Soil nutrients determine multidimensional absorptive root traits of Cryptomeria japonica var. sinensis plantations along a chronosequence in subtropical forest

Abstract

Absorptive roots are crucial for nutrient uptake and water absorption in forest ecosystems, yet variations in root traits and the underlying drivers during stand succession remains poorly understood. Here, we use a space-for-time substitution method to investigate the morphological traits (i.e., root diameter, RD; specific root length, SRL; and root tissue density, RTD) and chemical traits (i.e., concentrations of carbon, C; nitrogen, N; phosphorus, P; potassium, K; calcium, Ca; magnesium, Mg and manganese, Mn) in the absorptive roots of Cryptomeria japonica across five chronosequences in subtropical China. Simultaneously, we evaluated soil parameters and tree relative growth rate (RGR) to determine their influence on root traits. The results showed that RD, N, K, and Ca concentrations exhibited hump-shaped patterns with stand development (peaking in mature stands), whereas SRL and RTD exhibited opposite trends. Additionally, P and Mg concentrations in the roots decreased with stand age, whereas Mn concentration increased. Two trade-off strategies of absorptive root traits were identified: the first strategy characterized by RD, RTD, and root nutrients (N, Ca and Mg), potentially indicates a trade-off between nutrient acquisition and conservation. The second strategy related to SRL and K concentration represents a trade-off between resource foraging efficiency and nutrient allocation. Soil factors had a greater influence on root trait variations than tree RGR. Specifically, soil pH negatively influenced RD and Mn concentration but positively affected RTD. Root N and Ca concentrations increased with soil water content, while K concentration rose with soil nitrate-N availability. Conversely, P and Mg concentrations decreased with increasing soil ammonium-N. These findings demonstrate that forest stand development shapes adaptive adjustments in absorptive root traits through soil-mediated trade-offs between resource acquisition and conservation, highlighting edaphic factors as key regulators of nutrient foraging strategies.