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The intricate mechanisms controlling plant diversity and community composition are cornerstone of ecological understanding. Yet, the role of mycorrhizal symbiosis in influencing community composition has often been underestimated. Here, we use extensive species survey data from 1315 grassland sites in China to elucidate the influence of mycorrhizal symbiosis on plant phylogenetic diversity and community assembly. We show that increasing mycorrhizal symbiotic potential leads to greater phylogenetic dispersion within plant communities. Mycorrhizal species predominantly influence deterministic processes, suggesting a role in niche‐based community assembly. Conversely, non‐mycorrhizal species exert a stronger influence on stochastic processes, highlighting the importance of random events in shaping community structure. These results underscore the crucial but often hidden role of mycorrhizal symbiosis in driving plant community diversity and assembly. This study provides valuable insights into the mechanisms shaping ecological communities and the way for more informed conservation that acknowledges the complex interplay between symbiosis and community dynamics. [ABSTRACT FROM AUTHOR]

Climate projection requires an accurate understanding for soil organic carbon (SOC) decomposition and its response to warming. An emergent view considers that environmental constraints rather than chemical structure alone control SOC turnover and its temperature sensitivity (i.e., Q10), but direct long‐term evidence is lacking. Here, using compound‐specific radiocarbon analysis of soil profiles along a 3300‐km grassland transect, we provide direct evidence for the rapid turnover of lignin‐derived phenols compared with slower‐cycling molecular components of SOC (i.e., long‐chain lipids and black carbon). Furthermore, in contrast to the slow‐cycling components whose turnover is strongly modulated by mineral association and exhibits low Q10, lignin turnover is mainly regulated by temperature and has a high Q10. Such contrasts resemble those between fast‐cycling (i.e., light) and mineral‐associated slow‐cycling fractions from globally distributed soils. Collectively, our results suggest that warming may greatly accelerate the decomposition of lignin, especially in soils with relatively weak mineral associations. [ABSTRACT FROM AUTHOR]