Aaltonen Heidi, Lindén Aki, Heinonsalo Jussi, Biasi Christina, Pumpanen Jukka
Department of Forest Sciences, University of Helsinki, PO Box 27, 00014 Helsinki, Finland.
Department of Food and Environmental Sciences, University of Helsinki, PO Box 56, 00014 Helsinki, Finland.
Tree Physiol. 2017 Apr 1;37(4):418-427. doi: 10.1093/treephys/tpw119.
As the number of drought occurrences has been predicted to increase with increasing temperatures, it is believed that boreal forests will become particularly vulnerable to decreased growth and increased tree mortality caused by the hydraulic failure, carbon starvation and vulnerability to pests following these. Although drought-affected trees are known to have stunted growth, as well as increased allocation of carbon to roots, still not enough is known about the ways in which trees can acclimate to drought. We studied how drought stress affects belowground and aboveground carbon dynamics, as well as nitrogen uptake, in Scots pine (Pinus sylvestris L.) seedlings exposed to prolonged drought. Overall 40 Scots pine seedlings were divided into control and drought treatments over two growing seasons. Seedlings were pulse-labelled with 13CO2 and litter bags containing 15N-labelled root biomass, and these were used to follow nutrient uptake of trees. We determined photosynthesis, biomass distribution, root and rhizosphere respiration, water potential, leaf osmolalities and carbon and nitrogen assimilation patterns in both treatments. The photosynthetic rate of the drought-induced seedlings did not decrease compared to the control group, the maximum leaf specific photosynthetic rate being 0.058 and 0.045 µmol g-1 s-1 for the drought and control treatments, respectively. The effects of drought were, however, observed as lower water potentials, increased osmolalities as well as decreased growth and greater fine root-to-shoot ratio in the drought-treated seedlings. We also observed improved uptake of labelled nitrogen from soil to needles in the drought-treated seedlings. The results indicate acclimation of seedlings to long-term drought by aiming to retain sufficient water uptake with adequate allocation to roots and root-associated mycorrhizal fungi. The plants seem to control water potential with osmolysis, for which sufficient photosynthetic capability is needed.
随着预计干旱发生次数会随着气温升高而增加，人们认为北方森林将特别容易受到因水分胁迫、碳饥饿以及随之而来的易受虫害影响而导致的生长减缓及树木死亡率增加的影响。尽管已知受干旱影响的树木生长受阻，且碳向根部的分配增加，但对于树木适应干旱的方式仍知之甚少。我们研究了干旱胁迫如何影响暴露于长期干旱的苏格兰松（Pinus sylvestris L.）幼苗的地下和地上碳动态以及氮吸收。在两个生长季节中，总共40株苏格兰松幼苗被分为对照和干旱处理组。用13CO2对幼苗进行脉冲标记，并使用装有15N标记根生物量的凋落物袋来追踪树木的养分吸收。我们测定了两种处理下的光合作用、生物量分布、根和根际呼吸、水势、叶片渗透压以及碳和氮同化模式。与对照组相比，干旱处理的幼苗光合速率并未降低，干旱处理组和对照组的最大叶片比光合速率分别为0.058和0.045 μmol g-1 s-1。然而，干旱的影响表现为干旱处理幼苗较低的水势、增加的渗透压、生长减缓以及更高的细根与地上部分比值。我们还观察到干旱处理幼苗从土壤到针叶对标记氮的吸收有所改善。结果表明，幼苗通过将足够的水分吸收分配到根部及与根相关联的菌根真菌来适应长期干旱。植物似乎通过渗透作用来控制水势，而这需要足够的光合能力。
