共查询到20条相似文献，搜索用时 218 毫秒
1.
【目的】分析欧美杨107杨昼夜液流特征,量化夜间液流对整日液流的贡献率,探讨昼夜液流对树形因子和环境因子的响应差异,为深入认识树木水分利用策略对环境的响应机制提供理论依据。【方法】以北京市顺义新城滨河森林公园内的树种欧美杨107杨为研究对象,在样地内选择8株35年生、长势良好的样木,于2018年7—10月采用热扩散探针对样木进行树干液流变化监测,并同步监测环境因子。【结果】1)欧美杨小、中、大径阶的液流速率呈"昼高夜低"单峰曲线,前半夜液流活动比后半夜活跃;2)各径阶整日液流量为39.04～94.96 g·cm~(-2)d~(-1),夜间液流量为3.34～10.49 g·cm~(-2)d~(-1),夜间液流对整日液流的贡献率在4.2%～16.2%范围内波动,整日液流量与日间液流量(去除夜间液流的日总液流)差异性达极显著水平(P 0.01);3)日间和夜间液流对树形因子的响应关系一致,冠幅与昼夜液流呈显著正相关(P0.05),对昼夜液流的解释程度分别为80%和77%,树高和胸径对昼夜液流的影响不显著(P 0.05);4)饱和水汽压差(VPD)、太阳总辐射(Ra)、空气温度(T)和风速(Ws)是影响欧美杨整日液流量的主要环境因子;影响日间和夜间液流速率的环境因子存在差异,VPD、Ra、T和Ws是影响日间液流速率的主要环境因子,而夜间液流速率主要受VPD和Ws影响;Ws对昼夜液流速率的影响具有两重性,具体表现为白天促进树干液流速率,夜间抑制树干液流速率;日间液流量与夜间液流量极显著正相关(P 0.01),小、中、大径阶的日间液流量对夜间液流量的解释程度分别为37%、48%和47%。【结论】欧美杨存在明显的夜间液流,估算欧美杨耗水量时,忽略夜间液流会低估日常需水量。液流速率对环境因子的响应存在昼夜差异,估算和模拟树木蒸腾量时,应分日间和夜间考虑环境因子对液流速率的影响。 相似文献
2.
3.
以神农架华山松为研究对象,采用热扩散探针法对树干液流进行连续1 a的测定,结合同步观测的环境因子,分析华山松树干液流规律及其与环境因子的关系。结果表明:(1)华山松树干液流具有明显的昼夜与季节变化规律。全年夜间树干液流量占整日液流量的10.37%,树干液流速率在不同季节表现为夏季春季秋季冬季。(2)不同天气条件下树干液流速率表现为晴天阴天雨天,晴天和阴天树干液流速率日变化规律均为单峰曲线,而雨天树干液流日变化规律不明显。(3)空气相对湿度和蒸汽压亏缺为影响华山松树干液流月通量的主要因子。不同季节影响树干液流日通量的主要因子存在差异,春季主要影响因子是太阳总辐射和蒸汽压亏缺;夏季主要影响因子是风速、空气相对湿度和太阳总辐射;秋季主要影响因子是降水量、空气相对湿度、太阳总辐射和蒸汽压亏缺;冬季主要影响因子是空气温度、空气相对湿度和蒸汽压亏缺。 相似文献
4.
利用热脉冲技术对雷州半岛25年生加勒比松人工林旱季 (2000年10月至2001年2月)树干液流特征、耗水及环境因子的关系进行研究.结果表明:加勒比松边材不同位点的液流密度由外到内呈低-高-低的态势;观测期间林分日液流密度变幅为411～4 120 L·m-2·d-1,日平均液流密度为2 084 L·m-2·d-1;旱季无雨时,加勒比松日液流密度与太阳辐射、饱和蒸汽压差、气温及湿度相关性显著;有雨时,加勒比松日液流密度仅与饱和蒸汽压及湿度相关性显著;单株日耗水量变幅为6.4～169.5 L,日平均耗水量为55.5 L,林分日耗水量变幅为0.35～3.52 mm·d-1,日均耗水量为1.71 mm·d-1,旱季总耗水量为257.7 mm,占同期降水量的72.3%. 相似文献
5.
