干旱-高钙对麻栎幼苗非结构性碳水化合物含量和分配的影响

土壤高钙胁迫是干旱-半干旱区影响树木生长的重要环境因子,为阐明干旱-高钙对树木非结构性碳水化合物(Non-structural carbohydrate,NSC)的含量和分配的影响,以麻栎幼苗为研究对象,阐明干旱和干旱-高钙条件对其生长、光合特征及非结构碳水化合物含量与分配的影响。结果表明:干旱显著降低麻栎幼苗生物量,而干旱-高钙处理较干旱进一步降低了麻栎生物量;干旱-高钙在处理初期就能显著抑制麻栎幼苗净光合速率,处理3个月后干旱和干旱-高钙处理的麻栎幼苗光合速率均显著低于对照;干旱处理麻栎幼苗平均非结构性碳水化合物含量增加19.90%,干旱-高钙处理麻栎幼苗整株的平均NSC含量则显著降低25.62%;干旱和干旱-高钙对麻栎幼苗NSC在不同器官间分配也产生不同影响,干旱条件下麻栎幼苗茎中NSC含量增加最多,较对照增加了52.34%,且淀粉的增高幅度(61.94%)高于可溶性糖(25.53%),干旱、高钙共同作用下麻栎幼苗全株平均NSC含量显著减少的同时,NSC积累在叶中,叶NSC含量显著提高32.31%,根、茎中NSC含量则分别显著降低了49.38%和35.31%。干旱-高钙胁迫降低麻栎幼苗NSC含量,且会减少NSC向枝干和根系分配。

Effects of drought-high calcium on non-structural carbohydrate contents of Quercus acutissima

Forest decline in semiarid regions presents a serious ecological threat worldwide. However, the physiological mechanisms of forest trees for surviving in drought conditions are poorly understood. In recent years, the carbon starvation hypothesis has become a research hotspot in physiological processes of trees in drought conditions. Stored non-structural carbohydrates (NSC) could play an important role in tree survival in the face of drought conditions. It has been observed that the NSC concentration of treesvaries under drought conditions. Some studies have suggested that trees close their stomata to prevent hydraulic failure under drought conditions, causing the photosynthetic carbon uptake to decrease, which results in a negative carbon balance, while other studies have shown that trees can maintain the carbon balance and improve NSC storage under drought conditions using certain ecological strategies such as reducing their growth. High calcium is a key characteristic of the calcic horizon, which is widely distributed and considered an important factor affecting tree growth in semiarid areas. Meanwhile, calcium is a key signal substance regulating stomatal closure. Research on the combined effect of high calcium content and drought on carbon balance in trees should deepen the understanding of physiological mechanisms of trees inhabiting semiarid regions. In this study, we proposed two hypotheses: (1) The combined effects of drought and high calcium (drought-high calcium) would significantly reduce the NSC concentration compared with drought conditions alone; (2) These combined effects could alter the distribution of the NSC in different plant tissues and exacerbate the effect of negative carbon balance on trees. To test our hypotheses, we took Quercus acutissima which was not only one of the dominant species of natural forests but also an important afforestation species as experiment material. Then we investigated biomass, photosynthetic characteristics, and NSC concentration in different tissues under drought and drought-high calcium conditions. The results showed that drought stress significantly reduced the biomass of Q. acutissima when compared with the control group not subjected to drought stress, while drought-high calcium stress further reduced Q. acutissima biomass and this decrease was significant when compared with that under drought conditions. Drought-high calcium conditions could significantly decrease the net photosynthetic rate of Q. acutissima seedlings at the early stage of treatment. Photosynthetic rate of Q. acutissima seedlings under drought and drought-high calcium conditions were significantly lower than that of control seedlings after three months, and no difference was observed between the effects of drought and drought-high calcium conditions on photosynthetic rates of seedlings. Drought conditions significantly increased NSC concentration in all tissues of Q. acutissima seedlings, while drought-high calcium conditions significantly reduced the average NSC concentration. Drought and drought-high calcium conditions had different effects on the allocation of NSC to different tissues of Q. acutissima seedlings. Stem was the main tissue for Q. acutissima seedlings to store the increasing NSC under drought conditions in which stem NSC concentration was 52.34% higher than that of control seedlings, and the increase in starch concentration (61.94%) was higher than the increase in soluble sugar concentration (25.53%). Under the combined effects of drought and high calcium content, NSC concentration increased by 32.31% in leaves, but decreased by 49.38% in roots and by 35.31% in stems of Q. acutissima seedlings. We conclude that the combined drought and high calcium conditions decreased NSC concentration in trees as well as their allocation to the stem and root.