INTRODUCTION
Plant functional traits (i.e., plant height, leaf area and seed size)
have been considered as potentially powerful indicators of the
ecological processes of species, which can also be used as indicators or
reference for the maximum information of plant growth and resource
utilization strategies (Adler et al., 2013; Kooyma et al., 2010; Navarro
et al., 2010; Wilson et al., 1999). Plant traits have become a core
attribute to determine plant strategies and then to understand and
predict the evolution, distribution as well as ecological strategies of
plant species at the scale of population, community and ecosystem
(Chapin et al., 2000; Gaudet & Keddy, 1988; Kunstler et al., 2015),
because they directly affect the basic behavior and function of plants,
and reflect the survival strategies formed by plants adapting to
environmental changes (Ackerly & Cornwell, 2007). Plant strategies can
be quantified by measuring various functional characteristics that
affect plant fitness and ecological processes (Lavorel & Garnier,
2002). Westoby chose the plant ecological strategy scheme (LHS), i.e.,
the use of three functional traits (Westoby, 1998), specific leaf area
(SLA), plant canopy height and seed mass as representing three
fundamental and relatively independent axes of a plant’s ecological
strategy to classify plants according to meaningful axes of plant
specialization (Díaz et al., 2015; Laughlin et al., 2010; Vendramini et
al., 2002). Later on, ecologists have carried out a number of studies on
the relationship between plant height, leaf area and seed mass (Lavergne
et al., 2003; Wang et al., 2014; Wolf et al., 2022), and found
consistent relationship between plant traits, which further improves our
understanding of plant adaptation strategies (Koch et al., 2004).
Plant traits represent an outcome of evolutionary processes, therefore
its distribution reliably reflects their evolutionary history and
phylogenetic constrains (Larson et al., 2020; Reinhart et al., 2012;
Wang et al., 2008). Phylogenetically related species share a common
evolutionary history and may therefore have similar traits (Ibanez et
al., 2016; Losos, 2008). Although the whole point of the scheme is that
the LHS variables are not necessarily correlated with each other, much
of the literature has provided evidence that the correlated evolutionary
divergence of traits has led to trait correlations across plant species
(Gingerich, 1974; Revell et al., 2008; Xia et al., 2022), such as
correlation between leaf area and seed mass (Laughlin et al.,
2010)12. McCarthy et al. (2007) and Reich et al.
(2014) have shown that woody gymnosperms invest relatively more in
leaves than woody angiosperms. Poorter et al. (2012) provided further
evidence that herbaceous monocots have lower leaf mass fractions than
herbaceous eudicots because dicots invest relatively more than monocots
in leaves. Moreover, Damour et al. (2016) showed that dicots had higher
seed mass than monocots. Differing from the other monocots (Raven, 1988;
Tomlinson, 2006), palms build their tall primary stature and exhibit
unique features such as leaf development and anatomical characteristics,
and possibly the correlation of seed mass with leaf area and plant
height (Cámara-Leret et al., 2017; Moore, 2003; Sampaio & Scariot,
2008). Therefore, it remains debatable if plant species from different
clades will follow a specific LHS scheme at a higher classification
level (e.g., genus), though variety of ecological strategy schemes have
been proposed across plant species.
An important goal of plant ecology is to separate the key dimensions of
ecological variations across species and then to understand how and why
they function and vary between species. For example, the widely used LHS
scheme of Westoby propose that each dimension of LHS vary widely between
species at any given level of the other two, but it is not sufficient to
describe the main axes of trait variation of temperate woody species
(Westoby, 1998). Therefore, investigating the correlation of trait
characters in different plant clades will provide a sound basis further
our understanding of the evolution of functional characters among plants
(Pierce et al., 2014; Reich et al., 1999; Tjoelker et al., 2005).
However, to our knowledge, no study has so far investigated plant trait
variation across different clades, especially using large datasets in
the context of LHS scheme and phylogeny.
Consequently, it is still highly uncertain whether traits of different
plant clades will fit a specific LHS scheme. Or, do all plant species
within a specific clade support a plant ecological strategy scheme
(LHS)? Although several authors have investigated LHS scheme within each
clade such as palms, angiosperms, gymnosperms, annuals, perennials,
herbaceous or woody plants (Cámara-Leret et al., 2017; Falster &
Westoby, 2005; Kawai & Okada, 2020; Laughlin et al., 2010), but to our
knowledge no study has so far used large datasets to investigate
correlations of plant traits across different plant clades (i.e., palms,
other monocots, dicots, and gymnosperms). We addressed these questions
by conducting a meta-analysis of functional traits (plant height, leaf
size, and seed mass) from four plant clades, i.e., palms, other
monocots, dicots and gymnosperms with contrasting growth forms. The
primary aim of the current study was to understand if and how the
different plant clades are coordinated along the plant ecological
strategy scheme. Specifically, we first used phylogenetic generalized
linear mixed models (PGLMM) and partial R2lik logistic
regression model, to explore how potential forces drive variation in
plant traits between different clades, so as to better understand
evolution and correlation between functional traits among sets of plant
species (Zheng et al., 2009). We expected that each clade of plant
species will share the same plant ecological strategy scheme, while LSH
scheme would differ across different plant clades.