Plant growth is mainly N‐limited in the alpine grasslands because of slow mineralization of soil organic matter due to low air temperature. Different plant species dominate in soils of different N concentrations. For example, more forbs occur in severely degraded alpine meadows than do sedges and Gramineae. We hypothesized that a more efficient uptake of low soil N by forbs than by sedges and Gramineae was the mechanism that allowed forbs to dominate. The amount and rate of soil N uptake and N allocation were determined in seven dominant alpine plant species using ¹⁵N isotope tracer. The plants, which included one forb, Ajania tenuifolia, three sedges, Kobresia humilis, Carex scabrirostris, and Carex enervis, and three Gramineae, Elymus nutans, Festuca sinensis, and Stipa purpurea, were maintained in pots with four different N concentrations (0, 50, 100, and 150 kg ha⁻¹). The forb had the highest efficiency of N utilization (N uptake rate, 60.4%) in low N soil concentration, the Gramineae had intermediate efficiencies (27.9–47.9%), and the sedges had the lowest efficiencies (5.2–34.9%), and, consequently, our hypothesis was supported. N utilization of the seven species decreased with an increase in soil N concentration, from 32.1% at N50 to 18.0% at N150, which indicated that soil N uptake by plants was affected by soil N concentration. The mechanism used by forbs to be the dominant species in severely degraded alpine meadows was a more efficient utilization of soil N than Gramineae and sedges in conditions of low soil N. We concluded that plant species have different efficiencies in soil N uptake and utilization, which allow them to adapt and survive in habitats of different soil nutrition levels. These results implied that forbs should be reduced, and that Gramineae and sedges should be planted and N be added during the restoration and development of severely degraded grasslands on the Tibetan plateau when the soil N content is low.

中文翻译：

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jan，Ajania tenuifolia，有效利用土壤氮，使其在极度退化的草地上比莎草和禾本科植物更占优势：对青藏高原草地恢复和发展的意义

在高寒草原上，由于空气温度低，土壤有机物的矿化速度缓慢，植物的生长主要受N限制。不同植物物种在不同氮含量的土壤中占主导地位。例如，在严重退化的高山草甸中发生的草比莎草和禾本科植物更多。我们假设，相比于莎草和禾本科植物，前车更有效地吸收了低土壤氮，这是前车占主导地位的机制。使用¹⁵ N同位素示踪剂确定了7种主要高山植物物种的土壤氮吸收量和氮分配速率。这些植物包括一个forb，Ajania tenuifolia，三个莎草，Kobresia humilis，Carex scabrirostris和Carex enervis。和三个禾本科，披碱草，Festuca sinensis和紫花针茅在四个不同N浓度（0、50、100和150 kg ha ^-1的盆中）中^饲养。）。在低氮土壤浓度下，Forb具有最高的氮利用效率（氮吸收率，60.4％），禾本科具有中等效率（27.9–47.9％），而莎草的效率最低（5.2–34.9％），并且因此，我们的假设得到了支持。随着土壤氮浓度的增加，这七个物种的氮利用量从N50的32.1％降低到N150的18.0％，这表明植物对土壤N的吸收受到土壤N浓度的影响。在土壤低氮条件下，Forbs成为严重退化的高寒草甸优势种的机制是比禾本科植物和莎草更有效地利用土壤氮。我们得出结论，植物物种对土壤氮素的吸收和利用效率不同，这使他们适应并在不同土壤营养水平的生境中生存。