Effect of drought and nutrient availability on invaded plant communities in a semi-arid ecosystem

Ecosystem functions are heavily dependent on the functional composition of
the plant community, i.e., the functional traits of plants forming the
community. This, on the one hand, depends on plant occurrence, but on the
other hand depends on the intraspecific variability of functional traits
of the species, which are influenced by climate and nutrient availability
and affected by plant-plant interactions. To illustrate that, we studied
the effects of drought and nitrogen addition (+ N), two important abiotic
variables which are changing with ongoing global change, as well as their
combined effect on the functional responses of grassland communities in
semi-arid environments of Northern Africa comprising of natural and
invasive species. We conducted a plot plant experiment where we planted
three native species and one invasive plant species in artificial
communities as of 5 individuals per species per plot. We exposed these
communities to four different treatments: a drought treatment, a
N-addition treatment, the combination between drought and N-addition as
well as a control. To assess the performance of plants within treatments,
we measured selected plant functional traits (plant height, specific leaf
area (SLA), leaf dry matter content (LDMC), N content of the leaves
(Nmass), specific root length (SRL) and root diameter) for all individuals
occurring in our plots, and additionally assessed the above and
belowground biomass for each plant individual. We found that the invasive
species showed a higher performance (higher biomass accumulation, taller
plants, higher SLA, Nmass, SRL and root diameter as well as lower LDMC)
than the native species under drought conditions. The invasive species was
especially successful with the combined impact of drought + N, which is a
likely scenario in ongoing global change for our research area. Thus,
plant functional traits might be a key factor for invasion success of
plant species which will be even more pronounced under ongoing global
change.