1 Introduction
The timing and duration of plant flowering affect plant survival, reproduction and community assembly dynamics (Collins et al., 2021; Forrest et al., 2010). Our planet is currently experiencing abrupt environmental changes, including rising air temperatures and increased atmospheric nitrogen (N) deposition (IPCC, 2023). Numerous studies have demonstrated that warming leads to earlier flowering across the Northern Hemisphere (Piao et al., 2019; Shen et al., 2018; Wolkovich et al., 2012). To understand how these changes in plant phenology will affect the structure of ecosystems, it is crucial to understand the relative responses of different plant types to climate change (Collins et al., 2021; Piao et al., 2019; Post et al., 2008).
The effects of N deposition on flowering phenology are complex and can differ among species, plant functional groups and ecosystems (Zhou et al., 2023; Xia et al., 2015). For instance, in a semiarid, alpine meadow ecosystem on the central Tibetan Plateau, N addition resulted in delayed flowering of grasses, but slightly advanced flowering of forbs (Dorji et al., 2013). The responses of plant flowering phenology to both warming and N deposition are likely regulated by soil resource availability and plant resource acquisition, which are closely tied to plant traits, particularly in arid and semi-arid regions (Nord et al., 2009; Xia & Wan, 2013). The efficiency of nutrient and water absorption by plants can also impact their phenology (Dorji et al., 2013; Post et al., 2008).
Plant phenology affects plant growth and its temporal dynamics (Cleland et al., 2007). It, however, is less clear to what extent plant phenology influences community assembly and competition dynamics (Stone et al., 1998; Menzel, 2002; Piao et al., 2019). Differences in flowering times can affect plant density, thereby reducing pollinator competition or interspecific pollen transfer in symbiotic species (Wolf et al., 2017). Variation in phenological responsiveness can thus have a significant influence on population competition dynamics (Alexander & Levine, 2019; Wolkovich et al., 2012). Early-flowering plants may possess certain advantages over other competitors within the population, thus enabling them to adjust their strategies and adapt to a warming world (Fu et al., 2015). Conversely, plants that fail to keep pace with climate change may face disadvantages, but may also benefit if highly responsive species more frequently encounter climate risks, such as increased late frost damage (Cleland et al., 2012). However, we lack empirical evidence linking dryland plant phenology with community composition under field conditions.
Here, we present findings from a long-term (17-year) field manipulation experiment conducted in a temperate desert steppe in northern China. Our study region was located in the interior of the Asian continent, where particularly high rates of climate change have been observed (Zhang et al., 2011). We examined the responses of plant phenology to climate warming and N deposition, and tested the potential implications of these phenological changes on species composition. Our experiment aimed to address two research questions. Firstly, we investigated the differential effects of climate warming and nitrogen deposition on plant flowering phenology in a desert steppe. Secondly, we explored how the differences in plant phenological responses to changes in temperature and nitrogen availability contribute to shifts in plant community composition, specifically the relative abundance of C3and C4 plants in a community. By addressing these questions, our study provides unique insights into the dynamics of plant phenology and community composition in response to global change in the temperate desert steppe ecosystem.