Diversity and Enzyme Activity of Ectomycorrhizal Fungal Communities Following Nitrogen Fertilization in an Urban-Adjacent Pine Plantation

Abstract

Rapid economic development and accelerated urbanization in China has resulted in widespread atmospheric nitrogen (N) deposition. One consequence of N deposition is the alteration of mycorrhizal symbioses that are critical for plant resource acquisition (nitrogen, N, phosphorus, P, water). In this study, we characterized the diversity, composition, and functioning of ectomycorrhizal (ECM) fungal communities in an urban-adjacent Pinus elliottii plantation under ambient N deposition (~24 kg N ha −1 year −1 ), and following N fertilization (low N, 50 kg N ha −1 year −1 ; high N, 300 kg N ha −1 year −1 ). ECM functioning was expressed as the potential activities of extracellular enzymes required for organic N (protease), P (phosphomonoesterase), and recalcitrant polymers (phenol oxidase). Despite high ambient N deposition, ECM community composition shifted under experimental N fertilization, and those changes were linked to disparate levels of soil minerals (P, K) and organic matter (but not N), a decline in acid phosphatase (AP), and an increase in phenol oxidase (PO) potential activities. Based on enzyme stoichiometry, medium-smooth exploration type ECM species invested more in C acquisition (PO) relative to P (AP) following high N fertilization than other exploration types. ECM species with hydrophilic mantles also showed higher enzymatic PO:AP ratios than taxa with hydrophobic mantles. Our findings add to the accumulating evidence that shifts in ECM community composition and taxa specialized in organic C, N, and P degradation could modulate the soil nutrient cycling in forests exposed to chronic elevated N input.

Litter Management as a Key Factor Relieves Soil Respiration Decay in an Urban-Adjacent Camphor Forest under a Short-Term Nitrogen Increment

“…Similarly, in our study, all N addition treatments (>5 g N m −2 year −1 ) decreased Rs, which suggests that our experimental site reached N-saturation. Some studies reported that the reduction of Rs caused by the decreases of microbial biomass, fine roots, and/or shifts in the microbial community and enzyme functions through excessive N inputs [12,21,29,43]. Actually, the microbial biomass and fine root biomass in the same site decreased after N addition [31], which supported our statement.…”

“…However, there is still no consensus on the responses of Rs to litter management in different forest ecosystems [28]. In particular, the effects of incremental N deposition on litter decomposition usually show greater C stabilization through an inhibition of microbial and enzyme activity [29]. Therefore, it is crucial to detangle the effect of litter manipulation on Rs under N additions [30], especially for those of N saturated systems.…”

Adaptation of Soil Fungal Community Structure and Assembly to Long- Versus Short-Term Nitrogen Addition in a Tropical Forest

“…The positive effects of N addition on relative abundance of saprotrophic fungi may be supported by the “Gadgil effect,” in which N competition between EcM and saprotrophic fungi could benefit to saprotrophic growth ( Gadgil and Gadgil, 1971 ; Fernandez and Kennedy, 2016 ). Such shifts in fungal community composition could affect the soil enzymatic activities and litter decomposition and, thus, modulate soil C, N, and P cycling in forests exposed to atmospheric N deposition ( Ning et al, 2018 ). Recent studies demonstrated that soil pH and NO 3 – –N concentration were the key drivers influencing fungal community composition ( Francioli et al, 2016 ; Ullah et al, 2019 ; Wang et al, 2021 ).…”

Does Forest Soil Fungal Community Respond to Short-Term Simulated Nitrogen Deposition in Different Forests in Eastern China?

“…These phenomena may reflect the competition for limited organic resources between EcM and saprotrophic fungi, which can be supported by the “Gadgil effect” [ 52 ]. Such shifts in fungal functional composition could affect soil enzymatic activities and litter decomposition, thereby regulating soil biogeochemical cycling in forests exposed to atmospheric N deposition [ 53 ].…”