华北落叶松树体储水利用及其对土壤水分和潜在蒸散的响应: 基于模型模拟的分析

doi:10.3724/SP.J.1258.2011.00411

摘要/Abstract

摘要：

树体储水在树木水分传输中具有重要的作用, 不仅为蒸腾提供水分来源, 还具有缓冲作用, 可防止木质部导管水势过低以至于水分传输的失败。树体储水动态及其利用的研究对于认识树木对水分胁迫的响应机制具有重要意义。该研究构建了包含树体储水释放-补充作用的树干水分传输模型, 可模拟计算林分小时尺度的冠层蒸腾、边材液流、树体储水与木质部导管水流交换过程, 并以六盘山北侧的华北落叶松(Larix principis-rupprechtii)人工林为例, 在林分水平分析树体储水利用及其与土壤水分和潜在蒸散之间的关系。检验结果表明, 该模型能够精确地模拟出林分边材液流的日变化特征, 模拟与观测的小时液流速率决定系数R²为0.91 (n = 2 352)。模拟结果表明, 在典型晴朗天气下, 在日出时树体储水利用启动, 至9:00左右达到峰值(0.14 mm·h^-1), 午间降至0, 下午降为负值直至午夜, 即进入树体补水阶段; 树体储水日使用量(DJ_z)为0.04-0.58 mm·d^-1, 与日蒸腾量(DT_r)成正相关(R² = 0.91), 对蒸腾的贡献为25.6%。分析结果表明, 当潜在蒸散(ET_p)低于4.9 mm·d^-1时, ET_p是华北落叶松树体储水利用的主要驱动因子, DJ_z与ET_p成正相关(R² = 0.68); 当ET_p高于4.9 mm·d^-1时, DJ_z随着ET_p的增加呈现降低趋势; DJ_z与土壤水势没有显著相关关系(p > 0.05), 但最大树体储水日使用量(DJ_zmax)与土壤水分含量成正相关(R²= 0.79), 说明土壤水分是树体储水利用的限制因子。

关键词: 华北落叶松, 边材液流, 树干水分传输模型, 树体储水

Abstract:

Aims Water stored in the secondary xylem of the sapwood of large trees is not only a source for transpiration, but also may help avoid xylem cavitation and subsequent failure of water transfer in xylem. Our objective was to study the dynamics of tree water storage and use in order to understand the response mechanism of trees to water stress.
Methods A model simulating the diurnal pattern of water transfer within stems was designed. It combines a non-steady-state hydraulic model with a transpiration model that was based upon the Penman-Monteith equation and a Jarvis-type representation of the stomatal resistance including xylem conduct water potential (ψ_hx), vapor pressure deficit (D_s) and photosynthetically active radiation (IP). The combined model simulates the diurnal variation of water uptake, storage flow and transpiration rate directly from environmental variables. We simulated the sap flow of Larix principis-ruprechtii, which is planted in Diediegou catchments on the north sides of the Liupan Mountains, and analyzed the relationship between storage water use and environmental factors.
Important findings The hydraulic model accurately simulated diurnal patterns of measured sap flow under microclimatic conditions; the coefficient of determination (R²) between observed and simulated sap flow velocity in calibration sets was 0.91 (n = 2 532). On a typical sunny day, the highest rate of storage water use started at about 9:00 AM, decreased to zero at noon and turned to recharge throughout the afternoon until midnight. The daily storage water use varied between 0.04 and 0.58 mm·d^-1 and was positively related to transpiration. Storage water provided 25.5% of transpiration water. When potential evapotranspiration (ET_p) was < 4.9 mm·d^-1, daily storage water use (D_Jz) was positively related to ET_p_. D_Jz linearly increased with ET_p as ET_p increased, but decreased correspondingly when ET_p was >4.9 mmd^-1_. There was no significant relationship between D_Jz and soil water potential (p > 0.05), but the maximum D_Jz was positively related to soil water potential (R²= 0.79). Therefore, ET_p is the primary driving factor of water storage use, and soil water potential is the limiting factor.

Key words: Larix principis-ruprechtii, sap flow, stem water transfer model, tree water storage

孙林, 熊伟, 管伟, 王彦辉, 徐丽宏. 华北落叶松树体储水利用及其对土壤水分和潜在蒸散的响应: 基于模型模拟的分析. 植物生态学报, 2011, 35(4): 411-421. DOI: 10.3724/SP.J.1258.2011.00411

SUN Lin, XIONG Wei, GUAN Wei, WANG Yan-Hui, XU Li-Hong. Use of storage water in Larix principis-ruprechtii and its response to soil water content and potential evapotranspiration: a modeling analysis. Chinese Journal of Plant Ecology, 2011, 35(4): 411-421. DOI: 10.3724/SP.J.1258.2011.00411

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https://www.plant-ecology.com/CN/Y2011/V35/I4/411

