Majekovaetal_FunctionalEcology_2019

Majekovaetal_FunctionalEcology_201

Data from: Grassland plants show no relationship between leaf drought tolerance and soil moisture affinity, but rapidly adjust to changes in soil moisture

1. Assessing drought tolerance and the ability of plants to adjust to changes in available water resources is crucial for understanding current and future distributions of plant species. While turgor loss point (πtlp) has been recognized as a direct determinant of drought tolerance in woody plants, information on it for grassland species is largely missing. 2. We first validated a rapid method to estimate πtlp for grassland species, using osmometry measurements (πtlp-osm) of osmotic potential at full hydration (πo-osm), originally proposed for woody species. We confirmed that πo-osm was tightly positively related to πtlp measured by the classic pressure–volume curve (πtlp-pv). Cell wall elasticity was not important in the maintenance of turgor and neither specific leaf area nor leaf dry matter content influenced πtlp. 3. We then studied the relationship between πtlp-osm measured under controlled conditions and species’ soil moisture affinity (Ellenberg indicator values) in 40 diverse grassland species from the full range of soil moisture conditions found in temperate grasslands. On a subset of 12 species, we studied the adjustment in πtlp-osm to drought stress and recovery from drought. 4. We hypothesized that dry grassland species are better adapted to drier conditions by having comparatively higher leaf drought tolerance (more negative πtlp) and a better ability to adjust to acute drought stress. 5. We found that πtlp-osm was unrelated to species’ soil moisture affinity. However, all species developed higher leaf drought tolerance by decreasing πtlp-osm after seven weeks of drought stress. After only one week of recovery, all species reduced the leaf drought tolerance back to the πtlp-osm level comparable with non-stressed plants. 6. Our results considerably extend the relationship between πo-osm and πtlp, originally defined for woody species, and thus propose a yet unexploited direct method for assessing leaf drought tolerance via turgor loss point in herbaceous species. However, the lack of relationship between πtlp and soil moisture affinity suggests that, unlike in woody plants, leaf-level drought tolerance in grassland plants does not fully translate into whole-plant drought resistance, suggesting an importance of other drought resistance strategies

Effects of plastic fragments on plant performance are mediated by soil properties and drought

In recent years, the effects of plastic contamination on soil and plants have received growing attention. Plastic can affect soil water content and thus may interact with the effects of drought on soil and plants. However, the effects of plastic on soil are highly context-dependent, and interactions with drought have been hardly tested. We conducted two greenhouse experiments to test the combined effects of plastic fragments (of varying size and concentration), water availability and soil texture, on soil water content and performance of the plant Arabidopsis thaliana. Plastic fragments had stronger negative effects on soil water content in low water availability, and the shape of this response (linear vs. unimodal) was mediated by soil texture. Conversely, increasing concentration of plastic had positive effects on plant growth. We suggest that plastic fragments introduce fracture points within soil aggregates. This increases number and size of soil pores favoring water loss but also facilitating root growth. Our results suggest complex interactive effects of plastic and drought, that may lead to a decoupling of plant and soil response. These processes should be taken into account in ecological studies and agricultural practices

Functional traits and their plasticity shift from tolerant to avoidant under extreme drought

Under climate change, extreme droughts will limit water availability for plants. However, the species-specific responses make it difficult to draw general conclusions. We hypothesized that changes in species' abundance in response to extreme drought can be best explained by a set of water economic traits under ambient conditions in combination with the ability to adjust these traits towards higher drought resistance. We conducted a 4-year field experiment in temperate grasslands using rainout shelters with 30% and 50% rainfall reduction. We quantified the response as the change in species abundance between ambient conditions and the rainfall reduction. Abundance response to extreme drought was best explained by a combination of traits in ambient conditions and their functional adjustment, most likely reflecting plasticity. Smaller leaved species decreased less in abundance under drought. With increasing drought intensity, we observed a shift from drought tolerance, i.e., an increase in leaf dry matter content, to avoidance, i.e., a less negative turgor loss point (TLP) in ambient conditions and a constancy in TLP under drought. We stress the importance of using a multidimensional approach of variation in multiple traits and the importance of considering a range of drought intensities to improve predictions of species' response to climate change