应用热扩散技术法,于2010年4—8月对浙江天目山自然保护区内的2株柳杉古树的树干液流进行连续观测,结合所测定的相关环境因子,分析了柳杉树干液流和耗水量的变化规律,以及液流与各环境因子的关系。结果表明:不同季节柳杉树干液流速率日变化规律基本一致,呈单峰波动曲线,但树干液流启动时间、达到峰值时间及迅速下降时间存在明显差异;树干液流密度与光合有效辐射、空气温度和水汽压差间存在极显著正相关,与空气相对湿度和CO2浓度呈极显著负相关;液流密度随树干直径的增加,无明显变化差异,但液流速率和日均耗水量均随树干直径的增加而增大;胸径75.6 cm柳杉和胸径62.8 cm柳杉的日均耗水量季节变化过程相同,但2者变化差异较大,6月份日均耗水量最低,分别为(49.356±14.883) kg和(9.531±4.297)kg;4月份日均耗水量最高,分别为(110.022±21.890)kg和(49.352±2.629)kg。 相似文献
6.
【目的】研究西藏拉萨半干旱河谷地带藏川杨和北京杨树干液流的干湿季变化特征及环境影响因素,以期为该地区造林树种选择和合理配置提供科学依据。【方法】运用Granier热扩散探针技术,于2015年旱季和雨季在西藏拉萨半干旱河谷对藏川杨和北京杨的树干液流进行连续观测,并同步测定太阳辐射(Q)、空气温度(T_a)、土壤含水量(SWC)、饱和蒸气压亏缺(VPD)等环境因子。【结果】1)拉萨河谷区主要气象因子在旱季和雨季存在较大差异,雨季的Q、T_a、SWC、VPD等均高于旱季,主要气象因子的平均值为雨季的60%左右。2)藏川杨和北京杨的树干液流日变化表现出昼高夜低的规律,二者在雨季的日变化为多峰曲线,旱季为单峰曲线。旱季和雨季藏川杨液流速率均显著大于北京杨,北京杨液流密度在旱季和雨季相比藏川杨的液流密度分别下降71%和58%;相比雨季的液流密度,2种杨树的液流密度在旱季分别下降65%和76%。3)在旱季和雨季,主要环境因子Q和VPD与2种杨树树干液流间具有显著相关性,且Q和VPD的日变化与2种杨树的液流速率日变化之间存在明显的时滞效应。Q和VPD对北京杨树干液流的影响小于对藏川杨树干液流的影响。【结论】在拉萨河谷区旱季和雨季较大气候差异的环境下,藏川杨和北京杨树干液流速率均具有较为明显的昼夜节律。但2树种树干液流在峰值、日平均值、启动时间以及受环境因子的影响方面均存在明显差异,特别是在干旱季节尤为显著,藏川杨作为乡土树种显示出更强的适应性。 相似文献
7.
为探究减少穿透雨情况下樟子松树干液流速率的变化及其与环境因子的关系,采用热扩散式液流探针,对辽西北樟子松人工林的树干液流速率以及林内多个环境因子进行同步连续监测,分减少穿透雨样地(人工截留穿透雨30%)和正常降水样地(对照),测定2018年生长季(4—10月)樟子松树干液流速率,对不同天气情况下樟子松树干液流速率的日变化、夜间变化以及月变化进行分析讨论。结果表明：1)经过长期穿透雨减少处理后樟子松树干液流速率显著高于对照组,不同天气情况下白天和夜间的差异幅度均为：晴天>雨天>阴天。2)经过降水后,减雨处理的樟子松树干液流启动时间早于对照组,而对照组樟子松日树干液流平均速率经过降水后增长幅度高于减雨组。3)樟子松树干液流速率在生长季内先升高后降低,夏季高于春季和秋季。4)减雨样地与对照样地樟子松的树干液流速率均受气象因子的影响较大,与空气温度和光合有效辐射呈显著的正相关,与空气湿度呈负相关关系。降水减少增加了沙地樟子松的树干液流速率,这对未来人工林的管理提供了参考。 相似文献
8.
刺槐春夏季树干液流变化规律 总被引：8，自引：0，他引：8
用热扩散式树干茎流计(TDP)于4-8月对刺槐树干液流进行连续观测,结果表明:刺槐边材液流速率日变化呈宽峰曲线,每日6:50左右启动,13:00左右达到峰值,19:30左右开始迅速下降,没有明显的液流停止界限,夜间有较高的液流存在;夏季液流每天启动的时间早于春季10min左右,达到峰值的时间早于春季1h左右,迅速下降的时间晚于春季1h左右,即夏季液流高峰维持的时间长于春季,但是夏季的峰值、日平均液流速率和液流通量小于春季;树干液流速率与直径关系不大,但日周期单木耗水量随树干直径的增大而增加,与树干直径和边材面积相关显著,相关系数分别为0.983和0.999. 相似文献
9.
