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Introduction
Introduction
Forest productivity may be limited by single nutrients like nitrogen (N) and phosphorus (S), or by multiple nutrients simultaneously, referred to as co-limitation.
Forest productivity may be limited by single nutrients like nitrogen (N) and phosphorus (S), or by multiple nutrients simultaneously, referred to as co-limitation.
Nutrient limitation is likely to control the allocation of carbon and energy aboveground, to stems and leaves, vs below ground, to root systems.
Nutrient limitation is likely to control the allocation of carbon and energy aboveground, to stems and leaves, vs below ground, to root systems.
It is uncertain whether alleviating limitation increases above ground growth at the expense of belowground growth, or alternatively, whether both increase together.
It is uncertain whether alleviating limitation increases above ground growth at the expense of belowground growth, or alternatively, whether both increase together.
Therefore, we tested limitation of fine root growth in northern hardwood forests where aboveground growth is co-limited by N and P (Blumenthal et al. 2025).
Therefore, we tested limitation of fine root growth in northern hardwood forests where aboveground growth is co-limited by N and P (Blumenthal et al. 2025).
Methods
Methods
Our study includes 13 forest stands in the White Mountain National Forest of New Hampshire, USA (Figure 1, white area).
Our study includes 13 forest stands in the White Mountain National Forest of New Hampshire, USA (Figure 1, white area).
Four 50 x 50 m plots in each stand have been fertilized annually since 2011, with either P (10kg NaH2PO4 ha-1 y-1), N (30kg NH4NO3 ha-1 y-1), N + P, or nothing (control).
Four 50 x 50 m plots in each stand have been fertilized annually since 2011, with either P (10kg NaH2PO4 ha-1 y-1), N (30kg NH4NO3 ha-1 y-1), N + P, or nothing (control).
Figure 1: Study Area
Figure 1: Study Area
We tested limitation of root growth in 3 mid-successional stands by quantifying root growth into root-free cylinders of soil (ingrowth cores: 9 per plot, 5-cm diameter and 24 cm depth) over 1 growing season.
We tested limitation of root growth in 3 mid-successional stands by quantifying root growth into root-free cylinders of soil (ingrowth cores: 9 per plot, 5-cm diameter and 24 cm depth) over 1 growing season.
Roots were extracted from cores after 1 year’s ingrowth and cleaned prior to root length and biomass measurement (Figure 2).
Roots were extracted from cores after 1 year’s ingrowth and cleaned prior to root length and biomass measurement (Figure 2).
Treatment responses were tested using a mixed effects model with N, P, and the N x P interaction as fixed effects and plots nested within stands as random effects.
Treatment responses were tested using a mixed effects model with N, P, and the N x P interaction as fixed effects and plots nested within stands as random effects.
Picture: A
Picture: A
Picture B
Picture B
Picture C
Picture C
Picture D
Figure 2. Root ingrowth core extraction (A, B), root cleaning (C), and scanned image (D) for quantifying length using line-intercept method
Figure 2. Root ingrowth core extraction (A, B), root cleaning (C), and scanned image (D) for quantifying length using line-intercept method
Acknowledgements
Acknowledgements
We thank Shiyi Li and Anton Yushanov for outstanding field assistance, and the USDA Forest Service Bartlett and Hubbard Brook Experimental Forests.
We thank Shiyi Li and Anton Yushanov for outstanding field assistance, and the USDA Forest Service Bartlett and Hubbard Brook Experimental Forests.
This work is a contribution to the Hubbard Brook Ecosystem Study and is a product of the MELNHE (Multiple Element Limitation in Northern Hardwood Ecosystems) project funded by the NSF Long-Term Ecological Research Program and the USDA National Institute of Food and Agriculture.
This work is a contribution to the Hubbard Brook Ecosystem Study and is a product of the MELNHE (Multiple Element Limitation in Northern Hardwood Ecosystems) project funded by the NSF Long-Term Ecological Research Program and the USDA National Institute of Food and Agriculture.
References
References
Blumenthal N, Stevens MH, Goswami S, Yanai RD, Fahey TJ, Fisk MC. 2025. N and P co-limitation of forest growth in northern hardwoods. Ecology, in review.
Blumenthal N, Stevens MH, Goswami S, Yanai RD, Fahey TJ, Fisk MC. 2025. N and P co-limitation of forest growth in northern hardwoods. Ecology, in review.
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