Delicate Trade-Offs: Nonlinear Multiple Biotic Constraints on Absorptive Fine Root Lifespan Across Trees

Root lifespan is crucial for predicting carbon and nutrient cycling. While economic theories suggest root construction cost primarily determines root lifespan, the role of extrinsic biotic factors remains unexplored. We analysed 61,221 images from a subtropical common garden to quantify 21 factors influencing root lifespan across 16 tree species and developed a comparable global absorptive root lifespan dataset across biomes. Absorptive root lifespan in subtropical trees spanned 91 to 545 days, shorter than that in boreal forest. Root nitrogen concentration explained most of the variation (45%) in root lifespan, while phytopathogenic fungi, bacteria and herbivorous nematodes accounted for 36%. These three extrinsic biotic factors showed significant non-linear negative relationships with root lifespan. Interestingly, pathogenic microorganisms (28%) affected root lifespan more strongly than herbivorous nematodes (8%). These findings fill a gap in understanding root lifespan in subtropical forests and provide a holistic view of how multiple biotic factors shape it.