Ecological Stoichimetry Of Plantation Forest Ecosystem In The North Piedmont Of Qinling Mountain,China

Understanding how concentrations of elements and their stoichiometry change with plant growth and age is critical for predicting plant community responses to environmental change.Ecological stoichiometry is concerned with the balance of elements in ecological interactions and processes.It is a key aspect of ecological stoichiometry that organisms can maintain stoichiometric balance between their basic metabolic requirements and environmental resource availability.Stoichiometric balance is an important force linking individual organisms with ecosystem structure and functioning.However,understanding of ecological stoichiometry of terrestrial plants is limited under the framework of carbon(C),nitrogen(N),and phosphorus(P),and,until recently,few studies have considered the stoichiometry of below-ground organs(e.g.,the roots).A comprehensive study on stoichiometry of multielements in plants could advance our understanding of biogeochemical cycling and the response of the ecosystem to environmental changes.However,short-term data could limit the ability to predict nutritional limitations in forest ecosystems.In our study,we attempted to elucidate the variation tendency in C,N and P concentrations and their stoichiometries via long-term field experiments in a larch plantation.We used long-term field experiments to explore how the leaf,stem and root carbon(C),nitrogen(N)and phosphorous(P)concentrations and their stoichiometry changed with growth and stand age in a Larch principis-rupprechtii Mayr.plantations from 2012 to 2015 in Taibai county in the North Piedmont of Qinling Mountain,Shaanxi Province,China.Herein,we analyzed C,N and P concentrations and C:N:P Stoichiometry in leaves,stems fine roots of differently aged L.principis-rupprechtii Mayr.plantations in order to illuminate the scaling relationship of N and P in different plant organs,temporal patterns of stoichiometric traits and the potential drivers,and the pattern of multielements variability.Furthermore,we explored the effects of nitrogen and phosphorus fertilizers addition on leaves,stems and roots nitrogen(N),phosphorus(P)and N:P stoichiometry of L.principis-rupprechtii Mayr.plantations with a 5-year field experiment.The study would provide theoretical supports and science reference for vegetation management and protection of L.principis-rupprechtii Mayr.plantations in the North Piedmont of Qinling Mountain,China.The main findings of this dissertation are as follows:(1)The results showed that the C,N and P concentrations and stoichiometric ratios in different tissues of larch stands were affected by stand age,organ type and sampling month and displayed multiple correlations with increased stand age in different growing seasons.Generally,leaf C and N concentrations were greatest in the fast-growing season,but leaf P concentrations were greatest in the early growing season.However,no clear seasonal tendencies in the stem and root C,N and P concentrations were observed with growth.In contrast to N and P,few differences were found in organ-specific C concentrations.Leaf N:P was greatest in the fast-growing season,while C:N and C:P were greatest in the late-growing season.No clear variations were observed in stem and root C:N,C:P and N:P throughout the entire growing season,but leaf N:P was less than 14 form 2012 to 2016,suggesting that the growth of larch stands was limited by N in our study region.Compared to global plant element concentrations and stoichiometry,the leaves of larch stands had higher C,P,C:N and C:P but lower N and N:P,and the roots had greater P and C:N but lower N,C:P and N:P.Our study provides baseline information for describing the changes in nutritional elements with plant growth,which will facilitates plantation forest management and restoration,and makes a valuable contribution to the global data pool on leaf nutrition and stoichiometry.For the C,N and P concentrations and the C:N,C:P and N:P ratios in the different plant organs,significantly influenced by the plant age,which may be used as a new methodology to understand plant growth and formation in plant communities.(2)Allometric scaling relationships of C-N and C-P were not found in the leaves,stems and fine roots of differently aged L.principis-rupprechtii Mayr.Plantations.Generally,allometric scaling relationships of N-P were found in the leaves and fine roots of differently aged larch stands,but not in the stems.However,no clear seasonal tendencies in allometric scaling relationships of N-P in the leaves and root of larch stands.The allometric exponents of N-P in the leaves of differently aged larch stands varied between-1.50 and 2.25,the allometric exponents of N-P in the roots of differently aged larch stands varied between-2.76 and 3.59 from 2012 to 2016.Our results demonstrated that the nutrient allocation of differently aged larch stands showed a different response to environmental gradient.Furthermore,the conservatism of N and P allocation was not associated with organ functioning and plant life history strategy.(3)Our purpose was to explore the effects of nitrogen and phosphorus fertilizers addition on leaves,stems and roots nitrogen(N),phosphorus(P)and N:P stoichiometry and to assess their differences among different nitrogen and phosphorus fertilizers with a 5-year field experiment.Generally,N concentrations in the leaves,stems and roots of L.principis-rupprechtii Mayr.increased significantly under N addition or the compound fertilizers of nitrogen and phosphorus.The results indicated that the N addition promoted the absorption of N by plants in general.Compared with the effects of N concentrations in the stems and roots under N addition or the compound fertilizers of nitrogen and phosphorus,the effect in the leaves was highest,but lowest in the stems.Generally,P concentrations in the leaf,stem and root of L.principis-rupprechtii Mayr.increased significantly under P addition or the compound fertilizers of N and P.The results indicated that the P addition promoted the absorption of P by plants in general.However,nitrogen fertilizer addition limited the accumulation of P elements in the leaves and roots of L.principis-rupprechtii Mayr..Additionally,N:P ratios in the leaves,stems and roots of L.principis-rupprechtii Mayr.increased significantly under N addition or the compound fertilizers of nitrogen and phosphorus.The results indicated showed that the strength of N limitation was reduced by the N fertilizer addition or the compound fertilizers in our study region.Futhermore,the N:P ratios in the leaves,stems and roots of larch stands increased significantly under the N fertilizer addition.However,the N:P ratios in different organs of larch stands decreased significantly under the P fertilizer addition,indicating that the strength of N limitation was enhanced by N and P fertilizer addition.The results showed that the addition of nitrogen and phosphorus alleviated the growth-limited for L.principis-rupprechtii Mayr.by the N element in soil in our study region,and the different nitrogen and phosphorus fertilizer addition effect significantly reduced the strength of N limitation for the growth of L.principis-rupprechtii Mayr.by N or P element.However,the effects did not persist.Studies on the effects of artificial N and P fertilizer addition on the growth and C,N,P ecological stoichiometry of L.principis-rupprechtii Mayr.plantations could provide not only a new insight into the forecasting of how the interaction between soils and plants responses to long-term atmospheric N deposition increase,but also a scientific guidance for sustainable management of planted forest under global climate change.(4)The addition of nitrogen and phosphorus fertilizer effected significantly on the distribution pattern of N-P in different organs of L.principis-rupprechtii Mayr..During 2012-2016,allometric scaling relationships of N-P were found in the leaves of larch stands.However,there were not allometric scaling relationships of N-P were found in the stems and roots of larch stands from 2012 to 2016,indicating that the effects of different fertilization addition on the N,P distributions were not significant.With the increase of fertilization years,the effects of nitrogen and phosphorus addition on the distribution pattern of N-P elements in different organs of larch stands were increased.The results indicated that that N element was prioritized to the leaf compared with the stem and root,then convert N to prioritize to the leaf or root,which indicated that P was prioritized to the stem or root compared with the leaf.In the leaves and roots.Our results confirmed that the N and P fertilizer addition can affect N or P cycling in the forest ecosystem.With the continuation of N fertilizer addition,the growth of L.principis-rupprechtii Mayr.was limited by the N element and then gradually changed to be restricted by the P element.