Temperature Perturbation in Leptospermum scoparium Reveals Small Benefits of Soil Microbial Community to Plant Health and Survivorship

Background and Aims: Plant–soil feedbacks and their underlying mechanisms have received renewed interest in the light of climate change. Soil microbial communities mediate a variety of important functions for plant health, but whether these interrelationships will persist under sustained warming remains an open question. We investigated whether soil microbial communities influence the health of plants in increasingly warmer temperatures. Methods: Here, using a warming experimental design and mānuka ( Leptospermum scoparium ) as a model plant, we explore how plant health may be linked to either familiar or unfamiliar soil microbial (bacterial and fungal) communities by monitoring key elements of plant growth. The experimental warming treatment consisted of gradual warming (+Δ6 °C), heat wave (+Δ10 °C) and recovery (−Δ16 °C) phases. Results: We found that the presence of microbes was positively correlated with plant growth rate. Contrary to expectations, microbial community identity was not a significant determinant of plant health metrics, despite a weak trend in favour of familiar soil microbe communities. Our findings show that the presence of soil microbes may have some mild positive effect on plant health, as under the gradual warming phase, both familiar and unfamiliar microbial communities conferred some advantage, but this was negated under the heat wave . Conclusion: We provided evidence that (i) microbes are beneficial for plant health, (ii) the composition of the microbial community influenced plant health slightly differently and independently of the warming treatment and (iii) extreme warming events are a major risk to both plants and microbes.