Nationwide analysis of greenhouse effluents reveals robustness of crops as a modulator of ambient stoichiometry

Abstract

Crops are key players in agroecological nutrient dynamics. While the environmental impact of introduced agronomic nutrients has been widely studied, crop traits as modulators of environmental stoichiometry in agroecosystems have not been systematically considered. To observe crop-driven stoichiometric variation, we assessed nutrient variability of greenhouse substrate culture effluents on a nationwide scale in South Korea using 150 effluent samples collected from 10 different geographical locations over two consecutive pepper, tomato and cucumber growing seasons. We found that nutrient concentrations varied widely among crops, with cucumber effluents showing significantly lower quartile ranges (e.g., NO${}_3^{-}$${}_3^{-}$: 12.4-18.0 mM) compared to tomato and pepper (NO${}_3^{-}$${}_3^{-}$: 21.2-30.4 mM). However, when converted to molar fractions, the distributions between crops overlapped (NO${}_3^{-}$${}_3^{-}$ molar fraction quartile ranges: 0.42-0.54 for all crops) and the coefficient of variation (%CV) decreased from 30%-98% in concentration units to 12%-65% in molar fractions, with an average reduction of 18.5%p. This reduction in variability suggests that plant absorption kinetics contribute to the low variability in molar fractions. Further stochastic simulation analysis using a simple box model for root zone nutrient fluxes supported this finding. Our results demonstrate the robustness of plants as ambient stoichiometric modulators in agronomic systems. Such information on reduced plant parametric uncertainty may support future efforts to quantify agricultural nutrient budgets and design optimized agroecosystem stoichiometry for improved sustainability.