The effects of nutrient fertilization on belowground allocation in tropical dry forests: linking results from a model and an experiment
Abstract
Few nutrient fertilization experiments have been carried out in tropical dry forests. While a single previous experiment has suggested that fertilization can lead to increases in aboveground biomass, little is known about how fertilization might affect allocation in these forests. Here, we considered nutrient-driven changes in allocation from the perspective of a mechanistic numerical model and a new, ongoing field experiment. The model dynamically coupled ED2 (vegetation dynamics), MEND (microbial dynamics and enzyme-mediated decomposition), and N-COM (plant-microbe competition for nitrogen and phosphorus). It was used to simulate tropical dry forest secondary succession, focusing on a site in Guanacaste, Costa Rica. We analyzed how allocation varied in response to (1) different allocation strategies adopted by the model, and (2) fertilization treatment. The experiment, begun in 2015, involves 16 forest inventory plots in Guanacaste, Costa Rica, including controls and +N, +P, and +NP treatments. We predicted that: (1) after 3 years of a nutrient fertilization experiment, fertilization would result in significant changes in aboveground biomass, in accord with previous tropical dry forest fertilization experiment; and (2) allocation to fine roots would decrease, in accord with many temperate fertilization experiments.
In contrast to our expectations, little change in aboveground biomass production was realized in either our simulations or in the field experiment. However, in the field experiment and in some simulations, fine root biomass was larger in the +P and +NP plots than in the control or +N plots. We were able to use model simulations to diagnose the reason for this result. In the model, P fertilization shifted the vegetation from being more P-limited to being more water-limited. Thus, if the fine root allocation scheme compensated for these changes by shifting production to fine roots and away from leaves, water limitation was partially relieved, and plants achieved carbon-to-nutrient ratios more favorable for growing new structural tissue. These results indicate the surprising dynamics that can emerge in forest limited by both nutrients and water. Predicting their future will require us to further improve our knowledge of allocation as a function of changing hydrological and nutrient regimes.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B13D..07X
- Keywords:
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- 0410 Biodiversity;
- BIOGEOSCIENCESDE: 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0434 Data sets;
- BIOGEOSCIENCESDE: 0476 Plant ecology;
- BIOGEOSCIENCES