Soil seedbank analysis under experimental drought and delayed monsoon treatments in blue grama and black grama grassland at Sevilleta

This study investigated the question, "Does climate change affect vegetation and seed bank composition in desert grasslands?" The work was done in the Sevilleta National Wildlife Refuge, New Mexico, USA, in in the Extreme Drought in Grassland Experiment (EDGE). Vegetation and seed bank species composition were recorded in black grama (Bouteloua eriopoda) and blue grama (B. gracilis) grasslands at Sevilleta. At each site, two rainfall manipulations and ambient controls were established in 2013 (n=10). Treatments included extreme drought (-66% rainfall reduction) and delayed monsoon (precipitation captured during July-August and reapplied during September-October). Aboveground species composition was assessed and composite soil samples were collected in 2017, five years after the experiment started. Seed bank composition was evaluated using the seedling emergence method. Rainfall treatments increased aboveground species richness at both sites, and seed bank richness only in the blue grama community. Vegetation cover was reduced by both rainfall manipulations, but seed bank density increased or remained the same compared with controls. In aboveground vegetation, cover of annual and perennial forbs increased, and dominant perennial grasses decreased. In the soil seed bank, species composition was similar among all treatments and was dominated by annual and perennial forbs. The seed bank was more resistant to drought than aboveground vegetation. Because seed banks enhance long-term community stability, their drought resistance plays an important role in maintaining ecosystem processes during and following drought in these grassland communities.

本研究针对“气候变化是否会影响荒漠草原的植被与种子库组成”这一科学问题展开探究。本研究于美国新墨西哥州塞维莱塔国家野生动物保护区（Sevilleta National Wildlife Refuge）的草原极端干旱实验（Extreme Drought in Grassland Experiment, EDGE）站点开展。研究选取该保护区内的黑格兰马草（Bouteloua eriopoda）与蓝格兰马草（B. gracilis）草原样地，对其植被与种子库物种组成进行记录。2013年，于每个样地设置两种降雨调控处理与自然降雨对照组（n=10），处理方式分别为极端干旱（降雨量减少66%）与季风延迟处理（将7-8月的降雨截留，于9-10月重新施加）。实验开展5年后的2017年，对地上植被物种组成进行调查，并采集混合土壤样本。种子库组成采用幼苗萌发法（seedling emergence method）进行评估。降雨调控处理提升了两个样地的地上物种丰富度，仅在蓝格兰马草群落中提升了种子库物种丰富度。两种降雨调控措施均降低了植被盖度，但相较于对照组，种子库密度有所提升或保持不变。在地上植被中，一年生与多年生非禾本草本植物的盖度上升，而优势多年生禾草的盖度下降。在土壤种子库中，不同处理间的物种组成相似，且均以一年生与多年生非禾本草本植物为优势类群。相较于地上植被，土壤种子库对干旱胁迫具有更强的抗性。由于种子库能够提升群落的长期稳定性，其干旱抗性在这类草原群落的干旱期间及干旱过后的生态系统过程维持中发挥着重要作用。