| Leaves and roots are the most active vegetative organs in the aboveground and underground parts of plants.Their morphogenesis and material acquisition are closely related to the distribution of photosynthetic products,and play a vital role in regulating plant metabolism,growth and survival.Litter decomposition is a key link in soil nutrient cycling.Nutrient addition plays an important role in rapid restoration and improvement of grassland productivity.N and P are the key nutrient elements for plant growth and the main limiting elements for terrestrial ecosystem productivity.Carrying out N and P addition experiments can not only clarify the effects of N and P supply on the structure and function of grassland ecosystems,but also provide a scientific basis for grassland vegetation to cope with changing nutritional stress.In this study,the desert steppe in Yanchi,Ningxia was used as the research object.A two-factor randomized block experimental design was used to set up four N addition gradients:0 g/m2/a(N1),5 g/m2/a(N2),10 g/m2/a(N3),20 g/m2/a(N4);four P addition gradients:0 g/m2/a(P1),4 g/m2/a(P2),8 g/m2/a(P3),16 g/m2/a(P4),analysis of plant functional traits and the response of two dominant plant litters to nutrient addition.The main results are as follows:(1)The addition of N and P had some effects on the functional traits of desert steppe community leaves.When N was added alone,the low concentration of N2(5 g/m2/a)decreased the fresh weight,dry weight,leaf area,leaf volume and leaf dry matter content,and then showed a significant increasing trend with the increase of N concentration.The contents of C,N,P and C/N ratio,C/P ratio and N/P ratio in leaves of the community increased with the increase of N concentration.When P was added alone,leaf volume was the exception of leaf volume,and leaf C,N,P contents and C/N ratio,C/P ratio and N/P ratio were all lower than CK treatment.Under high concentrations of N and P,leaf fresh weight,dry weight,leaf area,leaf volume,specific leaf area,leaf tissue density,leaf dry matter content,leaf C,N,P and C/P ratio showed a significant increase trend(P<0.05),and the N/P ratio of leaf litter was lower than that of CK treatment.There was a significant negative correlation between C/N ratio and leaf N and N/P ratio.There was a significant positive correlation among leaf morphological characters(P<0.05).The root functional traits of desert steppe community had different responses to the addition of N and P.The addition of high concentrations of N and P increased the average diameter,specific root length and specific surface area of plant roots,while decreased the density of root tissues.Root dry weight,total root length,mean diameter,total projected area,total surface area and total volume were significantly lower at P3(8 g/m2/a)level than those in control group(P<0.05),but significantly increased at high N and high P treatment.The content of C,N and P and the C/P ratio of community root were increased,but the C/N ratio was decreased.The addition of P significantly decreased root N content and C/P ratio,and the addition of high concentration of N and P also significantly increased root N content and decreased the C/N ratio.There were significant positive correlations among total root length,total projected area,total surface area,average diameter,total volume and dry weight(P<0.05).There were significant negative correlations between root tissue density and specific root length and specific surface area,and negative correlations between root N and P content and C/N ratio.There was a significant negative correlation between root P content and C/P content(P<0.05).(2)There were differences in leaf and root functional traits under N and P supplementation.Leaf morphological traits were positively correlated with root C and root N,leaf volume and specific leaf area were positively correlated with root P,and there was no correlation between other traits.There was a significant positive correlation between leaf area and average root diameter,and there was a strong correlation between leaf and root N content There was a significant negative correlation between leaf tissue density and root tissue density.(3)The litters of Stipa breviflora and Agropyron mongolicum showed rapid decomposition stage during 0-30d.According to the prediction of exponential decay model,the decomposition time of 50%of S.breviflora litters is 0.38-1.84a,and the decomposition time of 95%is 1.61-11.64a,both of which are faster than that of litters.The decomposition time of 50%is 0.75-2.29a and the decomposition time of 95%is 3.43-10.06a.Appropriate addition of N and P separately and N+P together promoted the decomposition of litters.After 180 days of decomposition,the decomposition rate was higher than that of S.breviflora.The results of this study indicate that the addition of N and P has a significant impact on the functional traits and litter decomposition of dominant plants,and there are differences in the correlation between the leaves and roots of plants,as well as the correlation between the two,and the addition of N to a certain extent alleviates the restriction of P on plant growth;The response of litters from different species to N and P also varies due to their own properties.The results of this study are helpful to understand the adaptation mechanism of plants to the environment and the regulation mechanism of litter decomposition by understanding the functional characteristics of plants and the response of litter to changes in soil nutrient supply,and have important guiding significance for the restoration and construction of ecosystem functions and natural grassland. |
