1 Introduction
Climate change, such as extreme drought and rainfall, varies spatially
and temporally (IPCC 2007; Benestad et al., 2012). Such changes
significantly affect plants. For example, global warming caused
substantial damage on plants due to the drought and heat stress (Lipiec
et al., 2013; Elst et al., 2017). Rainfall variation impacted
terrestrial ecosystems since water limited plant growth, reproduction
and productivity (De Boeck et al., 2017). Resource allocation is a vital
strategy for plants to respond to the environmental variation (Harper et
al., 1970; Mokany et al., 2006). For instance, the energy originated
from photosynthesis of a plant can be allocated between aboveground and
belowground organs such as leaves and roots. The former enables plants
to do photosynthesis, while the latter could store resources for plants
to grow. Biomass allocation between aboveground and belowground organs
is known as root: shoot ratio (i.e. R: S, Guo et al., 2007). Several
studies explored the effects of climate change on plants (Bai et al.,
2008; Gonzalez-Dugo et al., 2010; Knapp et al., 2008, 2017). However,
contrasting results were found in plant growth and productivity, which
merits further research.
Previous studies found that abiotic factors such as temperature and
rainfall impacted the R: S (Fay et al., 2003; Yang et al. 2018). For
example, rainfall affected the biomass allocation and the belowground
ecological processes of plants (Fay et al., 2003), where plants
allocated more biomass to roots in order to explore soil water when they
growing on dry conditions (Bray 1963), while they allocated more biomass
to shoots in order to seize the light when plants growing on wet
conditions (Villar et al., 1998). Moreover, higher levels of soil
heterogeneity increased R: S (Michael et al., 2004; Wu et al., 2014; Liu
et al., 2017a), where plants growing on patches with low quality grew
more roots into their neighboring patches with high quality (Liu et al.,
2017b, Liu et al., 2019). However, effects of biotic factors on biomass
allocation were complicated. Some studies found that R: S was not
affected by the aboveground competition (Zhang et al., 2014), and
belowground competition did not increase the biomass allocation to
roots. However, some other studies found that R: S was influenced by the
type of grasslands (Coupland 1980) and plant growth (Gedroc et al.,
1996; James et al., 2003). Thus, further studies are needed.
Climate changes such as extreme drought are predicted to be more
frequency (Benestad et al., 2012; Felton et al., 2019). Thus, it is
crucial to explore the effects of such changes on plant productivity and
their allocation strategies (Bai et al., 1997; Cai et al., 2005 Lv et
al., 2016). Here an experiment was conducted to explore the effects of
water availability on biomass allocation of plants at the population
scale, where 4 plant species (Leymus chinensis , Stipa
grandis , Artemisia frigida , Potentila acaulis ) that
dominant at degraded grasslands in Inner Mongolia steppe were treated
with 8 levels of water additions, which was set to simulate the rainfall
scenarios in the face of climate change. Note that the degradation of
grasslands in Inner Mongolia are caused by activities such as grazing
(Liu et al., 2006, 2007), where L. chinensis and S.
grandis are the two dominant species in the lightly degraded grasslands
(Li et al., 2005), while A. frigida and P. acaulis are the
dominant species in the heavily degraded grasslands. We expect that
species at the lightly degraded grasslands will be more sensitive to the
rainfall variation since they grow fast and tend to have relatively
larger plant sizes, while species at the heavily degraded grasslands
could withstand the water additions as they tend to grow slowly and to
have relatively smaller plant sizes (Ma 2015). Specially, the biomass
allocation between the aboveground and belowground organs of L.
chinensis and S. grandis are expected to vary with water
availability; while water availability is expected to not impact the
biomass allocation of A. frigida and P. acaulis . This
study can improve our understanding of grassland management and the
restoration of degraded grasslands, especially in the face of climate
change.