Robinson David, Peterkin John Henry
School of Biological Sciences, University of Aberdeen, Aberdeen AB24 3UU, UK.
School of Biological Sciences, University of Portsmouth, Portsmouth PO1 2DY, UK.
Plants (Basel). 2019 Jul 10;8(7):212. doi: 10.3390/plants8070212.
We quantified how root-shoot biomass allocation and whole-plant growth rate co-varied ontogenetically in contrasting species in response to cooling. Seven grass and four forb species were grown for 56 days in hydroponics. Growth was measured repeatedly before and after day/night temperatures were reduced at 28 days from 20 °C/15 °C to 10 °C/5 °C; controls remained unchanged. Sigmoid trajectories of root and shoot growth were reconstructed from the experimental data to derive continuous whole-plant relative growth rates (RGRs) and root mass fractions (RMFs). Root mass fractions in cooled plants generally increased, but this originated from unexpected and previously uncharacterised differences in response among species. Root mass fraction and RGR co-trajectories were idiosyncratic in controls and cooled plants. The RGR-RMF co-trajectories responded to cooling in grasses, but not forbs. The RMF responses of stress-tolerant grasses were predictably weak but projected to eventually out-respond faster-growing species. Sigmoid growth constrains biomass allocation. Only when neither root nor shoot biomass is near-maximal can biomass allocation respond to environmental drivers. Near maximum size, plants cannot adjust RMF, which then reflects net above- and belowground productivities. Ontogenetic biomass allocations are not equivalent to those based on interspecific surveys, especially in mature vegetation. This reinforces the importance of measuring temporal growth dynamics, and not relying on "snapshot" comparisons to infer the functional significance of root-shoot allocation.
我们量化了在应对降温时，不同物种的根-茎生物量分配和整株植物生长速率如何在个体发育过程中共同变化。7种草和4种非禾本科草本植物在水培条件下生长56天。在第28天，昼夜温度从20℃/15℃降至10℃/5℃之前和之后，反复测量生长情况；对照组保持不变。根据实验数据重建根和茎生长的S形轨迹，以得出连续的整株植物相对生长速率（RGR）和根质量分数（RMF）。降温处理的植物根质量分数通常会增加，但这源于物种间意想不到的、先前未被描述的反应差异。在对照组和降温处理的植物中，根质量分数和RGR的共同轨迹是特异的。RGR-RMF共同轨迹在草类植物中对降温有反应，但在非禾本科草本植物中没有。耐胁迫草类植物的RMF反应预计较弱，但预计最终会超过生长较快的物种。S形生长限制了生物量分配。只有当根和茎生物量都未接近最大值时，生物量分配才能对环境驱动因素做出反应。在接近最大尺寸时，植物无法调整RMF，此时RMF反映了地上和地下的净生产力。个体发育过程中的生物量分配与基于种间调查的分配不同，尤其是在成熟植被中。这强化了测量时间生长动态的重要性，而不是依赖“快照”比较来推断根-茎分配的功能意义。
