Theinfluenceof bamboo culm water content on sap flux measurements by thermal dissipation probes: observations and modeling

Journal: Trees

Ting-Ting Mei 1,2,3†*, Dong-Ming Fang1 †, Alexander Röll1, Dirk Hölscher1

1 Tropical Silviculture and Forest Ecology, Georg-August-UniversitätGöttingen, Germany

2State Key Laboratory of Subtropical Silvilculture,Zhejiang Agriculture and Forestry University, Lin’an 311300, Zhejiang province,China.

3Zhejiang Provincial Key Laboratory of Carbon Cycling in Forest Ecosystems and Carbon Sequestration,Zhejiang Agriculture and Forestry University, Lin’an 311300, Zhejiang province,China.

† The authors contributed equally to this work.

*Correspondence:

Ting-Ting Mei, Tropical Silviculture and Forest Ecology, Georg-August-UniversitätGöttingen, Büsgenweg 1, Göttingen, 37077, Germany.

Contact email:

The thermal conductivity of the sample segments was calculated following the work of Vandegehuchte and Steppe (2012), who introduced a corrected thermal conductivity in the axial direction (Ka, W m-1 K-1), as shown in the following equation(Eq. 1):

(1)

WhereKw is the thermal conductivity of water (0.6 W m-1 K-1), θwood-FSP is θwood at the fiber saturation point, ρd and ρw are the density of dry wood and water (1000 kg m-3), and Fv-FSPis the void fraction of wood at the fiber saturation point according to (Vandegehuchte and Steppe 2012):

(2)

Where Fv-FSP is the void fraction of wood at the fiber moisture saturation point, ρcw is the density of cell walls (1530 kg m-3, Kollman and Côté 1968, Vandegehuchte and Steppe 2012a), Gb is the basic specific gravity as a function of dry mass per fresh volume divided by the density of water. θwood-FSP is θwood at the fiber saturation point (%) which refers to (Roderick and Berry 2001):

(3)

Where ρd is the density of oven dried wood (Inagaki et al. 2014):

(4)

Where ρairis the density of air at 20oC (1.2 kg m-3), ρovencw is the density of oven dried cell wall (1400 kg m-3) and Fovencw is the volume fraction of the oven dried cell wall.

(5)

Wherewcw is the weight of oven-dried cell wall (kg). In this study, we assumed wcw to be approximately equal to the weight of oven-dried wood. vfresh is the volume of the fresh wood (m3).

The specific heat capacity of the fresh wood was calculated following (Burgess et al. 2001), as shown in (6).

(6)

Where c is heat capacity of fresh wood (J kg-1 K-1), cdry and cw are heat capacity of dry wood (1200 J kg-1 K-1) and water (4186 J kg-1 K-1) at 20oC (Edwards and Warwick 1984), and wfresh and wdryare the respective weights of fresh and dry wood .

Because the wood domain contains both the wood matrix and sap (the latter approximately equal to water in physical properties), heat transfer in such porous media directly depends on the contact surface between the two phases. Such heat transfer is characterized by the interfacial area density (IFA, (7)) which is defined as the surface area per unit volume (m-1).

(7)

Where P is the number of conduits in 1 cm2 of the wood, which is approximately 250 for bamboos, according to Mohmod and Mustafa (1992).

References

Burgess SSO, Adams MA, Turner NC, et al (2001) An improved heat pulse method to measure low and reverse rates of sap flow in woody plants. Tree Physiol 21:589–598. doi: 10.1093/treephys/21.9.589

Edwards WRN, Warwick NWM (1984) Transpiration from a kiwifruit vine as estimated by the heat pulse technique and the Penman-Monteith equation. N Z J Agric Res 27:537–543. doi: 10.1080/00288233.1984.10418016

Inagaki T, Ahmed B, Hartley ID, et al (2014) Simultaneous prediction of density and moisture content of wood by terahertz time domain spectroscopy. J Infrared Millim Terahertz Waves 35:949–961. doi: 10.1007/s10762-014-0095-7

Kollman FF, Côté WA (1968) Principles of wood science and technology, vol I.

Mohmod AL, Mustafa MT (1992) Variation in anatomical properties of three Malaysian bamboos from natural stands. J Trop For Sci 5:90–96.

Roderick ML, Berry SL (2001) Linking wood density with tree growth and environment: a theoretical analysis based on the motion of water. New Phytol 149:473–485. doi: 10.1046/j.1469-8137.2001.00054.x

Vandegehuchte MW, Steppe K (2012) Improving sap flux density measurements by correctly determining thermal diffusivity, differentiating between bound and unbound water. Tree Physiol 32:930–942. doi: 10.1093/treephys/tps034