Plant uptake of available N from different layers varies among species in an alpine meadow of permafrost regions on the Qinghai-Tibetan Plateau

Abstract

The uptake of permafrost thaw released nitrogen (N) could benefit plant growth and change vegetation community composition in a warming climate in cold regions. However, the capacity of co-existing species to take up different forms of available N beyond the root zone remains largely unknown in permafrost areas with a deep active layer. In situ ¹⁵NH₄Cl, K¹⁵NO₃ and C₂H₅NO₂ (glycine) labelling were conducted up to 70 cm depth for five species. Averaged across the five species, the summed ¹⁵N recovery rate of the three tracers was 10.71% ± 10.69%, 1.69% ± 2.51%, 1.54% ± 4.16% and 0.7% ± 2.23% at 0‒15, 15‒30, 30‒50 and 50‒70 cm, respectively. Kobresia humilis had the largest N uptake diversity. The NO₃^‒-N recovered from 30‒70 cm for K. humilis and Saussurea japonica was much higher than other species, accounting for 23% and 13% of the total N recovered at 0‒70 cm. Root surface area was positively related to the recovery rate of inorganic N at soil below 15 cm whereas a species’ N requirement negatively to the N recovery at 0‒15 cm. The relative cover of a species in a community was negatively related to a species’ N requirement but showed no relationship with the N recovery rate or N uptake diversity. Plant communitycomposition may not be affected by vertical N uptake patterns of co-existing species. Species that can take up N from deep soil layers may gain competitive advantages, thereby altering the plant community structure in a warm climate in the future.

Graphical abstract

Keywords

nitrogen uptake / ¹⁵N tracing / alpine meadow / permafrost / plant functional groups

Highlight

	● The N uptake of five common species from different soil depths in alpine meadow was investigated.
	● Plants primarily took up more than 75% from the top 15 cm.
	● The dominant sedge species and rare forbs species could take up N from soil as deep as 70 cm.
	● The N uptake capacity is unrelated with the relative coverage.

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