摘要
应用数值方法 ,对中国西北干旱区 5个主要树种 (樟子松、榆树、二白杨、胡杨和沙枣 )的叶面蒸腾及气孔导度对气象因子的响应进行了探讨 ,时间尺度为日。两套综合环境观测系统分别安置在黑河中游的临泽和下游的额济纳旗 ,每半小时自动记录微气象因子、土壤水分和树汁流量。应用日平均树汁流量、饱和差、总辐射、平均气温和土壤含水量拟合树木叶面蒸腾及气孔导度的经验公式。气孔导度和单个气象因子之间具有很高的相关性。应用多个气象因子所建立的经验公式能够很好的模拟气孔导度 ,模拟效果比气孔导度与单一因子的相关性高。气孔导度总体上和饱和差和气温呈指数关系 ,与总辐射的关系多种多样 ,与土壤含水量的关系较复杂。在中游地区 ,二白杨气孔导度、叶面蒸腾量和单株树木树汁流量最大。试验期间下游试验点土壤水分充足 ,耐旱树种胡杨及沙枣树汁流量较大 ,但其气孔导度及叶面蒸腾量均较小。本次研究没有发现树木叶面蒸腾量和单一环境因子之间具有明显的相关性。叶面蒸腾模拟效果没有气孔导度模拟效果好 ,原因是叶面蒸腾是气孔导度和饱和差的函数。
A central issue in hydrology today is to establish relationships between hydrological and biological processes in ecosystems. Water availability is a sparse and often restricting factor for plant production in the Arid Regions of Northwest China (ARNC). Owing to the analogy between the transpiration and CO_2 diffusion processes, water shortage may limit CO_2 assimilation and reduce the photosynthetic process. While for the low vegetation density and high soil evaporation, the water use efficiency is very low in ARNC. In order to use the short water resources efficiently to get high plant production, and to protect the deteriorating environments such as desertification and sandstorm in ARNC, where a number of shelterbelts and some riparian forests are in existence, transpiration of the major five tree species in this region are measured using sapflow techniques in the summer and early autumn, 2002. Tree transpiration is the major pathway for both water and energy leaving the forest ecosystems, and it depends on soil moisture and other weather parameters strongly. The scale at which the forest is studied answers different questions in the context of energy and matter. Studies at tree level provide an averaged response of the mostly non-linear physiological processes, and are therefore, more useful for empirical modeling. The two experimental sites are located in the midstream and downstream of the Heihe river basin that is the second largest inland river basin of ARNC, named Linze and Erjinaqi, respectively. In the Linze site, the Mongol Scotch Pine (Pinus sylvestris var. mongolica Litvin), Dryland Elm (Ulmus glaucescens Franch) and Gansu Poplar (Populus gansuensis C. Wang et H.L.Yang) are the dominated tree species. A desert riparian forest in Erjinaqi is selected where the Euphrates Poplar (Populus euphratica Oliv.) and the Russia olive (Elaeagnus angustifolia Linn.) are the dominated tree species. An ENVIS System EERIL 3 (GMBH) was used to measure microclimate variables, soil moisture and sapflow every half an hour in each site. Sapflow was measured using sapflow sensors (UP GMBH) at 1.3m height for each selected tree, and the measuring principle is the heat diffusion method. The leaf area index (LAI, LAI2050,LI-COR INC.) and the projected area (PA) of each observed tree are measured. Fredrik et al. summarized the relationship between the sapflow and transpiration, and stated that the sum of transpiration totals could be assumed to equal the sum of transpiration in daily scale in usual conditions. Thus the transpiration per leaf area and the tree conductance (TC) are calculated in daily scale according to the methods:E=F×1000/(PA×LAI×24×60×60) Where E is the tree transpiration per leaf area (g·m^(-2)·s^(-1)), PA is the tree canopy projected area (m^2), LAI is leaf area index, and F is the daily sapflow (l·d^(-1)). Tree conductance (TC, m s^(-1)) is a function of daily averaged vapor pressure deficit (D, Pa) and the tree transpiration per leaf area E: TC=λEγρc_pDwhere λ is the latent heat of evaporation of water (2465 J·g^(-1)), γ is the psychrometer constant (65.5 Pa·K^(-1)), ρ is the density of the air (1225 g·m^(-3)), and c_p is the specific heat of air (1.01 J·g^(-1)·K^(-1)). In the observed period, the averaged sapflow of Euphrates Poplar is 22.64 l·d^(-1) and of Russia olive is 6.95 l·d^(-1). The averaged sapflow of Mongol Scotch Pine, Dryland Elm and Gansu Poplar is 4.03 l·d^(-1), 4.60 l·d^(-1) and 10.93 l·d^(-1), respectively. The averaged transpiration per leaf area of Euphrates Poplar and Russia olive is 0.34 and 0.13 mm·d^(-1), respectively, while of Mongol Scotch Pine, Dryland Elm and Gansu Poplar is 0.25mm·d^(-1), 0.55 mm·d^(-1) and 2.19 mm·d^(-1), respectively. The averaged TC of Euphrates Poplar and Russia olive is 0.00025 and 0.00011 m·s^(-1), respectively, while for Mongol Scotch Pine, Dryland Elm and Gansu Poplar, the averaged value is of 0.00037 m·s^(-1), 0.00082 m·s^(-1), and 0.0033 m·s^(-1),
出处
《生态学报》
CAS
CSCD
北大核心
2004年第3期477-485,共9页
Acta Ecologica Sinica
基金
中国科学院方向性资助项目(KZCX3- SW - 32 9)
国家自然科学基金资助项目( 40 30 1 0 1 0
4 0 2 350 53)
中国科学院知识创新重大资助项目(KZCX1 - 1 0 - 0 3- 0 1 )~~