通过测定元谋干热河谷地区几种相思和桉树自然条件下的蒸腾速率及其相关因子 ,分析了这些树种水分消耗量的日变化情况。根据水分消耗量公式计算 ,发现马占相思、肯氏相思、赤桉和窿缘桉、大叶相思、厚荚相思、绢毛相思、柠檬桉水分消耗最大、最小值的时间。结果表明 ,各树种全天水分消耗量依次为窿缘桉、肯氏相思、柠檬桉、赤桉、厚荚相思、绢毛相思、马占相思、大叶相思。此外 ,还预测了在 1.5m× 2m、2m× 2m、2m× 3m等 3种不同造林密度下 ,各树种每公顷的水分消耗量 ,水分消耗量最大的窿缘桉分别为 1876 . 81kg、14 0 7.75kg、96 8.12kg ;水分消耗量最小的大叶相思分别为 2 6 0 .77kg、195.58kg、130 .33kg 相似文献
10.
依据组织热平衡原理,运用热扩散探针法,于2015年3月1日—2016年3月1日对冀北山地小五台自然保护区华北落叶松的树干液流速率进行连续监测,并同步观测气温、相对湿度、净辐射、总辐射、风速等环境因子的变化,研究其树干液流特征以及与环境因子的关系。结果表明:(1)小五台地区,华北落叶松树干液流启动于4月下旬,结束于10月上旬,前后历时160多d。晴天条件下,不同月份树干液流速率日变化均呈典型的单峰曲线,且液流的启动、到达峰值、结束时间以及液流升降速率存在差异。(2)生长季华北落叶松树干液流速率峰值以7、8、9月最高,都达到0.034 kg·h~(1)cm~(1)以上;日均值以7、8月最高,达到0.014 kg·h~(1)cm~(1)以上。(3)华北落叶松树干液流速率与空气温度、净辐射、总辐射、水汽压亏缺、风速呈极显著正相关,与空气湿度呈极显著负相关。环境因子对树干液流速率影响的大小顺序为:净辐射空气温度总辐射空气湿度风速。(4)整个生长季华北落叶松单株总耗水量为2 145.73±379.30 kg,其中以7、8月耗水量最大,分别为517.23±54.60和515.01±71.58 kg。 相似文献
11.
Using thermal dissipation and the ICT-2000TE equipment made in Australia, the sap flow of Castanopsis jianfengensis and various environmental factors were measured simultaneously in a mixed tropical montane rainforest at Jianfengling Nature
Forest Reserve (18°369′N, 108°52′E, 860 m elevation) during the dry and rainy seasons of 2002. The results show that sap flow
velocity of C. jianfengensis exhibited a monopeak pattern on clear days and a multi-peak pattern on cloudy or rainy days. Sap flow velocity had significant
positive correlations with solar radiation, air temperature, vapor pressure deficit and wind speed and a negative correlation
with air relative humidity. In the dry season, sap flow velocity had a significant positive correlation with soil temperature
and poor correlation with soil moisture; it was the opposite in the rainy season, indicating that precipitation clearly affected
sap flow. Linear regression models between sap flow and environmental factors were established and were significant at the
0.005 level of probability. The mean transpiration rates of C. jianfengensis were 103.5 and 41.3 kg/d in our single tree and 1.94 and 0.77 mm/d in stand level in the dry and rainy season, respectively.
__________
Translated from the Chinese Journal of Applied Ecology, 2007, 18(4): 742–748 [译自:应用生态学报] 相似文献
12.
Plant biomass, species diversity and net primary productivity are presented for herb layer of banj oak (Quercus leucotrichophora A. Camus)-chir pine (Pinus roxburghii Sarg.) mixed forest in Kumaun, central Himalaya, India. The species diversity declined from a maximum (3.56) in September to a minimum (2.11) in December. The monthly live shoots biomass exhibited a single peak growth pattern with highest live shoot biomass of 185 g·m-2 in August. The seasonal pattern showed that the maximum above-ground production (131 g·m-2) occurred during the rainy season and the minimum (1 g·m-2) during winter season. The below-ground production was maximum during winter season (84 g·m-2) and minimum during summer season (34 g·m-2). The annual net shoot production was 171 g·m-2 and total below-ground production was 165 g·m-2. Of the total input 61% was channeled to above-ground parts and 39% to below-ground parts. Transfer of live shoots to dead shoots compartments and that of dead shoots to litter compartments was 61% and 66%, respectively. The total dry matter disappearance was 61% of the total input within annual cycle. The herb layer showed a net accumulation of organic matter, indicating the seral nature of the community. 相似文献
13.
