Belowground Biomass Response to Nutrient Enrichment Depends on Light Limitation Across Globally Distributed Grasslands

Cleland, Elsa E.; Lind, Eric M.; DeCrappeo, Nicole M.; DeLorenze, Elizabeth; Wilkins, Rachel Abbott; Adler, Peter B.; Bakker, Jonathan D.; Brown, Cynthia S.; Davies, Kendi F.; Esch, Ellen H.; Firn, Jennifer; Gressard, Scott; Gruner, Daniel S.; Hagenah, Nicole; Harpole, W. Stanley; Hautier, Yann; Hobbie, Sarah E.; Hofmockel, Kirsten; Kirkman, Kevin; Knops, Johannes M. H.; Kopp, Christopher W.; Pierre, Kimberly J. La; MacDougall, Andrew S.; McCulley, Rebecca L.; Melbourne, Brett A.; Moore, Joslin L.; Prober, Suzanne M.; Riggs, Charlotte E.; Risch, Anita C.; Schuetz, Martin; Stevens, Carly J.; Wragg, Peter D.; Wright, Justin P.; Borer, Elizabeth T.; Seabloom, Eric W.

doi:10.1007/s10021-019-00350-4

Cited by 42 publications

(47 citation statements)

References 71 publications

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“…Directly following aboveground biomass collection, five soil cores were collected from the clipped area, homogenized, and a subsample of the soil (c. 60 g) was used to estimate belowground plant biomass to a depth of 10 cm (Cleland et al, ). The subsample was suspended in water, and roots were captured with fine sieves and hand‐picked.…”

Section: Methodsmentioning

confidence: 99%

Nutrient availability controls the impact of mammalian herbivores on soil carbon and nitrogen pools in grasslands

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Wubs

Bakker

et al. 2020

Global Change Biology

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Grasslands are subject to considerable alteration due to human activities globally, including widespread changes in populations and composition of large mammalian herbivores and elevated supply of nutrients. Grassland soils remain important reservoirs of carbon (C) and nitrogen (N). Herbivores may affect both C and N pools and these changes likely interact with increases in soil nutrient availability. Given the scale of grassland soil fluxes, such changes can have striking consequences for atmospheric C concentrations and the climate. Here, we use the Nutrient Network experiment to examine the responses of soil C and N pools to mammalian herbivore exclusion across 22 grasslands, under ambient and elevated nutrient availabilities (fertilized with NPK + micronutrients). We show that the impact of herbivore exclusion on soil C and N pools depends on fertilization. Under ambient nutrient conditions, we observed no effect of herbivore exclusion, but under elevated nutrient supply, pools are smaller upon herbivore exclusion. The highest mean soil C and N pools were found in grazed and fertilized plots. The decrease in soil C and N upon herbivore exclusion in combination with fertilization correlated with a decrease in aboveground plant biomass and microbial activity, indicating a reduced storage of organic matter and microbial residues as soil C and N. The response of soil C and N pools to herbivore exclusion was contingent on temperature – herbivores likely cause losses of C and N in colder sites and increases in warmer sites. Additionally, grasslands that contain mammalian herbivores have the potential to sequester more N under increased temperature variability and nutrient enrichment than ungrazed grasslands. Our study highlights the importance of conserving mammalian herbivore populations in grasslands worldwide. We need to incorporate local‐scale herbivory, and its interaction with nutrient enrichment and climate, within global‐scale models to better predict land–atmosphere interactions under future climate change.

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Section: Methodsmentioning

confidence: 99%

Nutrient availability controls the impact of mammalian herbivores on soil carbon and nitrogen pools in grasslands

Sitters

Wubs

Bakker

et al. 2020

Global Change Biology

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“…For example, Graham and Mendelssohn () reported that long‐term (7 yr) additions of N reduced live root biomass of a S. lancifolia marsh, similar to our findings, but there was no effect of P. In contrast, Darby and Turner (2008 a ) found that P alone or in combination with N or Fe reduced root and rhizome biomass of salt marsh vegetation, which they attributed to decreased competition for P with the microbial community. Cleland et al () found that, in a globally distributed fertilization experiment of terrestrial grasslands, N and P applied singly reduced carbon allocated to roots and root biomass (0–10 cm), where most roots are located.…”

