Biomass allocation is a key factor in understanding how ecosystems respond to changing environmental conditions. The role of soil chemistry in the above‐ and belowground plant biomass allocation in restoring grassland is still incompletely characterized. Consequently, it has led to two competing hypotheses for biomass allocation: optimal partitioning, where the plants allocate biomass preferentially to optimize resource use; and the isometric hypothesis, which postulates that biomass allocation between roots and shoots is fixed. Here we tested these hypotheses over a chronosequence of alpine grasslandsion undergoing restoration in the Qinghai‐Tibetan Plateau, these range from severely degraded to those with 18 years of revegetation with an intact grassland (as a reference). A high proportion of biomass was allocated to the roots in the revegetated grasslands, and more biomass to shoots in the degraded and intact grasslands. The grasslands gradually decreased their root to shoot ratio as revegetation continued, with the lowest value in year 18 of revegetation. Our results showed that aboveground biomass (AGB) was increased by available phosphorus (P), soil moisture, and negatively related to bulk density, while belowground biomass (BGB) was positively impacted by total P and negatively by nitrate nitrogen (N). The trade‐off between them was positively associated with available P and nitrate‐N, and soil nutrient availability is more linked to increased AGB relative to BGB. Our study indicates that biomass allocation is highly variable during the revegetation period from degraded grassland, and is linked with soil properties, thus supporting the optimal partitioning hypothesis.

中文翻译：

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青藏高原时间序列植物生物量分配及其驱动因子

生物量分配是了解生态系统如何响应不断变化的环境条件的关键因素。在恢复草地中，土壤化学在地上和地下植物生物量分配中的作用仍不完全清楚。因此，它导致了生物质分配的两个相互竞争的假设：最佳分配，即植物优先分配生物质以优化资源利用的最佳分配；而等距假设则假设根与芽之间的生物量分配是固定的。在这里，我们在青藏高原经历恢复的高寒草地的时间序列上检验了这些假设，从严重退化的草地到具有完整草地的18年植被恢复的草地（作为参考）。高比例的生物量分配给了植被恢复的草原的根部，而更多的生物量分配给了退化和完整草原的枝条。随着植被的恢复，草原的根冠比逐渐降低，在植被恢复的第18年最低。我们的结果表明，地上生物量（AGB）受有效磷（P），土壤水分的影响而增加，与容重负相关，而地下生物量（BGB）受总P量正影响，而硝态氮（N）负影响。它们之间的权衡与有效磷和硝态氮呈正相关，并且土壤养分的有效性与相对于BGB的AGB的增加更为相关。我们的研究表明，在退化草地的植被恢复期间，生物量分配变化很大，