Effects of fertilization on photosynthetic characteristics and growth of Coffea arabica L. at juvenile stage under drought stress
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Abstract
To understand the enhancing effects of nitrogen (N) and phosphorus (P) on drought resistance of Coffea arabica L. at juvenile stage, a pot experiment was conducted at the Division of Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Kunming, Yunnan Province, China. The experiment consisted of eighteen treatments (in 3 × 3 × 2 design) with three N rates N0 (0 g·plant-1), N1 (2.5 g·plant-1) and N2 (7.5 g·plant-1), three P rates P0 (0 g·plant-1), P1 (2.5 g·plant-1) and P2 (7.5 g·plant-1) and two water treatments (normal water supply and drought stress). To learn the effects of different fertilizer and water treatments on various coffee traits, we mainly investigated coffee leaf relative water content (LRWC), photosynthetic characteristics, chlorophyll content, morphology and biomass allocation. The results showed that LRWC, maximum net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), chlorophyll content, specific leaf area (SLA) and biomass allocation under drought stress were lower than those under normal water supply. Both N and P slowed down LRWC depression induced by drought stress. The LRWC of C. arabica under fertilizer treatments (both single applications of N1, P1 and P2 and combined applications of N1 with P1 or P2) exceeded 72%, and was significantly higher than that of non-fertilizer treatment (N0P0). Both N and P enhanced photosynthetic characteristics of C. arabica. The maximum Pn and water use efficiency (WUE) of fertilizer treatments (N0P1, N0P2 and N1P2) were significantly higher than those of other treatments. Pn of N0P1, N0P2 and N1P2 fertilizer treatments were 2.09 times, 2.09 times and 2.40 times that of N0P0 (non-fertilizer treatment), while the corresponding WUEs were 1.37 times, 1.46 times and 1.58 times that of N0P0. Compared with N0P0, both gs and Tr of fertilizer treatments increased obviously, but with no significant difference among treatments. N and P increased chlorophyll content of coffee leaves and eased chlorophyll degradation rate caused by drought stress. Moreover, combined application of N and P performed better than single application of N or P. The morphology and biomass allocation of C. arabica were obviously influenced by both N and P. And drought stress promoted the distribution of photosynthetic products to underground system, increasing root mass fraction (RMF) and root-to-shoot ratio (R/S), all fertilizer treatments had higher RMF and R/S under drought stress than under normal water supply. N0P1 and N0P2 had the largest RMF and R/S, followed by N1P2 treatment, and root dry weight of N1P2 under drought stress was bigger than under normal water supply. The findings demonstrated that both N and P fertilization were critical for improving drought-resistance of C. arabica at juvenile stage, and N1P2 was the optimum treatment for C. arabica.
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