Simulation and analysis of pumpkin leaf growth-photosynthesis-yield relationship under water-fertilizer coupling by SEM

Pumpkin is an important cash crop in the northwestern arid region of China. Its yield is closely related to leaf growth and photosynthetic characteristics, which are nutritionally regulated by water-fertilizer coupling. Through a two year field experiment, the relationship between leaf growth, photosynthetic characteristics and yield under water-fertilizer coupling was analyzed. The results showed that leaf area index (LAI), soil and plant analyzer development value (SPAD), net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs) and yield all increased with increasing irrigation quota, and showed an increasing and then decreasing trend with increasing organic fertilizer application amount. Under F2W3 treatment (irrigation quota of 525 m(3)<middle dot>ha(-1) and total fertilization application of 5700kg<middle dot>ha(-1)), LAI, SPAD, Pn, Tr, Gs and yield were all the highest. Water-fertilizer coupling had highly significant effects on yield, SPAD and Gs(P < 0.01), significant effects on LAI at maturity stage and Tr at flowering stage (P < 0.05). Based on structural equation modeling (SEM), it was shown that a reasonable water-fertilizer coupling could regulate LAI and SPAD of pumpkin leaves, and then improve their photosynthetic characteristics, and ultimately increase pumpkin yield. Gs (as the key index of photosynthetic characteristics) and SPAD (as that of leaf growth) were extracted separately for a comprehensive evaluation of Yield-SPAD-Gs. It was found that the range of optimal irrigation quota regulated by water-fertilizer coupling was 510.57 similar to 526.9 m(3)<middle dot>ha(-1), and that of optimal organic fertilizer application was 5698.24 similar to 6465.54 kg<middle dot>ha(-1). Therefore, F2W3 treatment was recommended as the optimal treatment for pumpkin cultivation in the region.