Coupling Water Consumption And Carbon Sequestration Of Artificial Pinus Elliottii Forest In Sub-tropical Red Earth Hilly Area

Whole-tree sap flow density (SFD) was measured on 6 trees continuously in anartificial Pinus elliottii forest using Granier's thermal dissipation probe method withseveral environmental factors including meteorological variables and soil variablesmeasured simultaneously in Qian Yanzhou Experimental Station, located in Taihecounty, Jiangxi Province. At the same time, stem analysis and branch analysis wereutilized to investigate whole-tree growth. The aim of this paper was to explore thecoupling relationship between water consumption and carbon sequestration of P.elliottii and provide scientific methods and fundamental data for the research onwater-carbon coupling cycle in subtropical red earth hilly area of our country. Themain obtained results were as follows:First, significant quadratic correlations were found between three growth indexincluding diameter at breast height (DBH), tree height, stem volume and tree age withall r² high above 0.99. Stem growth and crown growth both correlated significantlywith DBH increment in power function, with r² 0.8242 and 0.9568 separately.Second, the DBH increment of P. elliottii in sunny slope was mainly affected by≥10℃accumulated temperature (≥10℃AT), sunshine hours (SH) and precipitation inthe year before (PB) with r² 0.935. The DBH increment in shady slope correlated onlywith relative humidity (RH) with r² 0.901. The height increment in both sunny slopeand shady slope were affected by average temperature (AT), SH, RH, PB with r²0.827 and 0.882 separately. The volume increment in both slope sides dependedmainly on AT,≥10℃AT, SH, RH with r² 0.749 and 0.723 separately. Precipitation inthe current year had no limitation to P. elliottii growth in this area. The correlationtests for all equations were significant at the level of 0.05.Third, the carbon content in different organs of P. elliottii decreased in the order ofleaf (52.62±0.38～54.38±0.26) %＞branch (51.18±0.55～52.26±0.41) %＞wood(51.41±0.39) %＞root (51.28±0.22～51.77±0.32) %＞bark (50.92±0.46)%. Thecarbon content in branches and leaves increased with the age of organs. The leaf carbon content of mid-layer was slightly higher than that of the mid-and up-layers.And the branch carbon content of the down-layer was much higher than that of theother two layers. The carbon content in shrub, herb and litter floor was (44.90±0.4545.47±0.35) %, (42.13±0.44～42.42±0.39)%, (40.88±0.31)%, respectively. Theaverage carbon content in the soil ranged between (0.26±0.07)% and (0.65±0.06)%, and declined with the soil depth. The average carbon content of P. elliottiicalculated from biomass weight methods was ablout (51.71±0.37)%. The totalcarbon storage of 19-year-old P. elliottii over storey amounted to 86·18t·hm^-2. Theannual net CO₂ fixation and O₂ production were calculated as 16.77t·hm^-2 and12.20t·hm^-2separately. The benefits from CO₂ fixation and O₂ estimated fromdifferent methods varied in the range of 6072.31～10610.78yuan.hm^-2·a^-1.Fourth, diurnal sap flow in different growing periods was basically similar. Butsome differences still occurred in the time of starting, reaching peaks and descending.The accumulative sap flux from March and September accounted for 4.3820%,7.7036%, 17.2084%, 18.4208%, 14.3629%, 11.2381%, 8.8279%, and 7.5221% of thewhole-year sap flux separately. To sum up, the growing periods and non-growingperiods occupied 89.6658% and 10.3342.% of total sap flux, respectively.Fifth, a significant quadratic correlation was found between sapwood area (SWA)and DBH with r² 0.943 of P. elliottii. SFD correlated well with DBH in powerfunctions with r² higher than 0.98. Daily cumulative sap flow in different growingperiods correlated linearly with sapwood area with all r² higher than 0.95.Six, SFD was mainly affected by three meteorological factors including canopytemperature (CT), canopy relative humidity (CRH) and photosynthetically activeradiation (PAR). Correlations between, SFD and the three separate factors wereexpressed well by linear regression models. Multiple-linear model between SFD andthe three integrated factors was also established. All equations and correlationparameters were significant at the level of 0.01. The sequence of correlated degrees ofthree factors was as follows: CRH＞PAR＞CT.(7) The total water consumption of P. elliottii stand (20m×20m) in 2004 was177.8526m³Â·a^-1(444.63mm·a^-1 expressed as water depth per area), much lower thanthe average annual precipitation (1000mm) in this area. Estimated from potential water consumption model, the water consumption of P elliottii plantation in futural10 years were 469.76mm, 494.92mm, 520.28mm, 545.66mm, 571.13mm, 596.67 mm,622.28mm, 647.96mm,673.72mm,699.54mm. Based on the results of tree growth andwater use, the WUE of P. elliottii was calculated as 58.5123μmolCO₂·mmol^-1H₂O or1.7731 gDW-kg^-1H₂O.