Increases and decreases in soil moisture in water-limited plant communities cause asymmetrical responses in biomass but not in diversity

Abstract

Aims

Changes in precipitation patterns, such as the predicted increases in the frequency of climatic extremes, are likely to alter plant communities, but whether responses to drought or to wetter conditions respectively cause consistent, opposite responses is debated. Here, we assessed the response in biomass production and species diversity of water-limited plant communities to the direction (increase or decrease) and magnitude (micro- and macro-climatic effects) of changes in soil moisture.

Location

We reciprocally translocated soils containing seed banks from two climates (semi-arid and mediterranean) at a micro-climatic (opposite slopes) and a macro-climatic scale (between climates) in Chile.

Results

Biomass production for the soils that were translocated from wetter to drier climates was unrelated to the available soil moisture. The lowest biomass was produced in the wettest climate on the wet slope. Biomass production increased after a translocation to the drier climate (representing the largest change in climate). Nonetheless, the highest overall biomass for the wet to dry translocation was produced on the mediterranean dry slope with intermediate soil moisture. However, on the same mediterranean dry slope, biomass was almost zero for soil translocated the other way round (from drier to wetter). Diversity after 24 months was unaffected by micro-climatic change, but soils transplanted toward the drier climate yielded a plant community with increased diversity.

Conclusion

Our results showed direction and magnitude of climate change but also the response factor that is studied matters to detect direction-dependent responses; i.e., species richness had a linear and reversible response. However, the response of biomass depended on the origin of the transplanted material (soil and plant community), indicating history dependence (hysteresis). This emphasizes that responses to unidirectional climate manipulation experiments may not be able to capture the entire nature of the response of plant communities to climate change.