Section: Discussionmentioning

confidence: 99%

“…Reduced MOM biomass in +N and +P plots relative to control and +NP plots (Table ) may be explained by the optimal allocation hypothesis (Gleeson and Tilman ). The theory predicts that when plant growth is limited by belowground resources such as nutrients, carbon allocation to roots should increase (Gleeson and Tilman ; Cleland et al ) but when the limitation is removed, in this case by fertilization, C allocation to belowground structures is reduced. This is especially true for N since reduced root foraging allows more N to be allocated aboveground where it is a component of the chlorophyll molecule and photosynthesis (Sterner and Elser ).…”

Section: Discussionmentioning

confidence: 99%

“…Reduced MOM biomass in +N and +P plots relative to control and +NP plots (Table 2) may be explained by the optimal allocation hypothesis (Gleeson and Tilman 1992). The theory predicts that when plant growth is limited by belowground resources such as nutrients, carbon allocation to roots should increase (Gleeson and Tilman 1992;Cleland et al 2019) but when the limitation is removed, in this case by fertilization, C Table 5. Spearman correlation coefficient (ρ, n = 16) for interactions between C-, N-, and P-acquiring and total extracellular enzyme activities and select soil properties.…”

Section: Effects Of Fertilization On Macrophyte Productivity and Belomentioning

confidence: 99%

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Effects of 10 yr of nitrogen and phosphorus fertilization on carbon and nutrient cycling in a tidal freshwater marsh

Schubauer‐Berigan

2020

Limnology & Oceanography

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Tidal freshwater marshes can protect downstream ecosystems from eutrophication by intercepting excess nutrient loads, but recent studies in salt marshes suggest nutrient loading compromises their structural and functional integrity. Here, we present data on changes in plant biomass, microbial biomass and activity, and soil chemistry from plots in a tidal freshwater marsh on the Altamaha River (GA) fertilized for 10 yr with nitrogen (+N), phosphorus (+P), or nitrogen and phosphorus (+NP). Nitrogen alone doubled aboveground biomass and enhanced microbial activity, specifically rates of potential nitrification, denitrification, and methane production measured in laboratory incubations. Phosphorus alone increased soil P and doubled microbial biomass but did not affect microbial processes. Nitrogen or P alone decreased belowground biomass and soil carbon (C) whereas +NP increased aboveground biomass, microbial biomass and N cycling, and N, P, and C assimilation and burial more than either nutrient alone. Our findings suggest differential nutrient limitation of tidal freshwater macrophytes by N and microbes by P, similar to what has been observed in salt marshes. Macrophytes outcompete microbes for P in response to long-term N and P additions, leading to increased soil C storage through increased inputs of belowground biomass relative to N and P added singly. The susceptibility of tidal freshwater marshes to long-term nutrient enrichment and, hence their ability to mitigate eutrophication will depend on the quantity and relative proportion of N vs. P entering estuaries and tidal wetlands.

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“…However, global patterns of root productivity are unclear. For instance, fine root biomass is high in grasslands but low in forests (Jackson et al 1997;Schenk and Jackson 2002;Cleland et al 2019). Furthermore, fine root productivity and biomass differ between life forms (Bauhus and Messier 1999;Pavon 2005).…”

Section: Introductionmentioning

confidence: 99%

Testing allometric scaling relationships in plant roots

et al. 2020

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Background Metabolic scaling theory predicts that plant productivity and biomass are both size-dependent. However, this theory has not yet been tested in plant roots. Methods In this study, we tested how metabolic scaling occurs in plants using a comprehensive plant root dataset made up of 1016 observations from natural habitats. We generated metabolic scaling exponents by log-transformation of root productivity versus biomass. Results Results showed that the metabolic scaling exponents of fine root (< 2 mm in diameter) productivity versus biomass were close to 1.0 for all ecosystem types and functional groups. Scaling exponents decreased in coarse roots (> 2 mm in diameter). Conclusions We found isometric metabolic scaling in fine roots, a metabolically active organ similar to seedlings or saplings. Our findings also indicate a shift in metabolic scaling during plant development. Overall, our study supports the absence of any unified single constant scaling exponent for metabolism-biomass relationships in terrestrial plants, especially for forests with woody species.

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Belowground Biomass Response to Nutrient Enrichment Depends on Light Limitation Across Globally Distributed Grasslands

Cited by 42 publications

References 71 publications

Nutrient availability controls the impact of mammalian herbivores on soil carbon and nitrogen pools in grasslands

Nutrient availability controls the impact of mammalian herbivores on soil carbon and nitrogen pools in grasslands

Effects of 10 yr of nitrogen and phosphorus fertilization on carbon and nutrient cycling in a tidal freshwater marsh

Testing allometric scaling relationships in plant roots

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