The Soil Respiration Characteristics Of Typical Forest Ecosystems At The Transitional Area From The Northern Subtropics To Warm Temperate

In order to ascertain the carbon emission and variation characteristics of total soilrespiration and its components in typical forest ecosystems at the transitional area from thenorthern subtropics to warm temperate, and to understand their carbon output process clearly,the variation process of total soil respiration and its components and relative environmental andbiological factors under the condition that the variation range of soil temperature, soil watercontent and litter water content is 26.60～26.94℃, 0.19～4).29 kg·kg^-1 and 1.85～1.96 kg·kg^-1respectively are simultaneously measured over the whole year in the 5 typical forestecosystems which account for 95% total forest area in this region with the support of BaoTianman forest ecosystem station and by using the approbatory methods of respirationmeasurement and respiration component partition. At the same time,the cultivation experimentof soil temperature and soil water content of Quercus aliena var.acuteserrata young stand wasset to understand the soil respiration characteristic at the larger scope of soil temperature. Thestatistical and simulated results show that:(1) There are three diel variation patterns of total soil respiration and its components,the first which occurs before foliage spread in spring and after defoliation in fall is that thevariations of total soil respiration and its components are all consistent with soil temperature;the second which only occurs in summer in young-growth forest is that the variation of R_T, R_Sand R_A have short-term decoupling with soil temperature and soil water content, but thevariation of R_H and R_L is same as soil temperature; the third which occurs in growth seasons ofsummer and fall is that only the variation of R_A has short-term decoupling with soil temperatureand soil water content, the variations of the other respiration are all consistent with soiltemperature. The smallest and the biggest R_T, R_S, R_H ,R_A and R_L is at 06:00 and at 15:00～21:00respectively. The diel variation patterns for total soil respiration and its components are allsingle modal curve. Whether the decoupling of R_A with soil temperature and soil water contentcan lead to the decoupling of R_T and R_S with soil temperature and soil water content isdetermined by the absolute and relatively amount of root respiration in different stands andseasons.The diel variation range of respiration is highest in summer, followed by in spring and fall, and lowest in winter, its seasonal trend is same as that of water content and temperature;The seasonal variation coefficients of diel range of root respiration and litter respiration aredecreasing with stand age increasing, but that of heterotrophic is increasing with stand agesincreasing; The seasonal variation in total soil respiration, soil respiration, root respiration andheterotrophic respiration is single modal curve, which is same as that of soil temperature, thelargest and lowest respiration is in January and July respectively, but the respiration is clearlyrestricted by lower water content; The seasonal variation in litter respiration is more affectedby litter water content than by temperature.(2) The relative importance of the effects of water and temperature on respiration hasseasonal variation, The respiration rate is largely controlled by temperature when soiltemperature and air temperature is below 15℃and 13℃respectively, while it is clearlylimited by water content when soil temperature is above 15℃and air temperature is above13℃respectively and soil water content and litter water content is below 0.20 kg·kg^-1 and 0.38kg·kg^-1 respectively. However, it is simultaneously affected by both temperature and watercontent under other condition. The soil water and temperature cultivation experiment indicatedthat the soil respiration is positively feedback with soil temperature increase, but the positivelyfeedback is restricted by water content which is over 0.35kg·kg^-1 in Quercus alienavar.acuteserrata young stand.(3) The relationship of soil temperature with total respiration, Soil respiration, rootrespiration and soil heterotrophie respiration is significant exponent function (P＜0.05) , soiltemperature can account for 80.62%～93.85%, 86.84%～92.23%, 79.05％～88.12% and82.63%～96.70% of diel and seasonal variation in above mentioned respiration respectively.The relationship of soil temperature with litter respiration is exponent function at diel scale butis quadratic equation at seasonal scale, soil temperature can account for 68.10%～81.58% ofdiel variation and 34.78%～54.24% seasonal variation in litter respiration. Respiration ispositively and negatively with water content at die and seasonal scale respectively, the simpleequation between soil water content and respiration indicates that soil water content canaccount for 24.8%～55.2% of seasonal variation in total soil respiration for 5 stands andaccount for 23.8%～47.1%, 20.45%～41.14% and 23.06%～48.45 of seasonal variation in soilrespiration, root respiration and soil heterotrophic respiration respectively for 4 stands (except for Quercus aliena var.acuteserrata old stand), but the cultivation experiment indicates therelationship between soil water content and respiration is quadratic equation. The relationshipbetween litter water content with litter respiration is significant single equation for 5 stands andlitter water content can account for 72.24%～79.5% of seasonal variation in litter respiration;The cultivation experiment indicates that soil water content increase can promote the soilrespiration when soil water content is very low and that soil water content increase can restrainsoil respiration when soil water is very high.