Microbially mediated effects on biomass
We show that live soil communities enhanced plant growth in high and low
aridity soils, and under control and water-stress conditions.
Additionally, bacterial alpha diversity across the soils, rhizospheres
and endospheres were positively correlated with T. triandra biomass, suggesting that a greater variety of unique bacteria, either
naturally present in the soil or recruited into the rhizospheres and
endospheres, leads to greater plant growth. Alpha diversity is a
well-known driver of plant productivity and is associated with greater
ecosystem functionality (Schnitzer et al. 2011; Byrnes et
al. 2014; Wang et al. 2019). Our findings support previous
research which shows that host-benefiting microbial functions are
present within T. triandra soils, rhizospheres and endospheres
(Hodgson et al. 2024a), and the importance of the habitat source
of microbes (e.g., arbuscular mycorrhizal fungi) for T. triandra drought response (Petipas et al. 2017). As such, there is now a
strong body of evidence to suggest that soil microbiota support T.
triandra growth across diverse ecosystems, under both stress and
non-stress conditions.
Our T. triandra plants developed larger root-mass fractions in
the sterilised high aridity soils, compared to the live high aridity
soils. This shows that a higher proportion of plant resources were
allocated to the development of roots under sterilised soil conditions,
perhaps in response to an absence of microbiota which typically aid the
acquisition or unblocking of nutrient resources in the soil
(Pérez-Harguindeguy et al. 2013; Bai et al. 2022; Wanget al. 2024). Interestingly, we observed the opposite trend in
the low aridity soils, where greater root investment occurred in the
live low aridity soils compared to those grown in sterilised low aridity
soils. As the bacterial communities were distinct, the low aridity soil
microbiota may not provide the same functional benefits as those found
in the high aridity soils – where different soil conditions, like
available moisture or organic matter, could create different host needs
(Hodgson et al. 2024a). Plants growing in the low aridity soils
may not typically produce such strong microbial-root interactions, given
the potential absence of these stress-tolerance benefits by the
microbiota (Comas et al. 2013; Hodgson et al. 2024a). The
importance of microbiota for plant growth, and the strength of the
interaction they form, may therefore depend on the aridity of the soil
and plant growth environment (De Long et al. 2019).