The effect of shoot pruning on leaf phenology, stem wood anatomy and sap flow was investigated on Senna spectabilis (DC.) Irwin and Barneby in Machakos, Kenya. Unpruned trees (single stem) were compared to hedges (two to four stems), pruned
4 times a year during two rainy seasons (April–June, 1997 and November, 1997–January, 1998) separated by a dry season (July–October
1997). Trees attained peak leaf area of 55 m2 plant−1 during the rainy seasons, and shed all their leaves naturally during the dry season. Maximum hedge leaf area was 4 m2 plant−1 between pruning events and 5.2 m2 plant−1 during the dry season. Pruning induced multiple stems and narrow xylem vessels with low hydraulic conductivity. Average cross
sectional area of conducting wood per plant was at least 1.8 times greater in trees than in hedges. Xylem lumen diameter at
5 mm depth below the cambium was significantly (P < 0.001) larger in trees (53.6 ± 6.21 μm) than that in hedges (36.2 ± 8.21 μm). Maximum sap flow occurred in the wet season
for trees (4800 g d−1 plant−1) and in the dry season for hedges (1400 g d−1 plant−1). Wet season pruning suppressed crown expansion and modified the natural phenology of senna, reducing transpiration rate
and therefore soil water depletion, causing crowns to grow. This enhanced the ecological combining ability of senna managed
as hedges with annual crops. 相似文献
14.
为探讨树干液流速率与气象因子之间的时滞特性,采取PS-TDP8型热耗散式树干液流测定系统持续监测,以掌握树体蒸腾耗水规律,从而为杏李科学灌溉提供理论依据。研究结果表明:杏李生长季液流速率日均最大值在6月18日;决定其第1主成分大小的是温度及水气压亏缺,决定第2主成分大小的是光照强度及空气相对湿度。4—8月液流速率均与1 h前第1、2主成分相关性最大;杏李生长季液流与1 h前光照强度相关性最大,相关系数为0.810,与1 h后的气温、空气相对湿度、水汽压亏缺相关性最大,系数分别为0.757,-0.572,0.736;回归方程中液流与实时气象因子拟合决定系数最大,为0.751。杏李生长季液流速率与实时气象因子回归拟合模型效果最好,体现了杏李在长期树干液流数据模拟中,可以不用考虑液流速率与气象因子的时滞效应。 相似文献
15.
H. R. Bazié J. Sanou J. Bayala A. Bargués-Tobella G. Zombré U. Ilstedt 《Agroforestry Systems》2018,92(6):1673-1686
Lack of data on water use of key species of drylands constitutes an obstacle to understanding their role in hydrological processes in this environment. To elucidate seasonal variation in water consumption by Vitellaria paradoxa, the dominant species of parklands of the semi-arid areas of West Africa, we’ve measured its transpiration using heat ratio method (HRM) and seven potential explanatory variables. Sap flux was found to be significantly different among years with 0.64, 0.59 and 0.67 L h?1 dm?2 in 2008, 2009 and 2010, respectively. Sap flux was significantly higher in the dry (0.73 L h?1 dm?2) than in the wet season (0.53 L h?1 dm?2). Nighttime sap flux during dry season (0.48 L h?1 dm?2) was significantly higher than that of the wet season (0.20 L h?1 dm?2) and it contributes on average to 26% of daily sap flow with a maximum reaching 49%. The mean transpiration rate per tree was 151 L day?1 and all measured variables except rainfall and soil water content were significantly correlated with sap flux. These correlations were stronger (higher R value) during the rainy than in the dry season. Vapor Pressure Deficit (VPD) explained the highest proportion of sap flux variation and their curve was of parabolic type (R2 = 0.54) indicating that V. paradoxa can probably down-regulate its canopy conductance beyond a certain threshold of VPD, which is about 3 kPa in the present study. Future studies should investigate such hypothesis as well as the impacts of the variation of V. paradoxa transpiration due to climatic variables on hydrological cycles. 相似文献
16.
