| Nutrient is one of the environmental factors limiting the productivity of terrestrial ecosystems.Nitrogen and phosphorus are the main nutrient limiting factors for plant growth.Nutrient resorption is a process in which plant tissues or organs transfer some nutrients(mainly nitrogen,phosphorus)to other living tissues before aging and shed,which can prolong the retention time of nutrients in plants,improve nutrient use efficiency and reduce plant's dependence on soil nutrient.It is the important strategies for plants to adapt to the environment and is significantly affected by factors which is closely related to soil nutrient levels.In this study,the dominant species of Phragmites communis in Wowachi wetland in Dunhuang yangguan was studied.The 30 plots in Wowachi were divided by soil water content to high(W1,33.52±1.87%)and medium(W2,26.44±1.25%),low(W3,11.05±1.35%)water gradients.Plants and soil were sampled and analyzed during the green and senescent periods.Then we explored the effects of soil water to physicochemical properties,plant community characteristics and the nitrogen and phosphorus content of the Phragmites communis during its green period.We finally analyzed the response characteristics of plant nutrient resorption to soil moisture and functional traits.The main findings are as follows:(1)There is a significant difference in soil water content between the three water gradients(P<0.01).The soil conductivity of the low water gradient is 1.25 times higher than the high water gradient,and the soil conductivity is 1.01 times higher than the medium moisture gradient.The low moisture gradient has a higher coverage.The water gradient W1 is reduced by 54.56%,and 53.13% lower than the medium moisture gradient.Compared with the medium moisture gradient,the density of the high moisture gradient is increased by 1.01 times,5.14 times higher than the low moisture gradient W3.Plant coverage and density were significantly positively correlated with soil moisture(P<0.01),and both strongly affected by soil moisture.(2)Plant functional traits varied with the decrease of soil moisture content.The thickness of reed leaves with high water gradient was significantly lower than that of medium and low water gradients(P<0.05),which increased by 10.2% and 36.22%,respectively.The leaf dry matter content with high water gradient was also significantly higher than that of medium water gradient(P<0.05).The increase was 13.16%.The specific stem density of high water gradient was significantly higher than the middle and low water gradient(P<0.05),which increased by 32.23% and 29.72%,respectively.Leaf thickness was significantly negatively correlated with soil water content(P<0.01),and there was a significant positive correlation between specific stem density and soil water content(P<0.05).There was a significant positive correlation between leaf area and soil water content(P<0.05).(3)The nitrogen and phosphorus contents in the leaves of the green period were significantly higher than those in the stem.The nitrogen content in the stems of the green period was significantly different in the three water gradients(P<0.05),and the nitrogen content in the leaves of low water gradient was significantly higher than medium and high water gradients(P<0.05).For the two organs of stems and leaves,the nitrogen and phosphorus contents in the green leaves were significantly higher than those in stem(P<0.001).There was a significant negative correlation between soil moisture and nitrogen content in green stems and leaves(P<0.01).There was a significant positive correlation between leaf thickness and nitrogen content in green stems and leaves(P<0.05),and leaf dry matter content was significantly negatively correlated with leaf nitrogen content during green period(P<0.05).(4)The leaf nitrogen resorption of low water gradient was significantly higher than that of medium and high water gradients(P<0.05).And the stem nitrogen resorption of low water environment was significantly higher than that of high moisture(P<0.05).Phosphorus resorption was significantly higher than medium and low water gradients(P<0.05),while leaf phosphorus resorption in high water gradient was significantly higher than which in medium water gradient(P<0.05).For the two organs of Phragmites communis,the nitrogen resorption of leaves was significantly higher than that of stems(P<0.01),and the nitrogen and phosphorus resorption efficiency of leaves were significantly higher than that of stems(P<0.01).The ratio of absorption efficiency was only higher in the middle water gradient than in the stem(P<0.01).(5)On the whole,there was a significant negative correlation between soil moisture and nitrogen resorption of stems and leaves(P<0.01).In the middle water gradient,leaf phosphorus resorption was significantly negatively correlated with soil moisture(P< 0.01).The leaf phosphorus resorption efficiency was significantly positively correlated with soil moisture(P<0.01).At high water gradient,the phosphorus resorption efficiency of Phragmites communis stem was significantly negatively correlated with soil moisture(P<0.05).The ratio of resorption efficiency was significantly positively correlated with soil moisture(P<0.05).There was a significant positive correlation between leaf thickness and nitrogen resorption proficiency of stems and leaves(P<0.05).Stem nitrogen resorption proficiency has a significant negative correlation with leaf dry matter content(P<0.05),and a significant positive correlation with specific stem density(P<0.05).The main influencing factors of stem NRP are soil water content and leaf dry matter content,the main influencing factor of leaf NRP is soil moisture.The main influence factor of leaf PRP and leaf PRE is specific stem density. |
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