ObjectiveThis study aims to identify leaf functional trait variation patterns and differences of Cotinus coggygria seedlings from different locations and to analyse the influences of different geographic-climatic factors on leaf functional trait variations under continuous drought environment.
MethodA standard continuous drought stress experiment was carried out using one-year-old C. coggygria seedlings from five different locations within China. Three levels of water regimes were set: control (CK, 75% ~ 80% of soil field capacity), moderate stress (MS, 55% ~ 65% of soil field capacity) and severe stress (SS, 35% ~ 45% of soil field capacity). ANOVA was used to identify the effects of drought, location and their interaction on leaf functional traits. On the other hand, the principal component analysis (PCA) and the redundancy analysis (RDA) were used to measure the relationship between location distribution of the species and the geographical-climatic factors and the influences of geographical-climatic conditions on leaf functional trait variation degree (TVD), respectively.
Result(1) Drought stress had significant effects on all the leaf functional traits. Seedlings under SS had lower leaf function traits in terms of leaf chlorophyll content (LChl, 17.61%, P < 0.001), relative water content (RWC, 3.71%, P < 0.001), specific leaf area (SLA, 10.89%, P = 0.002), and leaf area ratio (LAR, 17.22%, P = 0.001) compared to the seedlings under CK. However, seedlings under SS had higher leaf dry matter content (LDMC) and leaf density (LD) than control by 9.04% (P < 0.001) and 14.52% (P = 0.009), respectively. (2) Correlations among leaf functional traits became stronger in drought environment, which showed that SLA had significantly (P < 0.01) negative links with LDMC and LD, LDMC and LD had a significant (P < 0.01) and positive relation, and RWC had significantly positive correlations with LChl (P < 0.01), SLA (P < 0.01) and LAR (P < 0.05). (3) The leaf functional traits showed significant differences among C. coggygria locations under drought treatments. SLA (P = 0.002), LChl (P = 0.025) and LD (P = 0.026) were significantly different under MS treatment, and LChl (P < 0.001), LAR (P < 0.001) and RWC (P = 0.005) were significantly different under SS treatment. (4) Among the five different locations, C. coggygria seedlings from Yanqing County in Beijing had the highest average trait variation degree (the mean values of all trait variation degrees) of 17.57%, while the lowest was from Jiang County of Yuncheng City in Shanxi Province of 6.97%. (5) After the screening of RDA, precipitation of the driest month (DMP, P = 0.002), growing season mean monthly precipitation difference (GSPD, P = 0.008), Max. temperature of the warmest month (WMT, P = 0.016) and average annual precipitation (ANP, P = 0.036) had significant effects on leaf functional trait variation degree. Particularly, DMP had negative relationships with all trait variation degree, but had more significantly negative correlations with the variation degree of LDMC and LD. GSPD and ANP had significantly negative correlationss with the variation degree of SLA and LAR. WMT was closer to the variation degree of LChl.
ConclusionSignificant differences were found for leaf functional traits of C. coggygria among different drought treatments and different locations. The local climate (especially DMP, GSPD, WMT and ANP) was the main cause of leaf functional trait variation of C. coggygria from different locations under drought stress. Among seedlings from the five locations explored in our study, seedlings from Jiang County of Yuncheng City in Shanxi Province were more suitable to be introduced to the arid areas in northern China, as a result of a relatively high DMP, a proper GSPD and ANP, a relatively low WMT, and a low average leaf functional trait variation degree under drought stress.
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