Synergistic effects of drought and shade on component morphology and biomass allocation of Arthraxon hispidus

In this study, we examined the effects of drought and shade on wild Arthraxon hispidus. We set up 20 treatments using interactive combinations with five shade gradients (0, 10%, 30%, 50%, and 70%) and four drought gradients . The purpose was to analyze the synergistic effect of shade and drought on component form and biomass accumulation and allocation of A. hispidus. The results showed that shade, drought and their interaction all had significant effects on component form(P0.05). Drought had greater effects on roots than on stems and leaves, but shade had the opposite effect. Their interaction had greater effects on leaves than on roots and stems. Under the condition of moderate or severe drought (W2 or W3), leaf traits, internode lengths and number of branches was significantly reduced (P＜0.05). Root length significantly increased but the number of aerial roots decreased. Shade ≥10% decreased leaf number per plant, number of nodes, root length and the number of aerial roots but plant height increased. The interactive effect of W1×70% shade decreased leaf number by 66.94%, and increased plant height and internodes length by 86.11% and 46.17%. The interactive effect of W3×70% shade decreased node number, primary branch number and root number by 62.43%, 76.47% and 54.55%, respectively; no aerial roots were found. Shade, drought and their interaction all had significant effects on biomass accumulation and allocation (P0.05). Drought significantly reduced biomass per plant, stem and leaf biomass and allocation ratio of biomass. Under W3, biomass per plant and component biomass all decreased by about 50%, in which stem biomass increased to escape from severe drought. Shade ≥30% significantly increased leaf biomass but decreased root biomass. Under the condition of 50% shade, the distribution ratios of root and root∶shoot decreased by 81.48% and 86.79%, respectively. The interactive effect of drought and shade could offset or delay unbalanced growth caused by drought or shade. A. hispidus might adjust growth strategies by changing the quantity and quality traits of components and biomass allocation under drought or shade conditions. The synergistic effect of drought and shade enhanced resistance and adaptability of A. hispidus.