Leaf surface traits and water storage retention affect photosynthetic responses to leaf surface wetness among wet tropical forest and semiarid savanna plants

Abstract

While it is reasonable to predict that photosynthetic rates are inhibited while leaves are wet, leaf gas exchange measurements during wet conditions are challenging to obtain due to equipment limitations and the complexity of canopy-atmosphere interactions in forested environments. Thus, the objective of this study was to evaluate responses of seven tropical and three semiarid savanna plant species to simulated leaf wetness and test the hypotheses that (i) leaf wetness reduces photosynthetic rates (Anet), (ii) leaf traits explain different responses among species and (iii) leaves from wet environments are better adapted for wet leaf conditions than those from drier environments. The two sites were a tropical rainforest in northern Costa Rica with ~4200 mm annual rainfall and a savanna in central Texas with ~1100 mm. Gas exchange measurements were collected under dry and wet conditions on five sun-exposed leaf replicates from each species. Additional measurements included leaf wetness duration and stomatal density. We found that Anet responses varied greatly among species, but all plants maintained a baseline of activity under wet leaf conditions, suggesting that abaxial leaf Anet was a significant percentage of total leaf Anet for amphistomatous species. Among tropical species, Anet responses immediately after wetting ranged from -31% (Senna alata (L.) Roxb.) to +21% (Zamia skinneri Warsz. Ex. A. Dietr.), while all savanna species declined (up to -48%). After 10 min of drying, most species recovered Anet towards the observed status prior to wetting or surpassed it, with the exception of Quercus stellata Wangenh., a savanna species, which remained 13% below Anet dry. The combination of leaf wetness duration and leaf traits, such as stomatal density, trichomes or wax, most likely influenced Anet responses positively or negatively. There was also overlap between leaf traits and Anet responses of savanna and tropical plants. It is possible that these species converge on a relatively conservative response to wetness, each for divergent purposes (cooling, avoiding stomatal occlusion, or by several unique means of rapid drying). A better understanding of leaf wetness inhibiting photosynthesis is vital for accurate modeling of growth in forested environments; however, species adapted for wet environments may possess compensatory traits that mitigate these effects.

Diffuse light and wetting differentially affect tropical tree leaf photosynthesis

“…This is similar to Aparecido et al . (), who found reductions in photosynthesis in nine out of 10 species from a temperate savanna and tropical rainforest. However, both studies demonstrate notable variation across species.…”

The 18O‐signal transfer from water vapour to leaf water and assimilates varies among plant species and growth forms

“…Moreover, the observed differences in the 18 O‐signal transfer to sugars among plant species and growth forms may also be attributed to the photosynthetic response of each species to the high humidity conditions (Aparecido et al, ; Berry & Smith, ; Dawson & Goldsmith, ; Eller et al, ); however, A n was not related to Δδ 18 O Sugars (and thus to MRT Sugars ; Figure S3). We assume that the A n values measured before the experiment may not reflect the actual A n values occurring during the fog event.…”

Upscaling transpiration in diverse forests: Insights from a tropical premontane site

“…In water‐limited environments, greater magnitudes of hysteresis (area within the loop) for VPD have been associated with overnight rehydration (higher morning J s ) and stomatal limitation (lower afternoon J s )—especially in the drier months, associated with lower soil water potential (Zhang, Manzoni, Katul, Porporato, & Yang, ; Zheng, Wang, Zhu, Li, & Yu, ). However, no previous study has implicated leaf wetness as a driver of hysteretic trends (Zhang et al, ), which may be influenced by plant adaptations to wet leaf conditions in the humid tropics (Aparecido, Miller, Cahill, & Moore, ). We observed a larger magnitude of hysteresis for R s on dry days compared to wet days than previously reported (Zheng et al, ).…”