Epiphytes are characterized by their ability to survive without a root connection to the ground, but many basic life‐history traits and ecological trade‐offs of this unique aerial growth habit remain largely uncharacterized. Mortality causes are still not well understood, but falling from the host tree has been suggested as a leading cause of epiphyte mortality and community dynamics. Little empirical evidence exists for Here, we experimentally test two hypotheses regarding the drivers of epiphyte mortality in a cloud forest of central Panama. We test whether simple contact with terrestrial soil is deleterious to epiphytes, preliminarily testing the epiphyte enemy escape hypothesis, and test the vertical niche differentiation hypothesis, wherein epiphytes are specifically adapted for microsites throughout the vertical forest strata. By monitoring survival, leaf loss and health status of 270 transplanted epiphytes for a year and a half, we pinpoint the extent to which soil contact and height of origin regulate epiphyte performance. We found that contact with terrestrial soil itself was detrimental to epiphytes in situ, providing some of the first empirical data to explain why falling onto the ground, versus falling into the understorey, is particularly fatal to epiphytes. However, we also found that mortality rates vary substantially among taxonomic groups and among epiphytes that originally came from different height strata.
Decomposition is a major component of global carbon cycling. However, approximately 50% of wood necromass and a small proportion of leaf litter do not contact the forest floor, and the factors that regulate the decomposition above the forest floor are largely untested. We hypothesized that separation from soil resources causes slower decomposition rates above the forest floor. Specifically, we tested whether slower decomposition results from decreased nutrient availability (the nutrient limitation hypothesis) and/or microbial dispersal limitation (the dispersal limitation hypothesis) in the absence of soil resources. We tested these hypotheses by combining experimental manipulations of epiphytes and macronutrient fertilization with elemental analyses and community metabarcoding (fungi and prokaryotes). Specifically, we compared wood stick and cellulose decomposition among three treatments: an unaltered trunk section, an epiphyte mat, and a ‘removal treatment’ where an epiphyte mat was removed to test the effect of soil resources. We also performed a factorial fertilization experiment to test the effects of nitrogen (N) and phosphorus (P) on the decomposition of suspended cellulose. Decomposition rates were fastest on the epiphyte mats, intermediate in the removal treatment and slowest in the controls. Phosphorus addition increased decomposition rates in the fertilization experiment, and greater P concentrations, along with some micronutrients, were associated with increased rates of decomposition on the epiphyte mats and in the removal treatments. Locally dispersed fungi dominated the wood stick communities, indicating that fungal dispersal is limited in the canopy, and fungal saprotrophs were associated with increased rates of decomposition on the epiphytes. These experiments show that slowed decomposition above the forest floor is caused, in part, by separation from soil resources. Moreover, our findings provide support for both the nutrient limitation and dispersal limitation hypotheses and indicate that mechanisms regulating canopy‐level decomposition differ from those documented on the forest floor. This demonstrates the need for a holistic approach to decomposition that considers the vertical position of necromass as it decomposes. Further experimentation is necessary to quantify interactions between community assembly processes, nutrient availability, substrate traits, and microclimate.
A free
- NSF-PAR ID:
- 10459700
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Functional Ecology
- Volume:
- 33
- Issue:
- 12
- ISSN:
- 0269-8463
- Page Range / eLocation ID:
- p. 2417-2429
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract why epiphytes do not survive when forced to become terrestrial, and few studies exist that transplant epiphytes between high‐ and low‐forest strata to test trade‐offs between thriving in canopy environments and survival in the forest understorey.Synthesis . Plants that are adapted for the canopy experience a trade‐off with higher mortality when in contact with terrestrial soil. Follow‐up studies should explore the role of terrestrial soil microbes and physiological constraints as potential drivers of decreased grounded epiphyte survival. -
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Abstract Fungi represent a rapidly cycling pool of carbon (C) and nitrogen (N) in soils. Understanding of how this pool impacts soil nutrient availability and organic matter fluxes is hindered by uncertainty regarding the dynamics and drivers of fungal necromass decomposition.
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