| Betula platyphylla is widely distributed and growing rapidly in China,which is an important tree species in forestry development.Nutrient addition will change the soil environment and affect the physiological changes of plants.The experiment of nutrient addition of Betula platyphylla can provide theoretical basis for the sustainable development of Betula platyphylla forestry.In this paper,the changes of Stomatal density(SD),Gas exchange characteristics,Water use efficiency(WUE),leaf characteristics and growth status of current-year-old Betula platyphylla seedlings under different N(nitrogen fertilizer),K(potassium fertilizer)and P(phosphorus fertilizer)fertilizer ratios were studied by pot culture.The main conclusions are as follows:1)The SD in different regions of the same leaf did not differ significantly before and after the addition of nutrients.Nutrient addition significantly reduced SD(P<0.05),and SD had a significant negative correlation with leaf dry weight,leaf area,seedling height and ground diameter(P<0.05).The leaf enlargement of Betula platyphylla is the main reason for the decrease of SD.There was no significant correlation between gas exchange and SD in different regions(P<0.05).It is concluded that SD is not the main factor affecting the spatial heterogeneity of gas exchange in the leaves of Betula platyphylla.2)Nutrient addition also significantly increased leaf gas exchange rate(P<0.05).Nutrient addition increased net photo synthetic rate(Pn)and WUE of Betula platyphylla leaves,while reducing transpiration rate(Tr)and stomatal conductance(Gs).Gas exchange in different regions of Betula platyphylla leaves before and after nutrient addition was significantly different(P<0.05),and mainly reflected in the heterogeneity of tip to middle and base of leaves,and varied in different growth stages.Overall,the gas exchange at the tip was more than twice that in the middle and the base of the leaf,and it increased over time.In the growing season,the gas exchange in different regions of the leaves responded differently to nutrients,and the effect of P on the whole growing season was obvious.3)Although the gas exchange of Betula platyphylla leaves was heterogeneous before and after nutrient addition,there was no significant difference in WUE between different regions of Betula platyphylla leaves.The effect of nutrient addition on WUE in different regions of Betula platyphylla leaves was significant(P<0.05).The WUE after nutrient addition was significantly higher than that of Control check(CK).The most significant and average factor was P fertilizer,which indicated that P fertilizer could improve WUE of Betula platyphylla.4)The chlorophyll content of Betula platyphylla leaves increased significantly with the addition of nutrients until the end of the growing season.Leaf dry weight,leaf thickness,specific leaf weight(LMA),specific leaf area(SLA),leaf length and leaf width of Betula platyphylla seedlings changed significantly with time(P<0.05).The high nitrogen content is conducive to the growth of the ground diameter of Betula platyphylla.Increasing the application of phosphate fertilizer is conducive to the growth of Betula platyphylla.Low dosage of potassium fertilizer is beneficial to the high growth of Betula platyphylla,while the high dosage of potassium fertilizer is not conducive to the high growth of Betula platyphylla.that is,high phosphorus fertilizer,low potassium fertilizer and moderate nitrogen application are beneficial to the high growth of Betula platyphylla. |
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