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Background <p>Subtropical forests play a critical role in global carbon cycling but are highly sensitive to climate-driven precipitation and temperature variability. At China's Dinghushan Biosphere Reserve, observed warming (+ 1.5&#xa0;°C since 2002) and precipitation declines (8.2 ± 1.3 mm/yr) exceed global subtropical averages, yet their combined effects on water-use efficiency (WUE) and carbon exchange remain poorly quantified.</p> Methods <p>Using 21&#xa0;years of eddy covariance and meteorological data (2002–2022), we analyzed WUE (defined as NEE/ET; g C kg<sup>−1</sup> H<sub>2</sub>O) responses to drought events classified via the standardized precipitation index (SPI).</p> Results <p>The reserve experienced increasing drought frequency, with 7 extreme droughts (SPI ≤ –&#xa0;2.0) post-2010 versus 2 pre-2010. Soil moisture extremes (&lt; 0.15 m<sup>3</sup>&#xa0;m<sup>−3</sup>) reduced WUE by 2.35&#xa0;g C kg<sup>–1</sup> H<sub>2</sub>O. Carbon fluxes showed differential sensitivity: ecosystem respiration (RE) declined most sharply (–&#xa0;71.9 × 10<sup>–5</sup>&#xa0;g C m<sup>−2</sup>&#xa0;s<sup>–1</sup>) during extreme droughts, while gross primary productivity (GPP) exhibited non-linear reductions below a 1,200&#xa0;mm&#xa0;yr<sup>–1</sup> precipitation threshold. Late-successional forests maintained 0.94&#xa0;g C kg<sup>–1</sup> H<sub>2</sub>O higher WUE than mid-successional stands during droughts, linked to deeper rooting systems (120 ± 15&#xa0;cm). The identified 3-year recovery lag suggests targeted reforestation during wet intervals (SPI ≥ 1.5) could enhance resilience.</p> Conclusion <p>By establishing quantitative drought thresholds and revealing hydraulic versus non-hydraulic limitations, our findings provide actionable strategies for subtropical forest conservation under climate change.</p>

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Drought-driven declines in water-use efficiency reshape carbon dynamics of a subtropical forest

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年9月2日

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  • Brian Njoroge Mwangi,
  • Wyckliffe Ayoma,
  • Yuelin Li,
  • L. Adrian Bruijnzeel,
  • Juxiu Liu,
  • Jun Zhang,
  • Dennis Otieno,
  • Lindsay Sikuku,
  • Mengmeng Yang,
  • Vincent Suba,
  • Oluoch Emily Achieng,
  • Iheme Okechukwu,
  • Ayesha Akter,
  • Sohel Rana,
  • Guowei Chu,
  • Qianmei Zhang,
  • Xuli Tang,
  • Ze Meng,
  • Deqiang Zhang

摘要

Background

Subtropical forests play a critical role in global carbon cycling but are highly sensitive to climate-driven precipitation and temperature variability. At China's Dinghushan Biosphere Reserve, observed warming (+ 1.5 °C since 2002) and precipitation declines (8.2 ± 1.3 mm/yr) exceed global subtropical averages, yet their combined effects on water-use efficiency (WUE) and carbon exchange remain poorly quantified.

Methods

Using 21 years of eddy covariance and meteorological data (2002–2022), we analyzed WUE (defined as NEE/ET; g C kg−1 H2O) responses to drought events classified via the standardized precipitation index (SPI).

Results

The reserve experienced increasing drought frequency, with 7 extreme droughts (SPI ≤ – 2.0) post-2010 versus 2 pre-2010. Soil moisture extremes (< 0.15 m3 m−3) reduced WUE by 2.35 g C kg–1 H2O. Carbon fluxes showed differential sensitivity: ecosystem respiration (RE) declined most sharply (– 71.9 × 10–5 g C m−2 s–1) during extreme droughts, while gross primary productivity (GPP) exhibited non-linear reductions below a 1,200 mm yr–1 precipitation threshold. Late-successional forests maintained 0.94 g C kg–1 H2O higher WUE than mid-successional stands during droughts, linked to deeper rooting systems (120 ± 15 cm). The identified 3-year recovery lag suggests targeted reforestation during wet intervals (SPI ≥ 1.5) could enhance resilience.

Conclusion

By establishing quantitative drought thresholds and revealing hydraulic versus non-hydraulic limitations, our findings provide actionable strategies for subtropical forest conservation under climate change.