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 N
0 (0 g·plant
-1), N
1 (2.5 g·plant
-1) and N
2 (7.5 g·plant
-1), three P rates P
0 (0 g·plant
-1), P
1 (2.5 g·plant
-1) and P
2 (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 (P
n), stomatal conductance (g
s), transpiration rate (T
r), 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 N
1, P
1 and P
2 and combined applications of N
1 with P
1 or P
2) exceeded 72%, and was significantly higher than that of non-fertilizer treatment (N
0P
0). Both N and P enhanced photosynthetic characteristics of
C. arabica. The maximum
Pn and water use efficiency (WUE) of fertilizer treatments (N
0P
1, N
0P
2 and N
1P
2) were significantly higher than those of other treatments.
Pn of N
0P
1, N
0P
2 and N
1P
2 fertilizer treatments were 2.09 times, 2.09 times and 2.40 times that of N
0P
0 (non-fertilizer treatment), while the corresponding WUEs were 1.37 times, 1.46 times and 1.58 times that of N
0P
0. Compared with N
0P
0, 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. N
0P
1 and N
0P
2 had the largest RMF and R/S, followed by N
1P
2 treatment, and root dry weight of N
1P
2 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 N
1P
2 was the optimum treatment for
C. arabica.