Long-term warming compromises leaf physical traits involved with herbivore defense in subtropical forests

Abstract

Plant−herbivory interactions are traditionally expected to strengthen along warming temperature gradients. However, little is known about the impact of long−term warming on the forest leaf−level effects associated with herbivory. To address this gap, we simulated ecosystem warming by utilizing natural temperature variation along an altitudinal gradient using open-top chambers (OTCs), in which native forest tree species (Schima superba, Syzygium rehderianum, Machilas breviflora, and Itea chinensis) and soil were translocated from cooler high−elevation ecosystems (600 m) to warmer low−elevation ecosystems (300 and 30 m; +1℃ and +2℃, respectively), to investigate the effects of warming on leaf herbivory. After 12 years of ecosystem warming, +1℃ and +2℃ lead up to 10 % and 48 % increment in herbivory, respectively. Warming reduced leaf toughness and thickness while increasing leaf area, potentially weakening structural defenses. Warming also decreased lignin content and was associated with significant increases in herbivory, while changes in leaf chemistry were minor and had no detectable influence on herbivory. During the herbivory study period (Mar−Nov 2023) and relative to the control, a +2°C warming combined with +6% precipitation collectively enhanced herbivory. Our findings show that plants from higher elevation exhibit stronger leaf physical protective structures; however, these traits are reduced under long−term warming, thereby weaken leaf structural integrity and potentially influencing plant−herbivore dynamics. These findings enhance our understanding how warming could modify leaf structure and its relationship with herbivory in a subtropical forest ecosystem, thereby may improve predictions of potential ecological responses to future warming scenarios.