Divergent responses of nutrient biogeographical patterns in different shrub types across the arid region of Qinghai-Tibet Plateau.

BACKGROUND

The arid region of the Qinghai-Tibet Plateau has a harsh natural environment that spans a vast altitudinal range, where plant growth suffers from various environmental stresses such as low temperature and drought. Shrubs are one of the most important plant functional groups in this region, and different shrub types have developed various nutrient strategies in response to these environmental stresses. However, nutrient characteristics and biogeographical patterns in different shrub types have seldom been investigated. The aboveground concentrations of carbon (C), nitrogen (N), and phosphorus (P) of the three shrub types (leaf-normal, leaf-reduced, and succulent shrubs) and soil physicochemical properties were measured in 138 sampling sites in the arid region of the Qinghai-Tibet Plateau.

RESULTS

Mean C, N, and P concentrations in all shrubs were 382.09 mg/g, 24.63 mg/g, and 1.43 mg/g in the arid region of the Qinghai-Tibet Plateau. Mean C, N, and P concentrations were 347.64, 24.30, and 1.25 mg/g in succulent shrubs, which were significantly lower than those of leaf-normal shrubs (C: 418.43 mg/g; N: 24.57 mg/g; P: 1.55 mg/g) and leaf-reduced shrubs (C: 399.71 mg/g; N: 25.96 mg/g; P: 1.65 mg/g). With increasing in longitude, C, N, and P concentrations in leaf-normal and leaf-reduced shrubs increased but these nutrients in succulent shrubs decreased. Increasing altitude only increased N and P concentrations for leaf-normal shrubs. These results demonstrated that the three shrub types had divergent nutrient biogeographical patterns. N and P concentrations of leaf-normal and leaf-reduced shrubs were directly driven by soil total N and total P concentrations and indirectly regulated by mean annual temperature and mean annual precipitation, promoting the formation of longitude or altitude nutrient patterns. Meanwhile, N and P concentrations in succulent shrubs were only regulated by soil pH, total N, and total P concentrations, driving the formation of longitude nutrient patterns. These results indicated divergent driving factors for nutrient biogeographical patterns among the three shrub types.

CONCLUSIONS

Our study highlights the unique nutrient characteristics of succulent shrubs, reveals driving factors of nutrient biogeographical patterns in the three shrub types, and contributes to the understanding of biogeochemical cycling in arid ecosystems.