Nutrient mineralization from green leaves in litterbags of three mesh sizes in the LUQ-LTER Canopy Trimming 2 Experiment

Hurricanes generate disturbances in forests that alter physicochemical characteristics of the habitat by opening the canopy and depositing fresh wood and leaves. Our objectives were to evaluate the effects of simulated hurricane driven changes to nutrient fluxes from litter to soil immediately following canopy disturbance. This study used three complete replicated blocks with two canopy treatments, control and trim+debris. Measurements were made in three 5 x 5 m subplots within 20 x 20 m plots nested in the 30 x 30 m treatment areas. Anion and cation resin membranes were inserted into the fermentation layer at the litter-soil interface and retrieved after one week. The measurement intervals were 2-4 weeks before canopy trimming, 0-1, 1-2, 2-3 and 4-5 weeks after trimming. Nutrient mineralization differed significantly between control and trim+detritus. Total N and P fluxes occurred at 4-5 weeks after canopy trimming. Litter decomposition depends primarily on the interaction among climate, litter quality and biota, so consequently any change in habitat will result in changes in these factors. Our objectives were to evaluate the effects of hurricane driven changes to forests on green litter decomposition, invertebrate communities and nutrient mineralization. This study used three complete replicated blocks with two canopy treatments, control and trim+debris. Measurements were made in three 5 x 5 m subplots within 20 x 20 m plots nested in the 30 x 30 m treatment areas. Green leaves were enclosed in litterbags of three different mesh sizes in each subplot. Litterbags were retrieved after 21, 35, 84 and 168 days; decomposer fauna was extracted and identified, mineralized nutrients were measured using ion resin membranes, and weight loss was determined. Arthropod abundance differed significantly through time. In addition, the number of arthropod taxonomic groups and nutrient mineralization differed significantly between control and trim+detritus, and nutrient mineralization also differed significantly among litterbags mesh sizes. Specifically, nitrogen and phosphorous mineralization were higher in trim+detritus in large mesh size, and decomposer arthropod abundance was also highest in large mesh sized bags. Although % mass remaining changed significantly through time, it did not differ between canopy treatments or litterbag mesh sizes. Thus, our result showed that abundance of arthropods did not affect mass loss. Although canopy disturbance did not affect litter mass loss or arthropod abundance, invertebrate composition differed significantly between canopy treatments with greater dominance by shredders (lepidoptera and diptera larvae) in trim+debris, which corresponded to higher rates of nutrient mineralization from green leaves. Consequently, our results suggest that relative differences in nutrient fluxes from green leaf litter was related to changes in the litter invertebrate food web rather than rates of decomposition. \ 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.\