Alpine climate alters the relationships between leaf and root morphological traits but not chemical traits.

Leaves and fine roots are among the most important and dynamic components of terrestrial ecosystems. To what extent plants synchronize their resource capture strategies above- and belowground remains uncertain. Existing results of trait relationships between leaf and root showed great inconsistency, which may be partly due to the differences in abiotic environmental conditions such as climate and soil. Moreover, there is currently little evidence on whether and how the stringent environments of high-altitude alpine ecosystems alter the coordination between above- and belowground. Here we measured six sets of analogous traits for both leaves and fine roots of 139 species collected from Tibetan alpine grassland and Mongolian temperate grassland. N, P and N:P ratio of leaves and fine roots were positively correlated, independent of biogeographic regions, phylogenetic affiliation or climate. In contrast, leaves and fine roots seem to regulate morphological traits more independently. The specific leaf area (SLA)-specific root length (SRL) correlation shifted from negative at sites under low temperature to positive at warmer sites. The cold climate of alpine regions may impose different constraints on shoots and roots, selecting simultaneously for high SLA leaves for rapid C assimilation during the short growing season, but low SRL roots with high physical robustness to withstand soil freezing. In addition, there might be more community heterogeneity in cold soils, resulting in multidirectional strategies of root in resource acquisition. Thus our results demonstrated that alpine climate alters the relationships between leaf and root morphological but not chemical traits.