Abstract
Carbon cycling in wet tropical forests on highly weathered soils is
often limited by low plant-available phosphorus (P) concentrations. The
soil P cycle in these ecosystems is controlled by interactions with soil
organic matter (SOM), and iron (Fe) and aluminum (Al) minerals. Changes
in rainfall regimes associated with climate change are likely to affect
these interactions and alter P cycling. We used a well-defined high
rainfall gradient in wet tropical forests in Puerto Rico to test the
following hypotheses: 1) anoxic conditions under high rainfall regimes
drive the accumulation of organic P associated with increased SOM, and
2) loss of amorphous Fe and Al minerals via leaching will increase with
mean annual rainfall, decreasing the importance of sorbed and occluded
inorganic P fractions in wetter sites. We measured inorganic and organic
soil P fractions, soil organic C (SOC), and Fe and Al concentrations
from parallel transects of mixed forests and monodominant palm forests.
Along both transects, soil NaOH-extractable organic P and SOC
concentrations were higher at wetter sites, supporting our first
hypothesis. Contrary to our second hypothesis, high rainfall did not
reduce the concentrations of amorphous Fe and Al minerals. Instead, we
found a concurrent accumulation of these minerals with SOC and organic P
concentrations at wetter sites, suggesting that high rainfall promoted
the formation of organo-Fe/Al complexes that were protected from
leaching. With increasing rainfall, the NaOH-extractable inorganic P
fraction was depleted relative to soil total P concentrations. However,
the ratio of NaOH-extractable total P or residual P to soil total P
concentrations remained unchanged. These results highlight the
importance of organic matter accumulation and the associated P
concentrations in retaining P in soils under high rainfall conditions.
The coupling of SOC, organic P, and amorphous minerals were found along
both transects, indicating that vegetation did not impose a strong
control on these biogeochemical patterns along the gradients. Overall,
our results demonstrate that rainfall affected soil P fractions mainly
by altering organic matter accumulation. The coupling of SOC, organic P,
and amorphous minerals is likely central to predicting the responses of
soil biogeochemical cycling to climate change.
Original language | English GB |
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Title of host publication | American Geophysical Union, Fall Meeting 2018 |
Volume | 43 |
State | Published - 1 Dec 2018 |
Externally published | Yes |
Keywords
- 0414 Biogeochemical cycles
- processes
- and modeling
- BIOGEOSCIENCESDE: 0428 Carbon cycling
- BIOGEOSCIENCESDE: 0470 Nutrients and nutrient cycling
- BIOGEOSCIENCESDE: 0486 Soils/pedology
- BIOGEOSCIENCES