Effects of mixture of branch order-based roots and nitrogen addition on root decay in a subtropical pine plantation

Abstract

Non-additive effects may occur when branching order-based fine roots decompose in mixture, due to their distinct chemical composition. However, these effects and how they respond to increased nitrogen (N) availability are poorly known. We conducted a 524-day field litterbag experiment to examine the potential non-additive effects of orderbased fine root decomposition and their responses to different rates of N addition in a Pinus elliottii (slash pine) plantation in China. The intact fine roots of slash pine trees were hierarchically dissected and split into two groups (lower-order roots (the first and second order roots) and higher-order roots (the third to fifth order roots)). The decomposition of these two root groups was monitored either separately or in 1:1 mixture. The non-additive effects did not occur when the two root groups decomposed in mixture. However, high rate of N addition shifted the root group interactions from additive to synergistic effects through contrasting effects on individual root group (lower-order roots). High rate of N addition retarded the decomposition of lower-order roots more in isolation than in mixture, due to the decreased binding of acid-unhydrolyzable residue to inorganic N ions in mixture. Therefore, we suggest that although stoichiometric heterogeneity holds within the branching hierarchy of fine roots, the tight coupling of N with acid-unhydrolyzable residue of root tissues may limit N use by microdecomposers, and thereby causing the additive effect. Since the mixing effect of order-based root decomposition is affected by N addition, understanding the chemical heterogeneity within fine root systems and their linkage with ambient N availability during decomposition either in isolation or in mixture may facilitate the accurate prediction of root decomposition responses to N loading.

Are nitrate production and retention processes in subtropical acidic forest soils responsive to ammonium deposition?

“…fungal phenol oxidases and peroxidases of white-rot basidiomycetes) (Carreiro et al, 2000;Frey et al, 2004;Schimel and Bennett, 2004). Our previous field investigations have shown that fungal biomass and fungi to bacteria ratios (Wang et al, 2015) and decomposition of lower-order roots and needles (Kou et al, 2015a(Kou et al, , 2015b) exhibited a decreasing trend at high NH 4 þ additions. Moreover, long-term elevated N input has been found to enhance chemical stabilization of organic matter into recalcitrant compounds that are resistant to microbial decay (Neff et al, 2002;Swanston et al, 2004), thereby potentially impairing fungal metabolism (Maaroufi et al, 2015).…”

Adaptation Strategies of Seedling Root Response to Nitrogen and Phosphorus Addition

“…This effect is particularly noteworthy in acidic soils in subtropical regions of China [ 3 ]. In such soils, phosphorus tends to persist in an insoluble form through adsorption and fixation with substances like iron, aluminum, and soil clay [ 5 ]. Consequently, the conversion of inorganic phosphorus into insoluble phosphorus exacerbates the restriction of soil phosphorus on plant growth [ 3 , 5 ].…”

“…In such soils, phosphorus tends to persist in an insoluble form through adsorption and fixation with substances like iron, aluminum, and soil clay [ 5 ]. Consequently, the conversion of inorganic phosphorus into insoluble phosphorus exacerbates the restriction of soil phosphorus on plant growth [ 3 , 5 ]. As a dominant tree species in this region, C. kawakamii is also a rare and endangered evergreen broad-leaved tall tree unique to the southern edge of China’s central subtropical region, with a narrow natural distribution range [ 35 ].…”

“…Research has demonstrated that soil factors exert a significant influence on the root turnover process, encompassing growth and eventual death [4]. In response to changes in the soil environment, plants dynamically adjust their morphological structure and physiological activities, as evidenced by studies conducted by Kou et al [5] and Adams et al [6]. However, there are still many unresolved mysteries regarding how plant roots perceive and respond to changes under Plants 2024, 13, 536 2 of 14 different soil nutrient conditions [7].…”