The effects of defoliation on carbon allocation: can carbon limitation reduce growth in favour of storage?
The effects of defoliation on carbon allocation: can carbon limitation reduce growth in favour of storage?
复制标题
DOI：
10.1093/treephys/tpt093
复制
发表时间：
2013-11-01
期刊：
影响因子：
4
通讯作者：
Helliker, Brent R.
中科院分区：
文献类型：
--
作者：
Wiley, Erin;Huepenbecker, Sarah;Helliker, Brent R.
对于低水分和低温度等压力如何限制树木的生长，目前还没有达成共识。如果给定的压力没有导致非结构性碳水化合物(NSC)浓度或水平随着生长而下降，则通常可以推断出库容量对生长和生存的限制。然而，在适度的碳胁迫下，树木可以积极地维持或增加NSC水平，使生长减少而NSC增加的模式与碳限制相一致。为了测试这种可能性，我们使用完全和一半的落叶来对2年生的绒毛栎施以严重和中等的碳限制。在普通花园里生长的树苗。树苗在处理后3周或4个月收获，代表了对木本植物生长和NSC水平的短期和长期影响。在整个试验过程中，两种去叶处理的总叶面积都低于对照，没有光合作用上调的证据，总生物量也有类似的下降。在短期内，完全落叶的树苗的淀粉水平低于对照，而半落叶的树苗在短期和长期内都保持着控制的淀粉水平。从长期来看，完全落叶的幼树具有最大的淀粉浓度增量，使它们能够恢复到接近控制的淀粉水平。此外，在两个采收期之间，完全落叶和半落叶幼树分配给淀粉的新生物量比例高于对照。半落叶幼树的控制淀粉水平的维持表明，在生长达到碳饱和之前，这些树活跃地储存了大量的碳。此外，有利于在落叶树苗中储存的分配转变与这样的假设一致，即作为对日益增加的碳胁迫的适应，树木可以优先考虑碳储备的形成，而不是以生长为代价。我们的结果表明，随着碳限制的增加，增长放缓并不一定伴随着NSC浓度的下降。因此，缺乏NSC下降可能不是寒冷或水分胁迫下树木生长减慢的证据，这是由于库限制造成的。
There is no consensus about how stresses such as low water availability and temperature limit tree growth. Sink limitation to growth and survival is often inferred if a given stress does not cause non-structural carbohydrate (NSC) concentrations or levels to decline along with growth. However, trees may actively maintain or increase NSC levels under moderate carbon stress, making the pattern of reduced growth and increased NSCs compatible with carbon limitation. To test this possibility, we used full and half defoliation to impose severe and moderate carbon limitation on 2-year-old Quercus velutina Lam. saplings grown in a common garden. Saplings were harvested at either 3 weeks or 4 months after treatments were applied, representing short- and longer-term effects on woody growth and NSC levels. Both defoliation treatments maintained a lower total leaf area than controls throughout the experiment with no evidence of photosynthetic up-regulation, and resulted in a similar total biomass reduction. While fully defoliated saplings had lower starch levels than controls in the short term, half defoliated saplings maintained control starch levels in both the short and longer term. In the longer term, fully defoliated saplings had the greatest starch concentration increment, allowing them to recover to near-control starch levels. Furthermore, between the two harvest dates, fully and half defoliated saplings allocated a greater proportion of new biomass to starch than did controls. The maintenance of control starch levels in half defoliated saplings indicates that these trees actively store a substantial amount of carbon before growth is carbon saturated. In addition, the allocation shift favouring storage in defoliated saplings is consistent with the hypothesis that, as an adaptation to increasing carbon stress, trees can prioritize carbon reserve formation at the expense of growth. Our results suggest that as carbon limitation increases, reduced growth is not necessarily accompanied by a decline in NSC concentrations. Therefore, a lack of NSC decline may not be evidence that reduced tree growth under cold or water stress is caused by sink limitation.