Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/bg-2017-69
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
13 Mar 2017
Review status
This discussion paper has been under review for the journal Biogeosciences (BG). The manuscript was not accepted for further review after discussion.
Rainfall pattern greatly affects water use by Mongolian Scots pine on a sandy soil, in a semi-arid climate
Hongzhong Dang1, Lizhen Zhang2, Wenbin Yang1, Jinchao Feng1, Hui Han3, and Wei Li1 1Institute of Desertification Studies, Chinese Academy of Forestry, Beijing, 100091, China
2Institute of Resources and Environment, China Agricultural University, Beijing, 100094, China
3Institute of Sand Fixation and Afforestation of Liaoning Province, Fuxin, 123000, China
Abstract. We report new information on tree water use by Mongolian Scots pine (Pinus sylvestris var. mongolica) growing on a sandy soil, in a region characterised by an erratic rainfall pattern. Measurements were made over three successive years of contrasting annual rainfall – a wet year (2013), a dry year (2014), and a second dry year (2015). The result was the development of worsening levels of drought year by year. Over the three years, sap flux density (Js) was measured at individual tree level in up to 25 trees. The sap flux density values were up-scaled to estimate tree water use at plot level (Ts). Our measurements follow forest plot response to increasing levels of drought which developed over a three-year period as soil moisture conditions gradually worsened from wet, to moderate-drought, to severe-drought, to extreme-drought, in response to the dynamics of a variable rainfall pattern. Values of Ts did not exceed 3.03 mm day−1 (2013), 1.75 mm day−1 (2014) and 1.59 mm day−1 (2015) during the three growing seasons. Total annual stand transpiration over the same three years declined progressively from 290 mm (2013), to 182 mm (2014) and to 175 mm (2015). Satisfactory power-function relationships (R2 = 0.64) between daily Ts and the product of ET0 and the relative extractable soil water (REW) were found. This study helps elucidate the interplay between the effects of the atmosphere and soil moisture on tree water use. Tree water use responded to drought, with daily Ts values decreasing by 5–46 % in response to moderate drought, by 48–62 % in response to severe drought and by 65 % in response to extreme drought. Upon release of moderate drought by heavy rainfall in 2013, daily Ts recovered completely. However, under the severe and extreme droughts in the subsequent dry years, recovery of Ts following heavy rainfall was incomplete (57–58 %). Our results highlight the negative effects of water stress on the growth of mature forest trees, in a sandy soil, in a climate characterised by large intra- and inter-annual variances in rainfall. When the erratic rainfall and sandy soil were also coupled with a declining groundwater table, the result was tree water use fluctuated widely over quite short time scales (months or weeks). Overall, our findings account for the observed premature degradation of these MP plantations in terms of an eco-hydrological perspective.

Citation: Dang, H., Zhang, L., Yang, W., Feng, J., Han, H., and Li, W.: Rainfall pattern greatly affects water use by Mongolian Scots pine on a sandy soil, in a semi-arid climate, Biogeosciences Discuss., doi:10.5194/bg-2017-69, 2017.
Hongzhong Dang et al.
Hongzhong Dang et al.

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Short summary
The large intra- and inter-annual rainfall variances were insufficient to maintain soil moisture levels in the upper soil layers (where the majority of roots lie) at a level sufficient to avoid frequent drought. Daily stand transpiration was sensitive to drought, decreasing by 5–46 % under moderate drought, by 48–62 % under severe drought and by 65 % under extreme drought. This study will enable a much better understanding of the reasons for the observed serious degradation of Mongolian Scots pine.
The large intra- and inter-annual rainfall variances were insufficient to maintain soil moisture...
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