Carbon fluxes and their response to environmental variables in a Dahurian larch forest ecosystem in northeast China 总被引：1，自引：0，他引：1
WANG Hui-min SAIGUSA Nobuko ZU Yuan-gang WANG Wen-jie YAMAMOTO Susumu KONDO Hiroaki 《林业研究》2008,19(1):1-10
The Dahurian larch forest in northeast China is important due to its vastness and location within a transitional zone from boreal to temperate and at the southern distribution edge of the vast Siberian larch forest. The continuous carbon fluxes were measured from May 2004 to April 2005 in the Dahurian larch forest in Northeast China using an eddy covariance method. The results showed that the ecosystem released carbon in the dormant season from mid-October 2004 to April 2005, while it assimilated CO2 from the atmosphere in the growing season from May to September 2004. The net carbon sequestration reached its peak of 112 g.m^-2.month ^-1 in June 2004 （simplified expression of g （carbon）.m^-2.month^-1） and then gradually decreased. Annually, the larch forest was a carbon sink that sequestered carbon of 146 g-m^-2.a^-1 （simplified expression of g （carbon）.m^-2.a^-1） during the measurements. The photosynthetic process of the larch forest ecosystem was largely affected by the vapor pressure deficit （VPD） and temperature. Under humid conditions （VPD 〈 1.0 kPa）, the gross ecosystem production （GEP） increased with increasing temperature. But the net ecosystem production （NEP） showed almost no change with increasing temperature because the increment of GEP was counterbalanced by that of the ecosystem respiration. Under a dry environment （VPD 〉 1.0 kPa）, the GEP decreased with the increasing VPD at a rate of 3.0 μmol.m^-2.s^-1kPa -1 and the ecosystem respiration was also enhanced simultaneously due to the increase of air temperature, which was linearly correlated with the VPD. As a result, the net ecosystem carbon sequestration rapidly decreased with the increasing VPD at a rate of 5.2 μmol.m^-2.s-1.kPa^-1. Under humid conditions （VPD 〈 1.0 kPa）, both the GEP and NEP were obviously restricted by the low air temperature but were insensitive to the high temperature because the observed high temperature value comes within the category of the optimum range. 相似文献
17.
Hui-min Wang Nobuko Saigusa Yuan-gang Zu Wen-jie Wang Susumu Yamamoto Hiroaki Kondo 《林业研究》2008,49(Z2)
The Dahurian larch forest in northeast China is important due to its vastness and location within a transitional zone from
boreal to temperate and at the southern distribution edge of the vast Siberian larch forest. The continuous carbon fluxes
were measured from May 2004 to April 2005 in the Dahurian larch forest in Northeast China using an eddy covariance method.
The results showed that the ecosystem released carbon in the dormant season from mid-October 2004 to April 2005, while it
assimilated CO2 from the atmosphere in the growing season from May to September 2004. The net carbon sequestration reached its peak of 112
g·m−2·month−1 in June 2004 (simplified expression of g (carbon)·m−2·month−1) and then gradually decreased. Annually, the larch forest was a carbon sink that sequestered carbon of 146 g·m−2·a−1 (simplified expression of g (carbon)·m−2·a−1) during the measurements. The photosynthetic process of the larch forest ecosystem was largely affected by the vapor pressure
deficit (VPD) and temperature. Under humid conditions (VPD < 1.0 kPa), the gross ecosystem production (GEP) increased with
increasing temperature. But the net ecosystem production (NEP) showed almost no change with increasing temperature because
the increment of GEP was counterbalanced by that of the ecosystem respiration. Under a dry environment (VPD > 1.0 kPa), the
GEP decreased with the increasing VPD at a rate of 3.0 μmol·m−2·s−1·kPa-1 and the ecosystem respiration was also enhanced simultaneously due to the increase of air temperature, which was linearly
correlated with the VPD. As a result, the net ecosystem carbon sequestration rapidly decreased with the increasing VPD at
a rate of 5.2 μmol·m−2·s−1·kPa−1. Under humid conditions (VPD < 1.0 kPa), both the GEP and NEP were obviously restricted by the low air temperature but were
insensitive to the high temperature because the observed high temperature value comes within the category of the optimum range. 相似文献
18.
