|Rachel Tenni - Ecophysiology
University of Tasmania, Tasmania, Australia
EFFECT OF NUTRIENT ENRICHMENT ON HERBIVORY IN THE MANGROVE AVICENNIA
MARINA OVER FOUR SITES WITHIN AUSTRALIA.
forest ecosystems are under major threat from urban development and
increasing eutrophication due to run-off of fertilizers used in
agriculture. Little is
known of the effects of excessive eutrophication at a whole system
level. Not much is known of
how plant productivity and herbivory is affected with increased
eutrofication within mangrove forest systems.
Many studies have shown that the leaf area removal by herbivores
is an important ecological factor in determining plant productivity.
In this study I wished to understand the effect of nutrient
enrichment on the amount of leaf area removed by herbivores in mangrove
four sites that spanned 22° in latitude, individual trees of the
mangrove Avicennia marina (Forsk.) Vierh. sensu lato
(Tomlinson 1986) were fertilized with nitrogen (400 g urea per tree),
phosphorus (400 g triple phosphate) or unfertilized (left as controls).
Sites were located at Batemans Bay, NSW (27 trees), Exmouth, WA (21
trees), Cape Cleveland, QLD (18 trees), and Port Douglas, QLD (24
trees). Digital images were
taken of all leaves from representative twigs, and both total leaf area
and proportion leaf area lost to herbivory were measured under the
different nutrient treatments.
proportion of canopy leaf area removed by herbivores in A. marina
was high (10-25%), suggesting that herbivores may have a significant
negative impact on the productivity of mangrove forests. I found no
effect of nutrient enrichment on the proportion of leaf area removed by
herbivores at all sites. However, addition of nitrogen fertilizer
increased growth, and thus the total amount of leaf area removed by
herbivores was increased with fertilization with nitrogen, Over sites
there was an increase in the proportion of leaf area removed by
herbivores with increasing latitude. Sites with higher average annual
humidity had higher levels of herbivory than sites with lower humidity.
With further investigation we will be able to better understand mangrove ecosystems at a whole system level thereby aiding the preservation, management and education of future generations on the importance of mangrove ecosystems.
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