It is widely accepted that phosphorus (P) limits microbial metabolic processes and thus soil organic carbon (SOC) decomposition in tropical forests. Global change factors like elevated atmospheric nitrogen (N) deposition can enhance P limitation, raising concerns about the fate of SOC. However, how elevated N deposition affects the soil priming effect (PE) (i.e., fresh C inputs induced changes in SOC decomposition) in tropical forests remains unclear. We incubated soils exposed to 9 years of experimental N deposition in a subtropical evergreen broadleaved forest with two types of13C‐labeled substrates of contrasting bioavailability (glucose and cellulose) with and without P amendments. We found that N deposition decreased soil total P and microbial biomass P, suggesting enhanced P limitation. In P unamended soils, N deposition significantly inhibited the PE. In contrast, adding P significantly increased the PE under N deposition and by a larger extent for the PE of cellulose (PEcellu) than the PE of glucose (PEglu). Relative to adding glucose or cellulose solely, adding P with glucose alleviated the suppression of soil microbial biomass and C‐acquiring enzymes induced by N deposition, whereas adding P with cellulose attenuated the stimulation of acid phosphatase (AP) induced by N deposition. Across treatments, the PEgluincreased as C‐acquiring enzyme activity increased, whereas the PEcelluincreased as AP activity decreased. This suggests that P limitation, enhanced by N deposition, inhibits the soil PE through varying mechanisms depending on substrate bioavailability; that is, P limitation regulates the PEgluby affecting soil microbial growth and investment in C acquisition, whereas regulates the PEcelluby affecting microbial investment in P acquisition. These findings provide new insights for tropical forests impacted by N loading, suggesting that expected changes in C quality and P limitation can affect the long‐term regulation of the soil PE.
Most empirical and modeling research on soil carbon (C) dynamics has focused on those processes that control and promote C stabilization. However, we lack a strong, generalizable understanding of the mechanisms through which soil organic carbon (SOC) is destabilized in soils. Yet a clear understanding of C destabilization processes in soil is needed to quantify the feedbacks of the soil C cycle to the Earth system. Destabilization includes processes that occur along a spectrum through which SOC shifts from a ‘protected’ state to an ‘available’ state to microbial cells where it can be mineralized to gaseous forms or to soluble forms that are then lost from the soil system. These processes fall into three general categories: (1) release from physical occlusion through processes such as tillage, bioturbation, or freeze-thaw and wetting-drying cycles; (2) C desorption from soil solids and colloids; and (3) increased C metabolism. Many processes that stabilize soil C can also destabilize C, and C gain or loss depends on the balance between competing reactions. For example, earthworms may both destabilize C through aggregate destruction, but may also create new aggregates and redistribute C into mineral horizon. Similarly, mycorrhizae and roots form new soil C but may also destabilize old soil C through priming and promoting microbial mining; labile C inputs cause C stabilization through increased carbon use efficiency or may fuel priming. Changes to the soil environment that affect the solubility of minerals or change the relative surfaces charges of minerals can destabilize SOC, including increased pH or in the reductive dissolution of Fe-bearing minerals. By considering these different physical, chemical, and biological controls as processes that contribute to soil C destabilization, we can develop thoughtful new hypotheses about the persistence and vulnerability of C in soils and make more accurate and robust predictions of soil C cycling in a changing environment.
more » « less- NSF-PAR ID:
- 10305136
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Environmental Research Letters
- Volume:
- 14
- Issue:
- 8
- ISSN:
- 1748-9326
- Page Range / eLocation ID:
- Article No. 083004
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Increases in carbon (C) inputs to soil can replenish soil organic C (SOC) through various mechanisms. However, recent studies have suggested that the increased C input can also stimulate the decomposition of old SOC via priming. Whether the loss of old SOC by priming can override C replenishment has not been rigorously examined. Here we show, through data–model synthesis, that the magnitude of replenishment is greater than that of priming, resulting in a net increase in SOC by a mean of 32% of the added new C. The magnitude of the net increase in SOC is positively correlated with the nitrogen-to-C ratio of the added substrates. Additionally, model evaluation indicates that a two-pool interactive model is a parsimonious model to represent the SOC decomposition with priming and replenishment. Our findings suggest that increasing C input to soils likely promote SOC accumulation despite the enhanced decomposition of old C via priming.
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Abstract Despite the large contribution of rangeland and pasture to global soil organic carbon (
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