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Understanding the impacts of global warming on keystone species is fundamental to addressing the threat of climate change to biodiversity. Understory bamboo species play a crucial role in many forest ecosystems and provide food and shelter for numerous animals, including the giant panda (Ailuropoda melanoleuca). While previous studies projected that global warming would cause substantial shrinkage of bamboo distribution and threaten giant pandas, substantial uncertainties persist due to an incomplete understanding of the impacts of warmer temperatures on both the quantity and quality of bamboo as the food source for giant pandas. To address this research gap, we conducted the first field experiment in giant panda habitats to assess the impacts of warmer temperatures on the population dynamics and dietary quality of arrow bamboo, a main food source of giant pandas. We observed that warming generated a nonlinear impact on bamboo survival, with a potential warming threshold between 1.5 °C and 3 °C, beyond which warmer temperatures substantially reduced the survival rate of bamboo. Additionally, our plant content analysis showed that warmer temperatures lowered bamboo's nutritional value but enhanced its palatability as food for giant pandas. Furthermore, we found that warming could jeopardize the bamboo food supply for giant pandas by intensifying aphid infections in bamboo. These findings advanced the understanding of food web dynamics under global warming and provided crucial information for effective giant panda conservation planning in the face of climate change. • Warming generated a nonlinear impact on the survival of arrow bamboo. • Warming lowered bamboo's nutritional value but enhanced its palatability to pandas. • Warming jeopardized pandas' food supply by intensifying aphid infections in bamboo. [ABSTRACT FROM AUTHOR]

The giant panda, a strict herbivore that feeds on bamboo, still retains a typical carnivorous digestive system. Reference catalogs of microbial genes and genomes are lacking, largely limiting the antibiotic resistome and functional exploration of the giant panda gut microbiome. Here, we integrated 177 fecal metagenomes of captive and wild giant pandas to construct a giant panda integrated gene catalog (GPIGC) comprised of approximately 4.5 million non-redundant genes and reconstruct 393 metagenome-assembled genomes (MAGs). Taxonomic and functional characterization of genes revealed that the captivity of the giant panda significantly changed the core microbial composition and the distribution of microbial genes. Higher abundance and prevalence of antibiotic resistance genes (ARGs) were detected in the guts of captive giant pandas, and ARG distribution was influenced by geography, for both captive and wild individuals. Escherichia, as the prevalent genus in the guts of captive giant pandas, was the main carrier of ARGs, meaning there is a high risk of ARG transmission by Escherichia. We also found that multiple mcr gene variants, conferring plasmid-mediated mobile colistin resistance, were widespread in the guts of captive and wild giant pandas. There were low proportions of carbohydrate-active enzyme (CAZyme) genes in GPIGC and MAGs compared with several omnivorous and herbivorous mammals. Many members of Clostridium MAGs were significantly enriched in the guts of adult, old and wild giant pandas. The genomes of isolates and MAGs of Clostridiaceae harbored key genes or enzymes in complete pathways for degrading lignocellulose and producing short-chain fatty acids (SCFAs), indicating the potential of these bacteria to utilize the low-nutrient bamboo diet. Overall, our data presented an exhaustive reference gene catalog and MAGs in giant panda gut and provided a comprehensive understanding of the antibiotic resistome and microbial adaptability for a high-lignocellulose diet. [Display omitted] • Captivity of giant panda changed the composition and diversity of gut microbiome. • Lifestyle and geography influenced on ARGs abundance and distribution, respectively. • Escherichia was the main carrier of ARGs in the guts of captive giant pandas. • Clostridium harbored key genes in metabolisms of lignocellulose. [ABSTRACT FROM AUTHOR]