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