| Ecology stoichiometry is a very important theory in Ecology which provides a powerful theoretical tool to carry out the relationship between biology and environment.In terrestrial ecosystem,a great number of studies have investigated the stoichiometrical composition,spatial pattern of plants and insects at various scales,including global,regional and local scales,and explored their relationships with controlling factors.Plants can not migrate and move like animal and insect when they undergo climate change,sothey have to adjust their physiological and biochemical reactions with respect to environments.However,there is only less studies to measure interannual stoichiometry dynamics in plants,which is important to understand plant nutrient regulation strategies and plant-insect interaction under climate change.In the present study,the leaves,seeds and parasite weevil Curculiospp.samples of three oak species(i.e.Quercus alienavar.acuteserrata,Q.glandulifera,and Q.variabilis)were investigated through consecutive three to four years,and the multielement concentration of samples were measured.The aims were to explore the interspecific and interannual difference of leaves,seeds and parasite weevil as well as nutrient resorption efficiency,to examine the effects of interannual temperature,precipitation,plant functional traits and soil on their stocichiometry variation,and to investigate the adaptation of plant and insectin stoichiometric convergence and the co-evolution relationship between plant andinsect.Our main findings are as follows:(1)Leafstoichiometry in three oak species and their responses to interannual climate variationThere were significantly interspecific and interannual differences of leaf stoichiometry in three oaks.Mg,Zn and Ba in interspecific difference,and S and Zn in interannual difference played important distinguishing roles.Although three oaks had interspecific difference in chemical composition,they showed the convergence of stoichiometric adaption due to encountering similar climate change.The coefficient of variation(CV)decreased with increasing leaf element concentrations,supporting the stability of limiting elements hypothesis.Leaf N,P,S and C:N compared to other elements were more sensitive to interannual temperature and precipitation,and plant growth in this region were limited in growth by P according to N:P.The results indicate that plant leaf stoichiometry were jointly influenced by heredity and environment,and when climate change happened,plant could preferentially regulate the elements related to growth.(2)Acorn stoichiometry in three oak species and their responses to interannual climate variationLike leaf stoichiometry,acorn stoichiometry in three oaks also had significantlly interspecific and interannual differences.The interspecific differences could be mainly contributed to the changes of P,K,Zn and Ba,and interannual differences were primarily caused by the changes of C and K.There are profound difference in the element concentration of acorn and leaf,except for K,partly P and C:N that higher in acorns,other elements were lower than these in leaves.Moreover,there were weak correlations between acorn and leaf,and CV of acorn element concentrations increased with CV in leaf.Most element concentrations significantly increased(except for C:N and C:P decreased)in 2014 with low temperature and precipitation.The stoichiometry of three acorns also showed the convergence of adaption with interannual climate change,but they had individual responses for interannual temperature,precipitation,plant traits and soil.Our results suggested that acorn and leaf sotichiometry could be separately regulated by other perennial tissues,and acorn homeostasis was weaker than leaf homeostasis in order to better produce next generation.(3)Weevil stoichiometry in three oak species and their responses to interannual climate variationWeevil stoichiometry also showed similarly interspecific and interannual differences like their food.In interspecific difference,P,Mg and Zn could play more important in distinguishing them,and in interannual difference,these nutrient were C,S and Zn.Parasite weevil stoichiometry was totally different their food due to the difference between energy and metabolism,and weevil lived in one acorn and fed by this acorn,so their stoichiometry had highly dependent on the food,showing weevil nutrient concentration increased acorn nutrient concentrations.The CV of weevil element concentration increased with CV in their food,suggesting weevil could have weaker homeostasis than acorn.The results revealed that plant stoichiometry had a strong influence on insect stoichiometry,and plant and insect could be co-evolution to commonly adapt to interannual climate change.(4)Nutrient resorption of three oak species and their responses to interannual climate variationNutrient resorption efficiency(NuRE)varied substantially among different years,but not among species.The nucleic acid-protein(N,P,S and K)and photosynthesis-enzyme(C,Mg and Zn)elements had NuRE> 0,i.e.,these elements were re-absorbed as reserve for new growth next year.Comparatively,structural(Ca,Mn,Ba,and Na)and toxic(Al and Fe)elements had NuRE < 0,suggesting that these elements were excluded from plant to avoid unnecessary accumulation and toxic effects.This suggests that nutrient resorption among different elements is selective and co-ordinated in a trade-off manner(Trade-off Hypothesis of Nutrient Regulation).Our results also showed that elements of high resorption efficiency generally had low resorption variability(coefficient of variation).Interannual variations of precipitation and temperaturestrongly influenced on the resorption of growth related elements(C,N,P,and S),and in the next two decades their resorption might decline due to increasing drought.These findings help understand nutrient regulation mechanisms,adaption strategy of plants to possible precipitation and temperature changes expected under climate change.(5)Altitudinal and interannual patterns of leaf stoichiometry and nutrient resorption efficiency in Q.variabilisWe used single tree species(Q.variabilis)to compare with altitudinal and interannual patterns of leaf stoichiometry and nutrient resorption efficiency in this study.Leaf N,S and K increased with,C,Ca,Na,Fe,Mn,Cu and Ba decreased with,and P,Mg,Al,Zn and N:P did not change significantly with altitude.NRE and SRE increased with,and CRE decreased with altitude.The results also showed some similar changing trends through the comparative analyses of altitudinal and interannual leaf stoichiometry and nutrient resorption,such as N and S concentration were negatively correlated with temperature,P was strongly influence by soil P content,and in terms of nutrient resorption,NRE was negative with temperature,and PRE was positive with precipitation.The consistency of N,P and S in temporal and spatial scales showed that the adjustment of plant stoichiometry is a physiological and growth adaptation strategy to environmental change,and the environmental change had nothing to do with temporal and spatial scales.In this regulation process,temperature change had a strong influence on plant N and S,and soil P significantly affected on plant P concentration.In summary,the stoichiometric compostions of leaves,acorns and parasite weevil in three oaks showed significant inter-species and inter-annual differences,and in the face of same or similar interannual climate change,they all also revealed convergent stoichiomeric adaptation.There were strong difference between leaf and acorn element concentrations,and weaker correlation,which suggested that their nutrient could be separately regulated in plants.CV of weevil in element concentration increased with acorns,CV of acorn increased with leaves,so it is possible that the rank of homeostasis was leaf > acorn > weevil.Due to long-term evolution and adaptation,when plants encounter climate change,they could mainly regulate the elements that directly relate to plant growth in terms of stoichiometry and nutrient resorption.Deciduous plants may have a trade-off mechanism at the end of growing season to rebalance somatic nutrients.Plant nutrient responses under climate change could just relate to temperate and/or precipitation,has nothing to do with environmental scales.The study could be contribute to systematic understanding plant and insect nutrient regulation strategy under climate change. |
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