Abstract
Carbon assimilation is reduced by stress. Under such conditions, the trade-off between growth and non-structural carbohydrate (NSC) storage becomes crucial for plant survival and continued growth. However, growth and NSC responses to drought and shading in Pinus massoniana Lamb. remain unclear. Here, we investigated the effects of drought, shading, and combined drought and shading on leaf gas exchange parameters, stem basal diameter, plant height, biomass accumulation, and NSC concentration in 2-year old seedlings after a 2 month treatment. The results showed that (1) both drought and shading significantly reduced photosynthetic rate, increment of stem basal diameter and plant height, and biomass accumulation, while NSC concentration increased under drought but decreased under shading; (2) the combined drought-shading treatment had a stronger effect on photosynthetic rate and growth than either stress factor individually, whereas the concentration of NSC did not change significantly; and (3) drought, shading, and their combination had a lower effect on biomass than on NSC partitioning, in which case clear effects were observed. Drought increased NSC proportion in roots by 5.4%; conversely, shading increased NSC proportion in leaves by 3.7%, while the combined treatment increased NSC proportion in roots by 5.1% but decreased it in the leaves by 5.4%. These results suggest that the mechanism inhibiting P. massoniana growth is different under drought and shading conditions according to carbon partitioning. Furthermore, complex environmental stress may lead to different mechanisms of carbon partitioning compared with either dry or shaded environments. Our findings will be helpful in predicting the impact of climate change on P. massoniana growth.
Highlights
Water and light are important environmental factors that influence plant growth
Photosynthetic rate tended to decrease significantly under both drought and shading (Figure 1). These findings indicated that the trade-off between plant growth and non-structural carbohydrate (NSC) storage remained different when carbon supply was limited by drought or shading conditions
Storage of NSC prevents carbohydrate depletion and acute carbon starvation [61]; this is a reliable “conservative” mechanism when P. massoniana experiences drought stress. Under shading, both growth and NSC storage were restricted by the shortage of carbon supply, as respiratory losses were higher in shaded than in unshaded leaves [62], and relatively more carbon were incorporated into structural components [63], which was likely responsible for the slight increase in carbon partitioning to plant growth over NSC storage
Summary
The irregular distribution of precipitation and variable light conditions often cause drought and shading stress [1,2], thereby limiting growth [3,4,5,6,7]. Plants can alter their biomass distribution to improve their ability to capture resources and mitigate the damage caused by environmental stress [8,9,10]. Biomass partitioning varies greatly among different plant species [18,19,20]
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