Micronutrients enhance macronutrient effects in a meta-analysis of grassland arthropod abundance

Aim: Ongoing alterations to Earth’s biogeochemical cycles (e.g. via
fertilization, burning of fossil fuels, and pollution) are expected to
impact plants, plant consumers, and all subsequent trophic levels. While
fertilization experiments often reveal arthropod nutrient limitation by
nitrogen and phosphorus via effects on plant nutrient density and biomass,
these macronutrients are only two of many nutrients important to arthropod
fitness. Micronutrients are key to osmoregulation and enzyme function and
can interact synergistically with macronutrients to shape the geography of
arthropod abundance. We examine arthropod response to macro- and
micronutrient fertilization as a function of nutrient type, application
amount, duration, frequency, and plant responses to fertilization with the
goal of addressing how ongoing alterations to biogeochemical cycles will
shape future grassland food webs. Location: Global. Time period:
1987-2018. Major taxa studied: Invertebrates. Methods: We compiled a
database of 62 studies to test the response of six arthropod trophic
groups to multiple fertilizer types (compositions of varying macro- and
micronutrients), quantities, application frequencies, and application
durations. Additionally, we examined the role of plant nutrient content
and biomass in mediating arthropod responses to fertilization. Results:
Micronutrients applied alone had no effects on plant biomass nor arthropod
abundance. However, when added with macronutrients, micronutrients
amplified the effect of N, P, and K in promoting arthropod abundance, a
synergy which did not affect plant biomass. Micronutrients thus catalyzed
the ability of macronutrients to promote arthropod abundance across all
guilds studied. Main conclusions: In grasslands, the rules governing the
abundance of autotrophs and their consumers appear to differ fundamentally
in their response to Earth’s changing biogeochemistry. By revealing the
importance of micronutrients for arthropods using a global dataset, we
highlight a stoichiometric disjunction between limits of plants and
arthropods for metal cations whose biogeochemistry, along with N and P,
are being actively rearranged in the Anthropocene.