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<p>Understanding seasonal variability in physiological traits is critical for identifying <i>Hevea brasiliensis</i> clones with better adaptability and yield stability under changing climatic conditions. In this study, gas exchange parameters were measured in 56 <i>Hevea</i> clones across four seasons—early summer (March), late summer (May), monsoon (August), and post-monsoon (October) within the traditional rubber-growing region of India. Growth and early yield of these clones were evaluated to relate physiological responses to overall productivity. Photosynthetic leaf traits exhibited significant clonal and seasonal variation, with higher net CO<sub>2</sub> assimilation rate (A), stomatal conductance (g<sub>s</sub>), and transpiration rate (E) during the post‑monsoon period and the lowest levels in late summer. The pre‑monsoon showers did not enhance A until the monsoon onset as vapour pressure deficit (VPD) constrained gas exchange. Across seasons, A exhibited moderate repeatability, as the values were correlated between seasons. A correlated with annual yield during monsoon (r = 0.364, <i>p</i> &lt; 0.01) and post‑monsoon (r = 0.474, <i>p</i> &lt; 0.01), but not in early and late summer. Stepwise regression revealed that yield was mainly explained by girth (R ≈ 0.70). However, when excluding girth, a subsequent stepwise multiple regression revealed that post‑monsoon A accounted for 22%, emphasising its role in improving yield prediction in addition to growth parameters. Multi‑trait stability index (MTSI) highlighted strong “all‑rounders” combining stability, girth and yield (P 168, P 120, P 89, RRII 429, P 65, P 114, PB 260, RRIM 600, P 173, P 116, P 68); high yield/girth clones with lower stability (RRII 430, RRII 414, RRII 417, P 174, PB 235); and stable, moderately productive clones (IAN 45‑873, P 93, P 112, P 197). Hybridisation between low‑MTSI all‑rounders and top-yielding clones could combine stability and productivity to develop climate-resilient clones. Together, these findings emphasise incorporating seasonal physiological measurements into the clonal evaluation and selection process under variable climatic conditions.</p>

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Dynamics of photosynthetic response across seasons in Hevea brasiliensis and implications for climate-resilient clonal selection

  • 期刊论文

  • 发表日期：

    2026年5月21日

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  • Neethu N. Nair,
  • Suparna V. Ajith,
  • M. B. Mohamed Sathik

摘要

Understanding seasonal variability in physiological traits is critical for identifying Hevea brasiliensis clones with better adaptability and yield stability under changing climatic conditions. In this study, gas exchange parameters were measured in 56 Hevea clones across four seasons—early summer (March), late summer (May), monsoon (August), and post-monsoon (October) within the traditional rubber-growing region of India. Growth and early yield of these clones were evaluated to relate physiological responses to overall productivity. Photosynthetic leaf traits exhibited significant clonal and seasonal variation, with higher net CO2 assimilation rate (A), stomatal conductance (gs), and transpiration rate (E) during the post‑monsoon period and the lowest levels in late summer. The pre‑monsoon showers did not enhance A until the monsoon onset as vapour pressure deficit (VPD) constrained gas exchange. Across seasons, A exhibited moderate repeatability, as the values were correlated between seasons. A correlated with annual yield during monsoon (r = 0.364, p < 0.01) and post‑monsoon (r = 0.474, p < 0.01), but not in early and late summer. Stepwise regression revealed that yield was mainly explained by girth (R ≈ 0.70). However, when excluding girth, a subsequent stepwise multiple regression revealed that post‑monsoon A accounted for 22%, emphasising its role in improving yield prediction in addition to growth parameters. Multi‑trait stability index (MTSI) highlighted strong “all‑rounders” combining stability, girth and yield (P 168, P 120, P 89, RRII 429, P 65, P 114, PB 260, RRIM 600, P 173, P 116, P 68); high yield/girth clones with lower stability (RRII 430, RRII 414, RRII 417, P 174, PB 235); and stable, moderately productive clones (IAN 45‑873, P 93, P 112, P 197). Hybridisation between low‑MTSI all‑rounders and top-yielding clones could combine stability and productivity to develop climate-resilient clones. Together, these findings emphasise incorporating seasonal physiological measurements into the clonal evaluation and selection process under variable climatic conditions.