Abstract:
Understanding the factors that regulate the functioning of our ecosystems in response to environmental changes can help to maintain the stable provisioning of ecosystem services to mankind. This is especially relevant given the increased variability of environmental conditions due to human activities. In particular, maintaining a stable production and plant biomass during the growing season (intra-annual stability) despite pervasive and directional changes in temperature and precipitation through time can help to secure food supply to wild animals, livestock, and humans. Here, we conducted a 29-year field observational study in a temperate grassland to explore how the intra-annual stability of primary productivity is influenced by biotic and abiotic variables through time. In particular, we analyzed the relationship of community biomass intra-annual stability with plant diversity and seasonal distribution patterns of temperature and precipitation. We found that lower accumulated precipitation between June and September during the 29-year investigated contributed to lower intra-annual community stability because of a decrease in compensatory mechanisms among species (species asynchrony). Additionally, higher precipitation in July contributed to higher intra-annual stability because higher species richness with higher precipitation led to higher average intra-annual stability of all species in the community (species stability). In contrast, we found no evidence that temperature influenced community intra-annual stability. Our results indicates that ongoing reduced seasonal precipitation leading to reduced intra-annual stability in the temperate grassland, which has important theoretical significance for us to take active measures to deal with climate change.
KEYWORDS: long-term observation, seasonal temperature and precipitation, species richness, plant functional group intra-annual stability, dominant species intra-annual stability
INTRODUCTION
Stability is one of the most fundamental and studied properties of an ecosystem (Hautier et al., 2014; Xu et al., 2015; Ma et al., 2017). In particular, the stability of ecosystem primary productivity through time gives us information about the ability of an ecosystem to provide reliable biomass despite environmental fluctuations (Pimm, 1984; Jiang et al., 2009; Craven et al., 2018). Grasslands are one of the most widely distributed ecosystems worldwide (Häyhä et al., 2014), providing not only key habitat for biodiversity but also other important ecosystem functions and services to humanity (Toombs et al. 2010; Isbell et al. 2009). Understanding the processes that influence the stability of grasslands’ productivity is a pressing issue in ecology, especially given its vulnerability to anthropogenic and climatic changes (Ives and Carpenter, 2007).
Profound climate changes such as global warming and changes in precipitation patterns (Min et al., 2011; Orlowsky et al., 2012; IPCC, 2013; Putnam et al., 2017) are affecting the diversity and functioning of grassland ecosystems (Kardol et al., 2010). These changes in temperature and precipitation might be notably stronger at the seasonal rather than annual scale (Donat et al., 2016; Zhang et al., 2018), suggesting that the seasonal distribution patterns of temperature and precipitation may be the main driver of grassland stability. However, previous studies have primarily focused on the stability of primary productivity measured at one time during the growing season (usually at peak biomass production) each year over multiple years (inter-annual stability). Hence, whether the seasonal distribution patterns of temperature and precipitation affect the stability of productivity during the growing season (intra-annual stability) remains unknown. This is important given that intra-annual stability governs secure food supply to wild animals, livestock, and humans.
Previous studies in grasslands have shown that decreased precipitation in the early growing season results in a decline in aboveground net primary productivity (ANPP) by delaying plant phenology and limiting leaf expansion as well as reducing tillering, root range and microbial biomass carbon (De et al., 2012; Craine et al., 2012; Robinson et al., 2013; Yang et al., 2016; Chen et al., 2020). Additionally, different plant functional groups may respond differently to seasonal variability of temperature and precipitation based on differences in their physiology and life history (Huenneke et al., 2002; Munson et al., 2014; Mulhouse et al., 2017). For example, change in timing of maximum precipitation from summer to spring slightly favored C3 plants over C4 due to differences in C3 and C4 plant phenology in Colorado shortgrass prairie (Epstein et al., 1999). Algorithmic analysis based on seasonal water availability showed that the relative biomass of C3/C4 grasses is determined by the allocation of effective water and temperature between C3grasses and C4 grasses during the growing season (Winslow et al., 2003). Decreased precipitation in the early growing season mainly results in decreased ANPP of grass, whereas decreased precipitation in the late growing season primarily results in decreased ANPP of perennial forbs (Zhang et al., 2020). A study of semi-arid grassland in Inner Mongolia, China found that heavy rainfall in the late growing season reduced below-ground productivity and total biomass, while heavy rainfall in the middle of the growing season increased CO2 exchanges (Li et al., 2019). These changes in productivity through time may translate into lower stability of productivity in response to climate change. However, to our knowledge, our study is the first to investigate whether the seasonal variability of precipitation and temperature affects grassland ecosystem community intra-annual stability (Grime et al., 2008).
Previous studies suggests that climate change affects community stability through multiple mechanisms (Ma et al., 2017; Huang et al., 2020). First, a higher number of plant species usually results in a higher stability of biomass production (Tilman et al. 2006, Hector et al. 2010). Thus, a reduction in plant diversity in response to climate change may result in the reduction of stability (Campbell et al., 2011; Hautier et al., 2014; Zhang et al., 2018). Second, community stability may be driven primarily by the stability of dominant species and/or functional groups, especially when dominant species and/or functional groups account for a considerable proportion of community biomass (Hillebrand et al., 2008; Huang et al., 2020; Ma et al., 2021). Third, asynchronous dynamics among species may contribute largely to stabilizing community properties against environmental changes (Loreau and de Mazancourt 2013; Valencia et al. 2020). Species asynchrony usually increases with increasing species richness (Hector et al. 2010, Hautier et al. 2014). As a result, changes in temperature and precipitation may affect community stability by changing asynchronous dynamics among species which directly or indirectly are induced via changes in species richness (Hallett et al., 2014; Sasaki et al., 2019, Hautier et al. 2020). To summarize, seasonal variations of temperature and precipitation may affect community stability by changing species richness (Klein et al., 2004; Wilby et al., 2004; Arnone et al., 2011), dominant species stability (Xu et al., 2015), functional group stability (Huang et al., 2020) and/or species asynchrony (Zhang et al., 2018; Zhou et al., 2019).
Here, we collected long-term monthly data on community ANPP, community composition, species richness and climate of a temperate grassland from 1981–2011 in northern China. The temperate grassland is distributed extensively throughout the arid-semiarid regions of Eurasia. Long-term monitoring can reveal the long-term dynamic of plant communities in response to climate change, and the relationship between community stability with long-term climate change (Bai et al., 2004; Li et al., 2015; Zhou et al., 2019). We related community intra-annual stability of ANPP with changes in seasonal distribution patterns of temperature and precipitation as well as with plant diversity and community composition. Specifically, we explored the following questions: (1) Does the seasonal distribution of temperature and precipitation affect the intra-annual stability of community productivity? (2) Which mechanisms determine community intra-annual stability in response to seasonal change in temperature and precipitation, species richness, species asynchrony, dominant species stability or the stability of any specific functional group?
MATERIALS AND METHODS