Responses of biomass and non-structural carbohydrates to soil moisture gradient of two Carex species in an alpine meadow in Southeast Qinghai-Xizang Plateau

Changes in soil moisture content affect the variations in biomass and non-structural carbohydrates (NSC) in plants; different species may have different response strategies. In the alpine meadow of Dongda Mountain in Southeast Qinghai-Xizang Plateau, five quadrats were set up respectively along the soil moisture gradient which evolved from the drought habitat near the alpine screes to the wet habitat in the ravine. According to the natural distribution pattern of the two Carex populations, C. parvula and C. alatauensis are co-dominant species in this region. Root biomass constituted the greatest proportion of total biomass of two Carex species. The root biomass of C. alatauensis, stem biomass of C. parvula and leaf, above-ground, below-ground and whole plant biomass of two species all increased with the increase of soil moisture content (P < 0.05). The NSC, soluble sugar (SS) and starch concentrations in roots of C. parvula all increased with the increase of soil moisture content (P < 0.05), but those in roots of C. alatauensis reached an optimum, and then declined with the increase of soil moisture content (P < 0.05). The NSC and SS concentrations in stems and leaves of C. parvula reached an optimum, and then declined with the increase of soil moisture content respectively (P < 0.01), but those of C. alatauensis declined first, and then increased with the increase of soil moisture content (P < 0.05). The dry matter (DM) allocation of NSC in leaves of both species was the lowest, and the DMNSC, DMSS and DMstarch in organs and whole plant all increased with the increase of soil moisture content (P < 0.05), except those in roots and leaves of C. alatauensis. The SS concentration and DMstarch in roots of C. parvula and those in leaves of C. alatauensis were the main contributors of the two species to combat soil moisture changes. Both species kept the highest biomass allocation in roots and increased SS/Starch in leaves to adapt to drought habitat. In conclusion, the asymmetric responses of biomass and NSC in organs were exhibited to adapt to soil moisture changes in an alpine meadow. The variations and allocation patterns between two Carex species in an alpine meadow in Southeast Qinghai-Xizang Plateau and soil moisture content differ in biomass and non-structural carbohydrates.