Fungal litter mat cover in Cannopy Trimming Experiment (CTE) plots responses to canopy opening, hurricanes and drought

Fungi that bind leaf litter into mats and produce white-rot via degradation of lignin and other aromatic compounds influence forest nutrient cycling and soil fertility. Over three and a half years beginning in June 2014, 6 months before the second iteration of the Canopy Trimming Experiment (CTE), we measured quarterly the extent of white-rot litter mats formed by basidiomycete fungi in the Luquillo Mountains of Puerto Rico in response to disturbances – a simulated hurricane treatment executed by canopy trimming and debris addition in December 2014 (CTE0, a mid-year drought in 2015, and two hurricanes 10 days apart in September 2017. Percent fungal litter mat cover ranged from 0.4% after hurricanes Irma and Maria to a high of 53% in forest with undisturbed canopy prior to the 2017 hurricanes, with means mostly between 10 - 45% of fungal litter mat cover in undisturbed forest. Drought decreased litter mat cover in both treatments, except in one undisturbed plot dominated by a drought-resistant fungus, Marasmius crinis-equi. Percent fungal litter mat cover sharply declined after real hurricanes and the simulated hurricane treatment (CTE). We found that solar radiation had a significant treatment effect and was strongly negatively correlated with percent litter mat cover within each of the four climatic seasons. Solar radiation was also strongly negatively correlated with relative humidity, throughfall, rain and litter wetness. However, rainfall was negatively correlated with litter mat cover, possibly due to erosion or saturation during high rainfall events. Canopy opening reduced leaf litterfall rates but did not affect litter mat cover. The main negative effect on basidiomycete fungi that bind leaf litter into mats was lower litter moisture associated with increased solar radiation from canopy opening and high leaf fall during drought. Variation in drought tolerance among basidiomycete fungal litter mat formers provided some resilience to drought.
\ Support for this work was provided by grants BSR-8811902, DEB-9411973, DEB-9705814 , DEB-0080538, DEB-0218039 , DEB-0620910 , DEB-1239764, DEB-1546686, and DEB-1831952 from the National Science Foundation to the University of Puerto Rico as part of the Luquillo Long-Term Ecological Research Program. Additional support provided by the University of Puerto Rico and the International Institute of Tropical Forestry, USDA Forest Service.\