Phosphate addition enhanced soil inorganic nutrients to a large extent in three tropical forests

Abstract

Elevated nitrogen (N) deposition may constrain soil phosphorus (P) and base cation availability in tropical forests, for which limited evidence have yet been available. In this study, we reported responses of soil inorganic nutrients to full factorial N and P treatments in three tropical forests different in initial soil N status (N-saturated old-growth forest and two less-N-rich younger forests). Responses of microbial biomass, annual litterfall production and nutrient input were also monitored. Results showed that N treatments decreased soil inorganic nutrients (except N) in all three forests, but the underlying mechanisms varied depending on forests: through inhibition on litter decomposition in the old-growth forest and through Al3+ replacement of Ca2+ in the two younger forests. In contrast, besides great elevation in soil available P, P treatments induced 60%, 50%, 26% increases in sum of exchangeable (K++Ca2++Mg2+) in the old-growth and the two younger forests, respectively. These positive effects of P were closely related to P-stimulated microbial biomass and litter nutrient input, implying possible stimulation of nutrient return. Our results suggest that N deposition may result in decreases in soil inorganic nutrients (except N) and that P addition can enhance soil inorganic nutrients to support ecosystem processes in these tropical forests.

Elemental stoichiometry and compositions of weevil larvae and two acorn hosts under natural phosphorus variation

“…As with the study by Zhou, et al 20. on acorn leaf stoichiometric traits, some elemental concentrations and ratios of both acorn seeds and weevil larvae differed significantly between P-rich sites and P-deficient sites, likely due to the differences in soil P, Ca, Mg, Fe, Mn and Al between the two site types1220 (Figs 3, 4 and 6 and 7, Supplementary Tables S1, S2, S3 and S4). This suggests stoichiometric plasticity of both plants and their parasite in response to elemental variability in the environment4, as well as a strong influence of soil elements on different trophic organisms along a food chain.…”

“…For example, P rich soils have lower C:P and nitrogen (N):P ratios in plants8, higher P composition in plants910 and higher P and RNA content and population density of herbivore ( Sabinia setosa )11. The higher soil inorganic nutrients (N, P, potassium (K), calcium (Ca), magnesium (Mg))12 on P rich sites may also lead to reduced locust outbreaks that occur more often on N-deficient soils13. Long-term adaptation to nutritional differences and resultant differentiation in stoichiometric composition helps ecotype formation1415.…”

“…Ca, Mg, Fe and aluminum (Al))1225, providing an opportunity to study the stoichiometric plasticity and homeostatic regulation of organisms under different soil P availability. Research has indicated that plant species under these contrasting P conditions often develop ecotypes of distinct stoichiometric traits in P concentration and C:P ratios141520262728.…”

Effects of phosphorus addition on soil microbial biomass and community composition in a subalpine spruce plantation

“…In addition, Aciego Pietri and Brookes [24] concluded that soil pH had marked effects on microbial biomass through affecting the availability of biologically toxic Al and organic C solubility. In our study, the pH in the HP treatment was increased by 0.43 unit (from 4.92 to 5.35) compared to the control, which was in line with previous studies suggesting P addition increased soil base cations via stimulation on litter nutrient input and eventually elevated soil pH [9,10]. All in all, these results imply that soil pH may be another factor affecting soil microbial biomass in the HP treatment.…”

“…To date, multiple mechanisms have been proposed to explicate the P effects on soil microbes [e.g., 3,5,7,9] (Fig. 1).…”