BayCEER Workshop 2015

Plant species partitioning along soil moisture gradients: Is there a trade-off between drought and water-logging tolerance?

P 3.1 in Droughts, floods and hidden flowpaths: This research holds WATER

Introduction

How so many plant species can coexist within a local community remains a key question in plant ecology. Niche theory predicts that species partition resource gradients based on trade-offs in resource use, so that each is a superior competitor under a specific set of environmental conditions and niche overlap is minimized.

One of the most important plant resources is soil water, and species partitioning of soil moisture gradients has been shown in a variety of ecosystems worldwide. Hydrologically defined niches have therefore been suggested to be central to coexistence in plant communities, and a trade-off (i.e. a negative relation) between plant performance under drought and under waterlogging has been implied, although the mechanisms underlying such a trade-off remain unresolved.

Material and Methods

We conducted a literature review and a meta-analysis, to evaluate the evidence that there is indeed a trade-off between plant performance under dry vs. performance under wet conditions, i.e. that species tolerance to one stressor comes at the cost of increased sensitivity to the other stressor. Alternatively, we hypothesized that tolerance against several stressor converges, and is traded-off against high growth rates. We systematically searched the literature for robust data on species growth performance under both dry and wet conditions in a wide variety of biomes, and excluded all studies that did not include a control.

Results

We found that very few studies directly compared species performance under both conditions. Preliminary results combining data from different studies did not support a trade-off: While drought and waterlogging always reduced performance, drought-tolerant species were not necessarily flooding-sensitive, and vice versa.

Conclusions

Our analysis indicated that there is currently no rigorous support for a general trade-off between tolerance to drought and waterlogging, which could lead to species partitioning of soil moisture gradients, and allow for plant coexistence.

Keywords: Diversity, species coexistence, species partitioning, niche partitioning, trade-offs, water availability, drought stress, flooding, meta-analysis