Impact of fog-drip versus fog immersion on leaf-level function of Bishop pines
Abstract
Fog-water is known to be an important water source to plants in coastal, Mediterranean climates because it augments plant available water several months after the last winter rain, when conditions are otherwise warm and dry. While fog-drip to the soil surface is the most obvious contribution of fog to the water budget of an ecosystem, recent studies provide convincing evidence that foliar absorption of fog water is also possible. The focus of our research was to assess the relative importance of fog-drip and fog immersion on the photosynthetic capacity and gas exchange rates of a coastal pine species, Bishop pine (Pinus muricata, D.Don), a drought sensitive species restricted to the fogbelt of coastal California and offshore islands. We conducted a greenhouse study where we manipulated fog water inputs to potted Bishop pine saplings during a three-week dry-down period. Fifteen saplings were randomly assigned one of three treatments: 1) fog-drip and fog-immersion, 2) fog immersion alone, and 3) no fog water inputs. We artificially generated nighttime fog events using an ultrasonic device, which produces fog droplets. Given that the canopy architecture varied between saplings, we standardized the amount of fog-drip plants received by preventing direct fog drip from the canopy, and instead added the average amount of fog water that would have fallen from each canopy. To detect changes in soil moisture, we installed volumetric soil moisture probes in each pot at 2 and 10 cm depth. The plant response variables measured were photosynthetic capacity and maximum gas exchange rates of sapling trees. Our results show that plants which received both fog-drip and fog immersion sustained higher gas exchange rates and photosynthetic capacity through the dry-down period compared to trees in other treatment groups. Trees that received only fog immersion had lower rates of gas exchange and lower photosynthetic capacity relative to trees that received both fog-drip and fog immersion. However, trees that received only fog immersion still maintained higher levels of these leaf-level responses during the dry-down period compared to trees that received no fog at all (immersion or drip). Leaf-level function of trees that did not receive fog water inputs declined steadily as the soil moisture declined over the three weeks. Our results show that fog-immersion alone provides sufficient moisture to Bishop pines to sustain carbon assimilation rates even as soil moisture declines. While this result indicates that foliar absorption of fog water may be a viable mechanism by which Bishop pines use fog water, plant function is more strongly influenced by fog-drip, which increases plant-available water shallow in the soil profile. By coupling our results with efforts towards understanding how spatial and temporal variation in fog patterns impact the water budget of terrestrial ecosystems, and particularly coastal forest that are frequently immersed in fog, we can develop more accurate predictions of how ecological functioning of these forests may be impacted by potential changes in the fog regime.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.A41E0106B
- Keywords:
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- 0315 ATMOSPHERIC COMPOSITION AND STRUCTURE Biosphere/atmosphere interactions;
- 0476 BIOGEOSCIENCES Plant ecology