Nutrient limitations to bacterial and fungal growth during cellulose decomposition in tropical forest soils

Abstract

Nutrients constrain the soil carbon cycle in tropical forests, but we lack knowledge on how these constraints vary within the soil microbial community. Here, we used in situ fertilization in a montane tropical forest and in two lowland tropical forests on contrasting soil types to test the principal hypothesis that there are different nutrient constraints to different groups of microorganisms during the decomposition of cellulose. We also tested the hypotheses that decomposers shift from nitrogen to phosphorus constraints from montane to lowland forests, respectively, and are further constrained by potassium and sodium deficiency in the western Amazon. Cellulose and nutrients (nitrogen, phosphorus, potassium, sodium, and combined) were added to soils in situ, and microbial growth on cellulose (phospholipid fatty acids and ergosterol) and respiration were measured. Microbial growth on cellulose after single nutrient additions was highest following nitrogen addition for fungi, suggesting nitrogen as the primary limiting nutrient for cellulose decomposition. This was observed at all sites, with no clear shift in nutrient constraints to decomposition between lowland and montane sites. We also observed positive respiration and fungal growth responses to sodium and potassium addition at one of the lowland sites. However, when phosphorus was added, and especially when added in combination with other nutrients, bacterial growth was highest, suggesting that bacteria out-compete fungi for nitrogen where phosphorus is abundant. In summary, nitrogen constrains fungal growth and cellulose decomposition in both lowland and montane tropical forest soils, but additional nutrients may also be of critical importance in determining the balance between fungal and bacterial decomposition of cellulose.

Adaptation of soil microbial growth to temperature: Using a tropical elevation gradient to predict future changes

“…Our data on the ratio of bacterial/fungal growth (Figure a) showed relatively more bacterial than fungal growth at lower MAT in the highland soils. Our results might thus suggest that earlier studies indicating fungal dominance in cold environments may be explained by other environmental factors covarying with temperature (e.g., N availability; Nottingham, Hicks, et al (); Nottingham, Turner, et al ()). A further complicating factor is that the methodology provides proxies for bacterial and fungal growth and there may be small methodological errors when comparing results for bacterial growth (method reflects protein synthesis) with results for fungal growth (method reflects membrane synthesis).…”

Chemical Composition, Total Phenols and Flavonoids Contents and Antioxidant Activity as Nutritive Potential of Roasted Hazelnut Skins (Corylus avellana L.)

“…The highest content of selenium was reported for Sicilian hazelnut (86.5 µg/100 g) and Turkish Tombul hazelnuts (60 µg/100 g) [28,29]. The C, N, and P contents of HS are in the range of fungal biomass which varied from 38 to 57%, 0.23 to 15%, and 0.040 to 5.5%, respectively [30], indicating that HS might be a good nutrient for fungal growth. Fungi are known to have relatively higher C/P and C/N ratios, compared to bacteria, which may be related to their large size and small surface area to volume ratio, which decreases the relative demand for P-rich membrane phospholipids [31,32].…”

Arbuscular mycorrhizal fungi abundance was sensitive to nitrogen addition but diversity was sensitive to phosphorus addition in karst ecosystems

“…Liu et al (2013) found no significant correlation between N addition and soil pH in an Nsaturated system. Therefore, in N-limited or alkaline soil, soil pH would be sensitive to N and P addition, thereby affecting AMF community composition (Nottingham et al 2017). Other studies have shown that N and P applications can markedly change N and P availability (e.g., NH 4 + or NO 3 − ) (Egerton-Warburton et al 2007;Wang et al 2008).…”