Specifically, water stress resulted in the lowest increase in leaf area development , and leaf size tended to decrease with decreasing water supply. A study found that leaf area was strongly negatively correlated with leaf water loss,suggesting that bigger leaves of P. sibirica and U. pumila in 4 and 8 L h−1 irrigation levels may be less prone to water loss via evapotranspiration. The efficient use of irrigation and fertilizer has recently gained much attention in reforestation efforts in arid regions because of the highly variable or limited rainfall events. In this study, we revealed that the interaction of 4 and 8 L h−1 with NPK or COMP positively increased LB of all species. This can be attributed to enhanced cell divisionand physiological activities under water-sufficient or high turgor pressure conditions and improved nutrient availability.
Our result is consistent with that of some water and fertilizer experiments conducted in drylands . Similarly, Zhang and Xi observed that the aboveground plant biomass increased when precipitation increased and decreased when precipitation fluctuated significantly. A significant increase in aboveground biomass and leaf area was also detected when the plants were supplied with nitrate, and such a result was associated with the effects of nitrate on cell turgor pressure . Thus, the current result suggests that sustainable reforestation in arid and semiarid regions in Mongolia can be achieved with the use of a combination of the appropriate amount of water and fertilizer. This is because excess water and application of both organic and inorganic fertilizers can exacerbate land degradation and environmental damage in arid and semiarid regions. Contrary to our expectation, CONT and a low amount of irrigation have generally shown to have a higher total chlorophyll content compared with a high amount of irrigation with/without NPK or COMP, particularly in 2019 for both species.
The result of the present study agrees with the findings of Hassanzadeh et al. , who reported that irrigating the plots under flooding conditions led to a decrease in chlorophyll content and senescence, whereas drought stress increased chlorophyll content. Our result is attributable to the effects of moisture on photochemical activity and chlorophyll synthesis in leaves. Conditions such as excess water and nutrient availability may have hindered the chlorophyll synthesis of irrigated plants, particularly those grown in 4 or 8 L h−1 with NPK and compost. Several studies explained that low levels of chlorophyll in leaves might be poorly related to water conditions in the field because of interacting effects of the other environmental factors, such as soil characteristics, light, and air temperature . A change in the amount of far-red radiation and light reflectance of leaves was also cited as one of the reasons for the change in chlorophyll content with increasing soil moisture .
A study by Hamblin et al. also mentioned that the reduction in leaf chlorophyll content can reduce the heat load, thereby reducing water requirement to cool leaves. Nitrogen is an essential part of the chlorophyll molecule; hence, the lack of it in the mineral nutrient supply may significantly affect chlorophyll synthesis in plants. Here we revealed that adding NPK or compost to a higher amount of irrigation significantly decreased the chlorophyll content compared with CONT in all species, implying that some factors such as mineralization, leaching, and volatilization may have come into the picture. Because of the high amount of irrigation, the applied fertilizer may have been leached out, leading to N deficiency in plants. Another possible reason is that the high amount of irrigation may have facilitated the mineralization of the applied fertilizer in the soil, leading to a luxury consumption of N by plants. Such a luxury consumption produced excess N that may not be metabolized into functional or structural compounds necessary for chlorophyll synthesis. One study, however, reported that the stress-induced loss of chlorophyll was not linked to a lack of nitrogen .
This is probably because of the effect of water stress on nitrogen mineralization and uptake. Further, the significant reduction in leaf chlorophyll content may be a consequence of increasing the LA, SLA, and LB of the plants grown in a higher amount of irrigation with NPK or compost. The scientific name of the oriental persimmon is Diospyros kaki, and it is classified as a deciduous tree belonging to the family Ebenaceae of the genus Diospyros. The persimmon originates from northern China and is said to have been introduced to Japan during the Nara period, which took place over the years 710–794. The astringency of the peels of persimmon is caused by tannin, which is a condensation product of epigallocatechin,epicatechin, and their galloyl compounds. When persimmons ripen, acetaldehyde is generated within the flesh of the fruit and forms cross-links with the water-soluble tannin to form polymers, making the tannin insoluble and thus reducing the persimmon’s astringency .