Seasonal Variation Of C,N And P Stoichiometry In Yangguan Wetland Ecosystem,Dunhuang

Ecological stoichiometry is an important indicator to reflect the ecological process.It is of great significance to understand the key nutrient elements(C,N,P)and their stoichiometric ratios in fragile and sensitive ecosystems.Phragmites australis(P.australis),a common perennial reed grasses found in temperate and tropical wetlands around the world,provides many services and functions that are very important for wildlife and conservation,and for phytoremediation and others.However,with disturbances from global change and human,it is necessary to undestand seasonal variations in leaf stoichiometry of P.australis for their continued benefits towards ecosystem functions.This study quantified the seasonal dynamics of leaf stoichiometry of P.australis and soil from Yangguan wetland,Dunhuang,China as a case study,and the dominant factors affecting leaf stoichiometric characteristics in different growth periods were analyzed.The main results are as follows:(1)Leaf C concentration of P.australis varies with season and was 392.26g/kg,417.35 g/kg and 382.58 g/kg in initial growth,mature and decline phase,respectively.Leaf C concentration in mature phase was significantly higher than that in initial growth and decline phase.Leaf N and P concentration showed a significant downward trend from initial growth to decline phase,and their concentrations were 23.49 g/kg,17.54 g/kg,5.86 g/kg and 1.0 g/kg,0.75 g/kg,0.16g/kg,respectively in three phases.The maximum(77.68)and the minimum value(17.00)of leaf C/N was observed in decline and initial growth phase,respectively.Variation in leaf C/P with growth phase also showed similar trend,with the greatest value of 3015.91 in decline phase and the lowest value of 429.39 in initial growth phase.while the maximum(45.67)and minimum(24.18)of leaf N/P were in decline and mature phases,respectively,indicating that the growth of P.australis was mainly limited by P.(2)The variation of leaf C/P was the largest(CV = 0.14)and the smallest(CV= 0.01)at different growth stages.There was no significant correlation between C and N in the early growth stage,but there was a significant positive correlation between C and N in the mature stage and senescence stage(P < 0.05);there was a significant negative correlation between N and P in the mature stage(P < 0.05),but there was no significant correlation between N/P and C/N in the early growth stage,mature stage and senescence stage significant negative correlation(P < 0.01),and extremely significant positive correlation with leaf C/P.(3)Soil temperature was the highest in summer(August,22.67 ℃),which was significantly higher than that in spring(May,18.09 ℃)and autumn(October,12.5 ℃).Soil moisture,salinity and p H were not significantly different among different seasons(P > 0.05).Soil organic carbon was 5.79 g/kg,10.61 g/kg and6.89 g/kg in spring,summer and autumn,respectively.Soil organic carbon in summer was significantly higher than that in spring and autumn(P < 0.05).Soil C/N and N/P in different seasons showed similar performance to soil organic carbon.Soil C/P in summer was the highest(29.93),while that in spring was the lowest(13.71).Soil ammonium nitrogen(10.87 mg/kg)was significantly higher than nitrate nitrogen(9.05 mg/kg).Soil nitrate nitrogen was the highest in autumn(11.29 mg/kg)and the lowest in spring(6.34 mg/kg).(4)Redundancy analysis showed that the main soil factors affecting the leaf stoichiometry of P.australis were salinity,soil temperature,soil moisture,soil organic carbon,soil nitrate nitrogen and soil available phosphorus.Soil salinity was significantly positively correlated with leaf C and N(P < 0.01);soil moisture was significantly negatively correlated with leaf C(P < 0.05);soil nitrate was significantly positively correlated with leaf C,significantly negatively correlated with leaf N and P(P < 0.05);soil available phosphorus was significantly positively correlated with leaf C,significantly positively correlated with leaf P(P < 0.01).(5)At the early growth stage,the contents of N and P in leaves were higher,while the accumulation rate of C in leaves was relatively higher than that of N and P.In order to strengthen the effective utilization of resources and resist salt stress,P.australis adopted competitive strategy in the early growth stage to ensure the dominant position of the population,and adopted defensive strategy in the late growth stage to avoid excessive loss of nutrients.