Preprints
https://doi.org/10.5194/bg-2017-69
https://doi.org/10.5194/bg-2017-69
13 Mar 2017
 | 13 Mar 2017
Status: this discussion paper is a preprint. It 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 Dang, Lizhen Zhang, Wenbin Yang, Jinchao Feng, Hui Han, and Wei Li

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.

Hongzhong Dang, Lizhen Zhang, Wenbin Yang, Jinchao Feng, Hui Han, and Wei Li
 
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Status: closed
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Hongzhong Dang, Lizhen Zhang, Wenbin Yang, Jinchao Feng, Hui Han, and Wei Li
Hongzhong Dang, Lizhen Zhang, Wenbin Yang, Jinchao Feng, Hui Han, and Wei Li

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Latest update: 28 Mar 2024
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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.
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