Effect of aridity and soil texture the profile pattern of soil C:N:P stoichiometry in Tibetan alpine grasslands

Responses of soil carbon (C), nitrogen (N) and phosphorus (P) dynamics are closely related to aridity and soil texture. However, how aridity and texture influence the C:N:P stoichiometry of different soil layers in alpine ecosystems has not been examined. Here, we conducted soil sampling across a 1600-km transect to examine the regional profile pattern of soil C:N:P ratios with changes in aridity and soil texture based on observations from 20 sites on the Tibetan Plateau. The C:N and N:P ratios increased and decreased with soil depth, respectively, while the C:P ratios showed no significant changes with soil depth. The C:N ratios first decreased and then increased with increasing aridity index (AI) for the surface soil layers, while in deep soils, C:N ratios showed a negative relationship with increasing AI. The C:P ratios in bulk soils and all fractions significantly increased with increasing AI for the surface soil layers, but first increased and then decreased with increasing AI in the deep soil layers. N:P ratios in bulk soils and all fractions were positively related to increasing AI along the transect, but the growth rate slowed in wetter areas with a threshold at an AI value of 0.2. Across the transect, C:N ratios in bulk soils were positively related to clay contents in all soil layers, while N:P ratios in bulk soils were positively related to clay contents only in deep soil layers. C:P ratios and N:P ratios in bulk soils were negatively related to sand contents across most and across all soil layers. Generally, aridity played a more important role than soil texture in driving variations in soil C:N:P ratios along the transect. Our results highlight the role of aridity and soil texture in driving the stoichiometric flexibility of soil C:N:P ratios depending on soil layers in alpine grasslands.