Soil Enzyme Activity Indicates P Limitation in northern hardwood forest

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1) Soil enzyme activity can indicate nutrient limitations in forests. The ratios of carbon, nitrogen, and phosphorus acquiring enzymes respond to changes in nutrient availability in a way that minimizes limitation. 2) The study examined soil enzyme activity ratios in northern hardwood forests under long-term nitrogen, phosphorus, and nitrogen+phosphorus fertilization. 3) Results suggested phosphorus limitation based on a shift from phosphorus to nitrogen acquiring enzymes with phosphorus fertilization. Nitrogen limitation of carbon use was also suggested based on shifts with nitrogen fertilization.

Science

Soil Enzyme Activity Indicates P
Limitation in Northern Hardwood
Forests
Shan Shan1, Spencer Stutenroth1, Melany Fisk1*
1Department of Biology, Miami University, Oxford, OH

N P Colimitation
• Nutrient limitation & ecosystem productivity/function
• Single-nutrient limitation
• N P colimitation: larger productivity response to N+P together
than to either alone
Elser et al., 2007

Optimized Resource Acquisition & Nutrient
Limitation
Light limitation

• Decompose organic matter, release various nutrients
into the soil
• Indicate nutritional demands of plants and microbes
– High production = High demand for the target
nutrient
Soil Extracellular Enzymes
N-acquiring enzyme P-acquiring enzyme C-acquiring enzyme
aminopeptidase
N-acetyl-
glucosaminidase
phosphatase β-glucosidase
cellobiohydrolase

Hypothesis
• Ratios of C-, N-, and P-acquiring enzymes respond to
changes in nutrient availability in a direction that
minimizes limitation by any single nutrient.

Study Sites
Hubbard Brook
stands:
1 mid-age
1 mature
Bartlett stands:
3 young
3 mid-age
3 mature
Jeffers Brook
stands:
1 mid-age
1 mature
Stand locations in Central NH

N: 30 kg/ha/yr
as NH4NO3
P: 10 kg/ha/yr
as KH2PO4 )
N+P
Control
Annual fertilization began in
2011

Methods
• Soils
– Oe
– Oa
– Mineral
• Enzyme activity (fluorescent method)
– N: leucine aminopeptidase, alanine
amino peptidase
– P: acid phosphatase
– C: β-glucosidase, cellobiohydrolase
Average 4.9 cm

0.45
0.55
0.65
0.11 0.21 0.31
C/(C+N)
C / (C + P)
OeCon
N
P
NP
• P limitation is
suggested by
vector angles.
• N limitation of
organic horizon C
breakdown is
suggested by
vector length.

P effect on N-acquiring enzymes developed over time
P-enzyme ↓
N-enzyme −
P-enzyme ↓
N-enzyme ↑

Conclusions
• P limitation is suggested by shift from P- to N- acquiring
enzymes in response to elevated P.
• N limitation of C use is suggested by shift to C-acquiring
enzymes in response to elevated N.
• Delayed response of N-acquiring enzymes to P addition
suggests development of colimitation overtime.
Shan Shan
shans@miamioh.edu

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Sampling intensity affects the ability to detect changes over time in soil nutrient concentrations. Higher sampling intensity through more samples or sampling sites allows for detection of smaller minimum detectable differences. A study analyzed how sampling intensity over time and space impacted the minimum detectable annual percentage change for concentrations of total carbon, nitrogen, and exchangeable magnesium, calcium, and potassium at different soil depths. The results provide guidance on sampling designs to balance detecting desired changes against costs of sample collection and analysis for soil monitoring.

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