扩散效率。 4. 本研究证实了藓类孢子存在一种响应日间空气湿度变化的主动释放机制。该机制可通过两种途径促进长距离传播：一是增强垂直传播能力，二是清晨释放的孢子在夜间风速减弱前拥有更长的传播时长。此外，该机制还能延长整个生长季的传播窗口，这可被视为一种时间维度上的风险分摊策略，最终能够提升物种定植条件、传播距离与传播方向的多样性。