Response Of Stem Respiration Of Pinus Massonoana To Resin Tapping In Subtropical China

Respiration is an important physiological process that affects the net primary productivity of plants,and plays an important role in the carbon balance of forest ecosystems.Existing research shows that forest ecosystem respiration can consume more than 50%of the carbon fixed by photosynthesis,and stem respiration can account for 5%-40%of the carbon budget of the above-ground part of the tree.In mature forests,it can even exceed the leaf respiration.Therefore,the study of the gas exchange between the forest and the atmosphere must consider the contribution of stem respiration.In recent years,with the increasing environmental problems such as global warming,the sustainable management of planted forests has become one of the current research hotspots.Pinus massoniana is one of the most widely distributed Pinus species in China and one of the major lipid-producing species in China.How to use the right management method to manage the Pinus massoniana forest and to play the economic and ecological benefits of the Pinus massoniana plantation stably and efficiently are the main problems of forest management at present.Resin tapping is an important method for the management of Pinus massoniana plantation.However,previous studies have paid more attention to the economic benefits of resin tapping on the management of Pinus massoniana plantation,and less attention has been paid to how resin tapping changes the carbon distribution pattern of Pinus massoniana.In particular,the effects on stem respiration have not been reported.In this study,local flux measurement method and Picarro observation system were used to measure the temporal dynamic characteristics of CO₂ flux and its carbon isotopes on the surface of Pinus massoniana stem.The relationship between the changes in growth and stem temperature and sap flow;combined with mass balance method,the different components of the respiration of Pinus massoniana stem and their responses to resin tapping were analyzed.The result is as follows:（1）Diurnal variation of CO₂ flux and carbon isotope of Pinus massoniana show irregular fluctuations above and below the mean,and there are no obvious peaks during the day;the diurnal variations of tree stem temperature and tree sap flow are unimodal curves;the correlation of stem CO₂ flux and its carbon isotope with air temperature,stem temperature,and stem sap flow were not significant.The seasonal change of stem CO₂ flux of Pinus massoniana is a unimodal curve,and it has a good exponential function relationship with the stem temperature.The entire observation period is divided into growing season and non-growing season.It is found that the non-growing season stem CO₂ flux for the stem temperature changes are more sensitive;in addition,theδ¹³C seasonal characteristics of stem CO₂ flux of Pinus massoniana are also more significant,and theδ¹³C value in the growing season is lower than that in the non-growing season.From the entire observation period,the stem temperature has a negative correlation withδ¹³C.（2）Although stem CO₂ flux of Pinus massoniana was not significantly different between different treatments,stem CO₂ flux of Pinus massoniana and its stable carbon isotope were reduced to a certain extent after resin tapping;The amount of Q₁₀ was within the range of the previous research results（1.0-3.0）,and resin tapping did not change the Q₁₀ of stem CO₂ flux.After resin tapping treatment,the soluble sugar and starch concentrations of Pinus massoniana bark showed a downward trend.And the degree of decline was greater with the extension of the resin tapping time;compared with the control group,the cumulative growth of the DBH of Pinus massoniana in the resin tapping group was lower,indicating that resin tapping had a certain inhibitory effect on the growth of Pinus massoniana.（3）The contribution of different component fluxes of Pinus massoniana stem respiration to the total stem respiration and the diurnal variation trend are different,but stem CO₂ flux contributes the most to stem respiration both during the day and at night;it will be 24 hours divided into 4 periods,it is found that the relative contributions of different components to total respiration are different at different periods,and the effect of fluid flow velocity on the CO₂ transport flux within the stem varies from individual periods,and there are individual differences in the influence of flow velocity on the CO₂ transport flux inside the stem;resin tapping does not significantly change the different groups of stem respiration component and their relative contributions.