(4) The Q₁₀ value of total respiration, soil respiration, soil heterotrophie respiration androot respiration is 2.18～2.41 (mean is 2.30) , 2.30～2.44(mean is 2.38) , 2.09～2.35 (mean is2.19)与2.49～2.82 (mean is 2.61) respectively at the annual scale, the Q₁₀value of abovementioned respiration is significant (P＜0.05) ; The Q₁₀value of the other respiration typesexcept for root respiration is highest in winter, followed by in spring and fall, and lowest insummer, but the Q₁₀ value of root respiration is highest in spring, followed by in fall, andlowest in summer and winter; The higher Q₁₀ value for total soil respiration in Quercus alienavar.acuteserrata young stand is than old stand under the condition that there is no significantdifference of the soil temperature between the 2 stands and that ther is no water contentlimitation; The Q₁₀ value of root respiration is highest, followed by that of soil heterotrophicrespiration, that of litter respiration is lowest in many occasions, but the Q₁₀ value of soilheterotrophie respiration is highest, followed by that of litter respiration, that of rootrespiration is lowest in winter; the Q₁₀ value of total soil respiration is higer than that of soilrespiration regardless of diel and seasonal scale in 5 stands ; The order of Q₁₀ values ofdifferent respiration in different stand has differences.The cultivation experiment indicates thatthe effects of soil temperature on Q₁₀ value ,of soil respiration is very big ,but the effects of soilwater content on Q₁₀ value of soil respiration is very small, the Q₁₀ value of soil respiration isrestrained by very high soil water content too.(5) The carbon release of root respiration in Quercus aliena var.acuteserrata youngstand, Quercus aliena var.acuteserrata old stand, broadleaf/coniferous mixed stand, broadleafmixed forest and Quercus variabilis stand is 724.52 gC·m^-2·a^-1, 373.55 gC·m^-2·a^-1,441.56～441.87 gC·m^-2·a^-1, 427.14 gC·m^-2·a^-1 and 484.43 C·m^-2·a^-1 respectively; Their carbonrelease of soil heterotrophic respiration is 380.63 gC·m^-2·a^-1, 405.57 gC·m^-2·a^-1, 379.36～379.67 gC·m^-2·a^-1, 485.05 gC·m^-2·a^-1 and 415.07 gC·m^-2·a^-1 respectively if taking account of fine rootdecomposition in root-excluded quadrates; Their carbon release of litter respiration is 239.04gC·m^-2·a^-1, 119.79 gC·m^-2·a^-1, 218.60 gC·m^-2·a^-1, 115.03 gC·m^-2·a^-1 and 277.29 gC·m^-2·a^-1respectively; Their carbon release of fresh litter respiration is 86.59 gC·m^-2·a^-1, 56.72 gC·m^-2·a^-1,65.92 gC·m^-2·a^-1, 55.65 gC·m^-2·a^-1 and 98.84 gC·m^-2·a^-1 respectively; Their carbon release ofsoil respiration is 1105.15 gC·m^-2·a^-1, 779.12 gC·m^-2·a^-1, 821.23 gC·m^-2·a^-1, 912.19 gC·m^-2·a^-1and 899.50 gC·m^-2·a^-1 respectively; Their carbon release of total soil respiration is 1345.19gC·m^-2·a^-1, 897.23 gC·m^-2·a^-1, 1039.83 gC·m^-2·a^-1, 1027.22 gC·m^-2·a^-1and 1176.79 gC·m^-2·a^-1.The seasonal variation trend of soil respiration , soil heterotrophie respiration and rootrespiration is single modal curve, their smallest and biggest value is in January and July, Thepercentage of the carbon release of soil respiration, soil heterotrophic respiration and rootrespiration in summer and fall is 72.93%～76.55%, 54.03%～59.50% and 74.25%-82.21% ofannual release respectively for 5 stands; The carbon release of litter respiration is highest insummer, followed by in fall, lowest in spring and winter, the percentage of carbon release insummer and fall is 78.45%～83.67% of its annual release respectively for 5 stands(6) The annual contribution rate of root respiration for stand 1～stand 5 is 53.86%,41.63%, 42.46%～42.49%, 41.58% and 41.17% respectively; Their annual contribution rate ofsoil heterotrophie respiration is 28.57%, 45.21%, 36.48%～36.51%, 47.13% and 35.27%respectively if taking account of fine root decomposition in root-excluded quadrates; Thecontribution rate of litter respiration is 17.77%, 13.35%, 21.01%, 12.61% and 23.56%; Thecontribution rate of root respiration is biggest, followed by soil heterotrophic respiration andthat of litter respiration is the lowest for Quercus aliena var.acuteserrata young stand,broadleaf/coniferous mixed stand and Quercus variabilis stand; But the contribution rate of soilheterotrophie respiration is biggest, followed by root respiration and that of litter respiration isthe lowest for the other two stands; The biggest and smallest contribution rate of rootrespiration is before 15:00 and at 18:00～21:00 respectively, the biggest and smallestcontribution rate of soil heterotrophic respiration is at 18:00～21:00 and before 15:00respectively and the biggest and smallest contribution rate of litter respiration is at 15:00～18:00and beforel2:00; The contribution rate of root respiration in summer is the biggest, followedby in spring and fall, lowest in winter, that of soil heterotrophic in winter is the biggest, followed by in spring and lowest in summer and fall, that of litter respiration in fall is biggestfollowed by summer, and lowest in spring and winter; The most important dominant factorscontrolling the seasonal variation in contribution rate of litter respiration is litter water content,the second factor is existing litter amount, which can accounts for 62.60%～71.42% of thedifference of contribution rate of litter respiration among the five stands.(7) There is no significant differences in total soil respiration rate, soil respiration rateand the heterotrophic respiration rate among the five stands (P＞0.05), but the significantdifferences occur in the autotrophic respiration rate and litter respiration rote (P＜0.05). The livefine root biomass accounts for 94.71%of the difference of autotrophie respiration rates amongthe five stands, the existing litter amount accounts for 57.83% of the difference of litterrespiration among 5 stands in which the litter quality has obvious difference, but it canaccounts for 99.9% of the difference of litter respiration among 4 broadleaf stands in whichthe litter quality has no obvious difference.