Climate warming by open-top chambers enhances the flowering and fruit development of bog cranberry (Vaccinium oxycoccos L.)

<p>Changes in plant phenology belong to the important consequences of climate change. Earlier start of the bud bursting, leaf development, or root growth are reported for many species, including those growing in northern peatlands. The next generation of plants depends on the production of generative organs; therefore, flower and fruit development are essential stages of ontogenesis, which are strongly regulated by ambient temperature. In this work, we focused on the generative organs&#8217; development of bog cranberry (<em>Vaccinium oxycoccos</em> L.) under climate manipulation. The study was carried out in a nutrient-poor fen located in Western Poland, where two climate manipulation sites with different hydrology and vegetation composition were established in 2017. The site with a more stable water-table depth (WTD) and higher abundance of <em>Carex</em> spp. is named CL, and the site with a more fluctuating WTD and lower abundance of <em>Carex </em>spp. is named CR. Each site consists of three control (C) and six manipulated (M). The climate manipulation was induced by open-top chambers with the addition of 100 W infrared heaters that were switched on during nighttime. This manipulation resulted in an average annual increase of the air temperature 30 cm above ground in the period April-June of the studied year 2022 by 0.44&#176;C at the CL site and 1.07&#176;C at the CR site. The flower and fruit appearance and the flowering dynamics were analyzed from high-resolution images. We observed that flowering in M plots started on average 3.5 days sooner at CL and 14.5 days sooner at the CR site compared to respective Cs. The peak of flowering in warmed plots occurred 7.5 and 14 days earlier for CL and CR sites, respectively. The first fruit developed on average 11 days sooner in M plots of the CL site and 19 days sooner in M plots of the CR site than in respective Cs. In addition to the shifts in phenophases, the flowering dynamic was changed. The slow flower opening at the beginning and the faster opening towards the peak of flowering in C were changed to the fast opening at the beginning and slower towards the peak in M plots.</p><p>Our results show the earlier onset of the generative stages of bog cranberry with the warming climate. Additionally, a comparison of the two vegetation sites suggests that the vegetation community mediates the magnitude of the climate manipulation impact.</p><p><strong>&#160;</strong>The Research was co-founded by the National Science Centre of Poland (NCN) within grants No. 2016/21/B/ST10/02271 and 2020/37/ B/ST10/01213.</p><p>&#160;</p>