图/表 8

图1 树干水分输运示意图(参考Lhommea et al., 2001)。ψl, 叶水势; ψs, 土壤水势; ψx, 木质部导管水势; ψz, 木质部存水部水势; C, 水容; hsx, 根区土壤-木质部导管高差(m); Js, 木质部导管液流; Jz, 木质部导管与储水组织水分交换; rsx, 土壤-树干木质部导管阻力; rxl, 树干木质部导管-叶-大气阻力; rzx, 树体储水组织-树干木质部导管阻力; Tr, 蒸腾速率。

Fig. 1 Schematic diagram of water transfer within the tree stem (refer to Lhommea et al., 2001). ψl, leaf water potential; ψs, soil water potential conduct; ψx, xylem vessels water potential; ψz, xylem plant-reservoir water potential; C, hydraulic capacitance; hsx, the height of root to xylem vessels (m); Js, xylem conduct water flow; Jz, water exchange between the xylem vessels and the storage compartment; rsx, soil-xylem hydraulic resistance; rxl, xylem-leaf-air hydraulic resistance; rzx, storage hydraulic resistance; Tr, transpiration rate.

表1 观测华北落叶松样木信息

Table 1 Information of the sample trees in Larix principis-rupprechtii stand

样树编号 Sample tree number	胸径 DBH (cm)	树高 Tree height (m)	探头高度 Probe position (m)	探头位置树径 Diameter at probe position (cm)	边材面积 Sapwood area (cm²)	冠幅面积 Canopy area (m²)
4	13.1	9.9	1.5	13.1	78.54	16.33
17	11.2	7.1	2.0	10.0	50.84	10.25
18	6.4	11.1	2.0	5.7	19.85	6.31
25	8.5	7.9	1.5	8.5	38.42	6.31
40	9.1	8.4	1.5	9.1	43.01	6.87
51	10.2	8.6	1.5	10.2	51.93	7.94
55	10.8	7.9	1.5	10.8	57.08	8.53
65	13.0	8.1	1.5	13.0	77.55	10.77

表2 冠层导度模型参数

Table 2 Parameters of canopy conductance model

参数 Parameter	定义 Definition	数值 Value	单位 Unit	来源 Source
LAI	叶面积指数 Leaf area index	3.78	m²?m^-2	观测 Observed
ρ_s	林分边材密度 Stand sapwood density	15.63	cm²?m^-2	观测 Observed
g_smax	最大叶片气孔导度 Maximum leaf stomatal conductance	36.42	mm?s^-1	拟合 Fitted
k_IP	气孔导度光辐射驱动系数 Parameter of stomatal conductance drove by PAR	5.36		拟合 Fitted
k_D_s	气孔导度水汽驱动系数 Parameter of stomatal conductance drive by Dv_p	6.22		拟合 Fitted
ψ_hx	半气孔导度木质部水势 Xylem water potential at half g_smax	-0.70	MPa	拟合Fitted
k_ψx	气孔导度木质部水势系数 Parameter of stomatal conductance limit by xylem water potential	-5.04		拟合 Fitted
C	林分树体水容 Stand tree hydraulic capacitance	0.80	kg?m^-2?MPa^-1	率定 Calibrated
r_sx	土壤-木质部导管阻力 Hydraulic resistance of soil to xylem vessels	2.80	MPa?cm^-2?min^-1?g^-1	观测 Observed
r_zx	树体储水组织-木质部导管阻力 Hydraulic resistance between xylem vessels to the organism of tree water storage	0.85	MPa?cm^-2?min^-1?g^-1	率定 Calibrated
r_xl	木质部导管-叶阻力 Hydraulic resistance of xylem vessels to leaf	2.80	MPa?cm^-2?min^-1?g^-1	率定 Calibrated
w_zmax	树体最大储水 Maximum storage water	20.00	kg?m^-2	率定 Calibrated

图2 模拟与观测林分液流速率(A)和日液流量(B)检验(2005-07-01-2005-09-15)。

Fig. 2 Measured and modeled stand sap flow velocity (A), and daily water flux (B) form July 1 to Sept. 15, 2005 during the validation period.

图3 模拟与观测林分日液流量(A)、液流速率(B)进程比较。

Fig. 3 Comparision of Diurnal pattern of simulated and observed stand water flux (A), and sap flow velocity (B).

图4 模拟林分蒸腾、边材液流速率(A)和树体储水及其交换日进程(B) (2005-07-01-2005-09-15)。

Fig. 4 Daily change of simulated stand transpiration, sap flow velocity (A) and storage water exchange (B) from June 1 to Sept. 15, 2005.

图5 模拟日树干储水利用与冠层日蒸腾的关系。

Fig. 5 Relationship between simulated daily storage water and observed daily conapy transpiration.

图6 树体储水利用与土壤水势(A)及潜在蒸散(B)的关系。

Fig. 6 Relationship of storage water use with soil water potential (A) and potential evaporation (B).

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