Hua Wang Ping Zhao Quan Wang Xian Cai Ling Ma Xingquan Rao Xiaoping Zeng 《Frontiers of Forestry in China》2008,3(1):72-78
In this paper, we studied the nocturnal stem water recharge of Acacia mangium. It is helpful to improve the precision of canopy transpiration estimation and canopy stomatal conductance, and to further
understand the lag time of canopy transpiration to stem sap flow. In this study, the whole-tree sap flow in an A. mangium forest was measured by using Granier’s thermal dissipation probe for over two years in the hilly land of South China. The
environmental factors, including relative humidity (RH), precipitation, vapor pressure deficit (VPD), photosynthetically active radiation (PAR), and air temperature (T
a) were recorded simultaneously. The stem water recharge of A. mangium was analyzed on both daily and monthly scales. Sap flux density was lower at night than during the day. The time range of
nighttime sap flux density was longer in the dry season than in the wet season. The water recharging mainly occurred from
sunset to midnight. No significant differences were observed among inter-annual nighttime water recharges. Nighttime water
recharge had no significant correlation with environmental factors, but was well correlated with the diameter at breast height,
tree height, and crown size. In the dry season the contribution of nighttime water recharge to total transpiration had significant
correlations with daytime transpiration, total transpiration, VPD, PAR and T
a, while in the wet season it was significantly correlated with daily transpiration and total transpiration.
__________
Translated from Chinese Journal of Ecology, 2007, 26(4): 476–482 [译自: 生态学杂志] 相似文献
19.
[目的]为正确认识台风对桉树人工林蒸腾耗水的影响。[方法]采用热扩散茎流计对尾巨桉树干液流在台风前后进行连续监测,分析其对台风天气的响应,并同步测定林分气象条件,分析台风过程中树干液流与气象因子之间的相关性。[结果]表明:台风当天,树干液流密度与台风登陆前后(单峰)不同,呈不规律多峰型曲线,树干日均液流密度(2.89 mL·h~(-1)·cm~(-2))较台风前减少53%,夜间液流波动较大;日间最大峰值(7.76 mL·h~(-1)·cm~(-2))出现在下午,峰值较台风前降低55%,树干液流日通量极显著小于台风登陆前后;台风登陆前树干液流密度峰值(17.4 mL·h~(-1)·cm~(-2))及平均液流密度(6.15 mL·h~(-1)·cm~(-2))分别是台风登陆过后的1.24倍和1.14倍,台风后树干液流日通量较台风前均有所下降;台风当天,影响液流的主要气象因子为风速、大气温度、空气湿度、水汽压亏缺和降雨量,液流与风速的相关系数较台风前增大52%,与降雨量的相关系数是台风前的2.6倍,与其他因子的相关系数较台风前均下降了50%左右,而台风登陆前后之间的主要影响因子差异不大。[结论]台风当天的日均液流密度、白天的平均液流密度和日通量均极显著小于台风前后,而夜间液流显著大于台风前后;台风前后的日均液流密度差异不显著,夜间液流台风前显著大于台风后;台风过程中风速成为影响液流的关键因子,与太阳辐射相关性不显著,其他影响因子与台风前后相同,但相关系数除风速和降雨量外均显著下降。 相似文献
20.
Junhua Yan Xingzhao Liu Xuli Tang Guirui Yu Leiming Zhang Qingqing Chen Kun Li 《Journal of Forest Research》2013,18(1):21-30
A number of continuous eddy covariance measurements and long-term biomass inventories had proved that old-growth forests are carbon sinks worldwide. The present study estimated the net ecosystem productivity (NEP) for an old-growth subtropical forest at the Dinghushan Biosphere Reserve in South China to investigate the temporal pattern of carbon sequestration, both seasonally and annually. The measured NEP over 7 years (from 2003 to 2009) showed that this forest was a net carbon sink, ranging from 230 (in 2008) to 489 g C m?2 year?1 (in 2004). The greatest value of NEP was found in the driest year and the lowest value in the wettest year during the study period. Within a year, NEP during the dry season was about 81.4 % higher than for the wet season. Accordingly, the dry season at seasonal scale and dry years at interannual scale are key periods for carbon sequestration in this forest. The strong seasonality of ecosystem or soil respiration (ER or SR) compared with gross primary productivity (GPP) resulted in substantial amounts of carbon being sequestered during dry seasons. A decrease of GPP and an increase of ER or SR demonstrated the lower carbon uptake in rainy years. From this study, we conclude that GPP and living biomass carbon increment are not overriding parameters controlling NEP. The variations in ER or SR driven by the rainfall scheme were the dominant factor determining the magnitude of NEP in this forest in South China. 相似文献