Abstract
Research Highlights: Extraradical mycorrhizal fungal mycelium (MFM) plays critical roles in nutrient absorption and carbon cycling in forest ecosystems. However, it is often ignored or treated as a root uptake apparatus in existing biogeochemical models. Methods: We conducted a meta-analysis to reveal how MFM responds to various, coinciding environmental factors and their interactions. Results: Nitrogen (N) addition and N-phosphorus (P)-potassium (K) combination significantly decreased MFM. However, elevated CO2, organic matter addition, P addition, and CO2-N combination significantly increased MFM. In contrast, warming, K addition, N-P combination, and P-K combination did not affect MFM. Mycorrhizal fungal levels (individual vs. community), mycorrhizal type (ectomycorrhizal fungi vs. arbuscular mycorrhizal fungi), treatment time (<1 year vs. >1 year), and mycelium estimation/sampling method (biomarker vs. non-biomarker; ingrowth mesh bag vs. soil core) significantly affected the responses of MFM to elevated CO2 and N addition. The effect sizes of N addition significantly increased with mean annual precipitation, but decreased with soil pH and host tree age. The effect sizes of P addition significantly increased with N concentration in host plant leaves. Conclusions: The differential responses revealed emphasize the importance of incorporating MFM in existing biogeochemical models to precisely assess and predict the impacts of global changes on forest ecosystem functions.
Highlights
Mycorrhizal symbioses are common and extensive in terrestrial vegetation [1], and play a key role in biogeochemical cycles of forest ecosystems [2,3,4]
We found that the positive responses of mycorrhizal fungal mycelium (MFM) to elevated CO2 were significantly affected by mycorrhizal fungal level
We found that the effect sizes of N addition on MFM increased with mean annual precipitation (Qm = 8.98, p < 0.01) but it decreased with soil pH (Qm = 3.85, p < 0.05)
Summary
Mycorrhizal symbioses are common and extensive in terrestrial vegetation [1], and play a key role in biogeochemical cycles of forest ecosystems [2,3,4]. Mycorrhizal fungi transfer nutrients directly to their host plants in exchange for photosynthetically derived carbon [5]. In terms of root foraging, MFM of EM may permit a more thorough exploitation of soil mineral and organic nutrients [1,7]. In terms of absorptive efficiency, MFM of EM and arbuscular mycorrhizas (AM) is clearly more effective for obtaining greater absorption area per unit of carbon allocated to the mycelium than to the root [8]. Mycorrhizal fungi can greatly enhance the nutrient absorption capacity of the plant root system [9]. Some EM fungi are known to colonize organic matter, wood ash, and leaf litter by forming a dense mycelium [5,7], and to acquire nutrients from organic
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