Variable effects of nutrient enrichment on soil respiration in mangrove forests
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Background and Aims
Mangrove forests are globally important sites of carbon burial that are increasingly exposed to nutrient pollution. Here we assessed the response of soil respiration, an important component of forest carbon budgets, to nutrient enrichment over a wide range of mangrove forests.
We assessed the response of soil respiration to nutrient enrichment using fertilization experiments within 22 mangrove forests over ten sites. We used boosted regression tree (BRT) models to determine the importance of environmental and plant factors for soil respiration and its responsiveness to fertilizer treatments.
Leaf area index explained the largest proportion of variation in soil respiration rates (LAI, 45.9 %) followed by those of site, which had a relative influence of 39.9 % in the BRT model. Nutrient enrichment enhanced soil respiration only in nine out of 22 forests. Soil respiration in scrub forests showed a positive response to nutrient addition more frequently than taller fringing forests. The response of soil respiration to nutrient enrichment varied with changes in specific leaf area (SLA) and stem extension, with relative influences of 14.4 %, 13.6 % in the BRT model respectively.
Soil respiration in mangroves varied with LAI, but other site specific factors also influenced soil respiration and its response to nutrient enrichment. Strong enhancements in aboveground growth but moderate increases in soil respiration with nutrient enrichment indicated that nutrient enrichment of mangrove forests has likely increased net ecosystem production.
KeywordsSoil CO2 efflux Nitrogen Phosphorus Avicennia Rhizophora Growth Salinity Carbon cycling
This study was supported by the National Science Foundation under Grant DEB 99-81309, a WISC award from the American Association for the Advancement, the New Zealand Foundation for Research, Science and Technology (C01X0024, C01X0215, and C01X0307), the Smithsonian’s Marine Science Network, the Smithsonian Marine Station at Fort Pierce, the Caribbean Coral Reef Ecosystems Program and Australian Research Council awards LP0561498 and DP0774491. I thank Marilyn Ball and the staff of Carrie Bow Cay Research Station and Pelican Beach Resort, Belize. Thanks are also extended to the many people who helped in the field, including Fernanda Adame, Dianne Allen, Don Cahoon, Anne Chamberlain, Beth Clegg, Bettina Engelbrecht, Sharon Ewe, Ray Feller, Jane Halliday, Nicole Hancock, Helen Penrose, Brian Sorrell, Ann Maree Schwarz, and Rachel Tenni.
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